Abstract
Abstract. We investigate variations of the location and intensity of auroral currents during two magnetic storm periods based on magnetic field measurements from CHAMP separately for both hemispheres, as well as for the dayside and nightside. The corresponding auroral electrojet current densities are on average enhanced by about a factor of 7 compared to the quiet time current strengths. The nightside westward current densities are on average 1.8 (2.2) times larger than the dayside eastward current densities in the Northern (Southern) Hemisphere. Both eastward and westward currents are present during the storm periods with the most intense electrojets appearing during the main phase of the storm, before the ring current maximizes in strength. The eastward and westward electrojet centers can expand to 55° MLat during intense storms, as is observed on 31 March 2001 with Dst=−387 nT. The equatorward shift of auroral currents on the dayside is closely controlled by the southward IMF, while the latitudinal variations on the nightside are better described by the variations of the Dst index. However, the equatorward and poleward motion of the nightside auroral currents occur earlier than the Dst variations. The Space Weather Modeling Framework (SWMF) can capture the general dynamics of the storm time current variations. Both the model and the actual data show that the currents tend to saturate when the merging electric field is larger than 10 mV/m. However, the exact prediction of the temporal development of the currents is still not satisfactory.
Highlights
The intensification and equatorward expansion of the auroral electrojet are characteristic features of geomagnetic storm disturbances (Chapman and Bartels, 1940; Feldstein et al, 1997)
The above analysis shows that both eastward and westward electrojets flow during the storm periods, with the most intense currents appearing during the main phase of the storm, before Dst reaches its maximum
We have investigated the Northern and Southern Hemisphere auroral current characteristics during the March 2001 and April 2002 magnetic storms
Summary
The intensification and equatorward expansion of the auroral electrojet are characteristic features of geomagnetic storm disturbances (Chapman and Bartels, 1940; Feldstein et al, 1997). This work includes: (1) a report on the high resolution CHAMP observations of the dayside and nightside auroral electrojet current density and position during the 31 March 2001 and 17 April 2002 storms; (2) an investigation of the variation of the dayside and nightside electrojets in association with Dst and solar wind parameters; (3) a comparison of the storm time dynamics of the eastward and westward auroral electrojets; and (4) a comparison between CHAMP observations and the Space Weather Modeling Framework (SWMF) model outputs. During the two considered storms CHAMP was approximately in the late afternoon (daytime) – early morning (nighttime) meridian (15:00∼03:00 MLT at 475 km height for the March 2001 storm and 16:00∼04:00 MLT at 421 km height for the April 2002 storm) This constellation enables us to study the dependence of the dayside and nightside auroral currents on solar wind parameters and storm phases. Various papers have described these separate domain models and the results of the coupled simulations that can be achieved utilizing these models (e.g. De Zeeuw et al, 2004; Toth et al, 2007; Wang et al, 2008)
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