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Warner L. Ecklund

Bio: Warner L. Ecklund is an academic researcher from Cooperative Institute for Research in Environmental Sciences. The author has contributed to research in topics: Radar & Wind profiler. The author has an hindex of 39, co-authored 97 publications receiving 4525 citations. Previous affiliations of Warner L. Ecklund include University of Colorado Boulder & National Oceanic and Atmospheric Administration.


Papers
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Journal ArticleDOI
TL;DR: In this article, the authors summarize the results of 22 months of observations of Arctic mesosphere echoes with the 50-MHz radar at Poker Flat, Alaska and conclude that during summer months the mesospheric echoes are relatively continuous in time and extend from about 80 to 100 km with an unexpectedly strong peak in signal-to-noise ratio at about 85 km.
Abstract: In this report we summarize the results of 22 months of observations of Arctic mesosphere echoes with the 50-MHz radar at Poker Flat, Alaska. Operation with a partially complete system began in February 1979 and has continued on a nearly continuous basis to the present time. The altitude range of the mesospheric echoes obtained during this period shows a pronounced seasonal variation. During summer months the mesospheric echoes are relatively continuous in time and extend from about 80 to 100 km with an unexpectedly strong peak in signal-to-noise ratio at about 85 km. In contrast, in nonsummer months, mesospheric echoes are less intense and occur at lower altitudes in the range from 55 to 80 km. These lower-altitude nonsummer echoes are observed primarily during daytime hours when energetic auroral particle precipitation (as determined by the Poker Flat 30-MHz riometer) is present.

350 citations

Journal ArticleDOI
TL;DR: 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 is presented in this paper.
Abstract: 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.

217 citations

Journal ArticleDOI
TL;DR: In this paper, an algorithm was developed that classifies precipitating clouds into either stratiform, mixed stratiform/convective, deep convective, or shallow convective clouds by analyzing the vertical structure of reflectivity, velocity, and spectral width derived from measurements made with the vertical beam of a 915-MHz Doppler wind profiler.
Abstract: An algorithm has been developed that classifies precipitating clouds into either stratiform, mixed stratiform/convective, deep convective, or shallow convective clouds by analyzing the vertical structure of reflectivity, velocity, and spectral width derived from measurements made with the vertical beam of a 915-MHz Doppler wind profiler. The precipitating clouds classified as stratiform and convective clouds match the physical and radar properties deduced by Doppler weather radars in the GATE and EMEX programs. The mixed stratiform/convective cloud category is a hybrid regime containing a melting-layer signature associated with stratiform clouds yet is turbulent above the melting level similar to convective clouds. Shallow convective clouds have hydrometeors confined entirely below the melting level implying that warm rain processes are occurring exclusively. The algorithm is illustrated by classifying precipitating clouds from 10 months of observations at Manus Island (2°S, 147°E) in the western...

209 citations

Journal ArticleDOI
TL;DR: In this paper, a boundary layer radar was developed at NOAA's Aeronomy Laboratory for use in a hybrid mode with existing 50 MHz profilers in the tropical Pacific, and the system can equally be a stand-alone device to study boundary layer problems.
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.

205 citations

Journal ArticleDOI
TL;DR: In this article, a Rayleigh-Taylor gravitational instability operating on the bottom side of the F peak is explained for strong radar echoes typically observed in patch-like structures at high altitudes.
Abstract: Recent rocket probe, barium cloud and radar measurements conducted during equatorial spread F conditions are interpreted in terms of a Rayleigh-Taylor gravitational instability operating on the bottomside of the F peak. The persistent theoretical problems associated with strong radar echoes typically observed in patch-like structures at high altitudes are explained in terms of regions of depleted plasma density which buoyantly rise against the gravitational field.

