Origins of perturbations in dayside equatorial ground magnetograms

To determine the cause(s)of perturbations seen in dayside equatorial ground magnetograms,we conducted a systematic survey of simultaneous ground-based and geosynchronous satellite-based observations during the 90-day period from December 1,2020 to February 28,2021.We examined Huancayo ground magnetometer observations from 14:00:00 to 20:00:00 UT each day,during which Huancayo passed through local noon.From those data we chose perturbation events selected on the basis of large(>20 nT)event amplitude and classified the selected events as responding primarily to solar wind pressure,or to variations in the north/south component of the interplanetary magnetic field(IMF Bz),or perhaps in part to both.The results show that an equivalent number of events were identified for each model during this 90-day period.Variations in the lagged solar wind dynamic pressure routinely correspond to nearly simultaneous sudden impulses recorded at both geosynchronous orbit and on the ground.Variations in IMF Bz produce erosion signatures at geosynchronous orbit and can correspond to ground events if lag times for reconnection to enhance convection in the magnetosphere are taken into account.

Aurora morphology in the dayside

Day-side aurora phenomena are examined by using TV image data obtained at Ny-Alesund in Svalbard, Godhavn in Greenland and Zhongshan Station,Antarctica. Results are summarized as follows. During the quiet period, in the pre-and post-noon sectors. (1) Weak arc (Sun-aligned arc), (2) Corona aurora and (3) Band aurora are observed in these stations. During disturbed period,Corona aurora and Band aurora are also observed in the pre- and post-noon sectors. However. bright discrete aurora. instead of weak arc (Sun-aligned arc). develops from thc night side oval in the dawn and dusk sectors. Pre-noon corona and post-noon band aurora are observed in the lower latitude as compared with the location of those auroras during the quiet period.

Butterfly distribution of Earth＇s radiation belt relativistic electrons induced by dayside chorus

Previous theoretical studies have shown that dayside chorus can produce butterfly distribution of energetic electrons in the Earth＇s radiation belts by preferentially accelerating medium pitch angle electrons, but this requires the further confirmation from high- resolution satellite observation. Here, we report correlated Van Allen Probes data on wave and particle during the 1 I-13 April, 2014 geomagnetic storm. We find that a butterfly pitch angle distribution of relativistic electrons is formed around the location L = 4.52, corresponding to the presence of enhanced dayside chorus. Using a Gaussian distribution fit to the observed chorus spectra, we calculate the bounce-averaged diffusion rates and solve two-dimensional Fokker-Planck equation. Numerical results demonstrate that acceleration by dayside chorus can yield the electron flux evolution both in the energy and butterfly pitch angle distribution comparable to the observation, providing a further evidence for the formation of butterfly distribution of relativistic electrons driven by very low frequency （VLF） plasma waves.

Numerical study of asymmetric driven reconnection at dayside magnetopause

A two-dimensional compressible MHD code has been used to numerically study the asymmetric driven reconnection processes in the vicinity of the magnetopause. The initial magnetic field configuration is assumed to be in a mechanical equilibrium state. The cases with identical temperatures (T m0/T s0=1.0) and four different ratios of magnetic field strength (Q=B m0/B s0=1.0, 1.5, 2.0, 2.5), and the case withT m0/T s0=2.0 andQ=1.5 are investigated (B m0,T m0 andB s0,T s0 are the initial magnetic strength and temperature outside the current sheet on the magnetosphere and the magnetosheath, respectively). When the magnetic field on the magnetosheath side is set as southward, a recurrent formation of multiple magnetic bubbles with various scales occurs under the action of the inward plasma flow imposed at the left and right boundaries. In the simulation, some bubbles coalesce into a bigger one and then it is convected out of the simulation domain; the others are convected through the top boundary all alone. Thus, the plasmoid events with different scales and different time intervals take place intermittently and the impulsive features of magnetic reconnection are clearly shown. The multiple magnetic islands are all high-temperature and large-density regions in comparison with the ambient environment. The bipolar signatures or fluctuant variations of normal magnetic field component are generated by the formation of multiple magnetic islands. This result is similar to the FTEs signature.

Ground Observations of Post-Noon Aurora: a Case Study

The characteristics of the post-noon aurora observed at Antarctic Zhongshan station on June 12, 1999, were discussed and analyzed. In the condition of the magnetic activity is not large (K p≈1), for post-noon 630.0 nm emissions, the total fluxes of soft precipitating particles were increasing from 10∶50 UT to 13∶35 UT and were decreasing from 13∶35 UT to 18∶00 UT in almost monotonous way. Away from noon, the 557.7 nm emissions increased gradually from 10∶50 UT to 17∶10 UT. The behaviors of the precipitating particles for exciting 630.0 nm aurora and 557.7 nm aurora were quite different. The peak intensity of 630.0 nm and 557.7 nm emissions appeared at about 13∶35 UT and 15∶40 UT respectively, the time difference of two peaks is about 2 h. The energy of precipitating electrons remained fairly steady until 15∶00 UT when it rose dramatically.

Identification of optical auroras caused by mantle precipitation with the aid of particle observations from DMSP satellites

Particle observations of the Defense Meteorological Satellite Program(DMSP) show that discrete auroral structures commonly exist in the region of the plasma mantle, but the optical features of the aurora generated by particles from the plasma mantle(called ‘mantle aurora’ in this paper) have not been established. A comparison of 7-year optical auroral observations made at the Yellow River Station with conjugate particle observations obtained from the DMSP confirm that mantle auroras have common features and can be clearly identified from all-sky imager observations. The mantle auroras normally present as sporadic and weak auroral structures split poleward of the dayside auroral oval. They are observed in both the green and red lines with the intensity of the red line being greater than that of the green line. In this paper, we illustrate typical mantle auroras and provide statistics on 55 mantle aurora cases that are confirmed by particle observation by the DMSP. Statistical results show that the occurrence of the mantle aurora has no clear dependence on the IMF By and Bz conditions, but the motion of the mantle aurora strongly depends on the IMF By, which indicates that the generation of the mantle aurora is intimately related to the dayside magnetopause reconnection. With the fundamental criteria for distinguishing the mantle aurora presented in this paper, we will be able to independently identify the mantle auroras from ground optical observations. This will allow us to investigate the physical processes that occur in the plasma mantle by monitoring the evolution of the auroral forms.

The Auroral Station in Adventdalen, Svalbard

This paper describes the Auroral Station in Adventdalen near Longyearbyen, Svalbard (78°N, 15°E). The main instruments at the site are for optical observation of aurora and airglow, but magnetic and radar observations are also carried out. Emission spectra show the difference between the dayside and nightside optical aurora. A newly compiled mesospheric temperature series from the station is also presented, derived through 20 years of spectral measurements of the hydroxyl airglow layer.

FORMATION AND STRUCTURE OF THREE DIMENSIONS OF FLUX TRANSFER EVENTS

One of the most important finds observed by ISEE satellites (International Sun-Earth-Explorer) is the finding of the flux transfer events (FTE) at the dayside magnetopause region, which has had great influence upon the research in the couple between solar wind and the magnetosphere. Since 1978 when Russell and Elphic first published the observation results, many authors have worked on the