Sensitivity experiments for ensemble forecasts of the extratropical transition of typhoon Tokage (2004)
Author
Anwender, Doris
Jones, Sarah C.
Leutbecher, Martin
Harr, Patrick A.
Date
2010-01Metadata
Show full item recordAbstract
The extratropical transition (ET) of tropical cyclones often has a detrimental
impact on predictability in the vicinity of the event and downstream. Ensemble
forecasts provide an appropriatemeans by which to investigate both the uncertainty
and the dynamical development leading to the different ET scenarios. Sensitivity
experiments are presented using the European Centre for Medium-Range Weather
Forecasts (ECMWF) ensemble prediction system (EPS) to investigate different
methods of perturbing the ensemble forecast of the ET of Typhoon Tokage (2004).
During ET these perturbations have a notable impact on the ensemble spread
representing the uncertainty. Three experiments were performed: one of them
without singular vectors (SVs) targeted on the tropical cyclone, the second without
stochastic physics and the third excluding both perturbation methods.
The targeted perturbations are most important for sufficient spread in track and
intensity. Without the targeted perturbations, the analysis is not contained within
the ensemble spread. Stochastic physics leads to stronger reintensification of the
ensemble members after ET. The higher track spread leads to higher variability
in processes such as lower tropospheric latent heat release. This can be related
to a higher spread in the upper-level midlatitude flow for both perturbation
methods. A connection is drawn between the strength of ET and the modification
of the downstream midlatitude flow pattern. The uncertainty due to the targeted
perturbations propagates downstream with a Rossby wave train excited during
Tokage’s ET. For the case of stochastic physics, the uncertainty spreads to the
ridge directly downstream of the ET system but is not evident further downstream.
Description
The article of record as published may be located at http://dx.doi.org/10.1002/qj.527
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.Collections
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