SuperDARN HF Radars Research Articles

Transient production of F-region irregularities associated with TCV passage

Abstract. Transient production of F-region plasma irregularities due to traveling convection vortices (TCVs) was investigated using the Super Dual Auroral Radar Network (SuperDARN) combined with ground magnetometer networks and the POLAR ultraviolet imager. We selected two large-amplitude (100–200 nT) TCV events that occurred on 22 May 1996 and 24 July 1996. It is found that the TCV-associated HF backscatter arises in blobs with spatial scale of a few hundreds km. They traveled following tailward bulk motion of the TCV across the three fields-of-view of the SuperDARN HF radars in the prenoon sector. The spectra in the blobs showed unidirectional Doppler velocities of typically 400–600 m/s, with flow directions away from the radar. These unidirectional velocities correspond to the poleward and/or eastward convective flow near the leading edge of upward field-aligned current. The backscatter blobs overlapped the poleward and westward part of the TCV-related transient aurora. It is likely that the transient backscatter blobs are produced by the three-dimensional gradient drift instabilities in the three-dimensional current system of the TCV. In this case, nonlinear rapid evolution of irregularities would occur in the upward field-aligned current region. The spectral width of the backscatter blob is typically distributed between 50 and 300 m/s, but sometimes it is over 400 m/s. This suggests that the temporal broad spectra over 400 m/s are produced by Pc1–2 bursts, while the background spectral width of 50–300 m/s are produced by the velocity gradient structure of convection vortices themselves.Key words. Ionosphere (Electric fields and currents; Ionospheric irregularities; Plasma convection)

Variations in the polar cap area during two substorm cycles

Abstract. This study employs observations from several sources to determine the location of the polar cap boundary, or open/closed field line boundary, at all local times, allowing the amount of open flux in the magnetosphere to be quantified. These data sources include global auroral images from the Ultraviolet Imager (UVI) instrument on board the Polar spacecraft, SuperDARN HF radar measurements of the convection flow, and low altitude particle measurements from Defense Meteorological Satellite Program (DMSP) and National Oceanographic and Atmospheric Administration (NOAA) satellites, and the Fast Auroral SnapshoT (FAST) spacecraft. Changes in the open flux content of the magnetosphere are related to the rate of magnetic reconnection occurring at the magnetopause and in the magnetotail, allowing us to estimate the day- and nightside reconnection voltages during two substorm cycles. Specifically, increases in the polar cap area are found to be consistent with open flux being created when the IMF is oriented southwards and low-latitude magnetopause reconnection is ongoing, and decreases in area correspond to open flux being destroyed at substorm breakup. The polar cap area can continue to decrease for 100 min following the onset of substorm breakup, continuing even after substorm-associated auroral features have died away. An estimate of the dayside reconnection voltage, determined from plasma drift measurements in the ionosphere, indicates that reconnection can take place at all local times along the dayside portion of the polar cap boundary, and hence presumably across the majority of the dayside magnetopause. The observation of ionospheric signatures of bursty reconnection over a wide extent of local times supports this finding.Key words. Ionosphere (plasma convection; polar ionosphere) – Magnetospheric physics (magnetospheric configuration and dynamics)

A technique for accurately determining the cusp-region polar cap boundary using SuperDARN HF radar measurements

Abstract. Accurately measuring the location and motion of the polar cap boundary (PCB) in the high-latitude ionosphere can be crucial for studies concerned with the dynamics of the polar cap, e.g. the measurement of reconnection rates. The Doppler spectral width characteristics of backscatter received by the SuperDARN HF radars have been previously used for locating and tracking the PCB in the cusp region. The boundary is generally observed in meridional beams of the SuperDARN radars and appears as a distinct change between low spectral width values observed equatorward of the cusp region, and high, but variable spectral width values observed within the cusp region. To identify the spectral width boundary (SWB) between these two regions, a simple algorithm employing a spectral width threshold has often been applied to the data. However, there is not, as yet, a standard algorithm, or spectral width threshold, which is universally applied. Nor has there been any rigorous assessment of the accuracy of this method of boundary determination. This study applies a series of threshold algorithms to a simulated cusp-region spectral width data set, to assess the accuracy of different algorithms. This shows that simple threshold algorithms correctly identify the boundary location in, at the most, 50% of the cases and that the average boundary error is at least ~ 1–2 range gates (~ 1° latitude). It transpires that spatial and temporal smoothing of the spectral width data (e.g. by median filtering), before application of a threshold algorithm can increase the boundary determination accuracy to over 95% and the average boundary error to much less than a range gate. However, this is sometimes at the cost of temporal resolution in the motion of the boundary location. The algorithms are also applied to a year’s worth of spectral width data from the cusp ionosphere, measured by the Halley SuperDARN radar in Antarctica. This analysis highlights the increased accuracy of the enhanced boundary determination algorithm in the cusp region. Away from the cusp, the resulting SWB locations are often dependent on the choice of threshold. This suggests that there is not a sharp latitudinal SWB in regions of the dayside ionosphere away from the cusp, but that there is a shallower latitudinal gradient in spectral width near the boundary location.Key words. Ionosphere (instruments and techniques) – Magnetospheric physics (magnetopause, cusp and boundary layers; magnetosphere-ionosphere interactions)

