Weather is made up of different elements like temperature, precipitation, wind and more that can vary from day to day. Climate describes the average weather conditions in an area over a long period of time, usually 30 years. Some key aspects of weather include temperature, which is a measurement of how hot or cold something is, and humidity, which refers to the amount of water vapor in the air. Weather is caused by differences in air pressure and temperature between locations due to factors like the sun and Earth's rotation. Forecasting models are used to predict future weather conditions based on current data and understanding of atmospheric processes.

1. kWeather is made up of different things. Click on the different types of weather
above to find out more about them and how they can be measured.
Weather Definition
Weather is the day-to-day conditions of a particular place.
For example: It was raining today at school. Yesterday it was sunny at home.
What is Climate?
Climate is often spoken about at the same time as weather, but it is
something quite different. The climate is the common, average weather
conditions at a particular place over a long period of time (for example,
more than 30 years). We learn about different climates around the world.
Deserts have a hot and dry climate while the Antarctic has a very cold
and dry climate.
Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy,
[1] [2][3]
clear or cloudy. Most weather phenomena occur in thetroposphere, just below the stratosphere.
Weather generally refers to day-to-day temperature and precipitation activity, whereas climate is the term
[4]
for the average atmospheric conditions over longer periods of time. When used without qualification,
"weather" is understood to be the weather of Earth.
Weather is driven by air pressure (temperature and moisture) differences between one place and
another. These pressure and temperature differences can occur due to the sun angle at any particular
spot, which varies by latitudefrom the tropics. The strong temperature contrast between polar and tropical
air gives rise to the jet stream. Weather systems in the mid-latitudes, such asextratropical cyclones, are
caused by instabilities of the jet stream flow. Because the Earth's axis is tilted relative to its orbital
plane, sunlight is incident at different angles at different times of the year. On Earth's surface,
temperatures usually range ±40 °C (−40 °F to 100 °F) annually. Over thousands of years, changes in
Earth's orbit affect the amount and distribution of solar energy received by the Earth and influence long-
term climate and global climate change.
Forecasting
Forecast of surface pressures five days into the future for the north Pacific, North America, and north Atlantic ocean as on 9
June 2008
Weather forecasting is the application of science and technology to predict the state of theatmosphere for
a future time and a given location. Human beings have attempted to predict the weather informally for
[25][26]
millennia, and formally since at least the nineteenth century. Weather forecasts are made by

2. collecting quantitative data about the current state of the atmosphere and using scientific understanding
[27]
of atmospheric processes to project how the atmosphere will evolve.
Once an all-human endeavor based mainly upon changes in barometric pressure, current weather
[28][29]
conditions, and sky condition, forecast models are now used to determine future conditions. Human
input is still required to pick the best possible forecast model to base the forecast upon, which involves
pattern recognition skills, teleconnections, knowledge of model performance, and knowledge of model
biases. The chaotic nature of the atmosphere, the massive computational power required to solve the
equations that describe the atmosphere, error involved in measuring the initial conditions, and an
incomplete understanding of atmospheric processes mean that forecasts become less accurate as the
difference in current time and the time for which the forecast is being made (the range of the forecast)
increases. The use of ensembles and model consensus helps to narrow the error and pick the most likely
outcome
Weather
Weather is the state of the atmosphere at a given time and place. Most weather takes place in
thetroposphere, the lowest layer of the atmosphere.
Weather is measured and described in a variety of ways by meteorologists, scientists who study and
predict weather. Air temperature and pressure, the amount and type of precipitation, the strength and
direction of wind, and the types of clouds are all described in a weather report.
Weather changes each day because the air in our atmosphere is always moving, distributing energy from
theSun. In most places in the world, the types of weather events also vary throughout the year
as seasons change.
What is Weather?
The term weather describes the state of the air at a
Weather... particular place and time – whether it is warm or cold, wet
or dry, and how cloudy or windy it is, for example.
The normal pattern of weather experienced in a particular
area over a long period of time is known as theclimate.
Climate...
The climate tells us how hot, cold or wet it is likely to be in
different parts of the world at different times of year. For
example, tropical countries have hot climates and the
Antarctic has a cold climate.
What is climate?
Climate is the average weather usually taken over a 30-year time period

3. for a particular region and time period. Climate is not the same as
weather, but rather, it is the average pattern of weather for a particular
region. Weather describes the short-term state of the atmosphere.
What is our climate system?
The atmosphere covers the Earth. It is a thin layer of mixed
Atmosphere gases which make up the air we breathe. This thin layer also
helps the Earth from becoming too hot or too cold.
Oceans cover about 70 percent of Earth's surface. Their
Oceans large size and thermal properties allow them to store a lot of
heat.
Land covers 27 percent of Earth's surface and land
Land
topography influences weather patterns.
Ice is the world's largest supply of freshwater. It covers
the remaining 3 percent of Earth's surface including most of
Ice
Antarctica and Greenland. Ice plays an important role in
regulating climate, because it is highly reflective.
The biosphere is the part of Earth's atmosphere, land, and
Biosphere oceans that supports any living plant, animal, or organism. It
is the place where plants and animals, including humans, live.
What is weather?
The weather is just the state of the atmosphere at any time, including
things such as temperature, precipitation, air pressure and cloud cover.
Daily changes in the weather are due to winds and storms. Seasonal
changes are due to the Earth revolving around the sun.
What causes weather?
Because the Earth is round and not flat, the Sun's rays don't fall evenly

4. on the land and oceans. The Sun shines more directly near the equator
bringing these areas more warmth. However, the polar regions are at such
an angle to the Sun that they get little or no sunlight during the winter,
causing colder temperatures. These differences in temperature create a
restless movement of air and water in great swirling currents to
distribute heat energy from the Sun across the planet. When air in one
region is warmer than the surrounding air, it becomes less dense and
begins to rise, drawing more air in underneath. Elsewhere, cooler denser
air sinks, pushing air outward to flow along the surface and complete the
cycle.
Why do mountains affect weather and climate?
There are two sides to a mountain: wayward and leeward. Whenever it is
raining, the wayward side gets the rain. As a cloud goes up the mountain,
it keeps raining until there is no more water in the cloud. Now, as the
cloud starts to go down the other side of the mountain, there is no more
precipitation. So, the leeward side of the mountain doesn't get any rain.
The flat ground on this side of the mountain is dry and humid.
What is the Water Cycle?
Earth has a limited amount of water. So, that water keeps going around.
We call it the water cycle. The water cycle begins with evaporation.
Evaporation is when the sun heats up water in rivers, lakes or the ocean.
Then turns it into water vapor or steam. The water vapor or steam leaves
the body of water and goes into the air. Transpiration is the process by
which plants lose water out of their leaves. Condensation is when water
vapor in the air gets cold and changes back into water to form clouds.
Think of it this way, when you open a cold soda on a hot summer day, your
soda will start to sweat as water droplets form on the outside of the can.
Precipitation occurs when so much water has condensed that the air can't

5. hold it anymore. This is how we get rain or snow. Collection happens when
the precipitation falls and is collected back in the oceans, lakes and
rivers. When it falls to the ground, it will soak into the earth and become
ground water. This is the water cycle and it just keeps repeating.
Click Here to learn more about the Earth's water cycle.
Why do we have seasons?
As the Earth spins on its axis, producing night and day, it also moves
about the Sun in an elliptical (elongated circle) orbit that requires 365
1/4 days to complete. The Earth's axis is tilted at 23.5 degrees and is
why we have seasons. When the Earth's axis points towards the Sun, it is
summer for that hemisphere. When the Earth's axis points away, winter
can be expected.

