Large scale MHD properties of interplanetary magnetic clouds

Magnetic Clouds (MCs) are the interplanetary manifestation of Coronal Mass Ejections. These huge astrophysical objects travel from the Sun toward the external heliosphere and can reach the Earth environment. Depending on their magnetic field orientation, they can trigger intense geomagnetic storms. The details of the magnetic configuration of clouds and the typical values of their magnetohydrodynamic magnitudes are not yet well known. One of the most important magnetohydrodynamic quantities in MCs is the magnetic helicity. The helicity quantifies several aspects of a given magnetic structure, such as the twist, kink, number of knots between magnetic field lines, linking between magnetic flux tubes, etc. The helicity is approximately conserved in the solar atmosphere and the heliosphere, and it is very useful to link solar phenomena with their interplanetary counterpart. Since a magnetic cloud carries an important amount of helicity when it is ejected from the solar corona, estimations of the helicity content in clouds can help us to understand its evolution and its coronal origin. In situ observations of magnetic clouds at one astronomical unit are in agreement with a local helical magnetic structure. However, since spacecrafts only register data along a unique direction, several aspects of the global configuration of clouds cannot be observed. In this paper, we review the general properties of magnetic clouds and different models for their magnetic structure at one astronomical unit. We describe the corresponding techniques to analyze in situ measurements. We also quantify their magnetic helicity and compare it with the release of helicity in their solar source for some of the analyzed cases.     

Comparative analysis of TEC disturbances over tropical cyclone zones in the North–West Pacific Ocean

In this paper, we study ionospheric total electron content (TEC) disturbances associated with tropical cyclones (TCs). The study relies on the statistical analysis of six cyclones of different intensity which occurred in the North–West Pacific Ocean in September–November 2005. We have used TEC data from the international network of two-frequency ground-based GPS receivers and NCEP/NCAR meteorological archive. TEC variations of different period ranges (02–20 and 20–60 min) are shown to be more intense during TC peaks under quiet geomagnetic conditions. The highest TEC variation amplitudes are registered when the wind speed in the cyclone and the TC area are maximum. The intensification of TEC disturbances is more pronounced when several cyclones occur simultaneously. We have revealed that the ionospheric response to TC can be observed only after the cyclone has reached typhoon intensity. The ionospheric response is more pronounced at low satellite elevation angles.     

Study of magnetic flux emergence and related activity in active region NOAA 10314

We study the extremely complex active region (AR) NOAA 10314, that was observed from March 13–19, 2003. This AR was the source of several energetic events, among them two major (X class) flares, along a few days. We follow the evolution of this AR since the very first stages of its emergence. From the photospheric evolution of the magnetic polarities observed with SOHO/MDI we infer the morphology of the flux tube that originates the AR. Using a computation technique that combines Local Correlation Tracking with magnetic induction constrains, we compute the rate of magnetic helicity injection at the photosphere during the observed evolution. From our results we conclude that the AR originated by the emergence of a severely deformed magnetic flux tube having a dominantly positive magnetic helicity.     

Model-independent large-scale magnetohydrodynamic quantities in magnetic clouds

Magnetic clouds are the interplanetary manifestation of coronal mass ejections, which are transient expulsions of major quantities of magnetized plasma, from the Sun toward the heliosphere. The magnetic flux and helicity are two key physical magnitudes to track solar structures from the photosphere-corona to the interplanetary medium. To determine the content of flux and helicity in magnetic clouds, we have to know their 3D structure. However, since spacecrafts register data along a unique direction, several aspects of their global configuration cannot be observed. We present a method to estimate the magnetic flux and the magnetic helicity per unit length in magnetic clouds, directly from in situ magnetic observations, assuming only a cylindrical symmetry for the magnetic field configuration in the observed cross-section of the cloud. We select a set of 20 magnetic clouds observed by the spacecraft Wind and estimate their magnetic flux and their helicity per unit length. We compare the results obtained from our direct method with those obtained under the assumption of a helical linear force-free field. This direct method improves previous estimations of helicity in clouds.     

