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- Author or Editor: Robert E. McIntosh x
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Abstract
Millimeter-wave Doppler spectra obtained from the dual-frequency Cloud Profiling Radar System (CPRS) are used to retrieve both the drop size distribution and the vertical air motion in rain. CPRS obtains collocated spectra at W and Ka bands through a single 1-m-diameter lens antenna. The vertical air motion is determined primarily from the 95-GHz Mie scattering from rain, whereas turbulence effects are minimized by correlating the drop size distributions measured at both the 95- and 33-GHz frequencies. The authors describe an iterative procedure that estimates the drop sizes and vertical motions with range and horizontal resolution of 60 m and temporal resolution of 2 s. Model drop size distributions are used to initiate the procedure, but the retrieved distributions and vertical air motions are seen to be independent of the particular model used.
Data were gathered to test the procedure during the Ground-Based Remote Sensing Intensive Observation Period (GBRS IOP) sponsored by the Department of Energy Atmospheric Radiation Measurement (DOE ARM) program. The measurements represent the first simultaneous Doppler spectra of rain at these frequencies. The experiment took place in April 1995 at the Cloud and Radiation Testbed (CART) site in Lamont, Oklahoma. Radiosonde and surface measurements of temperature and pressure were used in the retrieval algorithm. Rain events from stratiform and transition region (i.e., decaying from the convective region toward the stratiform region of a storm) clouds were observed and are analyzed in this paper. The rain rate for the stratiform rain case was relatively uniform with small amounts of vertical air motion. Variations of the vertical winds for the transition region case, however, were larger and more frequent and were accompanied by short intense downbursts. The algorithm’s results are best for rain rates higher than 1 mm h−1.
Abstract
Millimeter-wave Doppler spectra obtained from the dual-frequency Cloud Profiling Radar System (CPRS) are used to retrieve both the drop size distribution and the vertical air motion in rain. CPRS obtains collocated spectra at W and Ka bands through a single 1-m-diameter lens antenna. The vertical air motion is determined primarily from the 95-GHz Mie scattering from rain, whereas turbulence effects are minimized by correlating the drop size distributions measured at both the 95- and 33-GHz frequencies. The authors describe an iterative procedure that estimates the drop sizes and vertical motions with range and horizontal resolution of 60 m and temporal resolution of 2 s. Model drop size distributions are used to initiate the procedure, but the retrieved distributions and vertical air motions are seen to be independent of the particular model used.
Data were gathered to test the procedure during the Ground-Based Remote Sensing Intensive Observation Period (GBRS IOP) sponsored by the Department of Energy Atmospheric Radiation Measurement (DOE ARM) program. The measurements represent the first simultaneous Doppler spectra of rain at these frequencies. The experiment took place in April 1995 at the Cloud and Radiation Testbed (CART) site in Lamont, Oklahoma. Radiosonde and surface measurements of temperature and pressure were used in the retrieval algorithm. Rain events from stratiform and transition region (i.e., decaying from the convective region toward the stratiform region of a storm) clouds were observed and are analyzed in this paper. The rain rate for the stratiform rain case was relatively uniform with small amounts of vertical air motion. Variations of the vertical winds for the transition region case, however, were larger and more frequent and were accompanied by short intense downbursts. The algorithm’s results are best for rain rates higher than 1 mm h−1.
Abstract
A recently developed 1.4 mm wavelengh incoherent radar has potential for remote sensing of low reflectivity atmospheric targets for ranges up to several kilometers. Power output of 60 W is achieved using an Extended Interaction Oscillator (EIO). Preliminary reflectivity measurements of clouds and fog for ranges between 36 and 1900 meters are believed to be the first such measurements at this wavelength Limitations on the accuracy of the reflectivity measurements are discussed, highlighting uncertainties due to highly variable attenuation.
Abstract
A recently developed 1.4 mm wavelengh incoherent radar has potential for remote sensing of low reflectivity atmospheric targets for ranges up to several kilometers. Power output of 60 W is achieved using an Extended Interaction Oscillator (EIO). Preliminary reflectivity measurements of clouds and fog for ranges between 36 and 1900 meters are believed to be the first such measurements at this wavelength Limitations on the accuracy of the reflectivity measurements are discussed, highlighting uncertainties due to highly variable attenuation.