6. What is the significance of the Sun to the Earth?
Without the Sun, there would be no weather. Earth is positioned as the
third planet, so our temperatures are sustainable for life. The average
temperature of Mars is much colder, while Venus is much hotter.
Climate
From Wikipedia, the free encyclopedia
For other uses, see Climate (disambiguation).
Worldwide Climate Classifications

7. Climate encompasses the statistics oftemperature, humidity, atmospheric pressure,wind, precipitation,
atmospheric particle count and other meteorological elemental measurements in a given region over long
periods. Climate can be contrasted to weather, which is the present condition of these elements and their
variations over shorter periods.
A region's climate is generated by the climate system, which has five
components:atmosphere, hydrosphere, cryosphere, land surface, and biosphere.[1]
The climate of a location is affected by itslatitude, terrain, and altitude, as well as nearbywater bodies and their
currents. Climates can beclassified according to the average and the typical ranges of different variables, most
commonly temperature and precipitation. The most commonly used classification scheme was originally
developed by Wladimir Köppen. The Thornthwaite system,[2] in use since 1948,
incorporates evapotranspiration along with temperature and precipitation information and is used in studying
animal species diversity and potential effects of climate changes. The Bergeron and Spatial Synoptic
Classification systems focus on the origin of air masses that define the climate of a region.
Paleoclimatology is the study of ancient climates. Since direct observations of climate are not available before
the 19th century, paleoclimates are inferred from proxy variables that include non-biotic evidence such as
sediments found in lake beds and ice cores, and biotic evidence such as tree rings and coral. Climate
models are mathematical models of past, present and future climates. Climate change may occur over long
and short timescales from a variety of factors; recent warming is discussed in global warming.
Why do the seasons change?
Answer:
Seasons change because the axis of the earth is tilted by 23.5 degrees (from a line perpendicular to its
orbit). As the earth moves around its orbit there is a time when it is tilted towards the sun and so
receives a higher concentration of the sun's energy (summer) and a time when it is tilted away and
receiving less energy (winter). This also explains why it is summer in N hemisphere when it is winter
in S hemisphere.
What are the five different world climate zones?
Answer:
In the Koppen system:
A - Tropical Moist Climates: all months have average temperatures above 18° Celsius.
B - Dry Climates: with deficient precipitation during most of the year.
C - Moist Mid-latitude Climates with Mild Winters.

8. D - Moist Mid-Latitude Climates with Cold Winters.
E - Polar Climates: with extremely cold winters and summers.
[1]
Temperature is a physical quantity that indicates degrees of hot and cold on a numerical scale. It refers
to states of matter or radiation in a local region. It is measured by a thermometer, which may
be calibrated to a variety oftemperature scales.
What is Temperature?
In a qualitative manner, we can describe the temperature of an object as that which
determines the sensation of warmth or coldness felt from contact with it.
It is easy to demonstrate that when two objectsof the same material are placed
together (physicists say when they are put in thermal contact), the object with the
higher temperature cools while the cooler object becomes warmer until a point is
reached after which no more change occurs, and to our senses, they feel the same.
When the thermal changes have stopped, we say that the two objects (physicists
define them more rigorously as systems) are in thermal equilibrium . We can then
define the temperature of the system by saying that the temperature is that quantity
which is the same for both systems when they are in thermal equilibrium.
If we experiment further with more than two systems, we find that many systems can
be brought into thermal equilibrium with each other; thermal equilibrium does not
depend on the kind of object used. Put more precisely,
if two systems are separately in thermal equilibrium with a third, then they must also
be in thermal equilibrium with each other,
and they all have the same temperature regardless of the kind of systems they are.
The statement in italics, called the zeroth law of thermodynamics may be restated as
follows:
If three or more systems are in thermal contact with each other and all in equilibrium
together, then any two taken separately are in equilibrium with one another. (quote
from T. J. Quinn's monograph Temperature)
Now one of the three systems could be an instrument calibrated to measure the
temperature - i.e. a thermometer. When a calibrated thermometer is put in thermal
contact with a system and reaches thermal equilibrium, we then have a quantitative

9. measure of the temperature of the system. For example, a mercury-in-glass clinical
thermometer is put under the tongue of a patient and allowed to reach thermal
equilibrium in the patient's mouth - we then see by how much the silvery mercury has
expanded in the stem and read the scale of the thermometer to find the patient's
temperature.
Temperature
A convenient operational definition of temperature is that it is a measure of the
average translational kinetic energy associated with the disordered microscopic
motion of atoms and molecules. The flow of heat is from a high temperature region
toward a lower temperature region. The details of the relationship to molecular motion
are described in kinetic theory.The temperature defined from kinetic theory is called
the kinetic temperature. Temperature is not directly proportional to internal
energy since temperature measures only the kinetic energy part of the internal energy,
so two objects with the same temperature do not in general have the same internal
energy (see water-metal example). Temperatures are measured in one of the three
standard temperature scales (Celsius, Kelvin, and Fahrenheit).
Humidity
Tropical forests often have high humidity.
Humidity is the amount of water vapor in the air. Water vapor is the gas phase of water and is
invisible.[1] Humidity indicates the likelihood of precipitation, dew, or fog. Higher humidity reduces the

10. effectiveness of sweating in cooling the body by reducing the rate of evaporationof moisture from the skin. This
effect is calculated in a heat index table, used during summer weather.
There are three main measurements of humidity: absolute, relative and specific. Absolute humidity is the
water content of air.[2] Relative humidity, expressed as a percent, measures the current absolute
humidity relative to the maximum for that air pressure and temperature. Specific humidity is a ratio of the
water vapor content of the mixture to the total air content on a mass basis
Types
[edit]Absolute humidity
Absolute humidity is an amount of water vapor, usually discussed per unit volume. The mass of water
vapor, , per unit volume of total air and water vapor mixture, , can be expressed as follows:
Absolute humidity in air ranges from zero to roughly 30 grams per cubic meter when the air is
saturated at 30 °C.[3] (See alsoClimate/Humidity table)
The absolute humidity changes as air temperature or pressure changes. This is very inconvenient
for chemical engineering calculations, e.g. for clothes dryers, where temperature can vary
considerably. As a result, absolute humidity is generally defined in chemical engineering as mass of
water vapor per unit mass of dry air, also known as the mass mixing ratio (see below), which is
much more rigorous for heat and mass balance calculations. Mass of water per unit volume as in the
equation above would then be defined asvolumetric humidity. Because of the potential
confusion, British Standard BS 1339 (revised 2002) suggests avoiding the term "absolute humidity".
Units should always be carefully checked. Most humidity charts are given in g/kg or kg/kg, but any
mass units may be used.
The field concerned with the study of physical and thermodynamic properties of gas-vapor mixtures is
named Psychrometrics.
Relative humidity
Relative humidity is the ratio of the partial pressure of water vapor in the air-water mixture to
the saturated vapor pressure of water at those conditions. The relative humidity of air is a function of
both its water content and temperature.
Relative humidity is normally expressed as a percentage and is calculated by using the following
equation. It is defined as the ratio of the partial pressure of water vapor (H2O) in the mixture to
the saturated vapor pressure of water at a prescribed temperature.
[3]

11. Relative humidity is an important metric used in weather forecasts and reports, as it is an
indicator of the likelihood of precipitation, dew, or fog. In hot summer weather, a rise in
relative humidity increases the apparent temperature to humans (and other animals) by
hindering the evaporation of perspiration from the skin. For example, according to the Heat
Index, a relative humidity of 75% at 80°F (27°C) would feel like 83.574°F ±1.3 °F (28.652°C
[4][5]
±0.7 °C) at ~44% relative humidity.
[edit]Specific humidity
Specific humidity is the ratio of water vapor to dry air in a particular mass, and is sometimes
referred to as humidity ratio. Specific humidity ratio is expressed as a ratio of mass of water
[6]
vapor, , per unit mass of dry air . This is in conflict with the ASHRAE 2009
Handbook, Ch1,1.2, (9a) which defines Specific humidity as "the ratio of the mass of water
vapor to total mass of the moist air sample".
That ratio is defined as:
Specific humidity can be expressed in other ways including:
or:
Using the definition of specific humidity, the relative humidity can be expressed
as
However, specific humidity is also defined as the ratio of water vapor to the
[7]
total mass of the system in meteorology. "Mixing ratio" is used to name
[8]
the definition in this section beginning.
[edit]Measurement
hygrometer
There are various devices used to measure and regulate humidity. A
device used to measure humidity is called a psychrometer or hygrometer.
A humidistat is a humidity-triggered switch, often used to control
a dehumidifier.

