Magnetospheric response and reconfiguration times following IMF B_y reversals

Abstract

The interaction between the interplanetary magnetic field (IMF) and the geomagnetic field at the dayside magnetopause leads to transfer of momentum and energy which changes the magnetospheric configuration, but only after a certain time. In this study we quantify this time, to advance our understanding of the causes for the delayed response of the magnetosphere. We study the response and reconfiguration time of the inner magnetosphere to IMF By reversals. A superposed epoch analysis of magnetic field measurements from four Geostationary Operational Environmental Satellite spacecraft at different local times both for negative to positive IMF By reversals and for positive to negative reversals is presented. The magnetospheric response time at geosynchronous orbit to the sudden change of IMF By is less than 15 (∼10) min from the bow shock (magnetopause) arrival time, while the reconfiguration time is less than 46 (∼41) min. These results are consistent with a By component induced on closed magnetic field lines due to the asymmetric loading of flux following asymmetric dayside reconnection when IMF By≠0. Our results also confirm our earlier studies that nightside reconnection is not required for generating a By component on closed field lines.

Magnetospheric “Penetration” of IMF Viewed Through the Lens of an Empirical RBF Modeling

“…The second very important factor is the contribution from the dayside Region 1 currents, whose intensification under southward IMF conditions, combined with their IMF B -induced overlapping in the noon sector results in large azimuthal fields, strongly correlated with the IMF B (e.g., , and references therein). As far as we know, the IMF B effects in the near-equatorial dayside region were studied only on the basis of geostationary measurements (Tenfjord et al, 2017(Tenfjord et al, , 2018Wing et al, 1995) and our obtained penetration coefficients 0.2-0.4 agree with those previous results. In this test example we set IMF B = +5 nT; it should also be noted in passing that, due to the assumed linear dependence of the model field on the IMF B (equations (6)- (7)), reversing the IMF B orientation does not affect the shape of the internal equatorial B distribution nor its absolute magnitude but only reverses its polarity.…”

“…Several interesting features can be seen in the plots. Note in this regard that a qualitatively similar result was found by Tenfjord et al (2017Tenfjord et al ( , 2018 and Cao et al (2014). The effect is clearly seen even in the noon area, where the penetration coefficient can reach nearly 0.4 (right panel).…”

Detailed Regression Model of Plasma Sheet By

“…Motoba et al (2011) and Rong et al (2015) suggested with the several case studies that penetration timescale can be 1-2 hr. Tenfjord et al (2017) concluded that the delay of magnetospheric reconfiguration to B i y polarity change at geostationary orbit is from 15 to 45 min. This publication also contains a detailed review of other relevant issues.…”

The Behaviors of Ionospheric Scintillations Around Different Types of Nightside Auroral Boundaries Seen at the Chinese Yellow River Station, Svalbard

“…On the nightside IMF delay depends on the solar wind velocity. For maintaining the IMF delay for the nighside auroral zone, we have delayed the IMF data by 60 min (Tenfjord et al, 2017). This delay in the IMF data is with respect to the ACE measurements, which maintains the propagation delay of the solar wind from the bow to the magnetotail lobe (Kullen et al, 2015).…”

“…Figure 2E, shows the IMF condition during the BBAE event of 27 January 2015 between 20:30 and 23:00 UT. Please keep in mind that we have delayed the IMF data by 60 min (Tenfjord et al, 2017). IMF B x (in blue line) has a negative value (∼−5 nT) from 20:30 to 22:40 UT.…”