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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 29, issue 12
Ann. Geophys., 29, 2259–2276, 2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 29, 2259–2276, 2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

  16 Dec 2011

16 Dec 2011

Characteristics of gravity waves generated in a convective and a non-convective environment revealed from hourly radiosonde observation under CPEA-II campaign

S. K. Dhaka1, R. Bhatnagar1,2, Y. Shibagaki3, H. Hashiguchi4, S. Fukao4, T. Kozu5, and V. Panwar1,2 S. K. Dhaka et al.
  • 1Radio and Atmospheric Physics Lab, Department of Physics, Rajdhani College, University of Delhi, Delhi, India
  • 2Department of Physics and Astrophysics, University of Delhi, India
  • 3Faculty of Information and Communication Engineering, Osaka Electro-Communication University, Japan
  • 4Research Institute for Sustainable Humanosphere, Kyoto University, Japan
  • 5Interdisciplinary Faculty of Science and Engineering, Shimane University, Japan

Abstract. Analyses of hourly radiosonde data of temperature, wind, and relative humidity during four days (two with convection and two with no convection) as a part of an intensive observation period in CPEA-2 campaign over Koto Tabang (100.32° E, 0.20° S), Indonesia, are presented. Characteristics of gravity waves in terms of dominant wave frequencies at different heights and their vertical wavelengths are shown in the lower stratosphere during a convective and non-convective period. Gravity waves with periods ~10 h and ~4–5 h were found dominant near tropopause (a region of high stability) on all days of observation. Vertical propagation of gravity waves were seen modified near heights of the three identified strong wind shears (at ~16, 20, and 25 km heights) due to wave-mean flow interaction. Between 17 and 21 km heights, meridional wind fluctuations dominated over zonal wind, whereas from 22 to 30 km heights, wave fluctuations with periods ~3–5 h and ~8–10 h in zonal wind and temperature were highly associated, suggesting zonal orientation of wave propagation. Gravity waves from tropopause region to 30 km heights were analyzed. In general, vertical wavelength of 2–5 km dominated in all the mean-removed (~ weekly mean) wind and temperature hourly profiles. Computed vertical wavelength spectra are similar, in most of the cases, to the source spectra (1–16 km height) except that of zonal wind spectra, which is broad during active convection. Interestingly, during and after convection, gravity waves with short vertical wavelength (~2 km) and short period (~2–3 h) emerged, which were confined in the close vicinity of tropopause, and were not identified on non-convective days, suggesting convection to be the source for them. Some wave features near strong wind shear (at 25 km height) were also observed with short vertical wavelengths in both convective and non-convective days, suggesting wind shear to be the sole cause of generation and seemingly not associated with deep convection below. A drop in the temperature up to ~4–5 K (after removal of diurnal component) was observed at ~16 km height near a strong wind shear (~45–55 m s−1 km−1) during active period of convection.

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