Observations of the Global Ionospheric Response During the January 2009 Stratospheric Sudden Warming Event

A major Stratospheric Sudden Warming(SSW) in January 2009 was the strongest and most prolonged in record.In the period of this warming event,the solar activity and geomagnetic disturbance are extremely low.Hence it provides a good opportunity to investigate the response of the ionosphere to SSW event.The Kriging method is adopted to construct map of N_mF_2,h_mF_2,and integrated Vertical TEC(VTEC) within height ranging from 110 km to 750 km with data derived form COSMIC radio occultation system.And global TEC maps in the Sun-fixed coordinate are also drawn from IGS GIMs.By comparing these maps,it can be found that N_mF_2,h_mF_2 and TEC increase in the morning hours and decrease in the afternoon and night.Under fixed location and local time bins,cases during SSW and non-SSW days from global COSMIC observations are compared,which shows that N_mF_2,h_mF_2,and VTEC during SSW days,on average,increase 17%, 12%,10 km in the morning,decrease 10%,15%,16 km in the afternoon,and decrease 19%,23%, 11 km in the afternoon respectively.According to the results of comparison of IGS GIMs during SSW and no SSW days,the main difference occurs in the middle and low latitude region,moves along with UT time and corresponds to the position of ionospheric anomaly.It also can be found that increase of TEC(VTEC and IGS TEC) is stronger in the northern hemisphere than in the southern hemisphere during the morning time.Furthermore,the phenomenon that N_mF_2,h_mF_2 and TEC(VTEC and IGS TEC) are decreased in the night hours has never been mentioned by previous studies.So altimeter observations by the OSTM/JASON-2 satellite are used for further verification and the phenomenon is validated at last.