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OCB Correction Values

Poleward boundaries of the auroral oval derived from satellite images of the aurora, such as those that we have estimated using the method described, can provide a reasonable approximation of the open-closed magnetic field line boundary (OCB) in the Earth's magnetosphere.  The accuracy of these poleward boundaries as a proxy for the OCB can be improved through calibration with particle precipitation boundaries measured by low-altitude satellites that sample the charged particles in the upper atmosphere. These measured particle precipitation boundaries are considered by some to provide the definitive location of the OCB. The drawback of these particle precipitation boundaries is that each satellite can only be used to provide a single point measurement for the location of the OCB at a time. By calibrating our poleward auroral boundaries derived from auroral images with particle precipitation boundaries, we can obtain an accurate proxy for the OCB on a global scale and at higher temporal resolution.

We have calibrated our poleward auroral boundaries with data from the DMSP satellite. General information about the DMSP satellite mission is available here. The algorithms used to determine particle precipitation boundaries from DMSP data are outlined in Newell et al. (1991, 1996), and Sotirelis and Newell (2000).

From this calibration, we have calculated offsets for each of the three FUV cameras and for each MLT sector that should be added to our poleward auroral boundaries to improve their accuracy as a proxy measure for the OCB. These offsets are listed in the table below. Correction values for some dayside MLT sectors (for WIC and SI12) are not available as the relationship between DMSP boundaries and these IMAGE boundaries cannot be established.


OCB offset values
MLT WIC SI12 SI13
0.5 -0.90 -0.77 -0.83
1.5 -0.53 -0.80 -0.67
2.5 -0.20 -0.60 -0.20
3.5 0.07 -0.87 -0.20
4.5 0.23 -0.83 0.10
5.5 -0.37 -0.97 -0.17
6.5 -0.07 -0.80 -0.13
7.5 -1.03 -0.97 -0.50
8.5 -1.57 -1.57 -1.37
9.5 -1.60 -1.80 -1.60
10.5 -1.93 -1.67 -1.40
11.5 -
-
-1.93
12.5 -
-
-1.57
13.5 -1.43  - -1.30
14.5 -1.33 -1.40 -1.27
15.5 -1.17 -0.63 -0.70
16.5 -1.07 -0.27 -0.67
17.5 -1.50 0.10 -1.10
18.5 -1.33 0.20 -0.87
19.5 -1.40 0.33 -0.93
20.5 -1.20 0.20 -1.00
21.5 -1.40 -0.40 -1.20
22.5 -1.27 -0.67 -1.07
23.5 -1.03 -0.57 -0.90
Correction values version 1.1, June 2010

Correction values for previously released versions of OCB data can be found here.

References