CHAMP observation of intense kilometer-scale field-aligned currents, evidence for an ionospheric Alfvén resonator

Abstract. Bursts of very intense kilometer-scale field-aligned currents (KSFACs) are observed quite frequently by the CHAMP satellite when passing through the auroral region. In extreme cases estimated current densities exceed 3 mA/m². Typical scale sizes of these KSFACs are 1 km. The low-Earth, polar orbiting satellite CHAMP allows one to assess KSFACs down to scales of a couple of 100 m based on its high-precision magnetic field vector data sampled at 50 Hz. Using data from 5 years (2001–2005) details of these currents can be investigated. In our statistical study we find that most of the KSFAC bursts and the strongest events are encountered in the cusp/cleft region. Significantly fewer events are found on the nightside. The affected region is typically 15°–20° wide in latitude. There seems to be some dependence of the current intensity on the level of magnetic activity, Kp. On the other hand, no dependence has been found on sunspot number, the solar flux level, F10.7 or the solar zenith angle. The latitude, at which KSFAC bursts are encountered, expands equatorward with increasing Kp. This trend follows well the auroral oval expansion during enhanced magnetic activity. These KSFACs are generally accompanying large-scale FAC sheets, and they are predominantly associated with Region 1 currents. We propose an explanation of the KSFACs in terms of Alfvén waves trapped in a ionospheric resonator, which is initiated when the convection electric field or current strength surpasses a critical value. Many properties of such a resonator are in agreement with our KSFAC results.

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Introducing the “VALOR” analysis framework for auroral field-aligned current sheets using observations from Swarm Alpha and Charlie

10.5194/egusphere-egu21-1263 ◽

2021 ◽

Author(s):

Leonie Pick ◽

Joachim Vogt ◽

Adrian Blagau ◽

Nele Stachlys

Keyword(s):

Magnetic Field ◽

Linear Correlation ◽

Large Scale ◽

Spatial Scales ◽

Time Lag ◽

Field Vector ◽

Auroral Oval ◽

Association Measure ◽

Field Aligned Current ◽

Scale Estimate

The investigation of auroral field-aligned current (FAC) sheets is crucial in the context of space weather research since they serve as main transmitters of energy and momentum across geospace domains. Different magnetosphere-ionosphere coupling modes are reflected by the FACs&#8217; multiscale nature with spatial scales, i.e., latitudinal extensions, ranging from below 1 km to hundreds of kilometers. The multiscale property can be addressed conveniently using ESA&#8217;s three-spacecraft mission Swarm. According to common practice a linear correlation analysis is performed on lagged and band-pass filtered scalar FAC density estimates from two nearby spacecraft.We introduce the framework VALOR (Vectorial Association of Linearly Oriented Residua) which generalizes the common approach in two ways. First, VALOR utilizes the full magnetic field vector primarily observed at both spacecraft without filtering. Second, VALOR allows to test statistical association measures other than linear correlation in dependence of both time and along-track spacecraft lag. The method is further refined by considering the current sheet&#8217;s polarization, i.e., the directional preference of the associated magnetic field perturbation, which additionally constrains the sheet&#8217;s orientation.Here, we apply VALOR to 1 Hz magnetic field observations from Swarm Alpha and Charlie and base the association measure on a vectorial version of the mean squared deviation. By means of a sample auroral oval crossing event we demonstrate that the incorporation of vectorial and polarization information helps to focus the association measure in the time-lag parameter plane leading to a smaller FAC spatial scale estimate. This result seems to hold in a statistical context including over 9000 quasi-perpendicular auroral oval crossings from 2014 to 2020. The fact that the VALOR derived FAC locations reflect the known ellipsoidal shapes of the auroral ovals speaks to the overall plausibility of the method as well as the independently supported finding that large-scale FACs (>300 km) dominate the dawn and dusk sectors while smaller scale FACs gain importance at noon and midnight. Among the various opportunities for future work are an application to 50 Hz high-resolution Swarm data as well as the investigation of the solar controlling parameters.

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Understanding Gender Differences in Leadership*

The Economic Journal ◽

10.1093/ej/uez050 ◽

2019 ◽

Cited By ~ 3

Author(s):

Sule Alan ◽

Seda Ertac ◽

Elif Kubilay ◽

Gyongyi Loranth

Keyword(s):

Gender Differences ◽

Gender Difference ◽

Field Experiment ◽

Large Scale ◽

Dramatic Decline ◽

Real Effort ◽

Scale Field ◽

Large Scale Field ◽

Using Data ◽

Risky Decisions

Abstract Using data from a large-scale field experiment, we show that while there is no gender difference in the willingness to make risky decisions on behalf of a group in a sample of children, a large gap emerges in a sample of adolescents. The proportion of girls who exhibit leadership willingness drops by 39% going from childhood to adolescence. We explore the possible factors behind this drop and find that it is largely associated with a dramatic decline in “social confidence”, measured by the willingness to perform a real effort task in public.

