TCAR - Typhoon Committee

282
ESCAP/WMO
Typhoon Committee Annual Review 2009
is spinned up by the global model with the force
of a bogus data. And then the first guess field
including TC vortex is introduced into global data
assimilation system-which generates analysis
data that contains TC vortex as the model initial
field. The flowchart of vortex formation is
described in Fig.2.
Fig.2. Flowchart of vortex formation
In the next global forecast time, there must exist
a vortex circulation in the first guess (that is the
global model 6-hourly forecasts at the first time).
Usually, the vortex is misplaced and weak against
the analyzed TC data by forecasters, but its
structure and circulation is “perfect” compared
to bogus vortex.
Two procedures need to be done for the weak
and misplaced vortex in the first guess as follows:
(2) Separate vortex from its environmental field,
and move vortex to the correct position. It is called
vortex relocation ( from NCEP) .
(3) Correct the TC vortex intensity by empirical
SLP distribution formula and gradient wind
relation in order that the TC vortex in first guess
is close to the observational TC data (such as
central pressure, maximum sustained wind). It is
called vortex modification.
The flowchart of vortex relocation and
modification is depicted in Fig.3.
Fig.3. Flowchart of vortex relocation and
modification
In the next third, fourth, fifth … global forecast time,
there always exist a TC vortex in the first guess.
So vortex relocation and modification procedures
as the same as step 2 and 3 are repeated for the
TC vortex in the first guess till TC is death (Qu et
la, 2009).
The flowchart of the CMA’s whole TS prediction
system is given in Fig.4.