Ionospheric boundary locations derived from IMAGE (Imager for Magnetopause-to-Aurora Global Exploration) satellite FUV (Far Ultra Violet) imager data covering the period from May 2000 until October 2002. These include poleward and equatorward auroral boundary data derived directly from the three imagers, WIC (Wideband Imaging Camera), SI12 (Spectrographic Imager 121.8 nm), and SI13 (Spectrographic Imager 135.6 nm). These also include the OCB (open-closed magnetic field line boundary) and EPB (equatorward precipitation boundary) derived indirectly from the auroral boundaries. The data set also includes model fitted circles for all the boundary data sets for all measurement times.
Chisham et al. (2022) also describe that the v2 data set also includes estimates of the OCB at each time, derived from a combination of the poleward auroral boundary measurements in combination with modelled statistical offsets between the auroral boundary and the OCB as measured by the DMSP spacecraft. The v2 data set also includes estimates of the EPB at each time, derived from a combination of the equatorward auroral boundary measurements in combination with modelled statistical offsets between the auroral boundary and the EPB as measured by the DMSP spacecraft.
The v2 data set also includes model circle fit boundaries for all times for all eight raw data sets. These model circle fits were estimated using the methods outlined in Chisham (2017) and Chisham et al. (2022), which involves fitting circles to the spatial variation of the boundaries at any one time.
The raw auroral boundaries were derived as outlined in Longden et al. (2010) (the original v1 data set) with the application of the additional selection criteria outlined in Chisham et al. (2022). For the creation of the original v1 data set, for each image, the position of each pixel in AACGM (Altitude Adjusted Corrected Geomagnetic) coordinates was established. Each image was then divided into 24 segments covering 1 hour of magnetic local time (MLT). For each MLT segment, an intensity profile was constructed by finding the average intensity across bins of 1 degree magnetic latitude in the range of 50 to 90 degrees (AACGM). Two functions were fit to each intensity profile: a function with one Gaussian component and a quadratic background, and a function with two Gaussian components and a quadratic background. The function with a single Gaussian component should provide a reasonable model when the auroral emission forms in a continuous oval. When the oval shows bifurcation, the function with two Gaussian components may provide a better model of the auroral emission. Of the two functions fit to each intensity profile, the one with the lower reduced chi-square goodness-of-fit statistic was deemed to be the better model for that profile. The auroral boundaries were then determined to be the position of the peak of the poleward Gaussian curve, plus its FWHM (full-width half-maximum) value of the Gaussian, to the peak of the equatorward Gaussian, minus its FWHM. In the case of the single Gaussian fit, the same curve is used for both boundaries. A number of criteria were applied to discard poorly located auroral boundaries arising from either poor fitting or incomplete data. Following Chisham et al. (2022), additional criteria were used to refine the data for the v2 auroral boundary data sets. These included dealing with anomalous data at the edges of the image fields of view, and dealing with anomalous mapping issues.
Funding was provided by:
STFC grant PP/E002110/1 - Does magnetic reconnection have a characteristic scale in space and time?
NERC directed grant NE/V002732/1 - Space Weather Instrumentation, Measurement, Modelling and Risk - Thermosphere (SWIMMR-T).
NERC BAS National Capability - Polar Science for Planet Earth.
Aurora, Boundaries, IMAGE, Ionosphere, Space Weather
Chisham, G. (2022). Ionospheric boundaries derived from IMAGE satellite mission data (May 2000 - October 2002) - VERSION 2.0 (Version 2.0) [Data set]. NERC EDS UK Polar Data Centre. https://doi.org/10.5285/fa592594-93e0-4ee1-8268-b031ce21c3ca
|Use Constraints:||This data is governed by the NERC data policy http://www.nerc.ac.uk/research/sites/data/policy/ and supplied under Open Government Licence v.3 http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/|
|ISO Topic Categories:||
|Organisation||British Antarctic Survey|
|Role(s)||Investigator, Technical Contact|
|Organisation||British Antarctic Survey|
|Quality:||Where possible, all data of questionable quality have been removed from the data set.|
|Lineage:||Derived and expanded from Version 1 auroral boundaries - https://doi.org/10.5285/75aa66c1-47b4-4344-ab5d-52ff2913a61e|
|Detailed Location||Northern hemisphere high-latitude ionosphere (~300 km altitude)|
|Distribution Media||Online Internet (HTTP)|
|Distribution Size||609 MB|
|Data Storage:||For the raw boundary data files in the 'raw_boundaries' directory: There are 8 files contained here, one for each boundary covering the complete measurement epoch. Each files is ~60-65 MB in size. The files are PALB_si12_v2, PALB_si13_v2, PALB_wic_v2, EALB_si12_v2, EALB_si13_v2, EALB_wic_v2, OCB_v2, EPB_v2, where PALB stands for Poleward Auroral Luminosity Boundary, EALB stands for Equatorward Auroral Luminosity Boundary, OCB stands for Open-Closed Boundary, and EPB stands for Equatorward Precipitation Boundary.
Each line in the files provides all the measured boundaries for a particular time in a space delimited format. The format for each line is...
YEAR (int), SECONDS_OF_YEAR (long), 24 X Latitude (float)
Where the 24 latitude values represent the boundary latitudes for magnetic local time (MLT) sectors extending from 00-01 MLT through to 23-24 MLT.
For the modelled circle fits in the 'circle_fit_boundaries' directory: There are 8 files contained here, one for each boundary covering the complete measurement epoch. Each file is ~8-20 MB in size. The files are PALB_si12_circle, PALB_si13_circle, PALB_wic_circle, EALB_si12_circle, EALB_si13_circle, EALB_wic_circle, OCB_v2, EPB_circle. These files have an 18 line header with each line starting with #. This was requested by the owners of a Python Space Physics package of which this data will eventually form a part.
Each line in the files provides information about the fitted boundary circles for a particular time in a space delimited format. The eight variables in each line are...
YR int Year
SOY long Seconds of Year
N_BOUNDS int Number of boundaries in circle fit
PHI_CENT float MLT angle of circle centre
R_CENT float Distance (degrees) from AACGM pole to circle centre
R_CIRC float Radius (degrees) of fitted circle
A_CIRC float Pseudo area of fitted circle (as in AACGM, not geographic)
RMS_ERROR float RMS error of fit
R_MERIT float Distance of fitted circle centre from criteria circle centre