Anomalous low tropospheric column ozone over Eastern India during the severe drought event of monsoon 2002: a case study
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Background, aim, and scope
The present study is an attempt to examine some of the probable causes of the unusually low tropospheric column ozone observed over eastern India during the exceptional drought event in July 2002.
We examined horizontal wind and omega (vertical velocity) anomalies over the Indian region to understand the large-scale dynamical processes which prevailed in July 2002. We also examined anomalies in tropospheric carbon monoxide (CO), an important ozone precursor, and observed low CO mixing ratio in the free troposphere in 2002 over eastern India.
Results and discussion
It was found that instead of a normal large-scale ascent, the air was descending in the middle and lower troposphere over a vast part of India. This configuration was apparently responsible for the less convective upwelling of precursors and likely caused less photochemical ozone formation in the free troposphere over eastern India in July 2002.
The insight gained from this case study will hopefully provide a better understanding of the process controlling the distribution of the tropospheric ozone over the Indian region.
KeywordsTropospheric ozone Convection South Asia Pollution
The authors are thankful to Prof. B.N. Goswami, Director, IITM, for encouragement during the progress of the work. MOPITT CO data were obtained from the NASA Langley Research Center Atmospheric Science Data Center. One of the authors (PSK) is financed through the “SPATRAM-MIGE Polar Project,” funded by the Portuguese Science Foundation—FCT. We thank to National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP-NCAR) reanalysis (http://www.cdc.noaa.gov/) for providing wind reanalysis data. The TRMM 3b42 data products used in this study were acquired using the GES-DISC Interactive Online Visualization and analysis Infrastructure (Giovanni) as part of the NASA's Goddard Earth Sciences (GES) Data and Information Services Center (DISC). We acknowledge the atmospheric science data center, NASA, for providing TES data and we are grateful to NASA (Moderate Resolution Imaging Spectroradiometer, http://modis.gsfc.nasa.gov/) for supplying MODIS water vapor products.
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