Applications of Satellite-Based

Microwave Data to Tropical Cyclone Analysis (Microwave Imagery and Scatterometer) by Roger T. Edson Science and Operations Officer NOAA/NWS WFO Guam 1 st TC-TRCG Technical Workshop , Jeju Island, ROK , May2009

INTRODUCTION

• • • • • •

Microwave Data in the Tropics Passive (SSMI) vs Active (‘Scat’) Characteristics of MI imagery patterns QuikSCAT Scatterometer Examples of uses in the Tropics and Mid-Latitudes Combined or Integrated Uses ------OPTIONAL (in back) -------

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•

(Suggested QuikSCAT Procedures) TC Life Cycle in Microwave Imagery

Passive Microwave

(SSMI/AMSR-E/CloudSAT/WindSAT/AMSU/TRMM)

Information given by naturally Occurring Microwave radiation

Why Use Microwave Data?

Three views of Super Typhoon Podul 125-140kts

Positioning in Microwave Imagery 37 Ghz color 85 Ghz color Try to position in the rain-free dry area—out of the convection

Positioning, Intensify and Genesis of a Tropical Cyclone: All from Microwave Data!

37 Ghz color 85 Ghz color Weak Rain/CU lines Vis Circular ‘blue region’

Where’s the Center? Help with Dvorak IR Dvorak IR

Where’s the Center? Unenhanced IR Dvorak IR Center

Where’s the Center? TRMM 85h GHz Center

Now, where’s the Center? TMI 37 GHz** Dvorak IR IR Center Visible Center 85 Center **Actually, COMBINED Reconnaissance gives the highest degree of Confidence**

ADVANTAGES OF USING 85 GHz AND 37 GHz Microwave Imagery

• • • • • •

‘Sees’ through clouds Positioning of TCs in difficult situations (especially in EARLY stages of development)

–

‘try’ animation of multiple 37GHz polar passes View of convective rain bands is more DIRECTLY related to intensification of the TC Less delay in seeing changes in intensification Lower altitude of TRMM/AMSR-E/WindSAT has increased resolution in BOTH 85 and 37 GHz Can still use in conjunction with existing techniques

Sources of Microwave Imagery For Tropical Cyclone Analysis

Tropical Cyclone Lifecycle in Microwave Imagery

(see optional section in back) I.

II.

III.

IV.

V.

TC Genesis Stage ~ 25-30kt Early Intensification and Development ~ 30-45kt Continued Intensification and Mature Stage Peaking and Initial Weakening Stage Dissipation and Extratropical Transition

EVALUATIONS OF CAT5/SUPER TYPHOONS (85h) VIEWS: Double eyes (red inner eye) STY Saomai 140kt STY Billis 135kt STY Ivan 155kt STY Shanshan 125kt TC Paul 125kt STY Bart 140kt All cyclones in this category are going in or out of eye cycle.

Intensification is near max. Any change dependent upon red in outer eye. Red in inner eye most important for evaluating current intensity.

Physics and Interpretation of Microwave Imagery

Storm Convection or Exposed Ocean? (85 GHz) Sea Surface ?

or Convection ??

85 GHz PCT Correction (color) Ambiguity Resolved

Sea Surface Convection Lower level Rain Bands

Some times the 87 GHz Imagery is not enough: Where’s the Eye of the Storm?

Another case for Using the 37 GHz: Eye Revealed

SSM/I Resolution and Footprints

85 GHz 37 GHz 22 GHz 19 GHz

Channel Frequency FOV Resolution (GHz)/Polarization km x km) 19.35 V,H 69 x 43 22.235 V 37.0 V,H 60 x 40 37 x 29 85.5 V,H (highest resolution)15 x 13

Microwave Physical Characteristicsz 85GHz vs 37GH

85GHz is VERY sensitive to Ice Extinction (rain is smaller) 85GHz more Sensitive to BOTH rain and ice rates than 37GHz Ice Extinction is relatively low in 37GHz (rain is larger) RAIN RATE mm/h

Properties of Microwaves Imagery for Tropical Cyclones

• 85 GHz

THINGS THAT APPEAR

COLD

: - Sea Surface and High portions of deep convection with where there are large ice phase precip (e.g., snow) THINGS THAT APPEAR

WARM

: - Land and Low-cloud fields

Properties of Microwave Imagery for Tropical Cyclones

• 37 GHz

THINGS THAT APPEAR

COLD

: - Sea Surface, but not deep convection: 37 GHz signal largely passes through ice (except when exceptionally dense).

