We propose to establish a physical connection between photospheric magnetic fields and the variability of solar UV intensity based on magneto-acoustic shocks produced by leaking p modes in magnetic regions. Based on multi-height Doppler and magnetic field measurements the amplitudes of upward traveling waves in the p-mode frequency range will be determined. As the pressure and density of the plasma decreases along the wave path pressure fluctuations of the wave can no longer be considered infinitesimal and hence the wave crest is significantly accelerated due to the temperature increase induced by the wave itself. This eventually leads to the formation of a shock front, i.e. a quasi non-linear increase of pressure and temperature. The shock front continues to travel upwards while dissipating its energy and thus heating the plasma. Numerical simulations of wave propagation and radiative transfer will be used to estimate the effect of such magneto-acoustic shocks on the UV emitting layers. The goal is to better understand the short-term (minutes) as well as long-term (decades, solar cycle) variability of UV irradiance. The result of such a simplified simulation is shown in Figure 1. Here, pure pressure waves were assumend and magnetic forces were neglected.
Motivating Science: The Magneto-Optical filter at Two Heights (MOTH) experiment has played an crucial role in our understanding of magnetoatmospheric (MA) waves and their interaction with the ever changing magnetic field (e.g., Jefferies et al. 2006, ApJL, 648, 151) by simultaneously observing Doppler signals at two "heights" in the solar chromosphere. Throughout January 2008 the second MOTH experiment will be deployed at South Pole Station and will observe simultaneous magnetograms and Dopplergrams of the full solar disk in K I (7770ﾅ) and Na I D1 (5896ﾅ) at ~2.5 arcsecond spatial and 10s temporal resolution. This truly unique dataset, especially when combined with SOT, will allow us to explore the dynamics of the quiet chromosphere over the whole disk including high-impact investigations of potential p-mode and (~1mHz) internal gravity waves (Straus et al. 2007, Submitted to Science, November 2007 - available on request) coupling to Alfvenic motions that are now being abundantly observed in the chromosphere and corona (Tomczyk et al. 2007, Science, 317, 1192; De Pontieu et al. 2007, Science, 318, 1574). We also hope to measure the energy flow through the "acoustic portals" that are driven by relentless magneto-convection (cf. the excitation of fibrils and mottles, e.g., De Pontieu et al. 2007, ApJ, 655, 624). |
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