Latitudinal and Seasonal Variations of Vertical Wave Number Spectra of Three‐Dimensional Winds Revealed by Radiosonde Observations

Abstract

AbstractAiming at investigating the vertical wave number spectral features of three‐dimensional winds in the lower atmosphere as well as their latitudinal and seasonal variations, we analyzed 11 year (1998–2008) radiosonde data from 92 United States stations in the Northern Hemisphere. The spatiotemporal variation of the horizontal wind spectral amplitude agrees well with that of the inertial gravity wave energy, revealing that the observed horizontal wind spectra are mainly attributed to the inertial gravity waves. The horizontal wind spectral slope is systematically and climatologically less negative than the canonical value of −3. For the first time we found that the vertical wind spectrum is much shallower than the horizontal wind spectrum over a wide latitude region, with slopes varying in −1.1 to −0.2 (−0.6 to 0.1) in the troposphere (lower stratosphere). Besides the slopes, the height, latitudinal, and seasonal variations of the vertical wind spectral showed evident difference from those of the horizontal wind spectrum. These differences are due to the horizontal and vertical wind spectra that might be constituted mainly by low and high frequency waves, respectively. Both the horizontal wind and vertical wind spectra exhibit evident universal features, which are more prominent in the lower stratosphere than in the troposphere, where it is thought to be the main source region of gravity waves, implying that the dynamical processes in the wave propagation might be the main cause of the universal spectrum. The background wind was found to have significant impact on the horizontal wind spectrum but has only weak impact on the vertical wind spectrum.