Scientific background:
The total solar irradiance varies by about 0.1% over the course of
the solar cycle, primarily due to the influence of magnetic
structures such as sunspots and faculae on the photospheric spectral
irradiance. Short-term irradiance variation (on the scale of days-to-
months) is well understood to be due to the balance of sunspots and
facular areas as they cross the disk. However on the decadal scale of
the solar cycle, questions remain as to why the irradiance variation
can lead and/or lag the active region count over the course of the
cycle. Explanations ranging from changes in the solar diameter in
response to magnetic flux storage in the convection zone to changes
in the surface area of the photosphere due to F-mode modulation have
been put forward. Seeing-free observations of both granulation and
magnetic flux on a large range of scales are now possible with the
SOT SP/FG instrument combination. We propose to observe with SOT on a
regular basis throughout the rise of Cycle 24 in order to better
understand the variation of irradiance with rising flux levels in the
photosphere. On 07-March-2007 we performed a test program which
produced a N-S scan of the central meridian with full SP normal maps
at 12 positions. In a separate program (08-March-2007) we produced E-
W scans of the +15 and -15 deg. latitude "active region" belts with
BFI continuum filtergrams and NFI Fe I 630.25 nm magnetograms. Both
of these programs produced unique data that are not possible to
obtain from any other visible light solar instrument. If performed on
a regular basis and ultimately analyzed with the data from the total
irradiance measurement satellites such as ACRIM and SORCE, these
observations have the potential to reveal new and important aspects
of the relation between solar irradiance and magnetic flux emergence
over the solar cycle.
Objective:
Measure large-sample statistical granulation properties such as size
and contrast in three continuum bands along with both line-of-sight
and vector magnetic field measurements for a variety of disk
positions over the course of Cycle 24. Ideally we would like to have
full-disk observations of these properties, but since the SOT field-
of-view is limited, the number of disk positions observed is limited
to the number of individual pointings that are practical in one
observing period.
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