E-Print Archive

There are 3783 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
Radial Distribution of Compressive Waves in the Solar Corona Revealed by Akatsuki Radio Occultation Observations  

Takeshi Imamura   Submitted: 2015-06-24 06:16

Radial variations of the amplitude and the energy flux of compressive waves in the solar corona were explored for the first time using a spacecraft radio occultation technique. By applying wavelet analysis to the frequency time series taken at heliocentric distances of 1.5-20.5 Rs (solar radii), quasi-periodic density disturbances were detected at almost all distances. The period ranges from 100 to 2000 s. The amplitude of the fractional density fluctuation increases with distance and reaches ~30% around 5 Rs, implying that nonlinearity of the wave field is potentially important. We further estimate the wave energy flux on the assumption that the observed periodical fluctuations are manifestations of acoustic waves. The energy flux increases with distance below ~6 Rs and seems to saturate above this height, suggesting that the acoustic waves do not propagate from the low corona but are generated in the extended corona, probably through nonlinear dissipation of Alfvén waves. The compressive waves should eventually dissipate through shock generation to heat the corona.

Authors: Mayu Miyamoto, Takeshi Imamura, Munetoshi Tokumaru, Hiroki Ando, Hiroaki Isobe, Ayumi Asai, Daikou Shiota, Tomoaki Toda, Bernd Häusler, Martin Pätzold, Alexander Nabatov, and Masato Nakamura
Projects: Other

Publication Status: ApJ (Published 2014 November 25)
Last Modified: 2015-06-24 14:44
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Outflow structure of the quiet Sun corona probed by spacecraft radio scintillations in strong scattering  

Takeshi Imamura   Submitted: 2015-06-24 05:53

Radio scintillation observations have been unable to probe flow speeds in the low corona where the scattering of radio waves is exceedingly strong. Here we estimate outflow speeds continuously from the vicinity of the Sun to the outer corona (heliocentric distances of 1.5-20.5 solar radii) by applying the strong scattering theory to radio scintillations for the first time, using the Akatsuki spacecraft as the radio source. Small, nonzero outflow speeds were observed over a wide latitudinal range in the quiet-Sun low corona, suggesting that the supply of plasma from closed loops to the solar wind occurs over an extended area. The existence of power-law density fluctuations down to the scale of 100 m was suggested, being indicative of well-developed turbulence which can play a key role in heating the corona. At higher altitudes a rapid acceleration typical of radial open fields is observed, and the temperatures derived from the speed profile show a distinct maximum in the outer corona. This study opened up a possibility of observing detailed flow structures near the Sun from existing vast amount of interplanetary scintillation data.

Authors: Takeshi Imamura, Munetoshi Tokumaru, Hiroaki Isobe, Daikou Shiota, Hiroki Ando, Mayu Miyamoto, Tomoaki Toda, Bernd Häusler, Martin Pätzold, Alexander Nabatov, Ayumi Asai, Kentaro Yaji, Manabu Yamada, Masato Nakamura
Projects: Other

Publication Status: ApJ (Published 2014 May 29)
Last Modified: 2015-06-29 11:55
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 


Key
Go to main E-Print pageGo to main E-Print page.
Download PreprintDownload Preprint.
Submitter's HomepageSubmitters Homepage.
Edit EntryEdit Entry.
Delete AbstractDelete abstract.

Abstracts by Author
Radial Distribution of Compressive Waves in the Solar Corona Revealed by Akatsuki Radio Occultation Observations
Outflow structure of the quiet Sun corona probed by spacecraft radio scintillations in strong scattering

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