Interhemispheric Comparison of Dipole Tilt Angle Effects on Latitude of Mid-Altitude Cusp

A statistical study of interhemispheric comparison of dipole tilt angle effect on the latitude of the mid-altitude cusp is preformed by a data set of the Cluster cusp crossings over a 5-year period. The result shows that the dipole tilt angle has a clear control of the cusp latitudinal location. When the dipole tilts sunwards, the cusp is shifted poleward. The northern cusp moves 1° ILAT for every 15.4° increase in the dipole tilt angle, while the southern cusp moves 1° ILAT for every 20.8° increase in the dipole tilt angle. This suggests that an interhemispheric difference appears in the dependence of cusp latitudinal location on the dipole tilt angle.     

Properties of Field Aligned Current in Plasma Sheet Boundary Layers in Magnetotail: Cluster Observation

Field aligned current （FAC） distribution in the plasma sheet boundary layers （PSBLs） in the magnetotail is studied statistically by analysing magnetic field data from the Cluster 4-point measurements. The results show that the FAC distribution on the dusk side is not the same as that on the dawn side in the magnetotail. On the each side earthward and tailward, FA C occurrences are different; occurrence and average current density of FA Cs in the northern hemisphere are different from those in the southern hemisphere. This implies that the FACs have dusk-dawn side asymmetry, polarity asymmetry and inter hemisphere difference in the magnetotail. The present results give a good observation evidence for study on the FAC mechanism.     

Probability of Field-Aligned Currents Observed by the Satellite Cluster in the Magnetotail

Field-aligned current （FAC） density distribution at the plasma sheet boundary layers is statistically studied. The FAC is calculated by the so-called curlometer technique with the data from FGM onboard the four Cluster spacecraft in 2001. By calculation we obtain a large number of FAC samples. In the samples, most of calculated FAC densities were very small and around zero caused by some errors or noise. In order to get the real FAC density distribution in the magnetotail, we use a three-Gaussian distribution to fit the errors, then subtract the estimated error contribution from the full distribution and obtain the FAC density distribution. The result shows that the FAC occurrence versus its density has a distribution consisting of a Gauss/an distribution with an additional decreasing exponential distribution. The most probable value of the FAC density is 3.45 pT/km.     

Bounce-averaged Pitch-angle Diffusion by Electromagnetic Ion Cyclotron Waves in Multi-ion Plasmas

We present a study on the gyroresonant interaction particles in multi-ion （H^＋, He^＋, and O^＋） plasmas between electromagnetic ion cyclotron waves and ring current We provide a first evaluation of the bounce-averaged pitch angle diffusion coefficient 〈Dαα〉 for three typical energies of 50, 100 and 150keV at L ≈ 3.5, the heart of the symmetrical ring current. We show that in the H^＋-band and He^＋-band, 〈Dαα〉 can approach - 10^-4 s^-1 for ion H^＋, and - 5 × 10^-5 s^-1 /or ion He^＋; meanwhile, in the O^＋-band, 〈Dαα〉 can reach - 10^-5 s^-1 for ions He^＋ and O^＋. The results above show that the EMIC wave can efficiently produce precipitation loss of energetic （- 100 keV） ions （H^＋, He^＋ and even O^＋）, and such a wave tends to be a serious candidate responsible for the ring current decay.     

Nonlinear-Ion-Acoustic-Wave Instability, Threshold, Half Width of Trapped Region and Transition Region

Nonlinear Landau damping of ion acoustic wave (IAW) is one of the most important phenomena in the ionosphere and in space and laboratory plasma as well. The instability growth rate of the IAW with electron drift, the amplitude threshold for exciting the nonlinear effects, the half widths of the trapped region with the trapped electrons are studied experimentally. Under the experimental conditions, it is shown that there is a frequency range of 140--160 kHz, within which the growth rate has the largest value of about 6×10⁴--1.5×10⁵ s^-1. We obtain the transitional region width caused by collisions theoretically and experimentally, for the first time to our knowledge. The experimental results are in good agreement with the theoretical prediction.     