Finland HF and Esrange MST radar observations of polar mesosphere summer echoes

Abstract. Peculiar near range echoes observed in summer with the SuperDARN HF radar in Finland are presented. The echoes were detected at four frequencies of 9, 11, 13 and 15 MHz at slant ranges of 105–250 km for about 100 min. Interferometer measurements indicate that the echoes are returned from 80–100 km altitudes with elevation angles of 20°–60°. Echo power (< 16 dB), Doppler velocity (between –30 and + 30 ms-1) and spectral width (< 60 ms-1) fluctuate with periods of several to 20 min, perhaps due to short–period atmospheric gravity waves. When the HF radar detected the echoes, a vertical incidence MST radar, located at Esrange in Sweden (650 km north of the HF radar site), observed polar mesosphere summer echoes (PMSE) at altitudes of 80–90 km. This fact suggests that the near range HF echoes are PMSE at HF band, although both radars did not probe a common volume. With increasing radar frequency, HF echo ranges are closer to the radar site and echo power becomes weaker. Possible mechanisms to explain these features are discussed.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; thermospheric dynamics; waves and tides; instruments and techniques)

Characterization of frequency effect in SuperDARN spectral width distributions

This study investigates the frequency dependence of spectral width distributions observed by the SuperDARN HF radars. The evolution of spectral width values with range is shown to be dependent on the operating radar frequency. First, this evolution is clearly pointed out using a multifrequency scanning mode. This study is then generalized and this effect is shown to affect the whole SuperDARN spectral width data set. Several studies are performed in order to determine the dependence of this effect upon season, beam orientation and mean radar orientation.

Ionospheric signatures of split reconnection X‐lines during conditions of IMF Bz < 0 and |By| ∼ |Bz|: Evidence for the antiparallel merging hypothesis

We present measurements of the convection electric field in the dayside ionosphere during extended intervals when the interplanetary magnetic field (IMF) has a negative Bz component and a significant By component (|By| ∼ |Bz|). Under these conditions, distinct differences in the ionospheric projection of the magnetopause reconnection X‐line are predicted by the antiparallel and subsolar merging hypotheses. Close to solstice, in the winter hemisphere the antiparallel merging hypothesis predicts two ionospheric merging lines which are significantly separated either side of noon. This prediction is not expected from any subsolar merging hypothesis (e.g., component merging). Using the method of global convection mapping with line‐of‐sight velocity data from the SuperDARN HF radar network, we present evidence of two distinct merging regions on the dayside magnetopause under these IMF and seasonal conditions. The two merging regions manifest themselves in the ionosphere as two regions of convection flow with a strong poleward component separated by a region of convection flow with either a weak poleward or equatorward component corresponding to an adiaroic portion of the polar cap boundary. The spatiotemporal nature of the actual convection scenario can be complicated, but the predicted pattern represents a recurring feature of the convection electric field under these IMF and seasonal conditions. These observations lend support to the hypothesis that antiparallel merging is the dominant form of magnetopause reconnection during these steady state IMF intervals. This suggests that the magnetic shear between magnetosheath and magnetospheric magnetic field lines plays the major role in determining the location of reconnection on the dayside magnetopause.

