| dc.description.abstract | On the typhoon prediction, the error of initial field will affect the accuracy of tracks along with the time. If we want to increase the accuracy of prediction, the first necessary factor is to improve the initial field accuracy of typhoon. By using different settings of potential vorticity Inversion could retrieved the potential vorticity perturbation and tangential wind perturbation field of typhoon. Therefore, we could get the new potential vorticity bogus vortex (PV Bogus Vortex) by using the potential vorticity perturbation field which is substituted for the original perturbation field. Then insert it to correct the initial field. It will have different simulate result by using different background error and horizontal scale.
In the WRF-3DVAR, the Fanapi typhoon’s intensity and steering flow are weak, so assimilate the bigger radius of PV Bogus Vortex and environmental field can correct the typhoon track so that the steering flow could be changed and the track would be more realistic. The outward divergence and larger correct range are using background error-cv3 to correct broad environment field. For the intensity of weaker typhoon, we can simulate the track efficiently by using the bigger PV Bogus Vortex and horizontal scale on the background error-cv3. It will over correct the strong typhoon’s track, because more environmental wind field will be alter when we assimilate the PV Bogus Vortex size of RMW and smaller horizontal scale. The background error-cv5 are opposed to the background error-cv3, it’s because cv5 is a regional model statistics results of a month on real simulate domain. The cv5 is focus on the typhoon center to correct the flow, which will make environment field not to be interfered with the insert position. For the intensity of stronger typhoon, we can simulate the track efficiently by using the smaller PV Bogus Vortex and horizontal scale on the background error-cv5.
The minimum track error of WRF-3DVAR of typhoon Fanapi and Megi will be replaced by WRF-4DVAR. In the part of Fanapi typhoon, to compare with the Ctrl Run on the initial field, the isobar don’t have obvious difference, but they will have stronger convergence wind field on the eyewall, and temperature of the north-east side of typhoon will increase. To compare with WRF-3DVAR on the initial field, the simulation result is looser and wider sphere of influence that isobar and wind field are divergence to effect the out region of typhoon, so it makes the track have larger error and doesn’t make landfall in Taiwan. In the part of Megi typhoon, to compare with the initial field of WRF-3DVAR, the simulation result shows the stronger cyclonic stream flow, but don’t have temperature change no matter background error-cv3 or cv5. To compare with WRF-3DVAR on the initial field, the simulation results is weaker than WRF-3DVAR that it have divergence wind pattern on the radius of typhoon, and decrease 0.5 Celsius degree on the typhoon center. The track simulation result can’t be better than WRF-3DVAR which has over 100 km track error when it land on Philippines.
On the part of assimilate PV Bogus Vortex, It can correct the track error of the Ctrl Run by using the WRF-3DVAR which makes the result better than WRF-4DVAR.
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