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Zhao J.S.,Chinese Academy of Sciences | Zhao J.S.,CAS National Astronomical Observatories | Wu D.J.,Chinese Academy of Sciences | Lu J.Y.,Nanjing University of Information Science and Technology | Lu J.Y.,National Center for Space Weather
Astrophysical Journal | Year: 2013

This study investigates the spectral structure of the kinetic Alfvén turbulence in the low-beta plasmas. We consider a strong turbulence resulting from collisions between counterpropagating wavepackets with equal energy. Our results show that (1) the spectra of the magnetic and electric field fluctuations display a transition at the electron inertial length scale, (2) the turbulence cascades mainly toward the magnetic field direction as the cascade scale is smaller than the electron inertial length, and (3) the parallel electric field increases as the turbulent scale decreases. We also show that the parallel electric field in the solar flare loops can be 102-10 4 times the Dreicer field as the turbulence reaches the electron inertial length scale. © 2013. The American Astronomical Society. All rights reserved..


Dai Y.,CNRS Paris Institute of Astrophysics | Dai Y.,Nanjing University | Auchere F.,CNRS Paris Institute of Astrophysics | Vial J.-C.,CNRS Paris Institute of Astrophysics | And 2 more authors.
Astrophysical Journal | Year: 2010

We present composite observations of a coronal mass ejection (CME) and the associated large-scale extreme-ultraviolet (EUV) disturbances on 2007 December 31 by the Extreme-ultraviolet Imager (EUVI) and COR1 coronagraph on board the recent Solar Terrestrial Relations Observatory mission. For this limb event, the EUV disturbances exhibit some typical characteristics of EUV Imaging Telescope waves: (1) in the 195 bandpass, diffuse brightenings are observed propagating oppositely away from the flare site with a velocity of 260 km s-1, leaving dimmings behind; (2) when the brightenings encounter the boundary of a polar coronal hole, they stop there to form a stationary front. Multi-temperature analysis of the propagating EUV disturbances favors a heating process over a density enhancement in the disturbance region. Furthermore, the EUVI-COR1 composite display shows unambiguously that the propagation of the diffuse brightenings coincides with a large lateral expansion of the CME, which consequently results in a double-loop-structured CME leading edge. Based on these observational facts, we suggest that the wave-like EUV disturbances are a result of magnetic reconfiguration related to the CME liftoff rather than true waves in the corona. Reconnections between the expanding CME magnetic field lines and surrounding quiet-Sun magnetic loops account for the propagating diffuse brightenings; dimmings appear behind them as a consequence of volume expansion. X-ray and radio data provide us with complementary evidence. © 2010. The American Astronomical Society. All rights reserved.


He F.,CAS Changchun Institute of Optics and Fine Mechanics and Physics | Zhang X.-X.,National Center for Space Weather | Chen B.,CAS Changchun Institute of Optics and Fine Mechanics and Physics | Fok M.-C.,NASA | Zou Y.-L.,CAS National Astronomical Observatories
Journal of Geophysical Research: Space Physics | Year: 2013

The EUV imager on board the Chang'E-3 lunar lander will image the Earth's plasmasphere from a lunar perspective to focus on some of the open questions in plasmaspheric researches (i.e., global structures, erosion, and refilling of plasmasphere). In order to achieve the understanding of the plasmaspheric dynamics in relation to these EUV images in lunar perspective, the He + 30.4 nm emission intensities and global structures of the plasmasphere viewed from the moon are investigated using a dynamic global core plasma model embedded with TS07 magnetic field model and W05 electric field model. Two typical storms observed by the IMAGE EUV imager are systematically simulated from the perspectives of the moon. It is found from the simulations that the maximum emission intensity of the plasmasphere is ~12.3 R which is greater than that detected from polar orbit, and the global shapes and temporal evolutions of large-scale plasmaspheric structures (plasmapause, shoulder, and plume) also have different patterns in moon-based simulated images. It is also shown that the plasmaspheric structures extracted from moon-based EUV images are in agreement with those from IMAGE EUV images. Systematic simulations demonstrate that specific latitudinal distribution of the plasmaspheric structures can only be imaged at specific positions in lunar orbit. It is expected that this investigation provides us with an overall understanding on moon-based EUV images and helps to identify the plasmaspheric structures and evolution patterns in future moon-based EUV imaging. Key Points First comprehensive simulation of the moon-based EUV imaging Plasmasphere exhibits new structure and evolution pattern in view of Moon Moon-based EUV imaging can solve the open questions in plasmaspheric research ©2013. American Geophysical Union. All Rights Reserved.


