High vertical resolution analyses of gravity waves and turbulence at a midlatitude station

Abstract

[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.

Vertical wavenumber spectra of three-dimensional winds revealed by radiosonde observations at midlatitude

“…In the troposphere, the amplitude varies from 0.02 to 0.05 m 2 s −2 cycle −1 km −1 , while a much larger spectral amplitude can be observed in the lower stratosphere, with the largest amplitude greater than 0.2 m 2 s −2 cycle −1 km −1 occurring in January 2002. In the troposphere, the spectral amplitudes show a regular annual cycle, with a larger (smaller) value in winter (summer), which is consistent with the gravity wave energy seasonal variation at middle latitude (Zhang et al, 2012). These spectral amplitudes are comparable to those radar observations in the lower atmosphere (Larsen et al, 1986(Larsen et al, , 1987Fritts and Chou, 1987) but obviously smaller than the lidar observations in the mesopause region (Gardner et al, 1998).…”

“…According to the GW theory, the vertical wavelength will decrease with the decrease in the intrinsic frequency, thus leading to the energy transportation from large vertical scale to smaller scale, in turn yielding a shallower spectrum in winter in the lower stratosphere. Radiosonde observations of gravity waves at the same station (Zhang et al, 2012) also indicated that GWs in the lower stratosphere have shorter vertical wavelengths compared with those in the troposphere. As a result, the horizontal wind spectral slopes have evident seasonal variations, with less negative values in winter.…”

“…In the troposphere, which is believed to be the main source region of GWs, the GWs could not be expected to be saturated and the spectra should be controlled mainly by the source characteristics. Previous observations (Zhang et al, 2012) indicated that the vertical wavelengths of GWs in the troposphere have no obvious seasonal variation. Thus, the spectral slopes of the horizontal wind fields only exhibit a slight seasonality, with mean values evidently less negative than the canonical slope of −3.…”

“…It is noted that the horizontal winds are more sensitive to horizontal advection activity, which usually has a low frequency and is more easily absorbed by the critical layer. Therefore, in winter months, resulting from the selective filtering of the strong jet, most GWs propagate against the zonal wind above the jet (Zhang et al, 2012). As a result of zonal wind decreasing with height, the intrinsic frequencies of GWs propagating against the zonal wind decrease with height.…”

“…By applying this assumption, Zhang et al (2012Zhang et al ( , 2013Zhang et al ( , 2014 directly calculated complete GW parameters and compared them with the results from other methods. The good consistency con- Figure 1.…”