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

Mathematical expressions have been constructed that allow the large-scale global convection characteristics of the high-latitude ionosphere to be reproduced. The model contains no discontinuities in the ion convection velocity and as such should be useful in F region chemical models. The number of variables in the model allow such features as the dayside throat and the Harang discontinuity to be modeled. The applicability of the model to magnetospheric physics is limited by the exclusion of large-magnitude small-scale flow features associated with discrete arcs and by the inability of the model to produce separate flow cells at the same local time.

A model of the high‐latitude ionospheric convection pattern

In this review we attempt to present a unified picture of transport in multispecies gas mixtures. To accomplish this task, it is necessary to outline the mathematical structure of the transport equations. Starting from Boltzmann's equation, we derive a general system of transport equations using an approach that is valid for flow situations in which there are large temperature and drift velocity differences between the interacting species. However, this system of equations, which is obtained by taking velocity moments of the Boltzmann equation, does not constitute a closed set, since the equation governing the velocity moment of order r contains the velocity moment of order r + 1. To close the system of transport equations, it is therefore necessary to adopt an approximate expression for the species velocity distribution function. For near-equilibrium flows, various levels of approximation are considered, including the 5-, 8-, 10-, 13-, and 20-moment approximations. The procedure for obtaining closed sets of transport equations for far-from-equilibrium flows is also discussed. When the transport equations are ordered with respect to the collisional mean free path, the result is the Euler, Navier-Stokes, or extended Navier-Stokes equations depending upon whether terms proportional to the zeroth, first, or second power of the mean free path are retained. For a collisionless plasma the analogous expansion using the Larmor radius yields the Chew-Goldberger-Low (CGL) equations to zeroth order and the extended CGL equations to first order.

Mathematical structure of transport equations for multispecies flows

A self-consistent kinetic model is developed to study dc flowing glow discharges in N/sub 2//O/sub 2/ mixtures. This model includes the calculation of electron energy distribution functions and electron rate coefficients coupled with detailed vibrational kinetics of N/sub 2/ molecules, chemical kinetics taking into account a large set of neutral, excited and charged species, interaction of N and O atoms at the discharge tube wall, and the thermal balance of the discharge. The results of this model agree reasonably well with the measurements of the electronic density, the gas temperature, the reduced electric field, the vibrational temperature of N/sub 2/ and the concentration of O, N atoms, NO molecules, N/sub 2/(C), N/sub 2//sup +/(B), and NO(/spl gamma/) excited states. The comparison was performed in a N/sub 2/-O/sub 2/ discharge at pressure p=2 Torr, for discharge currents I=15, 30, and 80 mA, a flow rate Q=100 sccm, and O/sub 2/ percentages ranging from 0 up to 100%,. >

Kinetic model of a low-pressure N/sub 2/-O/sub 2/ flowing glow discharge

Twelve electron-acceleration mechanisms and 10 generator mechanisms for auroral arcs are examined, and a characteristic auroral-arc thickness is worked out for each mechanism except one. The arc thicknesses are then mapped down to the ionosphere along the terrestrial magnetic-field lines; near the Earth, a dipole magnetic-field model is used, and farther from the Earth, the mapping includes the effects of magnetic-field-line draping. The 21 theoretical models all predict auroral-arc thicknesses that are at least an order of magnitude wider than the optically observed arcs. As an alternative explanation of the observed narrow auroral arcs, the acceleration of ionospheric electrons to produce airglow in electrical discharge mechanisms appears improbable. Also unsuccessfully explored is the possibility that the observed narrow auroral arcs are caused by interference effects when Alfven waves reflect off the ionosphere. Suggestions are made for future ground-based auroral-arc measurements.

Auroral arc thicknesses as predicted by various theories

With the incoherent scatter facility at Chatanika, Alaska, we have measured electron temperatures of up to 1200/sup 0/K near 110-km altitude in the polar E region in the presence of strong electric fields. No classical heat process can account for these high temperatures, which are clearly correlated with the dc electric field strength. We show that the enhancement is most probably caused by the unstable plasma waves known to exist in the disturbed polar E region.

