Approaches toward improving the modelling of midlatitude cyclones entering at the lateral boundary corner in the limited area WRF model. (26th July 2020) - Imberger, Marc
Abstract: Lateral boundaries can have a large effect on the introduction of external large‐scale structures in limited area models. This case study of a midlatitude cyclone using the advanced Weather Research and Forecasting (WRF) model examines challenges in simulating the storm intensity (characterised by sea level pressure, relative vorticity and wind speed) when a storm centre enters close to the lateral boundary corner in the outermost model domain. A domain shift, nudging techniques, adjustments of the WRF relaxation layer and the influence of the boundary condition update frequency are investigated as possible solutions. The update frequency of the lateral boundary conditions is found to be the most efficient in improving the storm intensity, while adjustments to the relaxation layer or nudging techniques did not overcome the lack of sufficiently updated lateral boundary conditions. This suggests that the modelling of the storm intensification requires sufficiently high temporal resolution. Abstract : Spatial and temporal adjustments are investigated to explore the challenge involved in introducing fast‐moving large‐scale meteorological information into the corner area of a limited area model. Adjustments include domain shift, nudging, relaxation layer adjustments and frequency of lateral boundary condition (LBC) updates. Spectral nudging reduces spatial distortion but smooths storm intensity, while increased LBC updates are beneficial in the case of fast‐propagating systems. This reduces artificially created distortions and smoothing due to temporal interpolation.