The Solar Activity Monitor Network-SAMNet

61 The Solar Activity Magnetic Monitor (SAMM) Network (SAMNet) is a future UK-led interna62 tional network of ground-based solar telescope stations. SAMNet, at its full capacity, will con63 tinuously monitor the Sun’s intensity, magnetic and Doppler velocity fields at multiple heights 64 in the solar atmosphere (from photosphere to upper chromosphere). Each SAMM sentinel will be 65 equipped with a cluster of identical telescopes each with different magneto-optical filter (MOFs) to 66 take observations in K I, Na D and Ca I spectral bands. A subset of SAMM stations will have white67 light coronagraphs and emission line coronal spectropolarimeters. The objectives of SAMNet are 68 to provide observational data for the space weather research and forecast. The goal is to achieve an 69 operationally sufficient lead time of e.g. flare warning of 2-8 hours, and provide much sought-after 70 continuous synoptic maps (e.g., LoS magnetic and velocity fields, intensity) of the lower solar at71 mosphere with a spatial resolution limited only by seeing or diffraction limit, and with a cadence 72 of 10 minutes. The individual SAMM sentinels will be connected into their master HQ hub where 73 data received from all the slave stations will be automatically processed and flare warning issued 74 up to 26 hrs in advance. 75


Introduction
diverging motions prior to the flare, which is illustrated with a red "U"-shaped parabolic curve in 226 the lower panel of Fig. 1a. This "U"-shaped precursor allows to estimate the expected onset time of 227 flare in a δ-type AR. 228 In summary, applying the WG M -method to photospheric data only yields an about 7 hrs gain in 229 lead time. Here, at this point, we wish to emphasise that achieving this progress is made by em-230 ploying a relatively low spatial resolution (of the order of an arcsec) that is typical for ground-based 231 observatories, as would be expected from e.g. SAMNet as a lower limit, routinely monitoring 232 the solar surface with a cadence of as low as about an hour. SAMNet will have, however, a bet- 233 ter cadence at about 10 mins for a fixed wavelength that enables then a more accurate flare 234 warning. In this section, we support the efforts that rely on how robust space weather forecasting, using LoS 237 magnetic data, can be against resolution issues, i.e. how suitable a ground-based seeing-limited 238 instrumentation is. We show that downgrading the HMI data does not really influence the skills 239 cores/probabilities of forecasting.  Based on these possible outcomes, the true skill score (TSS) (Eq 1) is considered as the index to 262 evaluate the model performance.

264
The performance of forecasting models built on magnetograms with different spatial resolutions 265 is shown in Fig. 3 Figure 4 illustrates the three-dimensional magnetic field of AR 11166 (left) and AR 12192 (right), 303 respectively, using the PF method described above. At horizontal crosscuts corresponding to  where this gap will be closed up by SAMNet. Figure 5 shows the application of the WG M method to     Fig. 7. A schematic illustration of the complete MOF instrument for photospheric observations. Collimated sunlight passes through a two-stage filtering process. The filter section consists of an atomic vapour subject to an axial magnetic field placed between crossed polarisers. The temperature of the vapour and the strength of the magnetic field are chosen to achieve a suitable narrow transmission profile -with two wings -centred on the atomic resonance. The second vapour cell and quarter waveplate are used to encode the transmission of the opposite handedness of circularly polarised light into vertical and horizontally polarised light, which are subsequently imaged by cameras CMOS1 and 2, respectively. (3 2 S 1/2 → 3 2 P 3/2 ), i.e. atomic resonance. Typically, the spectrum has two wings, in Fig. 8 (b), split 403 from the atomic resonance by the Zeeman effect. The wing blue-detuned from the atomic reso-404 nance, i.e. the wing on the left of 0 mÅ in Fig. 8 (b), is referred to as the blue wing (B) and the wing 405 on the right of 0 mÅ is known as the red wing (R).