Chen A.Q.,CAS National Astronomical Observatories | Chen A.Q.,National Center for Space Weather | Wang J.X.,CAS National Astronomical Observatories
Astronomy and Astrophysics | Year: 2012

Context. The vector magnetic field characteristics of superactive regions (SARs) hold the key for understanding why SARs are extremely active and provide the guidance in space weather prediction. Aims.We aim to quantify the characteristics of SARs using the vector magnetograms taken by the Solar Magnetic Field Telescope at Huairou Solar Observatory Station. Methods. The vector magnetic field characteristics of 14 SARs in solar cycles 22 and 23 were analyzed using the following four parameters: 1) the magnetic flux imbalance between opposite polarities; 2) the total photospheric free magnetic energy; 3) the length of the magnetic neutral line with its steep horizontal magnetic gradient; and 4) the area with strong magnetic shear. Furthermore, we selected another eight large and inactive active regions (ARs), which are called fallow ARs (FARs), to compare them with the SARs. Results.We found that most of the SARs have a net magnetic flux higher than 7.0×10 21 Mx, a total photospheric free magnetic energy higher than 1.0×10 24 erg cm -1, a magnetic neutral line with a steep horizontal magnetic gradient (≥300 GMm -1) longer than 30 Mm, and an area with strong magnetic shear (shear angle ≥80°) greater than 100 Mm 2. In contrast, the values of these parameters for the FARs are mostly very low. The Pearson χ 2 test was used to examine the significance of the difference between the SARs and FARs, and the results indicate that these two types of ARs can be fairly distinguished by each of these parameters. The significance levels are 99.55%, 99.98%, 99.98%, and 99.96%, respectively. However, no single parameter can distinguish them perfectly. Therefore we propose a composite index based on these parameters, and find that the distinction between the two types of ARs is also significant with a significance level of 99.96%. These results are useful for a better physical understanding of the SAR and FAR. © 2012 ESO.


Zhao J.S.,Chinese Academy of Sciences | Zhao J.S.,University of Chinese Academy of Sciences | Wu D.J.,Chinese Academy of Sciences | Lu J.Y.,National Center for Space Weather
Astrophysical Journal | Year: 2011

Kinetic Alfvén waves (KAWs) are small-scale dispersive AWs that can play an important role in particle heating and acceleration of space and solar plasmas. An excitation mechanism for KAWs created by the coupling between large-scale oblique AWs and small-scale KAWs is presented in this paper. Taking into account both the collisional and Landau damping dissipations, the results show that the net growth rate of the excited KAWs increases with their perpendicular wavenumber k ⊥ and reaches maximum at λe k ⊥ 0.3, where λe is the electron inertial length. However, for KAWs with shorter perpendicular wavelengths, the net growth rate decreases rapidly due to dissipative effects. The evaluation of the threshold amplitude of the AW implies that for KAWs with λe k ⊥ < 0.3, the relative threshold amplitude is well below 10%, which is easy to satisfy. In particular, when applying this mechanism to the case of a solar coronal hole containing a dense plume structure, our results show that KAWs with λe k ⊥ < 0.3 can be not only efficiently excited in the interplume region but also strongly dissipated in the dense plume due to the Landau damping. © 2011. The American Astronomical Society. All rights reserved.


Zhao J.S.,Chinese Academy of Sciences | Zhao J.S.,University of Chinese Academy of Sciences | Wu D.J.,Chinese Academy of Sciences | Lu J.Y.,National Center for Space Weather
Journal of Geophysical Research: Space Physics | Year: 2010

This paper considers the nonlinear decay of the kinetic Alfvén waves (KAW) in the space plasmas. By using a two-fluid model, we obtain a nonlinear equation to investigate the resonant interaction among three kinetic Alfvén waves. It is shown that the parametric instability of the kinetic Alfvén wave becomes important when its perpendicular wavelength is the order of the ion acoustic gyroradius or the electron inertial length. We give a detailed discussion for the KAW decay in the plasma inertial range and show that (1) the reverse decay of the kinetic Alfvén wave is stronger than its parallel decay for the arbitrary wavelength range; (2) the reverse decay is lager than the parallel decay for small angles of two perpendicular wave vectors of the decay waves, and these two decays are zero for large angles; (3) both growth rates depend on the choice of the wave number range of the decay waves; and (4) there exists two forbidden regions for the KAW decay. In this paper, we also discuss the nonlinear decay of the kinetic Alfvén waves in the auroral zone and show that the parametric instability can occur there and may play an important role in forming two reverse electron streaming fluxes in the electron acceleration region. Copyright 2010 by the American Geophysical Union.


