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Courtney D. Buckley
,
Robbie E. Hood
, and
Frank J. LaFontaine

Abstract

Inland flooding from tropical cyclones is a significant factor in storm-related deaths in the United States and other countries, with the majority of tropical cyclone fatalities recorded in the United States resulting from freshwater flooding. Information collected during National Aeronautics and Space Administration (NASA) tropical cyclone field experiments suggests that surface water and flooding can be detected and therefore monitored at a greater spatial resolution by using passive microwave airborne radiometers than by using satellite sensors. The 10.7-GHz frequency of the NASA Advanced Microwave Precipitation Radiometer (AMPR) has demonstrated high-resolution detection of anomalous surface water and flooding in numerous situations.

In this study, an analysis of three cases is conducted utilizing satellite and airborne radiometer data. Data from the 1998 Third Convection and Moisture Experiment (CAMEX-3) are utilized to detect surface water during the landfalling Hurricane Georges in both the Dominican Republic and Louisiana. Another case studied was the landfalling Tropical Storm Gert in eastern Mexico during the Tropical Cloud Systems and Processes (TCSP) experiment in 2005. AMPR data are compared to topographic data and vegetation indices to evaluate the significance of the surface water signature visible in the 10.7-GHz information. The results illustrate the AMPR’s utility in monitoring surface water that current satellite-based passive microwave radiometers are unable to monitor because of their coarser resolutions. This suggests the benefit of a radiometer with observing frequencies less than 11 GHz deployed on a manned aircraft or unmanned aircraft system to provide early detection in real time of expanding surface water or flooding conditions.

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Roy W. Spencer
,
H. Michael Goodman
, and
Robbie E. Hood

Abstract

The subject of this study is the identification of precipitation in warm and cold land and ocean environments from the Defense Meteorological Satellite Program's (DMSP) Special Sensor Micmwave/Imager (SSM/I). The high sensitivity of the SSM/I 85.5 GHz channels to volume scattering by precipitation, especially ice above the freezing level, is the basis for this identification. This ice scattering process causes SSM/I 85.5 GHz brightness temperatures to occasionally fall below 100 K. It is demonstrated that the polarization diversity available at 85.5 GHz from the SSM/I allows discrimination between low brightness temperatures due to surface water bodies versus those due to precipitation. An 85.5 GHz polarization corrected temperature (PCT) is formulated to isolate the precipitation effect. A PCT threshold of 255 K is suggested for the delineation of precipitation. This threshold is shown to be lower than what would generally be expected from nonprecipitating cloud water alone, yet high enough to sense relatively light precipitation rates. Based upon aircraft radiometric measurements compared with radar derived rain rates, as well as model calculations, the corresponding average rain rate threshold is approximately 1–3 mm h−1. The majority of precipitation that falls on the earth exceeds this rate.

Because the 85.5 GHz measurements of oceanic storms are often dominated by scattering due to precipitation above the freezing level, while the 19.35 GHz radiances are dominated by emission due to rain below the freezing level, there is independent information about the gross vertical structure of oceanic precipitation systems from the SSM/I. Apparent differences between storms in formative, mature, and dissipating stages are inferred from the diagnosed amounts of ice versus raindrops, and supported by time lapse GOES imagery. Deviations from the average relationship between 19.35 GHz warming and 85.5 GHz cooling are suggested for use as a diagnostic tool to evaluate lower level rain/upper level ice relative abundances. As an example of this capability, overrunning precipitation shows a horizontal offset between the advancing ice layer and the trailing rain area, consistent with idealized conceptual models of warm frontal precipitation.

Part II of this study will address global screening for the precipitation scattering signal, its statistical characteristics, and the false rain signatures frequently caused by snow cover and cold land.

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Gary McGaughey
,
Edward J. Zipser
,
Roy W. Spencer
, and
Robbie E. Hood

Abstract

This paper presents high-resolution passive microwave measurements obtained in the western Pacific warm pool region. These measurements represent the most comprehensive such observations of convection over the tropical oceans to date, and were obtained from the Advanced Microwave Precipitation Radiometer (AMPR) aboard the NASA ER-2 during the Tropical Ocean and Global Atmosphere Coupled Ocean-Atmosphere Response Experiment. The AMPR measures linearly polarized radiation at 10.7, 19.35, 37.1, and 85.5 GHZ.