THINGS THAT APPEAR

WARM

: - Land and rain at low level (rain very warm due to absorption versus 85 GHz).

Microwave Imagery Viewing Interpretation- Oceans * Oceans Appears Cool in 85h 85h (IR) * Oceans Appears Cold in 37v 37v Dry Moist Cold Cool Cool Cool OCEAN Warm Cold Cold Cold Warm

Ice Crystals Hail/Graupel Raindrops 85 GHz Parallax X Y Effective Level of hydrometeor s Freezing level

Ice Crystals Hail/Graupel Raindrops

37 GHz Parallax

X Y Effective Level of hydrometeors Freezing level

85 GHz

37 GHz

Advantages of 85 GHz

1. Identify peripheral low-level cloud bands, giving information about center of circulation.

2. Distinguish deep (cold) convection (heavy precipitation) from lightly-raining (warm) low cloud features.

3. Identify cirrus-covered eyes.

4. High Spatial Resolution

Limitations of 85 GHz

1. Cold Ocean may “look like” deep convection: Use 85 GHz Color Composite as a correction.

2. Parallax Error (10-20 km).

3. Saturates (no detail) in storm cores, misses structure

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Advantages of 37 GHz

1. Identify cirrus-covered eyes.

2. Resolve detail within the storm core missed by 85 GHz, sometimes can see eyes missed by 85 GHz.

3. Shows regions of low-level clouds/rain.

4. Little Parallax error compared to 85 GHz

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Limitations of 37 GHz

1. Does not show distinguish convection from low clouds bands. Eyes are sometimes poorly defined or not detectable. False eyes are common*.

2. Suffers from poor spatial resolution on SSM/I, SSM/IS, better on TMI, WindSAT and AMSR-E 3. Not available on AMSU-B

Active Microwave (Scatterometer)

Return pulse gives information

ADVANTAGES OF USING Microwave Data

• • • • • • •

‘Sees’ through clouds ( passive and active ) View of convective rain bands is more DIRECTLY related to intensification of the TC Positioning of TCs in difficult situations (especially in EARLY and LATE stages of development) Less delay in seeing changes in intensification Lower altitude of TRMM/AMSR-E has increased resolution in BOTH 85 and 37 GHz Imagery Can still use in conjunction with existing techniques (active and passive) Can detect winds on the ocean surface (active)***

Passive MI Wind Measurements

WindSAT SSM/I

RECENT/FUTURE SCATTEROMETERS SENSOR/SAT AGENCY LAUNCH SWATH (KM) GAP (KM) FREQ (GHZ) SCAT NSCAT SEAWINDS SEAWINDS ASCAT ERS 1 / 2 ADEOS1 QUICKSCAT ADEOS2 METOP1 ESA JPL JPL JPL ESA May 91 Aug 96 Jun 99 Late 2002 Jun 2006 /Apr 95 500 2x600 1800 1800 2x550 N/A 320 0 0 600 ANT 3 6 CIRCU CIRCU 6 RESOLUTION(KM) 50 (25) 25 25 (12.5) 25 25km SPEED (KT)/ ACCURACY(rms) DIRECTION (rms) 6-40 5-60 5-80 5-80 5-60?

4 OR 10% 2 OR 10% 2 or 10% 2 or 10% 2 or 10% 360 +/- 20 360 +/- 15 360 +/- 15 360 +/- 15 360 +/- 15 5.3 (C-BAND) 14.0 (Ku-BAND) 13.4 13.4 5.6 COVRG (90%) ASND NODE (LST) ~4 Days ~2 Days ~1 Day ~1 Day ~2 Days 10PM 10PM 6AM 6AM 10PM

Sources of Scatterometer Data

NOAA/NESDIS Storm Page (3-views) (2 deg grid) Ambiguity Solutions Wind Vectors NRCS



o V-pol forward

Build time?

ASCAT (NOAA/NESDIS site)

Which are the correct pair?

Physical Processes of Scatterometery

Bragg Scattering --NOT ocean waves!

