Study Of Characteristics Of Ion Upflows In Dayside Aurora Oval

The optical auroral emissions in the upper atmosphere are evidence of the collision of energetic particles from the solar wind or magnetosphere with atmospheric molecules and atoms.The energetic particles are precipitated along the magnetic field lines from magnetosphere to ionosphere in the polar region and the collision of molecules and atoms.The ions can move upward along the geomagnetic field lines in the polar ionosphere.The upward moving ions reaching the escape velocity of the Earth’s gravity can flow into the magnetosphere.From the perspective of energy transport,the auroral particle precipitation is in the opposite direction to the upward ions.However,there is a close relationship between the dayside auroral particle precipitation and the ion upflow.Studies of auroras and ion upflow can help further understand the coupling process of solar wind-magnetosphere-ionosphere.Firstly,the precipitating particles spectrum of dayside auroras is close related to the source regions and their dynamic processes in the dayside magnetospheric boundary layers.Based on the combination of ground-based auroral optical observation data of Chinese Arctic Yellow River Station from 2005 to 2009 and the particle data from DMSP satellite,the precipitating particle spectrums of four typical dayside discrete auroras(si.e.radial dayside corona aurora,drapery-like dayside corona aurora,hot spot aurora and dayside auroral arc)were analyzed.The results show that the average energies of accelerated electron are 429.65 e V,479.15 e V,961.81 e V and 898.32 e V,respectively.The source regions of precipitating particles correspond to the midday Low Latitude Boundary Layer(LLBL)/ Cusp,the prenoon closed LLBL,the postnoon LLBL/ Boundary Plasma Sheet(BPS),and the magnetospheric BPS.The direction of the three components of interplanetary magnetic field(IMF)has different effects on electric acceleration of four typical dayside discrete auroras.When IMF Bx is positive,the electron acceleration of hots pot aurora and dayside auroral arc increased significantly,while that of drapery-like dayside corona aurora decreased,and that of radial dayside corona aurora decreased slightly.When IMF By is negative,the electron acceleration of drapery-like dayside corona aurora and hot spot aurora decreases,while that of radial dayside corona aurora and dayside auroral arc increases.When IMF Bz is negative,the electron acceleration of drapery-like dayside corona aurora decreases,while that of radial dayside corona aurora,hot spot aurora and dayside auroral arc increases.Secondly,based on the observations of particle precipitation and ion drift from the DMSP F13 in January and July 2005,the ionospheric ion upflows in dayside auroral oval(06:00―18:00 MLT)can be divided into five types according to the velocity of ion upflows and the spectrum characteristics of auroral particle precipitation,and the distribution for different types of ion upflows is studied.1)Type A: the velocity of ion upflows has obvious peak range,and the entire range corresponds to single and continuous electron acceleration structure(type A1),or corresponds to multiple and discrete electron acceleration structures(type A2);2)Type B: the velocity of ion upflows has obvious peak range,but the peak range only has the corresponding electron acceleration structure for the ascending or descending segments;3)Type D: the velocity of ion upflows has no obvious change trend or complete peak interval,which corresponds to the electron acceleration structure;4)Type E: the velocity of ion upflows does not correspond to the electron acceleration structure.The results show that the ion upflows mainly occur in the geomagnetic latitude(MLAT)range of 70―80°.The main magnetospheric source region of ion upflows(type A1 and D)caused by the accelerated electron(mainly soft electron)corresponds to Low Latitude Boundary Layer(LLBL)and Cusp,and ion upflows of type A2 and B(related to the process of ambipolar diffusion caused by electron acceleration)mainly occur in LLBL and Boundary Plasma Sheet(BPS),while ion upflows of type E without electron acceleration mainly occurs in central plasma sheet(CPS).The dawn-dusk asymmetry is obvious in winter season,with the ion upflows mainly occurring on the dawn/dusk side ionosphere.But the ion upflows in summer mainly occurs at the magnetic noon,with a symmetric distribution centered at the magnetic noon.The occurrence of ion upflow in winter is significantly higher than that in summer,and is significantly enhanced during the period of moderate geomagnetic activity.The upward region expands to the lower latitude when the geomagnetic activity is enhanced.The effect of interplanetary magnetic field(IMF)components has also been studied in this paper.When IMF Bx is negative,the upflow occurrence increases in the region of 15:00―18:00 MLT and 06:00―09:00 MLT,with the MLAT range below 70°.The direction of IMF By may lead to the highincidence area reverse at the prenoon or postnoon region.The occurrence of ion upflows with the MLAT range below 75° increases significantly when IMF is southward.Type A events have the highest velocity of ion upflows,then is type E,and type D is the lowest.The average velocity of ion upflows in winter is significantly higher than that in summer.Finally,combining the optical features of aurora,electron acceleration and ion upflow,the characteristics of the ion upflow events associated with particle precipitation of four typical dayside discrete auroras are studied,and the possible acceleration mechanisms are analyzed.We found that(1)ion upflows of type A1 occurred more frequently in the process of auroral particle precipitating,then is type E,the occurrence of other types is relatively low.(2)Ion upflows mainly occurre in the range of 70―75° MLAT,and the accelerated electron corresponding to LLBL and BPS is the important heat source.(3)The horizontal velocity shear is also one of the important processe for accelerating the ionosphere ion upflow.(4)The enhancement of geomagnetic activity and the direction of the three components of IMF will also affect the precipitating of high-energy particles in the aurora acceleration region,which produces heating for ion upflows.In the events of drapery-like dayside corona aurora and radial dayside corona aurora,the upflow regions are 10:00―12:00 MLT and 11:00―13:00 MLT,respectively,corresponding to LLBL and BPS.In the events of hot spot aurora and dayside auroral arc,the upflow regions are 13:00―14:00 MLT and 17:00―18:00 MLT,respectively,corresponding to BPS;The average value of the peak velocity of type A1 is as follows: hot spot aurora(1123.1 m/s),drapery-like dayside corona aurora(1276.0 m/s),radial dayside corona aurora(1550.6 m/s),dayside auroral arc(1771.6 m/s),respectively.The maximum value of the peak velocity of type E is lower than that of type A1,and the average value is as follows:drapery-like dayside corona aurora(698.7 m/s),radial dayside corona aurora(1030.0m/s),dayside auroral arc(1962.3 m/s),respectively.