scholarly journals Changes in the response of the AL Index with solar cycle and epoch within a corotating interaction region

2009 ◽  
Vol 27 (8) ◽  
pp. 3165-3178 ◽  
Author(s):  
R. L. McPherron ◽  
L. Kepko ◽  
T. I. Pulkkinen ◽  
T. S. Hsu ◽  
J. W. Weygand ◽  
...  
Keyword(s):  
Solar Wind ◽  
Solar Cycle ◽  
Electric Field ◽  
Response Function ◽  
Dynamic Pressure ◽  
The State ◽  
Interaction Region ◽  
Corotating Interaction Region ◽  
Reference Time

Abstract. We use observations in the solar wind and on the ground to study the interaction of the solar wind and interplanetary magnetic field with Earth's magnetosphere. We find that the type of response depends on the state of the solar wind. Coupling functions change as the properties of the solar wind change. We examine this behavior quantitatively with time dependent linear prediction filters. These filters are determined from ensemble arrays of representative events organized by some characteristic time in the event time series. In our study we have chosen the stream interface at the center of a corotating interaction region as the reference time. To carry out our analysis we have identified 394 stream interfaces in the years 1995–2007. For each interface we have selected ten-day intervals centered on the interface and placed data for the interval in rows of an ensemble array. In this study we use Es the rectified dawn-dusk electric field in gsm coordinates as input and the AL index as output. A selection window of width one day is stepped across the ensemble and for each of the nine available windows all events in a given year (~30) are used to calculate a system impulse response function. A change in the properties of the system as a consequence of changes in the solar wind relative to the reference time will appear as a change in the shape and/or the area of the response function. The analysis shows that typically only 45% of the AL variance is predictable in this manner when filters are constructed from a full year of data. We find that the weakest coupling occurs around the stream interface and the strongest well away from the interface. The interface is the time of peak dynamic pressure and strength of the electric field. We also find that coupling appears to be stronger during recurrent high-speed streams in the declining phase of the solar cycle than it is around solar maximum. These results are consistent with the previous report that both strong driving (Es) and high dynamic pressure (Pdyn) reduce the coupling efficiency. Although the changes appear to be statistically significant their physical cause cannot be uniquely identified because various properties of the solar wind vary systematically through a corotating interaction region. It is also possible that the quality of the propagated solar wind data depends on the state of the solar wind. Finally it is likely that the quality of the AL index during the last solar cycle may affect the results. Despite these limitations our results indicate that the Es-AL coupling function is 50% stronger outside a corotating interaction region than inside.

scholarly journals Statistical analysis of the dependence of large-scale Birkeland currents on solar wind parameters

2010 ◽  
Vol 28 (2) ◽  
pp. 515-530 ◽  
Author(s):  
H. Korth ◽  
B. J. Anderson ◽  
C. L. Waters
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Mach Number ◽  
Electric Field ◽  
Large Scale ◽  
Dynamic Pressure ◽  
Dominant Factor ◽  
Total Current ◽  
Current Densities ◽  
Birkeland Currents

Abstract. The spatial distributions of large-scale field-aligned Birkeland currents have been derived using magnetic field data obtained from the Iridium constellation of satellites from February 1999 to December 2007. From this database, we selected intervals that had at least 45% overlap in the large-scale currents between successive hours. The consistency in the current distributions is taken to indicate stability of the large-scale magnetosphere–ionosphere system to within the spatial and temporal resolution of the Iridium observations. The resulting data set of about 1500 two-hour intervals (4% of the data) was sorted first by the interplanetary magnetic field (IMF) GSM clock angle (arctan(By/Bz)) since this governs the spatial morphology of the currents. The Birkeland current densities were then corrected for variations in EUV-produced ionospheric conductance by normalizing the current densities to those occurring for 0° dipole tilt. To determine the dependence of the currents on other solar wind variables for a given IMF clock angle, the data were then sorted sequentially by the following parameters: the solar wind electric field in the plane normal to the Earth–Sun line, Eyz; the solar wind ram pressure; and the solar wind Alfvén Mach number. The solar wind electric field is the dominant factor determining the Birkeland current intensities. The currents shift toward noon and expand equatorward with increasing solar wind electric field. The total current increases by 0.8 MA per mV m−1 increase in Eyz for southward IMF, while for northward IMF it is nearly independent of the electric field, increasing by only 0.1 MA per mV m−1 increase in Eyz. The dependence on solar wind pressure is comparatively modest. After correcting for the solar dynamo dependencies in intensity and distribution, the total current intensity increases with solar wind dynamic pressure by 0.4 MA/nPa for southward IMF. Normalizing the Birkeland current densities to both the median solar wind electric field and dynamic pressure effects, we find no significant dependence of the Birkeland currents on solar wind Alfvén Mach number.

