Solar wind control of the magnetopause shape, location, and motion
TL;DR: In this paper, the authors verified the pressure balance relationship between the solar wind dynamic pressure and the location of the subsolar magnetopause by assembling a data set of 1821 magnetopsause crossings.
Abstract: A data set of 1821 magnetopause crossings was assembled. Separate fits to subsets of this data set determine the magnetopause location as a function of solar wind dynamic pressure and interplanetary magnetic field orientation. Solar wind dynamic pressure variations produce self-similar magnetopause motion on time scales of one hour or longer. In this paper, the pressure balance relationship between the solar wind dynamic pressure and the location of the subsolar magnetopause are verified. The relationship between the IMF Bz, region 1 Birkeland current strength, the position of the subsolar magnetopause, and the shape of the dayside magnetosphere is quantified. Cross sections of the dayside magnetopause in planes perpendicular to the earth-sun line are oblate.
Citations
More filters
TL;DR: In this paper, the authors describe a new approach to the problem of fitting the magnetosphereic magnetic field to spacecraft data, based on fits to a large number of observed crossing (allowing a parametrization by the solar wind pressure).
Abstract: Empirical data-based models of the magnetosphereic magnetic field have been widely used during recent years. However, the existing models (Tsyganenko, 1987, 1989a) have three serious deficiencies: (1) an unstable de facto magnetopause, (2) a crude parametrization by the K(sub p) index, and (3) inaccuracies in the equatorial magnetotail B(sub z) values. This paper describes a new approach to the problem; the essential new features are (1) a realistic shape and size of the magnetopause, based on fits to a large number of observed crossing (allowing a parametrization by the solar wind pressure), (2) fully controlled shielding of the magnetic field produced by all magnetospheric current systems, (3) new flexible representations for the tail and ring currents, and (4) a new directional criterion for fitting the model field to spacecraft data, providing improved accuracy for field line mapping. Results are presented from initial efforts to create models assembled from these modules and calibrated against spacecraft data sets.
950 citations
TL;DR: In this article, the authors compare predictions of two models: the Petrinec and Russell [1996] model and the Shue et al. [1997] model along the flank.
Abstract: During the solar wind dynamic pressure enhancement, around 0200 UT on January 11, 1997, at the end of the January 6-11 magnetic cloud event. the magnetopause was pushed inside geosynchronous orbit. The LANL 1994-084 and GMS 4 geosynchronous satellites crossed the magnetopause and moved into the magnetosheath. Also, the Geotail satellite was in the magnetosheath while the Interball 1 satellite observed magnetopause crossings. This event provides an excellent opportunity to test and validate the prediction capabilities and accuracy of existing models of the magnetopause location for producing space weather forecasts. In this paper, we compare predictions of two models: the Petrinec and Russell [1996] model and the Shue et al. [1997] model. These two models correctly predict the magnetopause crossings on the dayside; however. there are some differences in the predictions along the flank. The Shue et al. [1997] model correctly predicts the Geotail magnetopause crossings and partially predicts the Interball 1 crossings. The Petrinec and Russell [1996] model correctly predicts the Interball 1 crossings and is partially consistent with the Geotail observations. We further found that some of the inaccuracy in Shue et al.'s predictions is due to the inappropriate linear extrapolation from the parameter range for average solar wind conditions to that for extreme conditions. To improve predictions tinder extreme solar wind conditions, we introduce a nonlinear dependence of the parameters on the solar wind conditions to represent the saturation effects of the solar wind dynamic pressure on the flaring of the magnetopause and saturation effects of the interplanetary magnetic field B z on the subsolar standoff distance. These changes lead to a better agreement with the Interball 1 observations for this event.
949 citations
TL;DR: In this article, a new functional form, r = r 0 [2/(1 + cos θ)] α, is used to fit the size and shape of the magnetopause using crossings from ISEE 1 and 2, Active Magnetospheric Particle Tracer Explorers/Ion Release Module (AMPTE/IRM), and IMP 8 satellites.
Abstract: In this study a new functional form, r = r 0 [2/(1 + cos θ)] α , is used to fit. the size and shape of the magnetopause using crossings from ISEE 1 and 2, Active Magnetospheric Particle Tracer Explorers/Ion Release Module (AMPTE/IRM), and IMP 8 satellites. This functional form has two parameters, τ 0 and α, representing the standoff distance and the level of tail flaring. The value r is the radial distance at an angle (θ) between the Sun-Earth line and the direction of τ. It is found that r 0 varies with the interplanetary magnetic field (IMF) B z component and has a break in the slope at B z = 0 nT. The best-fit value of τ 0 decreases with increasing southward IMF B z . For northward IMF B z , the best-fit value of τ 0 increases slightly with increasing B z . The best-fit value of α increases monotonically with decreasing IMF B z . The dynamic pressure (D p ) also changes τ 0 and α. The parameters D p and τ 0 are related by a power law of -1/(6.6±0.8). The best-fit value of α is slightly larger for larger dynamic pressure, which implies that D p also has a role in flux transfer from the dayside to the nightside, but the size of this effect is small. An explicit function for the size and shape of the magnetopause, in terms of D p and B z , is obtained by using multiple parameter fitting in a form that is useful for operational space applications such as predicting when satellites at geosynchronous orbit will be found in the magnetosheath.
715 citations
TL;DR: The Geotail spacecraft carries a high-resolution Magnetic Field Experiment to provide magnetic field data in the frequency range below 50 Hz as mentioned in this paper, which includes dual fluxgate magnetometers and a search coil magnetometer.
