The THEMIS mission provides unprecedented multi-point observations of the magnetosphere in conjunction with an equally unprecedented dense network of ground measurements. However, coverage of the magnetosphere is still sparse. In order to tie together the THEMIS observations and to understand the data better, we will use the Open Geospace General Circulation Model (OpenGGCM), a global model of the magnetosphereionosphere system. OpenGGCM solves the magnetohydrodynamic (MHD) equations in the outer magnetosphere and couples via field aligned current (FAC), electric potential, and electron precipitation to a ionosphere potential solver and the Coupled Thermosphere Ionosphere Model (CTIM). The OpenGGCM thus provides a global comprehensive view of the magnetosphere-ionosphere system. An OpenGGCM simulation of one of the first substorms observed by THEMIS on 23 March 2007 shows that the OpenGGCM reproduces the observed substorm signatures very well, thus laying the groundwork for future use of the OpenGGCM to aid in understanding THEMIS data and ultimately contributing to a comprehensive model of the substorm process.

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[1] In this case study we report a substorm, 23 March 2007, which exhibited oscillations with a period of $135 s in three substorm phenomena all of which were one-to-one correlated. The in-situ observations are from one THEMIS spacecraft (8.3 R E geocentric distance) and the geosynchronous LANL-97A spacecraft. The focus here is on the intensification phase during which THEMIS was conjugate to the region of auroral brightening and its foot point was near the high-latitude ground station Kiana. The following results will be demonstrated: (1) THEMIS and LANL-97A (time-delayed) recorded periodic ion injections (>100 keV). (2) Near-conjugate high-latitude ground magnetometer data show very large Pi2 (dH$150 nT) with a 6-s time delay compared to the THEMIS ion injections. (3) Low-latitude ground magnetometer data also show Pi2 with the same waveform as the high-latitude Pi2 but with longer time delays (20 -31 s). (4) Auroral luminosity was periodically modulated during the intensification phase. (5) All three signatures (ion injections, ground Pi2, optical modulation) had the same periodicity of $135 s but with various time delays with respect to the THEMIS ion injections. These observations demonstrate that the three substorm phenomena had a common source which controlled the periodicity.

A set of boundaries was chosen to model the principal observed magnetospheric regions. Those regions which extended out to the distant magnetotail were defined at Xsm = -20 R e. The Tsyganenko (1989) magnetic field model (T89) was used to project the boundaries down to the ionosphere. It was found that all field lines which passed within 3 R e of the magnetopause projected to the dayside ionosphere. Dayside arcs therefore generally map to the low-latitude boundary layer, the cusp/cleft, or the entry layer. The nightside auroral zone, and therefore field lines associated with the substorm current diversion process, primarily traced to portions of the plasma sheet that do not come in direct contact with flowing solar wind plasma. Several mapping problems were encountered. The first involved identifying certain boundaries in the magnetosphere model. The flanks of the magnetotail are not modeled realistically. As a result, we had difficulty in defining a T89 magnetopause in the equatorial plane. Other problems were that some magnetotail boundaries may have no ionospheric signature, and that some boundaries are influenced by cross-field plasma drift. Plasma boundaries are not tangent to field lines when drift is present, but all mapping was done by following field lines. Uncertainties of about 1ø of latitude in the resulting ionospheric projections were found for each 1 R e of drift near midnight at Xsm ------20 R E. The steady state magnetotail then was subdivided out to Xsm ----22 R E according to the expected characteristics of charged particle orbits. Orbits were traced in the modified Harris magnetic field model, with parameters adjusted to approximate the shapes of T89 magnetic field lines. The one-dimensional Harris model was used to eliminate some drift effects. This permitted a detailed study of each separate subregion. Curves defining various orbit types were projected to the ionosphere. It is suggested that low-or middle-altitude satellites may be able to detect regions of quasi-adiabatic and nonadiabatic equatorial orbits by monitoring the loss cones. For these highly field aligned loss cone particles, we found that the net effect of the complex interaction with the current sheet can be explained by an extremely simple model. The model involves shifting all generally field-aligned ions as a block through an energy-dependent "scatter" angle. When viewed microscopically, the resulting pitch angle changes are highly structured. Macroscopically it may be possible to describe the process in terms of pitch angle diffusion. Figures 1 and 2 show how structures map between the ionosphere and the equatorial plane in the K•, = 0 version of T89. In K90 we used color plates to present similar information for the Beard quiet magnetosphere model. Figures 1 and 2 were prepared by mapping field lines down from the equator to the ionosphere. 9307 9308 KAUFMANN ET AL.: MAPPING MAGNETOSPHERIC BOUNDARIES -lORE< x< I0 R E Kp =0 14 / 16 18 60 70 80 90 -60 R E < x < -I0 R E 80 2O 22 70 60 Quiet Magnetosphere

The objective of this report is to identify those features of commonly observed dayside auroras that can be explained easily by either of two processes: mapping distortions or distortions caused by nearby Birkeland currents. Mapping distortions in a quiet closed magnetosphere model yield very elongated arclike ionospheric images in the dayside auroral zone for a wide range of circular or elliptical tubelike equatorial sources. The length of a dayside auroral arc provides a good measure of the equatorial source dimension normal to the magnetopause. The orientation of the dayside arc provides a crude estimate of the solar magnetospheric×location of the equatorial source. Dayside arcs and Birkeland currents are found to map to both the dayside and the nightside magnetopause current layer and low latitude boundary layer. Nightside auroral arcs and Birkeland currents map to the magnetotail plasma sheet and plasma sheet boundary layer. Localized Birkeland currents produce characteristic distortions that are dependent on the current density gradient. Single and multiple linear and hooked auroral forms are easy to understand in terms of mapping distortions in a quiet magnetosphere. The shapes of bright twisted or folded auroral forms are more easily explained as distortions produced by localized Birkeland currents. Measurement of the size of a spiral auroral structure provides an estimate of the current magnitude. Relationships between the motion of ionospheric objects and the motion of equatorial sources are summarized by two color plates. Such motion sometimes differs markedly from what one might intuitively expect. For example, some tailward moving sources near the magnetopause can map to sunward moving ionospheric images.