W. L. Ecklund

Developments in UHF lower tropospheric wind profiling at NOAA's Aeronomy Laboratory

Developments in UHF profiling at 915 MHz are presented. Recent advances in UHF profiling are traced to early developments beginning about 8 years ago in the Aeronomy Laboratory at 915 MHz using microstrip antennas. This paper presents an overview of the architecture of the UHF profiler system as it has evolved over the past decade including the development of radio acoustic sounding system (RASS) capabilities. Hardware and software components are described and operational performance is summarized from experience gained from many installations, primarily from those in the tropics. Applications to wind profiling, boundary layer height determination, flux measurement, and precipitation profiling are considered.

A UHF Wind Profiler for the Boundary Layer: Brief Description and Initial Results

Abstract In this paper we describe a boundary layer radar recently developed at NOAAs 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.

Long-Term Mean Vertical Motion over the Tropical Pacific: Wind-Profiling Doppler Radar Measurements

Measurement from Christmas Island (2�N, 157�W) of long-term mean vertical motions in the tropical atmosphere using very-high-frequency wind-profiling Doppler radar show that there is a transition from downward motion in the free troposphere to upward motion in the upper troposphere and lower stratosphere. The observations in the free troposphere are consistent with a balance between adiabatic and diabatic heating and cooling rates in a clear atmosphere. Comparison of the results at Christmas Island during El Ni�o and non-El Ni�o conditions with earlier results obtained for stratiform rain conditions over Pohnpei, Federated States of Micronesia, show that cirrus clouds in the vicinity of the tropopause likely play an important role in determining the sense and magnitude of vertical motions in this region. These results have implications for the exchange of mass between the troposphere and stratosphere over the tropics.

Temperature sounding by RASS with wind profiler radars: a preliminary study

The radio acoustic sounding system (RASS) is a method of remotely measuring atmospheric temperature profiles by combining acoustic and radar techniques. This method has been applied to wind profiler radars in Colorado, and excellent performance in both height coverage and accuracy has been obtained. Various acoustic source functions are examined, and it is shown that FM-CW acoustic signals are less susceptible to error than pulsed acoustic systems when using pulsed radars for RASS. The remotely determined temperature profiles are compared with co-located radiosonde soundings, and good agreement is found. >

Wind profiler‐related research in the tropical Pacific

This paper is concerned with the application of wind-profiling Doppler radar technology to tropical atmospheric research. Examples of the use of wind profilers in the tropics are drawn from the Aeronomy Laboratorys wind profilers located on Pohnpei, Micronesia (7°N, 158°E), and Christmas Island (2°N, 157°W). The Pohnpei wind profiler was constructed in 1984 and has been used exclusively to observe vertical motions. The Christmas Island wind profiler has observed horizontal and vertical velocities routinely since 1986. These two wind profilers form part of a planned trans-Pacific network of wind-profiling radars that will eventually span the tropical Pacific.

Combined use of 50 MHz and 915 MHz wind profilers in the estimation of raindrop size distributions

To estimate raindrop size distributions aloft, we fit a theoretical Doppler spectrum of a model drop size distribution to observed Doppler power spectra measured by a 915 MHz profiler, while using concurrent information supplied by a 50 MHz profiler to correct for vertical winds. While several assumptions have been made in deriving the theoretical Doppler spectrum, model derived rainfall rates compare favorably with locally measured rainfall rates obtained from rain gauge estimates.

Continuous measurement of upper atmospheric winds and turbulence using a VHF Doppler radar: preliminary results

Abstract We report here preliminary results of a VHF radar experiment designed to monitor atmospheric winds and turbulence continuously over periods of many days. The radar system used in this experiment is a prototype of a much larger system under development and uses an average transmitted power of about 200 W and a 100 m × 100 m dipole array. With this system it is possible to observe winds and turbulence parameters regularly to about 19 km using a height resolution of 2.2 km. Similar results are reported for mesospheric heights between about 73 km and 82 km.

A 3-GHz Profiler for Precipitating Cloud Studies

Abstract A 3-GHz profiler has been developed by the National Oceanic and Atmospheric Administration’s Aeronomy Laboratory to observe the evolution and vertical structure of precipitating cloud systems. The profiler is very portable, robust, and relatively inexpensive, so that continuous, unattended observations of overhead precipitation can be obtained, even at remote locations. The new profiler is a vertically looking Doppler radar that operates at S band, a commonly used band for scanning weather radars (e.g., WSR-88D). The profiler has many features in common with the 915-MHz profiler developed at the Aeronomy Laboratory during the past decade primarily for measurement of lower-tropospheric winds in the Tropics. This paper presents a description of the new profiler and evaluates it in the field in Illinois and Australia in comparison with UHF lower-tropospheric profilers. In Illinois, the new profiler was evaluated alongside a collocated 915-MHz profiler at the Flatland Atmospheric Observatory. In Aust...

Wind profiler observations of Tropical Storm Flo at Saipan

Abstract Wind profiler and serial sounding observations extending to the upper troposphere are used to analyze Tropical Storm Flo (1990) as it passed within 115 km of the experimental site on Saipan. These data resolve details of the circulation and precipitation structure of the storm and its rainbands. Analysis of principal and secondary rainbands in outer radii indicate that there are considerable similarities with previous studies. Although the bands contained distinct precipitation maxima, there is no evidence of active convection and the mean structure is similar to that observed in the stratiform regions of squall lines. The vertical circulations in the rainbands are weak and complex, but distinct azimuthal wind maxima are observed that have maxima of relative vorticity and inertial stability on the inner edge. The divergence fields for the entire analysis period are strongly coherent and are indicative of vertically propagating gravity waves generated in the near inertially neutral outflow layer. ...

Fast type-I waves in the equatorial electrojet: Evidence for nonisothermal ion-acoustic speeds in the lower E region

[1] There is plenty of evidence to suggest that the phase velocity of large amplitude irregularities produced by the modified two-stream and the gradient-drift instabilities are the same as the threshold speed, namely, the nominal ion-acoustic speed in the modified two-stream case. In this context, it is rather puzzling to note that the phase velocity of type-I waves in the equatorial electrojet is known to easily exceed 400 m/s during strong electrojet conditions. This is puzzling because the ion-acoustic speed of the medium is expected to be 100 m/s slower than these observations. Explaining the observations as an increase in the nominal ion-acoustic speed through much higher neutral temperatures than expected or through electron heating by plasma waves is problematic at best. The first explanation violates everything we know about the neutral atmospheric temperature near the mesopause, while in the latter case, we only have to recall the emerging view that electron heating is done, at high latitudes, by parallel wave fields and that there is no evidence for the existence of such fields in the equatorial case. By contrast, we show that, contrary to what is normally assumed, electron thermal fluctuations cannot be neglected in the theoretical treatment of the instability when the ion collision frequency becomes large compared to the wave frequency and the wave aspect angle is small. These electron thermal fluctuations are caused by electron adiabatic heating and cooling effects related to the wave dynamics. When the electron thermal fluctuations are included in the calculations the derived instability threshold speeds match the upper limit reached by the observations. The increase becomes detectable at 108 km altitude and increases rapidly with decreasing altitude to become roughly 1.5 times as large as the isothermal ion-acoustic speed below 100 km altitude. We show in this paper that the new threshold speed provided by the nonisothermal threshold calculations provides an excellent match for the largest vertical type-I phase speeds that were observed during a very strong daytime electrojet event.