matthew miller and sandra yuter department of marine, earth, and atmospheric sciences north carolina...

Matthew Miller and Sandra YuterMatthew Miller and Sandra Yuter

Department of Marine, Earth, and Atmospheric SciencesDepartment of Marine, Earth, and Atmospheric Sciences

North Carolina State UniversityNorth Carolina State University

Raleigh, NC USARaleigh, NC USA

Phantom Precipitation and Other Phantom Precipitation and Other Problems in TRMM ProductsProblems in TRMM Products

Is data set adequate for purpose?What are strengths and weaknesses?

The 23-year (1979-2001) annual mean precipitation (mm day-1) based on GPCP Version 2 includes satellite, gauge, and radar (Adler et al. 2003)

TRMM 3 hour Global Rainfall

Motivations for Diagnosing Motivations for Diagnosing TRMM Error CharacteristicsTRMM Error Characteristics

Identify geographic regions and seasons Identify geographic regions and seasons where existing algorithm physics may be where existing algorithm physics may be incorrect or incompleteincorrect or incomplete

Region by region uncertainties aid Region by region uncertainties aid application of TRMM data sets into application of TRMM data sets into numerical models, forecasting, and climate numerical models, forecasting, and climate diagnosticsdiagnostics

TRMM TMI algorithm similar to that used TRMM TMI algorithm similar to that used with other passive microwave satelliteswith other passive microwave satellites

Relative Comparison Between Relative Comparison Between “Independent” Products:“Independent” Products:

Precipitation Radar (PR) vs. Precipitation Radar (PR) vs. TRMM Microwave Imager (TMI)TRMM Microwave Imager (TMI)

Important for regions without surface-Important for regions without surface-based rain estimatesbased rain estimates

Agreement Agreement Truth Truth But, lack of agreement implies problem But, lack of agreement implies problem

with one or both algorithmswith one or both algorithms Check physical consistency with empirical Check physical consistency with empirical

datadata

1500 km x 1500 km ocean region

Log10(R)

Num

ber

of P

ixel

s

Num

ber

of P

ixel

s

Log10(R)

PRTMI

Version 6Version 5

PRTMI

Both Unimodal TMI Bimodal

W Pacific Near Kwajalein

Comparison of TRMM Comparison of TRMM Instantaneous Rain Rate ProductsInstantaneous Rain Rate Products

47 days: 16 June – 1 Aug 2001

Version 6

Log10(R)

Num

ber

of P

ixel

s PRTMI

SW Pacific off Australia

16 June – 1 Aug 2001

Log10(R)

Bay of Bengal

Num

ber

of P

ixel

s PRTMI

16 June – 1 August 2001

Pink=TMI bimodal Blue=TMI unimodalGreen=TMI strongly skewed

1 January – 16 February 2002

Pink=TMI bimodal Blue=TMI unimodalGreen=TMI strongly skewed

Rain rate (mm/hr)

PD

F (

%)

V6 Global PDF, PR rescaled to 85 GHz scale

LAND

Stout and Kwiatkowski

Scattered Shallow Precip: Scattered Shallow Precip: Near Strait of GibraltarNear Strait of Gibraltar

PR Rain Rates TMI surface type

LANDMorocco

OCEAN

COAST

LAND-Spain

Scattered Shallow Precip: Scattered Shallow Precip: Near Strait of GibraltarNear Strait of Gibraltar

PR Rain Rates TMI surface typeTMI rain rates

Widespread Deep Convection: Widespread Deep Convection: Hurricane OpheliaHurricane Ophelia

TMI surface typeTMI surface typePR Rain Rates

Atlantic Ocean

USANorth Carolina

Widespread Deep Convection: Widespread Deep Convection: Hurricane OpheliaHurricane Ophelia

TMI surface typeTMI rain ratesPR Rain Rates

Widespread Deep Convection: Widespread Deep Convection: Hurricane OpheliaHurricane Ophelia

TMI surface typeTMI rain ratesPR Rain Rates

20 mm/hr

10 mm/hr

Coastal S-band Z

Widespread Deep Convection: Widespread Deep Convection: Hurricane OpheliaHurricane Ophelia

