Study On The Features Of The Ionospheric Changes In The Low And Middle Latitudes During Geomagnetic Storms

The phenomenon of the global severe disturbance of the earth's magnetic field caused by solar activity is called geomagnetic storm.During the magnetic storm,a variety of irregular structures are generated in the ionosphere,and they can have a serious impact on satellite communications,aviation operations and the Global GNSS(Global Navigation Satellite System)navigation and positioning system.Therefore,it is of great significance to research the characteristics of the ionosphere during the magnetic storm.The changes in the ionosphere during magnetic storm are very complicated.The decrease of electron density(Ne)or vertical total electron content(VTEC)in the middle and low latitudes ionosphere on a large scale is called negative storm.And the increase of Ne or VTEC in the middle and low latitudes ionosphere on a large scale is called positive storm.In the F layer of the ionosphere,the small increase of Ne is called Plasma Blobs.The results of previous studies have shown that during magnetic storms,plasma blobs are usually observed at night in the middle and low latitude ionosphere and related to the generation of plasma bubbles.In this paper,we have analyzed the characteristics of the ionospheric changes in the middle and low latitudes during storm.We focused on the positive storm,the negative storm and the abnormal mid-low latitude ionospheric plasma blobs during the magnetic storm.In this paper,the following observation data are used in studying the characteristics of the ionosphere changes in the middle and low latitudes during the magnetic storm,they are:(1)electron density and electron temperature(Te)data with 2Hz sampling rate of Swarm satellite and electron density data with 16Hz sampling rate,(2)electron density data with a sampling interval of 1s and oxygen atom and ion content(i.e.,O~+ion content,that is,the ratio of the density of oxygen atom and ions to the total ion density)data in the sampling interval of 4s of the DMSP satellite,(3)global VTEC data provided by IGS(International GNSS Service)(time resolution is 15 min,geographic latitude resolution is 2.5°,geographic longitude resolution is 5°).In order to use the above data facilitately,we have compiled programs to extract and process these data.Since 2017,few magnetic storm events have occurred due to calmer solar activity.The7-8 September 2017 magnetic storm event and the 26 August 2018 magnetic storm event are the most typical magnetic storm events in recent years.Taking these two magnetic storm events as examples,we studied the change characteristics of the mid-low latitude ionosphere during the magnetic storm.Some studies have analyzed the characteristics of ionospheric changes during these two typical magnetic storm events.In this paper,we have used a variety of observation data to study these two magnetic storm events in detail.Not only are the observations consistent with published papers,but also some new phenomena in the mid-low latitude ionosphere during the magnetic storm were observed.The new phenomena found in this article are summarized as follows.1.For the 26 August 2018 magnetic storm event,we found that the positive storm observed by the Swarm satellite is consistent with the result presented by the VTEC data,but the negative storm observed by the Swarm satellite cannot be supported by the VTEC data.2.For the 7-8 September 2017 magnetic storm event,we discovered the phenomenon of the ionospheric plasma blobs in middle and low latitude that has not been reported by other study.The results of previous studies indicated that plasma blobs were usually observed at night.However,the mid-and low-latitude ionospheric plasma blobs were found at daytime in this paper.These plasma blobs appeared simultaneously at the geomagnetic conjugate locations,i.e.,two locations with comparable geomagnetic latitude in the northern and southern hemisphere,and the Te reduced at the locations of these daytime plasma blobs.We found that the the daytime plasma blobs during the magnetic storm were not only at the altitude of 450–514 km(i.e.,Swarm satellite orbit altitude),but also at the altitude of 850km(i.e.,DMSP satellite orbit altitude).In addition,the duration of the plasma blobs that detected at the altitude of 850 km was at least 4.5 h,and the content of O~+ions in these plasma blobs was reduced compared with background value,which was opposite to previous studies.The occurrence of the decrease of the O~+ion content in the daytime plasma blobs is probably caused by the storm time electric field of magnetospheric origin.