Cosmic-Ray Modulation: An Empirical Relation with Solar and Heliospheric Parameters

Long-term variations of galactic cosmic rays were compared with the behavior of various solar activity indices and heliospheric parameters during the current solar cycle. This study continues previous works where the cosmic-ray intensity for the solar cycles 20, 21, and 22 was well simulated from the linear combination of the sunspot number, the number of grouped solar flares, and the geomagnetic index A _p. The application of this model to the current solar cycle characterized by many peculiarities and extreme solar events led us to study more empirical relations between solar-heliospheric variables, such as the interplanetary magnetic field, coronal mass ejections, and the tilt of the heliospheric current sheet, and cosmic-ray modulation. By analyzing monthly cosmic-ray data from the Neutron Monitor Stations of Oulu (cutoff rigidity 0.81 GV) and Moscow (2.42 GV) the contribution of these parameters in the ascending, maximum, and descending phases of the cycle was investigated and it is shown that a combination of these parameters reproduces the majority of the modulation potential variations during this cycle. The approach applied makes it possible to better describe the behavior of cosmic rays in the epochs of the solar maxima, which could not be done before. An extended study of the time profiles, the correlations, and the time lags of the cosmic-ray intensity against these parameters using the method of minimizing RMS over all the considered period 1996 – 2006 determines characteristic properties of this cycle as being an odd cycle. Moreover, the obtained hysteresis curves and a correlative analysis during the positive polarity (qA>0, where q is the particle charge) and during the negative polarity (qA<0) intervals of the cycle result in significantly different behavior between solar and heliospheric parameters. The time lag and the correlation coefficient of the cosmic-ray intensity are higher for the solar indices in comparison to the heliospheric ones. A similar behavior also appears in the case of the intervals with positive and negative polarity of the solar magnetic field.     

基于γ暴等观测限制宇宙学参数与暗能量模型

利用Union2 557个Ia型超新星数据限制宇宙学参数qo、jo和so,在红移z≤1.4范围内校准5个γ暴(gamma-ray burst,GRB)光度关系.假设γ暴光度关系不随红移演化,得到66个高红移γ暴的距离模数.最后综合利用宇宙微波背景(Cosmic Microwave Background,CMB)辐射观测数据、重子声波震荡(Baryon AcousticOscillations,BAO)观测数据与116个具有红移的γ暴数据限制几个常见的暗能量模型.根据贝叶斯判据(Bayesian Information Criterion,BIC),发现ACDM模型是最好的模型;根据Akaike判据(Akaike Information Criterion,AIC),发现JBP模型是最好的模型.     

Gamma-Ray Bursts and Other Observations: Constraints on Cosmographic Parameters and Dark Energy Models

We use the newly released Union2 SNe Ia dataset to constrain cosmographic parameters, namely the deceleration, jerk and snap parameters (q0, j0 and s0), then calibrate the five luminosity relations of Gamma-ray Bursts (GRBs) at redshift z ≤ 1.4. Assuming that the GRB luminosity relations do not evolve with the redshift, we obtain the distance moduli of 66 high-redshift GRBs. At last, we combine the observational datasets including the observations of the Cosmic Microwave Background (CMB), Baryon Acoustic Oscillation (BAO) and the 116 GRBs with known redshifts to constrain some widely-discussed dark energy models. We find that the ΛCDM model is the best according to the Bayesian Information Criterion (BIC), and the JBP model is the best according to the Akaike Information Criterion (AIC).     

The Model of Radio Two-way Time Comparison between Satellite and Station and Experimental Analysis

Time synchronization between satellite and station is the key technique of satellite navigation system and the foundation of realization of satellite navigation and positioning. Aiming at solving the problems of time synchronization, we have discussed a new method of radio two-way time comparison between satellite and station, deduced in detail the reduction model of up- and down-link pseudo ranges between satellite and station, and provided a practical calculation model of clock error between satellite and station. By calculating the differences between up- and down-link pseudo ranges, this method has eliminated the influences of common errors, such as the tropospheric delay, satellite ephemeris errors, ground station coordinates errors and so on. The ionospheric delay relevant to signal frequency is also weakened largely, thus this improves the accuracy of time comparison greatly. Finally, experimental analysis is conducted by using observational data, and the results show that the accuracy of radio two-way time comparison between satellite and station can attain about 0.34 ns, which validates the correctness of theoretical method and model.     