186 citations


Cited by
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Journal ArticleDOI
TL;DR: The role of wave-induced forces in the extratropical overworld is discussed in this paper, where the authors focus on the role of waves and eddies in the overworld overworld and show that the global exchange rate is determined by details of near-tropopause phenomena such as penetrative cumulus convection or small-scale mixing associated with upper level fronts and cyclones.
Abstract: In the past, studies of stratosphere-troposphere exchange of mass and chemical species have mainly emphasized the synoptic- and small-scale mechanisms of exchange This review, however, includes also the global-scale aspects of exchange, such as the transport across an isentropic surface (potential temperature about 380 K) that in the tropics lies just above the tropopause, near the 100-hPa pressure level Such a surface divides the stratosphere into an “overworld” and an extratropical “lowermost stratosphere” that for transport purposes need to be sharply distinguished This approach places stratosphere-troposphere exchange in the framework of the general circulation and helps to clarify the roles of the different mechanisms involved and the interplay between large and small scales The role of waves and eddies in the extratropical overworld is emphasized There, wave-induced forces drive a kind of global-scale extratropical “fluid-dynamical suction pump,” which withdraws air upward and poleward from the tropical lower stratosphere and pushes it poleward and downward into the extratropical troposphere The resulting global-scale circulation drives the stratosphere away from radiative equilibrium conditions Wave-induced forces may be considered to exert a nonlocal control, mainly downward in the extratropics but reaching laterally into the tropics, over the transport of mass across lower stratospheric isentropic surfaces This mass transport is for many purposes a useful measure of global-scale stratosphere-troposphere exchange, especially on seasonal or longer timescales Because the strongest wave-induced forces occur in the northern hemisphere winter season, the exchange rate is also a maximum at that season The global exchange rate is not determined by details of near-tropopause phenomena such as penetrative cumulus convection or small-scale mixing associated with upper level fronts and cyclones These smaller-scale processes must be considered, however, in order to understand the finer details of exchange Moist convection appears to play an important role in the tropics in accounting for the extreme dehydration of air entering the stratosphere Stratospheric air finds its way back into the troposphere through a vast variety of irreversible eddy exchange phenomena, including tropopause folding and the formation of so-called tropical upper tropospheric troughs and consequent irreversible exchange General circulation models are able to simulate the mean global-scale mass exchange and its seasonal cycle but are not able to properly resolve the tropical dehydration process Two-dimensional (height-latitude) models commonly used for assessment of human impact on the ozone layer include representation of stratosphere-troposphere exchange that is adequate to allow reasonable simulation of photochemical processes occurring in the overworld However, for assessing changes in the lowermost stratosphere, the strong longitudinal asymmetries in stratosphere-troposphere exchange render current two-dimensional models inadequate Either current transport parameterizations must be improved, or else, more likely, such changes can be adequately assessed only by three-dimensional models

2,342 citations

Journal ArticleDOI
TL;DR: In this article, the effects of mean winds and gravity waves on the mean momentum budget were investigated and it was shown that the existence of critical levels in the mesosphere significantly limits the ability of gravity waves to generate turbulence.
Abstract: It has been suggested (Lindzen, 1967, 1968a, b; Lindzen and Blake, 1971; Hodges, 1969) that turbulence in the upper mesosphere arises from the unstable breakdown of tides and gravity waves. Crudely speaking, it was expected that sufficient turbulence would be generated to prevent the growth of wave amplitude with height (roughly as (basic pressure)−1/2). This work has been extended to allow for the generation of turbulence by smaller amplitude waves, the effects of mean winds on the waves, and the effects of the waves on the mean momentum budget. The effects of mean winds, while of relatively small importance for tides, are crucial for internal gravity waves originating in the troposphere. Winds in the troposphere and stratosphere sharply limit the phase speeds of waves capable of reaching the upper mesosphere. In addition, the existence of critical levels in the mesosphere significantly limits the ability of gravity waves to generate turbulence, while the breakdown of gravity waves contributes to the development of critical levels. The results of the present study suggest that at middle latitudes in winter, eddy coefficients may peak at relatively low altitudes (50 km) and at higher altitudes in summer and during sudden warmings (70–80 km), and decrease with height rather sharply above these levels. Rocket observations are used to estimate momentum deposition by gravity waves. Accelerations of about 100 m/s/day are suggested. Such accelerations are entirely capable of producing the warm winter and cold summer mesopauses.

