Subjects: Geosciences >> Space Physics submitted time 2016-12-26
Abstract： The paper presents a method estimating the HY-2A altimeter ultra stable oscillator (USO) drift with a reconstructive transponder. The frequency of the USO of the in-orbit altimeter changes with age, and a bias between the actual frequency and the nominal one exists. The USO bias contributes a portion of the altimeter range drift. The HY-2A altimeter transmits signals at a fixed time interval during calibration, and the actual interval between adjacent altimeter transitions, which is controlled by the USO, is different from the nominal one due to the USO drift. The reconstructive transponder measures the arrival times of the altimeter transmitted signals accurately with the atomic clock. The drift of the USO on-board the HY-2A altimeter can be estimated accurately by using the ranges from the reconstructive transponder and the HY-2A altimeter. The USO drifts of around 40 cm/year are presented. Furthermore, the multi-mission crosscalibration provides preliminary validation of HY-2A altimeter USO drift.
Peer Review Status:
Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-12-26
Abstract： Independent clocks provide time tags for the precision orbit determination (POD) equipment and the radar altimeter onboard the HY-2A satellite, and a bias between POD data' time tag and corresponding range observation's time tag from the HY-2A altimeter exists. The time tag bias contributes a bias in the sea surface height observation due to the nonzero time rate of change of the HY-2A altimeter's height. A transponder for in-orbit radar altimeter calibration provides an approach to estimate the time tag bias. The altimeter receives the responding signals from the transponder and generates ranges. Pertinent reference ranges are obtained fromthe POD data and the transponder's coordinate. Using the ranges from the radar altimeter and the reference ranges, the time tag bias between the POD data and the altimeter observations can be estimated. During an in situ HY-2A altimeter calibration campaign using a reconstructive transponder from August 9, 2012, to July 20, 2014, 17 estimations of the altimeter's time tag bias were obtained. The preliminary results are presented in this letter.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-12-26
Abstract： A reconstructive transponder has been utilized for the in-orbit calibration campaign of the HY-2A radar altimeter since March 2012. The precision of final calibration result is influenced by echo signal's quality in the HY-2A altimeter's range window. As an indicator of the signal's quality, echo signal dwell time is analyzed considering its influence on signal quality and its uncertainty. In HY-2A altimeter calibration, the echo signal dwell time is determined by the radial orbit prediction uncertainty and the real-time signal processing mechanism of the reconstructive transponder. The real-time signal processing mechanism of the reconstructive transponder utilizes some incoming signal samples without sending echo signals before transmitting. Comparing with the length of the HY-2A altimeter's range window, the radial orbit prediction uncertainty is large. Large radial orbit prediction uncertainty and signal processing mechanism of the reconstructive transponder are two main factors that limit the echo signal dwell time in HY-2A altimeter calibration. Finally, approaches for increasing echo signal dwell time are briefly proposed.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-12-26
Abstract： Derivation of equivalent current systems (ECS) from a global magnetospheric magnetohydrodynamics (MHD) model is very useful in studying magnetosphere-ionosphere coupling, ground induction effects, and space weather forecast. In this study we introduce an improved method to derive the ECS from a global MHD model, which takes account of the obliqueness of the magnetic field lines. By comparing the ECS derived from this improved method and the previous method, we find that the main characteristics of the ECS derived from the two methods are generally consistent with each other, but the eastward-westward component of the geomagnetic perturbation calculated from the ECS derived from the improved method is much stronger than that from the previous method. We then compare the geomagnetic perturbation as a function of the interplanetary magnetic field (IMF) clock angle calculated from the ECS derived from both methods with the observations. The comparison indicates that the improved method can improve the performance of the simulation. Furthermore, it is found that the incomplete counterbalance of the geomagnetic effect produced by the ionospheric poloidal current and field-aligned current (FAC) contributes to most of the eastward-westward component of geomagnetic perturbation.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-12-26