Wind Direction (downwind example) Gravity-capillary waves Wavelength in centimeters

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Respond almost instantaneously to the strength of the local wind

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Microwave ( Bragg ) Scattering strongly depends on the amplitude

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Caps of these waves tend to align perpendicular to the local wind dir

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Sharp shape of leeward side of the capillary wave results in a different ocean radar return upwind (more) than in downwind (less) direction = I (incidence angle) More Less

QuikSCAT: SeaWinds Measurements

i = Incidence Angle z z i = 46 deg i = 54 deg V-pol H-pol From Dr. M. Freilich, Oregon State University

Red = V-pol Blue = H-pol

SeaWinds: Swath Geometry (3-views)

Subtrack View (4 solns,but small angle var) Edge View (2 solns) V-pol only

Forward Look

Ideal View (4 solns, 90 deg var)

Backward Look

From Dr. M. Freilich, Oregon State University

(less) Wind Speed 15 m/s



o More towards the sensor 10 m/s (approx equal) (cause of rain orientation) 05 m/s (Relative View Angle) Towards Cross Away Cross (from sensor)

Ambiguity Probability Solution

Wind Retrieval Process (Inverse of Radar Cross-Section Equation) 4- View ‘possible’ Solutions

QUIKSCAT RANKING SELECTION

( FROM A.C. VOORRIPS, DEC, 1999: QUIKSCAT PROGRESS REPORT, ROYAL NETHERLANDS METEOROLOGICAL INSTITUTE ) # SOLUTIONS IN 5 ORBITS (solid line) # SOLUTIONS CLOSEST TO NWP WIND VELOCITY (dashed line) 1 RANKS * Top #1 Rank dominates solution selection RATIO 1 RANKS

Normalized Radar Cross Section (NRCS)

--Thank you, Dr David Long (BYU)

(less) Wind Speed 15 m/s



o More towards the sensor (approx equal) 10 m/s 05 m/s (Relative View Angle) Towards Cross Away Cross (from sensor)

Large Eye/Eyewall Cycle

Some Problem Areas

(But….most can (have been) solved!) --Very High and Very Low winds --Rain Areas --Direction Confusion (i.e. Ambiguity Selection – not the instrument!) **MUST be Examined before Discarding!**

• • • •

QuikSCAT and TC Maximum Winds

Comparison of QuikSCAT maximum wind to best track and Dvorak intensity estimates shows limited skill – Lowest bias/MAE in tropical storms and weak hurricanes – Some low bias values due to cancellation errors of opposite sign Large positive bias in TD stage likely due to rain enhanced backscatter – Weak winds at surface overwhelmed by effects of rain Negative bias at high winds due to attenuation from rain, saturation of signal and limited resolution QuikSCAT winds must be used with care for intensity analysis – Interpretation ambiguous at best – Lack of co-located rain rate information – TRMM PR (or 37Ghz) can be used occasionally to get rain rate info 61

Edge of Swath Retrievals- comparison

Pass over TD9 at 0842 UTC 28 September Correct ambiguities chosen better resolved in new retrieval

3 Rain Effects

1) The radar signal is attenuated by the rain as it travels to and from the Earth’s surface

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σ 0 2) The radar signal is scattered by the raindrops. Some of this scattered energy returns to the instrument

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σ 0 3) The roughness of the sea surface is increased because of the splashing due to raindrops

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σ 0

Rain-enhanced (Light) Winds --Always check up and downstream

RAIN EFFECTS-Direction selection problem (Rain Blocks--Perpendicular to Swath) The “Rain Block” Swath Orientation Watch out for “False Center”!

Bad direction selection—Speeds are ‘good’.

Rain-enhanced (Light Wind) Directions

Rain-enhanced (Heavy Wind) Directions --not so bad

Ambiguity Solutions Ambiguity Format

RAIN EFFECTS (Wind and ambiguity solutions perpendicular to swath) Wind field perpendicular to swath angle Wind field discontinuity Note: ‘True’ rain affected area smaller than indicated in wind vector field 2-solution (some 3-) ambiguities perpendicular to swath (usually ‘rain flagged’)

Uses of QuikSCAT data for Tropical Cyclone Analysis

• • • • •

Positioning and Motion Minimum (at least) maximum wind Structure and Structure Change

(Wind Radii)

Genesis and (Surface) Genesis processes Extratropical Transition and Dissipation

Where is the center of this tropical storm?

Where is the center now?