12. Humidity is also measured on a global scale using remotely
placed satellites. These satellites are able to detect the concentration of
water in the troposphere at altitudes between 4 and 12 kilometers.
Satellites that can measure water vapor have sensors that are sensitive
to infrared radiation. Water vapor specifically absorbs and re-radiates
radiation in this spectral band. Satellite water vapor imagery plays an
important role in monitoring climate conditions (like the formation of
thunderstorms) and in the development of futureweather forecasts.
Atmospheric pressure
From Wikipedia, the free encyclopedia
"Air pressure" redirects here. For the pressure of air in other systems, see pressure.
Atmospheric pressure is the force per unit area exerted on a surface by the weight of air above that surface
in the atmosphere of Earth (or that of another planet). In most circumstances atmospheric pressure is closely
approximated by the hydrostatic pressurecaused by the mass of air above the measurement point. Low-
pressure areas have less atmospheric mass above their location, whereas high-pressure areas have more
atmospheric mass above their location. Likewise, as elevation increases, there is less overlying atmospheric
mass, so that atmospheric pressure decreases with increasing elevation. On average, a column of air one
square centimeter in cross-section, measured from sea level to the top of the atmosphere, has a mass of about
1.03 kg and weight of about 10.1 N (2.28 lbf) (A column one square inch in cross-section would have a weight
of about 14.7 lbs, or about 65.4 N). Over the area of your body, there is about 1,000 kg of air; this is
approximately the same as having a small car press down on you
What Is Atmospheric Pressure
Just answering the question ‘what is atmospheric pressure?’ is not enough to give a full understanding of its importance. By definition
atmospheric pressure is ‘force per unit area exerted against a surface by the weight of air above that surface’. Atmospheric pressure is
closely related to the hydrostatic pressure caused by the weight of air above the measurement point. The term standard atmosphere is used
to express the pressure in a system(hydraulics and pneumatics) and is equal to 101.325 kPa. Other equivalent units are 760 mmHg and
1013.25 millibars.
Mean sea level pressure (MSLP) is the pressure at sea level. This is the pressure normally given in weather reports. When home barometers
are set to match local weather reports, they will measure pressure reduced to sea level, not your local atmospheric pressure. The reduction
to sea level means that the normal range of fluctuations in pressure are the same for everyone.
Atmospheric pressure is important in altimeter settings for flight. A altimeter can be set for QNH or QFE. Both are a method of reducing
atmospheric pressure to sea level, but they differ slightly. QNH will get the altimeter to show elevation at the airfield and altitude above the air
field. QFE will set the altimeter to read zero for reference when at a particular airfield. QNH is transmitted around the world in millibars,
except in the United States and Canada . These two countries use inches (or hundredths of an inch) of mercury.
Atmospheric pressure is often measured with a mercury barometer; however, since mercury is not a substance that humans commonly come
in contact with, water often provides a more intuitive way to visualize the pressure of one atmosphere. One atmosphere is the amount of
pressure that can lift water approximately 10.3m. A diver who is 10.3m underwater experiences a pressure of about 2 atmospheres (1of air
plus 1of water). Low pressures like natural gas lines can be expressed in inches of water(w.c). A typical home gas appliance is rated for a
maximum of 14 w.c.(about 0.034 atmosphere).
You can see that understanding ‘what is atmospheric pressure’ is just the tip of the iceberg. Once you have the definition in mind, it really
comes together when you see the wide variety of applications.

13. Differences between air and wind?
Air is the mixture of gases that forms the atmosphere, which we have all around us. When this air
begin to move fast enough to matter, we call it wind.
Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer
space, solar wind is the movement of gases or charged particles from the sunthrough space,
while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space.
Winds are commonly classified by their spatial scale, theirspeed, the types of forces that cause them, the
regions in which they occur, and their effect. The strongest observed winds on a planet in our solar
system occur on Neptune and Saturn.
What is Air Pressure?
Imagine a group of acrobats at the circus. One climbs up and stands on another's
shoulders. The weight of the acrobat on top puts more pressure on the one below.
Then another acrobat climbs up and stands on the second acrobat's shoulders. Now
there's even more pressure on the acrobat on the bottom because he is under the
weight of the two acrobats above him. It's the same with air. Yes, air has weight, and
probably more than you think. In fact, the weight of the air on your desk at school
weighs about 11,000 pounds. That's about the same weight as a school bus! Since air
pressure pushes in all directions, the air pressure pushing up from under your desk
balances out the air pushing down on it, so the desk doesn't collapse under the weight.
Just like an acrobat with two people stacked on his shoulders would want to move to
where there wasn't so much pressure on him, air moves from areas where the pressure
is higher to where it is lower
The density of air,
The density of air, ρ (Greek: rho) (air density), is the mass per unit volume of Earth's atmosphere, and is
a useful value in aeronauticsand other sciences. Air density decreases with increasing altitude, as
does air pressure. It also changes with variances in temperature or humidity. At sea level and at 15 °C
according to ISA (International Standard Atmosphere), air has a density of approximately 1.225
3 3
kg/m (0.0023769 slugs/ft ).
Rain

14. Torrential rain in Greece.
Rain is liquid water in the form of droplets that have condensed fromatmospheric water vapor and
then precipitated—that is, become heavy enough to fall under gravity. Rain is a major component of the water
cycleand is responsible for depositing most of the fresh water on the Earth. It provides suitable conditions for
many types of ecosystem, as well as water for hydroelectric power plants and crop irrigation.
The major cause of rain production is moisture moving along three-dimensional zones of temperature and
moisture contrasts known as weather fronts. If enough moisture and upward motion is present, precipitation
falls from convective clouds (those with strong upward vertical motion) such ascumulonimbus (thunder clouds)
which can organize into narrow rainbands. In mountainous areas, heavy precipitation is possible where upslope
flow is maximized within windward sides of the terrain at elevation which forces moist air to condense and fall
out as rainfall along the sides of mountains. On the leeward side of mountains, desert climates can exist due to
the dry air caused by downslope flow which causes heating and drying of the air mass. The movement of
the monsoon trough, or intertropical convergence zone, brings rainy seasons to savannah climes.
rain·fall
1. A shower or fall of rain.
2. The quantity of water, expressed in inches, precipitated as rain, snow, hail, or sleet in a specified area
and time interval.
Rainfall
Rainfall in Ireland
Most of the eastern half of the country gets between 750 and 1000 (mm) of rainfall in the year. Rainfall in the west
generally averages between 1000 and 1400 mm. In many mountainous districts rainfall exceeds 2000mm per year.
The wettest months, in almost all areas are December and January. April is the driest month generally across the
country. However, in many southern parts, June is the driest. Hail and snow contribute relatively little to the
precipitation measured.
How Often Does it Rain?
The general impression is that it rains quite a lot of the time in Ireland, but two out of three hourly observations will not
report any measurable rainfall. The average number of wet days (days 1mm or more of rain) ranges from about 150
days a year along the east and south east coasts, to about 225 days a year in parts of the west.
How Heavy is the Rain?

