12-14 September, 2011, Lucknow - Earth Science India
12-14 September, 2011, Lucknow - Earth Science India
12-14 September, 2011, Lucknow - Earth Science India
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National Conference on <strong>Science</strong> of Climate Change and <strong>Earth</strong>’s Sustainability: Issues and Challenges ‘A Scientist-People Partnership’<br />
<strong>12</strong>-<strong>14</strong> <strong>September</strong>, <strong>2011</strong>, <strong>Lucknow</strong><br />
SPATIAL ASYMMETRY OF TEMPERATURE TRENDS<br />
OVER INDO-GANGETIC PLAIN AND POSSIBLE ROLE<br />
OF AEROSOLS<br />
D.R. Kothawale<br />
<strong>India</strong>n Institute of Tropical meteorology, Pune<br />
email: kotha@tropmet.res.in<br />
Increase in greenhouse gases viz., CO 2 , CH 4 , CFCs, N 2 O etc. and water vapour in<br />
the atmosphere are mainly responsible for the temperature warming, while aerosols in<br />
the atmosphere through their negative radiative forcing are responsible for lowering the<br />
land surface temperatures. Keeping this view, we examined dissimilarities of<br />
temperature trends both in space and time over the Indo Gangetic Plain (IGP) to look<br />
for signatures of aerosols influence. IGP temperature time series have been prepared for<br />
dry (November-May) and wet (June-October) seasons for the period 1901-2007 and<br />
trends for the entire period and different sub periods of 1901-50, 1951-1990 and 1991-<br />
2007 have been examined to isolate the aerosol and other greenhouse gas influences on<br />
temperatures. Similarly, for IGP, Aerosol Index (AI) monthly time series are prepared<br />
for the period 1979- 2005 (1993-1996 data is missing).<br />
Maximum (day-time) temperatures during dry season corresponding to IGP<br />
region showed significant warming trend of 0.8°C per hundred years during the period<br />
1901-2007. While, minimum temperature showed nebulous trend of 0.2°C per hundred<br />
years over IGP region. During the wet season, maximum temperature shows nearly half<br />
of dry season maximum temperature warming trend.<br />
However, asymmetry is observed in dry season maximum temperature trend<br />
during post industrial period 1951-1990 wherein IGP shows decreasing trend, while<br />
during the recent period 1991-2007 trend is positive. Spatial and temporal asymmetry in<br />
observed trends clearly point to the role of aerosols in lowering temperature trends over<br />
IGP. AI showed pronounced increasing trend for the months March, April, May, June<br />
and July. Increasing trend in the month of July might be due to occurrence deficient<br />
monsoon years during the study period. There is very little or no trend in AI for<br />
monsoon months August, <strong>September</strong> and October.<br />
In the post-industrial era, after 1951, IGP region during dry season, maximum<br />
temperatures show decreasing trend until 1990, while notable positive trend is observed<br />
there after up to 2007. The negative radiative forcing of aerosols dominates the<br />
temperature trends over IGP region during 1951-90 period and after 1991 it appears that<br />
the atmospheric concentrations of greenhouse gases and black carbon are more than<br />
compensating the aerosol related cooling and hence warming trends ensued.<br />
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