Closely spaced isobars or isohypses indicate a tight pressure gradient, which implies stronger winds. A tight pressure gradient means the pressure is changing rapidly over small distances. Since wind is caused by horizontal pressure differences, a tight gradient results in stronger winds as air moves from high to low pressure. Meteorologists analyze isobar/isohypse spacing to identify areas of stronger winds. Q2. How can isotherms help identify areas of warm or cold air advection? Answer: When isotherms are bunched closer together, it indicates warm air advection. When they are farther apart, it indicates cold air advection.

1. Arulalan.T
Final Year MCA
Saveetha Engg College

2. Project Title
Contour Analysis And
Visualization
Guide
Mr.Thyagarajan Shanmugham

3. Thanks To . . .
Mr.Charles Doutriaux
CDAT Developer
Dr. Krishna AchutaRao
Center for Atmospheric Science
IIT Delhi

4.
CDAT
Climate Data Analysis Tool

5. Installation
Working in Cdat
Edit Cdat Map
Isolines
NetCDF
Demo on creating current isotherm lines over on India map

6. System requirement
Hardware
* Dual Core Intel 2 Ghz Processor Machine
* Decent Broadband Connection
Software
* A linux distro ­ in my case Ubuntu 9.10
* CDAT
* Dependencies of CDAT

7. Dependencies :
# bison *
# byacc *
# flex *
# gawk *
# g++
# gfortran (for contrib packages)
# libxt­dev
# libx11­dev
# tcsh (just highly recomended)
# xorg­dev (also called xserver­xorg­dev)
#libpng (1.1 or later ) and freetype (1.4 or later)

8. Installation :
export CC=gcc
export FC=gfortran
export CXX=g++
svn export http://www­
pcmdi.llnl.gov/svn/repository/cdat/tags/5.2 cdat­5.2­src
./configure ­­prefix=/usr/local/cdat5.2/
­­with­externals=/usr/local/cdat5.2/cdat_ext.
sudo make

9. Cdat Working Directory :
# You can now start CDAT with the command
$ cd /usr/local/cdat5.2/bin
$ ./cdat

10. Cdat Working Directory :
# You can now start CDAT with the command
$ cd /usr/local/cdat5.2/bin
$ ./cdat

11. Example Program

12. #sample.py
import vcs, cdms2, cdutil, time, os, sys
import time
v = vcs.init()
filepath = os.path.join(sys.prefix,'sample_data/clt.nc')
cdmsfile = cdms2.open( filepath )
cf_asd = v.getboxfill( 'ASD' )
cf_asd.datawc(1e20,1e20,1e20,1e20)
cf_asd.level_1=1e20
cf_asd.level_2=1e20
cf_asd.color_1=240
cf_asd.color_2=240
data = cdmsfile('clt', longitude=(­180, 180), latitude = (­180., 180.))
#data = cdmsfile('clt', longitude=(60, 100), latitude = (5., 40.)) # For India
v.plot( data,cf_asd )

13. Cdat World Map ­ Outline

14. Cdat India Map ­ Outline

15. #sample1.py
import vcs, cdms2, cdutil, time, os, sys
import time
v = vcs.init()
filepath = os.path.join(sys.prefix,'sample_data/clt.nc')
cdmsfile = cdms2.open( filepath )
cf_asd = v.getboxfill( 'ASD' )
cf_asd.datawc(1e20,1e20,1e20,1e20)
cf_asd.level_1=1e20
cf_asd.level_2=1e20
cf_asd.color_1=240
cf_asd.color_2=240
data = cdmsfile('clt', longitude=(­180, 180), latitude = (­180., 180.))
#data = cdmsfile('clt', longitude=(60, 100), latitude = (5., 40.)) # For
India
v.plot( data,cf_asd , continents=4 )

16. Cdat World Map ­ Continents

17. Cdat India Map ­ Continents

18. How To Edit Cdat Map

19. Our Indian Political Map wrongly depicted in CDAT as below

20. 1) Correcting the Pakistan part , which belongs to India
2) Correcting the part of the land which is occupied by the
Chinese in the state of jammu and kashmir
While asking help from Mr.Charles Doutriaux [ CDAT ­
Developer ] regarding edit map in cdat, he gave the source
data of cdat world map in .shp binary file.