15. Unlike the rain in many other countries, especially in the tropics, average hourly rainfall amounts in Ireland are quite
low, ranging from 1 to 2mm. Short-term rates can of course be much higher: for example, an hourly total of 10mm is
not uncommon and totals of 15 to 20mm in an hour may be expected to occur once in 5 years. Hourly totals
exceeding 25mm are rare in this country and when they do occur they are usually associated with heavy
thunderstorms.
Information on the frequency of heavy rainfalls is often required by engineers, architects and others, usually in
connection with design criteria for water management or drainage schemes. A depth duration frequency model allows
for the estimation of point rainfall frequencies for a range of durations for any location in Ireland. For more
information, seewww.met.ie/climate/products03.asp .
An atmosphere (New Latin atmosphaera, created in the 17th century from Greek ἀτμός [atmos]
[1] [2]
"vapor" and συαῖρα [sphaira] "sphere" ) is a layer of gases that may surround a material body of
[3]
sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for
a longer duration, if the gravity is high and the atmosphere's temperature is low. Some planets consist
mainly of various gases, but only their outer layer is their atmosphere.
The term stellar atmosphere describes the outer region of a star, and typically includes the portion
starting from the opaque photosphere outwards. Relatively low-temperature stars may form compound
molecules in their outer atmosphere. Earth's atmosphere, which containsoxygen used by
most organisms for respiration and carbon dioxide used
by plants, algaeand cyanobacteria for photosynthesis, also protects living organisms from genetic
damage by solar ultraviolet radiation. Its current composition is the product of billions of years of
biochemical modification of the paleoatmosphere by living organisms.
The present atmosphere of the Earth is probably not its original atmosphere.
Our current atmosphere is what chemists would call an oxidizing atmosphere,
while the original atmosphere was what chemists would call a reducing
atmosphere. In particular, it probably did not contain oxygen.
Composition of the Atmosphere
The original atmosphere may have been similar to the composition of the solar
nebula and close to the present composition of the Gas Giant planets, though this
depends on the details of how the planets condensed from the solar nebula. That
atmosphere was lost to space, and replaced by compounds outgassed from the
crust or (in some more recent theories) much of the atmosphere may have come
instead from the impacts of cometsand other planetesimals rich in volatile
materials.
The oxygen so characteristic of our atmosphere was almost all produced by
plants (cyanobacteria or, more colloquially, blue-green algae). Thus, the present

16. composition of the atmosphere is 79% nitrogen, 20% oxygen, and 1% other
gases.
Layers of the Atmosphere
The atmosphere of the Earth may be divided into several distinct layers, as the
following figure indicates.
Layers of the Earth's atmosphere
Earth's Atmosphere
The atmosphere is a mixture of nitrogen (78%), oxygen (21%), and other gases (1%) that surrounds
Earth. High above the planet, the atmosphere becomes thinner until it gradually reaches space. It is
divided into five layers. Most of the weather and clouds are found in the first layer.
The atmosphere is an important part of what makes Earth livable. It blocks some of the Sun's dangerous
rays from reaching Earth. It traps heat, making Earth a comfortable temperature. And the oxygen within
our atmosphere is essential for life.
cryosphere
[1]
The cryosphere (from the Greek κρύος cryos "cold", "frost" or "ice" andσυαῖρα sphaira, "globe, ball" ) is
the term which collectively describes the portions of the Earth’s surface where water is in solid form,
including sea ice, lake ice, river ice, snow cover, glaciers, ice caps and ice sheets, and frozen ground
(which includes permafrost). Thus there is a wide overlap with thehydrosphere. The cryosphere is an
integral part of the global climate system with important linkages and feedbacks generated through its

17. influence on surface energy and moisture fluxes, clouds, precipitation, hydrology, atmospheric and
oceanic circulation. Through these feedback processes, the cryosphere plays a significant role in global
climate and in climate modelresponse to global change.
biosphere
The biosphere is the global sum of all ecosystems. It can also be called the zone of life on Earth, a
[1]
closed (apart from solar and cosmic radiation), and self-regulating system. From the
broadestbiophysiological point of view, the biosphere is the global ecologicalsystem integrating all living
beings and their relationships, including their interaction with the elements of
the lithosphere, hydrosphere, and atmosphere. The biosphere is postulated to have evolved, beginning
[2]
through a process of biogenesis or biopoesis, at least some 3.5 billion years ago.
In a broader sense; biospheres are any closed, self-regulating systems containing ecosystems; including
artificial ones such asBiosphere 2 and BIOS-3; and, potentially, ones on other planets or moons. but they
[3]
can be open systems too.
lithosphere
The lithosphere (Ancient Greek: λίθος [lithos] for "rocky", andσυαῖρα [sphaira] for "sphere") is the
[1]
rigid outermost shell of a rockyplanet. On Earth, it comprises the crust and the portion of the
uppermantle that behaves elastically on time scales of thousands of years or greater.
In the Earth, the lithosphere includes the crust and the uppermost mantle, which constitute the hard and
rigid outer layer of the Earth. The lithosphere is underlain by the asthenosphere, the weaker, hotter, and
deeper part of the upper mantle. The boundary between the lithosphere and the underlying
asthenosphere is defined by a difference in response to stress: the lithosphere remains rigid for very long
periods of geologic time in which it deforms elastically and through brittle failure, while the asthenosphere
deforms viscously and accommodates strain through plastic deformation. The lithosphere is broken
into tectonic plates. The uppermost part of the lithosphere that chemically reacts to
the atmosphere, hydrosphere and biospherethrough the soil forming process is called the pedosphere.
The concept of the lithosphere as Earth’s strong outer layer was developed by Joseph Barrell, who wrote
[2][3][4][5]
a series of papers introducing the concept. The concept was based on the presence of significant
gravity anomalies over continental crust, from which he inferred that there must exist a strong upper layer
(which he called the lithosphere) above a weaker layer which could flow (which he called the
asthenosphere). These ideas were expanded by Harvard geologist Reginald Aldworth Daly in 1940 with
[6]
his seminal work "Strength and Structure of the Earth" and have been broadly accepted by geologists
and geophysicists. Although these ideas about lithosphere and asthenosphere were developed long
before plate tectonic theory was articulated in the 1960s, the concepts that a strong lithosphere exists and
that this rests on a weak asthenosphere are essential to that theory.
There are two types of lithosphere:
Oceanic lithosphere, which is associated with Oceanic crust and exists in the ocean basins

18. Continental lithosphere, which is associated with Continental crust
The hydrosphere (from Greek ὕδωρ - hudōr, "water" and συαῖρα - sphaira, "sphere" ) in physical
[1] [2]
geography describes the combined mass of water found on, under, and over the surface of a planet.
18
The total mass of the Earth's hydrosphere is about 1.4 × 10 tonnes, which is about 0.023% of the
12
Earth's total mass. About 20 × 10 tonnes of this is in the Earth's atmosphere (the volume of one tonne of
water is approximately 1 cubic metre). Approximately 75% of the Earth's surface, an area of some 361
million square kilometers (139.5 million square miles), is covered by ocean. The averagesalinity of the
[3]
Earth's oceans is about 35 grams of salt per kilogram of sea water (3.5%)
The hydrosphere is the liquid water component of the Earth. It includes the
oceans, seas, lakes, ponds, rivers and streams. The hydrosphere covers
about 70% of the surface of the Earth and is the home for many plants and
animals.
(U.S. Fish and Wildlife Service/Craig Blacklock)
The hydrosphere, like the atmosphere, is always in motion. The motion of
rivers and streams can be easily seen, while the motion of the water within
lakes and ponds is less obvious. Some of the motion of the oceans and seas
can be easily seen while the large scale motions that move water great
distances such as between the tropics and poles or between continents are
more difficult to see. These types of motions are in the form of currents that

19. move the warm waters in the tropics toward the poles, and colder water from
the polar regions toward the tropics. These currents exist on the surface of the
ocean and at great depths in the ocean (up to about 4km).
The characteristics of the ocean which affects its motion
are its temperature and salinity. Warm water is less dense
or lighter and therefore tends to move up toward the
surface, while colder water is more dense or heavier and
therefore tends to sink toward the bottom. Salty water is
also more dense or heavier and thus tends to sink, while
fresh or less salty water is less dense or lighter and thus
tends to rise toward the surface. The combination of the
(NOAA Photo Collection/Commander water's temperature and salinity determines whether it
John Bortniak, NOAA Corps) rises to the surface, sinks to the bottom or stays at some
Large version intermediate depth.
ES0108 Hydrosphere/Atmosphere Interactions
Layers of the Atmosphere:
The earth is surrounded by the atmosphere, which is the body of air or gasses that protects the planet
and enables life. Most of our atmosphere is located close to the earth's surface where it is most dense.
The air of our planet is 79% nitrogen and just under 21% oxygen; the small amount remaining is
composed of carbon dioxide and other gasses. There are five distinct layers of the earth. Let's look at
each, from closest to farthest from the earth...
Troposphere:
The layer of the atmosphere closest to the earth is the troposphere. This layer is where weather
occurs. It begins at the surface of the earth and extends out to about 4-12 miles. The temperature of
the troposphere decreases with height. This layer is known as the lower atmosphere.

