Satellite Applications in Tropical Weather Forecasting
Mark DeMaria
Regional and Mesoscale Meteorology Team
NESDIS/CIRA
Colorado State University, Ft. Collins CO
Lenny 11/17/99
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)
1 2 3 4 5 1 2 3 4 5
Hadley Cell
Walker Cells
P (mb)
-90 -60 -30 0 30 60 90-90 -60 -30 0 30 60 90
DJF JJA
1979-1996 January Average 200 mb Streamlines
1979-1996 July Average 200 mb Streamlines
1979-1996 January Average 850 mb Streamlines
1979-1996 July Average 850 mb Streamlines
GMS, GOES, METEOSAT IR Imagery Composite
GMS, GOES, METEOSAT IR Imagery Composite
Global WV Imagery Composite 22 August 1998
0000 UTC
2100 UTC
(Real-time data available from CIMSS web site)
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
300 mb 700 mb
Cold-low in NCEP Analysis 8/19/96 0000 UTC
Perturbation Temperature Cross-Section from NCEP Analysis 8/26/96 0000 UTC
Schematic Representation of Cold Low Structure
(from Whitfield and Lyons, WF, 1992)
Radiation Analysis of WV Imager Channel for Idealized Sounding
16-Frame Water Vapor Imagery Loop7/26/98 02:45 to 7/29/98 20:45
Formation of a Cold-Low
Presentation
TPC Tropical Analysis and Forecast BranchCold-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
NCEP Aviation Model Cold-Low Average Track Error
Extrapolation
Persistence
Cold Lows
1996 Tropical Cyclones
200
400
600
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
Seasonal Mean PV at 750 mb (Molinari et al, 1997)
Mean meridional wind fromGATE wave composite(Reed et al, 1977)
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
Dakar Sounding (15 N, 18 W) Time Series August 1995-97
95
96
97
20 W 40 E20 W40 E
08/01/96
08/15/96
08/16/96
08/31/96
Tropical Strip Time Series40 E-40 W 0 N-15 N
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
Climtological Tropical Cyclone Frequency(From WMO Global Guide To TC Forecasting)
Formations per 5 days (67-98)
0
5
10
15
20
25
30
M J J A S O N D
No.
Sto
rms
Atl.BasinTrop.Atl.
(Tropical Atlantic: 0-20 N, 0-60 W)
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
45 Total Cases: 7 Un-named TDs 13 TS 9 Non-major Hurricanes 16 Major Hurricanes
Climatological Shear, Stability, WVBT (Scaled)
Marginal
Unfavorable
Favorable
Genesis Parameter in 1999
Shear Stability
WVBT GP
(www.cira.colostate.edu/ramm/gparm/genesis.asp)
5-Day Running Mean Cloud Cleared Water Vapor Imagery for August 1999
LOOP
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
T.S. Lisa Channel 4
T.S. Lisa
Curved Band PatternTS 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 PatternHurricane Bertha 7/11/96 2015 UTC
Shear Pattern DT Numbers
1° latitude = 60 nautical miles (nmi) = 111 km
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 PatternHurricane 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 Verificationfor 1997-98 Atlantic Seasons
Position (nm)
x-bias (nm)
y-bias (nm)
Max wind (kt)
Wind bias (kt)
TAFB 97 18.8 -3.8 -0.4 4.6 -1.2
SAB 97 19.7 -3.9 -3.0 5.9 -2.2
TAFB 98 21.1 -1.6 0.3 6.5 0.7
SAB 98 21.3 0.0 -2.1 6.5 -1.7
NHC Official Forecast Skill (1997-99)
-40
-30
-20
-10
0
12 24 36 48 60 72
Forecast Interval (hr)
No
rmal
ized
Err
or
(%)
Track
Intensity
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
300 mb AVN Winds and WV Image 19 Sept 1998
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
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
Vertical Wind Shear Analysis from GOES High Density Winds
Hurricane-Trough PV Interaction During Hurricane Elena 1985 (Molinari et al 1995)
8-Frame Water Vapor Imagery Loop 9/20/98 23:45 to 9/21/98 23:45
Hurricane/Trough Interaction
Presentation
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
Channel 3, 4 Convective Parameter (CP) for Hurricane Opal 1995 (From Bosart, et al 1999)
Min P P (mb)CP
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 20:10Hurricane Georges Approaching Puerto Rico
Presentation
Comparison of Operational and SRSOWinds for Hurricane Floyd
Hurricane Luis 9/6/95 1345 UTC
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 Jeanne
9/23/981021 UTC
From NRL web site
SSM/I Imagery for Hurricane Floyd13-14 September 1999
IR ImageryMarch 1, 1999
AMSU TemperatureRetrieval (570 mb)
Hurricane Floyd Analysis 14 Sept 1999 12 UTC
AMSU Swath IR Image Liquid Water
(www.cira.colostate.edu/ramm/tropic/amsustrm.asp)
WithoutCorrection
WithCorrection
Ta
V
Ta
V
Applications of Balanced Winds:Asymmetric Vortex Structure
850 mb Isotachs (m/s) from Floyd 14 Sept 99 12 UTC
-0-10-20-30-40
Gale Force (34 kt) Wind Radii Prediction
5 predictors selected, AE=18 nm, r2=83%
AMSU Variable Normalized Coefficient0-100 km Liquid water 29.1Max Temp anomaly 26.5 Storm latitude 25.3600-0 km pressure drop -17.2Radius of 15 kt wind at 3 km 8.1
R2 = 0.8331
0
50
100
150
200
250
300
0 50 100 150 200 250 300
Predicted Gale Radius (nm)
Ob
se
rve
d G
ale
Ra
diu
s (
nm
)
AMSU-A Rainfall Rate for Hurricane Georges (.01 inches/hr)
TRaP for Key West = 6.7 inches
GOES IR and SSM/I 85 GHzHuricane Floyd 10 UTC 11 Sep 1999
(from NRL web site)IR 85 GHz
Auto-Estimator>
<Multi-Spectral
Rainfall EstimationFrom GOES
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