????IGS?????????????TEC?仯???????

????1999~2009???IGS????????????????(TEC)????????????TEC???????I????dc????????????I????nc?????????仯??????仯????????о????????????????????????????????I????dc???????????????????????????????????????????????????????????????????????????I????dc?????????仯??????????????I????nc????????γ????????а???仯??????????I????dc???????I????nc????????仯????????????仯???仯????????????????85%?????????I????dc????????????????????????I????dc???????I????nc?????????仯?????澭γ??仯???????????????????仯??????????????????????I????dc????????I????nc?????????????P????????????????????????????0.9???????????D????st????K??p??A??p???????????????????????????С??0.4??????????????????????????????????????????TEC????仯????????????á?

Analysis of TEC Variation Characteristics in Daytime and Nighttime Based on the IGS Data

Based on 1999~2009 total electron content (TEC) data from IGS, we studied semiannual and seasonal variations of the global TEC in the daytime (Idc) and nighttime (Inc) as well as solar and geomagnetic effects on these variations. The main features are outlined as follows: the maximum values of Idc commonly appear in equinox seasons| in the northern ‘near-pole’ region and south America, the semiannual variation character of Idc is significant. Inc has only semiannual variation at low latitudes, and the semiannual variation of Idc and Inc change with the solar activity. At high solar activity years, in more than 85% area of the globe, the maximum value of Idc appears in equinox seasons.  Seasonal variation of Idc and Inc change with latitude and longitude, and seasonal variation is apparent at high solar activity years. The variation of Idc and Inc correlates well with the solar P index, where the correlation coefficient reached 0.9. However, it poorly correlated with geomagnetic Dst, Kp, Ap index, where the correlation coefficient is less than 0.4. We further demonstrate that ionosphere photochemical production rate, which is controlled by solar zenith angle, plays a major role in the overall variation of TEC.