Comparison of magnetotail magnetic flux estimates based on global auroral images and simultaneous solar wind—magnetotail measurements

Abstract

We compared simultaneous magnetotail magnetic flux F estimates, (1) based on in situ spacecraft measurements in the tail and solar wind ( F T ) with (2) the polar cap magnetic flux, estimated from global auroral images (using proton-induced or electron-induced emissions, F p or F e , respectively). Simultaneous F p and F e estimates gave the correlation coefficient CC=0.74, indicating that these measures are not absolutely precise. Regression analysis of F T versus F e and F p gave CC values 0.73 and 0.50, correspondingly. F T values, containing closed magnetic flux, are systematically higher than F p and F e by 20–30%. Motivated by diverse results, published by different groups, we reanalyzed the F dependence on the dayside merging electric field E m for different dynamical states. The linear regression F( E m ) for substorm onsets shows a large slope ∼ 0.07 – 0.12 GWb / ( mV / m ) for all F p , F e and F T , confirming the loading–unloading substorm scheme. For SMC intervals this slope is only 0.03 GWb/(mV/m).