Matthew Miller and Sandra Yuter Department of Marine, Earth, and Atmospheric Sciences North Carolina State University Raleigh, NC USA Phantom Precipitation and Other Problems in TRMM Products

Is data set adequate for purpose? What are strengths and weaknesses? The 23-year ( ) 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 TRMM Error Characteristics Identify geographic regions and seasons where existing algorithm physics may be incorrect or incomplete Identify geographic regions and seasons where existing algorithm physics may be incorrect or incomplete Region by region uncertainties aid application of TRMM data sets into numerical models, forecasting, and climate diagnostics Region by region uncertainties aid application of TRMM data sets into numerical models, forecasting, and climate diagnostics TRMM TMI algorithm similar to that used with other passive microwave satellites TRMM TMI algorithm similar to that used with other passive microwave satellites

Relative Comparison Between “Independent” Products: Precipitation Radar (PR) vs. TRMM Microwave Imager (TMI) Important for regions without surface- based rain estimates Important for regions without surface- based rain estimates Agreement  Truth Agreement  Truth But, lack of agreement implies problem with one or both algorithms But, lack of agreement implies problem with one or both algorithms Check physical consistency with empirical data Check physical consistency with empirical data

1500 km x 1500 km ocean region Log10(R) Number of Pixels Log10(R) PR TMI Version 6 Version 5 PR TMI Both UnimodalTMI Bimodal W Pacific Near Kwajalein Comparison of TRMM Instantaneous Rain Rate Products 47 days: 16 June – 1 Aug 2001

Version 6 Log10(R) Number of Pixels PR TMI SW Pacific off Australia 16 June – 1 Aug 2001 Log10(R) Bay of Bengal Number of Pixels PR TMI

16 June – 1 August 2001 Pink=TMI bimodalBlue=TMI unimodal Green=TMI strongly skewed

1 January – 16 February 2002 Pink=TMI bimodalBlue=TMI unimodal Green=TMI strongly skewed

Rain rate (mm/hr) PDF (%) V6 Global PDF, PR rescaled to 85 GHz scale LAND Stout and Kwiatkowski

Scattered Shallow Precip: Near Strait of Gibraltar PR Rain RatesTMI surface type LAND Morocco OCEAN COAST LAND-Spain

Scattered Shallow Precip: Near Strait of Gibraltar PR Rain RatesTMI surface type TMI rain rates

Widespread Deep Convection: Hurricane Ophelia TMI surface type PR Rain Rates Atlantic Ocean USA North Carolina

Widespread Deep Convection: Hurricane Ophelia TMI surface type TMI rain ratesPR Rain Rates

Widespread Deep Convection: Hurricane Ophelia TMI surface type TMI rain ratesPR Rain Rates 20 mm/hr 10 mm/hr

Coastal S-band Z Widespread Deep Convection: Hurricane Ophelia TMI rain rates

Unphysical Ice in Rain Layer Over Land TMI Precip Ice Profile 0 – 0.5 km altitude TMI Precip Ice Profile 1.5 – 2 km altitude 0  C height = 4.5 km

Atlantic Phantom Precip TMI rain ratesPR Rain Rates

Atlantic Phantom Precip TMI rain ratesCoastal S-band Z

Histogram of Phantom Precip Off East Coast Phantom Precip Rain Rate HistogramBounded area

Atlantic Phantom Precip IR indicates warm top low-level clouds Sounding derived cloud top height ~3100m 0° height at ~ 3300m GOES 12 IR

Erroneous Cloud Ice Upper Air Sounding Observed Cloud Top at ~3.1km TMI cloud ice from km Indicative of non- physical hydrometeor profile 14km TMI Cloud Ice

North Taiwan Coast 1 Feb 2000 Case from Berg et al Studied TMI/PR differences in rainfall detection Studied TMI/PR differences in rainfall detection Found large differences in frequency of detected precipitation between TMI and PR over East China Sea Found large differences in frequency of detected precipitation between TMI and PR over East China Sea Hypothesized TMI observed unusually high LWC cloud with relatively high emission, but low reflectivity (~18dBZ) due to high aerosol content Hypothesized TMI observed unusually high LWC cloud with relatively high emission, but low reflectivity (~18dBZ) due to high aerosol content

