Unusually distant bow shock encounters at Venus

Russell, C. T.; Zhang, T.-L.

doi:10.1029/92gl00634

Cited by 41 publications

(34 citation statements)

References 11 publications

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“… Farris and Russell [1994] investigated analytic hydrodynamic formula describing the bow shock and the boundary of an obstacle to the solar wind flow. Their model predicts that the bow shock will move toward infinity for very low upstream Mach numbers, which is what we expect both physically and observationally [ Fairfield and Feldman , 1975; Russell and Zhang , 1992; Cairns et al , 1995; Grabbe , 1997; Fairfield et al , 2001]. Farris and Russell [1994] obtained the relation

where M is the upstream Mach number, a s and a mp represent the distances from the origin to the nose of the bow shock and the obstacle, respectively.…”

Section: Introductionsupporting

confidence: 57%

A comparison of IMP 8 observed bow shock positions with model predictions

et al. 2003

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[1] Over 12 years of IMP 8, data was searched for observed bow shock crossings. Out of the total 4562 crossings found, we used the 2293 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; Němeček and Šafránková, 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 (IMF) 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, and CL95 are the most accurate, with F79 giving a slightly better result. 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. An independent evaluation of the dawn and dusk sectors suggests an asymmetry in the bow shock shape and/or a different reaction of the flanks to solar wind deviations from a radial flow. 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.

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where M is the upstream Mach number, a s and a mp represent the distances from the origin to the nose of the bow shock and the obstacle, respectively.…”

Section: Introductionsupporting

confidence: 57%

A comparison of IMP 8 observed bow shock positions with model predictions

et al. 2003

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“…Recently Cairns and Grabbe [1994] predicted that the subsolar magnetosheath thickness Ams and the standoff distance (nose location) of the bow shock as for at low Alfven Mash numbers MA • 6 should_ depend_ strongly on the orienta- In gasdynamics (GD), an argument for Ams/amp depending on Ms is that G D waves carrying information about the magnetopause obstacle can travel further upstream in a characteristic nonlinear steepening time vnt at low Ms, thereby leading to a greater Ams/amp at low Ms (provided vnt at worst decreases slowly with Ms). This expectation is often observed [Fairfield, 1971;Formisano et al, 1971;Slavin et al, 1993;Russell and Zhang, 1992; and seen in simulations [$preiter et al, 1966;Cairns and Lyon, 1995]. This expectation is often observed [Fairfield, 1971;Formisano et al, 1971;Slavin et al, 1993;Russell and Zhang, 1992; and seen in simulations [$preiter et al, 1966;Cairns and Lyon, 1995].…”

Section: Introductionmentioning

confidence: 87%

Magnetic field orientation effects on the standoff distance of Earth's bow shock

Cairns

Lyon

1996

Geophysical Research Letters

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Three‐dimensional, global MHD simulations of solar wind flow onto a prescribed magnetopause obstacle are used to show that a bow shock's nose location as and the relative subsolar magnetosheath thickness Δms/amp are strong functions of the IMF cone angle θ (between vsw and Bsw) and the Alfven Mach number MA For a given MA the shock is more distant for higher θ (restricted to the interval 0–90° by symmetries), while as/amp and Δms/amp increase with decreasing MA for θ ≳ 20° but decrease with decreasing MA for θ ∼ 0°. Large differences in Δms/amp are predicted between θ = 0° and 90° at low MA, with smaller differences remaining even at MA ∼ 10. The θ = 0° results confirm and extend the previous work of Spreiter and Rizzi [1974]. The simulations show that successful models for the subsolar shock location cannot subsume the dependences on MA and θ into a sole dependence on Mms. Instead, they confirm a recent prediction [Cairns and Grabbe, 1994] that as/amp and Δms/amp should depend strongly on θ and MA for MA ≲ 10 (as well as on other MHD variables). Detailed comparisons between theory and data remain to be done. However, preliminary comparisons show good agreement, with distant shock locations found for low MA and large θ ≳ 45° and closer locations found for θ ≲ 20° even at MA ∼ 8.

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“…The position and shape of Earth's bow shock are dependent upon the shape and size of the magnetopause obstacle and the condition of the impinging solar wind plasma [e.g., Spreiter et al , 1966; Spreiter and Stahara , 1985; Russell , 1985; Fairfield , 1971; Farris et al , 1991; Russell and Zhang , 1992; Cairns and Lyon , 1995; Peredo et al , 1995; Bennett et al , 1997; De Sterck and Poedts , 1999a; Verigin et al , 2001; Fairfield et al , 2001; Stahara , 2002; Merka et al , 2003a, 2003b; Chapman and Cairns , 2003]. In terms of MHD theory, the relevant solar wind parameters are the ram pressure P ram = ρ sw v sw 2 , Alfvén Mach number M A = v sw / v A , sonic Mach number M S = v sw / c S , fast magnetosonic Mach number M ms = v sw / v ms , the magnitude of the upstream magnetic field B IMF , and θ IMF (the angle between v sw and B IMF ).…”

Section: Introductionmentioning

confidence: 99%

MHD simulations of Earth's bow shock: Interplanetary magnetic field orientation effects on shape and position

et al. 2004

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[1] The location and geometry of Earth's bow shock vary considerably with the solar wind conditions. More specifically, Earth's bow shock is formed by the steepening of fast mode waves, whose speed v ms depends upon the angle q bn between the local shock normal n and the magnetic field vector B IMF , as well as the Alfvén and sound speeds (v A and c S ). Since v ms is a minimum for q bn = 0°and low Alfvén Mach number M A , and maximum for q bn = 90°and high M A , this implies that as q IMF (the angle between B IMF and v sw ) varies, the magnitude of v ms should vary also across the shock, leading to changes in shape. This paper presents 3-D MHD simulation data which illustrate the changes in shock location and geometry in response to changes in q IMF and M A , for 1.4 M A 9.7 and 0° q IMF 90°. Specifically, for oblique IMF the shock's geometry is shown to become skewed in planes containing B IMF (e.g., the x À z plane). This is also emphasized in the terminator plane data, where the shock is best represented by ellipses, with centers translated along the z axis. For the q IMF = 90°simulations the shock is symmetric about the x axis in both the x À y and x À z planes. Simulations for fieldaligned flow (q IMF = 0°) show a dimpling of the nose of the shock as M A ! 1. The simulations also illustrate the general movement of the shock in response to changes in M A ; high M A shocks are found closer to Earth than low M A shocks. Farris et al. 's [1991] magnetopause model is used in the simulations, and we discuss the limitations of this, as well as the expected results using a self-consistent model.

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Unusually distant bow shock encounters at Venus

Cited by 41 publications

References 11 publications

A comparison of IMP 8 observed bow shock positions with model predictions

A comparison of IMP 8 observed bow shock positions with model predictions

Magnetic field orientation effects on the standoff distance of Earth's bow shock

MHD simulations of Earth's bow shock: Interplanetary magnetic field orientation effects on shape and position

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