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_swith fbEs ≥ 3 MHz. Following the GPS‐RO to ionosonde comparison by Carmona et al. (2022),https://doi.org/10.3390/rs14030581the all‐E_srates are calculated using ionosonde data and an amplitude‐based S₄threshold for the GPS‐RO data while the moderate‐E_srates 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_sclimatologies and the ORs peak near 50% for all‐E_sand 25% for moderate‐E_smeasured 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_sare found to be stronger but less frequent with rates nearly equal to the moderate‐E_smid‐latitude maximums.

Sporadic-E ($E_s$) occurrence rates from Global Position Satellite radio occultation (GPS-RO) measurements have shown to vary by a factor of five between studies, motivating the need for a comparison with ground-based measurements. In an attempt to find accurate GPS-RO techniques for detecting $E_s$ formation, occurrence rates derived using five previously developed GPS-RO techniques are compared to ionosonde measurements over an eight-year period from 2010–2017. GPS-RO measurements within 170 km of a ionosonde site are used to calculate $E_s$ occurrence rates and compared to the ground-truth ionosonde measurements. The techniques are compared individually for each ionosonde site and then combined to determine the most accurate GPS-RO technique for two thresholds on sporadic-E intensity: no lower limit and fbEs $\ge 3$ MHz. Overall, the Yu$S_4$ method shows the closest agreement with ionosonde measurements for total $E_s$ occurrence rates without a lower limit on intensity, while the phase-based Chu technique shows the closest agreement for fbEs $\ge 3$ MHz. This analysis demonstrates that the variation in GPS-RO derived sporadic-E occurrence rates is due to varying thresholds on the sporadic-E intensities in terms of fbEs.

A global climatology of sporadic-E occurrence rates (ORs) based on ionosonde measurements is presented for the peak blanketing frequency, fbEs, and the ordinary mode peak frequency of the layer, foEs. ORs are calculated for a variety of sporadic-E frequency thresholds: no lower limit, 3, 5, and 7 MHz. Seasonal rates are calculated from 64 Digisonde sites during the period 2006–2020 using ionograms either manually or automatically scaled with ARTIST-5. Both foEs and fbEs ORs peak in the Northern Hemisphere during the boreal summer, with a decrease by roughly a factor of 2–3 in fbEs rates relative to foEs rates without a lower threshold on the sporadic-E intensity. This ratio of foEs to fbEs OR increases with increasing sporadic-E intensity, up to a factor of 5 for the 7 MHz threshold. An asymmetry is observed with the Southern Hemisphere peaks during the austral summer, with slightly lower rates compared with the Northern Hemisphere during the boreal summer. A drastic decrease in ORs is observed for the higher intensity thresholds, such that the fbEs occurrence rates for 7 MHz are nearly zero during most locations and seasons. These updated occurrence rates can be used for future statistical comparisons with GPS radio occultation-based sporadic-E occurrence rates.

Electromagnetic wave scattering and scintillation can occur at high latitudes of the Earth when polar cap patches are present. Polar cap patches range in size from 100 to 1,000 km and have densities on the order of 2–10 times that of the background ionosphere. Within polar cap patches, plasma irregularities caused by gradient drift instabilities are observed throughout the patch as elongated slivers. These irregularities vary in size from centimeters to tens of kilometers. Three major challenges must be overcome to thoroughly study high‐frequency electromagnetic wave interactions with polar cap patches: (1) the complex geometrical features of the irregularities within the patches must be accommodated; (2) the non‐approximated Maxwell's equations should be solved to account for all the physics of electromagnetic wave propagation, scattering, diffraction, etc.; and (3) the physics of electromagnetic wave interactions with magnetized ionospheric plasma must be included. In this paper, the finite‐difference time‐domain (FDTD) method is used to overcome the above three challenges and solve for electromagnetic wave interactions with plasma irregularities within a polar cap patch. Irregularities and patch profiles are generated using Defense Meteorological Satellite Program data and incorporated into the FDTD model. The transmission coefficients for high‐frequency electromagnetic wave propagation through perturbed and unperturbed ionospheres, as well as for magnetized and unmagnetized ionospheric plasma ionospheres are calculated. From these simulations, the effects of small‐scale irregularities on high‐frequency propagation are observed.

High-frequency skywave propagation can be heavily impacted by D- and E-region dynamics requiring accurate global measurements to optimize performance. A standard measurement technique is to use ionosondes, but they are unable to measure below 1 MHz and are only available at a limited number of land-locked sites around the globe. In contrast, the Global Navigation Satellite System radio occultation (GNSS-RO) bottom-up method is a new approach specifically designed to generate electron density profiles in the D- and E- region ionosphere. It takes advantage of satellite constellations that currently provide over 20,000 daily measurements and global coverage. In this paper, GNSS-RO profiles were compared against ionosonde profiles at four sites covering a wide latitudinal range, and FIRI modeled profiles corresponding to the same latitude and local solar time. This comparison was completed using daytime profiles when sporadic-E ($E_s$) was not present. The average GNSS-RO profile is found to be a few kilometers higher in altitude than the ionosonde profiles at the minimum frequency, fmin. When the ionosonde profiles are shifted so that the altitudes match at fmin, they are in good agreement up to the E-region peak altitude, hmE. Below fmin, the GNSS-RO profile is in good agreement with the FIRI profile, indicating that the profiles can measure the D- to E- transition region. The frequency of the E-region peak, foE, showed general agreement between the GNSS-RO and ionosonde measurements; however, the hmE agreement was weaker and the GNSS-RO profiles tend to have an hmE in a narrow altitude range for all profiles. Virtual heights were simulated for the GNSS-RO profiles using a numerical ray tracer for direct comparison with ionosonde observations, which showed agreement for many of the virtual heights near fmin, but also indicated a positive bias in the GNSS-RO virtual heights that may be due to low foE or elevated hmE estimates. For a quiet ionosphere, the shifted GNSS-RO electron density profiles were a good match for both measured ionosonde profiles and modeled FIRI profiles and the method is capable of providing global coverage of the D- and E-regions. Future work will require more data for seasonal and morning–afternoon comparisons as well as comparisons for the disturbed ionosphere when the sporadic-E layer is present.

Ground‐based radar sounders are used to characterize the dynamics and chemistry of Earth's upper atmosphere by using measurements of ionospheric peak electron density (N_mF₂) and its associated altitude (h_mF₂). Continuous sounder observations of the E and F regions of the ionosphere have been carried out regularly at dozens of stations worldwide since the midtwentieth century. A deep understanding of short‐ and long‐term upper atmospheric variability depends on a fundamental understanding of these observational data. The manual analysis of historical analog (predigital age) ionograms to derive the plasma frequency profiles and the ionospheric parameters h_mF₂ and N_mF₂ is a tedious procedure and susceptible to human error. In order to better understand this human error, a study is conducted in which ionograms from vertical sounders are manually scaled by a team of ionospheric researchers. The results of the study are then used to estimate the variability of the hand‐scaled ionospheric parameters f_oF₂ and f_oE. Those results are then used to estimate the downstream impact on ionospheric models that use f_oF₂ and f_oE as input. The results demonstrate that there can be large variability in the manual scaling of f_oF₂ and f_maxE from vertical incidence ionograms. However, the participants did typically better than 5% uncertainty for benign ionograms. A long‐term analysis of h_mF₂ modeling exhibits low sensitivity to statistical errors imposed on f_oF₂ and f_oE, but a short‐term analysis showed that modeled h_mF₂, neutral winds, and electron densities can be very different when small adjustments are made to f_oF₂ and f_maxE.