Global Heliospheric Parameters and Cosmic-Ray Modulation: An Empirical Relation for the Last Decades

We study empirical relations between the modulation of galactic cosmic rays quantified in terms of the modulation potential and the following global heliospheric parameters: the open solar magnetic flux, the tilt angle of the heliospheric current sheet, and the polarity of the heliospheric magnetic field. We show that a combination of these parameters explains the majority of the modulation potential variations during the neutron monitor era 1951 – 2005. Two empirical models are discussed: a quasi-linear model and a model assuming a power-law relation between the modulation potential and the magnetic flux. Both models describe the data fairly well. These empirical models provide a simple tool for evaluating various cosmic-ray related effects on different time scales. The models can be extended backwards in time or used for predictions, if the corresponding global heliospheric variables can be independently estimated.     

MSFC Stream Model Preliminary Results: Modeling Recent Leonid and Perseid Encounters

The cometary meteoroid ejection model of Jones and Brown [Physics, Chemistry, and Dynamics of Interplanetary Dust, ASP Conference Series 104 (1996b) 137] was used to simulate ejection from comets 55P/Tempel-Tuttle during the last 12 revolutions, and the last 9 apparitions of 109P/Swift-Tuttle. Using cometary ephemerides generated by the Jet Propulsion Laboratory’s (JPL) HORIZONS Solar System Data and Ephemeris Computation Service, two independent ejection schemes were simulated. In the first case, ejection was simulated in 1 h time steps along the comet’s orbit while it was within 2.5 AU of the Sun. In the second case, ejection was simulated to occur at the hour the comet reached perihelion. A 4th order variable step-size Runge–Kutta integrator was then used to integrate meteoroid position and velocity forward in time, accounting for the effects of radiation pressure, Poynting–Robertson drag, and the gravitational forces of the planets, which were computed using JPL’s DE406 planetary ephemerides. An impact parameter (IP) was computed for each particle approaching the Earth to create a flux profile, and the results compared to observations of the 1998 and 1999 Leonid showers, and the 1993 and 2004 Perseids.     

The Fe-Line Feature in the X-Ray Spectrum of Solar Flares: First Results from the SOXS Mission

We present the first results from the low-energy detector payload of the solar X-ray spectrometer (SOXS) mission, which was launched onboard the GSAT-2 Indian spacecraft on May 08, 2003 by the GSLV-D2 rocket to study solar flares. The SOXS low-energy detector (SLD) payload was designed, developed, and fabricated by the Physical Research Laboratory (PRL) in collaboration with the Space Application Centre (SAC), Ahmedabad and the Indian Space Research Organization (ISRO) Satellite Centre (ISAC), Bangalore. The SLD payload employs state-of-the-art, solid-state detectors, viz., Si PIN and Cadmium-Zinc-Telluride (CZT) devices that operate at near room temperature (−20 ^°C). The energy ranges of the Si PIN and CZT detectors are 4 – 25 and 4 – 56 keV, respectively. The Si PIN provides sub-keV energy resolution, while the CZT provides ~1.7 keV energy resolution throughout the energy range. The high sensitivity and sub-keV energy resolution of the Si PIN detector allows measuring the intensity, peak energy, and the equivalent width of the Fe-line complex at approximately 6.7 keV, as a function of time in all ten M-class flares studied in this investigation. The peak energy (E _p) of the Fe-line feature varies between 6.4 and 6.7 keV with increase in temperature from 9 to 58 MK. We found that the equivalent width (w) of the Fe-line feature increases exponentially with temperature up to 30 MK and then increases very slowly up to 40 MK. It remains between 3.5 and 4 keV in the temperature range of 30 – 45 MK. We compare our measurements of w with calculations made earlier by various investigators and propose that these measurements may improve theoretical models. We interpret the variation of both E _p and w with temperature as being to the changes in the ionization and recombination conditions in the plasma during the flare, and as a consequence, the contribution from different ionic emission lines also varies.     

两种样本输入方式下基于GRNN的日长变化预报结果的比较

针对广义回归神经网络用于日长变化预报过程中,样本的输入方式对预报结果的影响进行了研究。采用2种输入方式:即样本按不同跨度输入以及按连续输入,对日长变化进行预报。最终证明不同的样本输入方式对日长变化预报精度的影响较大,样本按跨度输入在超短期预报中预报精度较高,样本采用连续输入的方式在短期和中期预报中预报精度较高。     

Scalable Dynamics of High Energy Relativistic Electrons: Theory, Numerical Simulations and Experimental Results

Similarity theory, which is necessary in order to apply the results of laboratory astrophysics experiments to relativistic astrophysical plasmas, is presented. The analytical predictions of the similarity theory are compared with PIC numerical simulations and the most recent experimental data on monoenergetic electron acceleration in diluted plasmas and high harmonic generation at overdense plasma boundaries. We demonstrate that similarity theory is a reliable tool for explaining a surprisingly wide variety of laboratory plasma phenomena the predictions of which can be scaled up to astrophysical dimensions.     

