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B. B. Balsley
,
A. C. Riddle
,
W. L. Ecklund
, and
D. A. Carter

Abstract

We present the analysis of three months of continuous sea-surface current data obtained by a VHF wind profiling radar at Christmas Island in the central equatorial Pacific. These results, which were obtained during the construction phase of the profiler when the antenna had not yet been phased to eliminate sea scatter, show a number of interesting features of the coastal flow, as well as the flow at greater distances from the island. We report here both the average surface current characteristics as well as features of the shorter-term variability. In addition, we discuss the idea that such sea-surface current measurements could be obtained quite easily in the central Pacific, provided that they were made in conjunction with existing and/or proposed profiler sites.

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Wayne M. Angevine
,
W. L. Ecklund
,
D. A. Carter
,
K. S. Gage
, and
K. P. Moran

Abstract

Improved radio acoustic sounding system (RASS) technology for use with radar wind profilers has been developed and applied to 915-MHz and 50-MHz profilers. The most important advance is the simultaneous measurement of the wind velocity to correct the acoustic velocity measurement for air motion. This eliminates the primary source of error in previous RASS measurements, especially on short time scales. Another improvement is the use of an acoustic source that is controlled by the same computer that controls the radar. The source can be programmed to produce either a swept frequency or a random hopped frequency signal. Optimum choices of the acoustic source parameters are explored for particular applications. Simultaneous measurement of acoustic and wind velocity enables the calculation of heat flux by eddy correlation. Preliminary heat flux measurements are presented and discussed. Results of the use of RASS with oblique beams are also reported.

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K. S. Gage
,
W. L. Ecklund
,
A. C. Riddle
, and
B. B. Balsley

Abstract

The magnitude of backscattered power observed at vertical incidence by a VHF radar is related to atmospheric stability in accordance with the Fresnel scattering model. Utilizing a modified Fresnel scattering model, we can determine tropopause height objectively from the observed vertical profile of backscattered power. The method is tested with observations of the Alpine Experiment (ALPEX; France), Platteville, Colorado and Poker Mat, Alaska radars taken since 1979. Using 750 m resolution the tropopause is found to be within a few hundred meters of the tropopause determined from nearly simultaneous radiosonde observations and using 2.2 km resolution the tropopause is found to be within about 600 m. Furthermore, radar-determined tropopause heights can be automatically scaled from existing records, or even routinely determined on-line.

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R. R. Rogers
,
W. L. Ecklund
,
D. A. Carter
,
K. S. Gage
, and
S. A. Ethier

A small UHF radar wind profiler was operated over a 40-day period during the summer of 1990 at a site on the windward coast of the island of Hawaii. It provided continuous measurements of winds up to the height of the trade-wind inversion, which varied in altitude from about 2 to 4 km during the course of the experiments. The inversion was readily discernible in the data as an elevated layer of high reflectivity, caused by the sharp gradient of refractive index at that level. With a wavelength of 33 cm, the profiler has about the same sensitivity to light rain as to moderately reflective clear air. The data have provided unexpected information on rain development, wave motions on the inversion, sustained vertical air motions at low levels, and interactions between convection and the inversion echo. This paper gives examples of some of the observations, indicating the wide range of applications of boundary-layer profilers.

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B. B. Balsley
,
D. A. Carter
,
A. C. Riddle
,
W. L. Ecklund
, and
K. S. Gage

In this paper we provide a set of examples to demonstrate the potential of VHF radar wind profilers for studying tropical convection processes. Our examples were extracted from data obtained from the NOAA/CU Pacific Profiler Network, which has been in operation for a number of years and is currently being expanded.

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DA Carter
,
W.L. Ecklund
,
K.S. Gage
,
M. Spowart
,
H.L. Cole
,
W.F. Dabberdt
, and
J. Wilson

The Aeronomy Laboratory of the National Oceanic and Atmospheric Administration and the Atmospheric Technology Division of the National Center for Atmospheric Research are jointly developing Integrated Sounding Systems (ISS) for use in support of TOGA (Tropical Ocean Global Atmosphere) and TOGA COARE (Coupled Ocean–Atmosphere Response Experiment). Some of the ISS units will have to be operated on research ships during TOGA COARE's intensive observing period in late 1992 and early 1993. The greatest technical challenge in adapting the ISS to shipboard use is to stabilize the UHF wind profiler that is an integral part of the ISS. In June 1991 a UHF wind-profiling Doppler radar was installed on a stabilized platform aboard the NOAA research vessel Malcolm Baldrige on an eight-day cruise in the Atlantic Ocean. The wind profiler was gyrostabilized and profiler winds were corrected for ship motion utilizing the Global Positioning System. During the eight days at sea, CLASS (Cross-Chain LORAN Atmospheric Sounding System) and OMEGA Sounding System balloons were launched onboard ship for wind profile comparisons. Results of the comparisons show excellent agreement between wind profiles, with an rms difference of about 1 m s−1 in wind speed.