20. Stratosphere:
Above the troposphere is the stratosphere, which extends to about 30-35 miles above the earth's
surface. Temperature rises within the stratosphere but still remains well below freezing.
Mesosphere:
From about 35 to 50 miles above the surface of the earth lies the mesosphere, where the air is
especially thin and molecules are great distances apart. Temperatures in the mesosphere reach a low
of -184°F (-120°C). The stratosphere and the mesosphere are the middle atmosphere.
Thermosphere:
The thermosphere rises several hundred miles above the earth's surface, from 50 miles up to about
400 miles. Temperature increases with height and can rise to as high as 3,600°F (2000°C).
Nonetheless, the air would feel cold because the hot molecules are so far apart. This layer is known as
the upper atmosphere.
Exosphere:
Extending from the top of the thermosphere to 6200 miles (10,000 km) above the earth is the
exosphere. This layer has very few atmospheric molecules, which can escape into space.
Pauses...:
Between each layer of the atmosphere is a
boundary. Above the troposphere is the
tropopause; above the stratosphere is the
stratopause; above the mesosphere is the
mesopause; and above the thermosphere is the
thermopause. At these "pauses," maximum change
between the "spheres" occur.
The Layered Atmosphere
Stand outside and look up. What do
you see? You might see blue sky or
wooly clouds. At night you might see
stars, a satellite or a crescent moon.
What you are not seeing, however, is
the complexity of our atmosphere. The
atmosphere is a protective layer of

21. gasses that shelters all life on Earth, keeping temperatures within a relatively
small range and blocking out harmful rays of sunlight.
The atmosphere has five different layers that are determined by the changes
in temperature that happen with increasing altitude.
Troposphere
Living at the surface of the Earth, we are usually only aware of the events
happening in the lowest layer, the troposphere, where all weather occurs. The
base of this layer is warmer than its top because the air is heated by the
surface of the Earth, which absorbs the Sun’s energy.
Stratosphere
Above the troposphere lies the stratosphere where jet airplanes fly.
Temperatures increase with altitude because of increasing amounts of ozone.
The ozone layer within the stratosphere absorbs harmful ultraviolet rays of
sunlight.
Mesosphere
As the mesosphere extends upward above the stratosphere, temperatures
decrease. The coldest parts of our atmosphere are located in this layer and
can reach –90°C.
Thermosphere
In the forth layer from Earth’s surface, the thermosphere, the air is thin,
meaning that there are far fewer air molecules. The thermosphere is very
sensitive to solar activity and can heat up to 1,500°C or higher when the Sun
is active making an aurora that lights up the night sky. Astronauts orbiting
Earth in the space station or space shuttle spend their time in this layer.
Exosphere
The upper layer of our atmosphere, where atoms and molecules escape into
space, is called the exosphere.
Atmospheric pressure is the force per unit area exerted on a surface by the weight of air above that
surface in the atmosphere of Earth (or that of another planet). In most circumstances atmospheric
pressure is closely approximated by the hydrostatic pressurecaused by the mass of air above the
measurement point. Low-pressure areas have less atmospheric mass above their location, whereas high-
pressure areas have more atmospheric mass above their location. Likewise, as elevation increases, there
is less overlying atmospheric mass, so that atmospheric pressure decreases with increasing elevation.
On average, a column of air one square centimeter in cross-section, measured from sea level to the top
of the atmosphere, has a mass of about 1.03 kg and weight of about 10.1 N (2.28 lbf) (A column one
square inch in cross-section would have a weight of about 14.7 lbs, or about 65.4 N). Over the area of

22. your body, there is about 1,000 kg of air; this is approximately the same as having a small car press down
[1]
on you.
Pressure
Pressure is defined as force per unit area. It is usually more convenient to use pressure
rather than force to describe the influences upon fluid behavior. The standard unit for
pressure is the Pascal, which is a Newton per square meter.
For an object sitting on a surface, the force pressing on the surface is the weight of the
object, but in different orientations it might have a different area in contact with the
surface and therefore exert a different pressure.
Wind speed, or wind velocity, is a fundamental atmospheric rate.
Wind speed affects weather forecasting, aircraft and maritime operations, construction projects, growth
[1]
and metabolism rate of many plant species, and countless other implications.
Wind speed is now commonly measured with an anemometer but can also be classified using the
older Beaufort scale which is based on people's observation of specifically defined wind effects.
Climate variation factors
The climate of any region is largely determined by four geographic aspects:
Latitude, distance from the sea, direction of the prevailing winds and elevation.

23. Climate variation factors
Other factors influence the global climate system: atmosphere, oceans, ice, land and the various forms of
life.
Ultraviolet, visible and infra-red solar radiations are Earth's main sources of energy. There is an
established balance between the incmoing solar energy and the telluric infra-red radiation emitted by the
Earth. Part of the Earth's radiation is absorbed and reemitted by the 'greenhouse' effect and part is lost in
space. You'd be hard pressed to find people anywhere that don't have an opinion on the 'greenhouse'
effect or solar radiations one way or the other.
Horizontal variation of solar energy
The balance is fragile and any variation in the factors that affect this incoming and outgoing energy
process or which modifies the energy repartition will affect the world climate.
Natural factors
The climate changed during Earth's history. Ice ages alternating with warm periods provide an

24. example. Some changes were worlwide, while others simply affected an area or a hemisphere. In
addition, a number of natural factors contribute to modify the Earth's climate during various periods. It is
important to understand these factors when seeking to detect the influence of humanity on the climate:
Variations of the solar energy emissions. The quantity of energy emitted by the Sun is not constant.
There are evidences revealing that the Earth's temperature corresponds to a solar cycle. Long term
changes can occur.
Modifications of the Earth's orbit. The orbit of the Earth around the Sun changes slowly. This
influences the quantity of energy which is reflected and absorbed. It is thought that these variations of
Earth's orbit are one of the factors that triggered the ice ages.
Seasonal variations of the air temperature
The greenhouse effect. Approximately 1/3 of the energy emitted by the Sun returns to space after
penetrating Earth's atmosphere. A fraction of what remains is then absorbed by the atmosphere, but the
major part is absorbed by the Earth's surface. The surface returns infra-red energy and while part of this
energy is lost in space, another part is absorbed again and re-emitted by the clouds and gases like water
vapor, carbon dioxide, methane and oxide nitrous. This contributes to heat Earth's surface and the
troposphere to a temperature 33°C higher than what it would be otherwise.It is the natural greenhouse
effect which is essential for life.
Aerosols. These are very fine particles that remain in suspension in the atmosphere during a very long
time. They reflect the solar radiation and also absorb it. By modifying the quantity of the aerosols in the
atmosphere, one modifies the quantity of the reflected and absorbed solar energy.
Human factors
The greenhouse effect amplification. The greenhouse gases naturally present in the atmosphere
(e.g., water vapor, carbon dioxide, methane and oxide nitrous) keep the Earth at a sufficiently high
temperature so that life is possible. Scientific studies reveal that various human activities, whose
combustion of fossile fuels for producing electrical energy, heating and transport, produce greenhouse
gases. By increasing concentrations of these gases and by rejecting new greehouse gases such as
chloroflurocarbures (CFC), humans are likely to be contributing to increasing the average temperatures of
Earth.
Lan use evolution. By replacing forests with arable lands or the natural vegetation by asphalt and
concrete, humanity modifies the way in which terrestrial surface reflects sunlight and releases heat. All
these changes can also modify the regional configurations of evaporation, streaming and rains.

