Frequently, in a variety of experiments
though we miss what we expected to find,
yet something valuable turns out,
something surprising, and instructing,
though unthought of.
--Benjamin Franklin

David E. McKenzie  
Montana State University   
Solar Physics   

Research Topics

 

Flows Near Solar Flares

Since solar flares are the largest explosions in the solar system, it isn't surprising that they're often associated with high-velocity flows. Blobs of ejecta are frequently observed flying outwards from flares at speeds of several hundred kilometers per second. In 1999, however, we discovered the unexpected phenomenon of flows into the flare sites. Using the Soft X-ray Telescope on the Yohkoh solar observatory satellite, we detected features moving downward into the tops of post-eruption arcade at speeds of a few hundred kilometers per second. (See the publication by McKenzie & Hudson, 1999; and also the press release.)

We now believe that these flows represent the retraction of magnetic flux tubes, shrinking to relax magnetic tension after reconnection. My PhD student Sabrina Savage used Yohkoh, TRACE, and Hinode telescopes to make quantitative measurements of Supra-Arcade Downflows, in order to determine the observational characteristics of magnetic reconnection in flares. These observations formed the basis of Sabrina's dissertation, and we are still learning much these downflows about the conditions that control reconnection in current sheets.

Turbulent Flows in Flares

The ability of eruptive flares to imprint a signature onto the solar wind and inner heliosphere is well-documented. A component of this signature, hitherto unexplored, is due to the turbulent flows in flare current sheets, turbulence which is driven by the supra-arcade downflows. Our analysis has demonstrated that the plasma beta in these sheet-like structures can reach values of order unity, so that gas pressure forces and magnetic tensions have significant, and important, interplay in this crucial region. The high spatial and temporal resolution made available by the most recent solar telescopes (Hinode/XRT, SDO/AIA) facilitates tracking and measurement of these turbulent flows, through a local correlation tracking technique adapted by us for use in the corona. The velocity fields determined in this way show temporally and spatially varying vorticity, and cascades to smaller length scales--classic hallmarks of turbulence. With PhD students Roger Scott and Mike Freed, and with Prof. Dana Longcope and SAO's Dr. Kathy Reeves, we are using the measurements of turbulence in the flare current sheets to explore the conditions that initiate, accelerate, and prolong magnetic reconnection, as well as the generation of Alfven waves that radiate into the inner heliosphere.

Quantifying Magnetic Reconnection

In solar physics, we are now convinced that magnetic fields are rearranged, and magnetic energy is released, via a set of processes which we refer to as magnetic reconnection. However, we're lacking some specifics: How fast does reconnection occur? How much flux is included in a given reconnection event? What triggers an event? By combining observational measurements with analytical estimates and computer modeling, we hope to continue finding answers to some of these questions.

Current Solar Activity

A handful of links for checking on current solar activity. Each of these will open in a new browser window, since they are outside of the MSU site.



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