scholarly journals Statistical dependence of auroral ionospheric currents on solar wind and geomagnetic parameters from 5 years of CHAMP satellite data

2009 ◽  
Vol 27 (3) ◽  
pp. 1005-1017 ◽  
Author(s):  
L. Juusola ◽  
K. Kauristie ◽  
O. Amm ◽  
P. Ritter
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Field Data ◽  
Dynamic Pressure ◽  
Auroral Oval ◽  
Solar Wind Dynamic Pressure ◽  
Total Field ◽  
Magnetic Field Data ◽  
Champ Satellite ◽  
Field Aligned Current

Abstract. The effects of the solar wind dynamic pressure (P), the z component of the solar wind magnetic field (Bz), the merging electric field (Em), season and the Kp index on R1 and R2 field-aligned currents are studied statistically using magnetic field data from the CHAMP satellite during 2001–2005. The ionospheric and field-aligned currents are determined from the magnetic field data by the recently developed 1-D Spherical Elementary Current System (SECS) method. During southward IMF, increasing |Bz| is observed to clearly increase the total field-aligned current, while during northward IMF, the amount of field-aligned current remains fairly constant regardless of |Bz|. The dependence of the field-aligned current on Bz is given by |Ir[MA]|=0.054·Bz[nT]2−0.34·Bz[nT]+2.4. With increasing P, the intensity of the field-aligned current is also found to increase according to |Ir[MA]|=0.62·P[nPa]+1.6, and the auroral oval is observed to move equatorward. Increasing Em produces similar behaviour, described by |Ir[MA]|=1.41·Em[mV/m]+1.4. While the absolute intensity of the ionospheric current is stronger during negative than during positive Bz, the relative change in the intensity of the currents produced by a more intense solar wind dynamic pressure is observed to be approximately the same regardless of the Bz direction. Increasing Kp from 0 to ≥5 widens the auroral oval and moves it equatorward from between 66°–74° AACGM latitude to 59°–71° latitude. The total field aligned current as a function of Kp is given by |Ir[MA]|=1.1·Kp+0.6. In agreement with previous studies, total field-aligned current in the summer is found to be 1.4 times stronger than in the winter.

scholarly journals GPS phase scintillation at high latitudes during geomagnetic storms of 7–17 March 2012 – Part 1: The North American sector

2015 ◽  
Vol 33 (6) ◽  
pp. 637-656 ◽  
Author(s):  
P. Prikryl ◽  
R. Ghoddousi-Fard ◽  
E. G. Thomas ◽  
J. M. Ruohoniemi ◽  
S. G. Shepherd ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Geomagnetic Storms ◽  
Dynamic Pressure ◽  
Auroral Oval ◽  
Solar Wind Dynamic Pressure ◽  
Polar Cap ◽  
The North ◽  
Auroral Emission ◽  
Ground Magnetic

Abstract. The interval of geomagnetic storms of 7–17 March 2012 was selected at the Climate and Weather of the Sun-Earth System (CAWSES) II Workshop for group study of space weather effects during the ascending phase of solar cycle 24 (Tsurutani et al., 2014). The high-latitude ionospheric response to a series of storms is studied using arrays of GPS receivers, HF radars, ionosondes, riometers, magnetometers, and auroral imagers focusing on GPS phase scintillation. Four geomagnetic storms showed varied responses to solar wind conditions characterized by the interplanetary magnetic field (IMF) and solar wind dynamic pressure. As a function of magnetic latitude and magnetic local time, regions of enhanced scintillation are identified in the context of coupling processes between the solar wind and the magnetosphere–ionosphere system. Large southward IMF and high solar wind dynamic pressure resulted in the strongest scintillation in the nightside auroral oval. Scintillation occurrence was correlated with ground magnetic field perturbations and riometer absorption enhancements, and collocated with mapped auroral emission. During periods of southward IMF, scintillation was also collocated with ionospheric convection in the expanded dawn and dusk cells, with the antisunward convection in the polar cap and with a tongue of ionization fractured into patches. In contrast, large northward IMF combined with a strong solar wind dynamic pressure pulse was followed by scintillation caused by transpolar arcs in the polar cap.

scholarly journals Geosynchronous magnetic field responses to fast solar wind dynamic pressure enhancements: MHD field model

2012 ◽  
Vol 30 (8) ◽  
pp. 1285-1295 ◽  
Author(s):  
T. R. Sun ◽  
C. Wang ◽  
N. L. Borodkova ◽  
G. N. Zastenker
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Field Model ◽  
Dynamic Pressure ◽  
Solar Wind Dynamic Pressure ◽  
Geosynchronous Orbit ◽  
Total Field ◽  
Fast Solar Wind ◽  
Dominant Component ◽  
Mhd Simulations

Abstract. We performed global MHD simulations of the geosynchronous magnetic field in response to fast solar wind dynamic pressure (Pd) enhancements. Taking three Pd enhancement events in 2000 as examples, we found that the main features of the total field B and the dominant component Bz can be efficiently predicted by the MHD model. The predicted B and Bz varies with local time, with the highest level near noon and a slightly lower level around mid-night. However, it is more challenging to accurately predict the responses of the smaller component at the geosynchronous orbit (i.e., Bx and By). In contrast, the limitations of T01 model in predicting responses to fast Pd enhancements are presented.

scholarly journals Cluster survey of the mid-altitude cusp: 1. size, location, and dynamics