21. #make_world_co­ordinates.py
import vcsaddons
v = vcs.init()
world_continents = vcsaddons.continents.Guc(x=v)
data = world_continents.load_shapefile('/home/arul/Desktop/WORLD_COUNTRIES.shp')
#wrting the data into out.txt file
fileiter=open("/home/arul/Desktop/out.txt","w")
print >> fileiter, data[:]
fileiter.close()

22. 200 1 59.790276 83.623596 ­72.830238 ­12.204896
60.238045 ­43.123886
60.174297 ­43.109169
60.110275 ­43.086662
60.082497 ­43.124443
60.019024 ­43.140419
59.989437 ­43.193470
59.992493 ­43.238892
60.023605 ­43.331116
59.972763 ­43.358894
59.928326 ­43.395832
59.903320 ­43.501945
59.954636 ­43.488258
59.914711 ­43.572777
59.947212 ­43.724716
59.877213 ­43.653885
59.804436 ­43.849724
59.790276 ­43.902222
59.811661 ­44.006950
59.800545 ­44.061943
59.813538 ­44.109722
There are more than one lakh lines like this.
These are x,y co­ordinate points.
Simply says, these are Latitude and
Longitude values of the whole [real] world.
out.txt

23. My Hacks On Cdat Map

24. Over World

25. Over India

27. My Construction On
Cdat India Map

33. Finally

34. Our India

35. Now we have to save as the modified out.txt file
i.e WorldContinent.shp's text file in the name of
“data_continent_other7” in the path
“/home/arul/PCMDI_GRAPHICS/”
v.plot( data,cf_asd , continents=6 )

36. #sample2.py
import vcs, cdms2, cdutil, time, os, sys
import time
v = vcs.init()
filepath = os.path.join(sys.prefix,'sample_data/clt.nc')
cdmsfile = cdms2.open( filepath )
cf_asd = v.getboxfill( 'ASD' )
cf_asd.datawc(1e20,1e20,1e20,1e20)
cf_asd.level_1=1e20
cf_asd.level_2=1e20
cf_asd.color_1=240
cf_asd.color_2=240
#data = cdmsfile('clt', longitude=(­180, 180), latitude = (­180., 180.)) # For
the world
data = cdmsfile('clt', longitude=(60, 100), latitude = (5., 40.))
v.plot( data,cf_asd, continents=6 )

37. Corrected India Map in Cdat

38. Corrected India region in Cdat­World Map

39. Isolines

40. Isolines
­ Contour
­ Isotherm
­ Isobar

41. What is Contour ?
Contour is line drawn on a map connecting points of equal
height .
Contour lines (also isolines) connect a series of points of
equal elevation and are used to illustrate topography, or
relief
on a map.
They show the height of ground above Mean Sea Level
(M.S.L.) in either feet or meters and can be drawn at any
desired interval.

44.
What is Isotherm ?
An isotherm ( meaning 'heat') is a line that connects
points on a map that have the same temperature.
Therefore, all points through which an isotherm
passes have the same temperatures at the time
indicated.

45.
What is Isobar ?
A line of constant pressure. Isobars are found ONLY
on surface charts.
They most commonly connect lines of equal pressure
in the units of millibars.
High pressure isobars generally occurs with isobars
above 1010 mb while low pressure isobars occur with
lower than 1010 millibars.

46.
What are the Uses of Isotherm ?
Isotherms are used to find regions with
* Warm air advection
* Cold air advection
* Short waves
* Fronts
* Temperature gradient boundaries and
* Instability zones.
They are most commonly used at pressure
surfaces below 500 millibars and on surface charts.

47. Isolines in Cdat

48. Iso Lines Over India Map

49. CDAT User :
How can a user create their own Isolines
on cdat map?

50. CDAT User :
Generally we can't create our own isolines in
cdat map.
We can set only levels on isolines.

51. levels = [10,20,30]

52. Reason is . . .

53. NetCDF file

54. What is NetCDF File ?
NetCDF (network Common Data Form)
is a set of software libraries and machine-
independent data formats that support the creation,
access, and sharing of array-oriented scientific data.

