Geomagnetic control of polar mesosphere summer echoes     

J. Bremer  P. Hoffmann  T. L. Hansen 《Annales Geophysicae》2000,18(2):202-208

Using observations with the ALOMAR SOUSY radar near Andenes (69.3°N, 16.0°E) from 1994 until 1997 polar mesosphere summer echoes (PMSE) have been investigated in dependence on geomagnetic K indices derived at the Auroral Observatory Tromsø (69.66°N, 18.94°E). During night-time and morning hours a significant correlation between the signal-to-noise ratio (SNR) of the radar results and the geomagnetic K indices could be detected with a maximum correlation near midnight. The correlation becomes markedly smaller in the afternoon and early evening hours with a minimum near 17 UT. This diurnal variation is in reasonable agreement with riometer absorption at Ivalo (68.55°N, 27.28°E) and can be explained by the diurnal variation of ionization due to precipitating high energetic particles. Therefore, a part of the diurnal PMSE variation is caused by this particle precipitation. The variability of the solar EUV variation, however, has no significant influence on the PMSE during the observation period.  相似文献   

The role of sodium bicarbonate in the nucleation of noctilucent clouds     

J. M. C. Plane 《Annales Geophysicae》2000,18(7):807-814

It is proposed that a component of meteoric smoke, sodium bicarbonate (NaHCO₃), provides particularly effective condensation nuclei for noctilucent clouds. This assertion is based on three conditions being met. The first is that NaHCO₃ is present at sufficient concentration (10⁴ cm^–3) in the upper mesosphere between 80 and 90 km. It is demonstrated that there is strong evidence for this based on recent laboratory measurements coupled with atmospheric modelling. The second condition is that the thermodynamics of NaHCO₃(H₂O)_n cluster formation allow spontaneous nucleation to occur under mesospheric conditions at temperatures below 140 K. The Gibbs free energy changes for forming clusters with n = 1 and 2 were computed from quantum calculations using hybrid density functional/Hartree-Fock (B3LYP) theory and a large basis set with added polarization and diffuse functions. The results were then extrapolated to higher n using an established dependence of the free energy on cluster size and the free energy for the sublimation of H₂O to bulk ice. A 1-dimensional model of sodium chemistry was then employed to show that spontaneous nucleation to form ice particles (n > 100) should occur between 84 and 89 km in the high-latitude summer mesosphere. The third condition is that other metallic components of meteoric smoke are less effective condensation nuclei, so that the total number of potential nuclei is small relative to the amount of available H₂O. Quantum calculations indicate that this is probably the case for major constituents such as Fe(OH)₂, FeO₃ and MgCO₃.  相似文献   

Comment on “Concerning the generation of geomagnetic giant pulsations by drift-bounce resonance ring current instabilities” by K.-H. Glassmeier et al., Ann. Geophysicae, 17, 338/350, (1999)     

I. R. Mann  G. Chisham 《Annales Geophysicae》2000,18(2):161-166

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Energetic particle acceleration in a three-dimensional magnetic field reconnection model: the role of magnetohydrodynamic turbulence     

T. Kobak  M. Ostrowski 《Monthly notices of the Royal Astronomical Society》2000,317(4):973-978

The role of magnetohydrodynamic (MHD) turbulence in the cosmic ray acceleration process in a volume with a reconnecting magnetic field is studied by means of Monte Carlo simulations. We performed modelling of proton acceleration, with the three-dimensional analytic model of stationary reconnection of Craig et al. providing the unperturbed background conditions. Perturbations of particle trajectories resulting from a turbulent magnetic field component were simulated using small-amplitude pitch-angle momentum scattering, enabling modelling of both small- and large-amplitude turbulence in a wide wavevector range. Within the approach, no second-order Fermi acceleration process is allowed. Comparison of the acceleration process in models involving particle trajectory perturbations with the unperturbed model reveals that the turbulence can substantially increase the acceleration efficiency, enabling much higher final particle energies and flat particle spectra.  相似文献   

Non-linear amplification of a magnetic field driven by cosmic ray streaming     

S. G. Lucek  A. R. Bell 《Monthly notices of the Royal Astronomical Society》2000,314(1):65-74

One-, two- and three-dimensional numerical results of the non-linear interaction between cosmic rays and a magnetic field are presented. These show that cosmic ray streaming drives large-amplitude Alfvénic waves. The cosmic ray streaming energy is very efficiently transferred to the perturbed magnetic field of the Alfvén waves, and the non-linear time-scale of the growth of the waves is found to be very rapid, of the order of the gyro-period of the cosmic ray. Thus, a magnetic field of interstellar values, assumed in models of supernova remnant blast wave acceleration, would not be appropriate in the region of the shock. The increased magnetic field reduces the cosmic ray acceleration time and so increases the maximum cosmic ray energy, which may provide a simple and elegant resolution to the highest energy Galactic cosmic ray problem, where the cosmic rays themselves provide the fields necessary for their acceleration.  相似文献   

Energetic Particles Observed in the CUSP Region During a Storm Recovery Phase     

S. Y. Fu  Q. G. Zong  Z. Y. Pu  C. J. Xiao  A. Korth  P. Daly  H. Reme 《Surveys in Geophysics》2005,26(1-3):241-254

In this paper we report energetic ion behavior and its composition variations observed by the Cluster/RAPID instrument when the spacecraft was travelling in the high latitude magnetospheric boundary region on the day of the 31 March, 2001, strongest magnetic storm in the past 50 years. The Dst index reached −360 nT at about 09:00 UT. During its early recovery phase, large amounts of oxygen and helium ions were observed; the ratio of oxygen to hydrogen in the RAPID energy range reached as high as 250%, which suggests that the observed energetic particles might be of magnetospheric origin. The observations further show that enhanced energetic electron fluxes are confined in a very narrow region, while protons have occupied a larger region, and heavy ions have been observed in an even larger region. The flux of energetic electrons show a slight enhancement in a region where the magnetic field magnitude is around zero. These observed energetic ions could be quasi-trapped by the current sheet in the stagnation region of the cusp.  相似文献   