25. Atmospheric aerosols. Due to its agricultural and industrial activities, humanity adds great quantities
of fine particles called aerosols to the atmosphere. Most of the aerosols are quickly falling due to gravity
and precipitations, but they do not less influence the atmosphere radiative absorption. It is the quantity
and the nature of these particles as well as the nature of underneeth surface (land or water) that
determine if this have a heating effect of not. Nevertheless, the regional effects can be important.
Types of Climate Variation
Climate, although very slowly, keeps evolving. There are many causes behind variation in climate.
Climate variations can be categorized into two broad contexts.
Natural Climate Variation: There are several natural causes that force climate to change across time and scale. It
can be further drilled down into the following categories.
o Natural Forcings of the Climate System
Natural Forcings of the Climate System
Natural forcings are of two types.
External Forcings: These are essentially linked to changes
in the orbital parameters of the earth that control the
intensity and location of incident solar radiation, and
fluctuations in solar energy.
Internal Forcings: These comprise all those changes that
occur within the earth system itself, in particular volcanic
activity, fluctuations in ocean circulations and large-scale
changes in the marine and terrestrial biosphere or in the
cryosphere.

26. The Sun and the Global Energy Balance
The Sun is the prime source of external energy for the earth. Every moment, huge amount of energy reaches the
earth from the Sun. Let us see this animation that shows what happens to the solar radiation that reaches the earth.
Of the energy that remains in the earth (absorbed by atmosphere, clouds, and earth’s surface)
64% is radiated out into the space (atmosphere and clouds)
6% is radiated directly into the space by earth’s surface
7% is utilized in the movement of air
From the animation, we find that of the total energy that reaches the earth
6% is reflected by atmosphere
16% is absorbed by atmosphere
20% is reflected by clouds
3% is absorbed by clouds
51% is absorbed by oceans and land
4% is reflected by the surface of the earth
23% is utilized in evaporation of water from earth’s surface
This is how the balance of energy is maintained in the environment. The global energy balance is, therefore, the
balance between incoming energy from the Sun and outgoing heat from the earth.

27. Greenhouse Effect
Greenhouse effect is a phenomenon whereby earth’s atmosphere traps solar radiation, caused by the presence
of gases such as carbon dioxide, water vapour, and methane that allow incoming sunlight to pass through but absorb
the heat radiated back from earth’s surface. The gases that trap heat radiated from the earth are called
greenhouse gases (GHGs).
Let us see what exactly this mechanism is.
Except for GHGs, other gases have no extra capacity to absorb heat. Hence, GHGs are the main contributors in
trapping heat in the atmosphere.
GHG and non-GHG components in air:
Greenhouse effect is essential for our survival – without greenhouse effect, the
earth would become too cold to live.
The increasing greenhouse effect is the prime concern for our survival – being too
hot is not pleasing either
Greenhouse Gases Non-Greenhouse Gases
Water vapour, H2O Nitrogen, N2
Carbon dioxide, CO2 Oxygen, O2
Methane, CH4 Argon, Ar
Nitric oxide, NO2 Carbon monoxide, CO
Ozone, O3 Sulphur dioxide, SO2
Hydrocarbons
Chlorofluorocarbons
Internal and external forcings, global energy balance, radiative forcing and greenhouse effect together constitute the
natural forcings of the climate. These are the natural causes that forces climate to change.
Now let us study about the natural climate variability.

28. o Natural Variability of the Climate
Natural Variability of the Climate
Natural climate variability, as the name suggests, is caused by natural factors.
There are lots of natural factors that cause significant changes in the climate. These causes can
be within the earth or coming from outside the earth. Based on this, the natural climate
variability can be categorized into two groups.
Externally Induced Climate Variability: It refers
to the impact of some external factor that leads to
variability, such as the impact of
Variations in solar radiation
Solar and lunar tides
Internally Induced Climate Variability: It refers to
internal interactions between components of the
climate system, such as the interaction between
Ocean and atmosphere
Atmosphere and biosphere
 Externally and Internally Induced Climate Variability
 Feedback
Feedback
Feedback is the response of the climate to the internal variability of the climate system and to external forcings
Interestingly, the response of climate against a change can induce or reduce further change. Based on this, feed
can be classified into
Positive Feedback: A positive feedback cycle is a cycle where the effect reinforces the cause. This means that
impact will go on increasing. Let us understand the example shown in the screen.
When the surface temperature increases, it leads to increased evaporation from the ocean. This adds more wate
vapour to the atmosphere. Water vapour, being a GHG, further increases the surface temperature.
Thus, we find that an increase in surface temperature assists a further increase in the surface temperature. This
instance of positive feedback.

29. Negative Feedback: A negative feedback cycle is a cycle where the effect resists the cause. This means that th
impact will go on diminishing. Let us understand the example shown in the screen.
When surface temperature increases, it leads to a higher evaporation rate. More water vapour in the atmosphere
means more cloud formation. More clouds lead to increased albedo of the earth. This decreases the surface
temperature slightly. This leads to decreased evaporation from oceans. This leads to lesser clouds and lowering
earth’s albedo. This leads to decrease in surface temperature.
Thus, we find that an increase in surface temperature resists further increase in surface temperature. This is an
instance of negative feedback.
 Global and Hemispherical Variability
Global and Hemispherical Variability
Climate varies naturally on all time-scales. In the last few million years, the glacial periods and
the inter-glacial periods have alternated as a result of variations in earth’s orbit.

30. However, recently it was discovered that in the last glacial period large and very rapid
temperature variations took place over large parts of the globe, in particular in the higher
latitudes of the Northern Hemisphere. These led to an increase in temperature over these
regions by a few degrees. In contrast, the last 10,000 years appear to have been relatively more
stable, though locally quite large changes have occurred.
Recent analyses suggest that in the Northern Hemisphere climate of the past 1,000 years was
characterized by an irregular but steady cooling, followed by a strong warming during the 20th
century.
For the Southern Hemisphere, the data is not as precise, but it does indicate that temperature
changes in past centuries were markedly different from those in the Northern Hemisphere; the
only obvious similarity being the strong warming during the 20th century.
Over and above the global variability, climate can change at a regional level too. Let us find out
more about this.
o
 Regional Variability
Regional Variability
Regional or local climate is generally much more variable than climate on a hemispheric or
global scale because regional or local variations in one region are compensated for by opposite
variations elsewhere.
A good example for this kind of variability is the ENSO (El Niño Southern Oscillation).
ENSO (El Niño Southern Oscillation)
Source: NASA
It is a coupled phenomenon of ocean-atmosphere interaction. El Niño occurs in the Pacific

31. Ocean when there is a shift in ocean temperatures (towards warm) due to atmospheric
conditions in the tropical Pacific. These oceanic changes normally begin in December around
Christmas; hence the South Americans have named the phenomenon El Niño, meaning
‘Little Boy’. It has been observed that El Niño impacts weather patterns all over the
world. It occurs at regular intervals of about four years and primarily affects the Pacific coast of
South America, lasting for 8â€―10 months.
The Southern Oscillation is the see-saw pattern of reversing surface air pressure between the
eastern and western tropical Pacific; when the surface pressure is high in the eastern tropical
Pacific it is low in the western tropical Pacific, and vice-versa. Since the ocean warming and
pressure reversals are, for the most part, simultaneous, scientists call this phenomenon the El
Nino/Southern Oscillation or ENSO for short.
Normally, the trade winds blow towards the west across the Pacific, pushing warm surface
water away from the South American coast and this leads to upwelling of nutrients along the
Peru coast. Along this coast, the cold water is rich in nutrients and supports a diversity of
marine life and provides a good catch of fish for fishermen around this part of the year.
During an El Niño period, the winds slow down. Warm water accumulates at the surface and
causes significant reduction in the quantities of nutrients, plankton, and fish. This leads to
changes in weather patterns. A wide variety of disasters that have taken place all over the world
during these periods have been attributed to El Niño. When pressure is high in the Pacific
region, it tends to be low in the Indian Ocean, affecting the movement of the monsoon winds.
Thus, we find that natural climate variation manifests itself either globally or regionally. These
variations are caused by both internal and external factors. Common phenomena contributing to
climate variation include natural forcings, radiative forcing, greenhouse effect, and feedback
cycles.
Now, we will discuss the human-induced climate variation.
Human-induced Climate Variation: Human activities also influence the climate. The major
human-induced causes include changes in greenhouse gas (GHG) concentrations, changes
in aerosol levels, and changes in land use and land cover.
o Enhanced Greenhouse Effect
Enhanced Greenhouse Effect
Most human activities influence the climate by bringing about an increase in the concentration of greenhouse gases
in the atmosphere. An increase in the concentration of greenhouse gases leads to an increase in the magnitude of
the greenhouse effect. This is known asenhanced greenhouse effect.
The enhanced greenhouse effect is the direct result of human activities through processes such as the burning of
fossil fuels, industrial operations and forest clearing releasing carbon dioxide, methane and nitrous oxide into the
atmosphere. Chlorofluorocarbons, or CFCs, are also potent greenhouse gases, and as an added danger, they also
destroy the ozone layer.
A rough approximate of the contribution of GHGs is given in the following figures.

