| dc.description.abstract | For typhoon assimilation and prediction, the quality of observations and its location
plays an important role in the problem of acquiring useful analysis increment. To discuss the
impact of observation location on typhoon track and structure, a series of OSSEs were carried
out with the Weather Research and Forecasting (WRF) Local ensemble transform Kalman
filter (LETKF) system and the ensemble based forecast sensitivity method is used to estimate
the observation impact. In this study, five different sets of observation locations were
constructed based on the natural run, including ALL (on ocean and land), LAND (on land),
OCEAN (on ocean), LAND_PF (on land and dropsonde of penetrated flight) and ALL_PF (on
ocean and land and dropsonde of penetrated flight). The experiment results show that the
ensemble mean track forecasts are closer to the natural run when there are observations over
ocean. Mainly, the effective corrections for improving the track prediction are over the
northern and eastern side of typhoon. In this case, we also found that assimilating the
penetrating flight dropsonde is helpful for establishing reliable typhoon circulation, but is not
useful enough for improving the overall track prediction, due to the lack of environment
information.
Based on the results of ALL_PF, we use the ensemble-based forecast sensitivity to
observation (EFSO) method (Kalnay et al., 2012) to estimate the observation impact, and
investigate which location of observations can significantly reduce the forecast error. The
result indicates that most of observations outside the typhoon circulation and over the ocean
region can bring out best benefit within the 24hr forecast. Results also confirm that
observations with positive corrections are mainly located near north and east region of
typhoon, as we expected that assimilating these observations can improve the track forecast.
In addition, assimilating dropsondes provides positive contribution to the short forecast,
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especially with the observations in the typhoon inner core.
In addition, two sensitivity experiments were carried out to test the effectiveness of the
environment observations on improving the track forecast. Results are able to echoed the
observation impact calculated by EFSO. | en_US |