Characteristics of Ionospheric Storm on October 13, 2016 at the Greenwich Meridian

摘要

An ionospheric positive disturbance during a moderate geomagnetic storm on October 13, 2016 was studied with total electron content (TEC) from a chain of GNSS receivers and F2 layer peak parameters from two ionosondes at the Greenwich meridian. During a slow decrease of Dst, a large enhancement of the daytime TEC was observed from high to middle latitudes successively while there was small disturbance observed in low latitudes. The occurrence of TEC peak delayed with decreasing latitude. Similarly, positive disturbance of hmF2 and foF2 was recorded and their onsets were earlier in high latitude than middle latitude. These observations indicated that the ionospheric positive disturbance propagated equatorward which denied the dominant effect of prompt penetration eastward electric field (PPEF). Using the latitudinal and temporal variations of TEC peaks, the propagation velocity of the disturbance was estimated and found to decrease with decreasing latitude. Two available Fabry-Perot interferometers (FPI) at the meridian 70 degrees W of the Greenwich showed that nighttime equatorward wind in middle latitude increased significantly after the storm sudden commencement (SSC), while no change of that was observed in low latitude. The coincidence of the directional and latitudinal features between the ionospheric disturbance and the wind observation suggested the impact of the positive storm was most likely the equatorward wind surge which raised the ionosphere to higher altitude where lower chemical loss led to increase of electron density in the daytime.