Earth's Bow Shock: A New Three‐Dimensional Asymmetric Model With Dipole Tilt Effects

Abstract

Using the bow shock crossing events from four spacecraft: IMP 8, Geotail, Magion‐4, and Cluster 1, a new three‐dimensional asymmetric bow shock model is constructed. The model is parameterized by the solar wind dynamic pressure, the interplanetary magnetic field, magnetosonic Mach number, solar wind β, and the Earth's dipole tilt angle. It is shown that the shape and size of bow shock are both affected by the dipole tilt angle. The dipole tilt angle causes asymmetries in the meridional plane: (1) the bow shock subsolar standoff distance and the north‐south asymmetry increase with the dipole tilt angle; (2) as the dipole tilt angle increases, the shock flaring angle in the equatorial plane is slightly reduced, while in the meridional plane the flaring angle obviously decreases in Southern Hemisphere and keeps almost unchanged in the Northern Hemisphere. The flaring angle in the Northern Hemisphere is larger than in the Southern Hemisphere; (3) the effects of negative dipole tilt angle on shock flaring are just the opposite of those for positive tilt, and the effects of dipole tilt angle on the shape of the bow shock are north‐south symmetric. The model results are also validated by comparing with one previous empirical model and with observational crossings, and it is demonstrated that the new model is able to predict the observed crossings more accurately and can better describe the rotational asymmetry and north‐south asymmetry of the Earth's bow shock.

Dipole Tilt Effect on Magnetopause Reconnection and the Steady‐State Magnetosphere‐Ionosphere System: Global MHD Simulations

“…MHD simulations have shown that the magnetopause topology is highly sensitive to dipole tilt angle, with the location of the magnetopause nose (the point of first contact of the solar wind) shifting northward (southward) for a positive (negative) tilt angle, thus affecting the location of first contact with the solar wind and the predictions of component reconnection (Liu et al, 2012;Lu et al, 2013). Furthermore, observations have shown that the tilt introduces asymmetries in the bow shock (Jelínek et al, 2008;Lu, Zhou et al, 2019). Extending such a study beyond the terrestrial parameter range may reveal even more complex behavior.…”

Data‐Based Modeling of the Magnetosheath Magnetic Field

“…It is true that the purely visual definition of the polygons is inevitably subjective; however, first fitting runs based on data from larger polygons did not show any substantial difference in results, which supports our confidence in the method. Finally, an additional data filtering was carried out, based on Lin et al (2010) and Lu et al (2019) MP and BS models driven by concurrent interplanetary parameters. The purpose was to further refine the intermediate subset by taking out marginal data records, corresponding to most unusual positions of the boundaries.…”

“…Their inclusion was motivated by the need to accurately select the data taken in the MS, which is by no means a straightforward task, given extremely variable and hardly predictable instantaneous positions of the MP and BS, further complicated by a relatively narrow transverse extent of the MS between its boundaries. The existing MP and BS models, such as those of Lin et al (2010) and Lu et al (2019), are of little help in this sense, since they give only average positions of the boundaries and cannot accurately predict their dynamics. For that reason, a selection based solely on those models would inevitably result in gross contamination of the MS data with observations made in the magnetosphere and in the solar wind.…”

“…(2010) and Lu et al. (2019), are of little help in this sense, since they give only average positions of the boundaries and cannot accurately predict their dynamics. For that reason, a selection based solely on those models would inevitably result in gross contamination of the MS data with observations made in the magnetosphere and in the solar wind.…”

Physics‐Based Analytical Model of the Planetary Bow Shock Position and Shape

“…These observations are accompanied by almost continuous monitoring of the undisturbed solar wind (IMP‐8, Wind, ACE). These data served as the basis for various empirical models of the bow shock (Chao et al., 2002; Chapman & Cairns, 2003; Dmitriev et al., 2003; Fairfield, 1971, 2001; Formisano, 1979; Hall et al., 2019; Jelínek et al., 2012; Lu et al., 2019; Merka et al., 2003; Meziane et al., 2014; Nĕmeček & Šafránková, 1991; Peredo et al., 1995; Slavin & Holzer, 1981; Wang et al., 2020). Such models are very convenient and easy to use; they also agree well with the average location and shape of bow shock.…”