photometers and later combined with multi-wavelength radiometers have also been established in the region in order to quantify aerosol loads and resultant effects of pollution mostly from the combustion of biomass, bio-fuel/fossil fuel emissions and the transported mineral dust outbreaks not only on Earth-atmosphere radiation balance and air quality but also on hydrological cycle. Thus the IGB region is one of the hotspots for Indian aerosol research. Numerous attempts have been on by several Institutions, but more need to be done to enhance our scientific understanding of the aerosol extremes due to dust episodes, their origin, evolution and effects.
xiii) High-Altitude/Mountain and Glacier Aerosols
Measurements over high-altitude/mountain stations represent background levels of aerosol concentration. So, it would be possible to examine and assess the extent to which the clean remote areas have been affected by growing urbanization/industrialization. Moreover, background sites with presumably cleaner environments and clear-sky conditions offer an excellent opportunity to calibrate the performance of the optical monitoring sensors/equipment. Added, these stations lie in the boundary-layer during daytime and in the free troposphere during the nighttime, thus provide good opportunity to investigate the transport/mixing of aerosols and gases from/between the boundary-layer to/and the free troposphere. Under seasonally varying wind patterns, these stations being in the free troposphere during night, becomes very important for regional study of transport of pollutants, particularly during early morning/night transition period. Scenarios of climate change in the mountainous regions of the world are highly uncertain mainly because of lack of sufficient data. At high elevations in the Himalayas, for instance, an increase in temperature could result in faster recession of glaciers and a reduction in snowmelt water will put the dry season flow of the
snow-fed rivers under greater stress. The above-mentioned measurements over tropics are sparse and more so in India. Hence we need to gather more aerosol data to address the above issue including albedo.
xiv) Type-Segregated Aerosol Optical and Radiative Properties
By now, many groups in India have made extensive measurements of aerosol characterization, especially the columnar aerosol optical depth (a gross indicator of aerosol extinction) under different environments. All these measurements represent bulk effect. What is needed in the present-day understanding of the aerosol physico-chemical property is the type-segregated effects. Besides the complexity of internal and external mixing of aerosols, optical depth and associated radiative forcing due to different types (maritime, biomass, urban, industrial, desert dust etc.) of aerosols separately would provide clearer regional scenarios as compared to global means. Therefore, it is worthwhile to look into this issue by making fresh observations in this direction as well as re-analyze the large volumes of data already archived at some locations in India.
xv) Stratosphere-Troposphere Coupling / Exchange Processes
Campaign / co-experiment measurements involving the MST, X-band and Ka-Band radars, Mie-Rayleigh Lidar, Lower Atmospheric Wind Profiler (LAWP), Dual-Pol Micro Pulse, Doppler Wind and Raman Lidars in conjunction with GPS Radiosonde and Solar Radiometer facilities need to be organized to investigate the influence of temperature, vertical wind velocity (particularly during jet stream situations) on the height-integrated aerosol optical depth and size distribution, ozone and precipitable water content. Also, the role of structure and stratification of tropical tropopause in the variations of aerosol optical depth (as well as size distribution), which provide an insight into the stratosphere-troposphere coupling mechanisms, would form an interesting study.
xvi) Aerosol Modeling Activities
The complex interactions between meteorological elements including radiation, aerosols, cloud microphysics and dynamics make it difficult to assess the effect on precipitation change and climate. Due to uncertainty of these interactions and effects from local to global scale, a coordinated multi-disciplinary approach involving experiments and models is highly essential. The modeling efforts in these directions are very much limited and they need to be established and verified with long-term data sets. One potential way to resolve the current situation could be through new satellites and the associated products and sophisticated statistical methods. We need to concentrate on developing aerosol models (preferably coupled models) such as WRF-ARW, WRF-Chem., GCMs in order to delineate aerosol and pre-cursor gas influence on weather and climate through their modulating effects on radiation changes. For this purpose, we need good parameterization (super) schemes and data assimilation techniques. Sensitivity studies should also go on for continuous model improvements. Boundary-layer processes (e.g., entrainment), phase (external versus internal mixing, water versus ice etc.), composition (hydrophilic versus hydrophobic), latent heat release by clouds and complete chemistry (including nitrogen) need to be incorporated in the models.
Acknowledgements
I profoundly thank the support and cooperation, directly or indirectly, from all the authorities and colleagues at Amity Centre for Ocean-Atmospheric Science and Technology (ACOAST), Amity University Haryana (AUH), Panchgaon, and also at Indian Institute of Tropical Meteorology (IITM), Pune, India.
P. C. S. Devara
Amity Centre for Ocean-Atmospheric Science and Technology (ACOAST), Amity University Haryana (AUH), Panchgaon (Gurgaon-Manesar) 122413
E-Mail: pcsdevara@ggn.amity.edu
