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D. A. Carter and B. B. Balsley

Abstract

Results of an analysis of the summertime wind field between 80–93 km over Poker Flat, Alaska are presented. The data were obtained using the large, but as yet incomplete, MST radar at Poker Flat, and cover the periods 17 June–13 July 1979, and 22 June–22 July 1980. Zonal and meridional mean wind profiles and “tidal” components during these periods are examined and are compared with other observations at comparable latitudes as well as with current theoretical profiles. While our results agree reasonably closely with other observations and theory, some discrepancies exist and are discussed. In addition to the expected 8, 12 and 24 h components of atmospheric motions, we find strong evidence for a 16 h component, particularly during the 1979 data period. In addition, we show examples of the average power spectrum of wind fluctuations from 3 min to 8 days. These spectra not only show the expected “tidal” peaks, but show also that the spectral energy density is continuous between the shortest (8 h) tidal period and the shortest observed period (3 min), falling off with an f −5/3 power law. Some aspects of these spectral results are discussed, including the possible processes that may operate to produce such a spectral shape.

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J. Carter Ohlmann, David A. Siegel, and Curtis D. Mobley

Abstract

Radiative transfer calculations are used to quantify the effects of physical and biological processes on variations in the transmission of solar radiation through the upper ocean. Results indicate that net irradiance at 10 cm and 5 m can vary by 23 and 34 W m−2, respectively, due to changes in the chlorophyll concentration, cloud amount, and solar zenith angle (when normalized to a climatological surface irradiance of 200 W m−2). Chlorophyll influences solar attenuation in the visible wavebands, and thus has little effect on transmission within the uppermost meter where the quantity of near-infrared energy is substantial. Beneath the top few meters, a chlorophyll increase from 0.03 to 0.3 mg m−3 can result in a solar flux decrease of more than 10 W m−2. Clouds alter the spectral composition of the incident irradiance by preferentially attenuating in the near-infrared region, and serve to increase solar transmission in the upper few meters as a greater portion of the irradiance exists in the deep-penetrating, visible wavebands. A 50% reduction in the incident irradiance by clouds causes a near 60% reduction in the radiant heating rate for the top 10 cm of the ocean. Solar zenith angle influences transmission during clear sky periods through changes in sea-surface albedo. This study provides necessary information for improved physically and biologically based solar transmission parameterizations that will enhance upper ocean modeling efforts and sea-surface temperature prediction.

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

Abstract

In this paper we describe a boundary layer radar recently developed at NOAA's Aeronomy Laboratory. This radar extends wind profiler technology by using a small, relatively inexpensive radar to provide continuous, high-resolution wind measurements in the first few kilometers of the atmosphere. Although the radar was developed for use in a “hybrid” mode with existing 50 MHz profilers in the tropical Pacific, the system can equally well be a stand-alone device to study boundary layer problems.

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

Abstract

Wind profilers are radars that operate in the VHF and UHF hands and are designed for detecting the weak echoes reflected by the optically clear atmosphere. An unexpected application of wind profilers has been the revival of an old method of estimating drop size distributions in rain from the Doppler spectrum of the received signal. Originally attempted with radars operating at microwave frequency, the method showed early promise but was seriously limited in application because of the crucial sensitivity of the estimated drop sizes to the vertical air velocity, a quantity generally unknown and, at that time, unmeasurable. Profilers have solved this problem through their ability to measure, under appropriate conditions, both air motions and drop motions. This paper compares the drop sizes measured by a UHF profiler at two altitudes in a shower with those measured simultaneously by an instrumented airplane. The agreement is satisfactory, lending support to this new application of wind profilers.

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

Abstract

Average vertical profiles of the vertical wind obtained under clear sky conditions as weal as under conditions of both light-to-moderate and heavy rainfall am presented from data obtained using a radar wind profiler located on the island of Pohnpei (latitude 7°N, longitude 157°E). The average profiles for the precipitation conditions were obtained, insofar as possible, under conditions similar to those present within the stratiform and convective regions of tropical mesoscale convective complexes. Comparison between the vertical wind profiles obtained from the wind profiler and vertical wind profiles obtained earlier by wore conventional methods (i.e., deduced from the convergence-divergence of mesoscale horizontal winds) shows that, while the general features of the profiles obtained by both techniques are similar, the profiler results exhibit somewhat more detail. The profiler is able to resolve long-term average vertical motions down to the, ∼cm s−1 subsidence that occurs under clear air conditions. Additional evidence for an apparent difference between vertical wind profiles in the Atlantic and Pacific regions in heavy convection reported earlier, is presented.

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Wayne M. Angevine, S. K. Avery, W. L. Ecklund, and D. A. Carter

Abstract

A 915-MHz boundary-layer wind profiler radar with radio acoustic sounding system (RASS) capability has been used to measure the turbulent fluxes of heat and momentum in the convective boundary layer by eddy correlation. The diurnal variation of the heat flux at several heights between 160 and 500 m above ground level and values of the momentum flux for 2-h periods in midday from 160 to 1000 m are presented, as well as wind and temperature data. The momentum flux is calculated both from the clear-air velocities and from the RASS velocities, and the two results are compared.

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Robert Schafer, Susan K. Avery, Kenneth S. Gage, Paul E. Johnston, and D. A. Carter

Abstract

A method is presented that increases the detectability of weak clear-air signals by averaging Doppler spectra from coplanar wind profiler beams. The method, called coplanar spectral averaging (CSA), is applied to both simulated wind profiler spectra and to 1 yr of archived spectra from a UHF profiler at Christmas Island (1 October 1999–30 September 2000). A collocated 50-MHz wind profiler provides a truth for evaluating the CSA technique.

In the absence of precipitation, it was found that CSA, when combined with a fuzzy logic quality control, increases the height coverage of the 1-hourly averaged UHF profiler winds by over 600 m (two range gates). CSA also increased the number of good wind estimates at each observation range by about 10%–25% over the standard consensus method.

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