Satellite Applications in Tropical Weather Forecasting Mark DeMaria


НазваSatellite Applications in Tropical Weather Forecasting Mark DeMaria
Дата конвертації05.05.2013
Розмір492 b.
ТипПрезентации


Satellite Applications in Tropical Weather Forecasting

  • Mark DeMaria

  • Regional and Mesoscale Meteorology Team

  • NESDIS/CIRA

  • Colorado State University, Ft. Collins CO


Acknowledgments

  • RAMMT

    • Roger Phillips, Ray Zehr, Jack Dostalek, John Knaff, Bernadette Connell, Stan Kidder
  • TPC

    • Jiann-Gwo Jiing (SOO), Richard Pasch, Michelle Huber, Bill Frederick
  • CIMSS

    • Chris Velden, Gary Wade
  • NESDIS ORA

    • Roger Weldon


Outline

  • General Circulation in the Tropics

    • ITCZ
    • Subtropical Ridge
    • Tropical Upper Tropospheric Trough
  • Synoptic-Scale Weather Systems

    • Upper-level lows
    • Tropical Waves
  • Tropical Cyclones

    • Dvorak method
    • Environmental interactions
    • Measurements from Polar orbiting satellites


Terminology

  • Channel 1 - Visible - .6 m ( .52- .72)

  • Channel 2 - Shortwave IR - 3.9 m (3.78- 4.03)

  • Channel 3 - Water Vapor - 6.7 m (6.47-7.02)

  • Channel 4 - Longwave IR - 10.7 m (10.2-11.2)

  • Channel 5 - Split Window - 12.0 m (11.5-12.5)

  • Microwave frequencies 20-90 Ghz (1.5-0.3 cm)



















Tropical Upper-Level Lows

  • Typically form within TUTT

  • Cold-core systems

  • Shallower circulation than mid-latitude lows (little circulation below 500 mb)

  • Often produce precipitation

  • Can influence intensity and track of tropical cyclones

  • Can be tracked using water vapor imagery











16-Frame Water Vapor Imagery Loop 7/26/98 02:45 to 7/29/98 20:45 Formation of a Cold-Low



TPC Tropical Analysis and Forecast Branch Cold-Low Study

  • Period of Study: Aug. 12-Oct. 1, 1996

  • Domain: 0-35 N, 110-20 N

  • Cold-low centers tracked using GOES WV imagery

  • 47 lows during 50 days

  • Average Duration of 3 days, Max of 12 days

  • Up to 8 lows in domain at once (average of 3)

  • Vorticity center present in NCEP 200 mb analyses for nearly all cold lows identified by satellite observations

    • Average NECP analysis location error of 100 nm






Tropical Waves

  • Formation near western Africa

    • Barotropic/baroclinic instability, PV gradient changes sign
    • Secondary instability region in Western Caribbean
  • Maximum amplitude near 700 mb

  • Period of 2-5 days, wavelength 2-3000 km, May-Dec

  • Precipitation associated with waves

  • About 2/3 of Atlantic TC genesis associated with waves

  • Role in east Pacific tropical cyclogensis





TAFB Methods for Tracking Waves

  • TAFB tropical surface analysis generated 4 times per day, includes surface wave positions

  • Rawindsone time series

  • Surface data when available

  • Satellite analysis over west Africa

    • Animation of channels 1, 2 and 4 indicates rotation
  • Hovmoller satellite diagrams for continuity across tropical Atlantic

  • NCEP aviation model analyses and forecasts







Tropical Cyclogenesis

  • Eastern Pacific

    • Interaction of tropical waves/monsoon trough
    • Includes region of maximum global storm formation
  • Atlantic

    • 2/3 of storms from tropical waves
    • Some baroclinic, subtropical and monsoon trough developments
    • Very “peaked” season
    • Experimental genesis parameter under development






Tropical Atlantic Genesis Parameter

  • Developed from cases since 1991

  • Genesis variables

    • zonal shear (NCEP analyses)
    • vertical stability (NCEP analyses)
    • Mid-level moisture (Cloud-cleared GOES-8 water vapor brightness temperature, 1996-99)
    • 5-day running means 8-18 N, 30-50 W
  • Variables scaled from -1 to 1

  • Genesis parameter = shear x stability x moisture



Tropical Atlantic Genesis Locations 1991-99



Climatological Shear, Stability, WVBT (Scaled)



Genesis Parameter in 1999



5-Day Running Mean Cloud Cleared Water Vapor Imagery for August 1999



Tropical Cyclone Classification

  • NHC has responsibility for Atlantic and east Pacific basins

    • Atlantic: 10 storms, 6 hurricanes
    • East Pacific: 16 storms, 10 hurricanes
  • Aircraft recon available only for Atlantic west of 55 W

  • Majority of center and intensity estimates from GOES satellite data

  • TAFB, SAB, AFWA provide classifications



Overview of the Dvorak Technique

  • Visible and Infrared Technique

  • Simplified Visible Technique given here (See Technical Report for full details)

  • Uses patterns and measurements as seen on satellite imagery to assign a number (T number) representative of the cyclone’s strength.

  • The T number scale runs from 0 to 8 in increments of 0.5.



Overview of the Dvorak Technique Cont’d

  • In the following examples, only the Data T Number (DT) will be calculated, the final (official) T number assigned to a tropical cyclone includes further considerations.

  • DT computations familiarize one to various tropical cyclone patterns.



Four Basic Patterns

  • Curved Band Pattern

  • Shear Pattern

  • Central Dense Overcast (CDO) Pattern

  • Eye Pattern

    • Pattern is not always obvious
    • Pattern typically varies with time


Patterns and Associated T Numbers



Empirical relationship between T number and wind speed



Finding the Cloud System Center (CSC)

  • First step in the Dvorak technique

  • 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.”

