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One proxy for global climate change is the change in the total mass of the Greenland and Antarctic ice sheets. Several complementary techniques have been used to estimate these changes with varying degrees of success. In this article, we describe a new approach that relies on the resonant behavior of ice masses. For very low electromagnetic (EM) frequencies (i.e., ≤2 kHz), pure ice acts like a strong dielectric resonator. Resonances can be excited in ice sheets by ambient EM noise from, for example, distant thunderstorms. The EM frequency spectrum measured in the vicinity of the ice mass should exhibit corresponding resonant frequencies. The evolution of the resonant modes over time can be used to monitor changes in ice mass and shape. The same approach can be, in principle, applied to monitor changes in the volume of fresh water reservoirs.

Observations of turbulence in the planetary boundary layer are critical for developing and evaluating boundary layer parameterizations in mesoscale numerical weather prediction models. These observations, however, are expensive and rarely profile the entire boundary layer. Using optimized configurations for 449 and 915 MHz wind profiling radars during the eXperimental Planetary boundary layer Instrumentation Assessment (XPIA), improvements have been made to the historical methods of measuring vertical velocity variance through the time series of vertical velocity, as well as the Doppler spectral width. Using six heights of sonic anemometers mounted on a 300 m tower, correlations of up to R2 = 0. 74 are seen in measurements of the large-scale variances from the radar time series and R2 = 0. 79 in measurements of small-scale variance from radar spectral widths. The total variance, measured as the sum of the small and large scales, agrees well with sonic anemometers, with R2 = 0. 79. Correlation is higher in daytime convective boundary layers than nighttime stable conditions when turbulence levels are smaller. With the good agreement with the in situ measurements, highly resolved profiles up to 2 km can be accurately observed from the 449 MHz radar and 1 km from the 915 MHz radar. This optimized configuration will provide unique observations for the verification and improvement to boundary layer parameterizations in mesoscale models.

Stratocumulus (Sc) clouds occur frequently over the cold waters of the southeastern Pacific Ocean. Data collected during two Pan American Climate Study research cruises in the tropical eastern Pacific illuminate many aspects of this Sc-topped marine boundary layer (MBL). Here the focus is on understanding gaps in detectable wind-profiler reflectivities during two boreal autumn cruises. After rigorous quality control that included applying the Riddle threshold of minimum signal-to-noise ratio (SNR) detectability, there are many instances with no measurable atmospheric signals through a depth of up to several hundred meters, often lasting for an hour or more. Rain gauge data from the autumn 2004 cruise are used to calibrate the profiler, which allows SNR to be converted to both equivalent reflectivity and the structure-function parameter of the index of refraction . Profiles of statistics from the two profiler modes (resolutions) highlight the wide range of during a 24-h period and bound the atmosphere’s when low-mode gaps are not mirrored in the high-mode data. Considering the gaps in terms of allows them to be understood as indications of reduced “top down” buoyancy processes and/or reduced turbulent intensity, both of which have been demonstrated by previous researchers to be associated with decoupling within the Sc-topped MBL. A decoupling index calculated from surface and ceilometer data strongly suggests that decoupled conditions were common and that the MBL was coupled when gaps in profiler reflectivity were unlikely. Further study of data from other cruises may lead to a method of using profiler reflectivity as an indicator of decoupled conditions.

An experiment combining wind profiler and polarimetric radar analyses of intense, but shallow, tropical thunderstorms has been performed. These storms are important as they are very common along many tropical coasts and islands and are sometimes the precursors to large intense multicellular storms such as occur over the Tiwi Islands north of Darwin, Australia. All the storms sampled had a similar structure, with intense updrafts on the periphery of the cells producing significant-sized hail and downdrafts in the storm center. The hail concentrations are relatively small, but have a large effect on the radar reflectivity and polarimetric measurands because of the size (10–20 mm). It is this hail melting that produces characteristic ZDR columns in the polarimetric radar data.

Comparisons of data taken by collocated Doppler wind profilers using 100-, 500-, and 1000-m pulse lengths show that the velocity profiles obtained with the longer pulses are displaced in height from contemporaneous profiles measured with the shorter pulses. These differences are larger than can be expected from random measurement errors. In addition, there is evidence that the 500-m pulse may underestimate the wind speed when compared with the 100-m pulse. The standard radar equation does not adequately account for the conditions under which observations are made. In particular, it assumes that atmospheric reflectivity is constant throughout the pulse volume and that observations can be assigned to the peak of the range-weighting function. However, observations from several tropical profilers show that reflectivity gradients with magnitudes greater than 10 dB km−1 are common. Here, a more general radar equation is used to simulate the radar response to the atmosphere. The simulation shows that at...

This paper describes the results of an experiment that combines the data from a 5-cm-wavelength polarimetric radar and multiple-frequency wind profilers to examine the polarimetric signatures associated with the microphysical structure of several relatively shallow thunderstorms and also to examine quantitative rainfall measurements made with the polarimetric radar. These shallow storms produce considerable amounts of centimeter-sized hail. The presence and size of this hail are deduced from the wind profiler data. The melting hail particles produce a distinctive polarimetric signature with large values of differential reflectivity ZDR and suppressed values of the correlation coefficient between the signals at horizontal and vertical polarization. Comparisons between the mass-weighted mean drop diameter and differential reflectivity have been performed and show reasonable agreement with theoretical expectations, although the observed ZDR are somewhat smaller than expected. This may be associated ...

