Gravity Waves Associated with Jet/Front Systems. Part I: Diagnostics and their Correlations with GWs Revealed in High-Resolution Global Analysis Data

Abstract

Jet/front systems are the important sources of the atmospheric gravity waves (GWs). Based on mesoscale simulation results, dominant GWs associated with the jet/front systems have horizontal wavelengths of approximately 150 km, which need for parameterization in global models. Nevertheless, there is no comprehensive parameterization scheme of the jet/front GWs with a formulation of the GW momentum flux (GWMF) at launch level, due primarily to uncertainties in their generation mechanisms. In this study, we evaluate two diagnostics of the jet/front GWs, frontogenesis function (FF) and residual of the nonlinear balance equation (RNBE), by examining their spatiotemporal variations using two global reanalysis data sets over 32 years (1980？2011) and by examining correlations between the diagnostics and the GWMF resolved from high-resolution global analysis data in January and July of 2007. The FF and RNBE are maximal in the mid-to-high latitudes of the winter hemisphere, with local maxima in Greenland, East Asia, western North America, Antarctic Peninsula, and the Andes Mountains. The GWMF is dominant in two regions in the upper troposphere: (i) poleward of 30° in both hemispheres, with a larger value in the winter hemisphere, and (ii) tropical and subtropical regions in both hemispheres. The FF and RNBE are well correlated with theGWs in the mid-to-high latitudes following their seasonal variations, which successfully separate GWs in the tropics and subtropics generated by convective sources. In Part II, a parameterization based on the RNBE is developed and implemented in a climate model, and its impacts on the large-scale flow will be investigated.