Modification of IRI half-density height option for low latitudes

Abstract

The International Reference Ionosphere provides an option for using the half-density height h0.5 when determining the bottom-side electron density profile. For low latitudes the ratio h0.5/hmF2 (peak height) is modified using Arecibo incoherent scatter electron density profiles. A linear variation with latitude of the coefficients is introduced for nighttime and daytime in case h0.5 is located above the F1 layer heights (class 'A'). The profile semithickness is large when 0.5NmF2 value is less than NmF1 (class 'B'). At low latitudes class 'B' occurs during the first half of the day; at mid-latitudes, however, the Digisonde data from Millstone Hill show these to occur during most of the daytime.