Evidence for Solar-production as a Source of Polar-cap Plasma

The focus of the study is a region of enhanced ionospheric densities observed by the EISCAT Svalbard radar in the polar F-region near local magnetic noon under conditions of IMF B z <0. Multi-instrument observations, using optical, spacecraft and radar instrumentation, together with radio tomographic imaging, have been used to identify the source of the enhancement and establish the background ionospheric conditions. Soft-particle precipitation was ruled out as a candidate for the production. Tomographic observations identified a latitudinally restricted region of enhanced densities at sub-auroral latitudes, distinct from the normal mid-latitude ionosphere, which was likely to be the source. The evidence suggested that the increased sub-auroral densities were photoionisation produced at the equatorward edge of the afternoon high-latitude cell, where the plasma is exposed to sunlight for an extended period as it flows slowly sunward toward magnetic noon. It is proposed that this plasma, once in the noon sector, was drawn antisunward by the high-latitude convection toward polar latitudes where it was identified by the EISCAT Svalbard radar. The observations are discussed in terms of earlier modelling studies of polar patch densities.

by all-sky imaging photometers (Buchau et al., 1983; Weionospheric densities observed by the EISCAT Svalbard ber et al., 1984).The density enhancements and associated radar in the polar F-region near local magnetic noon under effects have since been studied by a variety of experimenconditions of IMF B, <0.Multi-instrument observations, us-tal techniques including incoherent scatter radar (Pederson et ing optical, spacecraft and radar instrumentation, together al., 1998), radio tomography (Walker et al., 1999), HF radar with radio tomographic imaging, have been used to identify (Ogawa et al., 1998) and radio scintillation (Buchau et al., the source of the enhancement and establish the background 1985), although comparisons of features observed by differionospheric conditions.Soft-particle precipitation was ruled ent techniques are not always straightforward, with differout as a candidate for the production.Tomographic observa-ent techniques involving differing criteria to define a patch.tions identified a latitudinally restricted region of enhanced An extensive review of the polar-cap plasma structure has densities at sub-auroral latitudes, distinct from the normal been given by Crowley (1996), who defined a patch as havmid-latitude ionosphere, which was likely to be the source.
ing a horizontal spatial dimension of at least 100 km and a The evidence suggested that the increased sub-auroral densi-density of at least two-fold above background level.Poties were photoionisation produced at the equatorward edge lar patches occur predominantly under conditions of IMF B, of the afternoon high-latitude cell, where the plasma is ex-negative (McEwan and Harries, 1996) and drift anti-sunward posed to sunlight for an extended period as it flows slowly across the polar cap at speeds of typically 300-1000 m s-1 .sunward toward magnetic noon.It is proposed that this They have been observed in both summer and winter at plasma, once in the noon sector, was drawn antisunward by sunspot maximum and minimum (Buchau and Reinisch, the high-latitude convection toward polar latitudes where it 1991) and have been seen in geomagnetically conjugate rewas identified by the EISCAT Svalbard radar.The observagions (Rodger et al., 1994a).The origin of patch ionisation tions are discussed in terms of earlier modelling studies of and the structure remain open to question.Most of the propolar patch densities.
posed mechanisms for patch production rely on the trans-Key words.Ionosphere (polar ionosphere; plasma temera-port of ionisation from lower latitudes into the cusp region, ture; plasma convection) with subsequent structuring into patches.Photoionisation at lower latitudes has been cited as a potential plasma source with the plasma being entrained into the polar cap by the high-latitude convection pattern.Patch densities compara-1 Introduction ble to those at dayside sub-auroral latitudes were reported by Buchau et al. (1985), with the observations of Valladares et The polar-cap ionosphere is a highly structured medium al. (1994), suggesting that the plasma was being convected in comprising irregularities in plasma density of a variety a tongue-of-ionisation (TOI) from sub-auroral latitudes into of scale sizes.The current study is concerned with lo-the polar cap.The modelling studies of Sojka et al. (1994) calised regions of enhanced density on horizontal scales of have indicated the presence of patches in all seasons but with --100-1000 km in the F region, known as polar patches, an occurrence that is modulated by UT.A subsequent study with particular interest being to establish the source of the by Bowline at al. (1996) discusses the dependency of the UT ionisation.The patches were originally identified by iono-modulation on the observing location.Soft-particle precipispheric sounders, with the associated airglow being observed tation in sub-polar regions has also been cited as a possible where the lifetime of plasma is sufficiently long for it to be sion of the polar convection was controlled by pulsed recontransported over the polar cap.In this instance, it is likely nection at the magnetopause or flux transfer events.Experithat spatial resonance between the plasma convection and the mental evidence for precipitation-produced plasma enhanceprecipitation region is required to allow sufficient time for ments with characteristics of polar patches was presented by the build-up of ionisation to patch levels.Weber et al. (1984) Walker et al. (1999), who showed that soft precipitation had noted that there might be sufficient time for the plasma build-played an important role in the direct formation of strucup if sunward convecting flux-tubes move along the cusp re-tured plasma at high altitude.In a subsequent study, Smith et gion for tens ofminutes before turning antisunward into the al. (2000) suggested that the structuring of plasma was linked polar cap.
