| The influence of space weather on the propagation of electromagnetic wave signals in the ionosphere usually originates from the sun.Intense solar flares and fast Corona Mass Ejection(CME)generated by the reconnection of the strong magnetic field of the sun can cause various Sudden Ionospheric Disturbances(SIDs)effects.Important questions in physics research.And the ionosphere,as a high reflector for short-wave broadcasting and long-distance communication,is not only affected by solar activity,but also by geomagnetic activity,low-level atmospheric activity,and coupling with the coexisting thermosphere.When a sudden disturbance occurs in the ionosphere,the density of electrons and ions,the collision frequency of electrons and neutral particles,and the change of the height of the ionosphere will affect long-distance short-wave communication,navigation and positioning,and detection and tracking radar systems.Therefore,it is necessary to study the ionospheric disturbance to avoid the economic damage of space weather events and maintain the safety of human space activities.The sudden increase in plasma density in the lower ionosphere caused by flares can induce significant high frequency(3-30 MHz)radar echo absorption effects.Using the Super Dual Auroral Radar Network(SuperDARN)to detect ionospheric plasma irregularities and their motion laws is helpful to analyze the problems related to ionospheric sudden disturbances.Based on the observation data received by the High-Frequency(HF)radar(-74.9 MLAT,97.2MLON)of the SuperDARN Zhongshan Station and the X-ray sensor of the GOES satellite,this paper analyzes the short-wave fadeout(SWF)of the diurnal ionosphere in the high latitudes of the southern hemisphere from 2010 to 2019.The SWF events included in this work were caused by extreme flares(12 events:9 X-class and 3 M-class).The main results of the paper are as follows:(1)SWFs are divided into short types and long types according to the duration characteristics of their onset phases,and the causes of different types of SWFs are analyzed.It is found that the magnitude of the background field-aligned current(FAC)is correlated with the difference between the two types of events.The short onset event is accompanied by a weak FAC,while the long onset event is accompanied by a strong FAC.(2)As a statistical study of SWF in the high latitudes of the southern hemisphere,we provide the typical characteristics of the ionospheric SWF in the high latitudes of the Antarctic.Onset phase duration:6 minutes and 54 seconds;Blackout phase:20 minutes and 24 seconds;Recovery phase:39 minutes and 36 seconds.(3)It is found that the durations of the three phases of SWF are strongly correlated with the flare duration,and are also significantly correlated with the integral of the effective X-ray flux,but not significantly related to the peak of the effective X-ray flux.It shows that the effective X-ray flux integral can better reflect the ionization effect of the ionosphere.(4)During the flare,the ionospheric echoes with different velocities decay at the same speed at the onset phase,but the ionospheric echoes with smaller speeds recover faster in the recovery phase.For the ionospheric echoes of different distance gates,the response of the close-range gate echoes to the flare X-rays is stronger than that of the mid-and long-distance gate echoes.When the ray flux exceeds 10-6W/m2.The echo starts to be absorbed and shows a downward trend.Overall,the duration of SWFs at high latitudes in the southern hemisphere is driven by the temporal distribution of radiation from different flares.The short-event X-ray flux rises rapidly,and the radiation energy required for complete absorption by HF can be obtained in a very short time,which is the main factor causing the long and short events.Furthermore,the strong FAC in long onset events may provide a channel for electron escape,and the reduction in the collision rate of radar signals with ionospheric electrons could prolong the duration of the onset phase. |
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