A Kinetic Model of Coronal Heating and Acceleration by Ion-Cyclotron Waves: Preliminary Results

We present a kinetic model of the heating and acceleration of coronal protons by outward-propagating ion-cyclotron waves on open, radial magnetic flux tubes. In contrast to fluid models which typically insist on bi-Maxwellian distributions and which spread the wave energy and momentum over the entire proton population, this model follows the kinetic evolution of the collisionless proton distribution function in response to the combination of the resonant wave-particle interaction and external forces. The approximation is made that pitch-angle scattering by the waves is faster than all other processes, resulting in proton distributions which are uniform over the resonant surfaces in velocity space. We further assume, in this preliminary version, that the waves are dispersionless so these resonant surfaces are portions of spheres centered on the radial sum of the Alfvén speed and the proton bulk speed. We incorporate the fact that only those protons with radial speeds less than the bulk speed will be resonant with outward-propagating waves, so this rapid interaction acts only on the sunward half of the distribution. Despite this limitation, we find that the strong perpendicular heating of the resonant particles, coupled with the mirror force, results in substantial outward acceleration of the entire distribution. The proton distribution evolves towards an incomplete shell in velocity space, and appears vastly different from the distributions assumed in fluid models. Evidence of these distinctive distributions should be observable by instruments on Solar Probe.     

The Global Solar Magnetic Field Through a Full Sunspot Cycle: Observations and Model Results

Based on 11 years of SOHO/MDI observations from the cycle minimum in 1997 to the next minimum around 2008, we compare observed and modeled axial dipole moments to better understand the large-scale transport properties of magnetic flux in the solar photosphere. The absolute value of the axial dipole moment in 2008 is less than half that in the corresponding cycle-minimum phase in early 1997, both as measured from synoptic maps and as computed from an assimilation model based only on magnetogram data equatorward of 60° in latitude. This is incompatible with the statistical fluctuations expected from flux-dispersal modeling developed in earlier work at the level of 7 – 10 σ. We show how this decreased axial dipole moment can result from an increased strength of the diverging meridional flow near the Equator, which more effectively separates the two hemispheres for dispersing magnetic flux. Based on the combination of this work with earlier long-term simulations of the solar surface field, we conclude that the flux-transport properties across the solar surface have changed from preceding cycles to the most recent one. A plausible candidate for such a change is an increase of the gradient of the meridional-flow pattern near the Equator so that the two hemispheres are more effectively separated. The required profile as a function of latitude is consistent with helioseismic and cross-correlation measurements made over the past decade.     

中俄等高仪国际合作第一期星表与国内其它等高仪星表的比较

PHAI已在俄罗斯伊尔库茨克进行了一年半的观测,获得了1146组观测资料．根据这些观和资料编算出第一期光电等高仪星表。为了说明这期星表的情况,本文特将它与国内几本光电等高仪星表进行比较。     

Solar Occultation Measurements of the Martian Atmosphere on the Phobos Spacecraft: Water Vapor Profile,Aerosol Parameters,and Other Results

The Auguste experiment onboard the Phobos spacecraft was devoted to solar occultation spectroscopy of the Martian atmosphere in the ultraviolet through infrared wavelength region. Despite the short duration of the space mission and problems associated largely with a fault in the solar pointing system, data have been obtained on the chemical composition and aerosol content in the atmosphere of Mars at sunset early in the summer at equatorial latitudes (in the northern hemisphere). This paper presents a somewhat detailed review of the experiment performed, the data obtained, and their interpretation, and compares these data with new results. Ozone traces were detected at altitudes of 40–60 km, and, in one case, an ozone profile was obtained. Nine profiles of water vapor content at altitudes between 12 and 50 km were obtained from absorption data in the 1.87-m band. At altitudes of 23–25 km, the mean H₂O concentration profile falls steeply to the value of 3 ppm, but at lower altitudes the relative H₂O content is approximately constant (130 ppm). The overall content of water vapor is estimated as 8.3^+2.5 _-1.5 m of settled water. The temperature profile for the saturated atmosphere yields a cooling rate of 2 ± 1 K/km at altitudes from 25 to 35 km. The atmospheric extinction profiles were measured at altitudes from 10 to 50 km at the wavelengths 1.9 and 3.7 m. The atmosphere is transparent up to 25–33 km; below this level radiation is attenuated by dust; it is also possible that a layer of water ice clouds is present at altitudes of 20–25 km. High-altitude transparent ( 0.03) clouds consisting supposedly of water ice were observed in 5 of 38 cases at altitudes z 50 km. The optical depth ₀ of the atmosphere was estimated to be 0.2 ± 0.1, and constraints on the form of the size distribution of dust particles were established. Spectral features in the 3.7 m range have been previously attributed to formaldehyde; its content is substantially higher than the limits deduced from new ground-based observations. The spectrum in the 3.7 m range is discussed and other unsettled problems are pointed out.     