55. Purpose of NetCDF (.nc)File
The main purpose of netCDF is to protect
the user from having to know the details of how
the data is stored in the netCDF file.
Cdat have clt.nc file which is reason to
create isolines on map.

56. My Project
is going to create our own isolines on
cdat map.

57. How to read/write NetCDF
(clt.nc) file ?

58. $ sudo apt-get install netcdf-bin
To convert .nc binary into editable text
$ ncdump clt.nc > clt.cdl
To generate clt.nc from edited clt.cdl file
$ ncgen -b clt.cdl

59. What is My Project ?
My Project going to create the isotherm
lines, which will be plot on India Cdat Map.
We have 4 processes to do this . . .
.

60. Process 1:
1.1 WebScrape the current temperature and
barometer (millibar) of all over cities in India and
its surroundings countries from the Internet.
1.2 Store the city name, temperature, millibar
into the file.

61. Process 2:
2.1 Combine the temperature and mb values with
latitude and longitude of corresponding cities, which
is already collected info file.
2.2 Make decision and covert lat into 4 intervals &
lon into 5 intervals

62. Process 3:
3.1 Create the binary iso.nc file which contains
current temperature values along with lat & lon.
3.2 Move the “iso.nc” to the cdat location in our
system.

63. Process 4:
4.1 Run the “isotherm.py” to create our isolines on
cdat India Map.
4.2 E­Mail to us with the attachment of the output
image, which is created by “isotherm.py”

64. To automate all the 4 processes
we may use “crontab”
to get isotherm update on India
for every one hour or . . .

65. Web Scraping
Program
Isothermal Lines
On Cdat Map
Google
Temperature
Values
Store the Google
Temperature Values
into the File
Draw Isothermal
Lines from the
File Values
Data Flow Diagram For Generating Isothermal Lines From Google Temperature

66. Before going to Demo . . .

67. On 12 th Mar 2010 isotherm
lines on India from
1 pm to 11 pm

68. 1 pm

69. 4 pm

70. 5 pm

71. 6 pm

72. 7 pm

73. 8 pm

74. 9 pm

75. 10 pm

76. 11 pm

77. 12 am

78. Demo . . . !

79. Coding . . .

80. Applications :
By the visualization of Isothermal lines on map, we can
analyses and obtain the temperature and pressure
values.
Using this we can analysis/predict the climate changes.

81. Applications :
.
Advection ­ The horizontal transfer of
heat
Forecaster ­ Someone who makes
predictions of the future

82. Applications of isolines :
­By Meteorologist Jeff Haby
Q1. What is meteorologically significant about isobars or
isohypses being closely spaced?
Answer: A forecaster can determine the amount of thermal
advection (temperature advection). Closely spaced contours
indicate stronger wind.
Source : http://www.theweatherprediction.com/basic/isopleths/

83. Applications of isolines :
­By Meteorologist Jeff Haby
Q2. Negative thickness advection is lower values of
thickness moving toward a fixed point. How can this be
determined by examining a thickness chart?
Answer: If height contours or isobars are overlaid on the
thickness field, a forecaster can determine the speed and
direction cold air will have. If the lower thicknesses are
advected by the height contours or isobars toward a fixed
point, that fixed point will experience a cooling of weather.
Source : http://www.theweatherprediction.com/basic/isopleths/

84. Applications of isolines :
­By Meteorologist Jeff Haby
Q3. In feet and meters, what is the average height of the
850, 700, 500 and 300 mb surfaces?
Answer:
850 mb (1,500 meters, 5,000 feet)
700 mb (3,100 meters, 10,000 feet)
500 mb (5,500 meters, 18,000 feet)
300 mb (9,300 meters. 30,000 feet)
Source : http://www.theweatherprediction.com/basic/isopleths/

85. Applications :
Isallobar / Height change contours­
A line of equal pressure change. They
are used to forecast the propagation of low
and high pressure systems

86. Applications of isolines :
­By Meteorologist Jeff Haby
Q4. How are isallobars significant to weather forecasting?
Answer: They give the indication of pressure change. Lows
tend to move toward the region with the greatest height falls.
Values tell a forecaster if a low or high is increase or
decreasing in intensity..
Source : http://www.theweatherprediction.com/basic/isopleths/

87. THANK YOU