A newly-released, novel ionospheric dataset of global gridded vertical total electron content (VTEC) is introduced in this paper. This VTEC dataset, provided by Los Alamos National Laboratory (LANL), is derived from very-high frequency (VHF; defined as 30-300 MHz) broadband radio-frequency (RF) measurements of lightning made by U.S. Department of Defense sensing systems on board Global Positioning System (GPS) satellites. This paper presents the new dataset (LANL VTEC), discusses the errors inherent in VHF TEC estimation due to ionospheric dispersion, and compares the LANL VTEC to two community standard VTEC gridded products: Jet Propulsion Laboratory’s Global Ionospheric Model (JPL GIM) and the CEDAR community’s Open Madrigal VTEC gridded measurements of L-band GNSS (global navigation satellite systems) TEC. We find that the LANL VTEC data has an offset of 3 TECU from CEDAR Madrigal GNSS VTEC, and a full-width-half-maximum (FWHM) of 6 TECU. In comparison, the offset between LANL VTEC and the JPL GIM model is -3 TECU, but with a FWHM of 5 TECU. We also compare to Jason-3 VTEC measurements over the ocean, finding an offset of less than 0.5 TECU and a FWHM of < 5 TECU. Because this technique uses a completely different methodology to determine TEC, the sources of errors are distinct from the typical ground-based GNSS L-band (GHz) TEC measurements. Also, because it is derived from RF lightning signals, this dataset provides measurements in regions that are not well covered by ground-based GPS measurements, such as over oceans and over central Africa.

Polar topside total electron content (TEC) enhancement (PTTE) above 1336 km altitude is reported for the first time. The results are based on measurements from 2008 to 2018 made using a GPS receiver onboard NASA’s Jason-2 satellite. The enhancement can exceed 5.5 TEC units or 78% relative to the dayside ambient state. Comparisons with COSMIC/FORMOSAT-3 topside TEC measurements confirm the PTTE events. Our statistical analysis reveals that PTTE mostly occurs in the southern dayside polar cap, with a seasonal preference of southern summer, regardless of geomagnetic conditions. Our case analysis indicates that PTTE is associated with the tongue of ionization. This suggests that the source of PTTE may be the dayside F region plasma that moves poleward following the anti-sunward plasma convection, and the plasma upflow driven by the polar wind may act to cause PTTE. The hemispheric asymmetry in PTTE occurrence remains to be a major unsolved puzzle.