Nadir brightness temperature scatterplots suggest that the three lower frequencies respond primarily to emission/absorption processes. Strong ice scattering is relatively rare, as absolute magnitudes of the ice-scattering signature do not approach those measured in strong convection over land. This is apparently related to the reported weaker updraft velocities over tropical oceans, which would create and suspend relatively smaller graupel or hail particles in the upper cloud. Observations within stratiform regions suggest that approximately 220 K is the minimum 85.5-GHz brightness temperature associated with ice scattering in regions of stratiform precipitation.

In agreement with other studies using high-resolution data, the relationships between data at the lower frequencies and the 85.5-GHz data exhibit considerable scatter. Traces through a hurricane eyewall and a squall line reveal the tilt of these convective systems away from the vertical. It is suggested that this observed tilt of convective lines is responsible, in part, for the finding that warm 10.7-GHz brightness temperatures (showing heavy rain at low levels) and cold 85.5-GHz brightness temperatures (showing large optical depth of ice particles aloft) are not consistently collocated. Observations of heavily raining clouds with little ice above or nearby are also presented, but it is shown that the heaviest rain rates are associated with ice scattering aloft.

The AMPR data are averaged to a 24-km resolution, in order to simulate a satellite footprint of that scale. Brightness temperature relationships become more linear, though the scatter is not significantly reduced. The effects of nonhomogeneous beamfilling are obvious. A description of brightness temperature variability within the simulated satellite footprint is also presented. Similar descriptions could be used to develop a beamfilling correction to increase the accuracy of microwave rain-rate retrievals over the tropical oceans.

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Robbie E. Hood
,
Daniel J. Cecil
,
Frank J. LaFontaine
,
Richard J. Blakeslee
,
Douglas M. Mach
,
Gerald M. Heymsfield
,
Frank D. Marks Jr.
,
Edward J. Zipser
, and
Michael Goodman

Abstract

During the 1998 and 2001 hurricane seasons of the western Atlantic Ocean and Gulf of Mexico, the Advanced Microwave Precipitation Radiometer (AMPR), the ER-2 Doppler (EDOP) radar, and the Lightning Instrument Package (LIP) were flown aboard the NASA ER-2 high-altitude aircraft as part of the Third Convection and Moisture Experiment (CAMEX-3) and the Fourth Convection and Moisture Experiment (CAMEX-4). Several hurricanes, tropical storms, and other precipitation systems were sampled during these experiments. An oceanic rainfall screening technique has been developed using AMPR passive microwave observations of these systems collected at frequencies of 10.7, 19.35, 37.1, and 85.5 GHz. This technique combines the information content of the four AMPR frequencies regarding the gross vertical structure of hydrometeors into an intuitive and easily executable precipitation mapping format. The results have been verified using vertical profiles of EDOP reflectivity and lower-altitude horizontal reflectivity scans collected by the NOAA WP-3D Orion radar. Matching the rainfall classification results with coincident electric field information collected by the LIP readily identifies convective rain regions within the precipitation fields. This technique shows promise as a real-time research and analysis tool for monitoring vertical updraft strength and convective intensity from airborne platforms such as remotely operated or uninhabited aerial vehicles. The technique is analyzed and discussed for a wide variety of precipitation types using the 26 August 1998 observations of Hurricane Bonnie near landfall.

