Combining incoherent scatter radar data and IRI‐2007 to monitor the open‐closed field line boundary during substorms

E E Woodfield,J A Wild,A Senior,S E Milan,A J Kavanagh

doi:10.1029/2010ja015751

Abstract

The size of the polar cap is very important for understanding the substorm process as well as reconnection rates in general. In this work we build on previous studies which use a combination of European Incoherent Scatter radar (EISCAT) electron temperature (Te) measurements from two radars running simultaneously to track the motion of the open‐closed field line boundary (OCB). The second radar gives an estimate of the background variation of Te with altitude, which can then be subtracted from the radar beam being used to estimate the OCB location. We demonstrate that using the international reference ionosphere 2007 (IRI‐2007) model can remove the second radar requirement and therefore increase the number of cases which could benefit from background Te subtraction. In this paper we focus our analysis on substorm intervals. We find that the IRI‐2007 method produces an OCB proxy location which on average is 0.25° altitude adjusted corrected geomagnetic coordinate latitude equatorward of the two‐radar method. On comparing both the two‐radar and IRI‐2007 Te OCB finding methods with the OCB identified in the DMSP particle data and IMAGE satellite data we find that both EISCAT methods perform quite well, and neither method is particularly favored over the other. We find that the magnitude of the mean offset to the IMAGE OCB varies between 0.1° and 2.7° latitude, dependent on the event and the IMAGE camera used.

Highlights

[2] The size of the polar cap and the amount of open magnetic flux contained within it is a very important quantity when it comes to understanding the substorm process as well as reconnection rates in general
Aikio et al [2006] refined the basic Te method for the European Incoherent Scatter radar (EISCAT) system by subtracting an estimate of the background Te dependence on altitude derived from the EISCAT Svalbard Radar (ESR) within the WOODFIELD ET AL.: EISCAT AND IRI-2007 open‐closed field line boundary (OCB)
This would increase the number of EISCAT experiments where this method could be used and potentially extend the method to other radar systems which do not have a second radar in the polar cap

Summary

Introduction

[2] The size of the polar cap and the amount of open magnetic flux contained within it is a very important quantity when it comes to understanding the substorm process as well as reconnection rates in general (see, e.g., the review by Chisham et al [2008]). There is an inherent difficulty with this particular method, namely the requirement to have two incoherent scatter radars running simultaneously in the necessary modes with minimal longitudinal separation In operational terms this means that the ESR field aligned beam needs to be running at the same time as the low‐elevation mode beam from the mainland EISCAT VHF system and/or the ESR steerable dish in low‐elevation mode pointing equatorward. It would be very beneficial in terms of the number of experimental intervals both past and future when this kind of method could be used if an ionospheric model could be used to replace the need for the ESR field aligned beam to be running This would increase the number of EISCAT experiments where this method could be used and potentially extend the method to other radar systems which do not have a second radar in the polar cap. We focus on substorm intervals to assess the capabilities of the method for this phenomenon where knowledge of the OCB location is especially important

Objectives

Methods

Results

Conclusion