CHROMOSPHERIC DYNAMICS BASED ON INFRARED SOLAR BRIGHTNESS VARIATIONS

We used the NASA Kuiper Airborne Observatory to observe far-infrared continuum brightness fluctuations in the lower chromosphere due to solar 5 minute oscillations on the quiet Sun. Brightness measurements made at 50, 100, 200, and 400-mu-m show a strong correlation with visible-line Doppler measurements from photospheric and chromospheric altitudes. The motion of the chromosphere is nearly in phase over a large range of heights, while the infrared brightness lags the Doppler velocity by phases varying from significantly less than 90-degrees at low altitudes to nearly 90-degrees at higher altitudes. We propose that this is the result of a nonadiabatic response of the chromospheric gas to compression and may indicate an important mechanism for wave dissipation. We estimate thermal relaxation times ranging from about 40 s at 340 km above the tau-5000 = 1 photosphere to approximately 300 s at 600 km.