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In diagnosing tropical cyclone cyclogenesis and intensification we
are interested in the 850 to 500hPa wind profiles.
We have observed the heaviest rainfall all over the world (to within 4 degrees
of the equator) to be associated with backing (SH) winds with height below
500hPa.
e.g.
50 year rainfall statistics Cairns Latitude 160 52’25” S
The mean wind producing 24 hour rainfall totals of 150mm or more and
averaged over the 24 hours leading up to when the rain gauge is read is:
950hPa 130/13 knots
850hPa 095/17 knots
700hPa 074/13 knots
500hPa 021/05 knots
A useful way to view this
wind profile is to plot the
700hPa winds (black) over
850 to 500hPa shears (red)
and draw isotherms or
thickness lines.
This slide shows Mumbai
Near 190N under 700hPa
flow from warm to cool
(isentropic upglide).
Mumbai
700hPa
Mumbai recorded 944mm
in the 24h to 0300UTC
27 July 2005
A theoretical example of this with a pattern
associated with a MCV in weak shear --This is a simple example of what is
frequently observed in cyclogenesis or
intensifying TCs
Throughout red (blue) arrows imply areas
of isentropic ascent descent
near 700hPa
Journal of the Atmospheric Sciences
A Theory for Long-Lived Mesoscale Convective Systems
D. J. Raymond1, and H. Jiang11.
Non Linear Balance Model
Long-lived mesoscale convective systems
can maintain themselves through an
interaction between quasi-balanced
vertical motions and the diabatic effects
of moist convection- Leading to creation
of a positive potential vorticity anomaly
in the lower troposphere.which can
interact with a sheared environment so
as to induce further lifting of low-level
air and subsequent release of conditional
instability.
The figure shows flow
around the PV anomaly
After 3 hours into the
Simulation.
We will then show 2 cases (MJO related) where
the EC can forecast cyclogenesis.
The following slide shows one at 700hPa a very
accurate EC 144hour forecast of cyclogenesis
and the corresponding 700hPa thermal pattern.
Is then cyclogenesis largely driven by the large
scale (we will also examine upper flow)?
132333Z
142333Z
152333Z
162333Z
Case not forecast well by models (Larry)
1st slide shows region from mid latitude extending
into tropics (LC1 pattern) Thorncroft et al QJRMS
119, 17-56.
2nd slide 700hPa pattern showing shears near 10 to 15
knots near cyclone (EC does’nt forecast these low
shear events well).
3rd slide showing rapid cyclogenesis from
microwave
Main Point is models don’t appear to forecast low
sheared events well
500hPa
L
L
L
L
L
L
L
H
H
H
L
H
0000UTC 14 Mar 2006
0000UTC 16 Mar 2006
0000UTC 15 Mar 2006
0000UTC 17 Mar 2006
0000UTC 14 Mar 2006
0000UTC 16 Mar 2006
0000UTC 15 Mar 2006
0000UTC 17 Mar 2006
Will show some null cases (failed to develop).
1. Due to strong upper winds
2. Due differential steering between 850 hPa and 500hPa
very common way of weakening
3.Further example (with dropsonde data) of this
differential steering in following 3 slides
1st slide 850 ridge building (steering towards west ) but
500hPa trough developing (retarding westward steering
at this level)
2nd slide showing 700hPa upglide with strong 850/500hPa
shears
3rd slide schematic of convective process.
