SWPC monitors the energetic proton detectors on NOAA's GOES satellites to determine when an SPE is in progress. (An SPE is defined as a flux of >10 MeV protons greater than 10 particles cm-2 sec-1 ster-1.) While the GOES satellite instrument can determine the presence and temporal profile of an SPE, those observations provide no information about the extent of the area over which those protons enter the atmosphere in the polar region or about which radio propagation paths are affected by the increased ionization.

NOAA's Polar Orbiting Environmental Satellites (POES) carry proton detectors similar to GOES. However, each POES satellite transits a polar region twice each orbit and can provide a direct measure of the boundaries and extent of the solar proton fluxes entering the atmosphere during an SPE.

The plots displayed above are designed to provide an up-to-date picture of the extent of the Northern and Southern polar area being affected during an SPE. This also provides an indication of those HF radio propagation paths that will be badly degraded because of the signal absorption.

In this display, all available satellite transits over the polar region during the most recent 8-hours are plotted. Currently there are four operating POES providing about a dozen transits over both the Northern and Southern polar regions within that time interval. The 16-second averaged count rates from the >15 MeV (nominally 15 -70 MeV) proton detector on each satellite are color coded and plotted along that satellite's transit. The geographic location of each data point is not the location of the sub-satellite point but rather the location mapped along the geomagnetic field from the satellite to 120 km altitude where the solar protons enter the atmosphere and produce the excess ionization. The beginning of the most recent satellite transit is marked with a red square and its end with a red triangle. Data plotted in white indicates insignificant count rates. The universal time at the start of the pass is given in the caption along with the name of the satellite providing the information.

Typically the sensor count rates are at cosmic ray background and the color plotted for each satellite transit is white. In the Southern Hemisphere display there is a geographic region over South America and the South Atlantic where the sensor count rates are normally high and are plotted yellow. This region is the southern extension of the South Atlantic Anomaly where the energetic particle intensities are normally large and does not indicate the presence of solar protons. In addition to the enhanced intensities associated with the South Atlantic Anomaly, there are regions of enhanced sensor responses (appearing as swathes of yellow and red) that appear within regions closer to the poles in both the northern and southern hemisphere. These elevated sensor responses are confined to data gathered by the SEM-1 instrument on NOAA POES satellites up to NOAA-14, and do not appear in data from the new SEM-2 instrument on NOAA POES satellites from NOAA-15 onward. This apparent high sensor response is, in fact, elevated background response due to high energy electrons from Earth's radiation belts and is not to be confused with regions of solar proton influxes. Improvements in the solid state detector electronics design has eliminated this problem in the SEM-2 instruments although it remains in the earlier SEM-1 design.

L-value Contour Lines