  • Center not always obvious, especially at night

  • TPC technique combines channel 2 and 4







Curved Band Pattern TS Ivan 9/23/98 11:15 UTC



Curved Band Pattern Cont’d

  • 1.0 2.0 2.5 3.0 3.5 4.0 4.5

  • DT Number



Shear Pattern Hurricane Bertha 7/11/96 2015 UTC



Shear Pattern DT Numbers



Central Dense Overcast (CDO) Hurricane Georges 9/21/98 1545 UTC



CDO

  • No eye

  • DT number determined by CF+BF=DT

    • CF=CENTRAL FEATURE
    • BF=BANDING FEATURE
    • DT=DATA T NUMBER


CDO Central Feature (CF)

  • Measure Diameter of CDO in degrees latitude

  • For a well defined CDO

    • 3/4 ° CF=2
    • 1 1/4 ° CF=3
    • 1 3/4 ° CF=4
    • >2 1/4 ° CF=5
  • For an irregular CDO

    • 1° to 1 1/2 ° CF=2
    • >1 1/2 ° CF=3


CDO - Banding Feature (BF)



Eye Pattern Hurricane Georges 9/19/98 1345 UTC



Eye Pattern

  • DT number determined by CF+BF=DT

    • CF=CENTRAL FEATURE
    • BF=BANDING FEATURE
    • DT=DATA T NUMBER


Banding Eye Hurricane Bonnie 8/25/98 2131 UTC



Infrared (IR) Technique

  • Can be used during night as well as during day

  • At times, more objective than visible technique

  • Fully objective version developed at CIRA

  • Updated objective technique from CIMSS



Example Digital IR: Hurricane Erika 1515 UTC 8 September 1997

  • Warmest eye pixel 16 °C

  • Warmest pixel 30 nmi (55 km) from center -71 °C

  • Nomogram gives Eye no. =7







Operational Dvorak Technique Verification for 1997-98 Atlantic Seasons







Input for NHC Track and Intensity Forecasts

  • Track

    • 70 % Numerical model guidance
    • 15 % Synoptic reasoning
    • 15 % Recent trends
  • Intensity

    • 50 % Recent trends
    • 40 % Synoptic reasoning
    • 10 % Numerical model guidance


Applications of Satellite Data to TC Forecasting

  • Track

    • Inclusion of remotely sensed data in NWP models
    • Diagnosis of model initial state
    • Evaluation of synoptic situation
  • Intensity

    • Evaluation of factors affecting intensity
      • SST changes
      • vertical shear (especially cloud track winds)
      • trough interaction
    • Inclusion in NWP models




NEW GOES WINDS PRODUCTS ARE BEING PRODUCED BY CIMSS/NESDIS: - HIGH - DENSITY WINDS DERIVED FROM IR AND HIGH-RESOLUTION VISIBLE CLOUD MOTIONS AS WELL AS WATER VAPOR MOTIONS, USING AUTOMATED ALGORITHMS - DISPLAYS OF THESE WINDS FOR UPPER- & LOWER-LEVEL LAYERS OVER THE TROPICS ARE ROUTINELY AVAILABLE VIA THE INTERNET -UWISC/CIMSS TC WEB SITE: http://cimss.ssec.wisc.edu/tropic/tropic.html











8-Frame Water Vapor Imagery Loop 9/20/98 23:45 to 9/21/98 23:45 Hurricane/Trough Interaction



Storm-Scale Structure

  • Convective transients, asymmetries

    • Velden and Olander (1998) technique
      • IR BT usually warmer than WV
      • Deep convection transport into stratosphere
      • WV BT warmer than IR
  • Concentric eye walls, eye wall cycles

  • Mesovortices within the eye

    • High spatial and time resolution imagery (RSO, SRSO)
    • Extra-high density satellite winds




GOES-East Scanning Strategies

  • Routine Scanning

    • Conus hr+01,31
    • Extended NH hr+15,45
    • (2 or 4 per hr)
  • Rapid Scan

    • Conus, NH 5-10 min
    • (8 per hr)
  • Super Rapid Scan

    • Selected Sector 1-5 min
    • (22 per hr)


10-frame Rapid-Scan Visible Imagery Loop 9/21/98 19:02 to 20:10 Hurricane Georges Approaching Puerto Rico









TC Measurements from Microwave Frequencies

  • Special Sensor Microwave Imager (SSM/I)

    • DMSP polar orbiting satellites
    • 19, 22, 37, 85 GHz, 25 km resolution
  • Advanced Microwave Sounding Unit (AMSU)

    • NOAA polar orbiting satellites (NOAA 15 +)
    • 15 channels 23-89 GHz, 50 km resolution
  • Can see “through” clouds

  • Depicts rainband, eye structure

  • Rainfall and surface wind algorithms

  • AMSU temperature retrievals









Hurricane Floyd Analysis 14 Sept 1999 12 UTC





Applications of Balanced Winds: Asymmetric Vortex Structure



Gale Force (34 kt) Wind Radii Prediction









Summary

  • Multispectral GOES imagery provides synoptic overview

    • ITCZ, Subtropical Ridges, TUTT and cold lows, waves, TCs
  • WV Imagery is especially useful for tracking cold lows

  • Continuity in imagery is primary tool for tropical waves

  • Dvorak method provides quantitative intensity estimates

    • Also provides framework for operational forecasting
    • Shortwave IR aids center location, especially at night
  • Sat. winds: environmental interactions, model intialization

  • WV- IR difference isolates tropical deep convection

  • Rapid-scan imagery: storm-scale fluctuations

  • Microwave imagery is useful for low-level storm structure

  • New AMSU data shows promise for hurricane analysis



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