Major Changes (since 2007**)

• • • • • Refinement of model function (backscatter-wind relationship—higher wind speeds!) Retrieval algorithm modification Development of new rain impact flag Improved edge of swath retrievals Reduced land mask for 12.5-km retrieval

**Seen in ‘Test’ mode, as of Sept 2007

Ultra Hi-Res Wentz Ultra Hi-Res

Diagnostic of NWP initial conditions

kts GFS – 3 hour forecast of wind speed 12.5 km QuikSCAT Maximum Wind speed 20 knots Maximum Wind speed 40 knots A GALE warning was issued!

Extratropical Transition Intensity

Scatterometer Winds over the Ocean (up to 100 kt!) Ex-Typhoon Bavi 14Oct2002

Hurricane Force Extratropical Cyclone

kts Intense, non-tropical cyclones with hurricane force winds Feb 09, 2007, North Atlantic

Hurricane Force Extratropical Cyclones Observed Data from the NOAA/NWS Ocean Prediction Center 65 64 60 55 50 51 45 40 35 30 25 20 23 24 23 37 33 31 34 22 15 10 14 15 11 9 5 0 1995-96 1996-97 1997-98 1998-99 1999-00 2000-01 2001-02 2002-03 2003-04 2004-05 2005-06 2006-07 Sep through May 2000-07 ( except Dec through April 2000-01 ) Atlantic Pacific

Combined or Integrated Analysis of Microwave Imagery and Scatterometer Data

Hur Fabian (10 L) ~17.5N 49.9W

105kt Streamlines shifted westward 31Aug0214 IR

Scatterometer Winds over the Ocean -Contribution to the Ocean wave model -Determining Swell Typhoon Sonca

Wind overlay over NRCS and 37Ghz data --Look for low wind and low rain region

Overlay

QuikSCAT winds and ambiguities over MI - 37Ghz imagery 35kt 65kt+ X 50kt 35kt

Questions?

PROCEDURES TO EVALUATE QUIKSCAT SOLUTIONS (extra)

• • • • •

Scatterometer Procedures Guide for Tropical Cyclone Reconnaissance (JTWC guide) TASK 1: Evaluation of Potential Suspect Area and Meteorological Environment (Preliminary Steps)

TASK 2: Use Scatterometer Wind and Ambiguity Data to Obtain a

TC Position

TASK 3: Use Normalized Radar Cross-Section (NRCS) Image to

Refine TC Position TASK 4: Comparison with Microwave and other Remote Sensing Data TASK 5: Reconciliation of Positions and Possible Re-Evaluation

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TASK 6: Determine Strongest Wind Speed(s) from Scatterometer Data

Scatterometer Procedures Guide for Tropical Cyclone Reconnaissance

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TASK 7: Obtain TC Outer Wind Radii from Scatterometer Data

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TASK 8: Determining Scatterometer Fix Position Accuracy

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TASK 9: Complete Scatterometer Worksheet and Include Fix into ATCF 5 Appendices A. Points of Contacts and Reference Web Sites B. QuikSCAT Problem Areas and Solutions C. Acronyms, Abbreviations and Terminology D. Scatterometer Worksheet E. Example

Isotach Solution Step 4: Perform a wind speed (isotach) determined above. analysis in the region - Look for a potential center in the lightest winds that are in close proximity to the highest winds in the analysis (may not exist for very small circulation centers).

-- Avoid wind speeds that appear excessively enhanced by rain.

- For very small circulation centers, a minimum wind speed vector may not exist. In this case look for the area within the highest wind speeds that best fits the cyclonic flow.

- In large asymmetric and in sheared situations, the strongest winds may be on one side of the center. In this case, look for a center along the cyclonic side of the highest wind speeds (versus in the geometric center).

Trough Axis Solution . In weaker systems (circulation less developed) look for a position in the lighter winds (usually within or near a trough axis) that could be considered on the cyclonic side of the highest wind speeds.

-- Especially important to avoid wind speeds that appear excessively enhanced by rain

“ISOTACH SOLUTION”

DMSP “Color” 02 Mar 1728Z This is NOT used in sheared situations. A center can often be found within a local minimum inside the highest isotach . Use in conjunction with available satellite imagery Eye 40kt 60kt 50kt Center found in local ‘min’ of isotach ring.