Stratospheric polar vortex as a possible reason for temporal variations of solar activity and galactic cosmic ray effects on the lower atmosphere circulation

Possible reasons for the temporal instability of long-term effects of solar activity (SA) and galactic cosmic ray (GCR) variations on the lower atmosphere circulation were studied. It was shown that the detected earlier ∼60-year oscillations of the amplitude and sign of SA/GCR effects on the troposphere pressure at high and middle latitudes (Veretenenko and Ogurtsov, Adv.Space Res., 2012) are closely related to the state of a cyclonic vortex forming in the polar stratosphere. The intensity of the vortex was found to reveal a roughly 60-year periodicity affecting the evolution of the large-scale atmospheric circulation and the character of SA/GCR effects. An intensification of both Arctic anticyclones and mid-latitudinal cyclones associated with an increase of GCR fluxes at minima of the 11-year solar cycles is observed in the epochs of a strong polar vortex. In the epochs of a weak polar vortex SA/GCR effects on the development of baric systems at middle and high latitudes were found to change the sign. The results obtained provide evidence that the mechanism of solar activity and cosmic ray influences on the lower atmosphere circulation involves changes in the evolution of the stratospheric polar vortex.     

Observational study of magnetic chirality of solar active regions

We present the evolution of magnetic field and relationship with the magnetic (current) helicity in solar active regions from a series of photospheric vector magnetograms obtained at Huairou Solar Observing Station near Beijing, and also longitudinal magnetograms by MDI of SOHO, white light and 171 Å images by TRACE and soft X-ray images by Yohkoh.The conclusions in the analysis of the formation process of complex and delta magnetic configuration in some super active regions are the following: (1) The magnetic shear and gradient provide the non-potentiality of the magnetic field of active regions reflecting the existence of electric current. (2) Some of large-scale delta active regions could be due to the emergence of highly sheared non-potential magnetic flux bundles from the subatmosphere with amount of magnetic helicity, in addition to the emergence of twisted magnetic ropes. (3) We also present some results on the study of the magnetic (current) helicity in solar active regions.     

Dynamics of the convection in the inner magnetosphere by observations of the diffuse aurora,SAR arc and ionospheric drift

The first results of the comparison of subauroral luminosity dynamics in 557,7 and 630,0 nm emission with simultaneous measurements of the ionospheric drift in the F2 region with a digisonde DPS-4 at the Yakutsk meridian (CGMC: 55–60N, 200°E) at Kp = 2–6 are presented. It is shown from the analysis of individual events that during the magnetospheric convection intensification after the turn of the IMF B_z – component to the south the equatorward extension of diffuse aurora takes place. At the same time the westward ionospheric drift velocity increases both in the diffuse aurora region and much equatorward of it due to the occurrence of the northward polarization electric field. We suppose that the generation of polarization field can be associated with the development of the region 2 FAC during the intensification of magnetospheric convection. The comparison of ground-based observations with measurements of the plasma drift aboard the DMSP-F15 satellite has been carried out.     

粘性耗散对重力波波包共振相互作用的影响

采用数值方法考察了粘性耗散对重力波波包共振相互作用的影响．结果表明,粘性耗散不仅衰减相互作用波的能量,而且强烈地影响波包之间局地能量的传递,使波包的形状发生进一步的改变．粘性耗散减缓相互作用过程的发展,阻止高波数的次级波与主波进行相互作用．在低热层高度上,耗散过程占支配地位,三波能量演变的特征发生了相当大的变化．大尺度主波通过与小尺度次级波的相互作用,更快地实现对大气的加热．      

损耗大气中惯性重力波的非线性相互作用方程及其初步讨论

根据弱相互作用理论,本文建立了损耗大气中极性重力波的非线性相互作用方程。这组方程在三个方面推广了前人的工作:考虑了波的空间传播;包含了粘滞产生的衰减;波谱可以是连续的。粘滞衰减率的大小与波的空间尺度以及传播方向有关。Coriolis力的引入使相互作用系数成为复量。根据这组方程,考察了惯性重力波的参量激发。结果表明:在共振条件满足时,主波存在一个阈值,阈值大小与次级波的损耗率成正比。当主波振幅大于这个阈值时,次级波将指数增长。在相互作用过程中,次级波的频率将发生变化,变化的大小与主波能量成正比。      

The role of helicity in the reconnection process

The change of helicity for magnetic reconnection is calculated with the help of a kinematic model. The results confirm the approximate conservation of magnetic helicity for reconnection in an almost ideal plasma as e. g. the solar corona. Different examples show the contributions of twist or linkage of flux tubes to the total helicity change in the process. However, they also show that helicity may be produced for reconnection processes in more extended non-ideal regions which is due to new magnetic flux linked to the reconnected flux tubes.     

