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.

DARN/SUPERDARN : A global view of the dynamics of high-latitude convection

The Super Dual Auroral Radar Network (SuperDARN) has been operating as an international co-operative organization for over 10 years. The network has now grown so that the fields of view of its 18 radars cover the majority of the northern and southern hemisphere polar ionospheres. SuperDARN has been successful in addressing a wide range of scientific questions concerning processes in the magnetosphere, ionosphere, thermosphere, and mesosphere, as well as general plasma physics questions. We commence this paper with a historical introduction to SuperDARN. Following this, we review the science performed by SuperDARN over the last 10 years covering the areas of ionospheric convection, field-aligned currents, magnetic reconnection, substorms, MHD waves, the neutral atmosphere, and E-region ionospheric irregularities. In addition, we provide an up-to-date description of the current network, as well as the analysis techniques available for use with the data from the radars. We conclude the paper with a discussion of the future of SuperDARN, its expansion, and new science opportunities.

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A decade of the Super Dual Auroral Radar Network (SuperDARN): scientific achievements, new techniques and future directions

Studying magnetically conjugate phenomena at very high latitudes requires a magnetic coordinate system that is smooth and well defined at the geographic poles In addition, it should provide for accurate comparisons at different altitudes In this report the authors present a variation on the corrected geomagnetic coordinate system that is well defined and smooth over the entire globe It provides an analytic expression relating geographic coordinates, including altitude, to the magnetic coordinates The coordinate system is produced by tracing magnetic field lines using the IGRF85 reference magnetic field model with time derivatives updating the model to 1988 An expansion of the relationship in terms of spherical harmonics has been determined, which then provides the required well-defined and smooth relationship over the entire globe Independent expansions for different altitudes show a smooth functional relationship of the coefficients of the expansion with altitude, and therefore simple interpolation schemes can be used to provide an appropriate expansion at any altitude between 0 km and approximately 600 km By reversing the process, the inverse expansions relating the magnetic coordinates to geographic coordinates have also been determined The effects of the seasonal variation in the Sun's declination along with the variation in the Sun's declinationmore » along with the variation in the Sun's apparent position due to the eccentricity of the Earth's orbit result in a variation of nearly 1 hour of magnetic local time for a fixed UT over the course of a year In many applications this variation may be important and should be included when presenting data in terms of magnetic latitude and MLT« less

A new magnetic coordinate system for conjugate studies at high latitudes

The HF radars of the Super Dual Auroral Radar Network (SuperDARN) provide measurements of the E × B drift of ionospheric plasma over extended regions of the high-latitude ionosphere. With the recent augmentation of the northern hemisphere component to six radars, a sizable fraction of the entire convection zone (approximately one-third) can be imaged nearly instantaneously (∼2 min). To date, the two-dimensional convection velocity has been mapped by combining line-of-sight velocity measurements obtained from pairs of radars within common-volume areas. We describe a new method of deriving large-scale convection maps based on all the available velocity data. The measurements are used to determine a solution for the distribution of electrostatic potential, Φ, expressed as a series expansion in spherical harmonics. The addition of data from a statistical model constrains the solution in regions of no data coverage. For low-order expansions the results provide a gross characterization of the global convection. We discuss the processing of the radar velocity data, the factors that condition the fitting, and the reliability of the results. We present examples of imaging that demonstrate the response of the global convection to variations in the interplanetary magnetic field (IMF). In the case of a sudden polarity change from northward to southward IMF, the convection is seen to reconfigure globally on very short (<6 min) timescales.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/98JA01288

Large-scale imaging of high-latitude convection with Super Dual Auroral Radar Network HF radar observations

The most intense, F region irregularities in the high-latitude ionosphere appear to be produced by convective plasma processes and in particular, by the fluid (gradient drift) interchange instability. Such irregularities are produced by convectively mixing plasma across a mean plasma density gradient with the transport of higher-density plasma into regions of lower-density plasma (and vice versa) leading to the development of an irregularity spectrum that extends in scale from about 10 km down to the ion gyroradius. The mean plasma density gradient that must be present to allow irregularity production by this interchange process appears to be associated with larger-scale (>10 km) plasma structure produced by other means. Because much of the recent progress on this research topic stems from this recognition, a significant portion of this review is dedicated to a description of the characteristics and processes of 10-km plasma structure and their relationships to those of smaller-scale irregularities. From this review, we synthesize a descriptive model of plasma structures in the high-latitude F layer that unifies most of the diverse and independent observations. For the large-scale plasma processes, the model includes (1) the formation of 1000-km-scale “patches” in the polar cap from solar-produced plasma that is transported poleward from lower latitudes; (2) the reconfiguration of patches as they convect into the auroral region and become the latitudinally confined, but longitudinally extended, plasma density enhancements near the equatorward auroral boundary; and (3) the production of localized enhancements and depletions along the poleward auroral boundary by soft-particle precipitation and large but localized electric fields. In the model, the most intense, smaller-scale irregularities are in spatial proximity to these large-scale plasma features, the implication being that the presence of the latter allows formation of the former. The irregularity characteristics are consistent with production by the instability and a morphology controlled by (1) a “slip” velocity (i.e., plasma drift relative to the neutral gas) that is moderately small except in regions of nonuniform plasma convection or under time-varying conditions (e.g., substorms, pulsation events) and (2) a highly conducting auroral E layer that damps irregularity growth and enhances decay. The final irregularity spectrum appears to be produced by (1) global convective processes acting on solar-produced plasma at the largest scales (>50 km), (2) particle precipitation at scales greater than 10 km, (3) perhaps some form of wave activity around 10 km, and (4) the instability at the smaller scales (<10 km).

