principles of the dvorak method
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Principles of the Dvorak Method. Andrew Burton, Severe Weather WA. Principles of the Dvorak Method. Overview. Origins. Measurements. Expectations. Pattern matching. Principles of the Dvorak Method. Overview. Origins. Measurements. Expectations. Pattern matching. - PowerPoint PPT PresentationTRANSCRIPT
Principles of the Dvorak Method
Andrew Burton, Severe Weather WA
APSATS 2002 Melbourne, Australia
•Origins
•Overview
•Measurements
•Expectations
Principles of the Dvorak Method
•Pattern matching
APSATS 2002 Melbourne, Australia
•Origins
•Overview
•Measurements•Expectations
Principles of the Dvorak Method
•Pattern matching
APSATS 2002 Melbourne, Australia
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
Some Terminology The (only) Boring slide
T Numbers for every occasion
T = Tropical
DT = Data T Number
MET = Model Expected T No
PT = Pattern T No
FT = Final T No
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
Developed with North West Pacific and Atlantic data.
Probably the single most important tool in tropical cyclone analysis to date.
Operational use since 1973
Ongoing development over 15 years.
Enhanced infrared technique 1978/1984
Origins
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
Locating the centre
From Dvorak (1985):
“The cloud system center is defined as the focal point of all the curved lines or bands of the cloud system. It can also be thought of as the point toward which the curved lines merge or spiral.”
Centre not always obvious, especially at night.
APSATS 2002 Melbourne, Australia
•Low level centre
•Use all available data – passive microwave to the rescue!
•Maintain track continuity.
•Centre location can influence intensity measurement
Principles of the Dvorak Method
Locating the centre
APSATS 2002 Melbourne, Australia
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
Pattern Types
•Eye
•Curved Band
•Shear
•Covered Centre
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method Intensity schematic
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
Eye patterns
Physical principle: strength of the thermal contrast between the eye and the surrounding convection indicates strength of the system
Method: Measure the warmest brightness temperature in the eye and the coldest surrounding temperature in the deep convection.
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
Hurricane Erika 1515 UTC 8 September 1997
• Warmest eye pixel 16 °C
• Coldest pixel 30 nmi from
center -71 °C
• Nomogram gives Eye no. =7
Eye pattern using digital IR
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
APSATS 2002 Melbourne, Australia
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
Curved bands
Physical principle: the “wrap-aroundness” of the convective bands indicates the vorticity associated with the system.
Method: Measure the curvature of the band
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
Curved Bands
APSATS 2002 Melbourne, AustraliaTS Ivan 23/9/98 11:15 UTC
Principles of the Dvorak Method
APSATS 2002 Melbourne, Australia
Measuring the arc length:• Follow the convection, not
cirrus blow-off• Easier to do with VIS than
Enhanced IR.• You may have small breaks
in convection and draw through
Principles of the Dvorak MethodCurved Bands
APSATS 2002 Melbourne, Australia
• Log10 spiral overlay.• Spiral should lie along the
axis of the of the band, and roughly parallel the inside edge of the band.
• Measure the arc length.• “Tightest inner curvature”• “Cloud minimum wedge”
LOG10Spiral
Principles of the Dvorak Method
Curved Bands
APSATS 2002 Melbourne, Australia
Measuring the arc length:• Can be very subjective.• Inexperienced analysts
tend to go too high (fooled by cirrus or outer bands).
• This storm is somewhere between 0.70 and 0.85.
