THE APPLICATION OF CONDITIONAL NONLINEAR OPTIMAL PERTURBATION TO THE BINARY TYPHOONS INTERACTION —FENGSHEN AND FUNG-WONG

The interaction between the typhoons Fengshen and Fung-wong over the Western Pacific in 2002 is studied with the Conditional Nonlinear Optimal Perturbation(CNOP) method.The study discovered that the CNOP method reveals the process of one-way interaction between Fengshen and Fung-wong.Moreover,if the region of Fung-wong was selected for verification,the sensitivity area was mainly located in the region of Fengshen and presented a half-ring structure;if the region of Fengshen was selected for verification,most of the sensitivity areas were located in the region between the Fengshen and the subtropical high,far away from Fung-wong.This indicated that Fung-wong is mainly steered by Fengshen,but Fengshen is mainly affected by the subtropical high.The sensitivity experiment showed that the initial errors in the CNOP-identified sensitive areas have larger impacts on the verification-area prediction than those near the typhoon center and their developments take a large proportion in the whole domain.This suggests that the CNOP-identified sensitive areas do have large influence on the verification-area prediction.

Binary interaction of typhoons Soulik and Cimaron in 2018—Part Ⅰ:Observational characteristics and forecast error

To understand structural changes and forecast error,a case study of binary typhoons in the western North Pacific(WNP)of 2018 was investigated using best track and reanalysis data.Soulik was generated on August 16 and Cimaron was generated on August 18,respectively.The 19 th typhoon Soulik and 20 th typhoon Cimaron co-existed from August 18 to 24 and approached each other.Soulik was located on the western side and Cimaron was located on the eastern side of the WNP.They were located approximately 1300 km from each other at 00 UTC August 22.The Soulik structure began changing around August 22 and became weak and slow,while Cimaron maintained its intensity,size,and moving speed.This observational evidence is likely caused by the binary interaction between two typhoons within a certain distance and environmental steering flow,such as the location of the North Pacific high and strong jet stream of the northern flank of the North Pacific high.Soulik was initially forecasted to make landfall and reach Seoul;however,its track changed from northward to northeastward from August 21 to 23 according to both official guidance and unified model(UM).Four global numerical weather prediction models forecasted different tracks of Soulik.UM and JGSM forecasted a northward track whereas ECMWF and GFS showed a northeastward track for 12 UTC August 21 through 12 UTC August 24.The latter models were similar to the best track.The track forecast error and spread of Soulik were larger than those of Cimaron.The mean absolute error of the maximum wind speed of Soulik was similar to the average of total typhoons in 2018.