Abstract： This letter presents a method for matching satellite radar altimeter data and transponder data generated during in situ calibration. The transponder generates a measurement error when it measures the arrival time of the altimeter’s transmitted signal and embeds the error in both the transponder’s recorded data and the altimeter’s recorded data. The secondorder finite difference sequence of this error sequence can be extracted from the raw data, thus, the correspondence between two identical but mismatched second-order difference sequences can be uniquely established. The measurement error is utilized,and a data matching method that can uniquely establish the correspondence between the altimeter’s recorded data sequence and the transponder’s recorded data sequence is presented.This post-processing method does not increase the real-time signal processing workload of the transponder. Furthermore,The principles underlying this method can be used for any transponder that can adjust the response signal delay during calibration.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-12-26
Abstract：开发高性能的磁流体力学数值模拟方法是提高空间天气数值预报研究的一个重要方 面。有限体积法的逆风分裂格式具有良好的间断捕获能力，Steger-Warming 和AUSM （Advection Upstream Splitting Method）格式是逆风分裂格式的FVS（Flux Vector Splitting） 方法中有代表性的两种格式。本文采用这两种格式求解具有伽利略不变性的扩展型广义拉格 朗日乘子磁流体力学（EGLM-MHD）方程组，对Orszag-Tang 涡流问题和三维爆炸波问题进行了数值模拟。结果表明两种格式均能得到稳定精确的数值结果。与Steger-Warming格式相比，AUSM 格式产生的磁场散度误差更小，计算速度更快。
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-12-26
Abstract：FY-3气象卫星上搭载的紫外臭氧总量探测仪TOU是我国自主开发研制的首台用于全球臭氧总量定量测量的探测仪，自发射以来已成功在轨运行近两年。由于TOU发射前辐亮度定标存在偏差，为了得到高精度的产品，TOU必须进行在轨定标。本文介绍了基于辐射传输模式计算对TOU辐亮度进行在轨道定标的方法，定标过程中用于模拟辐亮度计算的臭氧总量由与TOU观测时刻相近的国外臭氧总量探测仪器MetOp/GOME-2提供。文章将在轨定标后TOU的反演结果与AURA/OMI以及地基的产品进行比较，研究结果表明，用辐射传输模式对TOU辐亮度进行在轨定标的方法是可行的，反演结果能够真实的反映臭氧的时空分布特性，在全球部分地基观测站所处的位置上对TOU, OMI以及地基的臭氧总量进行比较的结果表明，TOU与OMI的相对偏差均方根约为2.52%， TOU与地基以及OMI与地基观测结果之间的相对偏差均方根分别为4.45%和3.89%。
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-12-26
Abstract： Nonlinear cascade of low-frequency Alfvenic fluctuations (AFs) is regarded as one candidate of the energy sources to heat plasma during the non-adiabatic expansion of interplanetary coronal mass ejections (ICMEs). However, AFs inside ICMEs were seldom reported in the literature. In this study, we investigate AFs inside ICMEs using observations from Voyager 2 between 1 and 6 au. It is found that AFs with high degree of Alfvenicity frequently occurred inside ICMEs, for almost all the identified ICMEs (30 out of 33 ICMEs), and 12.6% of ICME time interval. As ICMEs expand and move outward, the percentage of AF duration decays linearly in general. The occurrence rate of AFs inside ICMEs is much less than that in ambient solar wind, especially within 4 au. AFs inside ICMEs are more frequently presented in the center and at the boundaries of ICMEs. In addition, the proton temperature inside ICME has a similar distribution. These findings suggest significant contribution of AFs on local plasma heating inside ICMEs.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-12-26
Liu, Ying D.
Hu, Huidong
Wang, Chi
Luhmann, Janet G.
Richardson, John D.()
Yang, Zhongwei
Wang, Rui1()
Abstract： As a follow-up study on Sun-to-Earth propagation of fast coronal mass ejections (CMEs), we examine the Sun-to-Earth characteristics of slow CMEs combining heliospheric imaging and in situ observations. Three events of particular interest, the 2010 June 16, 2011 March 25, and 2012 September 25 CMEs, are selected for this study. We compare slow CMEs with fast and intermediate-speed events, and obtain key results complementing the attempt of Liu et al. to create a general picture of CME Sun-to-Earth propagation: (1) the Sun-to-Earth propagation of a typical slow CME can be approximately described by two phases, a gradual acceleration out to about 20-30 solar radii, followed by a nearly invariant speed around the average solar wind level; (2) comparison between different types of CMEs indicates that faster CMEs tend to accelerate and decelerate more rapidly and have shorter cessation distances for the acceleration and deceleration; (3) both intermediate-speed and slow CMEs would have speeds comparable to the average solar wind level before reaching 1 au; (4) slow CMEs have a high potential to interact with other solar wind structures in the Sun-Earth space due to their slow motion, providing critical ingredients to enhance space weather; and (5) the slow CMEs studied here lack strong magnetic fields at the Earth but tend to preserve a flux-rope structure with an. axis generally perpendicular to the radial direction from the Sun. We also suggest a "best" strategy for the application of a triangulation concept in determining CME Sun-to-Earth kinematics, which helps to clarify confusions about CME geometry assumptions in the triangulation and to improve CME analysis and observations.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-12-26
Abstract： We study the solar energetic particle (SEP) event associated with the 2012 July 23 extreme solar storm, for which Solar Terrestrial Relations Observatory (STEREO) and the spacecraft at L1 provide multi-point remote sensing and in situ observations. The extreme solar storm, with a superfast shock and extremely enhanced ejecta magnetic fields observed near 1 au at STEREO A, was caused by the combination of successive coronal mass ejections (CMEs). Meanwhile, energetic particles were observed by STEREO and near-Earth spacecraft such as the Advanced Composition Explorer and SOlar and Heliospheric Observatory, suggesting a wide longitudinal spread of the particles at 1 au. Combining the SEP observations with in situ plasma and magnetic field measurements, we investigate the longitudinal distribution of the SEP event in connection with the associated shock and CMEs. Our results underscore the complex magnetic configuration of the inner heliosphere formed by solar eruptions. Examination of particle intensities, proton anisotropy distributions, element abundance ratios, magnetic connectivity, and spectra also gives important clues for particle acceleration, transport, and distribution.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-12-26
