Conference paper or proceedings

Phase And Time Lags Between G-band, H-line And Magnetic Fluctuations In The Photosphere And Chromosphere

"We study the oscillatory power in two sequences of high-cadence, high-resolution images taken by the SOT on board Hinode. The sequences consist of simultaneous, co-registered G-Band (GB), Ca II H-Line (HL), and the absolute value of line-of-sight magnetic field (|B|) images, with pixel scale 80 km and fields of view 40 x 40 Mm and 80 x 40 Mm. The first sequence has cadence 21 s over 3 hours on 2007 April 14; the other has cadence 24 s over 2 hours on 2007 March 30. Both sequences include network and internetwork at heliocentric angle 35 degrees. We investigate phase relations between fluctuations of pairs of the three data sets as functions of their common frequencies. The height Z1 of the ""magnetic canopy,” where plasma beta equal 1, is estimated via a potential field extrapolation and the VAL 3C model atmosphere. The phase shifts at each frequency are taken as the maxima of normalized histograms made by binning the phase shifts for all space-time pixels segregated by high or low Z1. We interpret the phase shifts as a constant phase shift plus a constant time shift. For Z1 > 1.3 Mm G leads H with a constant time lag of 10 sec for frequencies above the acoustic cut-off, suggesting propagating acoustic waves. For Z1 < 1.15 Mm the time lag between the G and H signals is smaller. Both G and H lead the |B| fluctuations by a constant phase shift of 100 degrees for all Z1. For Z1 < 1.15 G also leads |B| by 3±1 sec and H trails |B| by 6±1 sec. For Z1 > 1.3 Mm these time lags disappear. Thus we can locate an effective ""height” of |B| about 20 km above GB and of HL about 40 km above |B|."