Abstract
This study investigates the effects of atmosphere-ocean coupling for medium-range forecasts by using coupled numerical weather prediction (NWP) experiments based on the unified model (UM) on a case study of the 2016 heatwave over the Korean Peninsula. Atmospheric nudging experiments were carried out to determine the key regions which may have large impacts on the forecasts of the heat wave. The results of the nudging experiments suggest that key forcing from the Mongolia region gives the largest impact to this case by causing a transport of warm air from the northwest part of Korea. Moreover, the Pacific region shows an important role in the global circulation in nudging experiments. Results from the atmosphere-ocean coupled model show no clear benefit for the extreme heat wave temperatures in this case. In addition, more model development seems to be needed to improve the representation of sea surface temperature (SST) in some key areas. Nevertheless, it is confirmed that the atmosphere-ocean coupled simulation produces a better representation of aspects of the large-scale flow such as the blocking high over the Kamchatka Peninsula, the high pressure system in the northwest Pacific and Hadley circulation. The results presented in this study show that atmosphere-ocean coupling can be an important way to improve the deterministic model forecasts as the lead time increases beyond a few days.
Highlights
Extreme weather events are an area of increasing concern due to their high impacts on human society and the environment and due to the likelihood that they may change in a future climate.forecasting extreme weather events in a timely way and with the right magnitude is clearly important for decision makers across many sectors
This section outlines the performance of the control experiment (CTL) simulation in reproducing the heat wave both in terms of extreme temperatures and large-scale atmospheric circulation (Section 3.1), examines the remote forcing or forecast errors through the nudging technique (Section 3.2) and explores the role of atmosphere-ocean coupling in reproducing the heat wave (Section 3.3)
In order to investigate changes in the performance of the numerical weather prediction (NWP) model, spatial patterns of the variables in a 7-day forecast are examined in Figure 2, averaged over the heat wave period of
Summary
Extreme weather events are an area of increasing concern due to their high impacts on human society and the environment and due to the likelihood that they may change in a future climate. As forecast lead times extend beyond a few days, systematic model biases begin to grow on larger spatial scales and generate difficulties in producing quantitative forecasts, generating substantial forecast errors in operational medium-range forecasts [4] This is because these models do not reflect the interaction between atmosphere and ocean but use prescribed sea surface temperatures (SSTs). Ham and Na [24] investigated whether positive SST anomalies in the south sea of Korea, associated with positive geopotential height anomalies, induced warm temperature advection and less cloud amount and increased the solar radiation over Korea in the summer of 2016 They showed that this interactive response appears distinctly from a weekly timescale, reflecting that atmosphere-ocean coupling has the potential to improve medium- to extended-range forecasts. Most results of each experiment are compared during 11–25 August 2016 when the heat wave phenomena hit the Korean Peninsula
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