Global-scale external magnetic fields at Mars measured at satellite altitude

2017 ◽  
Vol 122 (6) ◽  
pp. 1243-1257 ◽  
Author(s):  
A. Mittelholz ◽  
C. L. Johnson ◽  
R. J. Lillis
Keyword(s):  
Magnetic Fields ◽  
Global Scale ◽  
Satellite Altitude

THE PAST, PRESENT AND FUTURE OF THE SUN'S MAGNETISM

2012 ◽  
Vol 18 ◽  
pp. 130-135
Author(s):  
J. D. DO NASCIMENTO
Keyword(s):  
Magnetic Fields ◽  
Global Scale ◽  
Evolutionary Stage ◽  
The Sun ◽  
Fundamental Parameters ◽  
The Past ◽  
Bona Fide ◽  
The Subject ◽  
Solar Analogs ◽  
Active Investigation

Magnetic field in the Sun is produced through the dynamo process in a way that is not yet completely understood. The question whether the Sun is peculiar as compared with other stars has been the subject of active investigation over the past 5 decades, but no studies have been focused on the properties of rotation and surface magnetic fields. The availability of ESPaDOnS offers an exceptional possibility to study the specificity of rotation and magnetic properties of Sun-like stars by means of spectropolarimetric observations. In this review, we present some results concerning the investigation of magnetic fields and dynamo evolution in cool active solar-like stars. Our results are based on the systematic searching for genuine solar analogs and observation of a sample of bona fide solar twins and solar analogs, whose fundamental parameters and evolutionary stage was determined in our previous studies. Our main aim is to investigate how rotation and magnetism evolve and how the depth of the convection zone may influence the global-scale toroidal magnetic fields at the stellar surface.

Investigating global scale dust storms on Mars with ASPERA-3

2021 ◽  
Author(s):  
Catherine Regan ◽  
Andrew Coates ◽  
Geraint Jones ◽  
Anne Wellbrock ◽  
Mats Holmstrom ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Martian Atmosphere ◽  
Radar Data ◽  
Initial Study ◽  
Global Scale ◽  
Dust Storms ◽  
Lower Atmosphere ◽  
Time Base ◽  
Martian Surface ◽  
Plasma Measurements

<p>2007 and 2018 saw global scale dust storms engulfing the entirety of Mars, lasting several months. These events have a profound impact across Mars, with dust reaching altitudes up to 80 km and global temperatures rising by up to 40 K. This significant change in the Martian atmosphere may lead to changes in the ionosphere and above. During the 2007 storm, it was seen in Mars Express (MEx) radar data that ionisation created in the lower atmosphere is observed at higher altitudes, with an altitude dependent enhancement in plasma density over crustal magnetic fields (Venkateswara <em>et al.,</em> 2019). It may be likely that during these dust events, atmosphere loss is enhanced.</p> <p>MEx launched in 2003, became operational in 2004 and is still collecting data today. Onboard are seven scientific instruments which are answering questions about the atmosphere, surface and geology at Mars, whilst looking for signs of water and life. With a period of seven hours, MEx provides extensive coverage of data collection. One of the seven instruments, the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) has produced a long time-base of plasma measurements from as low as 250 km. ASPERA-3 aims to investigate the interaction of the solar wind with the Martian atmosphere, looking at the mechanisms that may enhance the loss of gases from Mars.</p> <p>ASPERA-3 will be used to investigate the effects the 2007 and 2018 global dust storms had on the plasma environment by comparing data before, during, and after the event.  Of particular interest are plasma measurements over radial magnetic fields from crustal anomalies, where transport of charged particles is guided out of the atmosphere.  The before, during, and after effects will shed light on to the influence dust storms have on the escaping plasma measured by ASPERA-3 and how dust changes the local plasma escape directly from the atmosphere. Our initial study focuses on data from the electron spectrometer (ELS) where we investigate how the energy distribution and peak energy value varies in altitude above the Martian surface. We will also relate our observations back down to the Martian surface, where we will investigate how surface features may influence the atmosphere and ionosphere above them. This will focus on the southern hemispheric crustal fields and geological features, such as impact basins and volcanoes.</p>

scholarly journals Global-scale wreath-building dynamos in stellar convection zones

