The terrestrial bow shock: Models and observations

J. Merka

Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771


Over 17 years of IMP 8 data was searched for observed bow shock crossings. Out of the total ~6100 crossings found, we used the 2950 unambiguous bow shocks for which upstream interplanetary magnetic field and solar wind parameters were available to study selected bow shock models under normal and unusual solar wind conditions. The chosen models were F79, NS91, FR94, FR94c, CL95 and P95 [Formisano, 1979; Nemecek and Safránková, 1991; Farris and Russell, 1994; Cairns and Lyon, 1995; Peredo et al., 1995]. This statistical study investigates these models' reliability not only for average solar wind plasma and interplanetary magnetic field (IMP) conditions but also for unusual conditions and as a result points out some deficiencies of these models. Statistically, the predictions of F79 and the phenomenological and MHD models FR94, FR94c, CL95 are the most accurate. The P95 model predicts standoff distances which are too large by ~20%. For large values of the IMF and its components all models except NS91 underestimate the bow shock distance. Furthermore, the models underestimate the bow shock distance when the upstream Mach numbers are low (£ 5). The models also do not properly reflect changes in the relative orientation of the IMF and solar wind velocity vectors. Near-simultaneous multi-point bow shock and magnetopause observations for the case of field-aligned solar wind flow suggest a necessity for better understanding of magnetospheric response to such upstream conditions. Taking the upstream parameters from a distant solar wind monitor (the WIND spacecraft) resulted in the models predicting the shock farther away from the Earth, which is likely a result of the spacecraft separation perpendicular to the solar wind flow, or of calibrational differences of the plasma density measurements by the spacecraft.

WDS 2002, Proceedings of Contribution Papers, Part II, ed. by J. Safrankova, pg. 219-231, 2002