JHU/APL's Auroral Particles and Imagery - NIGHTSIDE Boundaries Help Page

NIGHTSIDE Boundaries Format Explanation

Format of automated nightside boundary identifications The new system is based on a set of quantitative algorithms developed by Newell, Feldstein, Galperin, and Meng, JGR, 1996 (not the neural net system of Newell et al. 1991). For details consult this paper. A quick outline of the boundaries follows:

s: start of pass. Data at latitudes lower than this were not considered
b0: the first point at which precipitation above noise level is observed (often but not necessarily b0=~b1e=~b1i, but sometimes b2i is equatorward of b1e and b1i. Sometimes detached high energy ions ("nose events") lie equatorward of b1).
b1e: The "zero-energy" electron boundary (usually determined by the 32 and 47 eV e- channels, except when photoelectrons are present, in which case the 68 and 100 eV channels are used).
b1i: The "zero-energy" ion boundary (usually the 32 and 47 eV ion channels, except when spacecraft charging is present, in which case the 47 and 68 eV channels are used).
b2e: The point where the electron average energy is neither increasing nor decreasing with latitude: one interpretation of the start of the main plasma sheet.
b2i: The point where the energy flux of ions above 3 keV has a maximum. This boundary is similar to Sergeev's ion isotropy boundary, which has been shown by him to highly correlate with GOES magnetic field observations.
b3a: The equatorwardmost electron acceleration event identified (only cases of intense field-aligned acceleration by 3-4 times the thermal energy of the source electrons are included. Also events must be above 0.25 ergs/cm**2 s).
b3b: The polewardmost such event (in the case of polar cap arcs, this could lie outside the auroral zone).
b4s: The structured/unstructured boundary, based on the running average of correlation coefficients between individual electron spectra and their neighbors.
b5e: The poleward boundary of the auroral oval as determined by an abrupt drop in the electron energy flux.
b5i: Same for ions.
b6: Poleward boundary of subvisual drizzle roughly adjacent to the oval.
e: end (poleward limit) of the data considered by the program as part of the nightside pass.

The first line of each record list the satellite number (e.g., F07=DMSP F7), year, day of year (Jan 1 = 1), and geographic and magnetic (PACE) coordinates for boundary 0. The second line lists geographic and magnetic coordinates for boundary b1e and b1i:

b1e,b1i= (geo b1e)/(mag b1e) // (geo b1i)/(mag b1i)

    The third line does the same for b2e, etc. The 7th and 8th line give the universal times (hhmmss) of the various boundaries. The lines between 9 and 15 give averages over the regions and maxima within the regions. For example the line "s0" applies to the region between the start of the file and b0. It gives energy flux in ergs/cm**2 s of e- precipitation followed by ions, followed by electron average energy then ion ave energy (both probably meaningless between s and b0), then the peak electron energy flux then peak ion energy flux, then electron average energy at the electron peak, then ion average energy at the ion peak, then the ut (hhmmss) of observing the e- peak then the ut of observing the ion peak.
    For the purposes of doing the averaging, 01 --> region between b0 and b1i, 12 --> between b1i and b2i; 24 --> between b2i and b4s. The poleward boundary of the auroral oval, b5, is taken to be whichever of the two (b5e and b5i) lies further poleward.
    Note that geographic boundaries are given in a geocentric coordinate system, whereas we have previously distributed DMSP data in a geodetic system.

Send science questions/comments to Dr. Patrick Newell Patrick.Newell@jhuapl.edu
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