High-Latitude F-Region Irregularities: A Review and Synthesis

Since October 1983, a new coherent backscatter radar has been in operation at Goose Bay, Labrador, for the purpose of studying small-scale electron density structure in the high-latitude ionosphere This radar operates over a frequency band that extends from 8 to 20 MHz, and it uses an electronically phased array of 16 log-periodic antennas for both transmission and reception The radar transmits a seven-pulse pattern that enables one to determine 17-lag complex autocorrelation functions of the backscattered signals as a function of range and azimuth In this paper we present a complete description of the radar including explanations of the operation of the phasing matrix, the techniques of data acquisition and analysis as implemented in the radar microcomputer, and the possible on-line and automatic operating modes that may be instituted We also present examples of some of the initial results that we have obtained with the radar during the afternoon and late evening hours These examples include images of the two-dimensional distribution of small-scale structure and of their associated mean Doppler motion We also present examples of F region Doppler spectra derived from the complex autocorrelation functions These Doppler spectra show interesting differences from those of high-latitude E region irregularities

An HF phased‐array radar for studying small‐scale structure in the high‐latitude ionosphere

Several methods developed for mapping high-latitude plasma convection with a high-latitude HF radar are described, which utilize coherent backscatter from electron density irregularities at F-region altitudes to observe convective plasma motion. Several examples of two-dimensional convection-velocity maps are presented, showing instances of L-shell-aligned flow in the dusk sector, the reversal of convection near magnetic midnight, and counterstreaming in the dayside cleft.

Mapping high-latitude plasma convection with coherent HF radars

According to the theory of collective wave scattering by a non-uniform plasma, the fluid motion spectrum can be either the Gaussian Doppler spectrum due to velocity dispersion, or a Lorentzian spectrum when the scattering wavelength becomes longer than the correlation length of velocity fluctuations. These two types of Doppler spectra are present in data from the SHERPA HF coherent radar, which detects 8 to 20-m wavelength density fluctuations in the high-latitude ionosphere. Most autocorrelation functions are best fitted to an exponential shape, corresponding to a Lorentzian Doppler spectrum. Nevertheless, the fit is sometimes better for a Gaussian shape. Each of the two spectral shapes is related to values of the local ionospheric parameters. We present preliminary measurements of the correlation time and correlation length of the waves, and concluding remarks on the significance of spectral widths for geophysical studies

Interpretation of HF radar ionospheric Doppler spectra by collective wave scattering theory

A large number of Doppler spectra obtained at six HF frequencies in the E region with the SHERPA HF radar are analyzed statistically. They are characterized by their total power, their mean velocity and their spectral width. The observations cover geomagnetic conditions varying from quiet to disturbed. Due to the location of the auroral oval relative to the radar field of view, echoes are preferentially detected in the morning westward electrojet, with radial velocities away from the radar. This results in an asymmetrical velocity distribution. Both usual Type 1 and Type 2 Doppler spectra, associated with two-stream and gradient-drift waves, respectively, are at the origin of the two peaks in the distribution. Other spectral types do not appear in the statistics. Spectral widths remain narrow for both types. This is explained by a longer lifetime of wave trains compared to higher frequency waves detected by VHF radars. A decrease of the Doppler velocity with radar frequency is related to gradient effects on threshold, as predicted by the linear dispersion equation for the two-stream instability

C. Hanuise

Papers

DARN/SUPERDARN : A global view of the dynamics of high-latitude convection

An HF phased‐array radar for studying small‐scale structure in the high‐latitude ionosphere

Mapping high-latitude plasma convection with coherent HF radars

Interpretation of HF radar ionospheric Doppler spectra by collective wave scattering theory

Statistical study of high-latitude E-region Doppler spectra obtained with the SHERPA HF radar