“ Trough-Axis ” No (or incorrect) circulation center Trough Axis Solution . In weaker systems, look in lighter winds (near a trough axis), on the cyclonic side of the highest wind speeds. Avoid wind speeds that appear excessively enhanced by rain .

This situation occurs in small systems or when the equatorial westerlies are weak, or when the NWP mistakes the equatorial trough axis for the TC circulation center common in Atlantic and South Indian Oceans.

Ambiguity Streamline Strategy Step 5:Perform a streamline analysis with the ambiguity plots. - Use the higher confidence, 2-direction (line) solutions to assist with the correct environmental wind flow away from the center.

- Use the 3-direction, “Y-shaped”, solutions (assisted by common color coded wind speeds with similar directions) and the 2-direction, with curved orientation, to follow the flow into the center. - Try to streamline without using the lowest confidence areas; however for a rain-affected wvc, try to use the alternate 3rd and 4th choice when possible especially if these choices show a bias from one side of the circulation to the other.

- Adjust center to best fit with the position identified by the isotach analysis

Ambiguity Plotting Convention Ambiguity plotting convention: 1-4 possible wind directions are plotted from the center of the wind vector cell (wvc) OUTWARDS and towards the direction of the flow (this is opposite of conventional meteorological wind vector plotting routines).

(SH Circulation)

Step 5: High confidence (2-way) solutions primarily away from the center

Step 5: “Key” 2- and 3- way solutions near center

Task 3 Primary Steps – Obtain corresponding NRCS image from NOAA/NESDIS QuikSCAT Storm Page. Check date/time/grid/orbital path. Look for NRCS patterns. If reliable center found, try to verify this position with previous position found with the wind and ambiguity data.

Task 3(b) Steps, continued: Overlay scatterometer winds and ambiguities on to the NRCS image. Do all positions coincide? Check for position of dark band with respect to t he radial extent into the suspect area center region (almost all the way: wind di rections and speeds are reliable in this area —over 35kt). See alternate solutions (c ircled).

Tropical Cyclone Lifecycle in Microwave Imagery

I.

II.

III.

IV.

V.

TC Genesis Stage ~ 25-30kt Early Intensification and Development ~ 30-45kt Continued Intensification and Mature Stage Peaking and Initial Weakening Stage Dissipation and Extratropical Transition

TC LIFE CYCLE IN MICROWAVE IMAGERY MI STAGES 1 2 3 ( pre-stage 0) Developmental patterns in Dvorak as compared with the first 3 Stages of MI development

.

The Beginning?….no classification

IR TRMM 37 color TRMM 85h

Stage 1 (Pre-Typhoon Francesco-25kts) 18 Sep 1200

Tropical Storm Erin (06L) 45kts-- Stage 2 03Sep1200

STY Mitag (02W) (Mar 2002) ---MI Stages 0 – 3 (85 GHz H) **Initial development in low level cloud structure and (blue) moisture increase, deep banding structure not well defined.

Stage 1 – Genesis Stage 0 – Pre-genesis Stage 2 27 Feb 0947Z 35kt Early Intensification and Development Stage 3 Banding Structure 26 Feb 1001Z 25kt 25 Feb 1046Z

Signs for Rapid Intensification ‘PLUS’ 37GHz Ring has Formed!

EVALUATIONS OF CAT5/SUPER TYPHOONS (85h) VIEWS: Double eyes (red inner eye) STY Saomai 140kt STY Billis 135kt STY Ivan 155kt STY Shanshan 125kt TC Paul 125kt STY Bart 140kt All cyclones in this category are going in or out of eye cycle.

Intensification is near max. Any change dependent upon red in outer eye. Red in inner eye most important for evaluating current intensity.

EVALUATIONS OF CAT5/SUPER TYPHOONS (85h) VIEWS: Time changes in red inner eyes ‘PLUS’ TC Susan 70kt -26hr TC Susan 95kt -13hr TC Susan 120kt -06hr STY Zeb 95kt -24hr STY Zeb 140kt -00hr

Peaking and Initial Weakening Stage 07Apr2300 65kt 85 GHz ‘MINUS’ TC Dianne-Jery (21S) 09Apr0753 90kt 11Apr0000 60kt

Ex- TYPHOON KATE (04W ) Weakening Stage Sample T/ST#s T3.0/4.0

T2.0/2.0 ?

T1.5/2.5

T2.5/3.5

TRMM 37V TRMM 37v TRMM 85H