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Roy W. Spencer
,
Robbie E. Hood
,
Frank J. Lafontaine
,
Eric A. Smith
,
Robert Platt
,
Joe Galliano
,
Vanessa L. Griffin
, and
Elena Lobl

Abstract

An Advanced Microwave Precipitation Radiometer (AMPR) has been developed and flown in the NASA ER-2 high-altitude aircraft for imaging various atmospheric and surface processes, primarily the internal structure of rain clouds. The AMPR is a scanning four-frequency total power microwave radiometer that is externally calibrated with high-emissivity warm and cold loads. Separate antenna systems allow the sampling of the 10.7- and 19.35-GHz channels at the same spatial resolution, while the 37.1- and 85.5-GHz channels utilize the same multifrequency feedhorn as the 19.35-GHz channel. Spatial resolutions from an aircraft altitude of 20-km range from 0.6 km at 85.5 GHz to 2.8 km at 19.35 and 10.7 GHz. All channels are sampled every 0.6 km in both along-track and cross-track directions, leading to a contiguous sampling pattern ofthe 85.5-GHz 3-dB beamwidth footprints, 2.3 × oversampling of the 37.1-GHz data, and 4.4 × oversampling of the 19.35- and 10.7-GHz data. Radiometer temperature sensitivities range from 0.2° to 0.5°C. Details of the system are described, including two different calibration systems and their effect on the data collected. Examples of oceanic rain systems are presented from Florida and the tropical west Pacific that illustrate the wide variety of cloud water, rainwater, and precipitation-size ice combinations that are observable from aircraft altitudes.

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Elaine M. Prins
,
Christopher S. Velden
,
Jeffrey D. Hawkins
,
F. Joseph Turk
,
Jaime M. Daniels
,
Gerald J. Dittberner
,
Kenneth Holmlund
,
Robbie E. Hood
,
Arlene G. Laing
,
Shaima L. Nasiri
,
Jeffery J. Puschell
,
J. Marshall Shepherd
, and
John V. Zapotocny
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Gary A. Wick
,
Jason P. Dunion
,
Peter G. Black
,
John R. Walker
,
Ryan D. Torn
,
Andrew C. Kren
,
Altug Aksoy
,
Hui Christophersen
,
Lidia Cucurull
,
Brittany Dahl
,
Jason M. English
,
Kate Friedman
,
Tanya R. Peevey
,
Kathryn Sellwood
,
Jason A. Sippel
,
Vijay Tallapragada
,
James Taylor
,
Hongli Wang
,
Robbie E. Hood
, and
Philip Hall
Full access
Gary A. Wick
,
Jason P. Dunion
,
Peter G. Black
,
John R. Walker
,
Ryan D. Torn
,
Andrew C. Kren
,
Altug Aksoy
,
Hui Christophersen
,
Lidia Cucurull
,
Brittany Dahl
,
Jason M. English
,
Kate Friedman
,
Tanya R. Peevey
,
Kathryn Sellwood
,
Jason A. Sippel
,
Vijay Tallapragada
,
James Taylor
,
Hongli Wang
,
Robbie E. Hood
, and
Philip Hall

Abstract

The National Oceanic and Atmospheric Administration’s (NOAA) Sensing Hazards with Operational Unmanned Technology (SHOUT) project evaluated the ability of observations from high-altitude unmanned aircraft to improve forecasts of high-impact weather events like tropical cyclones or mitigate potential degradation of forecasts in the event of a future gap in satellite coverage. During three field campaigns conducted in 2015 and 2016, the National Aeronautics and Space Administration (NASA) Global Hawk, instrumented with GPS dropwindsondes and remote sensors, flew 15 missions sampling 6 tropical cyclones and 3 winter storms. Missions were designed using novel techniques to target sampling regions where high model forecast uncertainty and a high sensitivity to additional observations existed. Data from the flights were examined in real time by operational forecasters, assimilated in operational weather forecast models, and applied postmission to a broad suite of data impact studies. Results from the analyses spanning different models and assimilation schemes, though limited in number, consistently demonstrate the potential for a positive forecast impact from the observations, both with and without a gap in satellite coverage. The analyses with the then-operational modeling system demonstrated large forecast improvements near 15% for tropical cyclone track at a 72-h lead time when the observations were added to the otherwise complete observing system. While future decisions regarding use of the Global Hawk platform will include budgetary considerations, and more observations are required to enhance statistical significance, the scientific results support the potential merit of the observations. This article provides an overview of the missions flown, observational approach, and highlights from the completed and ongoing data impact studies.

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