<i>Letter to the Editor:</i> Solar-cycle variation of the daily <i>fo</i>F2 and M(3000)F2

Abstract

solar or ionospheric indices. One step towards optimising that adjustment is to examine the extent to which daily values depend on daily solar activity. The present investigations therefore consider the correlation with daily sunspot number R, whereas monthly median values are known to correlate best with 12-month running mean sunspot number R 12 . Data and analysesIn particular, Student's t-test and Fisher's F-test have been applied to determine the significance of the higher-order polynomial coefficients and at what points truncation should be introduced. ResultsFor foF2 these tests show that a 3 is significant at the 95% level in about 40% of the regressions examined, being negative in winter and the equinoxes, and positive in summer. Moreover, this same general pattern of variation is experienced at all stations considered. As an example, Table 1 for Slough shows the months and hours for which the term a 3 is significant and for these whether it is positive or negative. Retention of a 2 results in substantial improvement, being significantly different from zero in 85% of cases (Table 2). a 2 is negative in all seasons and exhibits this same pattern at all stations, i.e. tending towards saturation at the higher R. By contrast, in the case of M(3000)F2, b 3Ann. Geophysicae 16, 1039 -1042(1998) © EGS -Springer-Verlag 1998 Letter to the Editor Abstract. Daily values of the ionospheric characteristics fo F2 and M(3000)F2 for a given hour and month are correlated with the corresponding daily values of sunspot number using measured data collected at seven European locations. The significance of applying different-order polynomials is considered and the times are confirmed when the higher-order terms are important. Mean correlation coefficients for combined data sets over all hours, months and stations are determined, together with the standard errors of estimates. Comparisons are made with corresponding figures for monthly median values derived from the same data sets.

Statistical analysis of solar activity variations of total electron content derived at Jet Propulsion Laboratory from GPS observations

“…We identified that for application purposes, a quadratic regression is an optimum choice, and higher‐order regressions cannot significantly improve the fitting anymore. Similar quadratic regressions have been used in the work of Gupta and Singh [2001], Huang [1967], Kouris et al [1998], Liu et al [2004a], Sethi et al [2002], and so on. The same conclusion can also be drawn from the monthly median data, although we only showed the analyses of the daily data here.…”

“…As a result, the solar activity effects of electron density in the ionosphere show interesting altitudinal dependence [e.g., Su et al , 1999] and the behaviors of TEC and N m F 2 may be different in some aspects. Linear and saturation effects are found in the solar activity dependency of daytime N m F 2 or f o F 2 [e.g., Gorney , 1990; Huang , 1967; Kane , 1992; Kouris et al , 1998; Lei et al , 2005; Liu et al , 2004a, 2006; Pancheva and Mukhtarov , 1998; Richards , 2001; Rishbeth , 1993; Sethi et al , 2002; Whalen , 2004; Zhang and Holt , 2007]. The amplification effect can be detected sometimes in nighttime N m F 2 [e.g., Chen et al , 2008; Liu et al , 2004a].…”

“…Indeed, as primarily ionizations for the ionosphere, solar EUV, and X‐ray radiation can vary by more than a factor of 2 from solar minimum to solar maximum and by as much as 50% during a solar rotation [see Lean et al , 2001; Tobiska et al , 2000]. Thus the regular variations in solar EUV and X‐ray radiations will strongly affect the Earth's ionosphere [ Afraimovich et al , 2008; Balan et al , 1993, 1994; Chakraborty and Hajra , 2008; Chen et al , 2008; Huang , 1967; Huang and Cheng , 1995; Kane , 1992, 2003; Kouris et al , 1998; Liu et al , 2003, 2004a, 2006; Min et al , 2009; Rich et al , 2003; Richards , 2001; Rishbeth , 1993; Sethi et al , 2002; Su et al , 1999] and the thermosphere [e.g., Guo et al , 2007; Hedin , 1984; Liu et al , 2005, 2004b], producing prominent solar activity effects of the ionosphere and thermosphere. As a result, the most prolonged solar activity effects should be taken into account in ionospheric models constructed for single stations, regions, and global as well to reproduce the dominant patterns of ionospheric parameters [e.g., Belehaki et al , 2001; Bilitza , 2000; Holt et al , 2002; Liu et al , 2004a; Pancheva and Mukhtarov , 1998; Zhao et al , 2005].…”

“…and solar indices (sunspot number, solar 10.7 cm radio flux F 10.7 , etc.) or solar EUV fluxes has been found to be roughly linear [e.g., Balan et al , 1993, 1994; Chakraborty and Hajra , 2008; Gorney , 1990; Kane , 1992; Kouris et al , 1998; Lei et al , 2005; Rishbeth , 1993], two‐segmented linear pattern [e.g., Balan et al , 1994; Bilitza , 2000; Liu et al , 2003], quadratic or higher polynomial functions [ Belehaki et al , 2001; Chen et al , 2008; Gupta and Singh , 2001; Huang , 1967; Kouris et al , 1998; Liu et al , 2004a, 2006, 2007b; Pancheva and Mukhtarov , 1998; Richards , 2001; Sethi et al , 2002], and even more complicated patterns [ Su et al , 1999; Huang and Cheng , 1995]. Further, several investigations reported a hysteresis feature (i.e., the nonlinear dependency on the states of the historical solar cycle phase) [e.g., Burešová and Laštovička , 2000; Chakraborty and Hajra , 2008; Mikhailov and Mikhailov , 1995; Rao and Rao , 1969; Trísková and Chum , 1996], which is small at low and high latitudes but substantial at midlatitudes [ Kane , 1992].…”

Dusk-to-nighttime enhancement of mid-latitude <i>Nm</i>F2 in local summer: inter-hemispheric asymmetry and solar activity dependence

“…In general, ionospheric data may be roughly classified into the groups of solar maxima and solar minima according to solar activity indices such as F 10.7 (10.7 cm solar radio flux) to investigate ionospheric diurnal variations at different solar activity levels. The relationships between N mF2 and solar activity indices are usually nonlinear (e.g., Chen et al, 2008;Chen and Liu, 2010;Kouris et al, 1998;Richards, 2001;Sethi et al, 2002). In this paper NmF2-F 10.7 quadratic fittings are used to more accurately normalize N mF2 to two solar activity levels, F 10.7 = 80 (a low solar activity level) and F 10.7 = 200 (a high solar activity level).…”