Principles of the Dvorak Method
Curved Bands
APSATS 2002 Melbourne, Australia
Step 2A, Curved Band
Note: Southern Hemisphere Example
APSATS 2002 Melbourne, Australia
Step 2A, Curved Band
APSATS 2002 Melbourne, Australia
Step 2A, Curved Band
APSATS 2002 Melbourne, Australia
Step 2A, Curved Band
0.100.20
0.300.40
0.50
0.60
0.700.80
APSATS 2002 Melbourne, Australia
Step 2A, Curved Band
0.100.20
0.300.40
0.50
0.60
0.700.80
A wrap of 0.80would equal a Data T of T3.5
APSATS 2002 Melbourne, Australia
0.100.20
0.300.40
0.50
0.60
0.700.80
We could have addedWe could have addedan additional 0.05an additional 0.05for this portion of for this portion of wrap, giving a totalwrap, giving a totalwrap of 0.85wrap of 0.85
APSATS 2002 Melbourne, Australia
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
Physical principle: greater involvement of the low level centre with the deep convection indicates a stronger system.
Method: Measure the distance form the low level centre to the edge of the “dense overcast”
Shear patterns
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
Shear patterns
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
Shear pattern
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
70nm = T1.570nm = T1.5
Shear pattern
APSATS 2002 Melbourne, Australia
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
VIS=Central Dense Overcast (CDO)
IR=Embedded Centre (EC)
Covered Centre Patterns
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
Physical principle?: The weakest link?
Method: Appearance and size of the overcast + degree of banding.
Central Dense Overcast
“It is the pattern formed by the clouds of a tropical cyclone that is related to the cyclone’s intensity and not the amount of clouds in the pattern” - Dvorak 1984
Intensity measurement not dependent on centre location
Does size matter?
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
A quick diversion on size
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
Central Dense Overcast
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
Physical principle: Greater involvement of low level centre with deep convection indicates a stronger system.
Method: Measure coldest surrounding temperature.
Embedded Centre
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
Embedded Centre
•Restrictions on use.
•Sensitive to centre location.
•Methodology similar to eye patterns
•Best used after disappearance of an eye.
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
Just plain ugly!
Embedded Centre
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
Embedded Centre pattern – problematic
Dependent on a temperature measurement related to a centre you can’t see.
Dvorak temperature enhancement calibrated to North West Pacific.
Cyclones occur at higher latitudes in NH.
What might that mean for “southerners”?
APSATS 2002 Melbourne, Australia
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
Reality check! TCs Elaine & Vance, March Reality check! TCs Elaine & Vance, March 19991999
APSATS 2002 Melbourne, Australia
APSATS 2002 Melbourne, Australia
• Compare current image to image 24 hours ago.• Determine if the cloud features in the current
image look better defined, the same or worse.• If better, the trend is Developed (D)• If the same, the trend is Same (S)• If worse, the trend is Weakened (W)
Principles of the Dvorak Method
MET = Model Expected T number
APSATS 2002 Melbourne, Australia
• For systems with a 24-Hour Trend of D or W, determine pattern evolution and apply appropriate adjustment to Final-T from 24 hours ago.
• - Slow (+ .5)• Normal (+ 1.0) • + Rapid (+ 1.5)
• Assumes you are routinely doing Dvorak intensity estimates - can’t do a “one-timer”!
Principles of the Dvorak Method
MET = Model Expected T number
APSATS 2002 Melbourne, Australia
Select the pattern in the diagram that best matches your storm picture – within one column of the MET - SUBJECTIVE
A
B
C
EIR Patterns
Pattern T number – an adjustment to the MET.
Principles of the Dvorak Method
APSATS 2002 Melbourne, Australia
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
Choosing the best estimate – the Final T-no
•Use DT when cloud features are “clear cut”
•Otherwise use MET (possibly adjusted by “Pattern T-no)
More objective
RULES, RULES, RULES
And then…..
APSATS 2002 Melbourne, Australia
APSATS 2002 Melbourne, Australia
Principles of the Dvorak Method
Acknowledgements:
Paul J. McCrone
Chief Forecaster
HQ Air Force Weather Agency (AFWA)
Meteorological Satellite Applications
Mark DeMaria
Regional and Mesoscale Meteorology Team
NESDIS/CIRA
Colorado State University, Ft. Collins CO