Propagation in the ionosphere of convection changes following a sharp interplanetary magnetic field By transition

The nature of the response of the ionospheric convection to changes in the interplanetary magnetic field (IMF), either quasi‐simultaneous over the polar cap and auroral region or propagating with the flow velocity from the noon sector, remains to be understood. We examine the changes in the ionospheric plasma convection associated with a negative to positive transition in the dawn‐dusk component (By) of the IMF. A special mode of operation of the SuperDARN HF radars has been used, which provided both a large field of view and high‐resolution convection data on three beams. Close to noon, the most characteristic response concerns the position in magnetic local time (MLT) of the merging gap, the ionospheric footprint of the magnetopause reconnection line, which moves longitudinally with a velocity of 1 km/s. In addition, modifications of the convection, which are indirectly related to this motion, are observed. We attribute them to the “quasi‐instantaneous” effect related to the incompressibility of the plasma. Far from noon, in the morning sector, the convection reacts with an intermediate delay, which is neither instantaneous nor compatible with the above propagation velocity. A timing of the transition, based on the IMP 8 and Geotail satellites, located on the dawn flank of the magnetosphere and at the nose of the magnetopause, respectively, indicates that the ionospheric perturbation originates at the impact site of the By transition close to 1300 MLT, with a maximum delay of 3 min after it hits the nose of the magnetopause.

Ionospheric response to the interplanetary magnetic field southward turning: Fast onset and slow reconfiguration

This paper presents a case study of ionospheric response to an interplanetary magnetic field (IMF) southward turning. It is based on a comprehensive set of observations, including a global network of ground magnetometers, global auroral images, and a SuperDARN HF radar. There is a clear evidence for a two‐stage ionospheric response to the IMF southward turning, namely, fast initial onset and slow final reconfiguration. The fast onset is manifested by nearly simultaneous (within 2 min) rise of ground magnetic perturbations at all local times, corroborated by a sudden change in the direction of line‐of‐sight velocity near local midnight and by the simultaneous equatorward shift of the auroral oval. The slow reconfiguration is characterized by the different rising rate of magnetic perturbations with latitudes: faster at high latitude than at lower latitudes. Furthermore, a cross‐correlation analysis of the magnetometer data shows that the maximum magnetic perturbation is reached first near local noon, and then spread toward the nightside, corresponding to a dayside‐to‐nightside propagation speed of ∼5 km/s along the auroral oval. Global ionospheric convection patterns are derived based on ground magnetometer data along with auroral conductances inferred from the Polar UV images, using the assimilative mapping of ionospheric electrodynamics (AMIE) procedure. The AMIE patterns, especially the residual convection patterns, clearly show a globally coherent development of two‐cell convection configuration following the IMF southward turning. While the foci of the convection patterns remain nearly steady, the convection flow does intensify with time and the cross‐polar‐cap potential drop increases. The overall changes as shown in the AMIE convection patterns therefore are fully consistent with the two‐stage ionospheric response to the IMF southward turning.

Strong sunward propagating flow bursts in the night sector during quiet solar wind conditions: SuperDARN and satellite observations

Abstract. High-time resolution data from the two Iceland SuperDARN HF radars show very strong nightside convection activity during a prolonged period of low geomagnetic activity and northward interplanetary magnetic field (IMF). Flows bursts with velocities ranging from 0.8 to 1.7 km/s are observed to propagate in the sunward direction with phase velocities up to 1.5 km/s. These bursts occur over several hours of MLT in the 20:00–01:00 MLT sector, in the evening-side sunward convection. Data from a simultaneous DMSP pass and POLAR UVI images show a very contracted polar cap and extended regions of auroral particle precipitation from the magnetospheric boundaries. A DMSP pass over the Iceland-West field-of-view while one of these sporadic bursts of enhanced flow is observed, indicates that the flow bursts appear within the plasma sheet and at its outward edge, which excludes Kelvin-Helmholtz instabilities at the magnetopause boundary as the generation mechanism. In the nightside region, the precipitation is more spot-like and the convection organizes itself as clockwise U-shaped structures. We interpret these flow bursts as the convective transport following plasma injection events from the tail into the night-side ionosphere. We show that during this period, where the IMF clock angle is around 70°, the dayside magnetosphere is not completely closed.Key words. Ionosphere (Auroral ionosphere; Ionospheremagnetosphere interactions; Particle precipitation)

Noon ionospheric signatures of a sudden commencement following a solar wind pressure pulse

Abstract. Using experimental data from the Cutlass Super-DARN HF radars and from a subset of ground magnetometers of the IMAGE Scandinavian chain, the response of the ionosphere in the noon sector to a solar wind pressure increase is studied. The emphasis is on the signature of the convection vortices and of the Hall currents that are associated with the pair of opposite parallel currents flowing along the morning and afternoon high-latitude magnetic field lines. We show that the sudden commencement is characterised by an equatorward convection, immediately followed (within less than 3 min) by a strong poleward plasma motion. These results are shown to agree qualitatively with the global model of sudden commencement of Araki (1994).Key words. Ionosphere (plasma convection; electric fields and currents) – Magnetospheric physics (solar wind-magnetosphere interactions)

