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Auroral brightening is one of the most common phenomena that occur during substorm onset and is usually recognized as a projection of the substorm‐associated magnetospheric plasma dynamics to the ionosphere. However, electromagnetic fields and plasma features associated with the substorm brightening arc have not been well understood. In this study, we present a comprehensive observation of the source plasma and field variations of a substorm brightening aurora in the inner magnetosphere. We performed a unique conjugate observation of a substorm brightening auroral arc observed by a ground‐based camera and by the Arase satellite in the magnetospheric source region at L ∼ 6. The event was observed at Tromsø (69.6°N, 19.2°E), Norway, on 12 October 2017. The brightening arc indicates east‐west structures with longitudinal scales of ∼0.5°–2.0°. Field‐aligned bi‐directional electrons with an energy range between 66 and 1,800 eV were detected by the satellite, simultaneously with the appearance of the brightening arc in the camera. These electrons were probably supplied from the auroral brightening region in the ionosphere, indicating that the satellite was on the same field line of the brightening aurora. The magnetic and electric field data show characteristic fluctuations and earthward Poynting flux around the time that the satellite crossed the aurora. Anti‐phase oscillations between the thermal pressure and the magnetic pressure are also reported. Based on these observations, we suggest the possibility that a ballooning instability occurred in the source region of the substorm brightening arc in the inner magnetosphere at L ∼ 6. Plain Language Summary: A frequently occurring source of variations in the magnetosphere is the substorm, a process that causes energy dissipation into the atmosphere. Substorm is presented as the development of aurorae at high latitudes in the ionosphere. The study of substorm processes helps in understanding the near‐Earth space environment and the space weather. Along Earth's magnetic field lines, the aurora at a latitude of ∼65°N can be traced to ∼4–7 Earth radii away from the Earth at the equatorial plane in space. Using a ground‐based auroral camera, we can construct the correspondence between auroral motion and field and plasma variation at the satellite. This study reports such a unique event of substorm brightening arc observed at Tromsø, Norway, on 12 October 2017. Satellite observed bi‐directional electrons prove the connection between aurora break‐up at ∼100 km altitude and its source region in the magnetosphere at ∼30,000 km away from Earth. Based on the magnetic wave spectrograms, auroral bead‐like structures and other observational results, we suggest the possibility that a ballooning plasma instability occurred in the source region of the substorm brightening arc in the inner magnetosphere. Key Points: Observation of plasma and field features in the source region of a sudden brightening auroral arc during a minor substorm onset at L ∼ 6Energization of particles, field‐aligned electrons, and electromagnetic field fluctuations were observed during the arc crossing by AraseSeveral observational facts indicate the possibility of ballooning instability occurring at this substorm onset [ABSTRACT FROM AUTHOR]

Characterization of caprock shale is critical in CO2 storage site evaluation because the caprock shale acts as a barrier for the injected buoyant CO2 plume. The properties of shales are complex and influenced by various processes; hence, it is challenging to evaluate the caprock quality. An integrated approach is therefore necessary for assessing seal integrity. In this study, we investigated the caprock properties of the Lower Jurassic Drake Formation shales from the proposed CO2 storage site Aurora (the Longship/Northern Lights CCS project), located in the Horda Platform area, offshore Norway. Wireline logs from 50 exploration wells, various 2D seismic lines, and two 3D seismic cubes were used to investigate the variations of the caprock properties. The Drake Formation was subdivided into upper and lower Drake units based on the lithological variations observed. Exhumation and thermal gradient influencing the caprock properties were also analyzed. Moreover, rock physics diagnostics were carried out, and caprock property maps were generated using the average log values to characterize the Drake Formation shales. In addiiton, pre-stack seismic-inverted properties and post-stack seismic attributes were assessed and compared to the wireline log-based analysis. The sediment source controlled at 61° N significantly influenced the depositional environment of the studied area, which later influenced the diagenetic processes and had various caprock properties. The upper and lower Drake units represent similar geomechanical properties in the Aurora area, irrespective of significant lithological variations. The Drake Formation caprock shale near the injection site shows less-ductile to less-brittle brittleness values. Based on the caprock thickness and shaliness in the Aurora injection site, Drake Formation shale might act as an effective top seal. However, the effect of injection-induced pressure changes on caprock integrity needs to be evaluated. [ABSTRACT FROM AUTHOR]

• The Drake caprock shale possesses a relatively low brittleness indices value representing a ductile caprock. • A formation specific geomechanical properties range is proposed, which broadens the brittleness indices range hence higher resolution. • An initial basin-specific brittleness template has been proposed to evaluate NCS top seal shales. • The integrated caprock characterization workflow indicated the usefulness and viability of assessing any site-specific top seal. Evaluating top seal integrity is crucial for successful subsurface CO 2 storage. Caprock shale geomechanical properties are complex and influenced by various parameters and processes. It is challenging to understand the role of various factors affecting the geomechanical properties; therefore, an integrated approach is required to evaluate top seal shales. In this study, we investigated the caprock properties of the Early Jurassic shaly Drake Formation overlying the reservoir sandstones of Early Jurassic Cook and Johansen formations. The study area is the potential CO 2 storage site Aurora (the Longship CCS project), located in the Horda Platform area, offshore Norway. Based on lithological variations, the Drake Formation is subdivided into upper and lower Drake units. Variations of the geomechanical properties are investigated using wireline logs from 50 exploration wells, two 3D seismic cubes, and several 2D seismic lines. Elastic property-based brittleness indices of the Drake Formation caprock shales are evaluated to identify possible top seal quality. Moreover, seismic attributes and gas leakage scenarios are investigated qualitatively to assess the possibility of injected CO 2 escaping from the reservoir. Low brittleness indices value of the Drake Formation shale near the Aurora injection site indicated that the seal rock might diffuse the injection-related stress change and act as an effective top seal. Based on the integrated qualitative assessment, it is likely that the Drake caprock shale will be acted as an effective top seal in and around the Aurora storage site. However, due to the complex nature of caprock shales, we recommend field-scale numerical simulation to evaluate the injection-induced stress-strain effect. [ABSTRACT FROM AUTHOR]

Abstract: Current dayside optical studies of Aurora Australis from the Amundsen-Scott Research Station at the South Pole (74 degrees magnetic latitude) show some striking differences from optical results reported from Svalbard. A 6-channel meridian scanning photometer operating during the past three austral winters shows, in particular, the 630nm emission is much lower, on average, than the Arctic dayside aurora and very weak on some days. The 558nm intensity is higher relative to 630nm suggesting the incoming electrons have a higher average energy. There are notable differences in auroral forms, giving further evidence of asymmetries in the two dayside ovals. [Copyright &y& Elsevier]