Solar Phys (2018) 293:87
A Long-Term Dissipation of the EUV He
Segmentation in Full-Disk Solar Images
Received: 2 January 2018 / Accepted: 24 April 2018
© Springer Science+Business Media B.V., part of Springer Nature 2018
Abstract Some quiet-Sun days observed by the Atmospheric Imaging Assembly (AIA) on-
board the Solar Dynamics Observatory (SDO) during the time interval in 2010 – 2017 were
used to continue our previous analyses reported by Didkovsky and Gurman (Solar Phys.
289, 153, 2014a) and Didkovsky, Wieman, and Korogodina (Solar Phys. 292, 32, 2017).
The analysis consists of determining and comparing spatial spectral ratios (spectral den-
sities over some time interval) from spatial (segmentation-cell length) power spectra. The
ratios were compared using modeled compatible spatial frequencies for spectra from the
Extreme ultraviolet Imaging Telescope (EIT) on-board the Solar and Heliospheric Obser-
vatory (SOHO) and from AIA images. With the new AIA data added to the EIT data we
analyzed previously, the whole time interval from 1996 to 2017 reported here is approxi-
mately the length of two “standard” solar cycles (SC). The spectral ratios of segmentation-
cell dimension structures show a signiﬁcant and steady increase with no detected indication
of SC-related returns to the values that characterize the SC minima. This increase in spa-
tial power at high spatial frequencies is interpreted as a dissipation of medium-size EUV
network structures to smaller-size structures in the transition region. Each of the latest ratio
changes for 2010 through 2017 spectra calculated for a number of consecutive short-term
intervals has been converted into monthly mean ratio (MMR) changes. The MMR values
demonstrate variable sign and magnitudes, thus conﬁrming the solar nature of the changes.
These changes do not follow a “typical” trend of instrumental degradation or a long-term
activity proﬁle from the He
(30.4 nm) irradiance measured by the Extreme ultraviolet
Spectrophotometer (ESP) either. The ESP is a channel of the Extreme ultraviolet Variability
Experiment (EVE) on-board SDO.
Keywords Solar irradiance · Solar cycle, observations · Granulation
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