2010 ◽  
Vol 6 (S271) ◽  
pp. 78-85
Author(s):  
Benjamin P. Brown ◽  
Matthew K. Browning ◽  
Allan Sacha Brun ◽  
Mark S. Miesch ◽  
Juri Toomre
Keyword(s):  
Magnetic Fields ◽  
Parameter Space ◽  
Spherical Harmonic ◽  
Convection Zone ◽  
Global Scale ◽  
Temporal Organization ◽  
Dynamo Action ◽  
Rotation Rates ◽  
Stellar Convection

AbstractWhen stars like our Sun are young they rotate rapidly and are very magnetically active. We explore dynamo action in rapidly rotating suns with the 3-D MHD anelastic spherical harmonic (ASH) code. The magnetic fields built in these dynamos are organized on global-scales into wreath-like structures that span the convection zone. Wreath-building dynamos can undergo quasi-cyclic reversals of polarity and such behavior is common in the parameter space we have been able to explore. These dynamos do not appear to require tachoclines to achieve their spatial or temporal organization. Wreath-building dynamos are present to some degree at all rotation rates, but are most evident in the more rapidly rotating simulations.

scholarly journals Exploring the deep convection and magnetism of A-type stars

2010 ◽  
Vol 6 (S273) ◽  
pp. 111-115
Author(s):  
Nicholas A. Featherstone ◽  
Matthew K. Browning ◽  
Allan Sacha Brun ◽  
Juri Toomre
Keyword(s):  
Magnetic Fields ◽  
Differential Rotation ◽  
Large Scale ◽  
Deep Convection ◽  
Global Scale ◽  
Dynamo Action ◽  
Solar Mass ◽  
Near Surface ◽  
Strong Magnetic Fields ◽  
Core Convection

AbstractA-type stars have both a near-surface layer of fast convection that can excite acoustic modes and a deep zone of core convection whose properties may be probed with asteroseismology. Many A-type stars also exhibit large magnetic spots that are often attributed to surviving primordial fields of global scale in the intervening radiative zone. We have explored the potential for core convection in rotating A-type stars to build strong magnetic fields through dynamo action. These 3-D simulations using the ASH code provide guidance on the nature of differential rotation and magnetic fields that may be present in the deep interiors of these stars, thus informing the asteroseismic deductions now becoming feasible. Our models encompass the inner 30% by radius of a two solar mass A-type star, rotating at four times the solar rate and capturing the convective core and a portion of the overlying radiative envelope. Convection in these stars drives a strong retrograde differential rotation and yields a core that is prolate in shape. When dynamo action is admitted, the convection generates strong magnetic fields largely in equipartition with the dynamics. Remarkably, introducing a modest but large-scale external field threading the radiative envelope (which may be of primordial origin) can substantially alter the turbulent dynamics of the convective interior. The resulting convection involves a complex assembly of helical rolls that link distant portions of the core and stretch and advect magnetic field, ultimately yielding magnetic fields of super-equipartition strength.

Calculated Coronal Magnetic Fields and Their Comparison with the Coronal Structures as Observed during Five Solar Eclipses

1994 ◽  
Vol 144 ◽  
pp. 559-564
Author(s):  
P. Ambrož ◽  
J. Sýkora
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Coronal Magnetic Field ◽  
Coronal Magnetic Fields ◽  
Solar Eclipses ◽  
Coronal Structures

AbstractWe were successful in observing the solar corona during five solar eclipses (1973-1991). For the eclipse days the coronal magnetic field was calculated by extrapolation from the photosphere. Comparison of the observed and calculated coronal structures is carried out and some peculiarities of this comparison, related to the different phases of the solar cycle, are presented.

