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Earth Planets Space, Vol. 61 (No. 8), pp. 983-993, 2009

Characteristics of gravity waves observed with intensive radiosonde campaign during November-December 2005 over western Sumatera

M. Venkat Ratnam1,2, Simon P. Alexander3, T. Kozu4, and T. Tsuda1

1Research Institute for Sustainable Humanosphere (RISH), Kyoto University, Japan
2National Atmospheric Research Laboratory (NARL), Gadanki, India
3Australian Antarctic Division, Kingston, Tasmania, Australia
4Faculty of Science and Engineering, Shimane University, Japan

(Received February 16, 2008; Revised April 22, 2009; Accepted May 13, 2009; Online published October 19, 2009)

Abstract: Characteristics of gravity waves are studied using radiosonde campaign conducted during November-December 2005 at Koto Tabang (KT, 0.2°S, 100.32°E). Intensive sounding with hourly launches was also conducted on seven days to study the characteristics of short period (2-6 hours) waves along with EAR data. Gravity waves with period (τ) of 3 hours and vertical wavelength (λz) of 10 km seemed to be generated due to localized convection around KT, which is inferred from X-band Doppler radar. The energy of the gravity wave with period of 2-3 days and vertical wavelength of 3-5 km is largest between 15 and 20 km and 25 and 30 km. We also report the comparison of the wave activity and its interaction with background wind between the three campaigns (CPEA-I, CPEA-II and Nov. 2002). Most of the time waves are propagating towards east and the source of gravity waves is strongly related to the slowly eastward-advecting tropospheric convection, implying that the wave activity was generated at far distant sources located west of KT. A key finding of this study is neither short period nor long-period gravity waves are generated during stationary type of convection. The change in the propagation direction of the short period waves within the event is observed which is not expected.
Key words: Gravity waves, convection, background wind, radiosonde campaign, EAR.


Corresponding author E-mail: tsuda@rish.kyoto-u.ac.jp


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