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Session 73 - Solar Space Observations, SOHO & SERTS.
Display session, Friday, January 09
Exhibit Hall,
The SUMER spectrometer has obtained numerous high spatial and spectral resolution observations of optically-thin transition region line profiles in various solar features (quiet Sun, active region, coronal hole, etc.). Frequently, these line profiles show evidence for both steady and impulsive mass motions, which can have profound implications for the mass and energy balance of the transition region and corona. These motions can be quantified using the Velocity Differential Emission Measure (VDEM) technique to derive the distribution of emission with respect to the line-of-sight velocity. This VDEM distribution can then be used to infer mean plasma velocities, momenta, and energy fluxes. We have found that representations of the energy flux by either the ``mean flow approximation'' 1 øver 2n m\bar v^3 or by the ``enthalpy approximation''(whether in a purely thermal form nkT \bar v or incorporating nonthermal turbulence 1 øver 2n m øverline v^2 \bar v) all underestimate the true energy flux 1 øver 2 n m øverlinev^3 by up to an order of magnitude. In cases where lines formed at different temperatures have been observed in the SUMER spectral range simultaneously, we have estimated the divergence of the energy flux and so the energy deposition rate within the region bounded by the formation heights of the two spectral lines; implications for coronal heating are discussed. This work was supported by grants from the SoHO Guest Investigator Program and by the Office of Naval Research.