Simulation of Resonant Interaction between Energetic Electrons and Whistler-Mode Chorus in the Outer Radiation Belt

We construct a realistic model to evaluate the chorus wave-particle interaction in the outer radiation belt L = 4.5. This model incorporates a plasmatrough number density model, a field-aligned density model and a realistic wave power and frequency model. We solve the 2D bounce-averaged momentum-pitch-angle Fokker-Planck equation and show that the Whistler-mode chorus can be effective in the acceleration of electrons, and enhance the phase space density for energies of -1 MeV by a factor from 10 to 10^3 in about two days, consistent with the observation. We also demonstrate that ignorance of the electron number density variation along field line and magnetic local time in the previous work yields an overestimate of energetic electron phase space density by a factor 5-10 at large pitch-angle after two days, suggesting that a realistic plasma density model is very important to evaluate the evolution of energetic electrons in the outer radiation belt.     

Bounce-Averaged Acceleration of Energetic Electrons by Whistler Mode Chorus in the Magnetosphere

We construct the bounce-averaged diffusion coefficients and study the bounce-averaged acceleration for energetic electrons in gyroresonance with whistler mode chorus. Numerical calculations have been performed for a band of chorus frequency distributed over a standard Gaussian spectrum specifically in the region near L = 4.5, where peaks of the electron phase space density occur. It is found that whistler mode chorus can efficiently accelerate electrons and can increase the phase space density at energies of about 1 MeV by more than one order of magnitude about one day, in agreement with the satellite observations during the recovery phase of magnetic storms.     

Dynamic Evolution of Outer Radiation Belt Electrons due to Whistler-Mode Chorus

Following our preceding work, we perform a further study on dynamic evolution of energetic electrons in the outer radiation belt L=4.5 due to a band of whistler-mode chorus frequency distributed over a standard Gaussian spectrum. We solve the 2D bounce-averaged Fokker-Planek equation by allowing incorporation of cross diffusion rates. Numerical results show that whistler-mode chorus can be effective in acceleration of electrons at large pitch angles, and enhance the phase space density for energies of about 1 MeV by a factor of 10^2 or above in about one day, consistent with observation of significant enhancement in flux of energetic electrons during the recovery phase of a geomagnetic storm. Moreover, neglecting cross diffusion often leads to overestimates of the phase space density evolution at large pitch angle by a factor of 5-10 after one day, with larger errors at smaller pitch angle, suggesting that cross diffusion also plays an important role in wave-particle interaction.     

Characteristics of Wave--Particle Interaction in a Hydrogen Plasma

We study the characteristics of cyclotron way,particle interaction in a typical hydrogen plasma. The numerical calculations of minimum resonant energy Emin, resonant wave frequency ω, and pitch angle diffusion coefficient Dαα for interactions between R-mode/L-mode and electrons/protons are presented. It is found that Emin decreases with ω for R-mode/electron, L-mode/proton and L-mode/electron interactions, but increase with ω for R-mode/proton interaction. It is shown that both R-mode and L-mode waves can efficiently scatter energetic （10 keV-100 keV） electrons and protons and cause precipitation loss at L = 4, indicating that perhaps waveparticle interaction is a serious candidate for the ring current decay.     

Nonlinear Evolution of Lower-Hybrid Drift Instability in Harris Current Sheet

We perform 2.5-dimensional particle-in-cell simulations to investigate the nonlinear evolution of the lower hybrid drift instability (LHDI) in Harris current sheet. Due to the drift motion of electrons in the electric field of the excited low hybrid drift (LHD) waves, the electrons accumulate at the outer layer, and therefore there is net positive charge at the inner edge of the current sheet. This redistribution of charge can create an electrostatic field along the z direction, which then modifies the motions of the electrons along the y direction by E×B drift. This effect strongly changes the structure of the current sheet.     