to a variation in the IMF configuration and hence, to the location of the magnetopause reconnection site and the energy The formation of patch structure is also an open question, distribution of the precipitating particles.Observations near with several mechanisms being cited.For solar-produced winter solstice by Nielsen et al. (2003) showed density strucplasma, modelling work by Sojka et al. (1993) showed that tures in the pre-noon sector formed by a combination of local the break-up could occur by shearing of the TOI arising from precipitation and photo-production, and patches of photoiontemporal changes in the By component of the interplanetary isation near magnetic noon that had been transported from magnetic field (IMF).Rodger et al. (1994b) suggested that lower latitudes.enhanced recombination rates for plasma loss, accompanying high-velocity flow channel events, could fragment the The case study presented here is concerned with the oriionisation.Earlier, Anderson et al. (1988) had suggested gin of the ionisation in a polar enhancement, rather than the that an expansion of the convection throat of the polar cap mechanism for the fragmentation of the plasma into patches.into a region of solar ionisation at lower latitudes and then Multi-instrument observations have been used to establish its subsequent contraction, could directly give rise to a patch background ionospheric conditions and to identify the source structure that was drawn to the higher latitudes.A variation of a region of enhanced density observed by the EISCAT by Lockwood and Carlson (1992)  were made in the Svalbard region near winter solstice on 20 measurements with the beam aligned along the geomagnetic December 1998, when the general geomagnetic conditions field in the F region.The upper panel of Fig. 1 shows the were moderate with KP=3-.In this particular instance, the electron densities measured by the radar between 07:00 UT effects of photo-production and precipitation could be sepa-and 10:00 UT, processed using a post-integration time of rated, which is often not possible as the two processes com-60 s.Magnetic noon is broadly coincident with 09:00 UT. pete in a common region.
The density distribution throughout the interval shows evidence of multiple structures at various altitudes, but of particular interest to the study is the density enhancement between 2 Experimental observations 08:45 UT and 09:00 UT.This feature has a sharp bottomside edge at about 250 km with a more diffuse topside extend-2.1 Electron density at polar latitudes ing above 400 km.The peak density at an altitude of some 300 km, has a maximum value of 1.4x 1011 m-3 at 08:50 UT.The electron temperatures measured by the ESR radar are Time (UT) shown in the lower panel of Fig. 1.Two regions with temperatures in excess of 3500 K extending down to the lower Fig. 4. The three components of the IMF measured by the WIND F-region can be identified, indicative of soft-particle precip-spacecraft located in the solar wind, between 07:00 and 10:00 UT itation.The first occurs from the start of the interval to on 20 December 1998.07:40 UT, while the second extends from 09:00 UT to the end at 10:00 UT.The centre period between 07:40 and 09:00 UT the distribution of the intensity of the red-line as a function shows no pronounced electron heating.The plasma feature of elevation between 07:10 UT and 09:40 UT.The latitudiof interest between 08:45 UT and 09:00 UT occurred during nal position of the ESR radar field-of-view has been mapped this centre period of low electron temperatures and was thus onto the figure, and is illustrated by the dark line near 300 S not being produced locally by in-situ precipitation.
