Objective Dvorak Technique (ODT) AFWA/XOGM

Objective Dvorak Objective Dvorak Technique (ODT)Technique (ODT)

AFWA/XOGMAFWA/XOGM

UW-CIMSS Objective Dvorak TechniqueUW-CIMSS Objective Dvorak Technique• Tim Olander and Chris VeldenTim Olander and Chris Velden• University of Wisconsin - MadisonUniversity of Wisconsin - Madison• Cooperative Institute for Meteorological Satellite StudiesCooperative Institute for Meteorological Satellite Studies

In cooperation with :In cooperation with :

• Jeff HawkinsJeff Hawkins• Naval Research Laboratory - Monterey, CANaval Research Laboratory - Monterey, CA• Office of Naval ResearchOffice of Naval Research

Material for this training module largely comes from:

Objective Dvorak Technique Objective Dvorak Technique (ODT)(ODT)

- What is the ODT?- What is the ODT?

- How does it work?- How does it work?

- Why use it?- Why use it?

- How will we use it here? - How will we use it here?

OverviewOverview

Objective Dvorak Technique Objective Dvorak Technique (ODT)(ODT)

What is the ODT?What is the ODT?

ODT is a computerized method for ODT is a computerized method for determining the intensity of tropical determining the intensity of tropical cyclones. It was originally developed by cyclones. It was originally developed by the University of Wisconsin, and we are the University of Wisconsin, and we are able to perform some ODT functions able to perform some ODT functions currently.currently.

Ok, so how does it work?Ok, so how does it work?

ODT MethodologyODT Methodology


• Identification of two environmental temperatures (BTs)Identification of two environmental temperatures (BTs)– Uses IR data only– Eye Temperature (0-40 km)– Cloud Temperature (26-136 km)

• Scene identification performedScene identification performed– ODT is only performed for four types of features: – Eye, Embedded Center, CDO, and Shear– SIDAS version only handles EYE currently– Based on histogram and Fourier Transform Analysis

ODT MethodologyODT Methodology• Determination of the cloud pattern is performed

objectively (in other words, by the computer) by examining area histograms of cloud top temperatures and corresponding Fourier Analysis for the eye region and surrounding cloud region. Based on this analysis, four scene patterns can be categorized by ODT: Eye, Central Dense Overcast, Embedded Center, and Shear.


• Storm Center Location Storm Center Location – The only user input is the specification of the storm center location– ODT only does intensities

• EYE determination – If the storm has an eye, it uses the warmest pixel temperature within a 40 km radius of the chosen storm center – Warm values represent ocean surface or low cloud within the eye– This value is retained as the 'eye temperature'.


Warmest value = 'eye temperature'Warmest value = 'eye temperature'

ODT MethodologyODT Methodology• EYE determination (con’t)

– ODT analyzes temperatures on concentric rings (1 pixel wide) centered on the eye between 24 km and 136 km from the eye location (this range was empirically determined by many observations of coldest ring radii).

– For GOES data with 4km pixel resolution, this results in a total of 28 rings that are analyzed to determine the 'surrounding temperature'. – In addition, a continuous ring of cold temperatures surrounding the eye is more indicative of an organized (and more intense) storm than one with breaks in the

convection.– Therefore, the warmest temperature found on each ring is identified and stored, with the coldest of these retained as the final surrounding temp value. – ODT does not reposition the storm center, since it has been found that the subsequent analysis of the surrounding temperature field may be improperly influenced by

this adjustment in some cases ('false' eyes).



ODT MethodologyODT MethodologyThe warmest temperature is found on each ring...

ODT MethodologyODT MethodologyThis ring has “Light Grey”as its warmest temp.

