New Video: Dr. Murry Salby – ‘He was fired from his university for pointing out holes in the global warming story’
Nature Geoscience. doi:10.1038/ngeo2423
Author: Claire Newman
Titan's equatorial dunes seem to move in the opposite direction to the prevailing easterly winds. Infrequent methane storms at Titan's low latitudes may briefly couple surface winds to fast westerlies above, dominating the net movement of sand.
Nature Geoscience. doi:10.1038/ngeo2399
Authors: Dake Chen, Tao Lian, Congbin Fu, Mark A. Cane, Youmin Tang, Raghu Murtugudde, Xunshu Song, Qiaoyan Wu & Lei Zhou
Nature Geoscience. doi:10.1038/ngeo2406
Authors: Benjamin Charnay, Erika Barth, Scot Rafkin, Clément Narteau, Sébastien Lebonnois, Sébastien Rodriguez, Sylvain Courrech du Pont & Antoine Lucas
The equatorial regions of Saturn’s moon Titan are covered by linear dunes that propagate eastwards. Global climate models (GCMs), however, predict westward mean surface winds at low latitudes on Titan, similar to the trade winds on Earth. This apparent contradiction has been attributed to Saturn’s gravitational tides, large-scale topography and wind statistics, but none of these hypotheses fully explains the global eastward propagation of dunes in Titan’s equatorial band. However, above altitudes of about 5 km, