VHF radar observed characteristics of convectively generated gravity waves during wet and dry spells of Indian summer monsoon |
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| Authors: | KN Uma Karanam Kishore Kumar T Narayana Rao |
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| Institution: | 1. Institute of Atmospheric Composition, Chinese Academy of Meteorological Sciences, Beijing 100081, China;2. State Key Laboratory of Severe Weather & Key Laboratory of Atmospheric Chemistry of CMA, Chinese Academy of Meteorological Sciences, Beijing 100081, China;3. National Climate Center, China Meteorological Administration, Beijing 100081, China;4. Institute of Urban Meteorology, China Meteorological Administration, Beijing 100089, China;5. College of Atmospheric Sciences, Chengdu University of Information Technology, Chengdu 610225, China;6. Liaoning Meteorological Equipment Support Centre, Shenyang 110166, China |
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| Abstract: | 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. |
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