six seasonally averaged parameters.
① the Coriolis parameter ( f )
பைடு நூலகம்
② low-level relative vorticity (ζr ) ③ inverse of the tropospheric vertical wind shear (1/Sz )
Do all these parameters are necessary?
The external forcing source
Riehl (1950): theory of Easterly Wave (precondition: upper level divergence).
Gray (1968)：most of the tropical disturbances and storms formed in Equatorial Trough，and the upper level divergence is unnecessary.
Observations (1960’s)：ITCZ v.s. Easterly Wave.
Sadler (1970’s): Tropical Upper Tropospheric Trough ( TUTT ).
Fritsch et. al. (1990’s): Tropical Cloud Cluster and Preexisting Vortex.
dynamic
④ ocean thermal energy, manifest as ocean temperatures greater than 26℃ to a depth of 60 metres ( E )
thermal ⑤ the difference in equivalent potential temperature between the surface and 500hPa (Δθe) ⑥ relative humidity in the mid-troposphere ( RH )
Li Xianzhi(1950’s) and Wu Rongsheng(2003): Cold Surges.
The trigger mechanisms Classical Theories about TC Genesis
① Conditional Instability of Second Kind ( CISK ):
台风生成机制研究进展
Outline
Review the studies on the tropical cyclonegenesis
The large scale environmental influences. The external forcing source. The trigger mechanisms.
Gray 1968
the Coriolis parameter ( f ) is not necessary for Vaimei
JTWC best track
Simulated 3h
33h
accumulate
precipitation
36h
39h
1. Review
The largescale environmental influences:
c. Magnitude of latent heat release is proportional to Ekman pumping.
d. Atmosphere must be conditionally unstable.
CISK
Surface friction causes inflow into the disturbance to be “deflected” inward toward the surface center.
Mass continuity dictates upward motion. This process is called “Ekman Pumping”
Low
Upward motion causes saturation and thus latent heat release (LHR). If air is conditionally unstable, upward motion will continue and enhance secondary circulation.
dynamic
④ ocean thermal energy, manifest as ocean temperatures greater than 26℃ to a depth of 60 metres ( E )
thermal ⑤ the difference in equivalent potential temperature between the surface and 500hPa (Δθe) ⑥ relative humidity in the mid-troposphere ( RH )
Some preliminary result on the genesis of tropical cyclone over south China sea 2000 Further research
1. Review
The large scale environmental influences:
－Theory developed by Charney and Eliassen (1964)
－ Basic assumptions:
a. Initial perturbation is a synoptic-scale wave.
Jule Charney
b. Frictional convergence results in latent heat release above center of low-level cyclonic vorticity.
six seasonally averaged parameters.
① the Coriolis parameter ( f )
② low-level relative vorticity (ζr ) ③ inverse of the tropospheric vertical wind shear (1/Sz )