Solar Radio Bursts and Effects on GPS* Radio bursts are presumed due to a shock wave propagating (~1000 kms-1) outward through the solar corona. Electron energy is converted to plasma waves, which then excite electromagnetic waves at the local plasma frequency. EM waves can be generated from a few tens of MHz up to 3 GHz. GPS transmissions occur at L1 (1.57542 GHz) and L2 (1.2276 GHz) Wave polarization determined by B-field at generation site. Type II bursts are closely associated with solar flares. In the spectrograph record, these bursts appear as a narrow band of intense radiation that drifts from high to low frequency. Idealized illustration of the record of a complete solar radio outburst by a dynamic spectrograph *Reference and credits for materials and figures in this lecture: Cornell U. GPS Laboratory http://gps.ece.cornell.edu/

This movie depicts loss of GPS satellite observations due to a solar radio burst on 6 Dec. 2006. Data are taken from random sampling of IGS network receivers. The color of the dots represents the number of dual-frequency code observations made to each satellite. Solar radio bursts at GPS frequency reduce S/N in GPS receivers GPS receivers in sunlit hemisphere “lose lock” and cannot track enough satellites to get a “solution”

These graphs depict the total number of IGS receivers capable of producing a dual-frequency 4-satellite navigation solution on the sunlit hemisphere of the earth. Note that before and after the solar radio burst, >120 receivers on the sunlit hemisphere were producing a navigation solution. At the peak of the solar radio burst, the number of fully operational receivers dropped to less than 60.

Solar Radio Noise as Seen in the S4 Scintillation Index the S4 scintillation index defined as is the ratio of the standard deviation of the signal power fluctuations over the average signal power S4 index as calculated every UTC minute over 1 minute intervals on the 50 Hz data recorded from Arecibo on PRN 17 (same data as shown in previous plot). The S4 index is quite high indicating the rapid variations of the signal power caused by the solar radio burst. The S4 index is NOT high because of ionospheric irregularities causing diffraction/refraction of the GPS signal. C/No ratio for the day before the event (blue) compared to the day of the event (6 Dec. 2006) (red) [y-axis is C/No in dB-Hz, x-axis is UTC hours]. These are high data-rate receivers providing C/No at 50 Hz. The fades caused this particular receiver to lose lock at several points during the solar radio burst (the receiver is not capable of tracking below ~30 dB-Hz) . The receiver is an L1-only Cornell ScintMon receiver located at Arecibo Observatory, Puerto Rico.

What were the Impacts? No loss of Non-Precision Approach Brief loss of Vertical Guided Approach (in regions denoted in pink) (at least 4 satellites from all stations) WAAS Miami 12/06/06 FAA WAAS Network Latitude Number of Satellites (~1.5 minutes) Longitude TIME (UT) (Figure Courtesy of FAA Tech Center) “At approximately 2000Z on December 6 there was a widespread loss of GPS in the Mountain States region, specifically around the 4 corners region of NM/CO. Several aircraft reported losing lock on GPS and were tracking 7-9 satellites, and abruptly lost locks and were then tracking 0-1.” – GPSOC at Schriever AFB

Additional Examples & Backup Slides

Example Modest (8700 sfu) radio burst 7 Sept 2005 Arecibo Receiver 2.3 dB Effect is small, only 2.3 dB fade at L1 Only RHCP signals affect GPS 8,700 SFU Cerruti A. P., P. M. Kintner, D. E. Gary, L. J. Lanzerotti, E. R. de Paula, H. B. Vo (2006), Observed solar radio burst effects on GPS/Wide Area Augmentation System carrier-to-noise ratio, Space Weather, 4, S10006, doi:10.1029/2006SW000254.

The Large Radio Burst On December 6, 2006 X6 Solar Flare Peak fade of 20 dB Receiver has trouble tracking in pink region GPS frequencies Start of solar flare and solar radio burst

Solar Radio Burst Effects at L1 and L2 on a Global Positioning System Receiver, December 6, 2006 C/No ratio for the day before the event (blue) compared to the day of the event (6 Dec. 2006) (red) [y-axis is C/No in dB-Hz, x-axis is UTC hours]. The fades had a duration of about 1/2 hour and at L1 was observed to have a peak fade of >17 dB. The data is from the ZHU1 (Houston, TX) FAA WAAS receiver, PRN 4. The sampling rate is 1 Hz. The fades caused the receiver to lose L1 and L2 signal lock on a low-elevation satellite. C/No ratio for the day before the event (blue) compared to the day of the event (6 Dec. 2006) (red) [y-axis is C/No in dB-Hz, x-axis is UTC hours]. In this plot the L2 frequency is shown. The peak fade was about 20 dB. The data is also from the ZHU1 FAA WAAS receiver, PRN 4. The sampling rate is 1 Hz.

Solar Radio Burst Effects at L1 and L2 on a Global Positioning System Receiver, December 14, 2006 The data in the above two images was taken from the ZHU1 WAAS receiver in Honolulu Hawaii. The data shown are for the 14 December 2006 solar radio burst associated with the X-1 flare from AR 10930 at 2215 UT. Notice that in the L1 figure (left) that the fade from this solar radio burst is quite drastic (the flare exceeded 150,000 SFU), however in the L2 frequency there was hardly any response indicating that there was little solar radio burst power at GPS L2. Both plots are 1 Hz data for PRN 30.

How do December 2006 events fit into historical context? Region of observations that we do not understand Dec 14 Solar Radio Bursts 1960-2000 3 yr 11 yr 30 yr

Which GPS Receivers are Affected? All sunlit GPS receivers are affected. All GPS satellite signals tracked by a receiver are affected. Broad-band interference from solar radio burst decreases signal-to-noise ratio for all tracked signals equally. Both military and civilian signals are affected. Affects GPS receivers on the ground and in space. What can we Predict? Current data demonstrates that SRB of 8,700 SFU RHCP produces 2.3 dB signal fade across all tracked signals and sunlit receivers. Allows prediction that previously largest recorded SRB of 88,000 SFU will produce 12 dB signal attenuation, affecting some dual frequency GPS receivers. Prediction: Next solar maximum in 2011 should produce SRBs affecting some GPS receivers.