Previous: Introduction Next: Data Up: Ext. Abst.

Asia Pacific Wave in troposphere

Joseph and Srinivasan (1999), (now onwards JS) using NCEP/NCAR reanalysis data (Kalnay et al, 1996) showed the presence of a large amplitude standing Rossby Wave in the upper tropospheric westerlies during May confined between 10°N and 50° N latitudes. This wave has wavelength of about 50-60° longitude (zonal wave number 6 or 7) and has a spatial shift of about 20° longitude between deficient and excess Indian Summer Monsoon Rainfall (ISMR) years with a wave trough over the Arabian sea during deficient ISMR years. The spatial shift is due to the shift in the longitudinal position of the convective heat sources associated with the Inter Tropical Convergence Zone. Due to its geographical location, it was named by JS as Asia Pacific Wave (APW). It is reported that this wave has large amplitude around 200 hPa and the amplitude decreases with decreasing height in the troposphere. Although the lower portion of this wave has been studied in detail, nature of this wave above 200 hPa has not been documented. It is interesting to know whether the APW is seen above 200 hPa in the lower stratosphere. If it is present, first it could couple the troposphere and stratosphere directly on global scale and communicate some information from the tropospheric Indian summer monsoon activity to stratosphere and, secondly it could exchange tropical upper tropospheric air mass and extra tropical lower stratosphere air mass in meridional direction along isentropic surfaces.

In the present work, the nature of APW in wind above 200 hPa level is studied. The importance of the location of the APW and possible meridional mass exchange including that of ozone by this wave is highlighted. It is also shown how the environmental conditions associated with extreme ISMR affect the distribution of total ozone amount over an area in the inter-annual time scale.