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Abstract Weak but persistent synoptic-scale ascent may play a role in the initiation or maintenance of nocturnal convection over the central United States. An analytical model is used to explore the nocturnal low-level jets (NLLJ) and ascent that develop in an idealized diurnally varying frictional (Ekman) boundary layer in a neutrally stratified barotropic environment when the flow aloft is a zonally propagating Rossby wave. Steady-periodic solutions are obtained of the linearized Reynolds-averaged Boussinesq-approximated equations of motion on a beta plane with an eddy viscosity that is specified to increase abruptly at sunrise and decrease abruptly at sunset. Rayleigh damping terms are used to parameterize momentum loss due to radiation of inertia–gravity waves. The model-predicted vertical velocity is (approximately) proportional to the wavenumber and wave amplitude. There are two main modes of ascent in midlatitudes, an afternoon mode and a nocturnal mode. The latter arises as a gentle but persistent surge induced by the decrease of turbulence at sunset, the same mechanism that triggers inertial oscillations in the Blackadar theory of NLLJs. If the Rayleigh damping terms are omitted, the boundary layer depth becomes infinite at three critical latitudes, and the vertical velocity becomes infinite far above the ground at two of those latitudes. With the damping terms retained, the solution is well behaved. Peak daytime ascent in the model occurs progressively later in the afternoon at more southern locations (in the Northern Hemisphere) until the first (most northern) critical latitude is reached; south of that latitude the nocturnal mode is dominant. 

Abstract The meteorological characteristics associated with thunderstorm top turbulence and tropical cyclone (TC) gigantic jets (GJ) are investigated. Using reanalysis data and observations, the large-scale environment and storm top structure of three GJ-producing TCs are compared to three non-GJ oceanic thunderstorms observed via low-light camera. Evidence of gravity wave breaking is manifest in the IR satellite images with cold ring and enhanced-V signatures prevalent in TCs Hilda and Harvey and embedded warm spots in the Dorian and Null storms. Statistics from an additional six less prodigious GJ environments are also included as a baseline. Distinguishing features of the TC GJ environment include higher tropopause, colder brightness temperatures, more stable lower stratosphere/distinct tropopause and reduced tropopause penetration. These factors support enhanced gravity wave (GW) breaking near the cloud top (overshoot). The advantage of a higher tropopause is that both electrical conductivity and GW breaking increase with altitude and thus act in tandem to promote charge dilution by increasing the rate at which the screening layer forms as well as enhancing the storm top mixing. The roles of the upper level ambient flow and shear are less certain. Environments with significant upper tropospheric shear may compensate for a lower tropopause by reducing the height of the critical layer which would also promote more intense GW breaking and turbulence near the cloud top.