Abstract： With the non-local observables such as two point correlation function and holographic entanglement entropy, we probe the phase structure of the Born-Infeld-anti-de Sitter black holes. For the case bQ > 0.5, where b is the Born-Infeld parameter and Q is the charge of the black hole, the phase structure is found to be similar to that of the Van der Waals phase transition, namely the black hole undergoes a first order phase transition and a second order phase transition before it reaches a stable phase. While for the case bQ < 0.5, a new phase branch emerges besides the Van der Waals phase transition. For the first order phase transition, the equal area law is checked, and for the second order phase transition, the critical exponent of the heat capacity is obtained. All these results are found to be the same as that observed in the entropy-temperature plane.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-12-22
G. Hobbs
W. Coles
R. N. Manchester
M. J. Keith,1 R. M. Shannon
D. Chen
M. Bailes,4 N. D. R. Bhat
S. Burke-Spolaor
D. Champion
A. Chaudhary
A. Hotan
J. Khoo,1 J. Kocz
Y. Levin
S.Oslowski
B. Preisig
V. Ravi
J. E. Reynolds
J. Sarkissian
W. van Straten
J. P. W. Verbiest
D. Yardley
Abstract： Using observations of pulsars from the Parkes Pulsar Timing Array (PPTA) project we develop the first pulsar-based timescale that has a precision comparable to the uncertainties in international atomic timescales. Our ensemble of pulsars provides an Ensemble Pulsar Scale (EPS) analogous to the free atomic timescale 碋chelle Atomique Libre (EAL). The EPS can be used to detect fluctuations in atomic timescales and therefore can lead to a new realisation of Terrestrial Time, TT(PPTA11). We successfully follow features known to affect the frequency of the International Atomic Timescale (TAI) and we find marginally significant differences between TT(PPTA11) and TT(BIPM11). We discuss the various phenomena that lead to a correlated signal in the pulsar timing residuals and therefore limit the stability of the pulsar timescale.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-12-22
Abstract： With the assumption of radial motion and uniform longitudinal distribution of coronal mass ejections (CMEs), we propose a method to eliminate projection effects from the apparent observed CME latitude distribution. This method has been applied to SOHO LASCO data from 1996 January to 2006 December. As a result, we find that the real CME latitude distribution had the following characteristics: (1) High-latitude CMEs (theta > 60 degrees, where theta is the latitude) constituted 3% of all CMEs and mainly occurred during the time when the polar magnetic fields reversed sign. The latitudinal drift of the high-latitude CMEs was correlated with that of the heliospheric current sheet. (2) Four percent of all CMEs occurred in the range 45 degrees <= theta <= 60 degrees. These midlatitude CMEs occurred primarily in 2000, near the middle of 2002, and in 2005, forming a prominent three-peak structure. (3) The highest occurrence probability of low-latitude (theta < 45 degrees) CMEs was at the minimum and during the declining phase of the solar cycle. However, the highest occurrence rate of low-latitude CMEs was at the maximum and during the declining phase of the solar cycle. The latitudinal evolution of low-latitude CMEs did not follow the Sporer sunspot law, which suggests that many CMEs originated outside of active regions.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-12-22
Abstract： We study a holographic model with vector condensate by coupling the anti-de Sitter gravity to an Abelian gauge field and a charged vector field in (3 + 1) dimensional spacetime. In this model there exists a non-minimal coupling of the vector field to the gauge field. We find that there is a critical temperature below which the charged vector condenses via a second order phase transition. The DC conductivity becomes infinite and the AC conductivity develops a gap in the condensed phase. We study the effect of a background magnetic field on the system. It is found that the background magnetic field can induce the condensate of the vector field even in the case without chemical potential/charge density. In the case with non-vanishing charge density, the transition temperature raises with the applied magnetic field, and the condensate of the charged vector operator forms a vortex lattice structure in the spatial directions perpendicular to the magnetic field.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-12-22