406
Depending on the application, the transmission through the filter section MOF can be tailored to 407 give desirable features. For solar chromospheric observations, a transmission that has a single peak 408 centered on the atomic transition is required (Fig. 8 (a)), whereas, for both Doppler-and magnetic-409 field observations, a transmission that has two wings is necessary (Fig. 8 (b)). The transmission 410 shape and passband can be tailored by choosing appropriate filter section MOF parameters -soft-411 ware has been developed by Yang et al. (2011) to optimize these parameters, which agree with 412 experimental transmission profiles as shown in Fig. 8.

413
For photospheric observations, where a filter section MOF transmission with two wings is nec-414 essary, a second MOF is required to extinguish the unwanted wing. This is referred to as the "Wing  Using these four images, the velocity v LoS and magnetic field B LoS in line-of-sight can be derived: Measuring v LoS and B LoS serve as strong boundary conditions for modelling solar magnetic fields, 426 particularly in the lower region of the solar atmosphere where the magnetic field is highly non-427 force-free.  with two peaks were employed to observe the Sun. Fig. 9a shows a test magnetic skeleton of two    Table 1 for the line, wavelength, formation 542 height range and diffraction limit).   , is plotted in c) for varying magnetic field strength. Note that optical rotations of the order, or greater than, π are generated for these parameters, as is necessary for efficient atomic filtering. In d) the transmission profile is calculated for each of the associated Faraday rotation angles in c). The characteristic two-wing spectral profile is evident.  Table 1), it is clear that SAMM would produce superior, 587 multi-height synoptic LoS magnetograms.

588
A calcium filter section MOF (see Fig. 7 for descriptor reference) was simulated utilising the Ca 589 (4p 1 P 1 − 4s 1 S 0 ) strong transition at 422 nm, using an axial magnetic field strength of B = 0.04 T, 590 a cell length of 50 mm and a vapour temperature of T = 720 K (Fig. 14). As outlined in sec- . Figure 14 a)   SAMNet is now a UK-led international network with its scientific and observing HQ at Gyula The flare and CME onset warning is based on the WG M method as outlined in Sec. 2, while 643 the CME arrival will be predicted routinely using a new tool, CME Arrival Time Prediction using  Fig. 15. Potential host sites for future SAMNet sentinels (see Table 2 for further facility details). The blue marks highlight sentinels with about 5-8 hrs time zone differences to indicate where a coronagraph could be added as 4th OTA. Yellow marks are potential future expansion sites.
using multiple instruments. These sentinels will be connected to form a global network to provide toring, mount, tracking, optics, MOF detectors, camera, data acquisition, processing, data transmis-673 sion, remote control and automation).

674
As described in Sec. 5.1, the existing prototype has two unit telescopes with two SAMM MOF units 675 observing the K I and Na D lines. The sentinels used by SAMNet will expand on this to hold at 676 least three such unit telescopes, including the existing K and Na units alongside the proposed Ca

677
MOF under development (see Sec. 5.2.1). The unit telescopes will be aligned to point at the same 678 position, and small guide camera will also be mounted on-axis to ensure the mount reliably tracks 679 the Sun. The potential exists to expand this modular design to include a forth unit telescope, either 680 holding another MOF unit (e.g. He 1083) or a coronagaph-mounted spectrograph.

681
It is proposed that the SAMNet sentinels will use a similar hardware to their prototype: an array of 682 Celestron OTAs with Baader ND filters, attached to an Astelco mount. The mount may vary subject 683 to the local circumstances at a given station location. By using off-the-shelf hardware as much as 684 possible costs can be reduced and focused on improving the performance of the MOF instruments.

685
The complete SAMNet sentinel node will also include a robotic dome and weather-monitoring 686 stations, to ensure the dome remains closed when the weather is poor. Each SAMNet sentinel will be fully-automated, using custom software that autonomously manages 689 the telescope hardware and daily operations. The proposed system will be based on the control sys- to form a global network. The control software will comprise of multiple independent control dae-694 mons which are supervised by a master control program known as the "pilot". An initial design for 695 the core software architecture is shown in Fig. 16.

696
The primary elements of the control system will be the hardware daemons. A daemon is com-