Variability of f_oF₂ over Rome and Gibilmanna during three solar cycles (1976‐2000)

Abstract

Hourly validated values of the F2‐layer critical frequency (foF2) recorded at Rome, Italy (geographic coordinates 41.8°N, 12.5°E; geomagnetic coordinates 42.0°N, 93.8°E), and Gibilmanna, Italy (geographic coordinates 37.6°N, 14.0°E; geomagnetic coordinates 38.1°N, 93.6°E), along with the hourly quiet time reference values of foF2 (foF2QTRV) were considered around periods of minimum and maximum solar activity over the years 1976–2000. The foF2 data set was specifically organized in order to obtain an overall trend both for low and high solar activity, and different dispersion indices were used. The results obtained show that (1) at Rome, the foF2 variability is always greater during periods of high solar activity (HSA) in the hourly ranges 00:00–02:00 UT and 20:00–23:00 UT during winter months, and in the hourly ranges 00:00–10:00 UT and 04:00–16:00 UT during equinoctial and summer months respectively; (2) on the whole, around midday, for low solar activity (LSA), the foF2 variability is smaller at the equinoxes than at the solstices; for HSA, it is greater at equinoxes than at solstices; (3) for LSA, at Gibilmanna the foF2 variability is in general larger than at Rome, especially in summer, and it is characterized by a number of relative minimums and maximums greater than those observed at Rome; (4) at Rome, for both LSA and HSA, the passage of solar terminator at sunset significantly affects ionospheric variability in January, April, August, and November, at Gibilmanna in August, September, and November; (5) several variability peaks before sunrise and after sunset are observed in both stations; (6) on a monthly basis, for both LSA and HSA, a semiannual variation of foF2 variability is observed at both Rome and Gibilmanna; and (7) evidence of ionospheric variability at the typical heights of the F region, connected to upward propagating gravity waves triggered by solar terminator, is observed at Rome during some days characterized by HSA in the equinoctial months.

Comparison of maximum usable frequency (MUF) variability over Peninsular Malaysia with IRI model during the rise of solar cycle 24

“…The behaviour of MUF is very similar to foF2; therefore, the variability of MUF also increases, which is higher at night than during the daytime. The present findings are consistent with those of previous studies (Kouris et al, 1998;Akala et al, 2011;Pietrella et al, 2012) where it was found that increasing solar activity causes decreasing MUF variability and vice versa. In addition, low MUF VR indicates more consistent MUF data, while high MUF VR indicates inconsistent MUF data.…”

“…2(a-c) shows the plots of monthly hourly median for 2009 until 2011. Bilitza et al (2004), Akala et al (2010) and Pietrella et al (2012) discovered that variability of foF2/NmF2, MUF and h'F2 are characterized by pre-sunrise and post-sunset peaks; this is due to the steep electron density gradients occasioned by the onset and turn-off of solar ionisation. From Fig.…”

“…Furthermore, Akala et al (2010) also reported that the ionospheric foF2 over Southeast Asia is more vulnerable to variability during the nighttime than the daytime; thus, MUF VR results are equivalent to foF2 VR because MUF is the product of foF2. According to Somsikov (1995), Pietrella et al (2012) and reference therein, the nighttime variability is due to upward propagating gravity waves (GWs), and the main in situ source of GWs is the transition of solar terminator. This phenomena is the rapid increase/decrease of solar radiation at sunrise/sunset can act as a source of atmospheric irregularities and generate GWs in the F region (Somsikov and Ganguly, 1995).…”

Ionospheric equivalent slab thickness ingestion into the NeQuick model

“…Figure 3 collects the results for NmF2, which are typical for mid latitudes [Pietrella et al, 2012]. Since the F2-layer provides a large contribution to vTEC, NmF2 and vTEC share similar features concerning diurnal, seasonal, and solar activity variations.…”