Pitch Angle Distribution Evolution of Energetic Electrons by Whistler-Mode Chorus

We develop a two-dimensional momentum and pitch angle code to solve the typical Fokker-Planck equation which governs wave-particle interaction in space plasmas. We carry out detailed calculations of momentum and pitch angle diffusion coefficients, and temporal evolution of pitch angle distribution for a band of chorus frequency distributed over a standard Gaussian spectrum particularly in the heart of the Earth＇s radiation belt L = 4.5, where peaks of the electron phase space density are observed. We find that the Whistler-mode chorus can produce significant acceleration of electrons at large pitch angles, and can enhance the phase space density for energies of 0.5 - 1 MeV by a factor of 10 or above after about 24h. This result can account for observation of significant enhancement in flux of energetic electrons during the recovery phase of a geomagnetic storm.     

Second-Order Resonant Interaction of Ring Current Protons with Whistler-Mode Waves

We present a study on the second-order resonant interaction between the ring current protons with Whistler-mode waves propagating near the quasi electrostatic limit following the previous second-order resonant theory. The diffusion coefficients are proportional to the electric field amplitude E, much greater than those for the regular first-order resonance, which are proportional to the electric field amplitudes square E^2. Numerical calculations for the pitch angle scattering are performed for typical energies of protons Ek = 50 keV and 100 keV at locations L = 2 and L = 3.5. The timescale for the loss process of protons by the Whistler waves is found to approach one hour, comparable to that by the EMIC waves, suggesting that Whistler waves may also contribute significantly to the ring current decay under appropriate conditions.     

Correlations between Strong Range Spread-F and GPS L-Band Scintillations Observed in Hainan in 2004

Data from the DPS-4 digisonde and the GPS L-band ionospheric scintillation monitor are employed to study the correlations between strong range spread-F （SSF） and GPS L-band scintillations observed in the ionosphere over Hainan Island, China （19.5°N, 109.1°E geogr., dip lat. 9°N） in 2004. The SSF in the ionogram is different from the general range spread-F because it extends in frequency well beyond FoF2 and makes FoF2 difficult to be determined. The observations show that the SSF phenomenon is frequently accompanied by the occurrence of GPS L-band scintillations. The SSF and GPS L-band scintillations occur frequently in the equinoctial months （March, April, September, and October）, but rarely in the winter （January, February, November, and December） and summer （May-August）; especially, occurrence variations of the SSF and GPS L-band scintillations nearly have a same trend. The SSF and scintillations may be associated with the occurrence of topside plasma bubbles and could be explained by the eneralized Rayleigh-Taylor instability.     

Dynamic Processes of Cross-Tail Current in the Near-Earth Magnetotail

Current dynamic processes in realistic magnetotail geometry simulations under various driven conditions and Hall effects. are studied by Hall magnetohydrodynamic （MHD） Associated with the external driving force, a thin current sheet with a broad extent is built up in the near-Earth magnetotail. The time evolution for the formation of the current sheet comprises two phases： slow growth and a fast impulsive phase before the near-Earth disruption of the current sheet resulting from the fast magnetic reconnection. The simulation results indicate that as the external driving force increases, the site and the tailward speed of the near-Earth current disruption region are closer to the Earth and faster, respectively. Whether the near-Earth disruption of the current sheet takes place or not is mainly controlled by Hall effects. It is found that there is no sudden disruption of the current sheet in the near-Earth region if the ion inertial length is below di= 0.04.     

Theoretical Study on Ion Escape in Martian Atmosphere

Based on the observation that Martian magnetic moment is gradually reducing from the ancient to the present, we investigate the O^＋ ion flux distribution along magnetic field lines and the ion escaping flux in Martian tail with different assumed Martian magnetic moments. The results show that the O^＋ ion flux along magnetic field lines decreases with distance from Mars; the ion flux along the field line decreases more quickly if the magnetic moment is larger; the larger the magnetic moment, the smaller the ion escaping flux in the Martian tail. The ion escaping flux depends on Z-coordinate in the Martian tail. With decrease of the magnetic moment, the ion escaping flux in the Martian tail increases. The results are significant for studying the water loss from Mars S uFface.     

