Abstract
The occurrence of a Ural blocking (UB) event is an important precursor of severe cold air outbreaks in Siberia and East Asia, and thus is significant to accurately predict UB events. Using subseasonal to seasonal (S2S) models of the European Centre for Medium-Range Weather Forecasts (ECMWF) and the Environment and Climate Change Canada (ECCC), we evaluated the predictability of a persistent UB event on 18 to 26 January 2012. Results showed that the ECCC model was superior to the ECMWF model in predicting the development stage of the UB event ten days in advance, while the ECMWF model had better predictions than the ECCC model for more than ten days in advance and the decaying stage of the UB event. By comparing the dynamic and thermodynamic evolution of the UB event predicted by the two models via the geostrophic vorticity tendency equation and temperature tendency equation, we found that the ECCC model better predicted the vertical vorticity advection, ageostrophic vorticity tendency, the tilting effect, horizontal temperature advection, and adiabatic heating during the development stage, whereas the ECMWF model better predicted the three dynamic and the two thermodynamic terms during the decaying stage. In addition, during both the development and decaying stages, the two models were good (bad) at predicting the vortex stretching term (horizontal vorticity advection), with the PCC between both the predictions and the observations larger (smaller) than +0.70 (+0.10) Thus, we suggest that the prediction of the persistent UB event in the S2S model might be improved by the better prediction of the horizontal vorticity advection.
Highlights
Atmospheric blocking is a large-scale persistent high-pressure center of atmospheric circulation, which exerts a high impact on extreme weather events downstream and upstream of the blocking region.In the winter, the climatology of blocking frequency shows two peaks over the Euro-Atlantic and Pacific sectors [1,2]
Programme launched the subseasonal to seasonal (S2S) project in November 2013, and established a database containing hindcasts up to 60 days forecasting from 11 meteorological centers [35], in this study we evaluate the predictability of the persistent Ural blocking (UB) event in January 2012 using the model outputs from the European Centre for Medium-Range Weather Forecasts (ECMWF) and the Environment and Climate Change Canada (ECCC) participating in the S2S project
The occurrence of UB events is crucial for the severe cold air outbreaks in East Asia, so it is important to predict the UB event accurately
Summary
Atmospheric blocking is a large-scale persistent high-pressure center of atmospheric circulation, which exerts a high impact on extreme weather events downstream and upstream of the blocking region. In addition to the evaluation of the predictability of the wintertime blocking frequency, it is important to assess the performance of climate models in predicting persistent UB events. The long-lasting severe cooling in East Asia from mid-January to early February in 2012 was closely tied to the frequent occurrence of persistent UB events [33,34], and it is important to investigate the predictability of these persistent. Programme launched the subseasonal to seasonal (S2S) project in November 2013, and established a database containing hindcasts up to 60 days forecasting from 11 meteorological centers [35], in this study we evaluate the predictability of the persistent UB event in January 2012 using the model outputs from the European Centre for Medium-Range Weather Forecasts (ECMWF) and the Environment and Climate Change Canada (ECCC) participating in the S2S project. As suggested by Quinting and Vitart [36], both models have a higher resolution and a better forecasting skill in predicting the UB events
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