1. QINGNONG XIAO, XIAOLEI ZOU, and BIN WANG*
Initialization and Simulation of a Landfalling Hurricane Using a Variational Bogus Data Assimilation Scheme
QINGNONG XIAO, XIAOLEI ZOU, and BIN WANG*
Mon. Wea. Rev., 128,
報告：黃　小　玲

2. Introduction
Hurricane intensity change is closely related to the evolving 3D structure of the hurricane.
The difficulties in the prediction of hurricane intensity and inner-core structure are associated with insufficient observations over the oceans and with the limitations of forecast models.

3. Cumulus parameterization
Experimental design
Model domain
Resolution (km)
Dimension
( I × J × K )
Explicit moist scheme
Cumulus parameterization
A (fixed) 54
76 × 85
Dudiha’s simple ice
Grell
B1, B2, B3 (move) 18
112 × 130
Reisner mixed phase
Kain-Fritsch
C1, C2, C3 (move) 6
109 × 127
Reisner graupel No
27 half-σ levels
B1 _00hr, B2 _28hr, B3 _66hr
C1 _66hr, C2 _70hr, C3 _74hr

4. Vortex specification
The SLP of the hurricane vortex is specified according to Fujita’s formula (1952, Geophys. Mag., 23)
r is radial distance from the cyclone center, Pc is the hurricane’s central pressure (according to the NHC), ΔP is a parameter related to the hurricane gradient information, R is the estimated radius of maximum SLP gradient,
Vo(r) is gradient wind.

5. Hurricane Fran(1996)
NOAA/HRD(Hurricane Research Division) 1996/09/ UTC Pc = 977 hPa, Vmax = 75 kt (38.8 ms-1) RMW = 80 km
Vertical weighting profile of 1.0, 1.0, 0.95, 0.85, 0.65, and 0.35 at 1000, 850, 700, 500, 400, and 300 hPa.

6. Minimization procedure
A cost function is defined as
, where
X = (u, v, w, p’, T, q)T model variables at the initial time,
Jb , Jp and Jv is the background, pressure and wind term of the cost function,

7. X = (u, v, w, p’, T, q)T model variables at the initial time, Xb is the background analysis obtained from standard MM5 analysis fields with a crudely estimated diagonal error covariance matrix B, P(r) is the SLP of the model atmosphere, ti is carried out over half-hour windows at every 5 min. V(r,k) model wind velocity (sea level, 1000, 850, 700, 500, 400, 300 hPa), Ω is the 2D domain in the vicinity of the hurricane center (the area of Ω is related to R, and the average radius of Ω is about times of R), Wp and Wv is 1.6 hPa-2 and s2m-2

8. Numerical experiments
Hurricane Fran (1996) using the two-way interactive, triply nested,and movable mesh MM5.
CTL : NCEP 2.5o resolution global analysis.

9. Results from the BDA scheme

10. CTL_T
CTL_q
B80_T
B80_q

11. Experimental results from the simulation of Hurricane Fran (1996)

12. 95 kt (49.1 m/s)
90 kt (46.5 m/s)
56.3 m/s
49.6 m/s

13. T q V w

14. The tangential or swirling wind of the hurricane is strongly asymmetric. The maximum wind speed occurred around 900 hPa.
The ascending vertical motion around the eye increases the moisture in that region, while the descent inside the eye makes the area of the hurricane center drier in the lower to middle troposphere. Near the surface at the hurricane center, the specific humidity reaches its maximum value.
The compensating descent inside the hurricane eye is the main reason for the formation of the warm core.

15. Domain C (6 km)
WSR-88D radar

16. Sensitivities of the BDA results to the model resolution, RMW, and bogus variable specification

17. A220V
A220P
CTL
The assimilation of the bogused wind alone could not produce a hurricane SLP field with realistic intensity.

18. Although the low-level maximum wind of A220V at the beginning was very close to the observation, the forecast became poorer as the time of integration increased.
The pressure bogus is more efficient than the wind bogus in reproducing a realistic hurricane intensity forecast.

19. A220V_T
A220V_q
A220P_T
A220P_q

20. Summary
The BDA scheme is very efficient in recovering the initial structure of the hurricane using very little observational information.(a strong constraint, get a good hurricane track and make a moist warm-core hurricane structure.)
The simulation of the hurricane track was sensitive to the model resolution on which the BDA scheme was performed.(A80 and B80)
The RMW used in the BDA scheme is a sensitive parameter for the hurricane track and intensity forecast.
A220P is more effective than A220V. The hurricane simulation from the initial conditions produced by the use of bogused SLP low data is closer to observation than the use of bogused wind data only.