CAIPEEX

A study for the effectiveness of cloud seeding in enhancing rainfall has been recently conducted under CAIPEEX phase-4 by the Indian Institute of Tropical Meteorology (IITM).

Key findings of the study:

• All cumulus clouds do not produce rainfall when cloud seeding is done.
  • Cumulus clouds are detached, individual, cauliflower-shaped clouds usually spotted in fair weather conditions.
• 20-25% of cumulus clouds produce rainfall if cloud seeding is done correctly.
• The relative enhancement of rainfall was 46% as measured by automatic rain gauges.
  • However, the actual increase in rainfall was only 18%.

• The cost of producing water through cloud seeding will drop by more than 50% if indigenous seeding aircraft are used.

Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX phase-4):

• CAIPEEX phase-4 experiments were conducted by the Indian Institute of Tropical Meteorology (IITM), Pune.
  • IITM is an autonomous institute under the Ministry of Earth Sciences (MoES).
• Objective: To investigate the efficacy of hygroscopic seeding in deep convective clouds and develop a cloud seeding protocol.
  • Convective clouds are formed by convection, which is the process of warmer air rising since it is less dense than the surrounding atmosphere.
• It aims to understand the complexities of cloud behaviour, aerosol interactions, and precipitation enhancement.
• Tools employed: Two aircraft for cloud parameter study and seeding.
• Specific characteristics within a cloud, such as its liquid water content, vertical motion (indicative of its growth), and cloud depth can give an idea if it will rain or not.
• Convective clouds over 1 kilometer deep, are likely to evolve into deep cumulus clouds.

Cloud seeding:

• Cloud seeding is a technique in which cloud-forming particles are used to increase rainfall.
• It is of two types: Hygroscopic and Glaciogenic cloud seeding.

Hygroscopic Seeding:

• Hygroscopic seeding is a weather modification technique that involves dispersing hygroscopic (water-absorbing) materials, such as salts or compounds, into clouds or the atmosphere to encourage the formation of rain or snow.
• The seeding agents used in hygroscopic cloud seeding serve as efficient cloud condensation nuclei (CCN) or GCCN.
• They play a crucial role in strengthening the condensation and collision–coalescence process, thereby widening the droplet size distribution (DSD) and increasing the precipitation efficiency.
• Calcium chloride flare is used for seeding at the base of warm convective clouds during their growing stage.
• Convective cloud bases vary from 500-1,500 meters in the summer-monsoon season to 2,000 meters or higher during monsoon breaks, depending on lower atmospheric moisture.

Cloud Seeding Methods

• • Hygroscopic Cloud Seeding:
    • Disperses salts through flares or explosives in the lower portions of clouds. The salt grows in size as water joins with them.
  • Static Cloud Seeding:
    • It involves spreading achemical like silver iodide into clouds. The silver iodide provides a crystal around which moisture can condense.
    • The moisture is already present in the clouds, but silver iodide essentially makes rain clouds more effective at dispensing their water.
  • Dynamic Cloud Seeding:
    • It aims to boost vertical air currents, which encourages more water to pass through the clouds, translating into more rain.
    • The process is considered more complex than static cloud seeding because it depends on a sequence of events working properly.

Applications of Cloud Seeding

• • • Agriculture:
      • It creates rain, providing relief to drought-stricken areas.
        • g.: ‘Project Varshadhari’ in Karnataka in 2017.
      • Power Generation:
        • Cloud seeding experiments have shown to augment production of hydroelectricityduring the last 40 years in Tasmania, Australia.
      • Water Pollution Control:
        • Cloud seeding can help to maintain minimum summer flowsof the rivers and dilute the impact of treated wastewater discharges from municipalities and industries.
      • Fog Dispersal, Hail Suppression, and Cyclone Modification:
        • During the winter the cloud seeding programme is used toincrease the mountain snowpack so that additional runoff is received during the spring melt season.
        • “Project Sky Water”of the U.S.A. in 1962 for weather modification through cloud seeding aimed at fog dispersal, hail suppression, and cyclone modification.
      • Tackle Air Pollution:
        • Cloud seeding can potentially be used to settle down toxic air pollutants through the rain.
        • g.: Recently, the Central Pollution Control Boardalong with other researchers mulled the use of cloud seeding to tackle Delhi’s air pollution.
      • Tourism:
        • Cloud seeding can transform typically dry areas much more hospitable to enhance tourism.

Challenges involved in Cloud Seeding

• Potential Side-effects:
  • The chemicals used in cloud seeding might be potentially harmful to plants, animals, and people, or the environment.
• Abnormal Weather Patterns:
  • It might ultimately change climatic patterns on the planet. Places that normally receive moisture might start experiencing drought due to the artificial process of adding chemicals to the atmosphere to stimulate rain.
• Costly:
  • It involves processes such as delivering chemicals to the sky and releasing them into the air by flare shots or airplanes, which involves huge costs and logistic preparation.
• Pollution:
  • As artificial rain falls, seeding agents like silver iodide, dry ice or salt will also fall. Residual silver discovered in places near cloud-seeding projects is considered toxic.As for dry ice, it can also be a source of greenhouse gas that contributes to global warming, as it is basically carbon dioxide.

Short-lived halogens

Recently, a new study revealed that oceans play a crucial role in cooling the planet by releasing short-lived halogens, including chlorine, bromine, and iodine.

Key findings:

• These halogens currently contribute 8-10% of cooling, a figure projected to increase to 18-31% by 2100.
• The short-lived halogens from the ocean reduce warming by depleting ozone.
• They increase methane’s lifetime in the atmosphere by destroying hydroxyl radicals (OH).
• They have increased the global methane burden by 14 per cent and 9 per cent for pre-industrial and present-day conditions.
• Halogens increase the levels of water vapour, a greenhouse gas in the atmosphere.
• The emission of halogen from the ocean is not the same across the world.
• Over continents, the emissions are small, while it is bigger in polar regions and some places with higher ozone levels.

Short-lived halogens:

• Short-lived halogens refer to chlorine, bromine, and iodine compounds that have a relatively short lifespan in the atmosphere, typically less than six months.
• These halogens play a role in the Earth’s climate system by contributing to cooling and warming effects.

Impact of short-lived halogens on the substances that causes global warming:

• Ozone: Halogenscause a depletion of ozone in the Ozone is a greenhouse gas that traps outgoing radiation, leading to warming. The short-lived halogensfrom oceans reduce warming by depleting ozone. Its cooling effect was -0.24 ± 02 Watts per square metre (W m−2).
• Methane: However, their effect on methane is the opposite. Short-lived halogens increase methane’s lifetime in the atmosphere by destroying hydroxyl radicals (OH). OH is a sink as it is known to break down this greenhouse gas. These short-lived halogens increased the global methane burden by 14 per cent and 9 per cent for pre-industrial and present-day conditions, This leads to a warming effect of 0.09 ± 0.01 W m−2 of warming.

• Water Vapour: Similarly, these halogens increase the levels of water vapour, a greenhouse gas, in the atmosphere, causing a warming effect of 011 ± 0.001 W m−2.

• Aerosols: These short-lived halogens reduce the formation of cooling aerosols, which are minute particles suspended in the atmosphere that reflect sunlight. It causes a small warming of 03 ± 0.01 W m−2.

The overall impact of these short-lived halogens:

• Though these halogens drive an increase in warming by influencing methane, water vapour and aerosols, they compensate this by destroying ozone, which exerts a cooling effect.

Overall, the net cooling effect was found to be −0.13 ± 0.03 W m−2.