The Time and Regime Dependencies of Sensitive Areas for
Tropical Cyclone Prediction Using the CNOP Method |
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Authors: | ZHOU Feifan and MU Mu |
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Institution: | Laboratory of Cloud-Precipitation Physics and Severe Storms,
Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029 |
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Abstract: | This study examines the time and regime dependencies of sensitive areas
identified by the conditional nonlinear optimal perturbation (CNOP) method
for forecasts of two typhoons. Typhoon Meari (2004) was weakly nonlinear and
is herein referred to as the linear case, while Typhoon Matsa (2005) was
strongly nonlinear and is herein referred to as the nonlinear case.
In the linear case, the sensitive areas identified for special forecast
times when the initial time was fixed resembled those identified for other
forecast times. Targeted observations deployed to improve a special time
forecast would thus also benefit forecasts at other times. In the nonlinear
case, the similarities among the sensitive areas identified for different
forecast times were more limited. The deployment of targeted
observations in the nonlinear case would therefore need to be adapted to
achieve large improvements for different targeted forecasts. For both cases,
the closer the forecast time, the higher the similarities of the sensitive
areas.
When the forecast time was fixed, the sensitive areas in the linear case
diverged continuously from the verification area as the forecast period
lengthened, while those in the nonlinear case were always
located around the initial cyclones. The deployment of targeted observations
to improve a special forecast depends strongly on the time of deployment.
An examination of the efficiency gained by reducing initial errors within
the identified sensitive areas confirmed these results. In general, the
greatest improvement in a special time forecast was obtained by identifying
the sensitive areas for the corresponding forecast time period. |
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Keywords: | time dependence CNOP sensitive area typhoon targeted observations |
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