Therefore, these scattering techniques need to be improved for the development of realistic parameterization schemes for the local/regional/global weather and climate forecast/prediction models and their validation.
vii) Aerosol Indirect Effects
The indirect effects of aerosols on cloud microphysics and associated radiative forcing and climate change are very complex. Recent studies suggest that introduction of anthropogenic aerosols due to biomass-burning, fossil-fuel etc. would enhance cloud life time and drop size spectrum significantly but reduces precipitation. Studies in this direction are very scanty in the country. Therefore, experimental and data analysis techniques aiming at aerosol- cloud-climate interactions require further improvements. In this context, the on-going cloud observations using the ground-based dual-pol lidars at IITM, Pune, NARL, Gadanki and SPL, Trivandrum play a vital role. The polarization properties of lidar scattered signals would be very valuable in identifying the cloud phase and associated precipitation/radiative characteristics of cloud condensation nuclei/ice nuclei.
viii) Multi-dimensional Mapping of day-night aerosol characteristics over complex terrains
One of the most important future directions to the Indian aerosol research should be multi-dimensional mapping of aerosol characteristics and other related atmospheric parameters over different environments (associated with complex terrain and meteorological conditions) using a mobile (truck-mounted or trailer-based) lidar. This will serve as a very valuable input information to the climate models, particularly to account for the radiative forcing due to aerosols on different time scales.
The on-going experiments at Hanle, Kullu and neighboring regions, and on- going/proposed multi-organizational, multi-location and multi-field campaign programs will help filling such gaps. Moreover, aerosol studies over inaccessible regions like forests, lakes, mountain valleys, glaciers etc. are very sparse.
Mapping of aerosol parameters over such regions is possible with satellite data. However, the satellite data retrieval algorithms require validation (atmospheric correction for aerosol effects) with aerosol vertical distributions and height-integrated aerosol extinction (optical depth) from ground-based lidars and radiometers. The ongoing data validation schemes of Indian satellite missions would play a great role in obtaining information on aerosol index over different parts of the country.
ix) Interface between Aerosol, Water vapor, Ozone and Nitrogen Dioxide
Mechanisms involved in the generation and development of secondary aerosols and relationships between aerosol, ozone and water vapor need further understanding. In this context, studies relating to the stratosphere-troposphere exchange/coupling and feedback processes using lidars, radiometers and in-situ instruments are needed. The results of such studies will also help in understanding the radiation-induced thermal field variations due to aerosols. Such studies will form a potential base for understanding aerosol growth processes, heterogeneous chemistry involving O3 and NO2 with aerosol as catalyst.
Another important problem associated with aerosols is aerosol-aerosol interactions and interaction between aerosol and background. In detail, this implies that the interactions between primary and secondary aerosols (new particle formations due to gas-to-particle conversion processes) and their integrated influence on composite aerosol behavior are not known. Our knowledge on modulation of such interactions on back-ground aerosol levels in the formulations of local/regional aerosol radiative forcing is very poor.
x) Aerosol Studies during Natural / Anthropogenic Episodes
Besides regular aerosol measurements, by following careful calibration-validation techniques, for understanding the long-term effects, event-oriented studies such as air pollution episodes, volcanic eruptions using both lidars and radiometers also should be more concentrated in order to understand the
local/regional/continental/hemispherical/ global physico-chemical, radiative and dynamical properties of aerosols. Systematic monitoring of aerosol characteristics during volcanic eruptions employing lidar in combination with in-situ techniques will yield certain large scale dynamical parameters using aerosol-cloud-clusters as tracers, and possibility to assess the influence of volcanic aerosols on global climate variability.
xi) Polar Aerosols
The aerosols, and pre-cursor gases over the polar regions play great role not only in the Earth's radiation budget but provide reference levels for all the environmental and pollution studies due to their remoteness and restricted human activities. Moreover, the atmosphere over poles is very sensitive to human-induced changes in any part of the globe and dynamics of the atmosphere over poles itself seems to modify global weather and climate. Thus, the attenuation of solar irradiance and the processes of scattering and absorption by the aerosol particles may cause appreciable effects on the weather and climate of the Polar Regions. Albeit, some piece- meal observations on aerosols and associated parameters have been carried out by some Institutions in the country in coordination with National Centre for Antarctic and Ocean Research (NCAOR), Goa, we need to quantitatively attribute aerosol forcing to aerosol type (natural and anthropogenic) for highly diverse conditions and episodic situations.
xii) Dust Pollution over Indo Gangetic Basin (IGB)
Dust storms in IGB act aerosol-extreme-laden events and they are often (during dust- loading seasons in the northern and north-western parts of Indian sub-continent) responsible for complicated mixing of natural and anthropogenic aerosols. This is further complicated due to the fact that the IGB region is very diverse in topography, population distribution, meteorology and emission sources. These unique features will induce large uncertainty in satellite retrievals and thereby the Earth's global radiation budget. Recognizing this phenomenon, ground-based aerosol networks involving initially with sun-sky
