1. INTRODUCTION Monsoon Gyre (Lander 1994) Sudden northward TC track changes in the WNP (Carr and Elberry 1995) August 1991 low-frequency nearly circular cyclonic vortex a diameter of about 2500 km
A major challenge in operational TC forecasting (Wu et al. 2013 ） Numerical study of Morakot (2009) (Liang et al. 2011) Observation: Coalescence process, enhanced synoptic- scale southwesterly flows (Wu et al. 2011 a, b, Wu et al. 2013) Carr and Elberry (1995) TC MG A β-induced energy dispersion RECENT STUDIES mean forecast error in distance at the turning time average forecast error >
TC track changes associated with monsoon gyres: Sudden northward turning and Westward turning TC tracks (Wu et al. 2013, Mon. Wea. Rev) Q1: What types of TC tracks can happen within monsoon gyres ？ Q2: What affects TC track types within monsoon gyres?
2. EXPERIMENTAL DESIGN Three two-way interactive domains (27, 9, and 3 km) Large-scale monsoon gyre at 20°N and a samll TC Initial vertical profiles of environmental RH and T from the MERRA reanalysis Open ocean: SST = 29 ℃ Initial radial profiles TC: 81 km, 30 m/s, 1000km MG: 594 km, 10 m/s, 3000km
3. SIMULATED SUDDEN NORTHWARD TURNING TRACK within about 12 hours (75-87 h) TC: 400 km to the east of the MG center.
(1) Relationship with the steering flow PVT diagnostic approach (Wu and Wang 2000) 78 h72 h 84 h 90 h C : TC motion, HA : horizontal advection DH : diabatic heating
(2) Coalescence of two systems 700 hPa environmental winds ( TC removed, Kurihara et al. (1995)) 66 h 78 h84 h symmetrization Azimuthal mean asymmetric kinetic energy
42 h 66 h 75 h78 h 81 h84 h (3) Cyclonic rotaion of TC beta gyres Wavenumber-1 asymmetric components Cyclonic rotation of TC beta gyres Southward ventilation flow Slowdown of TC westward translation coalescence The MG catches up with the TC.
(4) Rotation of negative relative vorticity Azimuthal mean asymmetric kinetic energy rapidly increase `500 km `300 km 700 hPa relative vorticity （ shaded ） and wind fields (vector) Enhanced peripheral southwesterly winds
4. SENSITIVE EXPERIMENTS (1) Gaussian monsoon gyre Mallen et al. (2005) weaker cyclonic feature southwestward around 77 h The cyclonic rotation angle of TC beta drift is sensitive to the magnitude of cyclonic sheared environmental flows (Wang et al. 1997)
(1) Gaussian monsoon gyre 42h66h 75h84h Wavenumber-1 asymmetric components Smaller angle of the cyclonic rotation of the TC beta gyres The coalescence process does not happen. 700 hPa wind fields 60 h72 h 84 h96 h
(2) Other initial structural parameters of the MG Little effect on the sudden northward track changes
(3) Sensitivity to TC structure All simulated TCs experience the northward turning. The turning angle is more sensitive to the initial location of the TC.
(4) Sensitivity to TC outer strength T he less turning angle of the stronger TC is associated with the rapid reduced translation speed.
TC-MG INTERACTION & TRACK TYPES Q1: What types of TC tracks can happen within monsoon gyres ？ Q2: What affects TC track types within monsoon gyres? Sudden northward track Northward track without a sharp turning Westward turning track
5. CONCLUSIONS 1.The TC coalescence with the MG is a key process to the occurrence of sudden northward TC track changes. 2.The coalescence process is associated with a cyclonic rotation of TC beta gyres, which reduces the TC northwestward motion. 3.West-turning TC track is due to the relatively faster TC movement, while the relatively faster MG movement leads to northward tracks without a sharp turning. 4.The profiles of both MGs and TCs are important for successfully predicting the sudden track change in numerical models.