An unusual geometry of the ionospheric signature of the cusp: implications for magnetopause merging sites

Abstract. The HF radar Doppler spectral width boundary (SWB) in the cusp represents a very good proxy for the equatorward edge of cusp ion precipitation in the dayside ionosphere. For intervals where the Interplanetary Magnetic Field (IMF) has a southward component (Bz < 0), the SWB is typically displaced poleward of the actual location of the open-closed field line boundary (or polar cap boundary, PCB). This is due to the poleward motion of newly-reconnected magnetic field lines during the cusp ion travel time from the reconnection X-line to the ionosphere. This paper presents observations of the dayside ionosphere from SuperDARN HF radars in Antarctica during an extended interval ( ~ 12 h) of quasi-steady IMF conditions (By ~ Bz < 0). The observations show a quasi-stationary feature in the SWB in the morning sector close to magnetic local noon which takes the form of a 2° poleward distortion of the boundary. We suggest that two separate reconnection sites exist on the magnetopause at this time, as predicted by the anti-parallel merging hypothesis for these IMF conditions. The observed cusp geometry is a consequence of different ion travel times from the reconnection X-lines to the southern ionosphere on either side of magnetic local noon. These observations provide strong evidence to support the anti-parallel merging hypothesis. This work also shows that mesoscale and small-scale structure in the SWB cannot always be interpreted as reflecting structure in the dayside PCB. Localised variations in the convection flow across the merging gap, or in the ion travel time from the reconnection X-line to the ionosphere, can lead to localised variations in the offset of the SWB from the PCB. These caveats should also be considered when working with other proxies for the dayside PCB which are associated with cusp particle precipitation, such as the 630 nm cusp auroral emission.Key words. Ionosphere (plasma convection) – Magnetospheric physics (magnetopause, cusp, and boundary layers) – Space plasma physics (magnetic reconnection)

Ion acoustic HF radar echoes at high latitudes and far ranges

Using data taken over 18 months with the Iceland East (CUT‐LASS/Iceland) Super Dual Auroral Radar Network (SuperDARN) HF radar we have made a statistical study of a class of echoes which occur at ranges typically associated with F region echoes, but which have Doppler speeds near the ion acoustic speed Cs typical of E region echoes [Milan et al., 1997]. Comparison of the seasonal, diurnal, and range distributions of these echoes with the predictions of propagation models show that these are, indeed, E region echoes, differing in morphology from similar echoes at nearer ranges mainly because of the propagation conditions which are required to observe them. For the particular radar geometry of this study, conventional theory predicts that the effects of ionospheric gradients will result in phase velocities (radar Doppler velocities) which differ significantly from Cs. in disagreement with these observations. However, the observations are consistent with a new nonlinear theory of St.‐Maurice and Hamza [2001].

The dayside ultraviolet aurora and convection responses to a southward turning of the interplanetary magnetic field

Abstract. We examine the large-scale ultraviolet aurora and convection responses to a series of flux transfer events that immediately followed a sharp and isolated southward turning of the IMF. During the interval of interest, SuperDARN was monitoring the plasma convection in the dayside northern ionosphere, while the VIS Earth Camera and the Far Ul-traviolet Imager (UVI) were monitoring the northern hemisphere’s ultraviolet aurora. Reconnection signatures were seen in the SuperDARN HF radar data in the postnoon sector following a sharp southward turning of the IMF. The presence of flux transfer events is supported by measurements of a classic dispersed ion signature in the low-altitude cusp from the DMSP spacecraft. Subsequent to the onset of reconnection, the postnoon convection and ultraviolet aurora expanded in concert, reaching 18 MLT in half an hour. The auroral oval was found to move equatorward at the convection speed in the 16–18 MLT sector, implying that it was related directly to an adiaroic magnetospheric boundary. In the present study, we have estimated the field-aligned current response to magnetic reconnection in terms of the vorticity of the ionospheric plasma convection velocity. The convection velocities were obtained using two methods: (a) direct reconstruction of the full vector velocities from bistatic measurements of the convection by the SuperDARN HF radars in a relatively small region of the auroral zone, and (b) from global-scale spherical harmonic fits to the SuperDARN velocities deduced from the map potential model. Regions of high vorticity, which were predicted to be an estimate of a component of the total field-aligned current, agree extremely well with the images of the dayside UV aurora, indicating that, in this case, the plasma vorticity is an excellent estimator of the morphology of dayside field-aligned currents (FACs). The morphology of the aurora and ionospheric electric field in the postnoon sector supports the existence of a dayside current wedge induced in response to dayside reconnection.Key words. Magnetospheric physics (auroral phenomena; magnetosphere-ionosphere interactions; solar wind magne-tosphere interactions)

