OSCILLATIONS ABOVE SUNSPOT UMBRAE

Long time series of two dimensional filtergrams of the chromosphere above a sunspot in the line cores of H alpha (lambda 656.2nm), CaIIK (lambda 393.3nm) and in MgIb (lambda 517.3nm) were recorded simultaneously The following conclusions can be drawn: The Power spectra of Ha and CaIIK show two distinct distributions between 5 and 9 mHz. The first peak at 5.9 mHz is relatively narrow (FWHM = 1.2 mHz) and consists mainly of upward propagating waves travelling with sound speed (7 km/sec). There are indications that the oscillations found in this frequency domain have their origin in the underlaying layers. Therefore this first distribution may be a fingerprint of the photospheric resonator. A phase analysis of the horizontal propagations of the oscillations yields a typical inclination of the magnetic field lines in the umbral chromosphere of 5 degrees. A second distribution at 7.5 mHz has a width of 3.3 mHz. The involved oscillations have characteristics of standing waves. There is no correlation between the oscillations found in the chromosphere and these, located near the temperature minimum layers, so they are confined to the chromosphere itself.