TMI rain rates

TMI rain rates

Unphysical Ice in Rain Layer Unphysical Ice in Rain Layer Over LandOver Land

TMI Precip Ice Profile0 – 0.5 km altitudeTMI Precip Ice Profile 1.5 – 2 km altitude

0C height = 4.5 km

Atlantic Phantom PrecipAtlantic Phantom Precip

TMI rain rates PR Rain Rates

Atlantic Phantom PrecipAtlantic Phantom Precip

TMI rain rates Coastal S-band Z

Histogram of Phantom Precip Off Histogram of Phantom Precip Off East CoastEast Coast

Phantom Precip Rain Rate Histogram Bounded area

18 March 2005 Histogram

0

20

40

60

80

100

120

140

Rain Rate (mm/hr)

# P

ixe

ls

Atlantic Phantom PrecipAtlantic Phantom Precip•IR indicates warm top low-level clouds

•Sounding derived cloud top height ~3100m

•0° height at ~ 3300m GOES 12 IR

Erroneous Cloud IceErroneous Cloud Ice

Upper Air Sounding Upper Air Sounding Observed Cloud Top Observed Cloud Top at ~3.1kmat ~3.1km

TMI cloud ice from TMI cloud ice from 3.5-14km3.5-14km

Indicative of non-Indicative of non-physical hydrometeor physical hydrometeor profileprofile

14km TMI Cloud Ice

North Taiwan CoastNorth Taiwan Coast1 Feb 2000 Case 1 Feb 2000 Case from Berg et al. 2006from Berg et al. 2006

Studied TMI/PR differences in rainfall Studied TMI/PR differences in rainfall detectiondetection

Found large differences in frequency of Found large differences in frequency of detected precipitation between TMI and detected precipitation between TMI and PR over East China SeaPR over East China Sea

Hypothesized TMI observed unusually Hypothesized TMI observed unusually high LWC cloud with relatively high high LWC cloud with relatively high emission, but low reflectivity (~18dBZ) emission, but low reflectivity (~18dBZ) due to high aerosol contentdue to high aerosol content

North Taiwan CoastNorth Taiwan Coast1 Feb 2000 Case 1 Feb 2000 Case from Berg et al. 2006from Berg et al. 2006

TMI rain rates PR Rain Rates

Histogram of Phantom Precip Off Histogram of Phantom Precip Off North Taiwan CoastNorth Taiwan Coast

1 Feb 2000 Case 1 Feb 2000 Case from Berg et al. 2006from Berg et al. 2006

Phantom Precip Rain Rate Histogram Bounded area

1 Febuary 2000 Histogram

0

100

200

300

400

500

600

700

Rain Rate (mm/hr)

# P

ixe

ls

Coastal S-band Z

Radar data courtesy of T.-C. Chen

Erroneous Cloud IceErroneous Cloud Ice

Upper Air Sounding Upper Air Sounding Observed Cloud Top Observed Cloud Top at ~3.9kmat ~3.9km

TMI cloud ice from 4-TMI cloud ice from 4-14km14km

Indicative of non-Indicative of non-physical hydrometeor physical hydrometeor profileprofile

14km TMI Cloud Ice

Conclusions IConclusions I About half of regional ocean PDFs degraded About half of regional ocean PDFs degraded

in TMI V6 compared to V5in TMI V6 compared to V5 Implausible bimodal PDFs of rainrateImplausible bimodal PDFs of rainrate Most commonly occur during local summer and Most commonly occur during local summer and

heavy rainfall areasheavy rainfall areas Serious problems with TMI rainfall estimation Serious problems with TMI rainfall estimation

in coastal regionsin coastal regions Shallow precipitation missing over coast/land Shallow precipitation missing over coast/land

(no ice scattering or scattering too weak)(no ice scattering or scattering too weak) Widespread deep precipitation:Widespread deep precipitation:

Rain rate discontinuity at coast/ocean boundary Rain rate discontinuity at coast/ocean boundary (more obvious with heavier precipitation)(more obvious with heavier precipitation)

