Last week the sun sent a mass of charged particles tumbling towards Earth. According to the Space Weather Prediction Center's analysis, the most significant activity occured Friday September 12th, 2014 as shown in thier Kp Index Plot which reached a maximum of 8 near 18 - 21 hour UTC.
As discussed here, the Kp-Index is a global index and does not indicate where on the planet the geomagnetic activity is occuring. To get a better idea of the exact time and location of the geomagnetic activity at the earth's surface, we can use Natural Resources Canada magnetomter network of 14 active stations. Thier location is shown below:
Using their geomagnetic plotting service, we can plot the geomagnetic activity for each site over the periods before, during and after the solar storm reached the Earth. For the short analysis I selected two sites, Ottawa (OTT) and Resolute Bay (RES) as they also have (nearly) co-located GNSS receivers that we can compare to see if the solar storm had any impact on the GNSS signals.
Below are the plots of the rate-of-change of the magnetic field in the cartesian directions (X,Y,Z) and the overall intensity (F) for the two sites.
For Sept-11 the magnetic field is quiet for both sites. Then around noon time (local-time) we see a large spike in the activity for both sites. This matches very well with what we see in the planetary Kp-Index plot above which was expected. However, if you look at the scale of the Y-axis the variation for station OTT ranges from -60 to +60 nT/min where as for site RES, the y-axis ranges from -300 to 300 nT/min. This difference in the rate-of-change of the magnetic field agrees with the prediction made by the SWPC that the most affected areas would be poleward of 50 degree's geomagnetic latitude. Ottawa has a geomagnetic latitude of approximately 45 degrees, while Resolute Bay's geomagnetic latitude is well within the predication made by the SWPC.
GNSS Data Processing
To see the impact of the geomagnetic storm on GNSS data, I processed 24 hour RINEX files collected by NRCan for the two sites shown above (OTT and RES). For the processing I used NRCan Online PPP Software. Since PPP uses a combination of both L1 and L2 data it should be quite susceptible to any cycleslips or loss of lock due to the geomagnetic activity.
I downloaded the data for September 12, 2014 and fed it to the online PPP software. Ideally, 1Hz data would be used, but this takes a very long time to process so instead I only processed the 30 second data in kinematic mode.
Below are the results for the variation in height (top) as well as the number of satellites/% ambiguity reset at each station (bottom).
Overall the site near Ottawa (NRC1) shows little to no affect. The % amb reset (shown by the red x) shows little to no increase during the time of increased geomagnetic activity. On the otherhand, for station RES we notice an increase in the variation of the height solution around 18:00 UTC which last until the end of the day. Additionally, the % Ambiguity Reset has a noticeable increase during this time period which indicates that we were losing lock or experiencing outliers in the measurement data. This can most likely be attributed to the high geomagnetic activity caused by the solar storm.
Although Resolute Bay was affected by the geomagnetic storm, the overall position results are still quite good. This is the case since generally, the localized scintillation effects caused by geomagnetic activity only affect several satellites at a single time. Since we are observing between 8 - 12 satellites we still have enough satellites to achieve reasonable positioning results. As more GNSS's become available, this will continue to improve the robustness of GNSS receivers in the presence of geomagnetic activity. As predicted by the SWPC, station OTT, located at a lower latitude was not affected as much by the solar storm.