of zenith for an assumed emission altitude of 220 km.At the start of the interval the maximum intensity is marginally 2.2.2 Meridian Scanning Photometer south of the ESR location.A succession of poleward moving auroral forms can be identified at this time by the rapid pole-Additional information on the latitudinal structure of soft ward movements of the emission maximum breaking away precipitation can be inferred from observations by a meridian from the equatorward edge of the underlying emission.Howscanning photometer (MSP) located at Ny Alesund (78.90 N, ever, there is also a gradual trend in the location of the gen-12.00E), slightly north of the ESR radar.The instrument eral emission, revealed most clearly by the equatorward edge measures line-of-sight intensities of auroral 630.0nnm redof the enhanced intensities.At 07:10 UT the activity was line and 557.7 nm green-line emissions as a function of el-mostly equatorward of the ESR radar, but by about 07:40 UT, evation, essentially along the magnetic meridian with a scan it was entirely poleward of the radar, reaching its most poleduration of 16 s.The green-line observations relate to en-ward location broadly between 08:25 UT and 08:45 UT.Folergetic electrons ('-keV) that penetrate to E-layer altitudes, lowing a period north of the radar with diminishing intensity, while the red-line is indicative of softer precipitation (-,-few the emission intensified and advanced equatorward returning hundred eV) of relevance to the current study.Figure 2  The location of the red-line emission at the time of inter-.".
2o00Test can also be seen in the all-sky camera observations at 0 Longyearbyen (78.20 N, 15.3-N).Figure 3

Interplanetary magnetic field 2.4 Plasma flow
The latitudinal movements in the MSP 630.0 nm emissions 2.4.1 CUTLASS reflect the changes in the B, component of the interplanetary magnetic field (IMF).Figure 4 shows the compo-With B,<0 and By small and positive antisunward plasma nents of the IMF measured by the WIND spacecraft be-flow would be expected into the polar cap from a throat retween 07:00 and 10:00 UT upstream in the solar Wind at gion that is rotated towards the dawn sector of the magnetic (39.0, -58.4,14.0)Re.The most significant changes oc-noon meridian.Experimental support was provided by the cur in the B, component, with a gradual increasing trend CUTLASS Superdarn radar.Figure 5 shows the line-of-sight from -6 to -1 nT broadly between 07:00 and 08:25 UT, velocities measured by the Finland radar on a geographic followed by a period of reasonably constant magnitudes of co-ordinate grid at about 08:53 UT that are representative -1 to -2 nT between about 08:25 UT and 08:45 UT, and of the interval between 08:45 UT and 09:00 UT.The grey subsequently, a steep decrease to -7 nT between 08:45 and region above Svalbard indicates ground scatter, but to the 09:10 UT.Hence, the trend in the location, of the equator-north, within the polar cap, velocities away from the radar ward edge of the MSP red-line emission, with initial gradual were measured in excess of 400 m s-1.Antisunward compopoleward motion to its northernmost location, followed by nents were also observed between 670 N and 740 N that were a more rapid equatorward return, follows the broad trends generally less than 200 m s-i, with the exception of a small in the B, component as the polar cap contracts and then ex-region centred on 150 E, where the values were larger.pands.
During the time of interest, the solar wind speed was rea-2.4.2 DMSP sonably constant at about 420 km s-, so that a simple calculation indicates a delay of some 10 min for the manifestation Further support for the anticipated flow pattern was proof the effects of the IMF on the ionospheric plasma.Com-vided by measurements made by the F13 satellite of the parisons of the time of the minimum magnitude of B, with Defence Meteorological Satellite Programme (DMSP).The that of the most poleward position of the MSP emissions in-satellite followed an essentially east-to-west path north of dicates that the two correspond more closely than the antic-the ESR field-of-view, reaching a maximum latitude of ipated delay.However, geometrical considerations suggest about 770 MLAT and crossing the magnetic noon meridian that this can be attributed to the spacecraft location, with its at about 08:52 UT.The cross trajectory horizontal plasma relatively large displacement from the Earth in the negative flow velocities are shown in the bottom panel of Fig. 6.The Y direction, and the angle of the approaching IMF.It is thus generally negative values between 08:50 UT and 08:54 UT, possible that the spacecraft and the dayside ionosphere expe-infer that the plasma drift had an antisunward component as rienced the IMF and its effects, almost simultaneously.

0.9_
The tomographic images for the other two satellite passes 300-0 .9 -300 at 07:36 UT and 09:59 UT show broadly consistent iono--8 tudes.Superimposed on the plot is a possible high-latitude convection flow pattern, consistent with the CUTLASS observations near the noon meridian (not shown in the figure) and the DMSP flows and ion energy dispersion.The general form is typical of the flows expected with B, negative and By positive, comprising twin convection cells with a larger dusk cell.
