VHF radar observed characteristics of convectively generated gravity waves during wet and dry spells of Indian summer monsoon

• Published in: Journal of atmospheric and solar-terrestrial physics 2011-05, Vol.73 (7), p.815-824
• Main Authors: Uma, K.N., Kishore Kumar, Karanam, Narayana Rao, T.
• Format: Article
• Language: English
• Subjects: Convection Gravity Waves; Earth, ocean, space; Exact sciences and technology; External geophysics; Monsoon; Physics of the ionosphere; Physics of the magnetosphere
• ISSN: 1364-6826; 1879-1824
• DOI: 10.1016/j.jastp.2011.01.024

A powerful VHF radar observed characteristics of Convectively generated Gravity Waves (CGW) excited during the wet and dry spells of Indian summer monsoon over a tropical station Gadanki (13.5°N, 79.2°E) are discussed. The characteristics of gravity waves in the lower stratosphere during these two spells are discussed in terms of their wavelet spectra along with height–time sections of vertical velocity. A total of 31 events are analyzed and in more than 50% of the events, the lower stratospheric gravity wave amplitudes were found to be relatively large in dry spell compared to that in the wet spell. The wavelet analysis of lower stratospheric vertical velocities showed a dominant periodicity of about ∼20–40 min in wet spell and ∼10–20 min in dry spell. The analysis also indicates that wet spell is found to be more conducive for the generation of gravity waves. However, the propagation of these waves into the stratosphere is found to be more efficient in dry spell of monsoon. The strengthening/weakening of the tropical easterly jet during wet/dry spell of monsoon is found to be the main reason for the inhibited/enhanced wave activity in the lower stratosphere during wet/dry spell. The present analysis also suggests that the static stability of the mid- and upper-troposphere during these two spells have implications in the observed frequency of the CGW. Thus, the present analyses brought out for the first time the features of CGW during two distinctive regimes of convective systems and emphasized the importance of prevailing background conditions in exciting/filtering them. ► We discuss Convectively generated Gravity Waves during wet/dry spells of Indian monsoon. ► The strength of TEJ is found to be the main reason for inhibited/enhanced wave activity. ► Static stability of the mid-/upper-troposphere has implications in the observed frequency.