Conclusions IIConclusions II

TMI phantom precipitation over oceanTMI phantom precipitation over ocean Does not appear in either PR or more Does not appear in either PR or more

sensitive coastal radarsensitive coastal radar Occurs in stratus clouds under stable layerOccurs in stratus clouds under stable layer Phantom rain rates up to 2.3 mm/hr, modes Phantom rain rates up to 2.3 mm/hr, modes

vary with case (0.6 to 1.2 mm/hr)vary with case (0.6 to 1.2 mm/hr) TMI hydrometeor profile does not physically TMI hydrometeor profile does not physically

represent the actual situationrepresent the actual situation Unusually high LWC cloud (Berg et al. 2006) Unusually high LWC cloud (Berg et al. 2006)

would have Z values of ~18 dBZ would have Z values of ~18 dBZ Database issues more likely Database issues more likely

InterpretationInterpretation Non-physical TMI hydrometeor profiles Non-physical TMI hydrometeor profiles

appear to be symptom of “overreaching” in appear to be symptom of “overreaching” in databasedatabase Occurs in different meteorological situationsOccurs in different meteorological situations ““Closest” profile in GPROF database does not Closest” profile in GPROF database does not

pertain to actual situation pertain to actual situation Could use to determine locations and % of Could use to determine locations and % of

highly uncertain rain rateshighly uncertain rain rates

Adequacy for purpose of precipitation Adequacy for purpose of precipitation retrievalretrieval

Gulf Phantom PrecipGulf Phantom Precip

TMI rain rates PR Rain Rates

Gulf Phantom PrecipGulf Phantom Precip

TMI rain rates Coastal S-band Z

Histogram of phantom precip off Histogram of phantom precip off Gulf coastGulf coast

Phantom Precip Rain Rate Histogram Bounded area

5 March 2002 Histogram

0

50

100

150

200

250

300

350

Rain Rate (mm/hr)

# P

ixe

ls

Gulf Phantom PrecipGulf Phantom Precip•IR indicates warm top low-level clouds

•Sounding derived cloud top height ~4100m

•0° height at ~ 4200m GOES 8 IR

Erroneous Cloud IceErroneous Cloud Ice

Upper Air Sounding Upper Air Sounding Observed Cloud Top Observed Cloud Top at ~4.1kmat ~4.1km

TMI cloud ice from 6-TMI cloud ice from 6-18km18km

Indicative of non-Indicative of non-physical hydrometeor physical hydrometeor profileprofile

8km TMI Cloud Ice

Passive Microwave measurements Passive Microwave measurements are volumetric: are volumetric:

Emission channels sensitive to rain layerEmission channels sensitive to rain layer

Houze et al. 1989

Darker color = more brightness temperature signature

Passive Microwave measurements Passive Microwave measurements are volumetric: are volumetric:

Scattering channels sensitive to ice layerScattering channels sensitive to ice layer

Darker color = more brightness temperature signature

TMI rain rates

Florida Case: Florida Case: Minimum Surface Temp = 11 Minimum Surface Temp = 11 CC

TMI Precip Ice Profile0 – 0.5 km altitude

TRMM Satellite SensorsTRMM Satellite Sensors

Precipitation Radar (PR)Precipitation Radar (PR) 13.8 GHz13.8 GHzSwath width Swath width 245 km245 kmSpatial resolutionSpatial resolution 4.9 km 4.9 km Minimum sensitivity Minimum sensitivity ~18 dBZ~18 dBZ

TRMM Microwave Imager (TMI)TRMM Microwave Imager (TMI)five passive microwave channelsfive passive microwave channels

Swath width:Swath width: 872 km872 km

Rain Layer Emission: 19 GHz channel, 35 km pixelsRain Layer Emission: 19 GHz channel, 35 km pixelsIce Layer Scattering: 85 GHz channel, 7.7 km pixelsIce Layer Scattering: 85 GHz channel, 7.7 km pixels

Over OceanOver Land and Coast

TRMM Product ReleasesTRMM Product Releases

TRMM satellite launch—November 1997, TRMM satellite launch—November 1997, Version 1Version 1

Version 5 (V5)—November 1999Version 5 (V5)—November 1999 Version 6 (V6)—April 2004 Version 6 (V6)—April 2004

NEXRAD Scan StrategyNEXRAD Scan Strategy

ROIG Sounding - 1 Feb 2000 – 12ZROIG Sounding - 1 Feb 2000 – 12Z