Cloud Seeding

Soumyajit Basu

What is Cloud Seeding?The introduction of artificial substances (usually

silver iodide or dry ice) into a cloud for the purpose of either modifying its development or increasing its precipitation.

The attempt to change the amount or type of precipitation or the structure of clouds by dispersing substances into the air which allow water droplets or ice crystals to form more easily. The most common chemicals used for cloud seeding are silver iodide and dry ice.

Why do we use it?• By the year 2025 two thirds of the world population will live under severe water stress conditions as determined by studies of the World Meteorological Organization (WMO)

• The rapid growth of Agricultural and Industrial sector along with the population explosion makes India particularly vulnerable.

• Though India get high amount of rainfall compared to many other countries, the large infrastructure and water intensive agricultural practice makes India vulnerable to even to the minor swings (< 5%) in rainfall

• Water related problems within the states

Cloud Seeding• Cloud seeding is actually a very complex

process. In the simplest terms, it introduces other particles (CCN’s) into a cloud to serve as cloud condensation nuclei and aid in the formation of precipitation.

There are three types of cloud seeding: static mode, dynamic mode, and hygroscopic seeding.

•Static mode cloud seeding seeks to increase rainfall by adding ice crystals (usually in the form of silver iodide or dry ice) to cold clouds.

•Dynamic mode cloud seeding increases rainfall by enhancing "vertical air currents in clouds and thereby vertically process more water through the clouds." Basically, in this method of seeding, a much larger number of ice crystals are added to the cloud than in the static mode.

•In hygroscopic seeding, salt crystals are released into a cloud. These particles grow until they are large enough to cause precipitation to form. Clouds can be seeded from above with the help of airplanes that drop pyrotechnics, or from the ground by using artillery or ground-to-air rockets

20.32microns76.2 microns5080microns = 0.5cm5080micro

ns = 0.5cm

Cloud SeedingDepending on the preciitation cloud seeding can be divided into 2 types-

(i)Warm Cloud Seeding(water drops)

(ii) Cold Cloud seeding(ice crystals)

Technologies Required Cloud seeding requires advanced equipment and facilities including-

1)Aircraft2)A meteorological station network to

monitor the clouds,3) A rainfall monitoring ground network4) A network for data collection and

processing, 5) A satellite image transmission

networks.

Silver IodideWhy Silver Iodide ?

It has a crystalline structure similar to ice crystal, and it acts as an effective ice nucleus at temp. of -4°C and lowerSilver iodide, when burned, creates extra ice crystals in winter clouds to increase snow fall. (The first AgI generator could discharge 1016 particles per gram)

It can be distributed from the ground...

Silver Iodide…or from the air.

Ground based Generator Automated High-Output Ground Seeding System

Aircraft-mounted flaresCloud Seeding Aircraft

TITAN• TITAN means Thunder storm Identification Tracking Analysis and Now-casting

• It is a software developed for forecasting and analysis of thunder storms in weather modification programs

• TITAN gives 10 derived parameters of the cloud giving a scope to find latitude and longitude and cross sectional view of the clouds at any instant.

• The cloud parameters given by the TITAN are given as Area, Volume, Mass, Precipitation Flux, Vertical Integrated Liquid Content etc.,

--shown in next slide

1) Area (km2) :

Area (km2) covered by the cloud, it is the value of horizontal spread up of the cloud as observed by radar

2) Volume (km3) : Volume (km3) of the cloud, it is the value of the volume occupied by the cloud as observed by radar

3) Mass (k tons) : Mass (k tons) of the cloud, it is the value of the mass contained by the cloud as observed by radar

4) V I L (kg/m2) :

Vertical Integrated Liquid content (kg/m2) of the cloud, it is the value of the vertical integration of liquid matter present in the cloud as observed by the radar

5) P-flux (m3/sec) : Precipitation flux of the cloud, it is the value of the flux of mass ( Precipitation) falling down from the cloud as observed by the radar

6) Max- Z (dbz) :

Maximum reflection of the cloud, it is the value of the maximum reflection of the cloud as observed by the radar. Reflection depends on the type of the matter present in the cloud, basically if the matter if the matter present in the cloud is more, the reflection of the cloud will be more

7) Ht-maxZ (km) : Height of maximum reflection of the cloud, it is the value of the height from which maximum reflection is coming from the cloud as observed by the radar.

8) Centroid (km) : Centroid of the cloud is basically known as the centre of gravity of the cloud, it is the height at which the total weight of the cloud is said to be concentrated as observed by the radar

9) Cloud Base (km) :

Cloud Base is the height of the bottom part of the cloud from the earths surface as observed by the radar

10) Cloud Top (km): Cloud Top is the height of the top most part of the cloud from the earths surface as observed by the radar

Target and Control Method

• By using TITAN software we can compare various parameters of Seeded and Unseeded clouds which is known as

“Target and Control method”

• In the Target and Control method

Target means the Seeded cloud and the

Control means the Unseeded cloud.

TITAN images of the CLOUDS on AUGUST 11,2008

Control Cloud 137

Target Cloud 136/147

Control Cloud 134

Control Cloud 133

Seeding of Target Cloud 136/147

Advantages

• It contributes to augmenting freshwater resources to meet water demands, particularly in arid and semi-arid regions. It holds promise for regions facing water deficiencies. Its efficiency can be increased through research, experiments, and a better understanding of precipitation and cloud systems;

• Cloud seeding can contribute to increasing shallow underground storage water;

• It allows successful dissipation of fogs and low stratus clouds that can be an obstacle to aviation traffic at airports;

• It contributes to improving the productivity of rain-fed agricultural areas, either by increasing rainfall volumes or sometimes by controlling the spatial and temporal distribution of rainfall.

Disadvantages

•The disadvantages of this technology are as follows:•The effectiveness of this technology in drought situations is very limited, primarily due to inappropriate climatic conditions during such periods;•Positive benefits from a cloud-seeding process for one group of a community may be accompanied by negative effects on other groups;•For countries of limited areas, or along national boundaries, cloud seeding could result in problems relating to possible negative effects that might occur in neighboring countries. Cooperation in such cases is therefore essential, and may require issuance of legislation regulating the legal aspects of cloud seeding;•Cloud seeding requires advanced and costly equipment, as well as the recording, collection and analysis of relevant information. The seeding process also required qualified professional staff and modern equipment. Thus, the benefits may ultimately not be sufficient to cover the costs. A cloud-seeding program also will not produce effective results without accurate weather data, or an inability to carry out the seeding process at the suitable time or place;•Although planning of cloud-seeding programs may be successfully and efficiently carried out, accurate and practical assessment of the results may be hindered by the lack of physical and statistical evidence. The assessment process also may require the use of modeling techniques.

Cloud seeding operations-2008 25 Jul –

24 Nov 08 (120 days)

DistrictNo.of

SeedingsHygro's (1 Kg)

Hygro's (0.5 Kg)

ANANTAPUR 83 72 21

CHITTOOR 55 44 16

GUNTUR 0 0 0

KADAPA 76 71 16

KARIMNAGAR 7 7  

KURNOOL 64 64 10

MAHABUBNAGAR 105 102 21

MEDAK 11 13  

NALGONDA 35 35 8

NELLORE 8 5 5

PRAKASAM 16 10 12

RANGA REDDY 24 28 3

Total 484 451 112

12 Districts

Thank You