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Solar Physics

, Volume 81, Issue 2, pp 253–280 | Cite as

High resolution EUV structure of the chromosphere-corona transition region above a sunspot

  • K. R. Nicolas
  • O. Kjeldseth-Moe
  • J. D. F. Bartoe
  • G. E. Brueckner
Article

Abstract

Ion emission line intensities between 1170 and 1700 Å allow one to determine the differential emission measure (DEM) and electron pressure of the plasma in the solar transition region (TR). These line intensities together with their Doppler shifts and line widths are measured simultaneously for the first time above a sunsport from data obtained with the NRL High Resolution Telescope and Spectrograph with 0.06 Å spectral and 1″ spatial resolution.

The Doppler shifts show both subsonic and supersonic flow in the same line of sight over the umbra. The temperature structure for 40 resolution elements in the sunspot umbra and penumbra is derived from the DEM and the observed electron pressures.

Extrapolation of the emission measure curves supports the previous EUV and X-ray observations that coronal plasma above sunspots with Te>106 K is reduced while emission from TR plasma between 2×105 and 106 K is greatly enhanced relative to quiet or active regions. This enhancement shifts the minimum of the DEM to lower temperatures and increases the slope at 2×105 K by a factor of two.

New pressure diagnostics using the emission line intensity ratios of C iv to N iv are presented, and applied to the data.

The energy balance in the TR for the sunspot umbra is dominated by radiative losses from the large amount of TR plasma.

An estimate of the energy budget shows that an energy input is required to balance the radiative energy losses above the umbra. The observed divergence of the enthalpy flux for the umbral downflows can balance these radiative losses for Te between 30000 and 200 000 K.

A typical umbral model of Te versus reduced mass column density is compared with one for chromospheric temperatures determined from the Ca H and K lines.

Keywords

Supersonic Flow Radiative Loss Column Density Electron Pressure Differential Emission Measure 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© D. Reidel Publishing Co 1982

Authors and Affiliations

  • K. R. Nicolas
    • 1
  • O. Kjeldseth-Moe
    • 1
  • J. D. F. Bartoe
    • 1
  • G. E. Brueckner
    • 1
  1. 1.E. O. Hulburt Center for Space Research, Naval Research LaboratoryWashington, D.C.USA

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