9 research outputs found
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&
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
Correlated flares in models of a magnetized "canopy"
A model of the Lu-Hamilton kind is applied to the study of critical behavior
of the magnetized solar atmosphere. The main novelty is that its driving is
done via sources undergoing a diffusion. This mimics the effect of a virtual
turbulent substrate forcing the system. The system exhibits power-law
statistics not only in the size of the flares, but also in the distribution of
the waiting times.Comment: 5 pages + 9 figures, Accepted to Physica
A new class of discontinuous solar wind solutions
A new class of one-dimensional solar wind models is developed within the general polytropic, single-fluid hydrodynamic framework. The particular case of quasi-adiabatic radial expansion with a localized heating source is considered. We consider analytical solutions with continuous Mach number over the entire radial domain while allowing for jumps in the
ow velocity, density, and temperature, provided that there exists
an external source of energy in the vicinity of the critical point which supports such jumps in physical quantities. This is substantially distinct from both the standard Parker solar wind model and the original nozzle solutions, where such discontinuous solutions are not permissible. We obtain novel sample analytic solutions of the governing equations corresponding to both slow and fast wind.status: publishe
Evidence for Precursors of the Coronal Hole Jets in Solar Bright Points
© 2018. The American Astronomical Society. All rights reserved.. A set of 23 observations of coronal jet events that occurred in coronal bright points has been analyzed. The focus was on the temporal evolution of the mean brightness before and during coronal jet events. In the absolute majority of the cases either single or recurrent coronal jets (CJs) were preceded by slight precursor disturbances observed in the mean intensity curves. The key conclusion is that we were able to detect quasi-periodical oscillations with characteristic periods from sub-minute up to 3-4 minute values in the bright point brightness that precedes the jets. Our basic claim is that along with the conventionally accepted scenario of bright-point evolution through new magnetic flux emergence and its reconnection with the initial structure of the bright point and the coronal hole, certain magnetohydrodynamic (MHD) oscillatory and wavelike motions can be excited and these can take an important place in the observed dynamics. These quasi-oscillatory phenomena might play the role of links between different epochs of the coronal jet ignition and evolution. They can be an indication of the MHD wave excitation processes due to the system entropy variations, density variations, or shear flows. It is very likely a sharp outflow velocity transverse gradients at the edges between the open and closed field line regions. We suppose that magnetic reconnections can be the source of MHD waves due to impulsive generation or rapid temperature variations, and shear flow driven nonmodel MHD wave evolution (self-heating and/or overreflection mechanisms).status: publishe