Suppressing Grid-Point Storms in a Numerical Forecasting Model

Seung-Bu Park,Seung-Bu Park,Ji-Young Han

doi:10.3390/atmos12091194

Seung-Bu Park, Seung-Bu Park + Show 1 more

Open Access

https://doi.org/10.3390/atmos12091194

Copy DOI

Abstract

The convective parameterization scheme of the Korean Integrated Model (KIM) is tentatively modified to suppress grid-point storms in the Western Pacific Ocean. The KIM v3.2.11 suffers from the numerical problem that grid-point storms degrade forecasts in the tropical oceans and around the Korean Peninsula. Another convective parameterization scheme, the new Tiedtke scheme, is implemented in the KIM. The artificial storms are suppressed in the test version because the heating and drying tendencies of the new Tiedtke scheme are stronger than those of the default KIM Simplified Arakawa-Schubert (KSAS) scheme. Based on this comparison, the KSAS scheme is modified to strengthen its heating and drying tendencies by reducing the entrainment and detrainment rates. The modified KSAS scheme suppresses grid-point storms and thus decreases grid-scale precipitation in a summertime case simulation. Twenty 10-day forecasts with the default convection scheme (KSAS) and twenty forecasts with the modified scheme are conducted and compared with each other, confirming that the modified KSAS scheme successfully suppresses grid-point storms.

Highlights

Atmosphere 2021, 12, 1194. https://Improving precipitation processes in numerical weather prediction and climate models is one of the most important but difficult tasks for achieving better weather and climate prediction [1,2]
Twenty 10-day forecasts with the default convection scheme (KSAS) and twenty forecasts with the modified scheme are conducted and compared with each other, confirming that the modified KIM Simplified Arakawa-Schubert (KSAS) scheme successfully suppresses grid-point storms
These complicated evaluation results highlight that the new Tiedtke scheme nor the modified KSAS scheme guarantee a better performance when implemented in the Korean Integrated Model (KIM) the two schemes can suppress the grid-point storms

Summary

Introduction

Improving precipitation processes in numerical weather prediction and climate models is one of the most important but difficult tasks for achieving better weather and climate prediction [1,2]. Numerical models generally simulate clouds and precipitation using two kinds of parameterization schemes—cloud microphysics and deep/shallow cumulus convection schemes—which handle grid-scale and subgrid-scale moist processes, respectively. By generating clouds (precipitating), the two schemes remove grid-scale supersaturation and convective instability, respectively, stabilizing cloudy space. The grid-point storms often survive several days and impact nearby northward tropical cyclones (TCs), affecting convergent flow ahead of the TCs and precipitation over the Korean Peninsula. This kind of pattern deteriorates the boreal summertime skill scores of the KIM severely, we have been trying to mitigate this problem. The deep convection scheme in the KIM is modified to suppress the grid-point storms in the Western Pacific Ocean.

KIM and a Case Description

Grid-Point Storms and Heating and Drying Tendencies

Impact of Convection Scheme Modification

Summary and Concluding Remarks