How does the Sun Influence the Magnetospheres of Jupiter and Saturn?

2017 ◽  
Vol 13 (S335) ◽  
pp. 109-113
Author(s):  
Caitríona M. Jackman ◽  
Christopher S. Arridge
Keyword(s):  
Solar Wind ◽  
Solar Cycle ◽  
Dynamic Pressure ◽  
Current Data ◽  
Data Streaming ◽  
Cassini Mission ◽  
Flux Variability ◽  
Solar Uv ◽  
Complete Set ◽  
The Impact

AbstractSpacecraft have visited Jupiter and Saturn at all phases of the solar cycle and thus we have a wealth of data with which to explore both upstream parameters and magnetospheric response. In this paper we review upstream parameters including interplanetary magnetic field strength and direction, solar wind dynamic pressure, plasma beta and Mach number. We consider the impact of changing solar wind on dayside coupling via reconnection. We also comment on how solar UV flux variability over a solar cycle influences the plasma and neutral tori in the inner magnetospheres of Jupiter and Saturn, and thus estimate the solar cycle effects on internally driven magnetospheric dynamics. Finally we place our results in the context of the now complete set of data from the Cassini mission at Saturn and the current data streaming in from Juno at Jupiter, outlining future avenues for research.

scholarly journals Modelling three-dimensional transport of solar energetic protons in a corotating interaction region generated with EUHFORIA

2019 ◽  
Vol 622 ◽  
pp. A28 ◽  
Author(s):  
N. Wijsen ◽  
A. Aran ◽  
J. Pomoell ◽  
S. Poedts
Keyword(s):  
Solar Wind ◽  
Interplanetary Space ◽  
High Energy ◽  
Interaction Region ◽  
Corotating Interaction Region ◽  
Fast Solar Wind ◽  
Transport Code ◽  
Field Diffusion ◽  
Forward Shock ◽  
The Cross

Aims. We introduce a new solar energetic particle (SEP) transport code that aims at studying the effects of different background solar wind configurations on SEP events. In this work, we focus on the influence of varying solar wind velocities on the adiabatic energy changes of SEPs and study how a non-Parker background solar wind can trap particles temporarily at small heliocentric radial distances (≲1.5 AU) thereby influencing the cross-field diffusion of SEPs in the interplanetary space. Methods. Our particle transport code computes particle distributions in the heliosphere by solving the focused transport equation (FTE) in a stochastic manner. Particles are propagated in a solar wind generated by the newly developed data-driven heliospheric model, EUHFORIA. In this work, we solve the FTE, including all solar wind effects, cross-field diffusion, and magnetic-field gradient and curvature drifts. As initial conditions, we assume a delta injection of 4 MeV protons, spread uniformly over a selected region at the inner boundary of the model. To verify the model, we first propagate particles in nominal undisturbed fast and slow solar winds. Thereafter, we simulate and analyse the propagation of particles in a solar wind containing a corotating interaction region (CIR). We study the particle intensities and anisotropies measured by a fleet of virtual observers located at different positions in the heliosphere, as well as the global distribution of particles in interplanetary space. Results. The differential intensity-time profiles obtained in the simulations using the nominal Parker solar wind solutions illustrate the considerable adiabatic deceleration undergone by SEPs, especially when propagating in a fast solar wind. In the case of the solar wind containing a CIR, we observe that particles adiabatically accelerate when propagating in the compression waves bounding the CIR at small radial distances. In addition, for r ≳ 1.5 AU, there are particles accelerated by the reverse shock as indicated by, for example, the anisotropies and pitch-angle distributions of the particles. Moreover, a decrease in high-energy particles at the stream interface (SI) inside the CIR is observed. The compression/shock waves and the magnetic configuration near the SI may also act as a magnetic mirror, producing long-lasting high intensities at small radial distances. We also illustrate how the efficiency of the cross-field diffusion in spreading particles in the heliosphere is enhanced due to compressed magnetic fields. Finally, the inclusion of cross-field diffusion enables some particles to cross both the forward compression wave at small radial distances and the forward shock at larger radial distances. This results in the formation of an accelerated particle population centred on the forward shock, despite the lack of magnetic connection between the particle injection region and this shock wave. Particles injected in the fast solar wind stream cannot reach the forward shock since the SI acts as a diffusion barrier.

