Ionospheric absorption at Zhongshan Station, Antarctica during magnetic storms in early May, 1998

In the paper the high latitude ionospheric absorption events, monitored by an imaging riometer at Zhongshan Station, Antarctica, are examined during magnetic storms in early May, 1998. The storm absorption at ~0639 UT on May 2 was mainly an equatorward progressing absorption event, which were associated with a strong negative bay of the magnetic H component and with a large Pc3 range pulsation. There was a time lag of about 1. 5 hours between the onset of the ionospheric disturbance and the IMF southward turning in the solar wind. The event at 2222 UT on May 2 was a typical midnight absorption spike event. The absorption region took the form of an elongated strip with the length of 100 - 150 km and the width of 30 - 40 km. The absorption during 0830 - 1200 UT on May 6 was a polar cap absorption (PCA) event,caused by intense precipitation of high-energy protons erupted after a large solar flare explosion.

Dynamic variations of the outer radiation belt during magnetic storms for 1.5–6.0 MeV electrons

The CME’s structure of solar wind(interplanetary magnetic field)is different from CIR’s.The two processes in which plasma and solar wind energy are injected into the Earth’s inner magnetosphere are not the same.So,the variations of energetic elec- trons flux in the radiation belts are different between the storms associated with CMEs and CIRs.By using data from SAMPEX(Solar,Anomalous,and Magnetospheric Particle Explorer)satellite,we have investigated the dynamic variations of the outer radiation belt for 1.5–6.0 MeV electrons during 54 CME-driven storms and 26 CIR-driven recurrent storms.According to the superposed epoch analysis,for CME-and CIR-driven storms,when the Dst index reaches the minimum,the locations of the outer boundary move to L=4 and L=5.5,respectively.In the recovery phases,the locations of the outer boundary of the outer radiation belt are generally lower than and slightly higher than those before CME-and CIR-driven storms,respectively.We have found that the logarithmically decaying 1/e cut-off L-shell is a satisfying indicator of the outer boundary of the outer radiation belt.Furthermore,our study shows that the logarithmically decaying 1/e cut-off latitude is dependent on the Kp index in the main phases of CME-and CIR-driven storms,while in the recovery phases,there is no obvious correlation.In ad- dition,it has been shown that the locations of the peak electron flux are controlled by the minimum Dst index in the main phases of CME-driven storms.The influences of multiple storms on the electron flux of outer radiation belt have also been in- vestigated.

Magnetic storms in Mercury's magnetosphere

We present evidence of geomagnetic storms in Mercury’s magnetosphere based on MESSENGER magnetic field observations made just before the probe impacted the planet.Our findings answer the question of whether geomagnetic storms can occur in other planetary magnetospheres.The interaction of the solar wind with Mercury’s magnetosphere is known to involve flux transfer events in the dayside magnetosphere,plasmoids and flux ropes in the magnetotail,and substorm-like processes,all of which occur morphologically similar to Earth but with significant differences.The significantly weaker magnetic field,smaller magnetosphere,and much faster timescale of processes around Mercury,when compared with Earth,enable charged particles to escape its magnetosphere more efficiently through magnetopause shadowing and direct bombard of the surface.Our analysis of MESSENGER’s data during a coronal mass ejection(CME)proves that,despite these substantial differences,a bifurcated ring current can form in Mercury’s magnetosphere that initiates magnetic storms under strong solar wind driving.

Magnetic Storm Effects in the Auroral Ionosphere Observed with EISCAT Radar-Two Case Studies

Storm-time changes of main plasma parameters in the auroral ionosphere are analyzed for two intense storms occurring on May 15, 1997 and Sept. 25, 1998, with emphasis on their relationship to the solar wind dynamic pressure and the IMFB z component. Strong hard particle precipitation occurred in the initial phase for both storms, associated with high solar wind dynamical pressure. During the recovery phase of the storms, some strong particle precipitation was neither concerned with high solar wind pressure nor southward IMFB z. Severe negative storm effects depicted by electron density depletion appeared in theF-region during the main and recovery phase of both storms, caused by intensive electric field-related strong Joule/frictional heating when IMF was largely southward. The ion temperature behaved similarly inE-andF-region, but the electron temperature did quite different, with a strong increase in the lowerE-region relating to plasma instability excited by strong electric field and a slight decrease in theF-region probably concerning with a cooling process. The field-aligned ion velocity was high and apparently anticorrelated with the northward component of the ion convection velocity.

Numerical Simulation of Ionization Enhancement in the Topside Ionosphere of Cusp Foot-Point Region Caused by Low Energy Particle Precipitation

The Graz Ionospheric Flux Tube Simulations （GIFTS） has been improved. The improved GIFTS model was used to numerically investigate the energy particle precipitation on the distribution of electron density in the ionospheric cusp foot-point region under conditions of large plasma convection during magnetic storm. After including the effects of low energy incident particles, the ionospheric electron densities increase remarkably above altitude of -250 km, showing a peak at about 350 km. The percent enhancements of electron densities increase gradually with altitude, exceed- ing 60% near the upper boundary of the calculation. The calculated ionospheric F2-peak was remarkably enhanced and lifted up by the incident low energy electrons.

Storm-Time Ionospheric Disturbances Monitored by GPS Beacon Measurements

The Total Electron Content (TEC) during three great storms, from April to August 2000, was collected by means of a GPS receiver located in Jingzhou (30.4° N, 112.2° E). The time-latitude-dependent features of ionospheric storms are identified using TEC difference images based on the deviations of TEC during storm relative to quiet time. The responses of ionospheric TEC to magnetic storms were analyzed. The results show that: 1) In middle and low latitude, ionospheric storms effects are more apparent in local day time than at night: 2) Ionospheric storm effects are more dominant near the hump of the equatorial anomaly region than in other regions of TEC measurements; 3) The positive effects during the main phase of ionospheric storm may be caused by electric fields in low latitude; 4) During the recovery period of ionospheric storm, the negative phase of storm may be due to the perturbation of the neutral gas composition.

