sudden track changes of tropical cyclones in monsoon gyres: full-physics, idealized numerical...
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Sudden Track Changes of Tropical Cyclones in Monsoon Gyres: Full-Physics, Idealized
Numerical ExperimentsJia Liang and Liguang Wu
Pacific Typhoon Research Center, NUIST
21 January, 2015
Megi (2010)
Songda (2011)Sinlaku (2008)
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OUTLINE
1. Introduction
2. Experimental design
3. Simulated sudden northward turninng track
4. Sensitive experiments
5. Conclusions
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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
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• 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 >
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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?
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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
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3. SIMULATED SUDDEN NORTHWARD TURNING TRACK
• within about 12 hours (75-87 h)
TC: 400 km to the east of the MG center.
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(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
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(2) Coalescence of two systems
700 hPa environmental winds
( TC removed, Kurihara et al. (1995))
66 h
78 h 84 h symmetrization
Azimuthal mean asymmetric kinetic energy
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42 h 66 h
75 h 78 h
81 h 84 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.
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(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
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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)
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(1) Gaussian monsoon gyre
42h 66h
75h 84h
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 h 72 h
84 h 96 h
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(2) Other initial structural parameters of the MG
• Little effect on the sudden northward track changes
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(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.
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(4) Sensitivity to TC outer strength
• The less turning angle of the stronger TC is associated with the rapid reduced translation speed.
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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
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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.
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