In-situ ionisation production was ruled out as the source of the density enhancement, since the electron temperatures within the region remained near background level (Nilsson et al., 1994).Given the direction of plasma convection through the ESR region, it is therefore expected that the enhanced Fig. 9. Composite dial plot for comparison of observations by the density was carried by the flow into the field-of-view from a different instruments in the geomagnetic reference frame.It shows source region at lower latitudes.Of the two ionisation prothe locus of the ESR observations near 750 N, the equatorward edge duction processes likely to be operative at the lower latitudes, of the red-line emission observed by the MSP, the cross-trajectory soft-particle precipitation can be ruled out by the lack of optihorizontal flows measured by the F13 DMSP satellite, anticipated cal emissions in the region.Hence, in this instance, it appears plasma flow lines for the pertinent IMF conditions, and the 300 km intersections of the three tomography passes indicating the location that photoionisation was the likely source. of the maximum density of the sub-auroral enhancement.For a Three grey lines near noon in Fig. 9 show the ionospheric detailed description the reader is referred to the text.
intersections of the three tomographic images in the geomagnetic frame, with the crosses indicating the location of the maximum density of the sub-auroral enhancement.The lat-3 Discussion itudinal variation of the maximum density reflects the contraction and then expansion of the polar cap in response to As an aid to the interpretation of the measurements by the the changes in B,.The latitude of the enhancement suggests different instruments, the main features of interest have been that it may map broadly to the boundary between the sunplotted in Fig. 9 in the geomagnetic reference frame.The ward return flow of the dusk cell and the co-rotating flow locus of the ESR observations essentially follows 750 MLAT at lower latitudes.This density feature is clearly distinct between about 10:00 and 13:00 MLT, with the two markers from the auroral region and also from the main photoionione before 11:00 MLT and the other after 12:00 MLT show-sation regime at the southern extreme of Fig. 7, where the ing the respective times of the abrupt decrease and increase in TEC increased monotonically with decreasing latitude, bethe electron temperatures.The region of the enhancement in ing separated by a weak ionisation trough.The decrease in the electron density of particular interest to the current study the maximum electron density of the enhancement as time is slightly earlier than the later marker.The dotted trace inter-progresses towards local geographic noon, contrary to the exsecting the ESR locus near the two temperature markers indipected build-up of plasma in daylight, can now be explained cates the equatorward edge of the red-line emission observed if the enhancement is located slightly poleward of the stagby the meridian scanning photometer.Its coincidence with nation region in-between the two flow regimes, where the the markers is supportive of the precipitation being entirely plasma moves slowly sunward at the equatorward edge of the poleward of the radar field-of-view between about 11:00 and dusk cell.The long times spent by the plasma in sunlight as 12:00 MLT, and in particular at the time of the density en-it moves towards the flow reversal near magnetic noon allows hancement.
time for the photoionisation to build-up.The increased den-The cross-trajectory horizontal flows measured during the sities are then entrained into the polar-cap convection flow, east-to-west DMSP satellite pass are also shown in the fig- and subsequently swept antisunward in the noon sector to be ure.These have been extended to later MLTs than shown transported poleward in the tongue-of-ionisation toward the in Fig. 6.The satellite trajectory is indicated on the fig-cusp region.ure by the straight line extending from 09:3 0 MLT to almost Given this interpretation, the enhanced densities observed 17:00MLT, and is used as baseline for the cross-trajectory by the ESR equatorward of the cusp are likely to be those flow component.These flows are shown by the curve with of the tongue-of-ionisation before it enters the polar region.underside shading, with the displacement of the curve from Ionisation decay is expected as the plasma moves from sunthe baseline indicating the magnitude and direction of the lit lower latitudes to the dark winter polar cap.The tomocomponent.The regions near magnetic noon show the gengraphic image at 07:36 UT indicated a maximum density of eral antisunward component, while the sunward velocity about 3.2x 1011 m-3 for the sub-auroral enhancement near components in the afternoon sector correspond to the re-noon, while by the time it had reached the ESR field-ofturn flow of the dusk cell.Flows are significantly reduced view it had reduced to 1.4x10I0 m-3 .The time required at the extreme of the trajectory on the dusk-side, indicative for plasma to decay from 3.2x 1011 m-3 to 1.4x 1011 m-3 of slow moving plasma near the stagnation region between in the absence of production processes can be estimated by considering the rate of plasma loss in the F region.At al-Ny Alesund sector near local magnetic noon, although the titudes above approximately 250 km the primary ion con-density above the background level may not be as marked as stituent is 0+.The dominant processes for the chemical loss modelling studies would suggest for the evening hours. of the ion is through slow reaction with N 2 and 02 to form NO+ and 02+, respectively, followed by rapid dissociation of the molecules by reaction with electrons.Simple calcu-4 Conclusion lations, as in Walker et al. (1999)

