Physically Consistent Atmospheric Variational Objective Analysis Model and Its Applications over the Tibetan Plateau. Part I: Method and Evaluation

A physically consistent atmospheric objective analysis model, based on the constrained variational analysis method, was applied to the Tibetan Plateau for large-scale atmospheric structure analysis. This objective analysis model can deal with multisource measurements with different spatial and temporal resolutions, and satisfy the conservation of column-integrated mass, heat, moisture, and momentum using surface precipitation and flux data at the surface and top of the atmosphere to constrain the sounding measurements. An experiment during August 2014 around Naqu in the Tibetan Plateau shows that those state variables generated by the model can retain observational characteristics. The analyzed large-scale derivatives, such as vertical velocity, divergence, temperature and water vapor advection, apparent heat source, and apparent moisture sink, obtained by the objective analysis model, can reasonably demonstrate dynamic, thermal, and moisture structures during the analysis period, which is conducive to precipitation process studies. It also shows that the layer of 350–400 hPa is an important change center of dynamics, heat, and water vapor in the analysis region during August 2014. Different sources of measurements have different impacts on the final analysis fields in this model. The sounding measurement significantly impacts the upper-level wind, but the amplitude of this impact is small, within 1 m/s. Precipitation and flux measurements mainly affect the large-scale derivatives, such as vertical velocity, in which precipitation mainly affects the upward movement during precipitation periods, and flux data mainly affect the downward movement during light rain/no-rain periods. Generally, the physically consistent atmospheric variational objective analysis model has high stability and strong validity.