scholarly journals Solar wind dynamic pressure and electric field as the main factors controlling Saturn's aurorae

Nature ◽  
2005 ◽  
Vol 433 (7027) ◽  
pp. 720-722 ◽  
Author(s):  
F. J. Crary ◽  
J. T. Clarke ◽  
M. K. Dougherty ◽  
P. G. Hanlon ◽  
K. C. Hansen ◽  
...  
Keyword(s):  
Solar Wind ◽  
Electric Field ◽  
Dynamic Pressure ◽  
Solar Wind Dynamic Pressure ◽  
Main Factors

Numerical Simulation on the Propagation and Deflection of Fast Coronal Mass Ejections (CMEs) Interacting with a Corotating Interaction Region in Interplanetary Space

2020 ◽  
Author(s):  
Fang Shen ◽  
Yousheng Liu ◽  
Yi Yang
Keyword(s):  
Solar Wind ◽  
Coronal Mass Ejections ◽  
Interplanetary Space ◽  
Three Dimensional ◽  
Flux Rope ◽  
Interaction Region ◽  
The Sun ◽  
Corotating Interaction Region ◽  
The Common ◽  
Wind Flows

<p>Previous research has shown that the deflection of coronal mass ejections (CMEs) in interplanetary space, especially fast CMEs, is a common phenomenon. The deflection caused by the interaction with background solar wind is an important factor to determine whether CMEs could hit Earth or not. As the Sun rotates, there will be interactions between solar wind flows with different speeds. When faster solar wind runs into slower solar wind<br>ahead, it will form a compressive area corotating with the Sun, which is called a corotating interaction region (CIR). These compression regions always have a higher density than the common background solar wind. When interacting with CME, will this make a difference in the deflection process of CME? In this research, first, a three-dimensional (3D) flux-rope CME initialization model is established based on the graduated cylindrical shell (GCS)<br>model. Then this CME model is introduced into the background solar wind, which is obtained using a 3D IN (INterplanetary) -TVD-MHD model. The Carrington Rotation (CR) 2154 is selected as an example to simulate the propagation and deflection of fast CME when it interacts with background solar wind, especially with the CIR structure.</p><p>The simulation results show that: (1) the fast CME will deflect eastward when it propagates into the background solar wind without the CIR; (2) when the fast CME hits the CIR on its west side, it will also deflect eastward, and the deflection angle will increase compared with the situation without CIR.</p>

Revisiting the Strongest Martian X-Ray Halo Observed by XMM-Newton on 2003 November 19–21

2020 ◽  
Author(s):  
Limei Yan ◽  
Jiawei Gao ◽  
Lihui Chai ◽  
Lingling Zhao ◽  
Zhaojin Rong ◽  
...  
Keyword(s):  
Solar Wind ◽  
Solar Cycle ◽  
Direct Evidence ◽  
Dynamic Pressure ◽  
Mars Global Surveyor ◽  
Propagation Models ◽  
X Ray ◽  
Interplanetary Coronal Mass Ejection ◽  
Solar Cycle 23 ◽  
Mass Ejection

<p>On 2003 November 20–21, when the most intense geomagnetic storm during solar cycle 23 was observed at Earth, XMM-Newton recorded the strongest Martian X-ray halo hitherto. The strongest Martian X-ray halo has been suggested to be caused by the unusual solar wind, but no direct evidence has been given in previous studies. Here, based on the Mars Global Surveyor (MGS) observations, unambiguous evidence of unusual solar wind impact during that XMM-Newton observation was found: the whole induced magnetosphere of Mars was highly compressed. The comparison between the solar wind dynamic pressure estimated at Mars from MGS observation and that predicted by different solar wind propagation models suggests that the unusal solar wind is probably related to the interplanetary coronal mass ejection observed at Earth on 2003 November 20.</p>

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