14C.3
Typhoon Simulations with Assimilated GPS Occultation Refractivity
Ching-Yuang Huang, National Central University (Taiwan), Chung-Li, Taiwan; and Y. -. H. Kuo, S. H. Chen, and F. Vandenberghe
Typhoon Simulations with Assimilated GPS Occultation Refractivity
1Ching-Yuang Huang, 2Ying-Hwa Kuo, 3Shu-Hua Chen and 2 Francois Vandenberghe
1Department of Atmospheric Sciences, National Central University, Taiwan
2National Center for Atmospheric Research, Boulder, USA
3Department of Land, Air, and Water
Resources, University of California, Davis, USA
The mesoscale model (MM5)
with three-dimensional variational (3DVAR) assimilation is utilized to
investigate influences of GPS occultation refractivity on simulations of typhoons
past Taiwan. The GPS refractivity
data are taken from currently onboard CHAMP and SAC-C satellites, which provide
several profiles in the simulated oceanic region. Moisture increments
from ingested GPS refractivity exhibit a maximum magnitude of about 2 g kg-1
associated with much less temperature increments. The differences between the computed and
observed refractivities are only about 10 units at the middle levels with an
influential radius of several hundreds of km. For
the no-GPS run, the simulated Typhoon Nari in 2001 consistently moves
southwestward toward Taiwan but
then exhibits a further leftward track along northwestern Taiwan after landfall. With assimilated
GPS refractivity, the simulated track is closer to the west coast. Both rainfall
intensity and track at later stages are also improved for the GPS run. The
simulated rainfalls for Nakri in 2002 for the GPS and no-GPS runs in general
are similar, but for the former a more pronounced low is produced to southeast
of Taiwan and then results in clearer localized precipitation in northeast
Taiwan as observed. Both Nari and Nakri runs with GPS data show improved
prediction on 24-h accumulated rainfall as supported by higher threat scores
and smaller rms errors against observations on the island. A cycling 3DVAR is also explored in Nari
simulations to investigate the impact of complementary QuikSCAT near-surface
wind at the oceanic swath of the cyclone path. It was found that
inclusion of this surface wind results in an improved track with less
lagging.
Session 14C, Tropical cyclone simulation III: Initialization and Assimilation
Thursday, 6 May 2004, 1:30 PM-3:00 PM, Napoleon II Room
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