using recombination rates
Observations have been presented from a multi-instrument from Brekke (1997), give a decay time of some 45 min for study addressing the origin of a high-latitude plasma enplasma at an altitude of 300 km.The required time increases hancement in the dayside ionosphere in the European secto about 100 min at 325 km but reduces to about 20 min at tor The localised region of enhanced density observed by 275 km.Thus, at an altitude of 300 km it can be estimated the ESR radar was clearly not being produced in-situ by softthat the plasma takes about 45 min to drift from a latitude of particle precipitation.A fortuitous contraction of the polar about 73.5c N to 78.2p N, a distance of some 550km.This cap at the time of interest resulted in the optical emissions gives a calculated poleward velocity component of approxi-bentoheorhfteES•iwngein.Whteat-maey200 mnsi , which is in broad agreement wihtefo being to the north of the ESR viewing region.With the antimately mesurodthe flow sunward plasma flow, observed by the CUTLASS radar and components measured by the CUTLASS Finland radar near the northern Norwegian coastline, However, it is likely that a DMSP satellite, it was also possible to rule out soft precipithe calculatheddrift Nor egisaunderestline ved anth i velocity tation outside the field-of-view as a source.The likely source the calculated drift time is underestimated and theglecty in this instance was photoionisation at sub-auroral latitudes.overestimated due to ionisation production being neglected.
Three consecutive tomographic images showed that there In reality, photo-production would also have been operative, was enhanced density that was distinct from normal dayalbeit weakening significantly as the plasma moved toward time photoionisation at the lower latitudes of the co-rotating the dark polar cap at winter solstice, flow regime.The location indicated that it was found in a Various authors have suggested that break-up of the regime of slow sunward convection at the equatorward edge tongue-of-ionisation may be the source of the patches of en-of the afternoon convection cell, with the long time it spent in hanced density plasma found in the polar cap when B, is sunlight allowing for the build-up of density.It is proposed negative.Modelling studies have been carried out by Bow-that this enhanced density was subsequently entrained into line et al. (1996) to investigate ionisation in polar-cap patches a thisnhanc ed denitywa s e nt tr e into as afuntio ofUTdayof he earandloctio oftheob-a tongue-of-ionisation and carried poleward from the subas a function of UT, day of the year and location of the ob-auroral latitudes.The long lifetime ofF region plasma above servations.The study included modelling for Ny Alesund, 300 km allowed for the increased densities to be observed by some 1V latitude north of the ESR field-of-view.Comparison the ESR radar as it intercepted the tongue between 08:45 and of absolute density levels from their model near 09:00 UT 09:00 UT.It is possible that the tongue extended to times bewith those measured by ESR in the current study indicates yond 09:00 UT in the ESR observations, however, it cannot that the model values are generally double those measured.
be identified unambiguously at these later times because of However, the modelling work also included results relating to the expansion of the polar cap with the precipitation region the patch-to-background density ratio, so that another com-returning into the field-of-view of the radar.parison is possible.Figure 7  Tromso and the Norwegian Polar Research Institute in the tomothe value was generally less than 3, and occasionally be-graphic measurements is gratefully acknowledged.The CUTLASS low 2. On this basis the authors argued that the tongue-of-radar is a UK national facility funded by the Particle Physics and ionisation was unlikely to be observed at this site in the mag-Astronomy Research Council; the data used here have been supnetic noon sector.However, at the time of interest to the cur-plied by T. Yeoman.EISCAT is an international facility supported rent study, between 08:00 and 09:00 UT, the modelled patch-by the national science councils of Finland, France, Germany, Japan, Norway, Sweden and the United Kingdom.R. Lepping proto-background was about 2.5.Hence, while the density of the vided the WIND data that were obtained from the CDAWeb.RWS enhancement was not five times that of the background level, acknowledges receipt of a PPARC postgraduate studentship.it was nevertheless significantly increased, and indeed in ac-Topical Editor M. Lester thanks V. Howells for her help in evalcord with the patch definition of Crowley (1996) of two-fold uating this paper.above background.Estimation of the patch-to~background ratio from the ESR observations, with the patch density being taken as that measured between approximately 08:50 and 09:00 UT and the background between 08:10 and 08:25 UT gave a value of 2.6, in broad agreement with that obtained from the model.In consequence, it is not unreasonable to conclude that the tongue-of-ionisation can be observed in the

Fig. 2 .
