SOTSP: HOP79 irradiance scans
2016-10-14T21:23:00 to 2016-10-14T21:39:35
Science Goal: Synoptic SOT Irradiance Scans
Program: Normal map 30 arcsec, Shorter Irradiance: DO NOT MODIFY!
Target: Quiet Sun
xcen=-22 ycen=-378
Instrument: SOTSP
HOP/JOP: 79
Description:
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. In addition, work by Shiozu and Tsuneta has shown that HOP 79 N-S scan scan data can be used to infer the latitudinal temperature variation between the equator and the poles thus offering constraints on "thermal wind" theories of convection zone rotational profiles. This finding has prompted a change in the E-W pointing scans to include a disk-center scan in order to better calibrate the N-S scans (see Remarks section below).
