Ionospheric conductances derived from satellite measurements of auroral UV and X-ray emissions, and ground-based electromagnetic data: a comparison

摘要

Global instantaneous conductance maps can be derived from remotesensing of UV and X-ray emissions by the UVI and PIXIE camerason board the Polar satellite. Another technique called the 1-D method ofcharacteristics provides mesoscale instantaneous conductanceprofiles from the MIRACLE ground-based network in NorthernScandinavia, using electric field measurements from the STAREcoherent scatter radar and ground magnetometer data from the IMAGEnetwork. The method based on UVI and PIXIE data gives conductancemaps with a resolution of ~800km in space and ~4.5minin time, while the 1-D method of characteristicsestablishes conductances every 20s and with a spatialresolution of ~50km. In this study, we examine three periodswith substorm activity in 1998 to investigate whether the twotechniques converge when the results from the 1-D method ofcharacteristics are averaged over the spatial and temporalresolution of the UVI/PIXIE data.

In general, we find that the calculated conductance sets do notcorrelate. However, a fairly good agreement may be reached whenthe ionosphere is in a state that does not exhibit strong localturbulence. By defining a certain tolerance level of turbulence,we show that 14 of the 15 calculated conductance pairs duringrelatively uniform ionospheric conditions differ less than ±30%.The same is true for only 4 of the 9 data points derivedwhen the ionosphere is in a highly turbulent state. A correlationcoefficient between the two conductance sets of 0.27 is derivedwhen all the measurements are included. By removing the datapoints from time periods when too much ionospheric turbulenceoccurs, the correlation coefficient raises to 0.57. Consideringthe two very different techniques used in this study to derive theconductances, with different assumptions, limitations and scalesizes, our results indicate that simple averaging of mesoscaleresults allows a continuous transition to large-scale results.Therefore, it is possible to use a combined approach to studyionospheric events with satellite optical and ground-basedelectrodynamic data of different spatial and temporal resolutions.We must be careful, though, when using these two techniques duringdisturbed conditions. The two methods will only give results thatsystematically converge when relatively uniform conditions exist.