Zhao J.S.,Chinese Academy of Sciences | Zhao J.S.,University of Chinese Academy of Sciences | Wu D.J.,Chinese Academy of Sciences | Lu J.Y.,National Center for Space Weather
Physics of Plasmas | Year: 2011

A nonlocal coupling mechanism to directly transfer the energy from large-scale magnetohydrodynamic (MHD) Alfv́n waves to small-scale kinetic Alfv́n waves is presented. It is shown that the interaction between a MHD Alfv́n wave and a reversely propagating kinetic Alfv́n wave can generate another kinetic Alfv́n wave, and this interaction exists in the plasmas where the thermal to magnetic pressure ratio is larger than the electron to ion mass ratio. The proposed nonlocal interaction may have a potential application to account for the observed electron scale kinetic Alfv́n waves in the solar wind and solar corona plasmas. © 2011 American Institute of Physics.


He F.,CAS Changchun Institute of Optics and Fine Mechanics and Physics | Zhang X.-X.,National Center for Space Weather | Chen B.,CAS Changchun Institute of Optics and Fine Mechanics and Physics
Journal of Geophysical Research: Space Physics | Year: 2014

The solar cycle, seasonal, and diurnal variations of the subauroral ion drifts (SAIDs) are investigated for the first time to use such a large database of 18,226 SAID events observed by the DMSP satellites during 1987-2012. Statistical results show that SAIDs occur mostly at 60.1° invariant latitude and 2230 magnetic local time with a typical half width of 0.57°, move equatorward during high solar activities with large widths, and have two occurrence peaks in spring and fall equinoxes and two valleys in summer and winter solstices. The seasonal variation of SAID latitude has two valleys in spring and fall, and SAID width has a valley distribution with a minimum in summer. SAIDs exhibit a clear day-to-night difference in latitude. The diurnal variation of SAID width has a morning valley and an afternoon peak. The generation mechanism of SAID associated with the electron precipitation and the downward field-aligned current is also supported in this study. ©2014. American Geophysical Union. All Rights Reserved.


Du D.,National Center for Space Weather | Du D.,CAS Center for Space Science and Applied Research | Zuo P.B.,CAS Center for Space Science and Applied Research | Zhang X.X.,National Center for Space Weather
Solar Physics | Year: 2010

An extended Ulysses interplanetary coronal mass ejections (ICMEs) list is used to statistically study the occurrence rate of ICMEs, the interaction of ICMEs with solar wind, and the magnetic field properties in ICMEs. About 43% of the ICMEs are identified as magnetic clouds (MCs). It is found that the occurrence rate of ICMEs approximately follows the solar activity level, except for the second solar orbit; the rate is higher in the southern heliolatitude than in the northern heliolatitude; and it roughly decreases with the increase of ICME speeds. Our results show that the speed difference between the ICME and the solar wind in front of it shows a slight decrease with increasing heliocentric distance for ICMEs preceded by a shock, whereas no such dependence is found for the ICMEs without shock association. It is also found that approximately 23% of the ICMEs are associated with radial field events, in which the interplanetary magnetic field with near-radial direction lasts for many hours, in the Ulysses detected range, and these associated events are not necessarily confined to fast ICMEs or the trailing portions of ICMEs. Nearly all these associated events occur during the period of declining solar wind speed and most of them occur at low heliolatitudes. © 2010 Springer Science+Business Media B.V.


Zhao L.,National Center for Space Weather | Wang J.-S.,National Center for Space Weather
Journal of Climate | Year: 2014

This study provides evidence of the robust response of the East Asian monsoon rainband to the 11-yr solar cycle and first identify the exact time period within the summer half-year (1958-2012) with the strongest correlation between the mean latitude of the rainband (MLRB) over China and the sunspot number (SSN). This period just corresponds to the climatological-mean East Asian mei-yu season, characterized by a largescale quasi-zonal monsoon rainband (i.e., 22 May-13 July). Both the statistically significant correlation and the temporal coincidence indicate a robust response of the mei-yu rainband to solar variability during the last five solar cycles. During the high SSN years, the mei-yu MLRB lies 1.2° farther north, and the amplitude of its interannual variations increases when compared with low SSN years. The robust response of monsoon rainband to solar forcing is related to an anomalous general atmospheric pattern with an up-down seesaw and a north-south seesaw over East Asia © 2014 American Meteorological Society.

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