Abstract
Scatterometer model functions that directly estimate friction velocity have been developed and are being tested with radar and in situ data acquired during the Surface Wave Dynamics Experiment (SWADE) of 1991. Ku-band and C-band scatterometers were operated simultaneously for extensive intervals for each of 10 days during SWADE. The model function developed previously from the FASINEX experiment converts the Ku-band normalized radar cross-section (NRCS) measurements into friction velocity estimates. These are compared to in situ estimates of surface wind stress and direction across a wide area both on and off the Gulf Stream (for hourly intervals), which were determined from buoy and meteorological measurements during February and March 1991. This involved the combination of a local, specially derived wind field, with an ocean wave model coupled through a sea-state-dependent drag coefficient. The Ku-band estimates u∗ magnitude are in excellent agreement with the in situ values. The C-band scatterometer measurements were coincident with the Ku-band NRCSs, whose u∗ estimates are then used to calibrate the C band. The results show the C-band NRCS dependence at 20°, 30°, 40°, and 50° to be less sensitive to friction velocity than the corresponding cases for Ku band. The goal is to develop the capability of making friction velocity estimates (and surface stress) from radar cross-sectional data acquired by satellite scatterometers.
Abstract
Scatterometer model functions that directly estimate friction velocity have been developed and are being tested with radar and in situ data acquired during the Surface Wave Dynamics Experiment (SWADE) of 1991. Ku-band and C-band scatterometers were operated simultaneously for extensive intervals for each of 10 days during SWADE. The model function developed previously from the FASINEX experiment converts the Ku-band normalized radar cross-section (NRCS) measurements into friction velocity estimates. These are compared to in situ estimates of surface wind stress and direction across a wide area both on and off the Gulf Stream (for hourly intervals), which were determined from buoy and meteorological measurements during February and March 1991. This involved the combination of a local, specially derived wind field, with an ocean wave model coupled through a sea-state-dependent drag coefficient. The Ku-band estimates u∗ magnitude are in excellent agreement with the in situ values. The C-band scatterometer measurements were coincident with the Ku-band NRCSs, whose u∗ estimates are then used to calibrate the C band. The results show the C-band NRCS dependence at 20°, 30°, 40°, and 50° to be less sensitive to friction velocity than the corresponding cases for Ku band. The goal is to develop the capability of making friction velocity estimates (and surface stress) from radar cross-sectional data acquired by satellite scatterometers.
Abstract
This paper describes the turbulent eddy profiler (TEP), a volume-imaging, UHF radar wind profiler designed for clear-air measurements in the atmospheric boundary layer on scales comparable to grid cell sizes of large eddy simulation models. TEP employs a large array of antennas—each feeding an independent receiver—to simultaneously generate multiple beams within a 28° conical volume illuminated by the transmitter. Range gating provides 30-m spatial resolution in the vertical dimension. Each volume image is updated every 2–10 s, and long datasets can be gathered to study the evolution of turbulent structure over several hours. A summary of the principles of operation and the design of TEP is provided, including examples of clear-air reflectivity and velocity images.
Abstract
This paper describes the turbulent eddy profiler (TEP), a volume-imaging, UHF radar wind profiler designed for clear-air measurements in the atmospheric boundary layer on scales comparable to grid cell sizes of large eddy simulation models. TEP employs a large array of antennas—each feeding an independent receiver—to simultaneously generate multiple beams within a 28° conical volume illuminated by the transmitter. Range gating provides 30-m spatial resolution in the vertical dimension. Each volume image is updated every 2–10 s, and long datasets can be gathered to study the evolution of turbulent structure over several hours. A summary of the principles of operation and the design of TEP is provided, including examples of clear-air reflectivity and velocity images.
Abstract
The Polarization Diversity Pulse-Pair (PDPP) technique can extend simultaneously the maximum unambiguous range and the maximum unambiguous velocity of a Doppler weather radar. This technique has been applied using a high-resolution 95-GHz radar to study the reflectivity and velocity structure in severe thunderstorms. This paper documents the technique, presents an analysis of the first two moments of the estimated mean velocity, and provides a comparison of the results with experimental data, including PDPP images of high-vorticity regions in supercell storms.
Abstract
The Polarization Diversity Pulse-Pair (PDPP) technique can extend simultaneously the maximum unambiguous range and the maximum unambiguous velocity of a Doppler weather radar. This technique has been applied using a high-resolution 95-GHz radar to study the reflectivity and velocity structure in severe thunderstorms. This paper documents the technique, presents an analysis of the first two moments of the estimated mean velocity, and provides a comparison of the results with experimental data, including PDPP images of high-vorticity regions in supercell storms.
