A Wave Energy Flux Study from Noting Midtropospheric Sources in the Global Atmosphere with a Recipe for Forward- and Counter-Shear Transfers

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Abstract By diagnosing 30 years of atmospheric reanalysis, this study presents the three-dimensional distribution of wave energy fluxes (WEFs) globally within monthly climatological fields. The results, combined with a theoretical analysis, reveal two key dynamical features for midlatitude waves in westerly jets. First, in the lower troposphere, wave activity (WA) flux is directed upward, while the WEF is directed downward, originating from adiabatic (winter) and diabatic (summer) sources at the midtroposphere. The ratio between the vertical components of WEF and WA flux provides a measure confirming negative WA in the bulk lower troposphere. Second, the present study introduces a rotational flux in the zonal–vertical plane to an existing WEF diagnosis, which acts only in the presence of the vertically trapped modal structure of waves. This rotational flux provides upwind sinking and downwind rising of vertical WEFs, offering a way to identify the countershear nature of zonal WEFs. The upper layer of this system exhibits westward WEFs that are outcropped on the polar side of the westerly jets. The rotational flux fades in tropical regions, determining cross-equatorial upper-tropospheric WEFs in the eastern tropical Pacific in relation to the zonal variation of the Hadley ascending during austral summer. Significance Statement This study introduces a rotational flux in the zonal–vertical plane to obtain a vertically uniform-like structure in the total (mean flow advection plus wave intrinsic) zonal group velocity for illustrating coupling between the upper- and lower-layer waves in the Eady problem. This rotational flux consists of two kinds of zonal wave energy fluxes (WEFs). The first WEF (countershear Rossby) is written using the vertical second derivative of the zonal-mean velocity, corresponding to the so-called meridional gradient of background quasigeostrophic potential vorticity associated with the slope of isentropics. The second WEF (countershear modal) is identified in the present study as a term necessary in the Eady problem and remaining only for vertically trapped waves. Despite being trapped, wave energy is radiated from midheight, not from the surface.

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