Data collected during the Maritime Continent Thunderstorm Experiment (MCTEX) (10 November–10 December 1995) have been used to analyze boundary layer development and circulations over two almost flat, tropical islands. The two adjacent islands have a combined length of about 170 km from east to west and 70 km from north to south. Intense thunderstorms formed over these islands every day of the field campaign. The boundary layer depth, temperature, and circulation over the island have been measured over the full diurnal cycle using a multiple radar analysis combined with surface and radiosonde measurements. On average, the island boundary layer depth reaches 1.5 km by early to midafternoon coinciding with the development of the deep convection. Thus, the island boundary layer is significantly deeper than the typical tropical oceanic boundary layer. In the midafternoon, thunderstorm outflows and their associated cold pool stabilize the lower boundary layer, suppressing late convection. This is follo...

We show that the vertical polarization electric field (Ep) in the topside of the equatorial electrojet can be determined from the Doppler spectra of type-2 echoes obtained with a radar that is appropriately displaced in latitude from the magnetic dip equator. Using a 49.92 MHz radar on Christmas Island (2.9° magnetic dip latitude), we found unexpectedly large Ep at altitudes at least as high as 120 km over the dip equator. Another new and related finding is the transient appearance of type-1 echoes at 99 km over Christmas Island, which likely was produced by an Ep of at least 11 mV/m that must have appeared at 114 km altitude over the dip equator. Elevated electron temperatures inferred from the type-1 Doppler spectra are consistent with the presence of anomalous energetics.

Profilers operating in the UHF range are sensitive to both Bragg scattering from radio refractive index structure and to Rayleigh scattering from small point targets. Identification of the scattering process is critical for proper interpretation of these observations, especially the data collected from the vertical incident beam. This study evaluates the performance of Doppler velocity thresholds as a means to separate air motions from hydrometeor motions in vertical incident profiler observations. This evaluation consists of three different steps. First, using two collocated profilers operating at different frequencies, the observations are unambiguously identified as Bragg or Rayleigh scattering processes. Second, the observations are separated into either air or hydrometeor motion using only the data from one profiler. The third step quantitatively evaluates the performance of the single profiler separation techniques by counting the number of correct classifications and adjusting the count by...

First observations of meter-scale equatorial 150-km plasma irregularities outside the American longitude sector are reported. The observations conducted at Pohnpei (western Pacific) with a wind profiling ST radar demonstrate the feasibility of making ionospheric electric field measurements with low cost instruments and also reveal a potentially important anisotropy in the angular distribution of 150-km VHF radar echoes.

An experimental field campaign to measure synoptic-scale vertical velocities was conducted from 5 to 11 January 1991 in the Urbana-Champaign, Illinois, region, which is in very flat terrain far from mountains. Both the Flatland and the Urbana wind-profiling radars, which are separated by 23.1 km, participated in the campaign. Meteorological sounding balloons were also launched from the Flatland Observatory site. In this study, lime averages are compared of the vertical wind velocity measured directly by both radars in order to help verify the capability of wind-profiling radars to measure synoptic-scale vertical velocities. This comparison, of course, also provides an opportunity to evaluate the performance of both radars. The variance of the vertical velocity observed by the Flatland radar has been previously shown to be dominated by short-period fluctuations with most of the variance occurring at periods less than 6 h. Also, since March 1987 when the Flatland radar began operating nearly contin...

Nearly continuous observations of tropospheric wind at Christmas Island (2°N, 157°W) have been made since March 1986 using a VHF wind-profiling Doppler radar. The interannual zonal wind variations observed at this central Pacific location show a clear El Nino/Southern Oscillation (ENSO) signal with weaker than normal lower tropospheric easterlies and upper tropospheric westerlies during El Nino and stronger than normal lower tropospheric easterlies and upper tropospheric westerlies during La Nina. These dramatic changes in the tropospheric circulation over the central Pacific are related to variations in the zonal Walker Circulation, which in turn are associated with the Southern Oscillation. Observations recorded from 1986 to 1989 illustrate a complete ENSO cycle with the 1986–1987 El Nino followed by the 1988–1989 La Nina.

We describe the basic configuration of the Poker Flat, Alaska, MST (mesosphere-stratosphere-troposphere) radar currently under construction by NOAA's Aeronomy Laboratory. This 50-MHz coherent radar consists of a 4 × 104 m2 phased dipole array, a 6.4-MW peak power transmitter system (consisting of 64 separate 100-kW peak pulse power transmitter modules distributed throughout the array), and an on-line Doppler analysis/data recording system. With some limitations the system will be capable of measuring winds, waves, and turbulence throughout the 1- to 100-km height range. Data obtained from the portion of the Poker Flat system already in operation are presented and discussed.

A dual coherent 50 MHz auroral radar installed at Siple Station, Antarctica, continuously monitored echo intensity and mean-Doppler velocity from 29 December 1976 until late March 1978. We describe here the experimental technique and present some statistical results including yearly averaged echooccurrence patterns and irregularity drift velocity characteristics. Our results show that: 1. (1) the irregularity drifts are approximately westward (poleward electric fields) in the evening, and eastward (equatorward electric fields) in the morning following the electric field reversal in the region of the Harang discontinuity; 2. (2) the Harang discontinuity under disturbed conditions (average K p = 5 0 ) as seen by both radars is located around 2100–2300 MLT; 3. (3) the relationship between the irregularity drift velocity and the actual electron drift velocity is strongly dependent on the angle between the radar beam and the earth's magnetic field, as predicted by linear theory.

We describe initial results obtained during the first 60 days of continuous operation of the MST radar under construction at Poker Flat, Alaska. Tropospheric-stratospheric wind profiles obtained by the radar are compared with concurrent windsonde profiles. Mesospheric echoes between 57-72 km are observed during daytime periods of ionospheric absorption. Mesospheric winds obtained following a stratospheric warming show a more easterly component than winds measured somewhat later. The present system, which is three orders of magnitude less sensitive than the final system, is also capable of measuring ten day average winds between 83-95 km via meteor trail echoes.