2006 ◽  
Vol 24 (11) ◽  
pp. 3011-3026 ◽  
Author(s):  
F. Pitout ◽  
C. P. Escoubet ◽  
B. Klecker ◽  
H. Rème
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Time Delay ◽  
Interplanetary Magnetic Field ◽  
Statistical Study ◽  
Proper Time ◽  
Dynamic Pressure ◽  
Solar Wind Dynamic Pressure ◽  
Summer Hemisphere ◽  
External Conditions

Abstract. We present a statistical study of four years of Cluster crossings of the mid-altitude cusp. In this first part of the study, we start by introducing the method we have used a) to define the cusp properties, b) to sort the interplanetary magnetic field (IMF) conditions or behaviors into classes, c) to determine the proper time delay between the solar wind monitors and Cluster. Out of the 920 passes that we have analyzed, only 261 fulfill our criteria and are considered as cusp crossings. We look at the size, location and dynamics of the mid-altitude cusp under various IMF orientations and solar wind conditions. For southward IMF, Bz rules the latitudinal dynamics, whereas By governs the zonal dynamics, confirming previous works. We show that when |By| is larger than |Bz|, the cusp widens and its location decorrelates from By. We interpret this feature in terms of component reconnection occurring under By-dominated IMF. For northward IMF, we demonstrate that the location of the cusp depends primarily upon the solar wind dynamic pressure and upon the Y-component of the IMF. Also, the multipoint capability of Cluster allows us to conclude that the cusp needs typically more than ~20 min to fully adjust its location and size in response to changes in external conditions, and its speed is correlated to variations in the amplitude of IMF-Bz. Indeed, the velocity in °ILAT/min of the cusp appears to be proportional to the variation in Bz in nT: Vcusp=0.024 ΔBz. Finally, we observe differences in the behavior of the cusp in the two hemispheres. Those differences suggest that the cusp moves and widens more freely in the summer hemisphere.

How does the magnetosphere go to sleep?

2020 ◽  
Author(s):  
Therese Moretto Jorgensen ◽  
Michael Hesse ◽  
Lutz Rastaetter ◽  
Susanne Vennerstrom ◽  
Paul Tenfjord
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Interplanetary Magnetic Field ◽  
Exponential Decay ◽  
Rate Of Change ◽  
Total Field ◽  
Summer Hemisphere ◽  
Field Aligned Current ◽  
Field Lines ◽  
Line Tying

<p>Energy and circulation in the Earth’s magnetosphere and ionosphere are largely determined by conditions in the solar wind and interplanetary magnetic field. When the driving from the solar wind is turned off (to a minimum), we expect the activity to die down but exactly how this happens is not known.  Utilizing global MHD modelling, we have addressed the questions of what constitutes the quietest state for the magnetosphere and how it is approached following a northward turning in the IMF that minimizes the driving. We observed an exponential decay with a decay time of about 1 hr in several integrated parameters related to different aspects of magnetospheric activity, including the total field-aligned current into and out of the ionosphere.  The time rate of change for the cessation of activity was also measured in total field aligned current estimates from the AMPERE project, adding observational support to this finding.  Events of distinct northward turnings of the interplanetary magnetic field were identified, with prolonged periods of stable southward driving conditions followed by northward interplanetary magnetic field conditions. A well-defined exponential decay could be identified in the total hemispheric field-aligned current following the northward turning with a generic decay constant of 0.9, corresponding to an e-folding time of 1.1 hr. A possible physical explanation for the exponential decay follows from considering what needs to happen for the convection in the magnetosphere to slow down, or stop, namely the unwinding of the field-aligned current carrying flux tubes in the coupled magnetosphere-ionosphere system. A statistical analysis of the ensemble of events also reveals both a seasonal and a day/night variation in the decay parameter, with faster decay observed in the winter than in the summer hemisphere and on the nightside than on the dayside. These results can be understood in terms of stronger/weaker line tying of the ionospheric foot points of magnetospheric field lines for higher/lower conductivity.  Additional global modeling results with varying conductance scenarios for the ionosphere confirm this interpretation.   </p>

scholarly journals Magnetic field variations in the Jovian magnetotail induced by solar wind dynamic pressure enhancements

2005 ◽  
Vol 110 (A11) ◽  
Author(s):  
Chihiro Tao ◽  
Ryuho Kataoka ◽  
Hiroshi Fukunishi ◽  
Yukihiro Takahashi ◽  
Takaaki Yokoyama
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Dynamic Pressure ◽  
Solar Wind Dynamic Pressure ◽  
Magnetic Field Variations

scholarly journals Azimuthally asymmetric ring current as a function of <i>D<sub>st</sub></i> and solar wind conditions

2004 ◽  
Vol 22 (8) ◽  
pp. 2989-2996 ◽  
Author(s):  
Y. P. Maltsev ◽  
A. A. Ostapenko
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Spatial Distribution ◽  
Interplanetary Magnetic Field ◽  
Ring Current ◽  
Dynamic Pressure ◽  
Solar Wind Dynamic Pressure ◽  
Magnetic Data ◽  
Under Five ◽  
Solar Wind Parameters

Abstract. Based on magnetic data, spatial distribution of the westward ring current flowing at |z|<3 RE has been found under five levels of Dst, five levels of the interplanetary magnetic field (IMF) z component, and five levels of the solar wind dynamic pressure Psw. The maximum of the current is located near midnight at distances 5 to 7 RE. The magnitude of the nightside and dayside parts of the westward current at distances from 4 to 9 RE can be approximated as Inight=1.75-0.041 Dst, Inoon=0.22-0.013 Dst, where the current is in MA. The relation of the nightside current to the solar wind parameters can be expressed as Inight=1.45-0.20 Bs IMF + 0.32 Psw, where BsIMF is the IMF southward component. The dayside ring current poorly correlates with the solar wind parameters.

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