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