XRT: XBP
2007-11-23T11:04:32 to 2007-11-23T23:58:12
Science Goal: Synoptic SOT Irradiance Scans, Multi-point, high cadence EUV (and complementary) observations of the dynamic solar corona
Program: XBP
Target: QR
xcen=0 ycen=0
Instrument: XRT
HOP/JOP: 0
Description:
Daily Note: Weekly Meeting SOT: - Test run of HOP15 XRT: EIS: - Request 12 hours' observing of quiet Sun, tracking. Ideally with track judged to pass through DC at synoptic time, but depends on solar conditions: Network evolution with the wide slot in He II (Williams). SOT support would be good with Ca images at cadence better than 2 min if possible, with FG magnetograms (again if possible). XRT support at a similar cadence also requested with coolest filters available.
Request to XRT HOP Number 0046: Thin Al/Poly sub-field readout at each pointing position.
Other Instruments: eventual use of ACRIM and SORCE TIM irradiance measurements during analysis phase. No specific requests for coordinated operations since these instruments operate continually.
Scientific Objectives: 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.
Request to XRT HOP Number 0052: At least full disk high cadence (10s) in a single filter (Al poly) over the time period of the SOP.
Other Instruments: STEREO/SECCHI: From both A and B, full disk EUV images in a single filter (195 Angstrom say) with a cadence of at least 20-30s for 2-3 hours. Let us term this the SECCHI Observing Period (or SOP). Note that almost all other observations from STEREO would be suspended during this observing window. TRACE: Single filter to match SECCHI chosen line (195 Angstrom say) observed continuously with suitable cadence (20-30s say) during SOP. If there is a decent active region, then that would be the given target. Otherwise, quiet sun pointing at disc centre would be requested. Target position would be coordinated with SOHO/CDS and Hinode/EIS. SOHO/EIT: Full disk images in wavelength to match SECCHI (195 Angstrom say) at best possible cadence during SOP. Shutterless mode would be very welcome but author is aware that this is not undertaken very often. Images should be at full resolution (1024x1024) and if possible, synchronized with SECCHI images during SOP. SOHO/CDS: Similar to Hinode/EIS in that (a) if AR target then single slit, sit and stare observations (eg, LOOPS2D_5) somewhere over the active region loops (apex or footpoint)with an EJECT_V3 at beginning and end. Target position would be coordinated with Hinode/EIS and TRACE. or (b) if quiet sun, then suggest multiple repeats of a suitable version of EJECT_V3 on disk centre. SOHO/MDI: Full disk magnetograms at best possible cadence during SOP. If target region is within high-res fov high-res magnetograms and visible-light filtergrams with best cadence would be desired.
Scientific Objectives: The aim of this STEREO/SECCHI-led JOP is to use the singular vantage points of the STEREO spacecraft coupled to observations from SOHO, TRACE and Hinode in the Sun-Earth line to produce a unique dataset examining the time-dependent nature of the solar atmosphere. We know already that this magnetised, plasma environment is highly structured and dynamic. Here we concentrate upon two important aspects: 1. the detection and characterisation of guided wave-modes within active region loops and
2. the determination of the nature (birth, life, death) of small scale EUV brightenings. Outlining the significance of these dynamic features is beyond the scope of this short scientific justification. However, concentrating upon the importance of observing simultaneously this dynamic behaviour from several different vantage points, we see that there are some fundamental issues that could be addressed. These include: (i) for waves: It should be possible to observe the ?gsame?h propagating wave phenomena at the base of active region loops. Part of the problem with observing these oscillations on the disk from along the Sun-Earth line is that the angle of the emerging loop to the solar surface is unknown. Of course, it can be inferred indirectly from magnetic field extrapolations to a certain degree. Naturally this problem of a single viewing angle has an effect on the accurate calculation of the wave speed. Measuring this propagation speed from different viewpoints, will allow us to obtain a better-constrained value. Also, given that often the change in intensity related to these oscillations can only be 10 percent above the average intensity of the loop, the proper application of an appropriate background subtraction is very important. The different view-points should help to improve/verify the best way of doing this. (ii) for dynamic brightenings: We can ask: can we observe the ?gsame brightening?h from the three vantage points? Are there any discernable differences? If so, what are they? Does the opportunity of tracking the possible evolution of the 3D geometry of a ?glarge?h brightening help us understand their existence in the first place? Can we get obtain a rough estimate of the possible preferred height of these brightening above the limb (or are they ALL very low down in the atmosphere)? Of course, the above is certainly not an exhaustive list of what could be examined by this proposed unique dataset. In order to achieve these observations, a short, constrained (2 to 3 hour, approx. 20-30s cadence in a single filter) observing run using SECCHI/EUVI would be undertaken. This will take SECCHI out of its usual synoptic observing mode and possibly suspend all other STEREO observations during this observing period. A short test case at higher cadence (10s) for 10 minutes was undertaken on STEREO-A only in February 2007. Apart from that dataset, no other coordinated high cadence observing programme (and hence data) as suggested here exists. Thus, when these high cadence SECCHI observations are combined with observations from SOHO, TRACE and Hinode located along the Sun-Earth line, we have the capability to obtain near simultaneous observations of dynamic changes in the solar atmosphere from three lines of sight. EUV imaging in the same filter as SECCHI but from TRACE and SOHO/EIT will be requested along with complementary Hinode/XRT full disk observations. EUV spectroscopy will be undertaken by SOHO/CDS and Hinode/EIS to both increase the wavelength coverage as well as provide plasma diagnostics for the selected targets. Magnetograms from both SOHO/MDI and Hinode/SOT will provide details of the underlying photospheric magnetic field structures. The obtained time-series observations will be investigated by employing, say, wavelet analysis techniques and/or Bayesian analysed methods across the datasets.
