# Equinoctial Asymmetry in Solar Quiet Fields along the 120\({}^{\circ}\) E Meridian Chain
## 3 Results  
The residual \(\rm{dA}\) is then used to investigate seasonal variations of the SqH daily range. In the left panel of Figure 5, monthly \(\rm{dA}\) values derived for each year are plotted for each observatory (superimposed black curves). While the spread of the black curves suggests only small year-to-year variations, marked seasonal variations occur every year. The \(\rm{dA}\) value reaches peak around the equinoxes and is smallest in winter at all observatories, including CDP and WHN located near the Sq current focus. The right panel in Figure 5 shows the average \(\rm{dA}\) variations, the associated standard deviations (SD) \(\rm{d}\), and the standard error of the mean (SEM, where SEM equals \(SD/\sqrt{n}\), and \(\rm{n}\) is the number of the stacked curves) [11; 40] for each month. Seasonal variation--equinox maximum and winter minimum--is clearly visible at each observatory. Yearly \(\rm{dA}\) ranges (R) are calculated as the difference of the extreme monthly values. We obtain R values of 27.4, 23.8, 22.3, 30.4, 30.0, and 29.4 nT for MUT, GZH, WHN, CDP, LZH, and BMT, respectively, indicating small differences between the observatories. Corresponding monthly standard deviations (\(d\)) are within 4.4-12.0, 4.7-8.0, 3.3-6.0, 3.4-7.3, 3.7-7.9, and 4.0-7.7, respectively. This indicates significant monthly variations of \(\rm{dA}\) from year to year. Figure 5: Seasonal variations of the SqH range (\(\rm{dA}\)) over 1957 to 2013. Left panel: stacking curves of the monthly \(\rm{dA}\) for all available years at each observatory. Right panel: average \(\rm{dA}\) over all available observation years, associated standard deviations \(\rm{d}\) (in red short lines), and SEM (in green bars); values of the yearly range R and of the standard deviation \(\rm{d}\) are indicated. Equinoctial asymmetry in each year is then defined as the difference of dA averages around the spring (March-April) and autumn (September-October) equinoxes: \(AA=\overline{dA_{autumn}-dA_{spring}}\). To represent the equinoctial asymmetry variability, an \"asymmetry coefficient\" is further defined as \((dA_{autumn}-dA_{spring})/(dA_{autumn}+dA_{spring})\), and its values at each observatory are shown in Figure 6. By construction, the asymmetry coefficient absolute values cannot exceed \(|\pm 1|\). A positive value of \(AA\) or of the asymmetry coefficient indicates a greater SqH range in autumn than in spring (red bars), while negative values (blue bars) show reversed asymmetry, with smaller SqH range in autumn than in spring. The asymmetry coefficient is generally large--regardless of the year or the observatory--reaching, for example, \(-80\%\) at GZH in 1980. The latitudinal dependence of the equinoctial asymmetry is clearly seen in Figure 6. Most notably, variations of the asymmetry coefficient exhibit the same behavior at observat  
Figure 6: **(Top)**: yearly averaged F107 index over the period from 1957 to 2013. (**Bottom**): Equinoctial asymmetry coefficient calculated at each observatory for years with available observations and shown in red and blue bars for the positive and negative values respectively. side of the SqH current focus. Additionally, the asymmetry coefficient, generally positive at northern observatories (with a few exceptional years that displayed negative values, as shown in the blue box--for example, in years 1998, 2002, and 2012 at BMT station), changes sign around the Sq current focus (near WHN) and becomes mostly negative at southern observatories (also with a few exceptions that displayed positive values, as shown in the red box--for example, in years of 1958 and 1970 at MUT station). This means that dA is usually larger in spring than in autumn in most years at southern observatories but that the situation is reversed at northern observatories.