Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsh23b0364d&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #SH23B-0364
Physics
7507 Chromosphere, 7509 Corona, 7526 Magnetic Reconnection (2723, 7835), 7546 Transition Region, 7549 Ultraviolet Emissions
Scientific paper
We study the dynamical interaction of the solar chromosphere with the transition region (TR) in mossy and non-mossy active region plage, and find evidence for correlated brightness changes or upward travelling disturbances between the low chromosphere and the upper transition region. We carefully align image sequences taken with the Transition Region and Coronal Explorer (TRACE) in the ultraviolet passbands around 1550, 1600 and 1700 Å\ (indicative of low chromosphere and low TR) and the extreme ultraviolet passbands at 171 and 195 Å\ (indicative of upper transition region). We compute Fourier phase-difference spectra that are spatially averaged separately over mossy and non-mossy plage to study temporal modulations as a function of temporal frequency. We find that in non-mossy plage there is zero phase difference between 1550 Å\ and 171 Å. In mossy plage, the phase differences between all UV and EUV passbands show pronounced upward trends with increasing frequency, which abruptly changes into zero phase differences for frequencies beyond 4-6 mHz. The phase difference between the 171 and 195 Å\ sequences exhibits a shallow dip below 3 mHz and then also turns to zero phase difference beyond this value. We attribute some of the various similarities between the UV and EUV diagnostics that are evident in the phase-difference diagrams to the contribution of the C IV resonance lines in the 1550 and 1600 Å\ passbands. The strong upward trend at lower frequencies in the phase difference between all UV passbands (including 1700 Å) and 171 Å\ indicates the presence of upward travelling disturbances. Since 1700 Å\ does not contain C IV emission (low TR), this points to a correlation between brightness changes in the lower chromosphere and the upper TR, perhaps by slow-mode disturbances, or by a connection between chromospheric and coronal heating mechanisms. We find that such correlated brightness changes first occur in the low chromosphere, and are followed about 400 s later in the upper TR. The transition from the upward trend in phase difference at low frequencies to zero phase difference at higher frequencies is due to the intermittent obscuration by fibrils. These chromospheric jets occult the footpoints of hot loops, which are bright in the EUV and C IV lines, in oscillatory manner.
de Pontieu Bart
de Wijn Alfred G.
Rutten Robert J.
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