Radio Measurements of Coronal Magnetic Fields

1994 ◽  
Vol 144 ◽  
pp. 21-28 ◽  
Author(s):  
G. B. Gelfreikh
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Active Regions ◽  
High Sensitivity ◽  
Coronal Magnetic Field ◽  
Transverse Magnetic ◽  
Radio Sources ◽  
Radio Waves ◽  
Solar Active Regions

AbstractA review of methods of measuring magnetic fields in the solar corona using spectral-polarization observations at microwaves with high spatial resolution is presented. The methods are based on the theory of thermal bremsstrahlung, thermal cyclotron emission, propagation of radio waves in quasi-transverse magnetic field and Faraday rotation of the plane of polarization. The most explicit program of measurements of magnetic fields in the atmosphere of solar active regions has been carried out using radio observations performed on the large reflector radio telescope of the Russian Academy of Sciences — RATAN-600. This proved possible due to good wavelength coverage, multichannel spectrographs observations and high sensitivity to polarization of the instrument. Besides direct measurements of the strength of the magnetic fields in some cases the peculiar parameters of radio sources, such as very steep spectra and high brightness temperatures provide some information on a very complicated local structure of the coronal magnetic field. Of special interest are the results found from combined RATAN-600 and large antennas of aperture synthesis (VLA and WSRT), the latter giving more detailed information on twodimensional structure of radio sources. The bulk of the data obtained allows us to investigate themagnetospheresof the solar active regions as the space in the solar corona where the structures and physical processes are controlled both by the photospheric/underphotospheric currents and surrounding “quiet” corona.

Emergence of Twisted Magnetic Flux Related Sigmoidal Brightening

2000 ◽  
Vol 179 ◽  
pp. 263-264
Author(s):  
K. Sundara Raman ◽  
K. B. Ramesh ◽  
R. Selvendran ◽  
P. S. M. Aleem ◽  
K. M. Hiremath
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Ultra Violet ◽  
Active Regions ◽  
Morphological Properties ◽  
Energy Storage And Conversion ◽  
The Sun ◽  
X Rays ◽  
The Magnetic Field

Extended AbstractWe have examined the morphological properties of a sigmoid associated with an SXR (soft X-ray) flare. The sigmoid is cospatial with the EUV (extreme ultra violet) images and in the optical part lies along an S-shaped Hαfilament. The photoheliogram shows flux emergence within an existingδtype sunspot which has caused the rotation of the umbrae giving rise to the sigmoidal brightening.It is now widely accepted that flares derive their energy from the magnetic fields of the active regions and coronal levels are considered to be the flare sites. But still a satisfactory understanding of the flare processes has not been achieved because of the difficulties encountered to predict and estimate the probability of flare eruptions. The convection flows and vortices below the photosphere transport and concentrate magnetic field, which subsequently appear as active regions in the photosphere (Rust & Kumar 1994 and the references therein). Successive emergence of magnetic flux, twist the field, creating flare productive magnetic shear and has been studied by many authors (Sundara Ramanet al.1998 and the references therein). Hence, it is considered that the flare is powered by the energy stored in the twisted magnetic flux tubes (Kurokawa 1996 and the references therein). Rust & Kumar (1996) named the S-shaped bright coronal loops that appear in soft X-rays as ‘Sigmoids’ and concluded that this S-shaped distortion is due to the twist developed in the magnetic field lines. These transient sigmoidal features tell a great deal about unstable coronal magnetic fields, as these regions are more likely to be eruptive (Canfieldet al.1999). As the magnetic fields of the active regions are deep rooted in the Sun, the twist developed in the subphotospheric flux tube penetrates the photosphere and extends in to the corona. Thus, it is essentially favourable for the subphotospheric twist to unwind the twist and transmit it through the photosphere to the corona. Therefore, it becomes essential to make complete observational descriptions of a flare from the magnetic field changes that are taking place in different atmospheric levels of the Sun, to pin down the energy storage and conversion process that trigger the flare phenomena.

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