Critical Frequencies, Sunspots, and the Suns Ultraviolet Radiation

-Monthly values of el0, the critical frequency relative to the critical frequency at zero sunspots, have been averaged for a number of stations and tabulated for the eleven-year period 1937-47. The variations of el0 for the E-, Fi-, and F2-regions have been correlated with the solar data for sunspot-numbers, bright Ha and Ca floecult, faculae, and the coronal-line intensity. The variations correlated are found to lag behind the sunspot-number variations by the following parts of a month: Ha fiocculi, 0.15; Ca fiocculi,4).3!; ef0•, 0.43; faculae, 0.56; rføFx, 0.66; eœør2, 0.68; coronal line, 0.87; and this is interpreted as giving the order of increasing mean life of the relevant solar features. In the expression eS -(1 -[bR) -(•œ0)• relating relative ultra-violet intensity •S to sunspot-number R and critical frequency, the adopted values of n and b for the regions E, F1, and F2 respectively are n -4, 4, and 2, and b = 0.0097, 0.0124, and 0.0200. Values of n determined from the relation between critical frequency and the Sun's zenith-distance were 3.72 for the E-region, and 4.90 for Fl. The values of •r• are shown to vary with time, season, and station. The noon values however do not vary greatly and are generally close to the diurnal mean. A method of choosing stations reasonably free from the F2-anomaly is given, and the recombination and electronsdecay coefficients are determined from these stations. The number of quanta per cm • per sec outside the Earth's atmosphere at zero sunspots is given as: E, 5 X 10s; F1, 1.9 •( 109; and F2, 2.3 X !09. The variation of critical frequencies for a selection of ionospheric stations was studied for the period of decreasing sunspot-activity 193744 in an earlier paper [see 1 of "References" at end of paper]. In the present paper more recent ionospheric and solar observations are added to the earlier data, and the inter-relation of these observations for an eleven-year cycle is discussed. The main object of the work is to seek evidence on the variations and sources of the ultra-violet radiations which produce the ionospheric layers. (1) Monthly ionospheric and solar data during 1937%7--The method of analysing and expressing the critical frequencies has •ready been described [1]. From the pub!ished monthly means we determine the "relative critical frequency" z/ø, which is the ratio of fo the actual critical frec/uency to z/ø the critical frequency at the same hour and season extrapolated tozero sunspob-ac•ivity. Thevalues of af ø are therefore pure numbers, and, with certain exceptions discussed in Section 4, all Stations give the same values. The means of these values are therefore excellent measures ofsolar activity, and are independent ofunRs. In this respect they are superior to the well used "sunspot-number" for which the constants need careful monitoring by the originators at the Swiss Federal Observatory. The analysis of the four original stations Washington, Huancayo,