SH21B-01 INVITED
A Model for Coronal Hole Jets
The recent observations from XRT on Hinode show dramatically that coronal hole are populated with intense X-ray jets that can reach heights of solar radii. These jets appear to originate from closed magnetic-field regions inside the holes; consequently, a natural explanation for these jets is that they are due to interchange reconnection between the open field of the hole and the closed field of an embedded bipole. This type of interchange reconnection has long been postulated as the driver, not only of coronal jets, but also for the solar wind itself. We argue, however, that the explosive nature of the jets imposes severe requirements on the reconnection that are not easily satisfied by realistic 3D models. In particular, the reconnection must have a "switch-on" nature in that it stays off until a substantial store of free energy has been accumulated, but then turns on abruptly and stays on until much of this free energy is released. We discuss the possible magnetic topologies of an embedded bipole in an open field region and present recent 3D simulations of a model in which interchange reconnection does, indeed, yield a large burst of energy release. We also discuss the implications of these results for the Hinode observations. This work was supported, in part, by NASA, ONR, and the NSF. http://solartheory.nrl.navy.mil
SH21B-02 INVITED
Polar Coronal Jets During the 2007 Joint SOHO/Hinode Campaigns
We will present ultraviolet spectroscopy of polar coronal jets obtained by the Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) during the two SOHO/Hinode observing campaigns (9-21 January and 12-20 March, 2007) for the north and south polar coronal holes. The emphasis is on identifying and tracing polar jets from the solar surface out into the accelerating solar wind and determining their physical properties as a function of height and time. UVCS/SOHO observed ultraviolet counterparts in the extended corona of the hot jets resolved by Hinode/XRT. These polar jets observed by UVCS have different characteristics in the acceleration region of the solar wind than the cooler jets identified at the last solar minimum by LASCO, UVCS, and EIT. Observations such as these are needed to clarify the relationship between the episodic jets, the longer-lived polar plumes, and the fast solar wind. This work is supported by NASA grants NNX06AG95G and NNX07AL72G to the Smithsonian Astrophysical Observatory. SOHO is a project of international cooperation between ESA and NASA.
SH21B-03
Three-dimensional Resistive-MHD Model for X-ray Bright Points and Coronal Jets
Thirteen years ago a simple two-dimensional model for an X-ray bright point and associated cancelling magnetic feature was first proposed by Priest et. al (1994). Over the next decade this model was extended into three- dimensions and applied by many authors to many observed X-ray bright points. A two-dimensional model was proposed at about the same time for coronal jets associated with the emergence of magnetic flux (e.g. Yokoyama & Shibata 1995). Recently, however, new results from Hinode hint to the fact that X-ray bright points may not actually be created cancellation. Furthermore, images from XRT aboard Hinode reveal that coronal jets occur far more frequency than previously reported. We present results from resistive MHD experiments that show how it is possible to create an X-ray bright point and coronal jet without the need for either the emergence or cancellation of magnetic flux. Thus, the numbers of each event are not limited to the numbers of flux emergences or cancellations. Moreover, by following the evolution of the magnetic topology during the interaction we can show that reconnection at multiple (as opposed to single) separators is the energy release mechanism. Also, we reveal how it is possible to get dramatic changes in the coronal loop structures observed with hardly any changes in the magnetic footpoints below, in line with recent observations from Hinode.
SH21B-04
Analysis of a Bright Point Spectrum From the Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS) Sounding Rocket Instrument
We present a well-calibrated spectrum of a bright point observed with EUNIS on 2006 April 12. Coordinated observations with SOHO's EIT and MDI were also obtained. The bright point brightened around 06:30 UT during a period of emerging magnetic flux, and remained bright at least until the rocket flight around 18:12 UT while the magnetic flux merged and canceled. Density-sensitive line intensity ratios yield mutually consistent coronal electron densities log Ne ~ 9.5. Based on the method of Landi & Landini (1997), the differential emission measure (DEM) curve derived from the spectrum yields a peak of log DEM ~ 20.70 at log T ~ 6.15, and a local minimum of log DEM ~ 20.15 at log T ~ 5.35. We find that photospheric (not coronal) element abundances are required to achieve equality and consistency in the DEM derived from lines of Mg V, Mg VI, Mg VII, Ca VII (with a low first ionization potential, or FIP) and lines from Ne IV and Ne V (with a high FIP) formed at transition region temperatures. The bright point's photospheric abundance is likely produced by reconnection-driven chromospheric evaporation, a process that is not only central to existing bright point models (e.g., Priest, Parnell, & Martin 1994; Longcope 1998), but also consistent with measurements of relative Doppler velocities (e.g., ± 26 km/s for Fe XIV, ± 35 km/s for Fe XVI) previously presented by Brosius, Rabin, & Thomas (2007). The EUNIS program is supported by NASA's Heliophysics Division through its Low Cost Access to Space Program in Solar and Heliospheric Physics. We thank the entire EUNIS team for the concerted effort that led to a successful first flight.
SH21B-05 INVITED
The Acceleration of the Fast Solar Wind by Reconnections Between Open Magnetic Flux and Coronal Loops
It is possible to develop models for the acceleration of the solar wind in which the mass flux of the solar wind is determined by the release of material during the reconnection between open magnetic flux and coronal loops, and the energy source is the subsequent relaxation to equilibrium of open flux displaced by the reconnection process. Such models, if correct and verified by observations, may provide the basis for predictive models of the solar wind, since the governing parameters that determine the final speed of the solar wind are in principle observable on the solar surface, e.g., the rate of reconnection between open field lines and coronal loops as revealed by coronal jets and X-ray bright points. This theory for the acceleration of the solar wind will be reviewed along with the role of reconnection within the theory; the parameters that need to be observed to test the theory will be discussed.
SH21B-06 INVITED
Sources of fast solar wind streams observed on STEREO and at L1
Information on the sources of the fast solar wind during the recent period of low solar activity has been obtained by STEREO, ACE and SOHO, for the first time from three perspectives. These observations are complemented by routinely available global models that help us to infer connections between in-situ properties and specific solar features. During the end of the current declining phase, starting around Carrington Rotation 2050 and lasting for almost ten solar rotations, the high speed stream sources were well-defined mid-southern-latitude coronal holes, distinct from the main southern polar coronal hole in the images and the models. The ability to reproduce the solar wind velocity at this time with models that rely on coronal flux tube divergence as a parameter suggest that the global aspects of fast solar wind generation cannot be neglected. Another notable observation is the ability of the mid-to-low latitude sources to retain their coherence and importance in the face of the usual differential rotation, supergranular diffusion, and meridional circulation that act on their photospheric magnetic field boundary. We use the in-situ observations, particularly of solar wind and suprathermal electrons, together with the images of the corona and the models to investigate from the multipoint perspective how these fast solar wind sources work.