New Frontiers in Understanding the Structure of the Sun's Chromosphere I
Presiding: S W McIntosh, Southwest Research Institute; S M Jefferies, University of New Mexico, Maui Scientific; B DePontieu, Lockheed Martin Solar and Astrophysics Laboratory
SH11C-01 INVITED 08:30h
Chromospheric Heating, Transport Processes, and Small Scale Magnetic Fields
There are two basic categories of theories of chromospheric heating: hydrodynamic heating, and magnetohydrodynamic (MHD) heating. Hydrodynamic heating by shock wave dissipation appears to explain the origin of internetwork CaII bright points, but the associated heating rate appears to be at least one order of magnitude smaller than what is required to balance the chromospheric net radiative loss. Heating by high frequency acoustic waves is a proposed mechanism for chromospheric heating, at least in the internetwork, but so far there is no observational evidence that the energy in such waves is sufficient to heat the chromosphere. Increasing observational evidence for the existence of magnetic field concentrations at or below the spatial resolution limit with strengths ~ 102 - 103 G, the positive correlation between magnetic field strength and net radiative loss, and the differences between network, internetwork, and active regions in terms of magnetic field filling factor and net radiative loss suggest that a single MHD mechanism heats the network, internetwork, and active region chromospheres outside of flaring regions, and operates largely at or below the spatial resolution limit. A discussion of this suggestion in the context of the critical need to model proposed chromospheric heating mechanisms using realistic transport processes is presented along with an indication of why this heating mechanism is not effective in the transition region or corona, except possibly on spatial scales believed to characterize current sheets. This work was supported by NSF grant ATM-0242820 to the Institute for Scientific Research.
SH11C-02 INVITED 08:45h
Parker Lecture: Waves in the Magnetized Solar Atmosphere
Over the last few decades there has been tremendous progress in determining the detailed structure of solar and stellar interiors and envelopes through the observation and interpretation of the properties of p-modes (helioseismology) and g-modes (asteroseismology). These low-frequency modes derive from the broadband `noise' emitted by the star's turbulent convection zone. The high-frequency tail of the convective acoustic emission is not trapped within the stellar envelope, but is instead able to venture out into the optically thin atmosphere. There these waves encounter, amongst other things, the ambient magnetic field (also a by product of the turbulent convection). Close to the stellar surface, where the magnetic field is weak in the sense that the magnetic pressure is small compared to the thermal pressure, or equivalently, the Alfvén speed is much less than the sound speed, the high-frequency acoustic waves propagate freely with little regard for the magnetic field. However, at sufficiently high altitudes these waves will encounter surfaces where the two pressures and characteristic propagation speeds become comparable. In passing through these canopy or equipartition surfaces the incident acoustic waves are transformed into roughly equal amounts of the three magneto-acoustic gravity (MAG) waves. The transmitted MAG waves propagate at different phase speeds and along distinct trajectories through the overlying magneto-atmosphere. They leave distinct imprints on absorption line profiles and the continuum emission, and pave the way for seismology of the solar, and perhaps even stellar, atmospheres.
SH11C-03 09:15h
Tracing Coronal Waves Back to the Photosphere
There are now many observations of waves with periods around 5 minutes in the outer atmosphere of the Sun. We provide an observational overview of 5 minute periodicity in chromospheric spicules in active region plage, upper transition region moss and the low legs of coronal loops. Using a numerical model, we show that all of these phenomena are connected: normally evanescent photospheric oscillations can propagate into the low atmosphere as long as they are guided along magnetic field lines that are inclined away from the vertical. The leaked photospheric oscillations develop into shocks and lead to periodic upward chromospheric flows, which we have identified as active region spicules. These shocks continue upwards and enter into the corona. We suggest that TRACE observations of propagating acoustic waves in the corona are shocked and tunneled photospheric oscillations. Using SOHO/MDI, TRACE and Imaging Vector Magnetograph (Hawaii) data we explore how these coronal waves can be exploited to determine the connectivity between photosphere and corona,and thus allow seismology of the lower solar atmosphere.
SH11C-04 09:30h
Chromospheric Origins of the Solar Wind: Composition and Correlations
Diagnostics of atmospheric "depth" in the chromosphere are made for several observing periods in active, coronal hole and quiet Sun regions. We track the coronal outflows from these regions to 1 AU using a ballistic travel time approximation and correlate the chromospheric quantities with counterpart in situ quantities from the same packets of plasma Recently, we1 have shown that derived diagnostic quantities correlate very strongly with solar wind velocity and inversely with the ratio of ionic oxygen composition (O7+/O6+). We extend this work to show that strong correlations exist between the state of the chromosphere and other in situ observables, including proton temperatures, alpha particle temperatures and alpha/proton ratios. (1) McIntosh and Leamon, ApJL, submitted 2005
SH11C-05 09:45h
Dynamic Variations in the in Wave Behavior of the Solar Atmosphere
It has been speculated that observed dynamic variations in the in wave behavior of the solar atmosphere are indications of rapid changes in the solar atmosphere. In particular, Finsterle et al. (SoPh 220 317-331) report an observation of rapidly changing wave behavior associated with an EIT observation suggestive of the break up of a magnetic loop. We examine the transient wave behavior using 100 hours of velocity observations using the K (770nm) and Na (589) Frauenhaufer lines from the Magneto Optical filter at Two Heights (MOTH) experiment compared to EIT observations.