Dynamics of slantwise convection and sensitivities to model grid spacing under idealized frameworks
Student Seminar Series
Department of Atmospheric & Oceanic Sciences
presents
a talk by
Ting-Chen Chen
PhD student
Dynamics of slantwise convection and sensitivities to model grid spacing under idealized frameworks
Slantwise convection has been identified as one of the mechanisms for banded precipitation in baroclinic environments in many case studies. Our recent climatological analysis, based on ECMWF reanalysis data, also revealed the potential importance of slantwise convection in the intensification of midlatitude cyclones. Although a typical slantwise convective band has a width of several tens to about a hundred kilometers in the cross-band direction, the embedded smaller-scale processes might meaningfully regulate its evolution. In global/climate models with a typical horizontal grid spacing of O(10-100 km), convection is typically modeled by a cumulus parameterization scheme which does not consider slantwise ascent. It is therefore unclear whether mesoscale slantwise convection can be adequately resolved in these models. To address this issue, a series of idealized experiments of slantwise convection are performed using the two-dimensional, non-hydrostatic Weather Research and Forecasting Model, with the horizontal grid lengths varying between 1 to 40 km. The results show that the general features of the slantwise band and its larger-scale feedbacks converge numerically when the cross-band grid length ∆y=5 km is reached. By applying an accurate inline budget retrieval method to analyze the model output, we uncover new aspects of the slantwise convective dynamics and show that the non-hydrostatic pressure-perturbation field plays a significant role in the evolution of the cloud band. Such perturbations can only be adequately resolved with grid lengths of 5 km or less. Thus, important characteristics of slantwise convection may be poorly resolved in most operational numerical weather prediction and climate models and a slantwise convective parameterization would need to be implemented.