Variations in the polar cap area during two substorm cycles

By S. Milan, M. Lester, S. Cowley, K. Oksavik, M. Brittnacher, R. Greenwald, G. Sofko, J. Villain. 2003

226 citations recorded by the source corpus.

This study employs observations from several sources to determine the location of the polar cap bound- ary, or open/closed field line boundary, at all local times, allowing the amount of open flux in the magnetosphere to be quantified. These data sources include global auroral im- ages from the Ultraviolet Imager (UVI) instrument on board the Polar spacecraft, SuperDARN HF radar measurements of the convection flow, and low altitude particle measurements from Defense Meteorological Satellite Program (DMSP) and National Oceanographic and Atmospheric Administration (NOAA) satellites, and the Fast Auroral SnapshoT (FAST) spacecraft. Changes in the open flux content of the mag- netosphere are related to the rate of magnetic reconnection occurring at the magnetopause and in the magnetotail, al- lowing us to estimate the day- and nightside reconnection voltages during two substorm cycles. Specifically, increases in the polar cap area are found to be consistent with open flux being created when the IMF is oriented southwards and low-latitude magnetopause reconnection is ongoing, and de- creases in area correspond to open flux being destroyed at substorm breakup. The polar cap area can continue to de- crease for 100 min following the onset of substorm breakup, continuing even after substorm-associated auroral features have died away. An estimate of the dayside reconnection voltage, determined from plasma drift measurements in the ionosphere, indicates that reconnection can take place at all local times along the dayside portion of the polar cap bound- ary, and hence presumably across the majority of the dayside magnetopause. The observation of ionospheric signatures of bursty reconnection over a wide extent of local times sup- ports this finding.

Subfields: Astronomy and Astrophysics, Molecular Biology

View Paper: https://www.semanticscholar.org/paper/38fbb62c959cef938cf59805f7f1fb74917001e3

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Citations in the corpus

Substorm Current Wedge Revisited (2015, background): “…the polar cap increases, as indicated by an increase of the magnetic flux content in the tail lobes (McPherron 1972; McPherron et al. 1973a,b; Caan et al. 1973, 1978; Hsu and McPherron 2004) and an increase in the polar cap area (Frank and Craven 1988; Milan et al. 2003, 2008; Taylor et al. 1996).”
Relationship between interplanetary parameters and the magnetopause reconnection rate quantified from observations of the expanding polar cap (2012, methodology): “[18] Two methods allow FD to be measured almost directly and instantaneously: (1) measure the ionospheric convection flow across the ionospheric projection of the dayside OCB (in the frame of reference of the moving boundary) [e.g., Baker et al., 1997; Milan et al., 2003; Hubert et al., 2006a; Chish”
A decade of the Super Dual Auroral Radar Network (SuperDARN): scientific achievements, new techniques and future directions (2007, methodology): “It is now realized that many echoes from the E region have more than one spectral peak (known as two-peaked E-region echoes or TWOPEEs), and contain backscatter contributions from two or more of the echo types listed above (e.g. Milan et al. 2003a; Danskin et al. 2004).”
Saturn's polar ionospheric flows and their relation to the main auroral oval (2003, unknown): “…on the north-south component of the IMF, expanding in size with the amount of open flux when magnetopause reconnection is active for northward IMF, and contracting in size when magnetopause reconnection decreases with southward IMF, similar to the case for the Earth (e.g. Milan et al., 2003).”