Dawn‐dusk asymmetry of geosynchronous magnetopause crossings

Abstract

[1] Geosynchronous magnetopause crossing (GMC) data were collected from literature sources from 1967 and from the experimental data on magnetic measurements on GOES (129 GMCs) and plasma measurements on LANL (197 GMCs) geosynchronous satellites in 1994 to 2001. The dawn-dusk asymmetry of the magnetopause at geosynchronous orbit was examined by two independent methods using the collected data set of 515 GMCs. First, the large amount of accumulated GMCs permitted the revealing of a substantial dawn-dusk asymmetry in the local time (LT) distribution of the GMC occurrence probability, with a statistically significant maximum in the range from 1000 LT to 1100 LT. Second, an analysis of the dawn-dusk asymmetry dependence on the upstream solar wind conditions was performed using a scatter plot of the solar wind total pressure versus local time for various IMF Bz. There was no asymmetry revealed for large positive Bz. Under strong negative Bz we found a prominent magnetopause dawn-dusk asymmetry. The asymmetry is characterized by a shifting of the GMCs with the minimal required solar wind total pressure toward the dawn and by a significantly lower (about 3 times) solar wind pressures required for the GMCs in the dawn sector relative to the dusk sector. We found that the asymmetry cannot be attributed to the IMF orientation along the Parker spiral, which is not revealed for strongly disturbed solar wind conditions accompanying the GMCs. An application of the dawn-dusk asymmetry effect for the Chao et al. [2002] model provided a substantial increase in the model predictive capability interim of the geosynchronous magnetopause crossings. The standard deviation decreased by 20% from 0.55 R E for the initial version to 0.45 R E for the asymmetrical version of the model, with the magnetopause axis rotated by an angle of about 15°toward the dawn. The physical processes responsible for the magnetopause dawn-dusk asymmetry are discussed. We indicate the two most probable magnetospheric phenomena, which would contribute to the substantial dawn-dusk asymmetry of the magnetopause under disturbed solar wind and geomagnetic conditions. The first one is that magnetopause erosion would operate more intensively in the prenoon sector. The second phenomenon is an asymmetrical terrestrial ring current that would develop during geomagnetic storms.

Modeling the magnetospheric X‐ray emission from solar wind charge exchange with verification from XMM‐Newton observations

“…This asymmetry was also mentioned in Carter et al [2011], where they found that the empirical model fitted better in the dawnside. This dawn-dusk asymmetry could be related to the known asymmetries in either the magnetosheath plasma conditions [e.g., Walsh et al, 2012] or magnetopause position [e.g., Dmitriev et al, 2004], indicating that this asymmetry needs to be considered during the modeling process.…”

Asymmetry of magnetosheath flows and magnetopause shape during low Alfvén Mach number solar wind

“…[4] Apart from some debate related to the presence of an indentation at high latitudes near the polar cusps [Zhou and Russell, 1997;Dunlop et al, 2000;Lavraud et al, 2002Lavraud et al, , 2004Zhang et al, 2007] and dawn-dusk asymmetries [Dmitriev et al, 2004;Suvorova et al, 2005;Nishino et al, 2008], the shape of the magnetopause is often assumed to be axisymmetric about the aberrated Sun-Earth line, i.e., circular. This hypothesis has been used in most empirical models of the magnetopause [e.g., Sibeck et al, 1991;Petrinec and Russell, 1996;Shue et al, 1997;Kawano et al, 1999], although models using Artificial Neural Network techniques [Dmitriev and Suvorova, 2000] or fits to asymmetric shapes from theoretical expectations [e.g., Zhuang et al, 1981;Boardsen et al, 2000] have also been devised (cf.…”

The Shape of Strongly Disturbed Dayside Magnetopause

“…Discussing possible drivers of the asymmetry, Dmitriev et al (2004Dmitriev et al ( , 2011 showed convincingly that asymmetries in the upstream solar wind drivers, such as IMF orientation along/orthogonal the Parker spiral, were unlikely responsible for the dawn-duskward asymmetry of the magnetopause at geosynchronous orbit. Orientation of the IMF during geosynchronous magnetopause crossings is totally different from either Parker or ortho-Parker spiral, which are usually exhibited for the undisturbed solar wind.…”

“…The dawn-dusk asymmetry in the shape of dayside magnetopause has been convincingly shown on the basis of geosynchronous magnetopause crossings (GMCs) (Dmitriev et al 2004). They found that the GMCs occur most often in a prenoon sector.…”

“…During strong geomagnetic disturbances, the magnetopause exhibits unusual and nonlinear behavior such as reconnection saturation and prominent dawn-dusk asymmetry (e.g., Dmitriev et al 2004Dmitriev et al , 2011Suvorova et al 2005).…”