Influence and hazard of disastrous space weather on power grid in China

Based on the measured data of geomagnetically induced currents （GIC） in Guangdong Ling＇ ao 500 kV power networks during several magnetic storms at the peak years of 23rd Solar Cycle, the GIC calculation results of 750 kV planning power grid in Shartxi, Gansu, Qinghai and Ningxia, the structure and characteristics of power networks from 500 kV to 1 000 kV, and super magnetic storm in 1859 are analyzed in this paper. Through the analysis, the possible impacts of extreme space weather on the future ultra-high voltage （UHV） grid, the security of large-scale power system in China are expounded, and the research suggestions coping with the strong solar storms are proposed.

Dynamic variation and the fast acceleration of particles in Earth's radiation belt

We have quantitatively investigated the radiation belt's dynamic variations of 1.5-6.0 MeV electrons during 54 CME (coronal mass ejection)-driven storms from 1993 to 2003 and 26 CIR (corotating interaction region)-driven recurrent storms in 1995 by utilizing case and statistical studies based on the data from the SAMPEX satellite. It is found that the boundaries determined by fitting an exponential to the flux as a function of L shell obtained in this study agree with the observed outer and inner boundaries of the outer radiation belt. Furthermore, we have constructed the Radiation Belt Content (RBC) index by integrating the number density of electrons between those inner and outer boundaries. According to the ratio of the maximum RBC index during the recovery phase to the pre-storm average RBC index, we conclude that CME-driven storms produce more relativistic electrons than CIR-driven storms in the entire outer radiation belt, although the relativistic electron fluxes during CIR-related storms are much higher than those during CME-related storms at geosynchronous orbit. The physical radiation belt model STEERB is based on the three-dimensional Fokker-Planck equation and includes the physical processes of local wave-particle interactions, radial diffusion, and adiabatic transport. Due to the limitation of numerical schemes, formal radiation belt models do not include the cross diffusion term of local wave-particle interactions. The numerical experiments of STEERB have shown that the energetic electron fluxes can be overestimated by a factor of 5 or even several orders (depending on the pitch angle) if the cross diffusion term is ignored. This implies that the cross diffusion term is indispensable for the evaluation of radiation belt electron fluxes. Formal radiation belt models often adopt dipole magnetic field; the time varying Hilmer-Voigt geomagnetic field was adopted by the STEERB model, which self-consistently included the adiabatic transport process. The test simulations clearly indicate that the adiabatic process can significantly affect the evolution of radiation belt electrons. The interactions between interplanetary shocks and magnetosphere can excite ULF waves in the inner magnetosphere; the excited polodial mode ULF wave can cause the fast acceleration of "killer electrons". The acceleration mechanism of energetic electrons by poloidal and toroidal mode ULF wave is different at different L shells. The acceleration of energetic electrons by the toroidal mode ULF waves becomes important in the region with a larger L shell (the outer magnetosphere); in smaller L shell regions (the inner magnetosphere), the poloidal mode ULF becomes responsible for the acceleration of energetic electrons.

Multiple ground-based observations at Zhongshan Station during the April/May 1998 solar events

Simultaneous observations at Zhongshan Station, Antarctica, during May 1-7, 1998 are presented to show the responses of the polar ionosphere to the April/May 1998 solar events. One of the main geo-effects of the solar events resulted in the major magnetic storm on May 4. At the storm onset on May 2 the ionosphere F2 layer abruptly increased in altitude, the geomagnetic H-component started negative deviation and the spectral amplitude of the ULF wave intensified. Both large isolated riometer absorption and large negative deviation of the geomagnetic H-component occurred at about 0639UT. There was a time lag of about one hour and ten minutes between the storm onset and the IMF southward turning, as measured by the WIND satellite. The polar ionosphere was highly disturbed, as shown by frequent large deviations of the geomagnetic H-component, large riometer absorption events and strong ULF waves in all the courses of the storm. The absorption increased greatly causing the digisonde to be blackout most of the time. However, the data still showed a substantial decrease in the F2 electron density and oscillation of the F2 layer peak height with an amplitude exceeding 200 km.

Large-Scale Traveling Ionospheric Disturbances Observed by GPS Receivers in Antarctica

The paper examines the propagation direction and velocity of large-scale traveling ionospheric disturbances （LST1Ds） during extreme geomagnetic storms in the 23rd solar cycle （e.g., October 2003 and November 2003 storms） using GPS observations. In the analysis, the time delay between the vertical total electron content （VTEC） structures at Scott Base, McMurdo, Davis and Casey GPS stations and the distance between these stations were the main parameters in the determination of LSTIDs propagation speed and direction. The observations during October and November 2003 storms show obvious time delay between the total electron content （TEC） enhancement signatures at these stations. The time delay suggests a movement of the ionospheric disturbances from higher to lower latitudes during the October storm with a velocity of 800-1 200 m/s and poleward propagation of LSTIDs during the November storm with a ve- locity of 300-400 m/s. The equatorward or poleward expansion of LSTIDs during the October and November 2003 storms is probably caused by the disturbances of the neutral temperature occurring close to the dayside convection throat or by the neutral wind oscillation induced by atmospheric gravity waves （AGW） launched from the aurora region.