32. Global annual emissions of anthropogenic Share of different anthropogenic GHGs in total
GHGs from 1970 to 2004 emissions in 2004
World Climate Zones
Have you ever wondered why one area of the world is a desert, another a
grassland, and another a rainforest? Why are there different forests and
deserts, and why are there different types of life in each area? The answer is
climate.
Climate is the characteristic condition of the atmosphere near the earth's
surface at a certain place on earth. It is the long-term weather of that area (at
least 30 years). This includes the region's general pattern of weather
conditions, seasons and weather extremes like hurricanes, droughts, or rainy
periods. Two of the most important factors determining an area's climate are
air temperature and precipitation.
World biomes are controlled by climate. The climate of a region will determine
what plants will grow there, and what animals will inhabit it. All three
components, climate, plants and animals are interwoven to create the fabric of
a biome.
Some facts about climate

33. The sun's rays hit the equator at a direct angle between 23 ° N and 23
° S latitude. Radiation that reaches the atmosphere here is at its most
intense.
In all other cases, the rays arrive at an angle to the surface and are
less intense. The closer a place is to the poles, the smaller the angle
and therefore the less intense the radiation.
Our climate system is based on the location of these hot and cold air-
mass regions and the atmospheric circulation created by trade winds
and westerlies.
Trade winds north of the equator blow from the northeast. South of
the equator, they blow from the southeast. The trade winds of the
two hemispheres meet near the equator, causing the air to rise. As
the rising air cools, clouds and rain develop. The resulting bands of
cloudy and rainy weather near the equator create tropical conditions.
Westerlies blow from the southwest on the Northern Hemisphere
and from the northwest in the Southern Hemisphere. Westerlies
steer storms from west to east across middle latitudes.
Both westerlies and trade winds blow away from the 30 ° latitude
belt. Over large areas centered at 30 ° latitude, surface winds are
light. Air slowly descends to replace the air that blows away. Any
moisture the air contains evaporates in the intense heat. The tropical
deserts, such as the Sahara of Africa and the Sonoran of Mexico,
exist under these regions.
Seasons
The Earth rotates about its axis, which is tilted at 23.5 degrees. This
tilt and the sun's radiation result in the Earth's seasons. The sun
emits rays that hit the earth's surface at different angles. These rays
transmit the highest level of energy when they strike the earth at a
right angle (90 °). Temperatures in these areas tend to be the hottest
places on earth. Other locations, where the sun's rays hit at lesser
angles, tend to be cooler.
As the Earth rotates on it's tilted axis around the sun, different parts
of the Earth receive higher and lower levels of radiant energy. This
creates the seasons.

34. Köppen Climate Classification System
The Köppen Climate Classification System is the most
widely used for classifying the world's climates. Most
classification systems used today are based on the one
introduced in 1900 by the Russian-German climatologist
Wladimir Köppen. Köppen divided the Earth's surface
into climatic regions that generally coincided with world
patterns of vegetation and soils.
The Köppen system recognizes five major climate types
based on the annual and monthly averages of
temperature and precipitation. Each type is designated
by a capital letter.
A - Moist Tropical Climates are known for their high
temperatures year round and for their large amount of
year round rain.
B - Dry Climates are characterized by little rain and a
huge daily temperature range. Two subgroups, S -
semiarid or steppe, and W - arid or desert, are used with
the B climates.
C - In Humid Middle Latitude Climates land/water
differences play a large part. These climates have
warm,dry summers and cool, wet winters.
D - Continental Climates can be found in the interior
regions of large land masses. Total precipitation is not
very high and seasonal temperatures vary widely.
E - Cold Climates describe this climate type perfectly.
These climates are part of areas where permanent ice and
tundra are always present. Only about four months of the
year have above freezing temperatures.
Further subgroups are designated by a second, lower
case letter which distinguish specific seasonal
characteristics of temperature and precipitation.
f - Moist with adequate precipitation in all months and
no dry season. This letter usually accompanies the A, C,
and D climates.

35. m - Rainforest climate in spite of short, dry season in
monsoon type cycle. This letter only applies
to A climates.
s - There is a dry season in the summer of the respective
hemisphere (high-sun season).
w - There is a dry season in the winter of the respective
hemisphere (low-sun season).
To further denote variations in climate, a third letter was
added to the code.
a - Hot summers where the warmest month is over 22°C
(72°F). These can be found in C and D climates.
b - Warm summer with the warmest month below 22°C
(72°F). These can also be found in C and D climates.
c - Cool, short summers with less than four months over
10°C (50°F) in the C and D climates.
d - Very cold winters with the coldest month below -38°C
(-36°F) in theD climate only.
h - Dry-hot with a mean annual temperature over 18°C
(64°F) in Bclimates only.
k - Dry-cold with a mean annual temperature under 18°C
(64°F) in Bclimates only.
Major Climate Zones
(Printing tip: Set printer to landscape.)
Zone Latitudes Sunlight Temperatures Precipitatio

36. Tropics From Tropic of Direct sunlight Hot all year. Equator has
Capricorn (23.5 S Hours and intensity don’t most season
latitude) to Tropic of change much throughout Other parts
Cancer (23.5 N the year. tropics have
latitude) summers an
winters.
Subtropics From 23.5 N or S Intermediate between Typically hot; can Often dry; m
(Part of latitude to about 35 N tropics and other regions. go from hot in deserts are
southern U.S. or S latitude. daytime to cold at here.
and much of night.
Mexico)
Temperate From about 30 N Fluctuates with the Fluctuate with the Precipitation
(Most of U.S. latitude to about 65 N seasons. seasons. seasons. Var
and Canada.) latitude (Arctic Circle); Hours and intensity are
The farther south
From 30 N latitude to greater in summer, less in
and the closer to
about 65 N latitude winter.
the ocean, the less
(Antarctic Circle)
they fluctuate. *
Polar From 60 degree N or S Changes dramatically. Sun The winters are Very dry; litt
(Part of Canada latitude to each pole. is never direct (stays low very cold and the precipitation
and Alaska) on horizon). summers cool to and ice cove
Almost no light in winter; cold. round.
all light in summer.
* Maritime temperate zone: Water holds heat longer than land does, so temperatures in
locations near oceans don’t fluctuate as much during the year. These areas have cooler
summers and warmer winters than inland regions.
* Continental temperate zone: Areas in the middle of the continent, far from water, range
widely in temperature. They often have very cold winters and hot summers.

