Latitudinal Variation of α‐Chapman Scale Height During Quiet and Disturbed Geomagnetic Conditions

Abstract

Scale height is an important ionospheric parameter which determines the shape of the topside electron density profile. In this paper, the latitudinal variation of α‐Chapman scale height (Hm) is investigated using data obtained from four ground‐based ionosondes located in the African‐European longitudes. A Hm pattern reveals a marked dependence on seasons, latitudes, and magnetic activity. The daytime Hm peak magnitude decreases with increasing latitudes. Daytime Hm is higher relative to that of nighttime at low‐ and mid‐latitudes irrespective of the season. However, at high latitude, the opposite is observed in the solstice seasons and comparable magnitudes during equinoxes. Seasonally, Hm magnitude maximizes/minimizes in summer/winter at all latitudes considered – revealing hemispheric difference emanating from the opposite occurrence of winter and summer. Further, the difference in the magnitude of the summer‐winter Hm is most pronounced at high latitudes at all hours. However, at low latitude, magnitude of the difference between the nighttime summer‐winter values is insignificant. Hm also exhibits weak equinoctial asymmetry that reveals hemispheric difference. A strong positive linear relationship exists between Hm and a bottomside thickness parameter (B0) across all seasons and latitudes. However, Hm versus the total electron content, F2‐layer critical frequency (foF2), and peak height (hmF2) generally revealed a poor relationship and does not show any significant seasonal and latitudinal trends. The excellent Hm‐B0 relationship (r = 0.85–0.97) suggests a convenient method to develop an empirical model of Hm from a more easy‐to‐obtain B0 data regardless of the latitude.

Ratio Between Over‐Satellite Electron Content and Plasma Density Measured by Swarm: A Proxy for Topside Scale Height

“…Higher VSH during summer than in winter was reported by Adebiyi et al. (2020), Figure 2 and Prol et al. (2018), H 1 parameter in Figure 3.…”

“…For example, in Potula et al (2011), Figure 6 and Liu et al (2008), Figure 6, hemispheric asymmetry is nearly unidentifiable. Higher VSH during summer than in winter was reported by Adebiyi et al (2020), Figure 2 and Prol et al (2018), H 1 parameter in Figure 3. The discrepancy among previous studies seems to result from different definitions of VSH and the reference altitudes where VSH was estimated.…”

“…The only difference between the α and the equivalent slab thickness consists in the fact that the former only reflects regions at and above LEO (i.e., in‐situ N e and OSEC) and inherently misses information from below S/C (e.g., regions around the F‐region peak and bottom side). Nevertheless, the α can be of use because thickness of the bottom side ionosphere (conventionally known as B0 parameter) is known to be highly correlated with topside scale height (Adebiyi et al., 2020, Figure 3). That is, topside scale height (or α) can represent the bottom side one (and even the equivalent slab thickness as a whole) to a certain degree.…”