Exploring the magnetospheric boundary layer

Hapgood, M. A.; Bryant, D. A.

doi:10.1016/0032-0633(92)90099-a

Cited by 46 publications

(42 citation statements)

References 14 publications

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“…Hapgood and Bryant (1992) have shown that electron temperature varies in a consistent and repeatable manner with electron density throughout nearly all magnetopause crossings. Fluctuations in the time series of both quantities are produced by magnetopause motions, but these are effectively caused by the satellite moving back and forth along what is a continuous transition in the boundary rest frame.…”

Section: Distinguishing Of Open and Closed Models Of The Llblmentioning

confidence: 87%

“…Such a transition, seen in the moments of the electron gas, could be present for almost any process that causes mixing of the magnetospheric and magnetosheath populations. What is significant, however, is that using these electron data to indicate the satellite's relative position in the LLBL (the "transition parameter") reveals coherent structure in both the ion flows and magnetic field, which are independent of the electron measurements (Hapgood and Bryant, 1992;Hapgood and Lockwood, 1993). Recently, Lockwood and Hapgood (1997) have shown that the transition parameter (the degree of electron mixing) bears a simple relationship to time-elapsed since reconnection, showing that transition parameter works because there are open field lines coating the magnetospheric surface, i.e.…”

Section: Distinguishing Of Open and Closed Models Of The Llblmentioning

confidence: 99%

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Coordinated Cluster and ground-based instrument observations of transient changes in the magnetopause boundary layer during an interval of predominantly northward IMF: relation to reconnection pulses and FTE signatures

Lockwood

Fazakerley²,

Opgenoorth

et al. 2001

Ann. Geophys.

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Abstract. We study a series of transient entries into the lowlatitude boundary layer (LLBL) of all four Cluster spacecraft during an outbound pass through the mid-afternoon magnetopause ([X GSM , Y GSM , Z GSM ] ≈ [2, 7, 9] R E ). The events take place during an interval of northward IMF, as seen in the data from the ACE satellite and lagged by a propagation delay of 75 min that is well-defined by two separate studies: (1) the magnetospheric variations prior to the northward turning , this issue) and (2) the field clock angle seen by Cluster after it had emerged into the magnetosheath (Opgenoorth et al., 2001, this The events at Cluster have ion and electron characteristics predicted and observed by Lockwood and Hapgood (1998) for a Flux Transfer Event (FTE), with allowance for magnetospheric ion reflection at Alfvénic disturbances in the magnetopause reconnection layer. Like FTEs, the events are about 1 R E in their direction of motion and show a rise in the magnetic field strength, but unlike FTEs, in general, they show no pressure excess in their core and hence, no characteristic bipolar signature in the boundary-normal component. However, most of the events were observed when the magnetic field was southward, i.e. on the edge of the interior magnetic cusp, or when the field was parallel to the magnetic equatorial plane. Only when the satellite begins to emerge from the exterior boundary (when the field was northward), do the events start to show a pressure excess in their core and the consequent bipolar signature. We identify the events as the first observations of FTEs at middle altitudes.

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Section: Distinguishing Of Open and Closed Models Of The Llblmentioning

confidence: 87%

Section: Distinguishing Of Open and Closed Models Of The Llblmentioning

confidence: 99%

Coordinated Cluster and ground-based instrument observations of transient changes in the magnetopause boundary layer during an interval of predominantly northward IMF: relation to reconnection pulses and FTE signatures

Lockwood

Fazakerley²,

Opgenoorth

et al. 2001

Ann. Geophys.

