Table 1.
Scientific requirements for the OSCAR mission.
| Objective | Top level requirements | Second level requirements |
|---|---|---|
| 1 – Trigger mechanism(s) of CMEs in AR and their forecasting indices | Stereographic view of coronal loops at different heights in the lower corona | The separation angle shall be between 22 and 125°, as close to 68 degrees as possible (Fig. 1) |
| Capture the time scale of flares and of the triggering sequence of strong CMEs | Time resolution of 5 s for coronal loop images | |
| Resolve distinct coronal loops in ARs | Spatial resolution better than 500 km in the solar upper transition region | |
| Synchronised stereographic images to ensure a proper 3D reconstruction during the eruption process | The two spacecraft shall be synchronised with a precision of 0.1 s | |
| Observe the photospheric vector magnetic field in ARs | Spatial resolution better than 750 km, with a precision of 0.1 G for the longitudinal field and 20 G for the transverse field | |
| The duration of OSCAR shall ensure high statistics for the CME triggering | The duration of the mission shall be no less than 5 years | |
| 2.a – Provide data for the forecast of geo-affecting CMEs | Track geo-directed CMEs over the whole Sun-Earth distance | Observations from the lower corona to 1 AU shall be possible |
| Determine the shape, direction and velocity of the leading edge of the CME (common with 2.b) | The cadence shall be of 2 h and stereoscopic view shall be availablea | |
| Sufficient data to forecast the arrival time of all geo-directed CMEs | The data shall enable a 2-day forecast updated every 6 h | |
| 2.a – Provide data for the forecast of geo-effective CIRs | In-situ measurements of geo-affecting CIRs before they reach Earth | One spacecraft shall be positioned on a keplerian orbit close to 1 AU following Earth |
| Guarantee sufficient warning time | Minimal separation between the Earth-following spacecraft and Earth of 29.7° (warning time of 2.25 days) | |
| In-situ measurements of the magnetic field (common with 2.b) | The vector magnetic field shall be measured within the range ±200 nT with an accuracy of 0.1 nT and an operational time resolution of 1 minb | |
| Measurement of the in-situ solar wind proton plasma parameters (speed, temperature, density; common with 2.b) | The solar wind protons shall be measured up to a speed of 1000 km/s (with a 5% accuracy) with an operational time resolution of 1 minb | |
| 2.b – Measure the propagation and spatial expansion of CMEs out to 1 AU | Measure continuously the plasma parameters and the magnetic field at 1 AU (in CMEs and CIRs) | The solar wind proton speed, temperature and density, the electron 3D velocity distribution, prominent ion charge states of C, O, Si, Fe and magnetic field shall be measured every 15 minc |
| Measure high energetic electrons accelerated at CME shock fronts close to the Sun | The energetic electrons passing the spacecraft at 1 AU in the range 40 keV–300 keV shall be measured every minuted,e | |
| 2.b – Measure the evolution of CIR spatial structures at 1 AU | Remote-sensing and tracking of CIRs within one Carrington rotation | CIRs shall be monitored in the heliosphere over an elongation angle of 150° over 20 days (brightness sensitivity <3 × 10−16 the solar brightness)f |
| Multi-point observations at 1 AU to detect changes in the structure of CIRs within one Carrington rotation | Minimum seperation angle of 66° in longitude to catch major longitudinal changes, latitudinal separation <5°g | |
| Measure low energetic ion events accelerated at CIR shock fronts at or beyond 1 AU | The protons and alpha particles in the energy range 50 keV–4 MeV shall be measured every minuted,g |
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