E-Print Archive

There are 3898 abstracts currently viewable.


Search:

Advanced Search
Options
Main Page Add New E-Print Submitter
Information
Feedback
News Help/FAQ About Preferences
Manage Key Phrase
Notification
LOFAR observations of the quiet solar corona View all abstracts by submitter

Christian Vocks   Submitted: 2018-03-02 08:09

The quiet solar corona emits meter-wave thermal bremsstrahlung. Coronal radio emission can only propagate above that radius, Rω, where the local plasma frequency eqals the observing frequency. The radio interferometer LOw Frequency ARray (LOFAR) observes in its low band (10 - 90 MHz) solar radio emission originating from the middle and upper corona. We present the first solar aperture synthesis imaging observations in the low band of LOFAR in 12 frequencies each separated by 5 MHz. From each of these radio maps we infer Rω, and a scale height temperature, T. These results can be combined into coronal density and temperature profiles. We derived radial intensity profiles from the radio images. We focus on polar directions with simpler, radial magnetic field structure. Intensity profiles were modeled by ray-tracing simulations, following wave paths through the refractive solar corona, and including free-free emission and absorption. We fitted model profiles to observations with Rω and T as fitting parameters. In the low corona, Rω < 1.5 solar radii, we find high scale height temperatures up to 2.2e6 K, much more than the brightness temperatures usually found there. But if all Rω values are combined into a density profile, this profile can be fitted by a hydrostatic model with the same temperature, thereby confirming this with two independent methods. The density profile deviates from the hydrostatic model above 1.5 solar radii, indicating the transition into the solar wind. These results demonstrate what information can be gleaned from solar low-frequency radio images. The scale height temperatures we find are not only higher than brightness temperatures, but also than temperatures derived from coronograph or EUV data. Future observations will provide continuous frequency coverage, eliminating the need for local hydrostatic density models.

Authors: C. Vocks, G. Mann, F. Breitling, M. M. Bisi, B. Dabrowski, R. Fallows, P. T. Gallagher, A. Krankowski, J. Magdalenic, C. Marque, D. Morosan, H. Rucker
Projects: LOw Frequency ARray (LOFAR)

Publication Status: A&A, in print
Last Modified: 2018-03-05 17:15
Go to main E-Print page  Developments of Multi-wavelength Spectro-Polarimeter on the Domeless Solar Telescope at Hida Observatory  Statistics of   Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

Key
Go to main E-Print pageGo to main E-Print page.
Previous AbstractPrevious Abstract.
Next AbstractNext Abstract.
Download PreprintDownload Preprint.
Submitter's HomepageSubmitters Homepage.
Edit EntryEdit Entry.
View All Abstracts By SubmitterView all abstracts by submitter.
Delete AbstractDelete abstract.

Latest Entries
An Event-Based Verification Scheme for the Real-Time Flare Detection System at Kanzelhöhe Observatory
Computation of Relative Magnetic Helicity in Spherical Coordinates
Some characteristics of the GLE on 10 September 2017
Quasi-periodic Pulsations in a Solar Microflare
Homologous large-amplitude Nonlinear fast-mode Magnetosonic Waves Driven by Recurrent Coronal Jets
EUV Waves Driven by Sudden Expansion of Transequatorial Loops Caused by Solar Coronal Jets
Dispersively formed quasi-periodic fast magnetosonic wavefronts due to the eruption of a nearby mini-filament
Mini-filament Eruptions Triggering Confined Solar Flares Observed by ONSET and SDO
LOFAR observations of fine spectral structure dynamics in type IIIb radio bursts
Critical magnetic field strengths for solar coronal plumes in quiet regions and coronal holes?
Does Nearby Open Flux Affect the Eruptivity of Solar Active Regions?
Cyclic Changes of the Sun's Seismic Radius
Onset of Photospheric Impacts and Helioseismic Waves in X9.3 Solar Flare of September 6, 2017
Solar Cycle Variations of Rotation and Asphericity in the Near-Surface Shear Layer
Solar coronal loop dynamics near the null point above active region NOAA 2666
Energetics of small electron acceleration episodes in the solar corona from radio noise storm observations
The origin of the modulation of the radio emission from the solar corona by a fast magnetoacoustic wave
Indirect solar wind measurements using archival cometary tail observations
Helium abundance and speed difference between helium ions and protons in the solar wind from coronal holes, active regions, and quiet Sun
Always a Farm Boy

Related Pages
MSU Solar Physics.
Max Millennium Science Mail Archive.
Max Millennium Message of the Day Mail Archive.
Max Millennium Flare Catalog

Archive Maintainer
Alisdair Davey



© 2003 Solar Physics Group - Montana State University