DYNAMICS OF THE SOLAR CHROMOSPHERE .1. LONG-PERIOD NETWORK OSCILLATIONS

We analyze differences in solar oscillations between the chromospheric network and internetwork regions from a 1 hr sequence of spectrograms of a quiet region near disk center. The spectrograms contain Ca II H, Ca I 422.7 nm, and various Fe I blends in the Ca II H wing. They perm it vertical tracing of oscillations throughout the photosphere and int o the low chromosphere. We find that the rms amplitude of Ca II H line center Doppler fluctuations is approximately 1.5 km s-1 for both netw ork and internetwork, but that the character of the oscillations diffe rs markedly in these two regions. Within internetwork areas the chromo spheric velocity power spectrum is dominated by oscillations with freq uencies at and above the acoustic cutoff frequency. They are well corr elated with the oscillations in the underlying photosphere, but they a re much reduced in the network. In contrast, the network Ca II H line center velocity and intensity power spectra are dominated by low-frequ ency oscillations with periods of 5-20 minutes. Their signature is muc h clearer in our Ca II H line center measurements than in previously u sed diagnostics which are contaminated by signals from deeper layers. We find that these long-period oscillations are not correlated with un derlying photospheric disturbances, and we discuss their nature.