Super Dual Auroral Radar Network observations of fluctuations in the spectral distribution of near range meteor echoes in the upper mesosphere and lower thermosphere

Abstract. The Doppler shifts of meteor echoes measured by the SuperDARN HF radar network have been used in several studies to observe neutral winds in the upper mesosphere and lower thermosphere region. In the absence of accurate height information for individual meteors, it has been necessary to assume a statistical mean meteor layer where the variations in altitude were not correlated to changes in the horizontal winds. Observations of spectral width distribution variations made by the radars allow an independent determination of the systematic error in the height. We have investigated the dependence of this distribution on a number of factors including the radar geometry, diurnal and seasonal cycles, variations in solar UV irradiance and geomagnetic activity. Changes in the altitude of the mean meteor layer observed at different radar ranges provide us with some insight into the structure of the upper mesosphere and the lower thermosphere within which the meteors are being ablated. An examination of the spectral widths, as measured by the CUT-LASS Finland radar, in the days preceding and following a Storm Sudden Commencement in April 1997, illustrates how the spectral properties of the observed region can be affected. The variations in the widths were consistent with model calculations of the changes to the temperature profile over this interval. Further refinements in the determination of the spectral width are outlined for future experiments.Key words. Meterology and atmospheric dynamics (middle atmosphere dynamics; thermospheric dynamics; instruments and techniques)

On the altitude dependence of the spectral characteristics of decametre-wavelength E region backscatter and the relationship with optical auroral forms

Abstract. Observations of E region backscatter by the Ice-land East SuperDARN HF radar from the 30 minute period 2330 to 2400 UT on 13 September 1999 are presented, along with simultaneous observations of auroral luminosity from two all-sky cameras. Interferometric techniques are employed to estimate the altitude of origin of each echo observed by the radar. Under investigation is a region of backscatter which is L-shell aligned and exists in a region of low auroral luminosity bounded to the north and the south by two auroral arcs. The spectral characteristics of the backscatter fall into three main populations: broad, low Doppler shift spectra; narrow, high Doppler shift spectra; and exceptionally narrow, low Doppler shift spectra. The first two populations are similar to type II and type I spectra observed with VHF radars, respectively. These populations scatter from near the peak of the E region. The high Doppler shift population appears to exist in a region of sub-critical electric field. The third population originates below the E region peak at altitudes between 80 and 100 km. We argue that a non-coherent scattering process is responsible for this backscatter.Key words. Ionosphere (auroral ionosphere; ionospheric irregularities)

Flow transients in the postnoon ionosphere: The role of solar wind dynamic pressure

Super Dual Auroral Radar Network (SuperDARN) HF radar, magnetometer, and satellite data are used to study ionospheric convection flow bursts in the sunward return flow in the 1200–1500 MLT auroral region. A comparison between the latitudinal position of the flow bursts and the position of the open/closed field line boundary shows that the sunward bursts occur on closed field lines. The bursts occur simultaneously with poleward motions of the convection reversal boundary. Decreases in the solar wind dynamic pressure are shown to correlate well with the flow bursts. Comparison of radar arid magnetometer data shows that these observations can be explained in terms of the global current model proposed for sudden expansions of the rnagnetosphere [Araki and Nagano, 1988]. The sunward flow bursts are shown to be consistent with the high‐latitude dusk to dawn electric field predicted by the model during pressure decreases.

