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Ozone trends in the vertical structure of Upper Troposphere and Lower stratosphere over the Indian monsoon region
Fadnavis, S.; Dhomse, S.; Ghude, S.; Iyer, U.; Buchunde, P.; Sonbawne, S. & Raj, P. E.
Abstract
Ozone trends in the Upper Troposphere and
Lower Stratosphere over the Indian region are investigated
using three satellite data sets namely Halogen Occultation
Experiment (1993–2005), Stratospheric Aerosol and Gas
Experiment (1993–2005) II, and Aura Microwave Limb
Sounder (MLS, 2005–2011). Estimated ozone trends using
multi-variate regression analysis are compared with trends
at two Indian ozonesonde stations (Delhi, 28oN, 77oE and
Pune, 18oN, 73oE), and a 3-D Chemical Transport Model
(CTM, SLIMCAT) for the 1993–2005 time period. Overall,
all the observational data sets and model simulations
indicate significant increasing trend in the upper troposphere
(0–2.5 %/year). In the lower stratosphere, estimated
trends are slightly positive up to 30 mb and are negative
between 30 and 10 mb. Increasing trends in the upper
troposphere is probably due to increasing trends in the
tropospheric ozone precursor gases (e.g. CO, NOx,
NMHCs). Here, we argue that these contrasting ozonetrend
profiles might be partially responsible for insignificant
long-term trends in the tropical total column ozone.
On seasonal scale, positive trends are observed during all
the seasons in the upper troposphere while structure of
trend profile varies in lower stratosphere. Seasonal variations
of ozone trends and its linkages with stratospheric
intrusions and increasing trends in lightning flashes in the
troposphere are also discussed.
Keywords
Ozone trends; Upper troposphere and lower stratosphere; Indian monsoon region
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