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Corona during the total solar eclipse on March 20, 2015, and 24 cycle development

Solar-Terrestrial Physics ◽

10.12737/20995 ◽

2016 ◽

Vol 2 (2) ◽

pp. 3-14

Author(s):

Сергей Язев ◽

Sergey Yazev ◽

Александр Мордвинов ◽

Aleksandr Mordvinov ◽

Антонина Дворкина-Самарская ◽

...

Keyword(s):

Magnetic Fields ◽

Solar Eclipse ◽

Large Scale ◽

Magnetic Activity ◽

Total Solar Eclipse ◽

Asynchronous Development ◽

Current Cycle ◽

Polar Magnetic Fields ◽

Using Data ◽

Northern And Southern Hemispheres

We analyzed the structure of coronal features, using data on the March 20, 2015 total solar eclipse. The Ludendorff index characterizing the flattening of the corona is 0.09. The solar corona structure in the Northern and Southern hemispheres corresponds to the maximum and post-maximum phases of solar activity, respectively. The asynchronous development of magnetic activity in the Sun’s Northern and Southern hemispheres caused a substantial asymmetry of coronal features observed at the reversal of polar magnetic fields in the current cycle. The polar ray structures in the Southern Hemisphere are associated with the polar coronal hole, while in the Northern Hemisphere a polar hole has not been formed yet. We examine the relation between large-scale magnetic fields and location of high coronal structures.

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Correlation between lithospheric magnetic anomalies and tectonic structures in the Norwegian-Greenland region of the Arctic

Geodynamics & Tectonophysics ◽

10.5800/gt-2018-9-4-0388 ◽

2018 ◽

Vol 9 (4) ◽

pp. 1163-1172 ◽

Cited By ~ 1

Author(s):

D. Yu. Abramova ◽

L. M. Abramova ◽

S. V. Filippov

Keyword(s):

Geomagnetic Field ◽

Large Scale ◽

Deep Structure ◽

Magnetic Anomalies ◽

Field Vector ◽

Point Of View ◽

The Arctic ◽

Tectonic Structures ◽

Champ Satellite ◽

Marginal Seas

The studies of the deep structure and tectonics of the Arctic are important for solving the fundamental problems of modern geodynamics and developing its natural resources. This region is also of interest from the geopolitical point of view, in particular, considering the boundaries of the marginal seas. Our study aims to investigate the lithospheric (anomalous) geomagnetic field in the Norwegian-Greenland region of the Arctic and to correlate the identified anomalies with tectonic structures located in the region under study. The database includes the CHAMP satellite measurements of the modulus of the total geomagnetic field vector (the satellite operated at the altitude of ~280 km). This article describes the satellite data processing method applied to distinguish between the lithospheric part and other components of the geomagnetic field. Map showing the total vector modulus of the lithospheric field has been constructed for the studied area. The article discusses the possible nature of the lithospheric magnetic anomalies and their relation to the processes that occur under the territory of Greenland. According to our interpretation of the maps, the geomagnetic field anomalies are related to the modern large-scale geological and tectonic structures located in the studied area. The obtained results can facilitate further comprehensive geological and geophysical studies and contribute to modeling of the evolution of the lithosphere.

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A new method for studying the thermospheric density variability derived from CHAMP/STAR accelerometer data for magnetically active conditions

Annales Geophysicae ◽

10.5194/angeo-25-1949-2007 ◽

2007 ◽

Vol 25 (9) ◽

pp. 1949-1958 ◽

Cited By ~ 9

Author(s):

M. Menvielle ◽

C. Lathuillère ◽

S. Bruinsma ◽

R. Viereck

Keyword(s):