On determining the noon polar cap boundary from SuperDARN HF radar backscatter characteristics

Previous work has shown that ionospheric HF radar backscatter in the noon sector can be used to locate the footprint of the magnetospheric cusp particle precipitation. This has enabled the radar data to be used as a proxy for the location of the polar cap boundary, and hence measure the flow of plasma across it to derive the reconnection electric field in the ionosphere. This work used only single radar data sets with a field of view limited to ~2 h of local time. In this case study using four of the SuperDARN radars, we examine the boundary determined over 6 h of magnetic local time around the noon sector and its relationship to the convection pattern. The variation with longitude of the latitude of the radar scatter with cusp characteristics shows a bay-like feature. It is shown that this feature is shaped by the variation with longitude of the poleward flow component of the ionospheric plasma and may be understood in terms of cusp ion time-of-flight effects. Using this interpretation, we derive the time-of-flight of the cusp ions and find that it is consistent with approximately 1 keV ions injected from a subsolar reconnection site. A method for deriving a more accurate estimate of the location of the open-closed field line boundary from HF radar data is described.Key words: Ionosphere (ionosphere–magnetosphere interactions; plasma convection) · Magnetospheric physics (magnetopause · cusp · and boundary layers)

The response of the HF radar spectral width boundary to a switch in the IMF By direction: Ionospheric consequences of transient dayside reconnection?

In the high‐latitude dayside ionosphere, the movement of the HF radar spectral width boundary (SWB) provides a good proxy for the movement of the open‐closed field line boundary around magnetic local noon. By studying the dynamics of the spectral width boundary we can investigate features of the dayside ionospheric response to changes in the interplanetary magnetic field (IMF). The high temporal and spatial resolution of the Super Dual Auroral Radar Network (SuperDARN) HF radars make them good tools to study these features. In this paper, we use the Halley HF radar in Antarctica to study the equatorward motion of the SWB which appears to occur in response to a large change in the direction of IMF By. The spectral width boundary initially moves equatorward in the form of a U‐shaped bulge close to magnetic local noon. This bulge then expands longitudinally to earlier and later magnetic local times. Merged velocity vectors from two Antarctic HF radars describe the flow velocity variation in the boundary region. The flow equatorward of the boundary follows the contours of the boundary as it expands. The flow poleward of the boundary is directed at more oblique angles to the boundary. This study represents the first clear two‐dimensional observation of the formation of an equatorward bulge on the polar cap boundary which may be associated with changes in dayside reconnection and presents a unique observation of the variation of the ionospheric flow in the locality of the boundary. We discuss the possible interpretations of this event and its consequences to our present understanding of the ionospheric response to changes in the IMF.

On determining the noon polar cap boundary from SuperDARN HF radar backscatter characteristics

Abstract. Previous work has shown that ionospheric HF radar backscatter in the noon sector can be used to locate the footprint of the magnetospheric cusp particle precipitation. This has enabled the radar data to be used as a proxy for the location of the polar cap boundary, and hence measure the flow of plasma across it to derive the reconnection electric field in the ionosphere. This work used only single radar data sets with a field of view limited to ~2 h of local time. In this case study using four of the SuperDARN radars, we examine the boundary determined over 6 h of magnetic local time around the noon sector and its relationship to the convection pattern. The variation with longitude of the latitude of the radar scatter with cusp characteristics shows a bay-like feature. It is shown that this feature is shaped by the variation with longitude of the poleward flow component of the ionospheric plasma and may be understood in terms of cusp ion time-of-flight effects. Using this interpretation, we derive the time-of-flight of the cusp ions and find that it is consistent with approximately 1 keV ions injected from a subsolar reconnection site. A method for deriving a more accurate estimate of the location of the open-closed field line boundary from HF radar data is described.Key words: Ionosphere (ionosphere–magnetosphere interactions; plasma convection) · Magnetospheric physics (magnetopause · cusp · and boundary layers)

Electrostatic potential patterns in the high‐latitude ionosphere constrained by SuperDARN measurements

The recent addition of two radars to the existing network of six Super Dual Auroral Radar Network (SuperDARN) HF radars in the Northern Hemisphere has significantly extended the area in the high latitude where measurements of convecting ionospheric plasma are made. We show that the distribution of the electrostatic potential Φ associated with the “E × B” drift of ionospheric plasma can be reliably mapped on global scales when velocity measurments provide sufficient coverage. The global convection maps, or the equivalent electrostatic potential maps, are solved using an established technique of fitting velocity data to an expansion of Φ in terms of spherical harmonic functions. When the measurements are extensive, and especially when they span the region between the extrema in the potential distribution, the solution for the global pattern becomes insensitive to the choice of statistical model data used to constrain the fitting. That is, the statistical model data then only guide the solution in regions where no measurements are available, and the details of the model data have little effect on the gross features of the large‐scale convection patterns. The resulting total potential variation across the polar cap, ΦPC, is virtually independent of the statistical model. The ability to accurately determine ΦPC and the global potential Φ on the basis of direct measurements is an important step in understanding solar wind‐magnetosphere‐ionosphere coupling.