GRL Highlights

Eleven papers have made it to become the Geophysical Research Letters highlights. Those with particular reference to astrophysical matters include papers 1 and 5.

Paper 1 looks at the effect of solar forcing on the atmosphere with respect to a grand minimum. The minimum refers to solar cycles, which we see as increasing and then suddenly vanishing amounts of sunspots. During this period of time, which lasts on average eleven years, the magnetic field of the Sun gets twisted and the plasma environment near the Sun gets more choppy. Then it all reorders and goes quiet for a short time. Except once or twice it hasn’t, it has gone quiet for a long time. One example is the Maunder Minimum, which lasted from 1645 to 1715, roughly. There was a slight drop in solar output, the aurorae were confined to thin ovals and sunspots all but vanished. Recently, the very deep minimum the Sun went into was thought to be one way global warming could be offset as a grand minimum would suggest lower radiation levels for a long time. This paper aimed to quantify that and decided if a minimum lasted until 2100, there would be a cooling effect of 0.3 degrees. Unfortunately, warming over the same period would be higher, meaning a prolongued minimum would not be able to offset it. Furthermore since the Sun does come out of such grand minima after several decades, the cooling would switch off too. The paper can be accessed by subscribers here. “On the effect of a new grand minimum of solar activity on the future climate on Earth” by Georg Feulner and Stefan Rahmstorf.

Meanwhile paper 5 looks at the minimagnetosphere of the Moon. Unlike the Earth, the Moon has no global magnetic field to deflect the solar wind. Indeed the wind striking the surface and reacting with the chemicals there is responsible for the recent detection of amounts of water on the surface. But evidence is presented here for the Moon having magnetic anomalies like Mars, whose own dynamo shut down billions of years ago. The Indian space agency’s Chandrayaan-1 satelite had an instrument that observed low energy hydrogen atoms that bounce from the surface due to solar wind protons slamming into it and a small number exchanging charge with surface chemicals. At one point, not only did they discover an absence of the faster low energy hydrogen atoms (those above 150 eV), but the plasma instruments detected a sheath of higher density charged particle flows – the solar wind getting channeled around the shielded area. On top of this, an as yet unexplained observation was that low energy hydrogen atoms were still emitted from this region. The minimagnetosphere was 360 km wide and surrounded by a 300 km thick region where the plasma was channeled away to. The events occurred at the magnetic anomaly near the Crisium antipode. The paper, for subscribers only, is here. “First observation of a mini-magnetosphere above a lunar magnetic anomaly using energetic neutral atoms” by Martin Wieser, Stas Barabash, Yoshifumi Futaana, Mats Holmström, Anil Bhardwaj, R. Sridharan, M. B. Dhanya, Audrey Schaufelberger, Peter Wurz and Kazushi Asamura.

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