Atmospheric Scale Height as a Modifying Influence on Linear Trend of F-Region Electron Density with Sunspot Number

Abstract

IN the prediction of maximum usable frequencies a linear increase in foF2 with sunspot number is generally assumed for practical purposes¹. However, an analysis of maximum usable frequencies, estimated for a sunspot cycle interval from Christchurch ionospheric vertical sounding data obtained during 1947–58, indicated that the trend of twelve-month running average values of foF2 monthly medians with twelve-month running average sunspot number showed significant departures from linearity especially in the daylight hours and above running average sunspot number 170 at the 1957–58 sunspot maximum. Chun-Ming Huang² has observed a similar marked departure from linear trend at the 1957–58 maximum in an analysis of vertical sounding stations in the Western Pacific area, the time of onset relative to sunspot number varying with time of day and station latitude.