Abstract
AbstractThe observational impacts of satellite data assimilation on extended‐range forecasts of sudden stratospheric warmings (SSWs) are investigated by conducting ensemble forecast experiments. We use two Japanese novel reanalysis products: the Japanese 55‐year reanalysis (JRA‐55) and its subset that assimilates conventional observations only (JRA‐55C). A comparative examination on the reproducibility for SSWs between the two ensemble forecasts reveals that the impact of satellite observations is significant for forecasts starting 5 days before the SSW onset, with 20% less accuracy in the JRA‐55C forecasts. Moreover, some of forecasts of vortex‐splitting SSWs show a sudden appearance of deep difference, which lasts over a few months in the lower stratosphere and significantly affects the surface climate. These results highlight an important role of mesospheric and upper stratospheric circulations on the onset and development of SSWs.
Highlights
To improve our understanding and forecasting of the atmospheric environment, it is important to comprehend how analyses and forecasts produced by numerical weather prediction (NWP) systems are affected by each observational source
We have examined how accurately ensemble forecasts capture the onset timing of stratospheric warmings (SSWs) and to what extent it is affected by the assimilation of satellite data (Figure 1)
We have examined observational impacts of satellite data assimilation on extended‐range forecasts of SSWs by conducting ensemble forecast experiments for 20 SSW events using JRA‐55 and JRA‐55C combined with the flexible ensemble forecast system “Meteorological Research Institute Ensemble Prediction System (MRI‐EPS).”
Summary
Mesospheric and upper stratospheric initial conditions play an important role in forecasting the onset and development of sudden warmings. The 5‐day lead capture rate of the onset of major sudden stratospheric warmings degrades about 20% if satellite data are not assimilated. The absence of satellite observations could affect the extended‐range forecast skill related to downward‐propagating signals. Impact of satellite observations on forecasting sudden stratospheric warmings. Research Center for Environmental Modeling and Application, Japan Agency for Marine‐Earth Science and Technology, Yokohama, Japan, 2Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, Japan, 3Meteorological. Japan Meteorological Agency, Kashiwa, Japan, 4Graduate School of Science, Kyoto University, Kyoto, Japan
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