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Session 15 - The Sun and Solar Wind.
Display session, Monday, June 08
Atlas Ballroom,

[15.05] Are the cool CO clouds produced by the solar granulation?

H. Uitenbroek (Harvard-Smithsonian CfA)

The low temperatures measured in the cores of strong vibration--rotation lines of molecular CO near the solar limb do not agree with temperatures measured in most other spectral features like the UV continuum, the mm wavelength continuum and strong ionic lines like the Ca II H amp; K lines, which all form at similar altitudes in the solar atmosphere. However, the interpretation of observed intensities in terms of atmospheric temperatures is strongly model dependent, and with more detailed observations the one-dimensional plane-parallel hydrostatic models used to interpret solar spectra have been shown to be more and more at odds with the inherent dynamic and inhomogeneous nature of the solar atmosphere.

Time resolved long slit observations of the solar CO lines near 4.6 \mum with the Near Infrared Magnetograph (NIM) at the National Solar observatory at Kitt Peak have revealed that the dynamics of both the five-minute oscillations and the granulation play an important role in CO line formation. In these observations the darkest (coolest) elements seem to be associated with strong overshooting granules. Hydrodynamic granulation simulations have shown that over such granules the atmosphere is cooled by the rapid horizontal expansion of the upflowing material which is forced by the steep drop in density with height.

I have performed three-dimensional, Non-LTE CO line formation calculations in a snapshot taken from a granulation simulation, and will compare the calculated profiles with observed spectra to see whether the adiabatic cooling over upwelling granules can explain the dark CO line cores, or whether further dynamic effects like a disparity in the chemical formation and destruction time scales play a more decisive role.

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Program listing for Monday