Modelling and forecasting northeasterly cold surges during the East Asian winter monsoon

Abstract

Strong Cold Surges (CSs) commonly occur in East Asia during the North-East Monsoon and can severely affect human life and cause considerable economic losses. We analyzed three strong CS events (CSEs) that occurred over South China during the winters of 2008, 2009 and 2016 on two broad aspects. First, a regional modelling approach that combines high resolution regional climate modeling using the Weather Research and Forecasting (WRF) model together with datasets from reanalysis, satellite, and observational weather stations is used to model the CS in South China. Second, the influence of large scale synoptic meteorology on the outbreak of CS in East Asia is investigated using data analysis of reanalysis data sets and weather charts.

The WRF regional modelling approach using a two-way nesting technique reproduced the short range (hourly to daily), sudden increase in mean sea level pressure, the steep drop in surface temperature, and increased wind speed patterns during the three CSEs as observed at the Hong Kong weather station. The investigation of the large atmospheric systems over East Asia demonstrates that such CSEs originate, intensify and continue as unusually long persisting extreme cold advection due to the interaction of the three major atmospheric systems, Siberian Mongolian High, Aleutian Low and Jet Stream during the North-East Monsoon. We thus propose a new theoretical framework to explain the mechanism that leads to the development and formation of CSEs in East Asia.

We propose that a CS in South China is firstly pressure-gradient driven between the Siberian-Mongolian High and the South China Sea and is further influenced by the presence of an intense low-pressure systems developed near the coast of Japan. The latter also leads to the bifurcation of the CS air mass with the low-pressure system highly influencing the CS intensity and subsequent trajectory towards the South China Sea. We also propose new criteria based on daily and monthly pressure gradient for identifying and forecasting CS at time scales varying in days (i.e. short range) to a month (extended range) over East Asia. The methodology and criteria developed are also validated against past reported events. This proposed mechanism as based on the interaction of the three large atmospheric systems has significant potential to be used as a reliable forecasting tool. Such a tool can further provide advance information to decision makers and policy makers in developing response to weather extremes.