Sq field characteristics at Phu Thuy, Vietnam, during solar cycle 23: comparisons with Sq field in other longitude sectors

Abstract

Abstract. Quiet days variations in the Earth's magnetic field (the Sq current system) are compared and contrasted for the Asian, African and American sectors using a new dataset from Vietnam. This is the first presentation of the variation of the Earth's magnetic field (Sq), during the solar cycle 23, at Phu Thuy, Vietnam (geographic latitudes 21.03 • N and longitude: 105.95 • E). Phu Thuy observatory is located below the crest of the equatorial fountain in the Asian longitude sector of the Northern Hemisphere. The morphology of the Sq daily variation is presented as a function of solar cycle and seasons. The diurnal variation of Phu Thuy is compared to those obtained in different magnetic observatories over the world to highlight the characteristics of the Phu Thuy observations. In other longitude sectors we find different patterns.At Phu Thuy the solar cycle variation of the amplitude of the daily variation of the X component is correlated to the F.10.7 cm solar radiation (∼0.74). This correlation factor is greater than the correlation factor obtained in two observatories located at the same magnetic latitudes in other longitude sectors: at Tamanrasset in the African sector (∼0.42, geographic latitude ∼22.79) and San Juan in the American sector (∼0.03, geographic latitude ∼18.38).At Phu Thuy, the Sq field exhibits an equinoctial and a diurnal asymmetry:-The seasonal variation of the monthly mean of X component exhibits the well known semiannual pattern with 2 equinox maxima, but the X component is larger in spring than in autumn. Depending of the phase of the sunspot cycle, the maximum amplitude of the X component varies in spring from 30 nT to 75 nT and in autumn from 20 nT to 60 nT. The maximum amplitude of the X component exhibits roughly the same variation in bothCorrespondence to: H. Pham Thi Thu (hongnd76@yahoo.com) solstices, varying from about ∼20 nT to 50 nT, depending on the position into the solar cycle.-In all seasons, the mean equinoctial diurnal Y component has a morning maximum Larger than the afternoon minimum i.e. the equivalent current flow over a day is more southward than northward. During winter, the asymmetry is maximum, it erases the afternoon minimum. At the Gnangara observatory, in Asian Southern Hemisphere, the diurnal Y pattern is opposite and the current flow is more northward. It seems that in the Asian sector, the northern and southern Sq current cells both contribute strongly to the equatorial electrojet. The pattern is different in the African and American sectors where the northern Sq current cell contribution to the equatorial electrojet is smaller than the southern one. These observations can explain the unexpected maximum of amplitude of the equatorial electrojet observed in the Asian sector where the internal field is very large. During winter the Y component flow presents an anomaly, it is always southward during the whole day and there is no afternoon northward circulation.

Characterization of seasonal and longitudinal variability of EEJ in the Indian region

“…The equinoctial asymmetry in the EEJ strengths during the two equinoxes (i.e., spring and autumn) is also evident in Figures 2c and 2d. This could be attributed to the changes in relative strength of northern and southern Sq current cells, which contribute to the equatorial electrojet in the Asian/Indian sector [Pham Thi Thu et al, 2011]. The averaged EEJ strength is similar for both IQD and IDD (Figure 3).…”

Electrodynamics and energy characteristics of aurora at high resolution by optical methods

“…Lanchester et al [2009] demonstrated the strength of the method by determining the peak energy and flux of the precipitation forming a number of dynamic auroral events with widths of the order of 100 m perpendicular to the geomagnetic field. Dahlgren et al [2011] used the technique in an investigation of the role of sheared aurora at boundary regions. In the study, it was found that a thin, sheared auroral arc appeared on the boundary between two different precipitating electron populations of different energies, where an energy gradient and increased number flux were present.…”

Sq (H) Solar Variation at Yaoundé-Cameroon AMBER Station from 2011 to 2014

“…References [26] [27] [28] show that enhanced cowling conductivity along the magnetic equator is a major cause of EEJ. Figure 4 shows the that could exist between the Sq amplitude and the solar cycle variation as [9] had demonstrated in his works. observed at the Yaoundé station shows a unique variation pattern for the different months and seasons (see Figure 3 and Figure 6).…”

“…The diurnal and seasonal variations of the solar quiet (Sq) variations had been analyzed recently by several researchers [9] [10]. In this paper, we continue this analysis using the data provided by the Yaoundé station during quiet magnetic days from 2011 to 2014 in order to characterize it.…”