A Synoptic View of the Upscale Energy Cascade
Abstract
Moist processes can produce kinetic energy at subsynoptic scales, traditionally regarded as part of the -5/3 inertial subrange. Atmospheric kinetic energy cascades to both smaller and larger scales, so moist dynamics at the subsynoptic scales should in part cascade inversely into the synoptic scales. This process has heretofore been examined statistically using simplified models. In this study, for the first time, we examine this process using a case study approach with simulations of amplifying jet stream waves by the WRF mesoscale model. Pairs of simulations are carried out, with standard initial conditions and with subsynoptic-scale energy suppressed in the initial conditions. We make use of a two-dimensional wavelet filter to both remove subsynoptic scale incoherent constituents of the instantaneous stream function and velocity potential and to diagnose the resulting differences in the evolution of the scales and structures of simulated features.
Synoptic analysis of filtered and control simulation output shows that moist dynamics project onto the synoptic scales via the development of new PV gradients in the upper troposphere, altering the amplification rate and phase of the mid-latitude baroclinic waves. Differences in the location and magnitude of PV gradients depend largely on precipitation intensity and spatial coverage. Filtered simulations were observed to produce greater precipitation maxima and larger corresponding enstrophy maxima than the unfiltered simulations. These filtered enstrophy maxima emerged from areas with generally lower enstrophy than in the unfiltered simulations. Perturbation kinetic energy typically shifts back and forth between zonally elongated features and meridionally elongated features over the course of the multiday simulations. The onset of high amplitude jet stream waves and wave breaking coincides with a rapid increase in the perturbation kinetic energy of all subsynoptic and synoptic scales. The distribution of energy among perturbation scales and orientations follows patterns that coincide with common stages of cyclone development. Ensemble members with moist dynamics that produced different PV gradients aloft followed different pattern progressions that may reflect systematic life cycle differences, but additional case studies would be necessary to determine whether these differences are systematically determined by the energy differences of the initial states.
Citation
Coates, David A (2021). A Synoptic View of the Upscale Energy Cascade. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /193165.