Anomalous heating of the polar E region by unstable plasma waves 1. Observations

The rate coefficient of a chemical reaction is given by the equation k = ∫0∞ συ f(υ) dυ, where σ is an energy dependent cross section, υ is the relative speed of the reactants, and f(υ) is the relative speed distribution. For certain highly energy dependent ionospheric reactions, k is controlled by the population in the high-energy tail of the relative speed distribution. This leads to problems in the application of laboratory measurements of rate coefficients to the atmosphere where f(υ) can be significantly different for the same effective temperature. However, we show that the rate coefficients in the laboratory and in the thermosphere are approximately the same for the same value of the mean energy parameter KEcm if a thermal equilibrium apparatus such as a static or flowing afterglow system is used in the laboratory. The rate coefficients are in general not the same in the atmosphere as in drift tube experiments, although for O+ in a helium buffer the difference is about 25% or less. As an application of the present work we derive new expressions for the rate coefficients of O+ reacting with N2, O2, and NO in the ionosphere, using cross sections published by laboratory workers.

Nonthermal rate coefficients in the ionosphere: The reactions of O+ with N2, O2, and NO

Calculations based on simultaneous observations of the electric field magnitude, and individual measurements of ion drift velocity and particle precipitation, over the lifetime of the AE-C satellite, are used to determine high latitude Joule heating. Conductivities produced by an averaged seasonal illumination were included with those calculated from particle precipitation. It is found that high latitude Joule heating occurs in an approximately oval pattern, and consists of dayside cleft, dawn and dusk sunward convection, and night sector heating regions. On average, heating in the cleft and dawn-dusk regions contributes the largest heat input, and there is no apparent difference between hemispheres for similar seasons. Joule heat input is 50 percent greater in summer than in winter, due primarily to the greater conductivity caused by solar production.

Joule heating at high latitudes

Observations of strongly enhanced ion acoustic shoulders of the incoherent scatter spectrum at 933 MHz at altitudes from 138 to 587 km have been obtained with the European Incoherent Scatter UHF radar. The enhancements can be up to 1 or 2 orders of magnitude in total backscattered power and can occur at either one or both of the ion acoustic shoulders. They show a variation of frequency with height of about 2 to 1, the same as the normal ion line spectral width and the ion temperature. These unusual spectra appear in two preferred height regions having different characteristics, one below 200 km and one above about 300 km. The enhancements are associated with geomagnetic disturbance, high electron temperatures, auroral arcs, and red aurora in the F region. The observations, which are mainly along the magnetic field direction, indicate that field-aligned thermal electron drifts are destabilizing the ion acoustic waves. They confirm and extend the one other publication reporting on similar echoes. We suggest that field-aligned flows of soft electrons depositing their energy at horizontally poor conducting F region heights are the cause of parallel electric fields in the ionosphere. These fields then produce the thermal electron motions that we argue have to be the cause of the observations.

Naturally enhanced ion acoustic waves in the auroral ionosphere observed with the EISCAT 933‐MHz radar

It is found that anomalous electron temperatures in the disturbed high-latitude E region can be quantitatively explained in terms of heating by unstable plasma waves. The electron temperatures at 110 km have been measured to be as high as 1500 K instead of the expected value of about 300 K. It is shown that by using quasi-linear theory there is an ample source of heat in the unstable waves and that the measured electron temperature profiles have a shape very similar to what is expected from plasma wave heating by the modified two-stream instability. It is found that there is even more heating going to the ion gas, but that the resulting effect on the ion temperature may be difficult to measure. The best estimate of the wave heating rates leads to the conclusion that wave heating can be as much as 50% of the Joule heating for dc electric field strengths of the order of 45 mV/m or greater.

J.-P. St.-Maurice

Papers

Anomalous heating of the polar E region by unstable plasma waves 1. Observations

Nonthermal rate coefficients in the ionosphere: The reactions of O+ with N2, O2, and NO

Joule heating at high latitudes

Naturally enhanced ion acoustic waves in the auroral ionosphere observed with the EISCAT 933‐MHz radar

Anomalous heating of the polar E region by unstable plasma waves - 2. Theory