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B. E. Martner
,
D. B. Wuertz
,
B. B. Stankov
,
R. G. Strauch
,
E. R. Westwater
,
K. S. Gage
,
W. L. Ecklund
,
C. L. Martin
, and
W. F. Dabberdt

Several ground-based remote sensors were operated together in Colorado during February and March 1991 to obtain continuous profiles of the kinematic and thermodynamic structure of the atmosphere. Instrument performance is compared for five different wind profilers. Each was equipped with Radio Acoustic Sounding System (RASS) capability to measure virtual temperature. This was the first side-by-side comparison of all three of the most common wind-profiler frequencies: 50, 404, and 915 MHz. The 404-MHz system was a NOAA Wind Profiler Demonstration Network (WPDN) unit. Dual-frequency microwave radiometers that measured path-integrated water vapor and liquid water content were also evaluated. Frequent rawinsonde launches from the remote-sensor sites provided an extensive set of in situ measurements for comparison. The winter operations provide a severe test of the profiler/RASS capabilities because atmospheric scattering is relatively weak and acoustic attenuation is relatively strong in cold, dry conditions. Nevertheless, the lower-frequency systems exhibited impressive height coverage for wind and virtual temperature profiling, whereas the high-frequency units provided higher-resolution measurements near the surface. Comparisons between remote sensor and rawinsonde data generally showed excellent agreement. The results support more widespread use of these emerging technologies.

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Fiona J. Drummond
,
R. R. Rogers
,
S. A. Cohn
,
W. L. Ecklund
,
D. A. Carter
, and
J. S. Wilson

Abstract

The authors derive a relationship between the vertical Doppler spectrum of the rain just below the radar bright band and that of the snow just above. It neglects vertical air motions and assumes that each snowflake simply melts to form a raindrop of the same mass, disregarding other possible effects such as aggregation to form larger particles or breakup to create smaller ones. The relationship shows that, regardless of the dependence of particle fallspeed on size, the product of the equivalent reflectivity factor and the mean Doppler velocity of the snow is proportional to the same product for the rain, with a constant proportionality factor of 0.23, which equals the ratio of the dielectric factors of ice and water. Observed values of the reflectivity and mean Doppler velocity above and below the melting layer sometimes agree with this theoretical prediction but more often deviate from it in ways that may be interpreted as indicating the predominance of either aggregation or breakup processes. The data suggest that aggregation is occurring much of the time in the melting layer but that breakup effects become dominant in heavy precipitation. The analysis is extended by assuming relations between particle size and fallspeed for rain and snow. This enables the comparison of measured spectra with those derived theoretically. A simple allowance for aggregation or breakup in the spectral transformation from snow to rain is found to give improved spectral agreement in cases where these effects are indicated.

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K. S. Gage
,
J. R. Mcafee
,
W. L. Ecklund
,
D. A. Carter
,
C. R. Williams
,
P. E. Johnston
, and
A. C. Riddle

Abstract

After a decade of development, VHF wind profilers are being used for atmospheric research at several locations in the tropical Pacific. A prototype 50-MHz wind profiler was installed on Christmas Island in 1985 and has operated continuously since March 1986 to monitor tropical wind fields in the altitude range 1.8–1 8 km. This paper presents an overview of the Christmas Island wind profiler and reviews its performance. A survey of sample wind observations and a brief climatology of the observed winds are included.

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Madison J. Post
,
Christopher W. Fairall
,
Jack B. Snider
,
Yong Han
,
Allen B. White
,
Warner L. Ecklund
,
Klaus M. Weickmann
,
Patricia K. Quinn
,
Daniel I. Cooper
,
Steven M. Sekelsky
,
Robert E. McIntosh
,
Peter Minnett
, and
Robert O. Knuteson

Twelve national research organizations joined forces on a 30-day, 6800 n mi survey of the Central and Tropical Western Pacific on NOAA's Research Vessel Discoverer. The Combined Sensor Program (CSP), which began in American Samoa on 14 March 1996, visited Manus Island, Papua New Guinea, and ended in Hawaii on 13 April, used a unique combination of in situ, satellite, and remote sensors to better understand relationships between atmospheric and oceanic variables that affect radiative balance in this climatically important region. Besides continuously measuring both shortwave and longwave radiative fluxes, CSP instruments also measured most other factors affecting the radiative balance, including profiles of clouds (lidar and radar), aerosols (in situ and lidar), moisture (balloons, lidar, and radiometers), and sea surface temperature (thermometers and Fourier Transform Infrared Radiometers). Surface fluxes of heat, momentum, and moisture were also measured continuously. The Department of Energy's Atmospheric Radiation Measurement Program used the mission to validate similar measurements made at their CART site on Manus Island and to investigate the effect (if any) of large nearby landmasses on the island-based measurements.

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