E-Print Archive

There are 3945 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
Petschek-like Reconnection with Current-driven Anomalous Resistivity and Its Application to Solar Flares  

Dmitri Uzdensky   Submitted: 2008-11-06 09:35

Recent simulations of magnetic reconnection with localized resistivity demonstrated the development of a Petschek-like configuration with the width of the inner diffusion region of the order of the resistivity localization scale. In this paper, we combine this fact with a realistic model for locally enhanced current-driven anomalous resistivity. In the qualitative model that results, the size of the diffusion region and hence the reconnection rate are determined self-consistently by the functional dependence of anomalous resistivity on the current density. For the specific case of anomalous resistivity due to ion-acoustic turbulence, we express the main reconnection parameters directly in terms of the basic plasma parameters. Finally, we apply our model to solar flares and obtain typical reconnection times that are consistent with observations.

Authors: Dmitri A. Uzdensky
Projects: None

Publication Status: Astrophysical Journal, vol. 587, p. 450 (2003)
Last Modified: 2008-11-06 16:00
Go to main E-Print page  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

Self-regulation of Solar Coronal Heating Process via Collisionless Reconnection Condition  

Dmitri Uzdensky   Submitted: 2008-03-30 16:02

I put forward a novel view on the solar coronal-heating problem. I suggest that coronal heating is a self-regulating process working to keep the plasma marginally collisionless. The proposed mechanism is based on the coupling between two effects. First, the density affects the degree of plasma collisionality and thus the transition between the slow collisional Sweet-Parker and the fast collisionless reconnection regimes. In turn, coronal energy release events lead to chromospheric evaporation, which increases the ambient plasma density and hence inhibits subsequent reconnection involving the newly-reconnected loops. As a result, statistically, the density fluctuates around a certain critical value which turns out to be comparable with the observed coronal density. On the longer time-scale, coronal heating can be seen as a cyclic process consisting of fast reconnection events (nano-flares), followed by rapid evaporation episodes, followed by longer quiet periods of magnetic stress build-up by photospheric motions simultaneous with radiative cooling of the coronal plasma.

Authors: Dmitri A. Uzdensky (Princeton University/CMSO)
Projects: None

Publication Status: published in PRL 99, 261101 (2007)
Last Modified: 2008-09-23 21:11
Go to main E-Print page  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

Fast Collisionless Reconnection Condition and Self-Organization of Solar Coronal Heating  

Dmitri Uzdensky   Submitted: 2007-09-10 14:03

I propose that solar coronal heating is a self-regulating process that keeps the coronal plasma roughly marginally collisionless. The self-regulating mechanism is based on the interplay of two effects. First, plasma density controls coronal energy release via the transition between the slow collisional Sweet-Parker regime and the fast collisionless reconnection regime. This transition takes place when the Sweet-Parker layer becomes thinner than the characteristic collisionless reconnection scale. I present a simple criterion for this transition in terms of the upstream plasma density (n_e), the reconnecting (B_0) and guide (B_z) magnetic field components, and the global length (L) of the reconnection layer: L < 6.109 cm [n_e/(1010/cm^3)]-3 (B_0/30G)^4 (B_0/B_z)^2. Next, coronal energy release by reconnection raises the ambient plasma density via chromospheric evaporation and this, in turn, temporarily inhibits subsequent reconnection involving the newly-reconnected loops. Over time, however, radiative cooling gradually lowers the density again below the critical value and fast reconnection again becomes possible. As a result, the density is highly inhomogeneous and intermittent but, statistically, does not deviate strongly from the critical value which is comparable with the observed coronal density. Thus, in the long run, the coronal heating process can be represented by repeating cycles that consist of fast reconnection events (i.e., nanoflares), followed by rapid evaporation episodes, followed by relatively long periods (1-hour) during which magnetic stresses build up and simultaneously the plasma cools down and precipitates.

Authors: Dmitri A. Uzdensky
Projects: None

Publication Status: Accepted to the Astrophysical Journal
Last Modified: 2007-09-11 05:43
Go to main E-Print page  Edit Entry  Download Preprint  Submitter's Homepage 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
Petschek-like Reconnection with Current-driven Anomalous Resistivity and Its Application to Solar Flares
Self-regulation of Solar Coronal Heating Process via Collisionless Reconnection Condition
Fast Collisionless Reconnection Condition and Self-Organization of Solar Coronal Heating

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