Chromospheric Carbon Monoxide Formation around a Solar Pore

We present observations of NOAA AR 11159, obtained on 2011 February 14 in the 4.7 mu m band of carbon monoxide (CO) and coordinated with spectroscopic imaging of three atomic lines (Na i 5896 angstrom, Fe i 7090 angstrom, and Ca ii 8542 angstrom) which sample heights from the mid-photosphere to the chromosphere. Phase-difference spectra between the observed spectral lines instead indicate that the CO lines form at z approximate to 530-650 km in the quiet Sun. During the two hours of observations, seven long-lived cooling events (cold bubbles) were observed in CO in the region surrounding a large pore, but were not visible in the three atomic lines. These events show self-similar temporal evolution with time scales consistent with the chemical formation rate of CO at z approximate to 1000 km. Due to the lack of such features in the surrounding quiet Sun, we hypothesize that the magnetic canopy field surrounding the pore, which suppresses the upward propagation of acoustic waves into the chromosphere and the subsequent formation of shocks, depresses the rate of acoustic heating and allows CO to condense and cool the atmosphere at those heights. These cold bubbles may be a source of the chromospheric CO that produces the unexpectedly high (z approximate to 1000 km) limb extensions seen in the stronger CO lines, and may provide a unique opportunity to study this enigmatic component of the solar atmosphere in spatially resolved observations.

Automated summary

Observations suggest that carbon monoxide (CO) lines are formed at approximately 530-650 km in the quiet Sun, rather than at lower layers from the photosphere to the chromosphere. It was found that there were seven long-lived cooling events in the region surrounding a large pore, but they were not visible in the three atomic lines. These findings may be related to the magnetic canopy field surrounding the pore.