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“…Using the transition parameter introduced by Hapgood and Bryant (1992), we have analysed the basic characteristics of the cusp/magnetopause boundary layers observed by Cluster on the 25th January 2002, when Cluster passed from within the magnetosphere near the rim of the cusp (i.e. where the magnetospheric magnetic field turns from positive to negative GSE B Z ) via a boundary layer to the magnetosheath.…”

Section: Discussionmentioning

confidence: 99%

Cluster observations of bounday layer structure and a flux transfer event near the cusp

et al. 2005

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Abstract. On the 25th January 2002 between 10:00 and 12:00 UT, the four Cluster spacecraft passed through the northern high-latitude cusp, the dayside magnetosphere and into the magnetosheath in a linear formation. In the magnetosphere the PEACE electron spectrometers on the four spacecraft all observed a series of transient bursts of magnetosheath-like plasma, but without bipolar magnetic signatures in the magnetopause normal component as might be expected if the plasma had been injected by transient reconnection (flux transfer events -FTEs). Reordering the data using the magnetopause transition parameter reveals that these plasma observations, the related variations in the magnetic field and the balance of magnetic and thermal gas pressures are consistent with transient entries into a stable highlatitude boundary layer structure. However, once some of the spacecraft entered the magnetosheath, FTE signatures were observed outside the magnetopause at the same time as some of the boundary layer entries occurred at the other spacecraft inside. Thus, (a) the lack of a bipolar B N signature is inconsistent with the traditional picture of a magnetospheric FTE, and (b) the cause of the observed entry of the spacecraft into the boundary layer (pressure pulse or passing magnetosheath FTE) can only be determined by spacecraft observations in the magnetosheath.

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“…The clock angle is defined as arctan(B y /B z ), where the magnetic field vector is (B x , B y , B z ) in Cartesian GSM coordinates. The transition parameter for the magnetopause crossing is also calculated, in the manner set out by Hapgood and Bryant (1992). This transition parameter is derived by fitting a cubic curve to the temperature (T) and number density (N) data, with log 10 N as the independent variable and log 10 T as the dependent variable.…”

Section: Crossing Identificationmentioning

confidence: 99%

A multi-spacecraft survey of magnetic field line draping in the dayside magnetosheath

Coleman

2005

Ann. Geophys.

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Abstract. When the interplanetary magnetic field (IMF) encounters the Earth's magnetosphere, it is compressed and distorted. This distortion is known as draping, and plays an important role in the interaction between the IMF and the geomagnetic field. This paper considers a particular aspect of draping, namely how the orientation of the IMF in a plane perpendicular to the Sun-Earth line (the clock angle) is altered by draping in the magnetosheath close to the dayside magnetopause. The clock angle of the magnetosheath field is commonly estimated from the interplanetary magnetic field (IMF) measured by upstream monitoring spacecraft either by assuming that the draping process does not significantly alter the clock angle ("perfect draping") or that the change in clock angle is reasonably approximated by a gas dynamic model. In this paper, the magnetosheath clock angles measured during 36 crossings of the magnetopause by the Geotail and Interball-Tail spacecraft are compared to the upstream IMF clock angles measured by the Wind spacecraft. Overall, about 30% of data points exhibit perfect draping within ±10 • , and 70% are within 30 • . The differences between the IMF and magnetosheath clock angles are not, in general, well-ordered in any systematic fashion which could be accounted for by hydrodynamic draping. The draping behaviour is asymmetric with respect to the y-component of the IMF, and the form of the draping distribution function is dependent on solar wind pressure. While the average clock angle observed in the magnetosheath does reflect the orientation of the IMF to within ∼30 • or less, the assumption that the magnetosheath field direction at any particular region of the magnetopause at any instant is approximately similar to the IMF direction is not justified. This study shows that reconnection models which assume laminar draping are unlikely to accurately reflect the distribution of reconnection sites across the dayside magnetopause.

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Exploring the magnetospheric boundary layer

Cited by 46 publications

References 14 publications

Coordinated Cluster and ground-based instrument observations of transient changes in the magnetopause boundary layer during an interval of predominantly northward IMF: relation to reconnection pulses and FTE signatures

Coordinated Cluster and ground-based instrument observations of transient changes in the magnetopause boundary layer during an interval of predominantly northward IMF: relation to reconnection pulses and FTE signatures

Cluster observations of bounday layer structure and a flux transfer event near the cusp

A multi-spacecraft survey of magnetic field line draping in the dayside magnetosheath

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