Use of TEC to determine foF2: differences and similarities at high and low latitudes

The total electron content TEC finds wide application in various scientific and technological areas. One of applications is the use of TEC to obtain critical frequencies foF2 of the ionosphere. The most studied is the situation in middle latitudes. High and low latitudes are considered as problematic zones. In the present work, the situation in high and low latitudes is investigated, including at comparison with results in middle latitudes. Possibility of the TEC use to obtain foF2 is connected with their high correlation however in details this correlation was not investigated. In the present work, on an example of three stations of the American zone (Thule, Millstone Hill, Puerto Rico), latitudinal section of the northern hemisphere on a meridian 75°W it is shown, that: 1) correlation coefficients p(TEC, foF2) between foF2 and TEC lay in a range 0.7-1.0 in a seasonal course and 0.6-0.85 in a daily course with the least values for the station Thule. 2. The most clear seasonal dependence is related to that in the winter (January, December) correlation is worse, in an equinox (March, September) is better. 3. There is a tendency to higher correlation and smaller scatter of values in years of high solar activity, than in low activity. 4. Correlation coefficients ρ(δTEC, δfoF2) of deviations between δTEC and δfoF2 lay in the same range, as coefficients for magnitudes, and not strongly worsen during the disturbed periods, the least values here are at the station Puerto Rico. Estimation of a dependence ρ(δTEC, δfoF2) from indexes Kp and Dst and its approximations by a polynomial with degree n has shown, that: 1) degree of polynomial approximation and the best index of correlation depend on latitude (for high-latitude stations the greatest correlation is observed with index Kp, for middle - and low-latitude stations correlation with Dst can prevail). 2. Degree and the best index of correlation depend on a season (the greatest correlation is observed in winter months for high-latitude stations and in the summer for low-latitude stations). 3. Degree n=3 is insufficient for approximation, often degree of reliability R^2 for n=4-6 exceeds reliability for n=3 twice. 4. Reliability degree can exceed the level 0.5 testifying strong dependence and possibility of the forecast of parameters. As a whole, differences between high and low latitudes consist in a difference of coefficients of correlation, similarities - in possibility of the TEC use to obtain foF2 practically at all latitudes, i.e., details of behavior of TEC can differ, but the main result is identical: the use of TEC allows to improve conformity of the calculated values of foF2 to experimental data in 1.5-2.5 times. Residual deviations do not exceed 10 %.