Nowcasting maps of F2-layer basic maximum usable frequency and corresponding skip distances over the European region

This work presents the IRI&LKW new UP procedure, which generates nowcasting maps of the F2-layer basic maximum usable frequency (MUF) and corresponding skip distances over Europe. IRI&LKW new UP is a four-step procedure based on: (1) deriving two effective values of the 12-month running mean of the sunspot number ( R 12) according to autoscaled fo F2 and M (3000)F2 ionosonde measurements; (2) using these two values of R 12 as input for the International Reference Ionosphere (IRI) model to calculate the ordinary critical frequencies fo E and fo F2 of the E and F2 layers, respectively, and the obliquity factor M (3000)F2; (3) feeding the Lockwood algorithm with these values of fo E, fo F2, and M (3000)F2 to compute a discrete grid of MUF values; and (4) mapping these grids of values to generate nowcasting maps of MUF and corresponding skip distances. The maps cover the European sector from 9°W to 45°E in longitude and from 34°N to 65°N in latitude, with a 1°×1° spatial resolution, with 15-minute time resolution. They are centered on six selected transmitting points: Stockholm (18.1°E, 59.3°N), Warsaw (21.1°E, 52.2°N), Pruhonice (14.6°E, 50.0°N), Paris (2.3°E, 48.8°N), Rome (12.5°E, 41.9°N), and Athens (23.7°E, 37.9°N). The internal consistency of the IRI&LKW new UP procedure and its sensitivity to storm-time departures from climatology are assessed by comparing MUF maps retrospectively generated by IRI&LKW new UP for the main and recovery phases of the May 2024 extreme geomagnetic storm with their corresponding quiet-time and climatological counterparts. Results show that IRI&LKW new UP produces observation-informed MUF and corresponding skip-distance maps that exhibit substantial storm-time departures from climatological conditions. Although an independent validation against oblique-sounding observations is not available for the analyzed epochs, the results indicate that IRI&LKW new UP has the potential to provide supporting information for HF-dependent applications in surveillance, civil protection, aviation, and defense, particularly during adverse space weather conditions such as those associated with the May 2024 superstorm.