Abstract: The Geotail spacecraft carries a high-resolution Magnetic Field Experiment to provide magnetic field data in the frequency range below 50 Hz. This experiment includes dual fluxgate magnetometers and a search coil magnetometer. Fluxgate sensors are mounted at distances of 4 m and 6 m from the spacecraft on a deployable mast to reduce spacecraft-generated noises. Both outboard and inboard fluxgate magnetometers have 7 automatically switchable ranges from ±16 nT to ±65536 nT (full scale) and resolutions equivalent to a 15-bit A/D conversion in each range. The basic sampling rate for the A/D conversion is 128 Hz for both magnetometers
703 citations
TL;DR: In this paper, a new empirical magnetic field model has been developed, representing the variable configuration of the inner and near magnetosphere for different interplanetary conditions and the ground disturbance levels.
Abstract: [1] A new empirical magnetic field model has been developed, representing the variable configuration of the inner and near magnetosphere for different interplanetary conditions and the ground disturbance levels. This paper describes the mathematical structure of the model, while the results of fitting it to a new set of spacecraft data are presented in a companion paper. The general approach remains the same as in the earlier T96 model, but the mathematical description of all major sources of the magnetospheric field now applies recently developed new methods. In particular, the field deformation technique is extensively used, making it possible to realistically and flexibly represent the fields of the cross-tail current, the ring current, and the Region 1 and 2 Birkeland currents. The new model ring current includes not only the axisymmetric component but also a partial ring current with field-aligned closure currents, a feature absent in earlier data-based models. The field of the cross-tail current includes two modules whose current densities vary along the Sun-Earth line with different rates. The cross-tail current sheet warps in two dimensions in response to the geodipole tilt, its inner edge shifts along the Sun-Earth line with growing disturbance, and its thickness varies along and across the tail. Birkeland currents of Regions 1 and 2 vary in response to interplanetary conditions, so that at ionospheric altitudes they shift in latitude and change their distribution in local time. The magnetospheric boundary is specified using a most recent empirical model [Shue et al., 1998]; its size is controlled by the solar wind ram pressure, and its shape also varies in response to changes of the Earth's dipole tilt angle. The model magnetopause ensures a full confinement of the fields of all sources inside the magnetopause, regardless of its shape and size. The model also includes an interplanetary magnetic field–controlled interconnection field, allowing a finite normal Bn at the magnetopause and hence open magnetospheric configurations.
492 citations
Cites background from "Solar wind control of the magnetopa..."
...It is known [e.g., Sibeck et al., 1991; Roelof and Sibeck, 1993; Petrinec and Russell, 1993; Shue et al., 1998] that a negative IMF Bz results in a larger tailward flaring rate of the magnetopause on the nightside....
[...]
References
More filters
TL;DR: In this article, it was found that a model with a southward interplanetary magnetic field leads to a natural explanation of the SD currents and speculative aspects of the problem as they appear at this time are discussed.
Abstract: : It was found that a model with a southward interplanetary magnetic field leads to a natural explanation of the SD currents. Speculative aspects of the problem as they appear at this time are discussed. It should be remembered that this problem is amenable to revolutionary progress by observations from rockets or satellites which go out more than a few earth's radii.
3,818 citations
01 Dec 1978
Abstract: The magnetic field profiles across the magnetopause obtained by the ISEE-1 and -2 spacecraft separated by only a few hundred kilometers are examined for four passes. During one of these passes the magnetosheath field was northward, during one it was slightly southward, and in two it was strongly southward. The velocity of the magnetopause is found to be highly irregular ranging from 4 to over 40 km s-1 and varying in less time than it takes for a spacecraft to cross the boundary. Thicknesses ranged from 500 to over 1000 km.Clear evidence for reconnection is found in the data when the magnetosheath field is southward. However, this evidence is not in the form of classic rotational discontinuity signatures. Rather, it is in the form of flux transfer events, in which reconnection starts and stops in a matter of minutes or less, resulting in the ripping off of flux tubes from the magnetosphere. Evidence for flux transfer events can be found both in the magnetosheath and the outer magnetosphere due to their alteration of the boundary normal. In particular, their presence at the time of magnetopause crossings invalidates the usual 2-dimensional analysis of magnetopause structure. Not only are these flux transfer events probably the dominant means of reconnection on the magnetopause, but they may also serve as an important source of magnetopause oscillations, and hence of pulsations in the outer magnetosphere. On two days the flux transfer rate was estimated to be of the order of 2 × 1012 Maxwells per second by the flux transfer events detected at ISEE. Events not detectable at ISEE and continued reconnection after passage of an FTE past ISEE could have resulted in an even greater reconnection rate at these times.
985 citations
TL;DR: The magnetic field profiles across the magnetopause obtained by the ISEE-1 and -2 spacecraft separated by only a few hundred kilometers are examined for four passes as discussed by the authors, during which the magnetosheath field was northward, during one pass it was slightly southward, and in two it was strongly southward.
Abstract: The magnetic field profiles across the magnetopause obtained by the ISEE-1 and -2 spacecraft separated by only a few hundred kilometers are examined for four passes. During one of these passes the magnetosheath field was northward, during one it was slightly southward, and in two it was strongly southward. The velocity of the magnetopause is found to be highly irregular ranging from 4 to over 40 km s-1 and varying in less time than it takes for a spacecraft to cross the boundary. Thicknesses ranged from 500 to over 1000 km.
934 citations
TL;DR: MHD equations applied to hypersonic flow of solar plasma around magnetosphere and approximation with simpler equations of gas dynamics were used to simulate the solar plasma in the magnetosphere.
920 citations
TL;DR: The average and unusual locations of magnetopause and bow shock positions observed by IMP spacecraft were analyzed in this paper, showing that the bow shock position is unusual for the Earth's magnetic field.
Abstract: Average and unusual locations of magnetopause and bow shock positions observed by IMP spacecraft
870 citations