| Understanding gravity wave sources is essential to gravity wave research, and has profound effect on improving general circulation models (GCMs). My Ph.D. work is to analyze, diagnose and simulate the source behaviors of gravity waves that are observed in the US high vertical-resolution radiosonde data. Two sources---convection and jet imbalance---are of the major interest.;I used a ray-tracing gravity wave model GROGRAT to characterize the "mean" source spectrum of gravity waves in the lower stratosphere that are observed from US high vertical-resolution radiosonde profiles on a monthly scale. With a fixed source spectral function, one can get "best-fits" for most of the stations. A universal source function is found to be most powerful in capturing the major features of the variations, while another, which represents the convection source, works better for tropical stations. "Fits" are generally better for winter than for summer, indicating possible jet-related sources.;I furthermore examined the perturbation field of the ascent rate that is likely to be representative of higher-frequency gravity waves that are generated from the convection sources. The newly defined variable, VE, as well as the apparent dominant vertical wavelength analyzed from the ascent rate fluctuations turned out to be collocated very well with moist convection in the troposphere, especially during warm seasons. The waves tend to have higher frequencies, and this seems consistent with theory.;Forcing terms associated with the jet imbalance source are analyzed on a climatological basis. The derived forcings reveal some characteristics of the jet imbalance source, which we can sometimes see in the radiosonde profiles. GROGRAT and a linear forcing-response model are used to study a specific case, which sheds some light on parameterizations of gravity wave drag associated with the jet imbalance. |
