Climate implications of large warming by elevated aerosol over India

Abstract

Wide‐ranging multi‐platform data from a major field campaign conducted over Indian region was used to estimate the energy absorbed in ten layers of the atmosphere. We found that during pre‐monsoon season, most of Indian region is characterized by elevated aerosol layers. Three‐fold increase in aerosol extinction coefficient was observed at higher atmospheric layers (>2 km) compared to that near the surface and a substantial fraction (as much as 50 to 70%) of aerosol optical depth was found contributed by aerosols above (reflecting) clouds. Consequent absorption and hence strong warming above clouds was found larger by several degrees (K) compared to that near the surface. The aerosol‐induced elevated warming was mostly confined below 2 km over northern Indian Ocean while found up to 4 km over central India, thus exhibiting strong meridional gradients (∼4 K) at atmospheric levels above 2 km. Climate implications of the large elevated warming are discussed.

Atmospheric pollutant outflow from southern Asia: a review

“…On the other hand, the solar heating of the LT can lead to the dissipation of trade cumulus clouds as they are sensitive to solar absorption, which enhances the solar radiation penetration to the surface (Ackerman et al, 2000). When clouds are present the vertical distribution of the aerosols is of key importance, in particular when the pollution is located above the clouds, which can cause the net aerosol cooling to change sign (Haywood and Shine, 1997;Satheesh et al, 2008). Thus, it is not so much the TOA forcing by anthropogenic aerosols which is most rele- atmosphere-surface system, which can exert strong climate influences.…”

“…During the dry season the reverse occurs due to the enhanced boundary layer heating by the black carbon. Furthermore, the heating by absorbing aerosol pollution over Tibet may act as an "elevated heat pump", which carries moist air into the region and can persist into the pre-monsoon period (Lau et al, 2006;Satheesh et al, 2008). It appears that precipitation over land is relatively sensitive to changes in SST gradients (Rotstayn and Lohmann, 2002;Chung and Ramanathan, 2007).…”

Technical Note: One year of Raman-lidar measurements in Gual Pahari EUCAARI site close to New Delhi in India – Seasonal characteristics of the aerosol vertical structure

“…The proposed "elevated heat pump" effect suggests that atmospheric heating by absorbing aerosols (dust and black carbon), through water cycle feedbacks, may lead to a strengthening of the South Asian monsoon (Lau et al, 2006b;Lau et al, 2008). Elevated aerosol layers, especially during the pre-monsoon season, are likely to have larger radiative impacts when located above clouds (Satheesh et al, 2008). Overall, it has been suggested that the atmospheric brown cloud in Asia contributes to the regional lower-tropospheric warming as much as the recent increase of the anthropogenic greenhouse gases (Ramanathan et al, 2007b).…”

Spring-Time Enhancement in Aerosol Burden over a High-Altitude Location in Western Trans-Himalaya:Results from Long-Term Observations

“…A number of field experiments have been devised for aerosol measurements in the Himalayan region 5,[11][12][13][14][15][16][17] . The observational evidence of the persistent elevated aerosol layers over the Indian region and the northward gradient in atmospheric warming due to such layers, which was unravelled during the multi-platform field experiment 'Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB)' 18,19 , led to the formation of Regional Aerosol Warming EXperiment (RAWEX) under the Indian Space Research Organisation Geosphere Biosphere Program (ISRO-GBP) 20 . One of the important objectives of RAWEX is the quantification of amplitude, frequency of occurrence, seasonal trends of elevated aerosols and atmospheric warming caused by them over the Indian region, and also to delineate the share of long-range transport and local contributions to this phenomenon.…”