Abstract： We continue to study the holographic p-wave superconductor model in the Einstein-Maxwell-complex vector field theory with a non-minimal coupling between the complex vector field and the Maxwell field. In this paper we work in the AdS soliton background which describes a conformal field theory in the confined phase and focus on the probe approximation. We find that an applied magnetic field can lead to the condensate of the vector field and the AdS soliton instability. As a result, a vortex lattice structure forms in the spatial directions perpendicular to the applied magnetic field. As a comparison, we also discuss the vector condensate in the Einstein-SU(2) Yang-Mills theory and find that in the setup of the present paper, the Einstein-Maxwell-complex vector field model is a generalization of the SU(2) model in the sense that the vector field has a general mass and gyromagnetic ratio.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-12-22
Abstract： In 2012 March the Sun exhibited extraordinary activities. In particular, the active region NOAA AR 11429 emitted a series of large coronal mass ejections (CMEs) which were imaged by the Solar Terrestrial Relations Observatory as it rotated with the Sun from the east to west. These sustained eruptions are expected to generate a global shell of disturbed material sweeping through the heliosphere. A cluster of shocks and interplanetary CMEs were observed near the Earth, and are propagated outward from 1 AU using an MHD model. The transient streams interact with each other, which erases memory of the source and results in a large merged interaction region (MIR) with a preceding shock. The MHD model predicts that the shock and MIR would reach 120 AU around 2013 April 22, which agrees well with the period of radio emissions and the time of a transient disturbance in galactic cosmic rays detected by Voyager 1. These results are important for understanding the "fate" of CMEs in the outer heliosphere and provide confidence that the heliopause is located around 120 AU from the Sun.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-12-22
Abstract： We study competition between s-wave order and d-wave order through two holographic superconductor models. We find that once the coexisting phase appears, it is always thermodynamically favored, and that the coexistence phase is narrow and one condensate tends to kill the other. The phase diagram is constructed for each model in terms of temperature and the ratio of charges of two orders. We further compare the behaviors of some thermodynamic quantities, and discuss the different aspects and identical ones between two models.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-12-22
Abstract： In a recent paper, arXiv:1309.4877, a holographic p-wave model has been proposed in an Einstein Maxwell-complex vector field theory with a negative cosmological constant. The model exhibits rich phase structure depending on the mass and the charge of the vector field. We investigate the behavior of the entanglement entropy of dual field theory in this model. When the above two model parameters change, we observe the second order, first order and zeroth order phase transitions from the behavior of the entanglement entropy at some intermediate temperatures. These imply that the entanglement entropy can indicate not only the occurrence of the phase transition, but also the order of the phase transition. The entanglement entropy is indeed a good probe to phase transition. Furthermore, the "retrograde condensation" which is a sub-dominated phase is also reflected on the entanglement entropy. (C) 2015 The Authors. Published by Elsevier B.V.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-12-05
Abstract：本文基于长江中游城市群2015年1月1日-2015年12月15日的空气质量指数（AQI）日报数据，在VAR模型框架下，采用非线性Granger因果检验方法对长江中游城市群城市间大气污染的非线性传导关系进行科学识别，并借助社会网络分析方法全面揭示其联动网络结构特征。研究发现：长江中游城市群城市间大气污染存在较为显著的非线性传导关系，它们构成了复杂的联动网络。在稳健性网络（R-Network）中，黄石、荆门、南昌、萍乡、黄冈、荆州、宜昌、株洲、常德、孝感、鄂州11个城市处于网络核心，其它16个城市处于网络边缘。在最大可能性网络（ML-Network）中，处于网络核心位置的包括黄石、荆门等18个城市，联防联控的核心区域范围扩大。基于上述结论，本文认为完善大气污染的联防联控，首先应从稳健性网络入手，以核心城市为重点，在此基础上可以依据最大可能网络构建包括长江中游所有城市的联防联控机制。
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-12-01
G. Hobbs
W. Coles
R. N. Manchester
M. J. Keith,1 R. M. Shannon
D. Chen
M. Bailes,4 N. D. R. Bhat
S. Burke-Spolaor
D. Champion
A. Chaudhary
A. Hotan
J. Khoo,1 J. Kocz
Y. Levin
S.Oslowski
B. Preisig
V. Ravi
J. E. Reynolds
J. Sarkissian
W. van Straten
J. P. W. Verbiest
D. Yardley
Abstract： Using observations of pulsars from the Parkes Pulsar Timing Array (PPTA) project we develop the first pulsar-based timescale that has a precision comparable to the uncertainties in international atomic timescales. Our ensemble of pulsars provides an Ensemble Pulsar Scale (EPS) analogous to the free atomic timescale 碋chelle Atomique Libre (EAL). The EPS can be used to detect fluctuations in atomic timescales and therefore can lead to a new realisation of Terrestrial Time, TT(PPTA11). We successfully follow features known to affect the frequency of the International Atomic Timescale (TAI) and we find marginally significant differences between TT(PPTA11) and TT(BIPM11). We discuss the various phenomena that lead to a correlated signal in the pulsar timing residuals and therefore limit the stability of the pulsar timescale.
Peer Review Status:Awaiting Review
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