Numerical Study of Influence of Mountain Ranges in Taiwan on a cold Front

by

Wen-Yih SunNational Center for High Performance Computing

Hsin-chu, Taiwanand

Jiun-Dar Chern Laboratory for Atmospheres, NASA Goddard Space Flight Center

Greenbelt, MD 20771, USAICMCS-V Oct. 31-Nov. 3, 2006

Isochrones of the leading edge of the cold air determined from the surface and satellite data. The designator hhZdd is used to denote the UTC hour (hh) and the day (dd) in June 1987. (After Chen and Hui, 1990)

x

x

Fig. 1b: Wind component parallel to the front (solid) and cross-front wind component (dashed) from P-3 aircraft data. (After Chen and Hui, 1990)

Pre. Grad. (∆x ≈ 30 - 40 km) ≈ 6.5 - 8.7 10-4m s-2, Coriolis f (≈ 6 x 10 -4m s-2).

Sun and Chern, 2006. JMSJ,, Vol. 84. pp. 27-46

Inviscid without f Density current

Initial condition: ECMWF surface v & V at 0000UTC14 June 1987

A

A’

B’

B

wind vector and streamline at 06Z15 June 1987 at z=25m

EC

PRM

800

1000

600

400

80

200

hpa

800

1000

600

400

80

200

hpa

A A’ A A’

EC

PRM

Vertical cross section along AA’ for v & cross-front wind component at 06Z15 June 87

Vertical cross section along BB’ for v & cross-front wind component at 06Z15 B’ B B’ B

the ageostrophic forcing (–7.8 x 10-4 m s-2), advection term (-6.7 x 10-4 m s -2), and friction (-9.0 x 10-4 m s-2) are comparable in CONTROL case in the lower PBL

With ∆Tv= 1 K, H= 800 m, and =1.1, CH obtained 5.5 m s-1

speed of density current

Kelvin shock wave is:

The propagation speed of the simulated frontal leading edge along AA’ was about -2.8 m s-1 between 1800 UTC 14 and 0600 UTC 15, which is comparable with the ECMWF analysis, but much slower than ~ 6 m s-1 estimated by CH.

30N

120E

Wind and v at 00Z15 June 1987 for INVISCID Case

Wind and v at 12Z15 June 1987 for INVISCID Case

.231E+02

MAXIMUM VECTOR

Wind and v at 12Z15 June 1987 for INVISCID and without mountains in Taiwan

Wind and v at 18Z14 June 1987 for INVISCID with f=0 Case

Thanks