Average and substorm conditions in the lobe and plasma sheet regions of the earth's magnetotail are studied as a function of downstream distance and east‐west location using ISEE 3 magnetometer and plasma analyzer measurements. On the basis of 756 magnetopause crossings a low‐latitude magnetotail diameter of 60±5 RE at |X| = 130 ‐ 225 RE is determined. The strength of the lobe magnetic field from |X| = 20 to 130 RE is shown to fall off as X−0.53±0.05. Flaring ceases on average at |X| = 120 ± 10 RE with a relatively constant BL = 9.2 nT beyond that distance. The ratios |By/Bx| and |Bz/Bx| in the translunar tail lobes are small and relatively constant with mean values of 0.10 and 0.06, respectively. These results are shown to be in good agreement with the Coroniti‐Kennel flaring tail models of lobe magnetic field configuration with slightly enhanced By due to Maxwell stresses exerted at the magnetopause by the solar wind. The plasma parameters Vx, ne, βe, and MA in the lobes all increase with distance down the tail while Te decreases. The mean values of these lobe quantities at |X| = 200 ‐ 220 RE are Vx = −200 ‐ 250 km/s, n = 0.1 ‐ 0.2 cm−3, βe = 0.02 ‐ 0.05, MA = 0.3 ‐ 0.4, and Te = 5 ‐ 8×105 °K. Strong density and weak velocity and temperature gradients are observed as ISEE 3 moves from the center of the lobes out toward the magnetopause. In particular, factor of 3–6 increases in plasma density are observed as the spacecraft moves from the center of the tail at |Y′| < 10 RE (Y′ refers to the aberrated GSM system) toward the dawn and dusk portions of lobes at |Y′| > 20 RE. Good agreement is found between the leaky magnetopause model of Pilipp and Morfill (1978) and the strong density/weak velocity gradients observed in the lobes. Substorm activity, as measured by AE(9), is only weakly correlated with magnetic field strength, electron beta, or Alfvénic Mach number in the lobes at |X| > 200 RE. The plasma sheet magnetic field intensity and electron temperature decrease with increasing downstream distance, while flow speed, density, and Alfvénic Mach number all increase. Average plasma sheet parameters at |X| = 200 ‐ 220 RE are B = 4.0 nT, Vx = −500 km/s, ne = 0.3 cm−3, Te = 1.2×106 °K, and MA = 2.7. Electron beta is independent of downstream distance with a mean value of approximately 0.7. On the basis of pressure balance arguments the estimated total plasma beta in the |X| > 60 RE plasma sheet is 4.5, and the Ti/Te ratio is 5.5. With respect to reconnection, the most significant results are the correlations between Bz, Vx, and AE(9) in the plasma sheet, the variation in these parameters with X and ± Y, and their implications for the location of the distant neutral line. The highest tailward flow speeds are found to be proportional to the magnitude of the embedded southward Bz. Furthermore, both tailward Vx and southward Bz are shown to be well correlated with AE(9). Earthward of |X| = 100 RE the average Bz is northward and the flow is on average sub‐Alfvénic. Between |X| = 100 and 180 RE the flow becomes predominan...

Abstract. THEMIS was launched onDuring the coast phase the probes were put into a string-of-pearls configuration at 100s of km to 2R E along-track separations, which provided a unique view of the magnetosphere and enabled an unprecedented dataset in anticipation of the first tail season. In this paper we describe the first THEMIS substorm observations, captured during instrument commissioning on March 23, 2007.THEMIS measured the rapid expansion of the plasma sheet at a speed that is commensurate with the simultaneous expansion of the auroras on the ground. These are the first unequivocal observations of the rapid westward expansion process in space and on the ground. Aided by the remote sensing technique at energetic particle boundaries and combined with ancillary measurements and MHD simulations, they allow determination and mapping of space currents.These measurements show the power of the THEMIS instrumentation in the tail and the radiation belts. We also present THEMIS Flux Transfer Events (FTE) observations at the magnetopause, which demonstrate the importance of multi-point observations there and the quality of the THEMIS instrumentation in that region of space.2

[1] Magnetically active times, e.g., Kp > 5, are notoriously difficult to predict, precisely the times when such predictions are crucial to the space weather users. Taking advantage of the routinely available solar wind measurements at Langrangian point (L1) and nowcast Kps, Kp forecast models based on neural networks were developed with the focus on improving the forecast for active times. To satisfy different needs and operational constraints, three models were developed: (1) a model that inputs nowcast Kp and solar wind parameters and predicts Kp 1 hour ahead; (2) a model with the same input as model 1 and predicts Kp 4 hour ahead; and (3) a model that inputs only solar wind parameters and predicts Kp 1 hour ahead (the exact prediction lead time depends on the solar wind speed and the location of the solar wind monitor). Extensive evaluations of these models and other major operational Kp forecast models show that while the new models can predict Kps more accurately for all activities, the most dramatic improvements occur for moderate and active times. Information dynamics analysis of Kp suggests that geospace is more dominated by internal dynamics near solar minimum than near solar maximum, when it is more directly driven by external inputs, namely solar wind and interplanetary magnetic field (IMF).

