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  • Author or Editor: A. C. Riddle x
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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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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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Anthony C. Riddle
,
Leslie M. Hartten
,
David A. Carter
,
Paul E. Johnston
, and
Christopher R. Williams

Abstract

One limiting factor in atmospheric radar observations is the inability to distinguish the often weak atmospheric signals from fluctuations of the noise. This study presents a minimum threshold of usability, SNRmin, for signal-to-noise ratios obtained from wind profiling radars. The basic form arises from theoretical considerations of radar noise; the final form includes empirical modifications based on radar observations. While SNRmin was originally developed using data from the 50-MHz profiler at Poker Flat, Alaska, it works well with data collected from a wide range of locations, frequencies, and parameter settings. It provides an objective criterion to accept or reject individual spectra, can be quickly applied to a large quantity of data, and has a false-alarm rate of approximately 0.1%. While this threshold’s form depends on the methods used to calculate SNR and spectral moments, variations of the threshold could be developed for use with data processed by other methods.

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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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J. M. Wilczak
,
R. G. Strauch
,
F. M. Ralph
,
B. L. Weber
,
D. A. Merritt
,
J. R. Jordan
,
D. E. Wolfe
,
L. K. Lewis
,
D. B. Wuertz
,
J. E. Gaynor
,
S. A. McLaughlin
,
R. R. Rogers
,
A. C. Riddle
, and
T. S. Dye

Abstract

Winds measured with 915- and 404-MHz wind profilers are frequently found to have nonrandom errors as large as 15 m s−1 when compared to simultaneously measured rawinsonde winds. Detailed studies of these errors which occur only at night below about 4 km in altitude and have a pronounced seasonal pattern, indicate that they are due to the wind profilers' detection of migrating songbirds (passerines). Characteristics of contaminated data at various stages of data processing are described, including raw time series, individual spectra, averaged spectra, 30- or 60-s moments, 3- or 6-min winds, and hourly averaged winds. An automated technique for the rejection of contaminated data in historical datasets, based on thresholding high values of rnoment-level reflectivity and spectral width, is shown to be effective. Techniques designed for future wind profiter data acquisition systems are described that show promise for rejecting bird echoes, with the additional capability of being able to retrieve the true wind velocity in many instances. Finally, characteristics of bird migration revealed by wind profilers are described, including statistics of the spring (March–May) 1993 migration season determined from the 404-MHz Wind Profiler Demonstration Network (WPDN). During that time, contamination of moment data occurred on 43% of the nights monitored.

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