1. WANG Jianjun 1, YANG Dongmei 2 ， ZHANG Suqing 2 ， ZHU Rong 2 1 Earthquake Administration of Gansu Province, China, wjj_1229@163.com 2 Institute of Geophysics, CEA, China 0 Introduction Assumed that Sq current-system is a symmetrical vortex-like structure, the spatial distribution of S qH in low latitudes should have the following characteristics according to the right-hand rule. A. The shape of S qH is morphologically converse around noon of local time at the northward and southward sides of Sq current-systems focus along the same longitudinal chain, mainly downwards at north stations and upwards at south stations. B. The amplitude decreases from both north and south sides towards the Sq current focus, and reach the minimum near the focus as Figure 1 showed. C. The S qH shape and amplitude observed by the observatories should be consistent along the same latitudinal chain. Figure 1. Sketch map of S qH in northern hemisphere 1 Data Preparation and research methods a.Continuous data from 2008 to 2009 from 39 reliable stations in China were selected, and these stations composed two longitudinal and five latitudinal chains as Figure 2 shows. b.Local time is used for all the data. Daily variation of S RH of a single quiet day was calculated by the FMI method. Quarterly S qH was calculated from the S RH of magnetic quiet days in different seasons. c.The magnetic quiet day is selected from the 10 international magnetic quiet days per month announced by Helmholtz Centre Potsdam in Germany (GFZ). We used those continuous quiet days, and removed the isolated and discontinuous quiet days or the quiet day whose previous day is disturbed day. Figure 2. Selected geomagnetic station chain (geographical coordinates) 2 Dependence of Sq on Longitude 2.1 Spatial distribution of quarterly S qH Figure 3 (a.b.c) shows that there was obvious prenoon-postnoon asymmetry of S qH in Summer and Equinox, prenoon valley descending from north to south and postnoon peak increasing from north to south. The shape of S qH became from single valley in the northernmost station to the single peak in the southernmost station, and the reverse shape between North and South side in Summer and Equinox was not as obvious as winter. Figure 3 (d.e.f) shows that the daily range of S qH decreased from the north and south sides to middle latitude in Summer, Equinox and Winter. We assumed that the latitude with smallest amplitude was located below the Sq current focus. It can be roughly estimated from the Figure 3 that the averaged Sq current focus position was 27°N, 29°N and 35°N, respectively in Summer, Equinox and Winter. a. Quiet daily variation of S RH b. Amplitude of S RH Figure 4. Typical example of S RH along longitudinal chains (Jan. 25, 2009) Similar examples also appeared on Jan.4, Feb. 25, Dec. 20, Feb.7, Feb.8 in 2008 2.2 Typical example of S RH along longitudinal chain. 2.2.1 Amplitude decreased from south to north along both longitudinal chains In Figure 4b, amplitude decreased from south to north along both longitudinal chains. It seems that the focus of Sq current might appeared in the north of MZL station (50°N). 2.2.2 Amplitude decreased from middle latitude to both south and north sides In Figure 5b, amplitude decreased from middle latitude to south and north sides along both longitudinal chains. It seems that the current vortex appeared at both the north and south sides this day. The decreased amplitude of high latitude could be caused by the polar current. So the focus of Sq current might appear in the south of QGZ station (19°N). a. Quiet daily variation of S RH b. Amplitude of S RH Figure 5. Typical example of S RH along longitudinal chains (Sep.12, 2008). Similar examples also appeared on Sep. 11,2008; Sep.13, 2008; Jul. 18, 2009; Sep.23, 2009; Sep. 25, 2009; Dec. 8, 2009; Dec. 9, 2009; Dec. 29, 2009 a. Quiet daily variation of S RH b. Amplitude of S RH Figure 6. Typical example of S RH along longitudinal chains (Nov. 19, 2008) Similar examples also appeared on Jul.8, 2008, Dec.1, Jun.1, Jun.12, Jul.16, Oct.18, Dec.1of 2009. 2.2.3 latitudinal trend inconsistencies in two longitudinal chain In Figure 6b, daily variation along 108°E chain decreased from south to north. Daily variation along 117°E chain decreased from south and north sides to XIC station (29°N). Latitude difference between two point located at different chain but with the smallest amplitude exceeded 10 degrees in latitude. It seems that there could exist latitudinal migration when the Sq current vortex moved from 117°E to 108°E during nearly half an hour. 3 Conclusion and Discussion (1) It is found that there was obvious prenoon-postnoon asymmetry of S qH in Summer and Equinox, prenoon valley descending from north to south and postnoon peak increasing from north to south. (2) The averaged focus position of Sq current-systems located at geographical latitude 27°N, 29°N and 35°N respectively in Summer, Equinox and Winter, but that is only the averaged location. The location of Sq current-systems in a single quite day may be far away the averaged one. The examples of both Fig. 4 and Fig. 5 show that the focus of Sq current could appeared in the north of 50°N and in the south of 19°N in a single quiet day. (3) The examples of both Fig. 6 and Fig. 7 show that there was a latitudinal migration of Sq current vortex as well as longitudinal migration of it. (4) The example of Fig. 6 shows the migration of Sq current vortex is very complex. It is not enough to use the data along one longitudinal chain to describe the spatial distribution of Sq current system. a. S qH in Summerb. S qH in Equinoxc. S qH in Winter d. Amplitude of S qH in Summere Amplitude of S qH in Equinoxf. Amplitude of S qH in Winter Figure 3. Seasonal Mean of S qH along longitudinal chain a. Dependence of S RH on Latitude (Mar.4, 2008) Similar examples also appeared on Jul.9, Aug.28 and Nov.22 of 2008 b. Dependence of S RH on Latitude (Sep.25, 2008) Similar examples also appeared on Sep.23, Dec.30 of 2008 and Jan.12, Mar.2, May.12, Aug.24 、 Aug.25 、 Sep.9 、 Sep.24 、 Dec.4 of 2009 Figure 7. Typical example of S RH along latitudinal chain 3 Dependence of Sq on Latitude Figure 7a shows that amplitude increased from east to west along all five latitudinal chains. It seems that eastern stations is nearer to Sq current focus than western stations on Mar. 4, 2008. Figure 7b shows that amplitude decreased from east to west along most chains. It seems that eastern stations is farther to Sq current focus than western station on Sep.25, 2008. Above examples showed that there was a latitudinal migration of Sq current vortex as well as longitudinal migration of it. Please note that we use S RH to denote the daily H changes in a single quiet day and S qH to denote the averaged H variation during magnetic quiet days observed by the ground observatories, and all listed dates are magnetic quiet days in this poster. Research on the Distribution of Geomagnetic Daily Variations of Horizontal Component on Quite Days in China Abstract The Sq temporal and spatial distribution of horizontal component (H) in China was analyzed based on the geomagnetic digital data observed by the geomagnetic observatories in China. It was found that 1) there was obvious prenoon-postnoon asymmetry of S qH in Summer and Equinox ； 2) in Summer, Equinox and Winter ， the averaged focus position of Sq current-systems located at geographical latitude 27°N, 29°N and 35°N respectively. But in a single quiet day, the focus position could appeared at north of 50°N or south of 19°N; 3) there were some special behavior of the S RH distributions such as the latitudinal trend inconsistencies in two longitudinal chain, the reverse phase of Sq variations in the same latitudinal chain and increased (decreased) daily amplitudes from east to west. It seems that there could exist latitudinal migration of Sq current-systems position or current intensity change during the longitudinal migration of Sq current-systems focus from east to west.