37. Tropical savanna climate or tropical wet and dry climate is a type of climate that corresponds to
the Köppen climate classification categories "Aw" and '"As."
Tropical savanna climates have monthly mean temperature above 18°C in every month of the year and
typically a pronounced dry season, with the driest month having precipitation less than 60 mm and also
less than (100 − [total annual precipitation {mm}/25]). This latter fact is in direct contrast to a tropical
monsoon climate, whose driest month sees less than 60 mm of precipitation but has more than (100 –
[total annual precipitation {mm}/25]). In essence, a tropical savanna climate tends to either see less
rainfall than a tropical monsoon climate or have more pronounced dry seasons.
There are generally four types of a tropical savanna climate:
One form of the tropical savanna climate features distinct wet and dry seasons of relatively equal
duration. Most of the region’s annual rainfall is experienced during the wet season and very little
precipitation falls during the dry season.
The second type of a tropical savanna climate features a lengthy dry season and a relatively short
wet season. This version features seven or more dry season months and five or less wet season
months. There are variations within this version. On one extreme, the region receives just enough
precipitation during the short wet season to preclude it from a semi-arid climate classification. This
drier variation of the tropical savanna climate is typically found adjacent to regions with semi-arid
climates. On the other extreme, the climate features a lengthy dry season followed by a short but
extremely rainy wet season. However, regions with this variation of the climate do not experience
enough rainfall during the wet season to qualify as a tropical monsoon climate.
The third type of a tropical savanna climate features a lengthy wet season and a relatively short dry
season. This version features seven or more wet season months and five or less dry season months.
This version’s precipitation pattern is similar to precipitation patterns observed in some tropical
monsoon climates. However, regions with this variation of the climate do not experience enough
rainfall during the wet season to qualify as a tropical monsoon climate.
The fourth, rarer form of the tropical savanna climate features a dry season with a noticeable amount
of rainfall followed by a rainy wet season. In essence, this version mimics the precipitation patterns
more commonly found in a tropical monsoon climate. However, regions with this version of the
climate fall short of a tropical monsoon climate categorization because it either does not receive
enough precipitation during the dry season, or it does not receive enough annual precipitation.
Tropical climate
From Wikipedia, the free encyclopedia

38. Locations of tropical climates, with subtypes.
Af—Tropical rainforest climate.
Am—Tropical monsoon climate.
Aw—Tropical savanna climate.
Beach in Naples, Florida lined with coconuttrees is an example of a tropical climate. Although it lies in the subtropics over a
hundred miles north of the tropic of cancer, the warm waters of theGulf of Mexico give it a monthly mean temperature never
under 18 °C (64 °F), classifying its climate as tropical.

39. Intertropical Convergence Zone vertical velocity at 500 hPa, July average in units of pascals per second. Ascent (negative
values) is concentrated close to the solar equator; descent (positive values) is more diffuse.
A tropical climate is a climate of the tropics. In the Köppen climate classification it is a non-arid climate in
which all twelve months have mean temperatures above 18 °C (64 °F). Unlike the extra-tropics, where there
are strong variations in day length and temperature, with season, tropical temperature remains relatively
constant throughout the year and seasonal variations are dominated by precipitation.
Contents
[hide]
1 Subtypes
2 Intertropical Convergence Zone
3 References
4 External links
[1]
Tropical rainforest climate (Af): All twelve months have average precipitation of at least 60 mm
(2.4 in). These climates usually occur within 5–10° latitude of the equator. In some eastern-coast
areas, they may extend to as much as 25° away from the equator. This climate is dominated by
the Doldrums Low Pressure System all year round, and therefore has no natural seasons.
[1]
Tropical monsoon climate (Am): This type of climate, most common in Southand Central
America, results from the monsoon winds which change direction according to the seasons. This
climate has a driest month (which nearly always occurs at or soon after the "winter" solstice for that
side of the equator) with rainfall less than 60 mm, but more than (100 − [total annual precipitation
{mm}/25]).
[1]
Tropical wet and dry or savanna climate (Aw): These climates generally have a pronounced dry
season, with the driest month having precipitation less than 60 mm and also less than (100 − [total
annual precipitation {mm}/25]).

40. Temperate climate
From Wikipedia, the free encyclopedia
For the usage in virology, see temperateness (virology).
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be challenged and removed.(January 2013)
Part of the nature series
Weather
Calendar seasons
Spring
Summer
Autumn
Winter
Tropical seasons
Dry season
Wet season
Storms
Thunderstorm (Thundersnow)
Supercell

41. Downburst
Lightning
Tornado
Waterspout
Tropical cyclone (Hurricane)
Extratropical cyclone
Winter storm
Blizzard
Ice storm
Dust storm
Firestorm
Cloud
Precipitation
Drizzle (Freezing drizzle)
Rain (Freezing rain)
Snow (Rain and snow mixed • Snow grains • Snow roller)
Graupel
Ice pellets

42. Hail
Topics
Meteorology
Climate
Weather forecasting
Heat wave
Air pollution
Cold wave
Weather portal
V
T
E
Temperate climate (shown in green in the map)

43. In geography, temperate or tepidlatitudes of the globe lie between thetropics and the polar regions. The
changes in these regions betweensummer and winter are generally relatively moderate, rather than extreme
hot or cold.
However, in certain areas, such asAsia and central North America, the variations between summer and winter
can be extreme because these areas are far away from the sea, causing them to have a continental climate. In
regions traditionally considered tropical, localities at high altitudes(e.g. parts of the Andes) may have a
temperate climate.
The north temperate zone extends from the Tropic of Cancer (at about 23.5 degrees north latitude) to
the Arctic Circle (at approximately 66.5 degrees north latitude). The south temperate zone extends from
the Tropic of Capricorn (at approximately 23.5 degrees south latitude) to the Antarctic Circle (at approximately
66.5 degrees south latitude). [1][2]
In a very broad sense, temperate climate also includes a subtropical climate, variants: subtropical
semidesert/desert, humid subtropical, oceanic subtropical and Mediterranean climate. However, a typical
temperate climate is one of the four climate zones in the world, beside polar regions (subarctic climate, arctic
climate, tundra climate,ice cap climate) and the subtropics, tropics.
The maritime climate is affected by the oceans, which help to sustain somewhat stable temperatures
throughout the year. In temperate zones the prevailing winds are from the west, thus the western edge of
temperate continents most commonly experience this maritime climate. Such regions include Western Europe,
and western North America at latitudes between 40° and 60° north (65°N in Europe).
Continental, semi-arid and arid are usually situated inland, with warmer summers and colder winters. Heat
loss and reception are aided by extensive land mass. In North America, the Rocky Mountains act as a climate
barrier to the maritime air blowing from the west, creating a semi-arid and continental climate to the
east.[3][4][5] In Europe, the maritime climate is able to stabilize inland temperature, because the major mountain
range – the Alps – is oriented east-west (the area east of the long Scandinavian mountain range is an
exception).
The vast majority of the world's human population resides in temperate zones, especially in the northern
hemisphere because of the mass of land.[6]

44. The temperate climate refers to zones in a range of latitudes between 40° and 60/70°.
No as hot as the subtropical climate and milder than the polar climate, it is usually
defined but by what it is not.
A sub-type is the moderate oceanic climate oceanic : windy and without excessive
temperatures, which characterizes the Western shores of Europe. The four seasons are
well marked. In these climate zones you tend to find a wide range of architecture as well
due to the need for housing that can with stand both the cold and snow as well as the
summer heat. Common place in these dwellings is to have both air conditioning
systems and heating systems as well as ceiling fans with lights to help circulate the air.
It is associated by leafy tree forests and meadows. It alternates relatively fresh
summers with mild and wet winters.
Another sub-type is the continental moderate climate which dominates the steppes. It is
cold and dry in winter while being rather hot and rainy in the summer. There are
frequent storms and the transition of seasons are short. The hypercontinental climate
has short summers and dry and very cold winters. It extends over Siberia, Alaska and
Canada which are covered with coniferous tree forests. ·
Polar and highland climates
temperature is key (again)
• cold due to limited solar radiation
• low angle of incidence of insolation
Moisture is relatively scarce all the time
except where oceans intercede
Annual fluctuation is much greater than diurnal changes
Earth - Sun relationships