Detailed analysis of dynamic evolution of three Active Regions at the photospheric level before flare and CME occurrence

We present a combined analysis of the applications of the weighted horizontal magnetic gradient (denoted as ${\mathit{WG}}_M$ in Korsós et al. (2015)) method and the magnetic helicity tool (Berger and Field, 1984) employed for three active regions (ARs), namely NOAA AR 11261, AR 11283 and AR 11429. We analysed the time series of photospheric data from the Solar Dynamics Observatory taken between August 2011 and March 2012. During this period the three ARs produced a series of flares (eight M- and six X-class) and coronal mass ejections (CMEs). AR 11261 had four M-class flares and one of them was accompanied by a fast CME. AR 11283 had similar activities with two M- and two X-class flares, but only with a slow CME. Finally, AR 11429 was the most powerful of the three ARs as it hosted five compact and large solar flare and CME eruptions. For applying the ${\mathit{WG}}_M$ method we employed the Debrecen sunspot data catalogue, and, for estimating the magnetic helicity at photospheric level we used the Space-weather HMI Active Region Patches (SHARP’s) vector magnetograms from SDO/HMI (Solar Dynamics Observatory/Helioseismic and Magnetic Imager). We followed the evolution of the components of the ${\mathit{WG}}_M$ and the magnetic helicity before the flare and CME occurrences. We found a unique and mutually shared behaviour, called the U-shaped pattern, of the weighted distance component of ${\mathit{WG}}_M$ and of the shearing component of the helicity flux before the flare and CME eruptions. This common pattern is associated with the decreasing-receding phases yet reported only known to be a necessary feature prior to solar flare eruption(s) but found now at the same time in the evolution of the shearing helicity flux. This result leads to the conclusions that (i) the shearing motion of photospheric magnetic field may be a key driver for solar eruption in addition to the flux emerging process, and that (ii) the found decreasing-approaching pattern in the evolution of shearing helicity flux may be another precursor indicator for improving the forecasting of solar eruptions.     

Planetary wave transience effects on the zonal mean flow: simulations with the COMMA-LIM model

A 3D circulation model has been used to investigate the role of the quasi two-day wave propagation, its dissipation and variability in the formation of the middle atmosphere zonal mean circulation. According to linear theory, the accelerations due to dissipation of steady planetary waves are relatively weak. This study shows that the transient quasi two-day wave is able to shift the summer jet towards the equator thereby attenuating the seasonal weakening of the westward jet.     

2011年8月4日螺旋状日冕物质抛射爆发事件

利用多卫星多波段的综合观测数据,通过追踪光球表面等离子体速度分析计算了耀斑爆发前后磁螺度的变化,发现耀斑爆发前活动区中光球表面存在强的水平剪切运动,活动区磁螺度的注入主要由这种剪切运动所产生;使用CESE-MHD-NLFFF重建了耀斑爆发前后活动区的磁场位形,推测出耀斑过程中存在磁绳结构的抛射.基于这些分析,给出了这一螺旋状抛射结构的形成机制：爆发前暗条西侧足点的持续剪切运动驱动磁通量绳增加扭转,高度扭缠的通量绳与东侧足点附近的开放磁力线重联并与东侧足点断开,进而向外抛出并伴随解螺旋运动.另外,利用1AU处WIND卫星的观测数据在对应的行星际日冕物质抛射中找到典型磁云的观测特征.这表明除了传统上双足点均在太阳表面的磁云模型,这种单足点固定于太阳表面的磁通量绳爆发图景同样可能在行星系际空间形成磁云结构.研究结果对进一步认识磁云结构具有重要意义.     

螺旋结构日珥的内螺度

本文导出了螺旋结构日珥内螺度的表达式,并利用观测资料计算内螺度．结果表明,内螺度的大小与日珥的稳定性有关;宁静日珥的内螺度较小,爆发日珥的内螺度较大;在日用从宁静-爆发-匀速上升的演化过程中,螺度将不断积累-释放-转移到日冕空间．      

The MAGO experiment for dust environment monitoring on the Martian surface

Among the main directions identified for future Martian exploration, the study of the properties of dust dispersed in the atmosphere, its cycle and the impact on climate are considered of primary relevance. Dust storms, dust devils and the dust “cycle” have been identified and studied by past remote and in situ experiments, but little quantitative information is available on these processes, so far. The airborne dust contributes to the determination of the dynamic and thermodynamic evolution of the atmosphere, including the large-scale circulation processes and its impact on the climate of Mars. Moreover, aeolian erosion, redistribution of dust on the surface and weathering processes are mostly known only qualitatively. In order to improve our knowledge of the airborne dust evolution and other atmospheric processes, it is mandatory to measure the amount, mass-size distribution and dynamical properties of solid particles in the Martian atmosphere as a function of time. In this context, there is clearly a need for the implementation of experiments dedicated to study directly atmospheric dust. The Martian atmospheric grain observer (MAGO) experiment is aimed at providing direct quantitative measurements of mass and size distributions of dust particles, a goal that has never been fully achieved so far. The instrument design combines three types of sensors to monitor in situ the dust mass flux (micro balance system, MBS) and single grain properties (grain detection system, GDS + impact sensor, IS). Technical solutions and science capabilities are discussed in this paper.     

