As part of the modernization of the magnetic field models and geospace region definitions used in the Satellite Situation Center (SSC) software, a radical change was introduced between Versions 2.1 and 2.2 in terms of the philosophy used to define regions of geospace. Versions 2.1 and earlier essentially employed a single "index" to identify regions, without distinction between regions in space and regions on the ionosphere (or ground). Version 2.2, in contrast, involves multiple indices to specifically differentiate the region in geospace that the satellite resides in, and the (mapped) regions on the ionosphere (or ground) that the subsatellite point or magnetic footpoint(s) fall in. Thus, the new geospace region definitions involve a family of "spacecraft regions," and a family of "mapped regions," as listed below:
|Spacecraft Region||Code recorded when output = CDF|
|High Latitude Boundary Layer||8|
|Low Latitude Boundary Layer||9|
|Mapped Region||Code recorded when output = CDF|
|Northern Auroral Oval||5|
|Southern Auroral Oval||6|
|Northern Polar Cap||7|
|Southern Polar Cap||8|
Users may request, independently, information on any of the four region identifier indices: 1) spacecraft region, 2) radially mapped region (i.e. the subsatellite point), 3) northern magnetic footprint region, 4) southern magnetic footprint region. Magnetic field traces are performed using a user-selectable combination of internal and external magnetic field models.
For the Magnetopause, the Roelof and Sibeck model (JGR, 98, 21421, 1993) is employed. The model represents the boundary as a "quadratic function" in aberrated GSE coordinates; namely:
For the Bow Shock, a Modified version of Fairfield's 1971 model (JGR, 76, 6700, 1971) arranged to move in and out in response to solar wind and IMF changes, in unison with the magnetopause, and constrained to fixed ratio between the subsolar distances to the bow shock and magnetopause, Rbs/Rmp=1.3
The Neutral Sheet definition is based on the current sheet model used in new Tsyganenko models (JGR, 100, 5599, 1995). The current sheet surface is described by the expression:
The Plasma Sheet model, as labelled in the SSC, is meant to include both the plasma sheet (PS) and plasma sheet boundary layer (PSBL) since no community-accepted models exist (as far as we know) to represent these regions independently. The PS region is thus defined as a strip extending 3 Re above and below current sheet surface.
The High Latitude Boundary Layer (HLBL) and Low Latitude Boundary Layer (LLBL) regions are defined in relation to the magnetopause and neutral sheet. Using GSM coordinates, an anular strip of thickness D = D(X) is defined inside magnetopause; D widens from 0.4 Re at the terminator to 4 Re at X=-40 Re, and is held fixed at 4 Re tailward of X=-40 Re. Points inside the strip and within 3 Re of the neutral sheet surface are labelled as LLBL, while those in the strip but more than 3 Re from the neutral sheet are tagged as HLBL.
The Tail Lobe region is defined as points tailward of the "hinging distance" (Rh = 8), inside the tail but not in PS, HLBL or LLBL.
The following diagram illustrates graphically, the layout of the regions described above:
The Auroral Oval boundaries AOHI and AOLOW are described by:
Finally, the Mid-latitude and Low-latitude regions are defined in terms of ranges in MLAT according to: Mid-lat from MLAT = 30 degrees up to the equatorward edge of auroral oval, and Low-lat by MLAT = -30 degrees to 30 degrees.
The various mapped regions are illustrated in the following sketch: