| 摘要(英) |
First of all, this research has successfully established a tool to generate those wanted scenarios of balanced I.C.s for idealized WRF simulations and use WRF high resolution nested domains to figure out the rainfall patterns on the terrain. There are two experiments, one is to control vortex parameters, the other is to control terrain parameters. In the controlling vortex parameters experiment, we use a fixed terrain comparable to CMR with width 100km and length 300km. We find that the speed of steering flow cause the negative effect on the tropical cyclones track deflection and accumulated rainfall amount and the results are the same as previous studies. There is an interesting phenomenon that the patterns of rainfall are in phase between U1 group and U2 group neglecting the amount of rainfall. The results of the controlling terrain parameters experiments show that there is obvious evidence for that the direction of the tropical cyclones track deflection is dominated by the terrain length L_y and the degree of track deflection is dominated by the terrain altitude H. The tropical cyclones will turn left for enough large value of Ly. For example, case W1L3H. (about 3000km with H=1500m, critical value of non-dimensional parameter R_mw/L_y=0.027). Overall, the terrains make the cyclones speed down for 96-hr average translation speed both of two experiments and the faster the steering flow is, the more deceleration the cyclones will be. While only considering the upstream average translation speed of cyclones, U1 group is an exception. The terrain makes the U1 group most cases speed up. The upstream de-acceleration value is about 20% of the steering flow speed. With the vorticity budget analysis, the advection term dominate the voriticity tendency upstream, and the stretching term dominate when the cyclones passing through the mountain with strong blocking. Tilting term also has much contribution to the vorticity tendency while the cyclones across the terrain. The results of vorticity budget analysis are the same as Lin et al (2011). According to the results of terrain steepness experiments, the upstream track deflection is not sensitive to the steepness of the terrain (parallel to the moving direction of cyclones) of the mountain. At last, the direction of cyclones track deflection has a lot of to do with the horizontal asymmetric wind field. The cyclone tends to turn right with the maximum wind appearing at the east side of the cyclone, and tend to turn left with the maximum wind appearing at the west side of the cyclone. This can also be applied to explain the phenomenon of the upstream anti-cyclone track found by Yeh and Elsberry (1993). |
| 參考文獻 |
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