Models and Regions of Geospace in the Satellite Situation Center Software, V. 2.2

(Hitchhiker's Guide to the SSC Geospace)

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:

Regions of Geospace

Spacecraft Regions:

Spacecraft Region	Code recorded when output = CDF
None	0
Interplanetary Medium	1
Dayside Magnetosheath	2
Nightside Magnetosheath	3
Dayside Magnetosphere	4
Nightside Magnetosphere	5
Plasma Sheet	6
Tail Lobe	7
High Latitude Boundary Layer	8
Low Latitude Boundary Layer	9
Dayside Plasmasphere	10
Nightside Plasmasphere	11

Mapped Regions:

Mapped Region	Code recorded when output = CDF
None	0
Northern Cusp	1
Southern Cusp	2
Northern Cleft	3
Southern Cleft	4
Northern Auroral Oval	5
Southern Auroral Oval	6
Northern Polar Cap	7
Southern Polar Cap	8
Northern Mid-latitude	9
Southern Mid-latitude	10
Low-latitude	11

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.

Regions and Boundaries in the SSC Software: Algorithms

Spacecraft Regions:

The Interplanetary Medium, Magnetosheath, and Magnetosphere regions are defined by model boundaries for the magnetopause and bow shock surfaces.

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:

where S1, S2 and S3 are functions of the solar wind dynamicd pressure Psw and the IMF-Bz component.

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:

where (x,y, z) are aberrated GSM coordinates, psi is the tilt angle, and the "scaling" parameters are set to: Rh = 8, d = 4, G=10, Ly = 10.

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 Plasmapause is defined according to the model of Gallagher, et al., (Adv. Space Res. 8, 15, 1988) which represents the plasma density n as a function of the L-parameter, the magnetic local time (MLT) and the height, h, above the Earth's surface. Figure: Equation

In the previous expression, lambda is the geomagnetic latitude. We define plasmapause as the surface give by log(n)=1.5 The region labelled Magnetosphere corresponds to points inside magnetopause but not in other s/c regions.

Mapped Regions:

The Cusp and Cleft regions are based on "statistical" description by Newell and Meng (JGR, ???); namely, the Cusp is defined as the region MLAT= 75-76 degrees, MLT=09:00-13:00, while the Cleft is given by MLAT = 74-78 degrees, MLT=08:00-13:30.

The Auroral Oval boundaries AOHI and AOLOW are described by:

where C=22.5 degrees if MLT<22:50 and 337.5 degrees if MLT>22:50; S=+/-1 (nightside/dayside).

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:

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