Characteristics of the intraseasonal oscillations in the lower and middle atmosphere over Gadanki

Abstract

Systematic measurement of the tropical intraseasonal oscillation (ISO) has been carried out with radiosonde, TIMED Doppler Interferometer, European Center for Medium Range Weather Forecasting zonal wind data as well as Outgoing Longwave Radiation (OLR) data over Gadanki (13.5°N, 79.2°E). There is an emphatic signature of ISO modulation by dominant annual oscillation in the lower troposphere and upper stratosphere. Periodogram analysis has revealed dominant oscillations in the periodicity range 20–100 days. ISO amplitudes are significantly higher in Mesosphere and Lower Thermosphere (MLT) in comparison with the Troposphere and Stratosphere. ISO activity is found to be intermittent in the troposphere and consistent in MLT. Signature of the ISO is found to be insignificant in the stratosphere. Normally, there is good correlation between convection and zonal wind during all seasons within ISO scale of variability. Also mean latitudinal and longitudinal ISO amplitudes in OLR show common pattern of variability with higher activity during winter over summer during certain times, which is affirmed by ECMWF filtered wind results. These findings indicate presence of some complex mechanisms which alter the direct impact of convection on the tropical ISO during certain times.