Modeling the solar cosmic ray event of 13 December 2006 using ground level neutron monitor data

In order to understand the physics under extreme solar conditions such as those producing ground level enhancements of solar cosmic rays, it is important to use accurate and reliable models. The NM-BANGLE Model is a new cosmic ray model which couples primary solar cosmic rays at the top of the Earth’s atmosphere with the secondary ones detected at ground level by neutron monitors during GLEs. This model calculates the evolution of several GLE parameters such as the solar cosmic ray spectrum, anisotropy and particle flux distribution, revealing crucial information on the energetic particle propagation and distribution. The total output of the NM-BANGLE Model is a multi-dimensional GLE picture that gives an important contribution to revealing the characteristics of solar energetic particle events recorded at ground level. In this work, the results of the NM-BANGLE Model application to the recent GLE of 13 December 2006 are presented and discussed. Moreover, a comparison with the extreme event of 20 January 2005 (GLE69) has been realized.     

Radiative and dynamical impacts of Arctic and Antarctic ozone holes: General circulation model experiments

Radiative and dynamical impacts of Arctic and Antarctic ozone holes on the general circulation are investigated with the aid of a general circulation model developed at Kyushu University. The model includes a simplified ozone photochemistry interactively coupled with radiation and dynamics. Resultant temperature structure consisting of a cooling in the polar lower stratosphere and a warming in the polar upper stratosphere brings about the intensification of the polar night jet. The cooling is caused by the decrease of solar ultraviolet heating due to the ozone depletion, while the warming is caused by adiabatic heating due to the enhancement of downward motion.     

A study on possible solar and geomagnetic effects on the precipitation over northwestern Argentina

The precipitation over Tucuman (26.8°S; 65.2°W), which is representative of the Northwestern region of Argentina, is analyzed in search of an association with solar and geomagnetic activity, with the purpose of contributing to the controversial issue on the connection between climate variation and anthropogenic vs. natural forcing. Monthly time series of precipitation, sunspot number (Rz), and aa index were used for the period 1884–2010. A wavelet analysis was performed first which, due to the time series length, shows significant results only for periodicities lower than 32 years. Due to the transient character and non-constant phase of the results, any sustained wavelet coherence between precipitation and either sunspots or aa could be noticed. Moving averages and correlations were also assessed. The 11 and 22-year running mean of precipitation is positively correlated to Rz and aa when the whole period of analysis is considered. However, a shift in the long-term behavior of precipitation is noticed around 1940, which implies different correlation values with Rz and aa when the period before or after this year are considered. The solar cycle length is also considered for this statistical study and partly confirms the results obtained with Rz and aa. We propose plausible physical explanations based on geomagnetic activity and total solar irradiance effects over atmospheric circulation that could support the statistical result. A deeper analysis and broader geographical coverage is needed in order to detect a connection between precipitation and solar variability discernible from greenhouse gases effects. We emphasize the idea of the importance of recognizing and quantifying the different forcing acting on precipitation (or any other climate parameter), which sometimes can be barely evident from a solely statistical analysis.     

Energy requirement of magnetic reconnection during magnetospheric substorms

Methods are discussed to estimate energy transfer from the solar wind to the magnetosphere during substorm growth phases. Observational and modeling constraints are then used to assess quantitatively the total amount of energy stored in the magnetotail. The major avenues of energy dissipation are examined and the energy that is released in the form of plasma sheet heating, ionospheric Joule heating, plasmoids, and energetic particle production during substorms is assessed. Energy sources are evaluated to drive substorm evolution in a particularly well-observed case: stored tail-lobe energy is sufficient to drive observed substorm dissipation processes (by large margins). On the other hand, energy in the closed field lines of the plasma sheet is insufficient to supply the substorm energy. Hence, magnetic reconnection is required on energy grounds during well-observed substorm cases.     

Thermospheric signature of magnetospheric energy dissipation

Dissipation of magnetospheric energy leads to an upper atmospheric disturbance zone whose extent varies with local time. A statistical analysis of ESRO 4 data reveals that (1) in the afternoon/evening sector the boundary location is determined by the region of electric current dissipation along the auroral oval; (2) in the midnight/early morning sector dynamical effects extend the disturbance zone to lower latitudes; and (3) in the late morning sector direct heating effects are superimposed on the residuals of the early morning disturbance.