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Ann. Geophys., 26, 2005-2018, 2008
www.ann-geophys.net/26/2005/2008/
© European Geosciences Union 2008
Intensive radiosonde observations of gravity waves in the lower atmosphere over Yichang (111°18´ E, 30°42´ N), China
Shao Dong Zhang1,2,3, Fan Yi1,2,3, Chun Ming Huang1,2,3, and Ze Yu Chen4
1School of Electronic Information, Wuhan University, Wuhan, Hubei, People's Republic of China
2Key Laboratory of Geospace Environment and Geodesy, Ministry of Education, Wuhan, Hubei, People's Republic of China
3State Observatory for Atmospheric Remote Sensing, Wuhan, People's Republic of China
4Institute of Atmospheric Sciences, Chinese Academy of Sciences, Beijing, People's Republic of China
Abstract. The characteristics of dynamical and thermal
structures and inertial gravity waves (GWs) in the troposphere and lower
stratosphere (TLS) over Yichang (111°18´ E, 30°42´ N) were
statistically studied by using the data from intensive radiosonde
observations in August 2006 (summer month) and January 2007 (winter month)
on an eight-times-daily basis. The background atmosphere structures observed
in different months exhibit evident seasonal differences, and the zonal wind
in winter has a prominent tropospheric jet with a maximum wind speed of
about 60 ms−1 occurring at the height of 11.5 km. The statistical
results of the inertial GWs in our two-month observations are generally
consistent with previous observations in the mid-latitudes. In the summer
month, the mean intrinsic frequency and vertical wavelength of the inertial
GWs in the troposphere are still larger than those in the lower stratosphere
with the absence of intensive tropospheric jets, suggesting that the Doppler
shifting due to the tropospheric jets cannot completely account for the
differences between the GWs in the troposphere and lower stratosphere.
Compared with the observations in the summer month, some interesting
seasonal characteristics of the GWs are revealed by the observations in the
winter month: 1) more and stronger tropospheric GWs are observed in the
winter month; 2) less and weaker GWs are observed in the lower stratosphere
in winter; 3) the ratio of the mean GW kinetic energy density to potential
energy density is smaller than 1 in winter, which contrasts to that in
summer. Most of the seasonal differences can be explained by the intensive
tropospheric jets in winter. In both the summer and winter months, the fitted
spectral slopes of the vertical wave number spectra for GWs are generally
smaller than the canonical spectral slope of −3. Correlation analyses
suggest that the tropospheric jet induced wind shear is the dominant source
for GWs in both the troposphere and lower stratosphere. Moreover, the
tropospheric (lower stratospheric) GWs are found to be modulated by the
quasi-7-day (10-day) PW, and the impacts of the diurnal tide on the GWs are
relatively weak.
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