天文大气折射的较差测量方法及试观测结果

受到大气折射的影响,天文观测上通常回避仰角15°以下的目标的观测,但作为大气折射的完整理论研究,低仰角下的大气折射仍然是值得分析探究的.特别是对某些工程应用方面,低仰角的目标有时必须要观测.提出了一套新的利用较差方法测定大气折射的思路.利用一台较大视场的望远镜从天顶开始,在不同高度上对星空作一系列观测,计算不同天顶距处大气折射函数的各阶导数,最后经数值积分可给出大气折射实测值.该方法不依赖于严格的地方参数和复杂精密的观测仪器,并且观测原理相对简单. 2007年底,利用一台简易的大视场望远镜在兴隆观测站进行了试验观测,根据较差方法实测得到真天顶距44.8°至87.5°的大气折射值,初步证明了大气折射较差测量方法的可行性.受到观测条件的限制,本次实测结果精度有限,偶然误差最大约为6",并且存在一定的系统差.在天顶距84°时,与普尔科沃大气折射表的差值约为15".如何消除因积分模型误差引入的累积误差是今后需要解决的关键问题.     

Recent Experimental Results and Modelling of High-Mach-Number Jets and the Transition to Turbulence

In recent years, we have carried out experiments at the University of Rochester’s Omega laser in which supersonic, dense-plasma jets are formed by the interaction of strong shocks in a complex target assembly (Foster et al., Phys. Plasmas 9 (2002) 2251). We describe recent, significant extensions to this work, in which we consider scaling of the experiment, the transition to turbulence, and astrophysical analogues. In new work at the Omega laser, we are developing an experiment in which a jet is formed by laser ablation of a titanium foil mounted over a titanium washer with a central, cylindrical hole. Some of the resulting shocked titanium expands, cools, and accelerates through the vacuum region (the hole in the washer) and then enters a cylinder of low-density foam as a jet. We discuss the design of this new experiment and present preliminary experimental data and results of simulations using AWE hydrocodes. In each case, the high Reynolds number of the jet suggests that turbulence should develop, although this behaviour cannot be reliably modelled by present, resolution-limited simulations (because of their low-numerical Reynolds number).     

Models with convective overshoot: Tables of isochrones

In this paper we briefly summarize the content of extensive tabulations of theoretical isochrones, integrated magnitudes and colours, and luminosity functions at varying age and chemical composition, to be presented elsewhere. These isochrones are based on stellar models incorporating the effect of convective overshoot.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Quantitative Comparison of a New Ab Initio Micrometeor Ablation Model with an Observationally Verifiable Standard Model

The Arecibo UHF radar is able to detect the head-echos of micron-sized meteoroids up to velocities of 75 km/s over a height range of 80–140 km. Because of their small size there are many uncertainties involved in calculating their above atmosphere properties as needed for orbit determination. An ab initio model of meteor ablation has been devised that should work over the mass range 10⁻¹⁶ kg to 10⁻⁷ kg, but the faint end of this range cannot be observed by any other method and so direct verification is not possible. On the other hand, the EISCAT UHF radar system detects micrometeors in the high mass part of this range and its observations can be fit to a “standard” ablation model and calibrated to optical observations (Szasz et al. 2007). In this paper, we present a preliminary comparison of the two models, one observationally confirmable. Among the features of the ab initio model that are different from the “standard” model are: (1) uses the experimentally based low pressure vaporization theory of O’Hanlon (A users’s guide to vacuum technology, 2003) for ablation, (2) uses velocity dependent functions fit from experimental data on heat transfer, luminosity and ionization efficiencies measured by Friichtenicht and Becker (NASA Special Publication 319: 53, 1973) for micron sized particles, (3) assumes a density and temperature dependence of the micrometeoroids and ablation product specific heats, (4) assumes a density and size dependent value for the thermal emissivity and (5) uses a unified synthesis of experimental data for the most important meteoroid elements and their oxides through least square fits (as functions of temperature, density, and/or melting point) of the tables of thermodynamic parameters given in Weast (CRC Handbook of Physics and Chemistry, 1984), Gray (American Institute of Physics Handbook, 1972), and Cox (Allen’s Astrophysical Quantities 2000). This utilization of mostly experimentally determined data is the main reason for calling this an ab initio model and is made necessary by the fact that individual average meteoroid mass densities are now derivable from Arecibo observations.