Study Of The Effect Of Plasma Convection On The Peak Value Of NmF2 In The Ionosphere In The Polar Region

The peak electron density of the polar ionosphere(Nm F2)is one of the key parameters of the polar ionosphere,which is influenced by solar radiation,plasma convection and particle settling.The International Reference Ionosphere(IRI)model is the most widely used empirical model in ionospheric studies.The lack of ionospheric observations in the North and South polar regions has reduced the applicability of the IRI model in the North and South Poles.Based on this,this paper investigates the effect of plasma convection on the ionospheric Nm F2 in the polar region and assesses the applicability of the IRI model in the polar region,using longterm observations of more than one solar activity week at three stations,namely,Zhongshan Station(ZHS)in Antarctica,Tromso(TRO)in the Arctic and Longyearbyen(LYB).The main research efforts are as follows.1.The north-south component Bz of the interplanetary magnetic field is classified by solar activity conditions and seasons,and the temporal distribution characteristics of the peak daily variation of Nm F2 under persistent southward and persistent northward conditions are studied in comparison,and the different contributions of inverse solar convection to the formation process of the peak daily side of the ionosphere in the latitudes of the polar gap region and the latitudes of the auroral zone are analysed.The results show that under the northerly conditions of the interplanetary magnetic field in high solar activity years,the inverse solar convection is easily formed near the magnetic noon at the latitudes of ZHS and LYB stations in the polar gap region,causing a significant rise in Nm F2 and producing the magnetic noon anomaly.The effect of inverse solar convection on Nm F2 is much weaker in low solar activity years than in high solar activity years,and plasma convection only has a weak effect on Nm F2 near magnetic noon at the ZHS station;in both high and low years,Nm F2 at TRO stations in the auroral zone latitudes is hardly affected by plasma convection,and there is no significant magnetic noon anomaly in their daily variation curves.2.The plasma convection images observed by Super DARN HF radar were statistically analysed,and the distribution of the peak ionospheric Nm F2 with convection images was investigated,and the causes of the magnetic noon peak at the latitude stations in the auroral zone and the magnetic noon peak at the two Arctic stations were further analysed.The results show that the Nm F2 magnetic noon anomalies at ZHS and LYB stations at latitudes in the polar gap region are consistent in time with the inverse solar convection observed by the Super DARN radar,which confirms that inverse solar convection is the main cause of the magnetic noon anomalies at latitudes in the polar gap region;under the continuous southward direction of the interplanetary magnetic field,the high-density plasma on the dayside will cross the polar cap region with different morphological structures to reach the nightside in In high solar activity years,the presence of plasma convection on the nightside is observed by Super DARN radar at all times when the magnetic sub-night peak exists at LYB,suggesting that plasma convection is the main cause of the magnetic sub-night anomaly at LYB.However,this high-density plasma structure is deflected to the faint side by the convection model before it reaches the TRO station,and no significant convection exists on the night side in low solar activity years,suggesting that plasma convection makes little contribution to the night-side peak at the TRO station,which is mainly caused by auroral substorms.3.The measured ionospheric Nm F2 data of the three stations were compared with the International Reference Ionosphere IRI-2016 prediction data under different solar activity conditions.The results show that the correlation is best at TRO station,followed by ZHS station and worst at LYB station;the IRI model underperforms physical processes specific to the polar ionosphere,such as plasma convection and competent particle deposition,and overestimates the role of photoionization on the polar ionosphere;it is barely applicable at the latitude of the auroral zone at TRO station,but not at the latitude of the polar gap region at both stations,suggesting that the IRI model is based on a wide range of long-term observations of the polar ionosphere(e.g.GPS satellite TEC observations,GPS occultation observations)to form an empirical model of the polar ionosphere.