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

摘要

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 ~0.07-0.12GWb/(mV/m) for all F_p, F_e and F_T, confirming the loading-unloading substorm scheme. For SMC intervals this slope is only 0.03GWb/(mV/m).