Polar cap influx

J Macdougall,P T Jayachandran

doi:10.5194/angeo-23-1755-2005

Abstract

Abstract. This study uses digital ionosonde data from a cusp latitude station (Cambridge Bay, 77° CGM lat.) to study the convection into the polar cap. Days when the IMF magnetic field was relatively steady were used. On many days it was possible to distinguish an interval near noon MLT when the ionosonde data had a different character from that at earlier and later times. Based on our data, and other published measurements, we used the interval 10:00-13:00 MLT as the cusp interval and calculated the convection into the polar cap in this interval. The integrated convection accounted for only ~1/3 of the open polar cap flux. If the convection through the prenoon/postnoon regions on either side of the cusp was calculated the remaining 2/3 of the flux could be accounted for. The characteristics of the prenoon/postnoon regions were different from the cusp region, and we attribute this to transient flank merging versus more steady frontside merging for the cusp. Keywords. Ionosphere (Plasma convection) Magnetospheric physics (Polar cap phenomenon)

Highlights

The polar cap that is the subject of this paper is the region lying poleward of the auroral oval and may be defined as the region of ‘open’ magnetic field that is connected to the solar wind magnetic field
There are a number of ways of determining the open polar cap size, the most common being satellite particle detectors to determine the area where there is only very soft “polar rain” precipitation (Gussenhoven et al, 1984), and satellite optical images to determine the region where there is very low optical emission
The study of cusp location by Aparicio et al (1991) using Viking satellite particle measurements shows it to be closely the 3 hour interval 10:00–13:00 MLT, there is about a 1/2 h timeshift depending on the sign of the IMF By component

Summary

Introduction

The polar cap that is the subject of this paper is the region lying poleward of the auroral oval and may be defined as the region of ‘open’ magnetic field that is connected to the solar wind magnetic field. There are a number of ways of determining the open polar cap size, the most common being satellite particle detectors to determine the area where there is only very soft “polar rain” precipitation (Gussenhoven et al, 1984), and satellite optical images to determine the region where there is very low optical emission. These determination of the polar cap open area often show that there is some particle precipitation poleward of the main auroral oval. This latitude is very suitable for observing the dayside cusp region (e.g. Fig. 5 of Wing et al, 2001)

Measurements

Discussion

Is the cusp much wider than 3 hours?

Is the width of open polar cap flux compatible with the cusp width?