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Proposal ID Clette_10

Date of Proposal

Frederic Clette

Observatoire Royal de Belgique

Avenue Circulaire, 3
B-1180, Belgique




Short Title: Search for Short-term Brightness Fluctuations
in the Corona

EIT Keywords: Signatures of Coronal Heating; Coronal Waves;

Proposal: We propose to search for and characterize short-
term brightness fluctuations that may exist in spatially
resolved features of the solar corona. The emphasis of
this proposal is to search for periodic phenomena but we may
also detect aperiodic phenomena (microflares) that have
been hypothesized to heat the corona. Detection and
characterization of periodic fluctuations, such as their
location, brightness, periodicity or other measure of
spectral power density may provide information on energy
transport, deposition, and losses in the outer solar
atmosphere and hence be a discriminant for evaluating the
presence of Alfven wave in the corona and theories of
coronal heating. Lack of such detection, but observation
of counterparts to chromspheric microflares would also be a
valuable contribution to research on energy transport and
heating mechanisms.

While a simultaneous determination of spectral power in
intensity fluctuations, line width, and wavelength (Doppler
shifts) would be most desirable, ground-based data suggest
that velocity fluctuations may be only 1-2% and therefore be
marginally observable by CDS and SUMER. Two other SUMER
programs directed toward studying Doppler broadening
changes (but not intensity fluctuations) with altitude and
loop orientation (BROAD and WAVES, respectively,) have been
proposed and EIT will be able to support these programs with
appropriately targeted images.

The present proposal, on the other hand, focuses on possible
brightness fluctuations in coronal features. EUV
fluctuations of 8.6% in O IV and 5.9% in Mg X have been
reported from an active region with high EUV radiance by
Antonucci, Gabriel, and Patchett (1984) and we will attempt
to reproduce this observation.

EIT Data Required: This proposal cannot be satisfied by EIT
synoptic observations. EIT observations will need to be
taken at a high cadence rate, which implies observations, at
least initially, in only one wavelength band ( no filter
wheel changes). The program should begin with Fe IX/X
obervations, but eventally cover all four bands and several
solar regions. Data at a specific solar location should be
taken at a rate of at least twice the frequency of the
highest frequency expected. Antonucci at al. reported an
intensity periodicity of 117 s and so EIT images should be
recorded at least once a minute. A higher rate (twice a
minute, or even higher, using the EIT split image readout
would be optimum. The observations should continue for one
hour in each run and be as regular as possible to allow
analysis of Fourier components. Data rates will be
minimzed by recording only a small portion of the EIT FOV.

Other SOHO observations: The CDS and SUMER instruments may
wish to review this proposal and consider complementary

Collaborating EIT Consortium members: Delaboudiniere,
Neupert, Moses, Portier



Search for Short-term Brightness Fluctuations in the Corona

update added on 2003/02/20 at 22:19:39

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