Global Sporadic-E Occurrence Rate Climatology Using GPS Radio Occultation and Ionosonde Data

An updated global climatology of blanketing sporadic E (E-s) is developed from a combined data set of Global Positioning System (GPS) radio occultation (RO) and ground-based ionosonde soundings over the period of September 2006-January 2019. A total of 46 sites and 3.2 million total soundings from the Global Ionosphere Radio Observatory network in combination with 3.0 million occultations from the Constellation Observing System for Meteorology, Ionosphere, and Climate constellation are used to calculate global occurrence rates (ORs) for two blanketing frequency thresholds: all blanketing sporadic-E with no limit on intensity (all-E-s) and moderate-E-s with fbEs >= 3 MHz. Following the GPS-RO to ionosonde comparison by Carmona et al. (2022), https://doi.org/10.3390/rs14030581 the all-E-s rates are calculated using ionosonde data and an amplitude-based S-4 threshold for the GPS-RO data while the moderate-E-s rates use a primarily phase-based technique. Occurrence rates are separated by intensity, season, month, and solar local time for quiet geomagnetic conditions. Overall, the general geomagnetic trends agree with previous E-s climatologies and the ORs peak near 50% for all-E-s and 25% for moderate-E-s measured in the mid-latitudes during local summer in the late afternoon. Low ORs are observed near the South Atlantic Anomaly and North America, and a general asymmetry is observed between hemispheres with higher ORs in the Northern Hemisphere. High-latitude and late morning blanketing E-s are found to be stronger but less frequent with rates nearly equal to the moderate-E-s mid-latitude maximums.