Observations of the 7-day Kelvin Wave in the Tropical Atmosphere During the CPEA Campaign

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  • SRIDHARAN Sundararajan
    Research Institute for Sustainable Humanosphere (RISH), Kyoto University, Uji
  • TSUDA Toshitaka
    Research Institute for Sustainable Humanosphere (RISH), Kyoto University, Uji
  • NAKAMURA Takuji
    Research Institute for Sustainable Humanosphere (RISH), Kyoto University, Uji
  • KOZU Toshiaki
    Faculty of Science and Engineering, Shimane University, Matsue
  • MORI Shuichi
    Institute of Observational Research for Global Change (IORGC), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka
  • RUSSELL James M.
    Department of Physics, Hampton University

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Abstract

Radiosonde observations of winds and temperature over several sites in Southeast Asia during the CPEA radiosonde observation period (10 Apri1-9 May, 2004) reveal the presence of a 7-day wave in the upper troposphere and lower stratosphere (UTLS), especially during the first half of the radiosonde observation period. Many of the characteristics of the wave resemble those of Kelvin waves. The wave amplitude peak is observed at altitudes of 20-21 km. The vertical phase structure of the wave is consistent with altitude over the radiosonde sites considered. The vertical wavelength of the wave is found to be in the range of 5.5-6.5 km. The correlative analysis among the different radiosonde sites and analysis of TIMED-SABER data sets reveals that the wave is more active in the longitude band of 0-180°E and has a zonal wave number of 3. A wave of similar periodicity and zonal structure observed in OLR suggests that tropical convection could be a source for these waves. A slight shift is observed in the peak of wave amplitude toward the northern hemisphere. Moreover, the latitudinal width of the wave is narrower than that predicted by theory. This is discussed based on the existing model results, which indicate that the latitudinal structure of the wave may be affected by strong vertical shear in zonal wind, such as that reported in the present work.

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