CIMSS Vertical Shear Advisories
TROPICAL STORM 13P (Kate) 0:00UTC 23February2006
UW-CIMSS Experimental Vertical Shear TC Intensity Trend Estimates
CIMSS Vertical Shear Magnitude : 4.3 m/s
Direction : 288.3 deg
Outlook for TC Intensification Based on Current Env. Shear Values
Forecast Interval : 6hr 12hr 18hr 24hr
VF VF VF VF
This means 3 hPa per hour deepening
TROPICAL STORM 13P (Kate) 6:00UTC 23February2006
UW-CIMSS Experimental Vertical Shear TC Intensity Trend Estimates
CIMSS Vertical Shear Magnitude : 4.7 m/s
Direction : 274.4 deg
Outlook for TC Intensification Based on Current Env. Shear Values
Forecast Interval : 6hr 12hr 18hr 24hr
VF VF VF VF
This means 3 hPa per hour deepening
H
H
850 hPa 0000UTC 20/8/2001
850 hPa 0000UTC 21/8/2001
H
500 hPa 0000UTC 20/8/2001
500 hPa 0000UTC 21/8/2001
Dropsondes 1958UTC to 2207 UTC
20 August 2001700hPa winds ((black)
and shears in red for
850/500hPa and 850hPa/600hPa
Dropsondes 2234UTC to 2334 UTC
20 August 2001700hPa winds ((black)
and shears in red for
850hPa/600hPa
Conceptional model of Chantal (Heymsfield et al) JAS 63, 268-287)
437
439
439
438
438
700hPa warm/cold air advection pattern
developing as typhoon Ewiniar formed
between latitude 6 and 10 degrees North.
Formation of a microwave eye for typhoon Ewiniar
note the main rainband on the warm air advection
side of the storm and the lack of convection on the
cold air advection side of the storm.
700hPa pattern at the commencement of the period of rapid
intensification to a super typhoon and compared with the forecast
for this time from 72 hours earlier when the system was still a weak
tropical depression.
200hPa and 700hPa sequence
just prior to cyclogenesis of
Oliver during February 1993
Major point- role of large scale versus
mesoscale processes- revisit TC Oliver
(Simpson et al MWR 125, 2643-2661)
We will show development of the
pattern leading up to cyclogenesis –
following slide shows cyclogenesis at
700hPa using dropsonde and NCEP
reanalyses data
200hPa 2300UTC 31 Jan 1993
200hPa 2300UTC 1 Feb 1993
200hPa 2300UTC 2 Feb 1993
200hPa 2300UTC 3 Feb 1993
700hPa 2300UTC 31 Jan 1993
700hPa 2300UTC 1 Feb 1993
700hPa 2300UTC 2 Feb 1993
700hPa 2300UTC 3 Feb 1993
700hPa 1700UTC 4 Feb 1993 Dropsondes
1509UTC to 1729UTC
700hPa 2300UTC 4 Feb 1993 Dropsondes
1753UTC to2144UTC
700hPa 2300UTC 4 Feb 1993
200hPa 2300UTC 4 Feb 1993
Oliver named as a tropical cyclone
Cyclogensis of tropical cyclone
Harvey
SSMI 85H
1129UTC 5 Feb 2005
SSMI 85H
2050UTC 5 Feb 2005
AQUA-1 89H
1616UTC 6 Feb 2005
AQUA-89H
0430UTC 7 Feb 2005
700hPa 2300UTC 4 Feb 2005
700hPa 2300UTC 6 Feb 2005
700hPa 2300UTC 5 Feb 2005
Tropical storm Gabrielle
Final point addresses rapidly developing strongly
sheared systems where 500hPa vortex/trough
moves over centreNot forecast well by models and applying Dvorak
constraints prevents warnings being issued
Example of rapid development in following slide.
700hPa observations during rapid genesis of Kelvin
200hPa observations (right) and storm relative
winds and streamlines in blue.
tropical cyclone Kelvin at Peak intensity near
Willis Island at 12300UTC 25 February 1991.
The wind at Willis Island was southerly
averaging 65 knots and gusting to 85 knots.
2332UTC 7 March 2005
Undulation
+
Warm air advection 200hPa
250 hPa outflow
0330 UTC 7 March 2001
0330 UTC 8 March 2001
Arrows Marks Yamba. Worst
Damage There Between 0800 UTC
and 1000 UTC.
warm
-51.10C