Abstract. We use Polar ultraviolet imager (UVI) and

While in the lobes of the distant magnetotail, ISEE‐3 encountered regions of compressed magnetic field, δB/Bo=0.3‐0.1, at a rate of several per day. The duration of these events was 5 to 20 minutes and they were observed 10 to 30 minutes following the onset of substorm activity near the earth. During each event, the lobe magnetic field tilted first northward and then southward with the inflection point near the time of peak field strength. Following the compression events, the lobe field weakened and retained a southward component for 20 to 40 minutes. It is suggested that these traveling compression regions (TCR’s) are the lobe signatures of plasmoids moving rapidly down the tail in the plasma sheet. Comparison of ISEE‐3 compression event times with substorm onset times yielded propagation speeds of 350 to 750 km/s.

[1] We employ 2.5-D electromagnetic, hybrid simulations that treat ions kinetically via particle-in-cell methods and electrons as a massless fluid to study the formation and properties of a newly discovered boundary named the foreshock compressional boundary (FCB). This boundary forms in the ion foreshock and is associated with enhanced densities and magnetic field strengths. At times, but not always, the FCB separates the pristine solar wind plasma from the ion foreshock. In this study, we investigate the dependence of FCB characteristics on solar wind Mach number and cone angle (the angle between flow velocity and interplanetary magnetic field). We show that the strength of the foreshock compressional boundary increases with the Mach number. This enhancement is in turn tied to the density and velocity of the backstreaming ions in the foreshock whose interaction with the solar wind results in ULF turbulence which is ultimately responsible for the formation of FCB. During small cone angles the foreshock compressional boundary is symmetric with respect to the radial direction. As the cone angle increases, the FCB becomes less symmetric and eventually is confined to one side of the foreshock. The strength of the FCB also decreases with increasing cone angle but depending on the Mach number can exist for cone angles of 40°and beyond. A recent study that compared data from a global hybrid simulation of the foreshock with Cluster spacecraft observations showed that encounters with foreshock cavities can be interpreted as back and forth motion of a FCB causing spacecraft to move from the solar wind through the FCB into the foreshock and back into solar wind. An example of a FCB observed by the Cluster spacecraft is presented and shown to be in general agreement with model predictions.

The substorm injection boundary model has enjoyed considerable success in explaining plasma signatures in the near‐geosynchronous region. However, the injection boundary has remained primarily a phenomenological model. In this paper we examine 167 dispersionless energetic ion injections which were observed by AMPTE CCE. The radial and local time distribution of the events as a function of Kp is qualitatively similar to that envisioned in the injection boundary model of Mauk and McIlwain (1974). We will argue that particles observed during dispersionless injections are locally energized during the disruption of the cross‐tail current sheet. Therefore we identify the injection boundary, as derived from the spatial distribution of dispersionless injections, with the earthward edge of the region of the magnetotail which undergoes current sheet disruption during the substorm expansion phase. We will show that this qualitative model for the generation of the injection boundary can provide an explanation for the dispersionless nature, the double spiral shape, and the Kp dependence of the boundary.

This paper reports the multisatellite and ground observations of two pseudo‐substorm onset events that occurred successively at 0747 UT and 0811 UT, May 30, 1985, with more attention to the 0747 UT onset. The distinguishing features of the 0747 UT event are as follows. (1) The substorm‐associated tail reconfiguration started in a very localized region in the near‐Earth magnetotail. (2) The magnitude of the current disruption decreased markedly as the disruption region expanded tailward. (3) On the ground the onset of a very small negative bay (∼ 40 nT) was observed simultaneously with the onset of the current disruption, but over a much wider local time sector than the near‐Earth tail reconfiguration. Positive bay onsets at mid‐latitudes also had a longitudinally wide distribution. From these features we infer that in the present event the current disruption took place filamentarily near AMPTE/CCE at ∼8.8 RE. It is also inferred that pseudo‐substorm onsets are distinguished from standard substorm onsets by the absence of a global expansion of the current disruption, and that the spatial scale of the onset region in the magnetosphere is not a major difference between the two. The present study suggests that the spatial distribution of the magnetic distortion before onsets is an important factor to determine the expansion scale of the current disruption. It is also suggested that the current disruption is basically an internal process of the magnetosphere.