Variations of electron density based on long‐term incoherent scatter radar and ionosonde measurements over Millstone Hill

Abstract

Measurements from the incoherent scatter radar (ISR) and ionosonde over Millstone Hill (42.6°N, 288.5°E) are analyzed to explore ionospheric temporal variations. The F 2 layer peak density N m F 2 , peak height h m F 2 , and scale height H are derived from a Chapman α layer fitting to observed ISR electron density profiles. Diurnal, seasonal, and solar activity variations of the ionospheric characteristics are presented. Our study on the solar activity dependence of N m F 2 , h m F 2 , and H indicates that the peak parameters ( N m F 2 and h m F 2 ) of the F 2 layer increase with daily F 10.7 index and saturate (or increase with a much lower rate) for very high F 10.7 ; however, they show almost linear dependence with the solar proxy index F 10.7p = ( F 10.7 + F 10.7A )/2, where F 10.7A is the 81‐day running mean of daily F 10.7 . This suggests that the overall effect of solar EUV and neutral atmosphere changes on the solar activity variation of ionospheric ionization is linear with F 10.7p . The rate of change in the ionospheric characteristics with solar activity exhibits a seasonal and local time variation. Over Millstone Hill, N m F 2 in summer is characterized by the evening peak in its diurnal variation, and N m F 2 exhibits winter anomaly under low and high solar activity levels. The temporal variations of the topside effective scale height H 0 can be explained in terms of those in the slab thickness. The IRI model overestimates the N e effective topside scale height over Millstone Hill; therefore our analysis for the effective topside scale height from the Millstone Hill measurements might help to improve the IRI topside profiles at middle latitudes.