1,967 citations

Journal ArticleDOI
TL;DR: CloudSat as discussed by the authors is a satellite experiment designed to measure the vertical structure of clouds from space, and once launched, CloudSat will orbit in formation as part of a constellation of satellites (the A-Train) that includes NASA's Aqua and Aura satellites, a NASA-CNES lidar satellite (CALIPSO), and a CNES satellite carrying a polarimeter (PARASOL).
Abstract: CloudSat is a satellite experiment designed to measure the vertical structure of clouds from space. The expected launch of CloudSat is planned for 2004, and once launched, CloudSat will orbit in formation as part of a constellation of satellites (the A-Train) that includes NASA's Aqua and Aura satellites, a NASA–CNES lidar satellite (CALIPSO), and a CNES satellite carrying a polarimeter (PARASOL). A unique feature that CloudSat brings to this constellation is the ability to fly a precise orbit enabling the fields of view of the CloudSat radar to be overlapped with the CALIPSO lidar footprint and the other measurements of the constellation. The precision and near simultaneity of this overlap creates a unique multisatellite observing system for studying the atmospheric processes essential to the hydrological cycle. The vertical profiles of cloud properties provided by CloudSat on the global scale fill a critical gap in the investigation of feedback mechanisms linking clouds to climate. Measuring these profi...

1,929 citations

Journal ArticleDOI
TL;DR: The largest convective clouds are mesoscale convective systems, which account for a large portion of Earth's cloud cover and precipitation, and the patterns of wind and weather associated with mesoscales are important local phenomena that often must be forecast on short timescales.
Abstract: The largest convective clouds are mesoscale convective systems, which account for a large portion of Earth's cloud cover and precipitation, and the patterns of wind and weather associated with mesoscale convective systems are important local phenomena that often must be forecast on short timescales. They often produce floods. Mesoscale convective systems are generally much larger than the individual cumulonimbus and lines of cumulonimbus discussed in Chapter 8 . They develop circulations on the mesoscale, which are larger in scale than the updrafts and downdrafts of individual cumulonimbus clouds. The mesoscale circulations produce large regions of stratiform (nimbostratus) precipitation of the type discussed in Chapter 6 . Often the stratiform precipitation regions trail a squall line consisting of convective cells, and a mesoscale convective vortex tends to form in the stratiform region. The heating profile in the stratiform region is positive at upper levels and negative at lower levels due to evaporation and melting of the precipitation particles. The dynamics of mesoscale circulations involve a joint adjustment to the wind shear and thermodynamic stratification of the large scale environment. Gravity-wave dynamics also contribute to the maintenance of mesoscale convective systems. This chapter reviews both the observed structure of mesoscale systems and their unique dynamics.

1,151 citations

Journal ArticleDOI
TL;DR: The Dual Auroral Radar Network (DARN) is a global-scale network of HF and VHF radars capable of sensing backscatter from ionospheric irregularities in the E and F-regions of the high-latitude ionosphere as mentioned in this paper.
Abstract: The Dual Auroral Radar Network (DARN) is a global-scale network of HF and VHF radars capable of sensing backscatter from ionospheric irregularities in the E and F-regions of the high-latitude ionosphere. Currently, the network consists of the STARE VHF radar system in northern Scandinavia, a northern-hemisphere, longitudinal chain of HF radars that is funded to extend from Saskatoon, Canada to central Finland, and a southern-hemisphere chain that is funded to include Halley Station, SANAE and Syowa Station in Antarctica. When all of the HF radars have been completed they will operate in pairs with common viewing areas so that the Doppler information contained in the backscattered signals may be combined to yield maps of high-latitude plasma convection and the convection electric field. In this paper, the evolution of DARN and particularly the development of its SuperDARN HF radar element is discussed. The DARN/SupperDARN network is particularly suited to studies of large-scale dynamical processes in the magnetosphere-ionosphere system, such as the evolution of the global configuration of the convection electric field under changing IMF conditions and the development and global extent of large-scale MHD waves in the magnetosphere-ionosphere cavity. A description of the HF radars within SuperDARN is given along with an overview of their existing and intended locations, intended start of operations, Principal Investigators, and sponsoring agencies. Finally, the operation of the DARN experiment within ISTP/GGS, the availability of data, and the form and availability of the Key Parameter files is discussed.

1,051 citations