Abstracts submitted by Daniel Mueller
A Mechanism for Coronal Hole Jets
D. Mueller [1], S. K. Antiochos [2]
[1]European Space Agency; [2]Naval Research Laboratory, Washington, DC
Bald patches are magnetic topologies in which the magnetic field is concave up over part of a photospheric polarity inversion line. A bald patch topology is believed to be the essential ingredient for filament channels and is often found in extrapolations of the observed photospheric field. We demonstrate that although common in closed field regions, bald patches are unlikely to occur in the open field topology of a coronal hole. We use an analytic source-surface model to calculate the magnetic topology of a small "active region" dipole embedded in a central magnetic dipole field. While bald patches readily occur in closed-field regions, we show that there is only a highly limited parameter range for them to form in open-field regions. Furthermore, the inclusion of a finite gas pressure and solar wind is likely to destroy even this limited parameter range for the existence of bald patches in coronal holes. Our results give rise to the following question: What happens to a bald patch topology when the surrounding field lines open up? This would be the case when a bald patch moves into a coronal hole, or when a coronal hole forms in an area that encompasses a bald patch. Our magnetostatic models show that, in this case, the bald patch topology almost invariably transforms into a null point topology with a spine and a fan. We argue that the time-dependent evolution of this scenario will be very dynamic since the change from a bald patch to null point topology cannot occur via a simple ideal evolution in the corona. We discuss the implications of these findings for recent Hinode XRT observations of coronal hole jets and give an outline of planned time-dependent 3D MHD simulations to fully assess this scenario. |
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