The influence of particle composition on thorium scavenging in the NE Atlantic ocean (POMME experiment)     

M. Roy-Barman  C. Jeandel  M. Souhaut  M. Rutgers van der Loeff  I. Voege  N. Leblond  R. Freydier 《Earth and Planetary Science Letters》2005,240(3-4):681-693

²³⁰Th, ²³²Th and ²³⁴Th were analyzed in sinking particles collected by moored and drifting sediment traps in the NE Atlantic Ocean (POMME experiment) in order to constrain the phase(s) carrying Th isotopes in the water column. It reveals a contrasted behaviour between ²³⁴Th and ²³⁰Th. ²³⁴Th is correlated to the particulate organic carbon suggesting that it is primarily scavenged by organic compounds in the surface waters. ²³⁰Th_xs is correlated with Mn, Ba and the lithogenic fraction that are enriched in small suspended particles and incorporated in the sinking particulate flux throughout the water column. The lack of correlation between ²³⁰Th_xs and CaCO₃ or biogenic silica (bSi) indicates that CaCO₃ and bSi are not responsible for ²³⁰Th scavenging in the deep waters of this oceanic region. ²³⁰Th is generally correlated with the lithogenic content of the trapped material but this correlation disappears in winter during strong atmospheric dust inputs suggesting that lithogenic matter is not directly responsible for ²³⁰Th scavenging in the deep waters or that sufficient time is required to achieve particle–solution equilibration. MnO₂ could be the prevalent ²³⁰Th_xs-bearing phase. The narrow range of K_{d_MnO2}^Th obtained for very contrasted oceanic environments supports a global control of ²³⁰Th_xs scavenging by MnO₂ and raises the possibility that the ²³⁰Th–²³¹Pa fractionation is controlled by the amount of colloidal MnO₂ in seawater.  相似文献   

High-Altitude CUSP: The Extremely Dynamic Region in Geospace     

Jiasheng Chen  Theodore A. Fritz 《Surveys in Geophysics》2005,26(1-3):71-93

The high-altitude dayside cusps (both northern and southern) are extremely dynamic regions in geospace. Large diamagnetic cavities with significant fluctuations of the local magnetic field strength have been observed there. These cusp diamagnetic cavities are always there day after day and are as large as 6 R_E Associated with these cavities are charged particles with energies from 20 keV up to 10 MeV. The intensities of the cusp energetic ions have been observed to increase by as much as four orders of the magnitude when compared with regions adjacent to the cusp which includes the magnetosheath. Their seed populations are a mixture of ionospheric and solar wind particles. The measured energetic ion fluxes in the high-altitude cusp are higher than that in both the regions upstream and downstream from the bow shock. Turbulent electric fields with an amplitude of about 10 mV/m are also present in the cusp, and a cusp resonant acceleration mechanism is suggested. The observations indicate that the dayside high-altitude cusp is a key region for transferring the solar wind mass, momentum, and energy into the Earth’s magnetosphere.  相似文献   

Distribution of trace metals in the Odra River system: Water–suspended matter–sediments     

Edeltrauda Helios Rybicka  Ewa Adamiec  Urszula Aleksander-Kwaterczak 《Limnologica》2005,35(3):185-198

Extensive investigations of trace metals concentrations in water, suspended particulate matter (SPM) and bottom sediments of the whole Odra River system were carried out over the years 1997–2000. The vertical distribution of selected metals and their mobility were also studied in the sediment cores from upper and middle river sections. Significant levels of metal contamination were found. Median concentrations (Cd, Pb, Cu, Zn and As) in the SPM and sediments were (mg kg⁻¹) 7.1 and 8.9 Cd, 128 and 146 Pb, 81 and 119 Cu, 1198 and 1204 Zn, 48 and 54 As, respectively. The highest metal pollution of the Odra River solids was found with cadmium, zinc, lead and arsenic, showing high similarity in their frequency distributions in both SPM and sediments. Cd, Zn and As appear to be of particular concern because of the high levels, that appear to be bioavailable, and their high mobility. The exchangeable and carbonate chemical forms of Cd and Zn reached up to 50% of their total amount. Besides the determination of total metal concentration, the metal chemical forms in river solids were investigated. The results of very wide studies of the Odra River system through 4 years suggest that metal pollution decreased, especially for Zn, Pb and Cu. Among all metals studied in the Odra River sediments, substantial reductions of Cd contamination were observed neither in the period after ’97 flood, nor if compared with the earlier results obtained before ’97. No essential differences of the metal contents were observed among the samples for the same river compartment, from the same locality, taken within the five sampling campaigns. The pattern of spatial and vertical metal distributions in the river solids indicates that a variety of sources might be responsible for the contamination; very intensive, historical and current mining and smelting activities probably are the most important ones.  相似文献   

An application of Mie's series to soft particles     

A. Y. Perelman 《Pure and Applied Geophysics》1978,116(6):1077-1088

Summary The scattering of electromagnetic radiation from soft particles has been studied by a new method which allows to transform the Mie series into a simplified form through the use of some auxiliary expansions derived in the Appendix of this article. This simplified form (eq. 1) converts into the Hulst and Rayleigh-Debye-Gans' formulae if the parameters of eq. I are properly restricted. A further simplified form (eq. II), improves the well-known Hulst approximation.  相似文献