ODT MethodologyODT MethodologyOf those temps that areleft, the coldest is takenas the surrounding ring


• “No Eye” Condition – ODT can handle Central Dense Overcast (CDO)/Embedded Center– Temperatures near the storm center are dominated by cold cloud tops and a warm eye is not resolvable. – The value of the pixel at the user-defined storm center location is used as the 'eye’ temperature– Shear scenario is also detected in ODT – The SHEAR, CDO/EMBD CTR ARE NOT YET AVAILABLE IN SIDAS VERSION OF SOFTWARE

ODT MethodologyODT Methodology• Initial intensity estimate determined Initial intensity estimate determined (Raw T#)(Raw T#)

– Based on original Dvorak Rules for different patterns and cloud top temperatures. Eye temperature serves as adjustment

• Use history file with previous storm analysis data Use history file with previous storm analysis data

(Final T#)(Final T#)– Provide data for 12-hour time weighted time averaging scheme– This means we have to perform ODT every hour– Data is saved in SIDAS interface

• Implementation of Dvorak Rule 9 for weakening storms Implementation of Dvorak Rule 9 for weakening storms (CI#)(CI#)– Corrects underestimate bias in weakening storms– Hold T# constant for 12 hours after initial weakening, add 1.0 T# until dissipation or

restrengthening– Not currently implemented in SIDAS

ODT PurposeODT PurposeOk, but why use it?Ok, but why use it?

1. 1. It’s It’s OBJECTIVEOBJECTIVE• Doesn’t depend on opinions of human beingDoesn’t depend on opinions of human being• Done the same way every timeDone the same way every time• Can be more accurate (sometimes)Can be more accurate (sometimes)

2. 2. It’s It’s FASTFAST• Computer derivedComputer derived• Some storms are harder than othersSome storms are harder than others

3. 3. It’s It’s WANTEDWANTED• JTWC has formally requested that we do thisJTWC has formally requested that we do this• We are holding off until full capability is hereWe are holding off until full capability is here• Test mode only for nowTest mode only for now

Current User StatusCurrent User Status

Operational UseOperational Use• NOAA/NESDIS Satellite

Analysis Branch

• NHC/Tropical Analysis Forecast Branch

Experimental UseExperimental Use• Joint Typhoon Warning

Center

• Air Force Weather Agency

• Central Pacific Hurricane Center

• Australian Bureau of Meteorology

• Japanese Meteorological Agency

ODT Past PerformanceODT Past Performance

Legend : TAFB - Tropical Analysis Forecast Branch - NOAA/NCEPSAB - Satellite Analysis Branch - NOAA/NESDISAFWA - U.S. Air Force Weather Agency

Legend : TAFB - Tropical Analysis Forecast Branch - NOAA/NCEPSAB - Satellite Analysis Branch - NOAA/NESDISAFWA - U.S. Air Force Weather Agency

Units in hPa Bias RMSE SampleODT +1.69 7.34 407Op. Center +4.31 10.35 407

Units in hPa Bias RMSE SampleTAFB +2.29 10.76 305ODT +1.58 7.46 305

SAB +4.88 10.42 319ODT +1.45 7.35 319

AFWA +5.55 12.06 146ODT +0.53 7.39 146

Developmental Data SampleDevelopmental Data Sample1995-19971995-1997

Units in hPa Bias RMSE SampleODT -0.72 7.97 397Op. Center -0.05 10.38 397

Units in hPa Bias RMSE SampleTAFB -1.25 10.65 341ODT -0.62 8.72 341

SAB +0.58 9.91 334ODT -0.53 8.75 334

AFWA +1.83 10.40 334ODT -0.43 8.07 334

Independent Data SampleIndependent Data Sample1998-19991998-1999

Super Typhoon Bilis (18W)Super Typhoon Bilis (18W)

• Good agreement with operational center and Best Track estimates– Slight overestimate during intensification and at peak– CI#s compare better with Best Track during weakening than Final T#s– Rapid weakening indicated by Final T#s supported by AMSU data (landfall)

– SAB ODT estimates differ from JTWC ODT during intensification

http://pzal.npmoc.navy.mil/jtwc_archive/2000/STORM_FOLDERS/NORTHWEST_PACIFIC/18W/Time_Intensity_Chart/18W_ti.gif://pzal.npmoc.navy.mil/jtwc_archive/2000/STORM_FOLDERS/NORTHWEST_PACIFIC/18W/Time_Intensity_Chart/18W_ti.gif

Super Typhoon Saomai (22W)Super Typhoon Saomai (22W)