Fig. 2. Intensity of the 630.0nm (red-line) auroral emission measured by the MSP at Ny Alesund from 07:10 UT to 09:40 UT, on 20 December 1998, as a function of zenith angle.The dark line near 300 S of zenith shows the latitudinal location of the ESR radar mapped into the zenith angle scale.

Fig. 3 .
Fig. 3. Intensity of 630.Onm (red-line) emission measured by the all-sky camera at Longyearbyen at 08:43 UT, 20 December 1998, representative of the time period of interest.The white traces show the geographic grid, while geomagnetic latitudes are shown by the 0 superimposed red curves.The intersection of the ESR radar beam with an altitude of 220 km is indicated by the yellow dot near 750 MLAT.
shows an all-sky 1$ image for red-line emissions at 08:43 UT, which is typical o• *of the time period.The white grid relates to geographic co-70N -N00 ordinates, whilst geomagnetic latitudes are shown by the superimposed red curves.The intersection of the ESR radar beam with an altitude of 220 km is indicated by the yel-.-800 low dot near 75' MLAT.A band of emission containing fine structuring is seen extending in longitude across the field-of-Gon view.The latitudinal location is clearly north of ESR, with .c .Gater no optical manifestation at magnetic latitudes equatorward of 3451E O°E 15YE 30*E the ESR radar, except for a very weak emission at the western extreme of the field-of-view.Taken together, the optical Fig. 5. Line-of-sight velocity components measured by the UK Suobservations all support that there was no soft-particle pre-perdam radar (CUTLASS) located in Finland on a geographic cocipitation above or equatorward of the radar at the time of ordinate grid at about 08:53 UT on 20 December 1998.The illusthe plasma enhancement.trated flows are representative of the broader time interval of interest between 08:45 UT and 09:00 UT.

Fig. 6 .Fig. 7 .
Fig. 6.Particle data and horizontal cross trajectory plasma flow velocities measured by the F13 satellite of the Defence Meteorological Satellite Programme (DMSP) along an essentially east-to-west geomagnetic path, crossing the noon meridian at about 08:52 UT on 20 December 1998.
third.Such motion can be interpreted as a re-LATITUDE sponse to a decrease and then an increase in the magnitude of Fig.8.Tomographic images for three satellite passes that crossed Bz, with the polar cap contracting and then expanding again.750N at 07:36 UT .(toppanel), 08:10 UT (centre panel) and Also of note is the decrease in the maximum electron den-09:59 UT (bottom panel) on 20 December 1998.The reconstrucsity of the enhancement between the first and the third pass, tion in the centre panel has been obtained from the total electron from 3.2x 1011 m-3 to 2.4x 1011 m-3 .This decrease occurs content illustrated in Fig.7.as time progresses towards the local geographic noon near 11:00 UT and is contrary to the expected build-up of plasma in daylight.S. E. Pryse et al.: Evidence for solar-production as a source of polar-cap plasma the sunward flow and the co-rotation regime at lower lati-3 12 of the Bowline et al. paper illustrates the ratio under conditions of By negative and By Acknowledgements.Financial support for the project was provided positive.For the winter solstice conditions with By >O, per-by the UK Particle Physics and Astronomy Research Council untinent to the current study, the ionisation enhancement was der grant PPA/G/O/2001/00012 and the Norwegian Research Counmost marked in the evening sector, with the ratio attaining a cil and AFOSR Task 231 lAS.The assistance of the University of value of 5 between 17:00 UT and 22:00 UT.At other times the interval the maximum intensity had returned to eleva-0853 01 s (354) 12.400 MHz tions equatorward of the ESR.Between 08:45 UT and 09:00 UT there was no evidence of red-line aurora or soft-particle shows to the ESR field-of-view marker near 09:00 UT.By the end of .............................................. .