Intensive radiosonde observations of gravity waves in the lower atmosphere over Yichang (111°18´ E, 30°42´ N), China

摘要

The characteristics of dynamical and thermalstructures and inertial gravity waves (GWs) in the troposphere and lowerstratosphere (TLS) over Yichang (111°18´ E, 30°42´ N) werestatistically studied by using the data from intensive radiosondeobservations in August 2006 (summer month) and January 2007 (winter month)on an eight-times-daily basis. The background atmosphere structures observedin different months exhibit evident seasonal differences, and the zonal windin winter has a prominent tropospheric jet with a maximum wind speed ofabout 60 ms occurring at the height of 11.5 km. The statisticalresults of the inertial GWs in our two-month observations are generallyconsistent with previous observations in the mid-latitudes. In the summermonth, the mean intrinsic frequency and vertical wavelength of the inertialGWs in the troposphere are still larger than those in the lower stratospherewith the absence of intensive tropospheric jets, suggesting that the Dopplershifting due to the tropospheric jets cannot completely account for thedifferences between the GWs in the troposphere and lower stratosphere.Compared with the observations in the summer month, some interestingseasonal characteristics of the GWs are revealed by the observations in thewinter month: 1) more and stronger tropospheric GWs are observed in thewinter month; 2) less and weaker GWs are observed in the lower stratospherein winter; 3) the ratio of the mean GW kinetic energy density to potentialenergy density is smaller than 1 in winter, which contrasts to that insummer. Most of the seasonal differences can be explained by the intensivetropospheric jets in winter. In both the summer and winter months, the fittedspectral slopes of the vertical wave number spectra for GWs are generallysmaller than the canonical spectral slope of −3. Correlation analysessuggest that the tropospheric jet induced wind shear is the dominant sourcefor GWs in both the troposphere and lower stratosphere. Moreover, thetropospheric (lower stratospheric) GWs are found to be modulated by thequasi-7-day (10-day) PW, and the impacts of the diurnal tide on the GWs arerelatively weak.