Cluster Observation of Eelectrostatic Solitary Waves around Magnetic Null Point in Thin Current Sheet

Electrostatic solitary waves （ESWs） are observed in the vicinity of the magnetic null of the widely studied magnetic reconnection taking place at the near-earth tail when current sheet becomes dramatic thinning during substorm time on 1 October 2001. We use the Imada method for the 2-D reconnection model and study the characteristics of ESWs near the X-line region and the magnetic null points. The result shows that the amplitude of the observed ESWs in the vicinity of X-line region ranges from 0.1mV/m to 5mV/m, and the amplitude is larger near the magnetic null points. The generation mechanism and the role of ESWs associated with magnetic reconnection are also discussed.     

Changes of geomagnetic transmissivity in the disturbed magnetosphere: ground-based and CORONAS-F observations

We report increases of cosmic-ray intensity at lowL shells, on the ground as well as on the altitude of 500 km, during the selected intervals when magnetosphere was strongly disturbed. The geomagnetic transmissivity for cosmic ray vertical access has been computed for four events, using two geomagnetic field models. The first event, namely, dated November 20–22, 2003, led to an increase of galactic cosmic-ray intensity due to the improvement of magnetospheric transmissivity at neutron monitors with high nominal cut-off rigidity. Other two events with high-energy solar proton emissions, namely, dated October 28 and November 2, 2003, caused different responses at middle latitudes. The first one followed by the strong geomagnetic disturbance led to the shift of the penetration boundary of protons, having(50–90) MeV at CORONAS-F satellite toL<3, coinciding approximately with the cut-off reduction expected byDst depression, while the other one, without remarkableDst decrease, did not shift the outer boundary of penetration belowL ≈ 4. And the fourth of the events, on November 8, 2004, with strong geomagnetic disturbance, yielded a complicated structure of cosmic-ray time profiles: superimposed on the cosmic-ray decrease, viewed by neutron monitors and by CORONAS-F at high latitude; an increase of intensity at middle latitudes both on the ground and on the altitude of 500 km has been observed during theDst depression. This work was supported by the Slovak Research and Development Agency under the contract No. APVV-51-053805. The work at Technical University was supported by VEGA grant 2/4064.     

Low Energy Ion Channelling in Single-Wall Nanotubes

Monte Carlo simulation is used to study the low energy He ion channelling in a （17, 0） single-wall nanotube and its rope. The simulation shows that the channelling critical angle ψc = 48E^-1/2 （E is incident energy） for a 1.31-nm-diameter initial beam into the nanotube, while ψc = 45E^-1/2 for the 1.31-nm-diameter initial beam into its rope.     

Strong vertex corrections from weak disorder in 2D d-wave superconductors

We show that weak static random potentials have pronounced effects on the quasiparticle states of a 2Dd-wave superconductor close to a node. We prove that the vertex correction coming from the simplest crossed diagram is important even for a nonmagnetic potential. The leading frequency and momentum dependent logarithmic singularities in the self-energy are calculated exactly to second order in perturbation theory. The self-energy corrections lead to a modified low energy density of states which depends strongly on the type of random potential and which can be measured in experiments. There is an exceptional case for a potential with extremely local scatterers and opposite nodes separated by (, ) where an exact cancelation takes place eliminating the leading frequency dependent singularity in the simplest crossed diagram. A comparison of the perturbative results with a self-consistent CPA (coherent potential approximation) for the nonmagnetic disorder reveals qualitative differences in the self-energy at the smallest energies which are due to the neglectance of vertex corrections in CPA.