Equatorial wave activity during 2007 over Gadanki, a tropical station

Abstract

ECMWF Re-Analysis (ERA-interim) data of winds for the year 2007 between the pressure levels 1 and 1000 hPa (0–49 km) have been analyzed for equatorial wave activity over a tropical station Gadanki (13.5°N, 79.2°E). Available wind observations made by MST radar located at the same site have also been used to investigate the wave activity in the troposphere and lower stratosphere. Waves in the period bands 7–10, 12–15 and 20–30 d are observed. Temporal variability of the wave activity has been investigated by constructing wavelet spectra. The longer period waves show strong seasonal variability with maximum and minimum activities during winter and summer months respectively. Short period activity is more prominent during June–July–August in the tropospheric region. The waves are found to be generated in the troposphere by wind shear and convection. Propagation of the waves to higher altitudes is found to depend strongly on background zonal wind and phase of the quasi-biennial oscillation (QBO). The waves are inhibited to propagate through the negative wind shear zone. Meridional waves might be generated by non-linear wave CISK.