[1] We proposed a broad spectral data-analyzing method to study the altitude and seasonal variability of gravity wave (GW)-associated dynamics in the lower atmosphere at a midlatitude by using the radiosonde data from Miramar Nas (32.87°N, 117.15°W), California, during 1998California, during -2008. Generally, the presented primary statistical features of GW parameters and their seasonal variation are consistent with previous radiosonde observations by using the conventional hodograph analysis method based on monochromatic GW theory. These consistencies suggest our proposed analyzing method is feasible in extracting GW parameters from the radiosonde data. More interesting, our analyses can reveal the altitude variations of GW parameters, which have been seldom reported in previous radiosonde observations. Similar to previous observations, most seasonal and height variability of GW parameters is closely connected with tropospheric jet, suggesting the important role of the jet in determining GW parameters as well as the lower atmospheric dynamics and thermal structure. Mainly due to the broad spectral nature of the observed GWs, there are also some differences between our results and previous studies based on monochromatic GW extraction. By using the perturbation of vertical ascent rate, we directly calculated GW momentum and heat fluxes, which can only be indirectly derived from the hodograph analysis. Furthermore, the directly derived heat flux can explain the frequently observed tropospheric inversion in winter. Besides GW parameters, turbulent energy dissipation rate and diffusion coefficient were also derived. The derived turbulence parameters and their altitude variations are in good agreement with radar observations reported elsewhere.

[1] Gravity wave activities and background dynamical structure in the troposphere and lower stratosphere (TLS) over five stations at latitudes from 10°N to 40°N were statistically studied by using the data from Radiosonde observation on a twice daily basis at 0800 and 2000 LT. The background dynamical structure exhibits evident latitudinal and seasonal variations and has a profound influence on inertial gravity waves in the TLS. In the analyses of inertial gravity waves, according to the background structures, the observation height coverage is divided into two segments, which are the tropospheric (0-10 km) and lower-stratospheric segments (18-25 km). The observational results indicate that the tropospheric jet is the most important excitation source for gravity waves both in the troposphere and lower stratosphere, and it plays different roles in determining the morphology of gravity waves in these two segments. The jet-excited gravity waves in the troposphere can propagate both upward and downward, and only part of the upward-propagating waves can penetrate into the stratosphere because of the Doppler shifting by the jet, while in the lower stratosphere, gravity waves excited by the tropospheric jet propagate upward. Most differences between the tropospheric and lowerstratospheric results can be explained from the linear dispersion relations of gravity waves and the Doppler shifting by the strong tropospheric jet. However, such an explanation is qualitative rather than quantitative. Generally, the observations reveal that the tropospheric gravity waves are mainly controlled by their excitation sources, implying the wave characteristics may be regarded as (at least an indicator of) the wave excitation source characteristics. These results suggest that in order to attain a more realistic source parameterization for gravity waves propagating in the middle and upper atmosphere, more attention should be paid to the gravity waves in the troposphere. Moreover, the causes of the pronounced peak of lower-stratospheric gravity wave intensity at tropical latitudes revealed by previous observations are also discussed.Citation: Zhang, S. D., and F. Yi (2007), Latitudinal and seasonal variations of inertial gravity wave activity in the lower atmosphere over central China,

Abstract. The latitudinal and seasonal variations of gravity wave (GW) potential energy density (E P ), kinetic energy density (E K ), and total energy density (E T ), i.e, the sum of potential and kinetic energy densities in the tropospheric (typically 2-10 km) and lower stratospheric (typically 18-25 km) segments have been derived from 10 years (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007) of radiosonde observations over 92 United States stations in the Northern Hemisphere. The latitudinal variation of E P in the lower stratosphere is in good agreement with satellite observations. However, E K and E T in the lower stratosphere are different from satellite observations and the difference is believed to be linked with the latitudinal dependence of GW sources. Our analysis reveals that GW energy properties exhibit distinctive latitudinal and seasonal variations. The upward-propagating GW energy in the troposphere is larger than that in the lower stratosphere at low latitudes but the opposite holds true at high latitudes. The transition latitude, where the upward-propagating energies in the two altitude regions are the same, occurs at 35 • N throughout the year. So striking differences between GW activity in the troposphere and lower stratosphere are not likely explained only by the background wind Doppler shifting due to strong tropospheric jets. Our analysis indicates that the region around tropopause, roughly from 10 km to 18 km, is an important source region, especially at latitudes below 35 • N. Our studies strongly suggest that in order to fully understand the global GW activity in the lower atmosphere, the GW kinetic energy and its geographical and seasonal variations should be included, and more attention should be given to GWs in the troposphere and GW sources within the intermediate region, especially the upper troposphere.