• Good agreement with operational center and Best Track estimates– Underestimate during weakening with Final T#s (should use CI#s)– Initial estimates off due to very cold cloud top temperatures (~-80ºC)– SAB ODT analysis very similar to JTWC ODT analysis


Super Typhoon Shanshan (26W)Super Typhoon Shanshan (26W)

• Slight disagreement with operational center and Best Track estimates– Over/Underestimate during strengthening/weakening processes– CI#s compare better with Best Track during weakening than Final T#s– Rapid intensification cycles noted but led to ODT overestimates– SAB ODT analysis very similar to JTWC ODT analysis


Summary and ConclusionsSummary and Conclusions• 6 storm sample for 2000 West Pacific season6 storm sample for 2000 West Pacific season

– Overall, good comparison between JTWC and SAB ODT estimates

– JTWC and SAB ODT Final T# estimates were typically within 0.5 T# of JTWC Best Track estimates

– Very cold cloud temperatures led to high bias in Final T# relative to JTWC Best Track estimates (cloud temperatures < upper -70°C)

– Rapid intensification flag correctly identified events but led to large Final T# high bias when coupled with very cold cloud top temperatures (tuning to West Pacific needed)

• Slight differences between JTWC and SAB ODT estimatesSlight differences between JTWC and SAB ODT estimates

– Possible errors with ocean basin identification (basin flag is manually adjusted; could be automated)

– Implementation of 48 Hour Rule is slightly different between JTWC and SAB due to different ODT versions (fixed vs. time-weighted value)

• Overall, CI#s provided better fit to JTWC Best Track estimate than Final T#s during Overall, CI#s provided better fit to JTWC Best Track estimate than Final T#s during weakeningweakening

Future DirectionsFuture Directions• Operational ODT UsageOperational ODT Usage

– Full operational test at JTWC during 2001 with devoted analyst (patterned after SAB and TAFB evaluation)

– Experimental use only here at AFWA• Research FocusResearch Focus

– Further tune ODT for West Pacific based on JTWC and SAB 2000 results– Expand analysis range for tropical storms and weaker systems (will

remove need for 48 Hour Rule)– Investigate application of rapid intensification flag based on user analysis

and feedback– Begin development of Multispectral Dvorak Technique (MDT),

incorporating multiple satellite and channel information (AMSU, SSM/I, visible, water vapor, etc.)

• JTWC uses it on NSDS-EJTWC uses it on NSDS-E• SAB uses it in MCIDASSAB uses it in MCIDAS

• How will we use it here?How will we use it here?– SIDASSIDAS– New Eye Intensity CalculationNew Eye Intensity Calculation

ODT IS ODT IS ALWAYSALWAYS TO BE PERFORMED TO BE PERFORMED AFTERAFTER YOU YOU COMPLETE YOUR OWN INDEPENDENT COMPLETE YOUR OWN INDEPENDENT ANALYSIS!ANALYSIS!

ODT ImplementationODT Implementation









ODT Method

Previous SIDASMethod

ODT MethodologyODT MethodologyODT uses rings….

Previous SIDAS MethodPrevious SIDAS MethodThe SIDAS method usesradial measurements oftemperature. ODT andSIDAS are different!

Neither includeany banding features!


Hit the button

The SIDAS methodis only for a “pointin time”. The ODTis time averaged.

~So…..we need to

save this ODT calculation……..


Hit the button:

Once you hitthe button,

the names ofall availableODT storm

archives willappear

ODT ImplementationODT ImplementationHighlight theODT stormarchive file

that you need

ODT ImplementationODT ImplementationHighlight theODT stormarchive file

that you need

Then Hit the button:


Remember thatyou will need to

do this every hour(while the storm

has an EYE!)

Questions?Questions?

Objective Dvorak Objective Dvorak Technique (ODT)Technique (ODT)

AFWA/XOGMAFWA/XOGM

Date post:	02-Feb-2016
Category:	Documents
Upload:	ranit
View:	60 times
Download:	0 times

Objective Dvorak Technique (ODT) AFWA/XOGM

Documents