Geomagnetic Activity ◽

Large Scale ◽

Singular Vector ◽

Temporal Variations ◽

Global Scale ◽

Magnetic Activity ◽

Accelerometer Data ◽

Champ Satellite ◽

Time Variations ◽

The Impact

Abstract. Thermospheric densities deduced from STAR accelerometer measurements onboard the CHAMP satellite are used to characterize the thermosphere and its response to space weather events. The STAR thermospheric density estimates are analysed using a Singular Value Decomposition (SVD) approach allowing one to decouple large scale spatial and temporal variations from fast and local transients. Because SVD achieves such decomposition by using the reproducibility of orbital variations, it provides more meaningful results than any method based upon data smoothing or filtering. SVD analysis enables us to propose a new thermosphere proxy, based on the projection coefficient of the CHAMP densities on the first singular vector. The large scale spatial variations in the density, mostly related to altitude/latitude variations are captured by the first singular vector; time variations are captured by the associated projection coefficient. The study presented here is focused on time dependent global scale variations in the thermospheric density between 50 N and 50 S geographic latitudes. We show that the time variations in the projection coefficient do in fact represent those in the global density that are associated with magnetic activity as well as with solar EUV radiations. We also show that the NRLMSISE-00 empirical model better accounts for the density forcing by Solar radiations when tuned using Mg II indices. Using the so modified model with an additional geomagnetic parameterization corresponding to quiet geomagnetic situation enables one to define time reference values which are then used to evaluate the impact of geomagnetic activity. The ratio of CHAMP density projection coefficient to the quiet model projection coefficient is a global quantity, independent of altitude and latitude, which quantifies the thermospheric density response to auroral energy deposition. It will serve as a proxy of the response of thermospheric density to geomagnetic activity forcing.

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What can we tell about global auroral-electrojet activity from a single meridional magnetometer chain?

Annales Geophysicae ◽

10.1007/s00585-996-1177-1 ◽

1996 ◽

Vol 14 (11) ◽

pp. 1177-1185 ◽

Cited By ~ 19

Author(s):

K. Kauristie ◽

T. I. Pulkkinen ◽

R. J. Pellinen ◽

H. J. Opgenoorth

Keyword(s):

Relative Error ◽

Statistical Study ◽

Auroral Oval ◽

Magnetic Activity ◽

The Other ◽

Real Situation ◽

The Real ◽

Global Indices ◽

Using Data ◽

Transient Variations

Abstract. The AE indices are generally used for monitoring the level of magnetic activity in the auroral oval region. In some cases, however, the oval is either so expanded or contracted that the latitudinal coverage of the AE magnetometer chain is not adequate. Then, a longitudinal chain in the key region would give more information of the real situation, but, of course, only during some limited UT-period. In order to find out the UT coverage of a single meridional chain, we have compared the global AL and AU indices with corresponding local indices determined using data from the meridional part of the EISCAT Magnetometer Cross during the years 1985–1987. A statistical study shows that the local indices are close (within relative error of 0.2) to the global AU and AL during periods 1500–2000 UT (~1730–2230 MLT) and 2130–0130 UT (~0000–0400 MLT), respectively. In the middle of these optimal MLT-sectors the EISCAT Cross sees more than 70% of the cases when the global AE chain records activity. Then, also the correlation between the local and global indices is generally good (>0.7). Thus we conclude that five to six evenly located meridional chains are needed for covering all the UT-periods. On the other hand, already the combination of IMAGE, CANOPUS, and the Greenland chains catches ~50% of the substorms. Case-studies show that usually during 2130–1100 UT the AL achieved from these chains reproduces the real AL with good timing, although it does not follow all transient variations.

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Global magnetic fields: variation of solar minima

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312004723 ◽

2011 ◽

Vol 7 (S286) ◽

pp. 113-122

Author(s):

Andrey G. Tlatov ◽

Vladimir N. Obridko

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Large Scale ◽

Sunspot Cycle ◽

Magnetic Activity ◽

Small Scale ◽

The Sun ◽

Large Scale Magnetic Field ◽

Scale Field ◽

Large Scale Field

AbstractThe topology of the large-scale magnetic field of the Sun and its role in the development of magnetic activity were investigated using Hα charts of the Sun in the period 1887-2011. We have considered the indices characterizing the minimum activity epoch, according to the data of large-scale magnetic fields. Such indices include: dipole-octopole index, area and average latitude of the field with dominant polarity in each hemisphere and others. We studied the correlation between these indices and the amplitude of the following sunspot cycle, and the relation between the duration of the cycle of large-scale magnetic fields and the duration of the sunspot cycle.The comparative analysis of the solar corona during the minimum epochs in activity cycles 12 to 24 shows that the large-scale magnetic field has been slow and steadily changing during the past 130 years. The reasons for the variations in the solar coronal structure and its relation with long-term variations in the geomagnetic indices, solar wind and Gleissberg cycle are discussed.We also discuss the origin of the large-scale magnetic field. Perhaps the large-scale field leads to the generation of small-scale bipolar ephemeral regions, which in turn support the large-scale field. The existence of two dynamos: a dynamo of sunspots and a surface dynamo can explain phenomena such as long periods of sunspot minima, permanent dynamo in stars and the geomagnetic field.

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