Auroral electrojet activity indexAEand its universal time variations

Abstract

An index, denoted by AE, is derived as a measure of global electrojet activity. The basic data used are 2.5‐minute readings of the H trace in the standard magnetograms from seven auroral‐zone observatories. The readings are referenced to a level determined for each observatory from quiet intervals. All the data from the seven observatories are then plotted against UT, and two envelopes are drawn to embrace all the points. The index AE at any epoch is defined by the distance (or separation) between the upper and lower envelopes at that epoch. When viewed as functions of UT the upper and lower envelopes themselves show development and decay of positive and negative variations. It is found that a positive excursion usually accompanies a negative (larger) variation, confirming the well known feature of polar disturbance. The AE index for a 6‐day period, February 10–15, 1958, shows that polar disturbances statistically repeat with a time interval of about 4 hours, and that the average duration of their most active phase is a little more than 1 hour. It is pointed out that the average repetition time of 4 hours is comparable with that of the electron flux enhancements observed by Anderson et al. in the magnetosphere tail. It is suggested that polar disturbances are directly related to Anderson's ‘electron islands’ in the magnetosphere tail.

Energy conversion regions as observed by Cluster in the plasma sheet

“…The AE index measures the auroral electrojet [Davis and Sugiura, 1966], and the Dst index measures variations in the ring current [Akasofu and Chapman, 1964]. Hamrin et al [2010] observed that plasma sheet energy conversion is influenced similarly by the geomagnetic activity as measured by variations in Kp and AE.…”

“…Note that the AE index is designed to measure auroral activity by capturing the behavior of the auroral electrojet [Davis and Sugiura, 1966]. Hamrin et al [2010] showed that the occurrence frequency, as well as the power density strength, of both CLRs and CGRs increase during times of high AE [see Hamrin et al, 2010, Figures 3 and 6a].…”

Auroral electrojet indices in the Northern and Southern Hemispheres: A statistical comparison

“…The auroral electrojet index (AE) developed by Davis and Sugiura [1966] is well correlated with the strength of the auroral electrojet currents in the Northern Hemisphere ionosphere and is traditionally employed as an indicator of the magnitude of global geomagnetic activity. The AE index is defined as the difference between the auroral electrojet upper (AU) and lower (AL) indices.…”

A superposed epoch investigation of the relation between magnetospheric solar wind driving and substorm dynamics with geosynchronous particle injection signatures

“…[5] Another signature of substorm onset is the enhancement of geomagnetic activity as measured by the AL and AU geomagnetic indices, defined by Davis and Sugiura [1966]. During the substorm growth phase, enhanced plasma convection leads to an observed gradual increase in both the AL and the AU indices [McPherron, 1970].…”