Statistical Survey of the Terrestrial Bow Shock Observed by the Cluster Spacecraft

Abstract

The terrestrial bow shock provides us with a unique opportunity to extensively investigate properties of collisionless shocks using in situ measurements under a wide range of upstream conditions. Here we report a statistical study of 529 terrestrial bow shock crossings observed between years 2001 and 2013 by the four Cluster spacecraft. By applying a simple timing method to multipoint measurements, we are able to investigate their characteristic spatiotemporal features. We have found a significant correlation between the speed of the bow shock motion and the solar wind speed. We have also compared obtained speeds with time derivatives of locations predicted by a three-dimensional bow shock model. Finally, we provide a list of bow shock crossings for possible further investigation by the scientific community. Plain Language SummaryThe Sun is continuously emitting a stream of charged particles-called the solar wind-from its upper atmosphere. The terrestrial magnetosphere forms the obstacle to its flow. Due to supersonic speed of the solar wind, the bow shock is created ahead of the magnetosphere. This abrupt transition region between supersonic and subsonic flows has been frequently observed by the four Cluster spacecraft. Using a timing analysis, we have retrieved speed and directions of the bow shock motion for a large number of crossings. We have correlated the bow shock speed with the solar wind speed and predictions of the bow shock locations by the empirical model. A better understanding of the bow shock kinematics may bring new insights to wave-particle interactions with applications in laboratory plasmas.

Statistical Properties of Sub‐Ion Magnetic Holes in the Solar Wind at 1 AU

“…The terrestrial bow shock is characterized by an abrupt jump in the magnetic field strength as well as the ion number density and velocity when a satellite crosses the bow shock (Kruparova et al, 2019). We select the time interval of the MMS spacecraft in the solar wind by visually identifying the spacecraft entering or leaving the solar wind from the bow shock using the MMS1 data from December 2016 to May 2019.…”

Determination of the Configurations of Boundaries in Space

“…The new method has been first applied to the determination of the shape of the Earth's bow shock. The data set for the bow shock normals of 516 Cluster crossing events from Kruparova et al (2019) has been used in this investigation. For most of the cases, the zenith angle α N of the shock normal is less than the corresponding zenith angle α of the crossing points.…”

“…Kruparova et al (2019) have investigated 529 terrestrial bow shock crossings between Years 2001 and 2015 observed by the four Cluster spacecraft (Escoubet et al, 2001) (the quasi‐parallel bow shock crossings, which are more turbulent, are not included). The Cluster data can be retrieved from the Cluster Science Archive (Laakso et al, 2010).…”

“…The variation of α n versus α in the GSE coordinates corrected by the aberration of the solar wind for the bow shock crossing events between Years 2001 and 2015 in Kruparova et al (2019). (a and b) All 516 bow shock crossing events (13 events in the original data set cannot be used due to the unavailability of the S/C position data of MMS) and the 463 events with α N < α , respectively.…”

“…The measurements with multiple S/C, such as Cluster and MMS, provide new opportunities for determining the configurations of the boundary layers in space. The timing algorithm (Harvey, 1998; Russell et al, 1983; Schwartz, 1998) has been put forward to find the normal of the discontinuity (Horbury et al, 2001; Kruparova et al, 2019). Mottez and Chanteur (1994) have tried to obtain the metric of curved surfaces, but their method is too complicated for the practical applications.…”