North Taiwan Coast 1 Feb 2000 Case from Berg et al TMI rain ratesPR Rain Rates

Histogram of Phantom Precip Off North Taiwan Coast 1 Feb 2000 Case from Berg et al Phantom Precip Rain Rate HistogramBounded area Coastal S-band Z Radar data courtesy of T.-C. Chen

Erroneous Cloud Ice Upper Air Sounding Observed Cloud Top at ~3.9km TMI cloud ice from 4- 14km Indicative of non- physical hydrometeor profile 14km TMI Cloud Ice

Conclusions I About half of regional ocean PDFs degraded in TMI V6 compared to V5 About half of regional ocean PDFs degraded in TMI V6 compared to V5 Implausible bimodal PDFs of rainrate Implausible bimodal PDFs of rainrate Most commonly occur during local summer and heavy rainfall areas Most commonly occur during local summer and heavy rainfall areas Serious problems with TMI rainfall estimation in coastal regions Serious problems with TMI rainfall estimation in coastal regions Shallow precipitation missing over coast/land Shallow precipitation missing over coast/land (no ice scattering or scattering too weak) Widespread deep precipitation: Widespread deep precipitation: Rain rate discontinuity at coast/ocean boundary (more obvious with heavier precipitation) Rain rate discontinuity at coast/ocean boundary (more obvious with heavier precipitation)

Conclusions II TMI phantom precipitation over ocean TMI phantom precipitation over ocean Does not appear in either PR or more sensitive coastal radar Does not appear in either PR or more sensitive coastal radar Occurs in stratus clouds under stable layer Occurs in stratus clouds under stable layer Phantom rain rates up to 2.3 mm/hr, modes vary with case (0.6 to 1.2 mm/hr) Phantom rain rates up to 2.3 mm/hr, modes vary with case (0.6 to 1.2 mm/hr) TMI hydrometeor profile does not physically represent the actual situation TMI hydrometeor profile does not physically represent the actual situation Unusually high LWC cloud (Berg et al. 2006) would have Z values of ~18 dBZ Unusually high LWC cloud (Berg et al. 2006) would have Z values of ~18 dBZ Database issues more likely Database issues more likely

Interpretation Non-physical TMI hydrometeor profiles appear to be symptom of “overreaching” in database Non-physical TMI hydrometeor profiles appear to be symptom of “overreaching” in database Occurs in different meteorological situations Occurs in different meteorological situations “Closest” profile in GPROF database does not pertain to actual situation “Closest” profile in GPROF database does not pertain to actual situation Could use to determine locations and % of highly uncertain rain rates Could use to determine locations and % of highly uncertain rain rates Adequacy for purpose of precipitation retrieval Adequacy for purpose of precipitation retrieval

Gulf Phantom Precip TMI rain ratesPR Rain Rates

Gulf Phantom Precip TMI rain ratesCoastal S-band Z

Histogram of phantom precip off Gulf coast Phantom Precip Rain Rate HistogramBounded area

Gulf Phantom Precip IR indicates warm top low-level clouds Sounding derived cloud top height ~4100m 0° height at ~ 4200m GOES 8 IR

Erroneous Cloud Ice Upper Air Sounding Observed Cloud Top at ~4.1km TMI cloud ice from 6- 18km Indicative of non- physical hydrometeor profile 8km TMI Cloud Ice

Passive Microwave measurements are volumetric: Emission channels sensitive to rain layer Houze et al Darker color = more brightness temperature signature

Passive Microwave measurements are volumetric: Scattering channels sensitive to ice layer Darker color = more brightness temperature signature

TMI rain rates Florida Case: Minimum Surface Temp = 11  C TMI Precip Ice Profile 0 – 0.5 km altitude

TRMM Satellite Sensors Precipitation Radar (PR)13.8 GHz Swath width 245 km Spatial resolution4.9 km Minimum sensitivity ~18 dBZ TRMM Microwave Imager (TMI) five passive microwave channels Swath width:872 km Rain Layer Emission: 19 GHz channel, 35 km pixels Ice Layer Scattering: 85 GHz channel, 7.7 km pixels Over Ocean Over Land and Coast

TRMM Product Releases TRMM satellite launch—November 1997, Version 1 TRMM satellite launch—November 1997, Version 1 Version 5 (V5)—November 1999 Version 5 (V5)—November 1999 Version 6 (V6)—April 2004 Version 6 (V6)—April 2004

NEXRAD Scan Strategy

ROIG Sounding - 1 Feb 2000 – 12Z