30 research outputs found
Twisted magnetic flux tubes in the solar wind
Magnetic flux tubes in the solar wind can be twisted as they are transported
from the solar surface, where the tubes are twisted owing to photospheric
motions. It is suggested that the twisted magnetic tubes can be detected as the
variation of total (thermal+magnetic) pressure during their passage through
observing satellite. We show that the total pressure of several observed
twisted tubes resembles the theoretically expected profile. The twist of
isolated magnetic tube may explain the observed abrupt changes of magnetic
field direction at tube walls. We have also found some evidence that the flux
tube walls can be associated with local heating of the plasma and elevated
proton and electron temperatures. For the tubes aligned with the Parker spiral,
the twist angle can be estimated from the change of magnetic field direction.
Stability analysis of twisted tubes shows that the critical twist angle of the
tube with a homogeneous twist is 70, but the angle can further decrease
owing to the motion of the tube with regards to the solar wind stream. The
tubes with a stronger twist are unstable to the kink instability, therefore
they probably can not reach 1 AU.Comment: 4 pages, 4 figures, accepted in ApJ
Magnetic Rossby waves in the solar tachocline and Rieger-type periodicities
Apart from the 11-year solar cycle, another periodicity around 155-160 days
was discovered during solar cycle 21 in high energy solar flares, and its
presence in sunspot areas and strong magnetic flux has been also reported. This
periodicity has an elusive and enigmatic character, since it usually appears
only near the maxima of solar cycles, and seems to be related with a periodic
emergence of strong magnetic flux at the solar surface. Therefore, it is
probably connected with the tachocline, a thin layer located near the base of
the solar convection zone, where strong dynamo magnetic field is stored. We
study the dynamics of Rossby waves in the tachocline in the presence of a
toroidal magnetic field and latitudinal differential rotation. Our analysis
shows that the magnetic Rossby waves are generally unstable and that the growth
rates are sensitive to the magnetic field strength and to the latitudinal
differential rotation parameters. Variation of the differential rotation and
the magnetic field strength throughout the solar cycle enhance the growth rate
of a particular harmonic in the upper part of the tachocline around the maximum
of the solar cycle. This harmonic is symmetric with respect to the equator and
has a period of 155-160 days. A rapid increase of the wave amplitude could give
place to a magnetic flux emergence leading to observed periodicities in solar
activity indicators related with magnetic flux.Comment: 34 pages, 5 figures, accepted in Ap
Association between Tornadoes and Instability of Hosting Prominences
We studied the dynamics of all prominence tornadoes detected by the Solar
Dynamics Observatory/Atmospheric Imaging Assembly from 2011 January 01 to
December 31. In total, 361 events were identified during the whole year, but
only 166 tornadoes were traced until the end of their lifetime. Out of 166
tornadoes, 80 (48%) triggered CMEs in hosting prominences, 83 (50%) caused
failed coronal mass ejections (CMEs) or strong internal motion in the
prominences, and only 3 (2%) finished their lifetimes without any observed
activity. Therefore, almost all prominence tornadoes lead to the
destabilization of their hosting prominences and half of them trigger CMEs.
Consequently, prominence tornadoes may be used as precursors for CMEs and hence
for space weather predictions.Comment: 16 pages, 5 figures, Accepted in Ap
Statistical properties of coronal hole rotation rates: Are they linked to the solar interior?
The present paper discusses results of a statistical study of the
characteristics of coronal hole (CH) rotation in order to find connections to
the internal rotation of the Sun. The goal is to measure CH rotation rates and
study their distribution over latitude and their area sizes. In addition, the
CH rotation rates are compared with the solar photospheric and inner layer
rotational profiles. We study coronal holes observed within latitude
and longitude degrees from the solar disc centre during the time span from the
1 January 2013 to 20 April 2015, which includes the extended peak of solar
cycle 24.We used data created by the Spatial Possibilistic Clustering Algorithm
(SPoCA), which provides the exact location and characterisation of solar
coronal holes using SDO=AIA 193 {\AA} channel images. The CH rotation rates are
measured with four-hour cadence data to track variable positions of the CH
geometric centre. North-south asymmetry was found in the distribution of
coronal holes: about 60 percent were observed in the northern hemisphere and 40
percent were observed in the southern hemisphere. The smallest and largest CHs
were present only at high latitudes. The average sidereal rotation rate for 540
examined CHs is degrees/d. Conclusions. The latitudinal
characteristics of CH rotation do not match any known photospheric rotation
profile. The CH angular velocities exceed the photospheric angular velocities
at latitudes higher than 35-40 degrees. According to our results, the CH
rotation profile perfectly coincides with tachocline and the lower layers of
convection zone at around 0.71 ; this indicates that CHs may be
linked to the solar global magnetic field, which originates in the tachocline
region.Comment: 8 pages, 8 figures, Accepted for publication in A&
Solar Science with the Atacama Large Millimeter/Submillimeter Array — A New View of Our Sun
The Atacama Large Millimeter/submillimeter Array (ALMA) is a new powerful tool for observing the Sun at high spatial, temporal, and spectral resolution. These capabilities can address a broad range of fundamental scientific questions in solar physics. The radiation observed by ALMA originates mostly from the chromosphere—a complex and dynamic region between the photosphere and corona, which plays a crucial role in the transport of energy and matter and, ultimately, the heating of the outer layers of the solar atmosphere. Based on first solar test observations, strategies for regular solar campaigns are currently being developed. State-of-the-art numerical simulations of the solar atmosphere and modeling of instrumental effects can help constrain and optimize future observing modes for ALMA. Here we present a short technical description of ALMA and an overview of past efforts and future possibilities for solar observations at submillimeter and millimeter wavelengths. In addition, selected numerical simulations and observations at other wavelengths demonstrate ALMA’s scientific potential for studying the Sun for a large range of science cases