614 research outputs found
On red shifs in the transition region and corona
We present evidence that transition region red-shifts are naturally produced
in episodically heated models where the average volumetric heating scale height
lies between that of the chromospheric pressure scale height of 200 km and the
coronal scale height of 50 Mm. In order to do so we present results from 3d MHD
models spanning the upper convection zone up to the corona, 15 Mm above the
photosphere. Transition region and coronal heating in these models is due both
the stressing of the magnetic field by photospheric and convection `zone
dynamics, but also in some models by the injection of emerging magnetic flux.Comment: 8 pages, 9 figures, NSO Workshop #25 Chromospheric Structure and
Dynamic
3. Wochenbericht M80/3
FS Meteor Reise M80/3
(Dakar, Senegal – Gran Canaria, Spanien)
3. Wochenbericht, 11. bis 17. Januar 201
Observational Signatures of Simulated Reconnection Events in the Solar Chromosphere and Transition Region
We present the results of numerical simulations of wave-induced magnetic
reconnection in a model of the solar atmosphere. In the magnetic field geometry
we study in this article, the waves, driven by a monochromatic piston and a
driver taken from Hinode observations, induce periodic reconnection of the
magnetic field, and this reconnection appears to help drive long-period
chromospheric jets. By synthesizing observations for a variety of wavelengths
that are sensitive to a wide range of temperatures, we shed light on the often
confusing relationship between the plethora of jet-like phenomena in the solar
atmosphere, e.g., explosive events, spicules, blinkers, and other phenomena
thought to be caused by reconnection.Comment: 13 pages, 22 figures. Submitted to The Astrophysical Journa
4. Wochenbericht M80/3
FS Meteor Reise M80/3
(Dakar, Senegal – Gran Canaria, Spanien)
4. Wochenbericht, 18. bis 24. Januar 201
1. Wochenbericht M80/3
FS Meteor Reise M80/3
(Dakar, Senegal – Gran Canaria, Spanien)
1. Wochenbericht, 27. Dezember 2009 bis 3. Januar, 201
Observing the Roots of Solar Coronal Heating - in the Chromosphere
The Sun's corona is millions of degrees hotter than its 5,000 K photosphere.
This heating enigma is typically addressed by invoking the deposition at
coronal heights of non-thermal energy generated by the interplay between
convection and magnetic field near the photosphere. However, it remains unclear
how and where coronal heating occurs and how the corona is filled with hot
plasma. We show that energy deposition at coronal heights cannot be the only
source of coronal heating, by revealing a significant coronal mass supply
mechanism that is driven from below, in the chromosphere. We quantify the
asymmetry of spectral lines observed with Hinode and SOHO and identify faint
but ubiquitous upflows with velocities that are similar (50-100 km/s) across a
wide range of magnetic field configurations and for temperatures from 100,000
to several million degrees. These upflows are spatio-temporally correlated with
and have similar upward velocities as recently discovered, cool (10,000 K)
chromospheric jets or (type II) spicules. We find these upflows to be pervasive
and universal. Order of magnitude estimates constrained by conservation of mass
and observed emission measures indicate that the mass supplied by these
spicules can play a significant role in supplying the corona with hot plasma.
The properties of these events are incompatible with coronal loop models that
only include nanoflares at coronal heights. Our results suggest that a
significant part of the heating and energizing of the corona occurs at
chromospheric heights, in association with chromospheric jets.Comment: 14 pages, 5 figures, accepted for publication in ApJ letter
Modelling of EIS spectrum drift from instrumental temperatures
An empirical model has been developed to reproduce the drift of the spectrum
recorded by EIS on board Hinode using instrumental temperatures and relative
motion of the spacecraft. The EIS spectrum shows an artificial drift in
wavelength dimension in sync with the revolution of the spacecraft, which is
caused by temperature variations inside the spectrometer. The drift amounts to
70 km s in Doppler velocity and introduces difficulties in velocity
measurements. An artificial neural network is incorporated to establish a
relationship between the instrumental temperatures and the spectral drift. This
empirical model reproduces observed spectrum shift with an rms error of 4.4 km
s. This procedure is robust and applicable to any spectrum obtained with
EIS, regardless of of the observing field. In addition, spectral curvatures and
spatial offset in the North - South direction are determined to compensate for
instrumental effects.Comment: 16 pages, 12 Figures, accepted for publication in Solar Physics.
Added description of neural networ
The Role of Partial Ionization Effects in the Chromosphere
The energy for the coronal heating must be provided from the convection zone.
The amount and the method by which this energy is transferred into the corona
depends on the properties of the lower atmosphere and the corona itself. We
review: 1) how the energy could be built in the lower solar atmosphere; 2) how
this energy is transferred through the solar atmosphere; and 3) how the energy
is finally dissipated in the chromosphere and/or corona. Any mechanism of
energy transport has to deal with the various physical processes in the lower
atmosphere. We will focus on a physical process that seems to be highly
important in the chromosphere and not deeply studied until recently: the
ion-neutral interaction effects (INIE) in the chromosphere. We review the
relevance and the role of the partial ionization in the chromosphere and show
that this process actually impacts considerably the outer solar atmosphere. We
include analysis of our 2.5D radiative MHD simulations with the Bifrost code
(Gudiksen et al. 2011) including the partial ionization effects on the
chromosphere and corona and thermal conduction along magnetic field lines. The
photosphere, chromosphere and transition region are partially ionized and the
interaction between ionized particles and neutral particles has important
consequences on the magneto-thermodynamics of these layers. The INIE are
treated using generalized Ohm's law, i.e., we consider the Hall term and the
ambipolar diffusion in the induction equation. The interaction between the
different species affects the modeled atmosphere as follows: 1) the ambipolar
diffusion dissipates magnetic energy and increases the minimum temperature in
the chromosphere; 2) the upper chromosphere may get heated and expanded over a
greater range of heights. These processes reveal appreciable differences
between the modeled atmospheres of simulations with and without INIE.Comment: 25 pages, 3 figures, accepted to be published in Royal Societ
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