SEP Nowcast Technical Overview

Normal and Highly Active Proton Level Map Examples.

The examples show SEP flux maps during high geomagnetic activity and low geomagnetic activity. The high activity map shows solar proton levels during the Halloween 2003 solar storm, 30 October 2003 23h UT (Kp = 9). High proton flux levels were caused by the 17 large solar flares over a two week period. This was the most intense geomagnetic activity occurring in more than 20 years and was responsible for electricity blackouts in Northern Europe, communication disruptions, re-routing of commercial polar flights, and anomalies experienced by satellites and spacecraft (for more details see the NOAA SWPC report on this extreme storm found here). The map for 26 March 2013 23h UT (Kp = 1) shows typical solar proton levels on a normal, low activity day. Color-coding of the map shows proton levels 10 times or more below the warning level in blue, near the warning level in yellow, at to 10 times the warning level in green, and 10 - 1,000 times the warning level in orange/red.

Dangerous Days: High Activity Proton Levels During the Most Intense Storm in the Past ~20 Years

Solar Proton Levels reached hazardous levels during the intense Halloween 2003 storm. The map shows levels during the event, on 30 October 2003. Proton levels were as high as 10 - 100 times the warning level (orange) over much of North America and Europe at an altitude of 10,000 km (a medium Earth orbit for satellites).

Safe Days: Normal Low Activity Proton Levels

Solar Proton Levels during a normal, safe day on 26 March 2013.
The proton levels are 10 - 100 (cyan) or 100 - 1,000 (blue) times lower than the hazardous warning level.

Technical Details on Measuring SEP Levels.

The National Oceanic and Atmospheric Administration's (NOAA) Space Weather Operations division defines hazardous SEP events as those with a measured > 10 MeV proton flux of 10 pfu or above. A list of all such classified events is available here. During low solar activity, few to none of the hazardous events may occur during the whole year, while highly active times can cause a few events per month. Real-time values of SEPs at high altitude are available through the NOAA operated Geostationary Operational Environmental Satellites (GOES). SEP 5-minute averaged integral proton flux is available for energy thresholds > 1 MeV, > 5 MeV, > 10 MeV, > 30 MeV, > 50 MeV, and > 100 MeV in units of Protons/cm2-s-sr or pfu. Differential proton flux is also available in eleven energy bands ranging from 0.7 - > 700 MeV. Thus, with these data, the present risk from SEPs is easily assessed in the geostationary orbit of approximately 35,790 km above the Earth.

To adjust the proton energy, geographic location, and altitude for which the SEP level will be predicted, users can use the Full Real-Time Nowcast. Users can select the latitude (-90 to +90 degrees), longitude (-180 to 180 degrees), and altitude (km above the Earth). Selectable energy levels include all of the integral energy bands from GOES.

Using this input and the current geomagnetic planetary index, Kp, obtained through NOAA SWPC ( Kp index available here), the effective geomagnetic cutoff energy is calculated using the Shea & Smart cutoff model (e.g., Smart et al. 1999abc, 2000). In short, the cutoff rigidities and energies are computed through a trajectory-tracing technique using the Tsyganenko magnetospheric model for the geomagnetic field, given the magnetic activity level indicated by Kp (where Kp = 0 is quiet and 9 is an extremely strong storm).

The effective cutoff energy along with the geosynchronous orbit integral flux data from GOES are used to construct the integral spectrum at the input position. A plot of this spectrum is shown as the Current Integral Flux Particle Spectrum. By using the cursor position, the exact predicted proton flux can be determined for the selected location, altitude, and energy, allowing for more accurate measurements of the proton flux than seen in the color contours of the SEP maps.

Map of the Integral Solar Proton Flux Level

The user may select an integral proton energy value (e.g., > 10 MeV) to display a map of SEP flux at the chosen energy and altitude. This plot is produced using the GOES geosynchronous spectrum and cutoff calculations over a wide grid of locations. Color levels of the SEP flux range from blue (low SEP level) to red (high SEP level). Very low SEP flux values, below 0.001 pfu, are shown in blue. Values >10 pfu are potentially hazardous and indicated by yellow, orange, or red on the map. Examples of what these maps may look like during low/high activity are shown above for a high SEP level/"dangerous" day and normal SEP level/"safe" day.

Go to the AER SEP nowcast page.

Go to the Real-Time SEP nowcast with selectable altitude, location, and energy page.