GVAX

Ganges Valley Aerosol Experiment (GVAX)

13 June 2011 - 31 March 2012

Lead Scientist: V. Rao Kotamarthi

Observatory: AMF , PGH

The Ganges valley region is one of the largest and most rapidly developing sections of the Indian subcontinent. The Ganges River, which provides the region with water needed for sustaining life, is fed primarily by snow and rainfall associated with Indian summer monsoons. Impacts of changes in precipitation patterns, temperature, and the flow of the snow-fed rivers could be immense. Recent satellite-based measurements have indicated that the upper Ganges valley has some of the highest persistently observed aerosol optical depth values. The aerosol layer covers a vast region, extending across the Indo-Gangetic Plain to the Bay of Bengal during the winter and early spring of each year. The persistent winter fog in the region is already a cause of much concern, and several studies have been proposed to understand the economic, scientific, and societal dimensions of this problem. During the INDian Ocean EXperiment (INDOEX) field studies, aerosols from this region were shown to affect cloud formation and monsoon activity over the Indian Ocean. This is one of the few regions showing a trend toward increasing surface dimming and enhanced mid-tropospheric warming. Increasing air pollution over this region could modify the radiative balance through direct, indirect, and semi-indirect effects associated with aerosols. The consequences of aerosols and associated pollution for surface insolation over the Ganges valley and monsoons in particular are not well understood. The proposed field study was designed for use of 1) the ARM Mobile Facility to measure relevant radiative, cloud, convection, and aerosol optical characteristics over mainland India during an extended period of 12 months; and 2) the G-1 aircraft* and surface sites to measure relevant aerosol chemical, physical, and optical characteristics in the Ganges valley during a period of 8-12 weeks. The aerosols in this region have complex sources, including burning of coal, biomass, and biofuels; automobile emissions; and dust. The extended AMF deployment enabled measurements under different regimes of the climate and aerosol abundance — in the wet monsoon period with low aerosol loading; in the dry, hot summer with aerosols dispersed throughout the atmospheric column; and in the cool, dry winter with aerosols mostly confined to the boundary later and mid troposphere. Each regime, in addition, has its own distinct radiative and atmospheric dynamic drivers. The aircraft operational phase assisted in characterizing the aerosols at times when they have been observed to be at the highest concentrations. A number of agencies in India collaborated with the proposed field study and provided support in terms of planning, aircraft measurements, and surface sites. The high concentration of aerosols in the upper Ganges valley, together with hypotheses involving several possible mechanisms with direct impacts to the hydrologic cycle of the region, gave researchers a unique opportunity to generate data sets that will be useful both in understanding the processes at work and providing answers regarding the effects of aerosols on climate in a region where the perturbation is the highest. *As of April 1, 2011, the G-1 no longer participated in this field campaign.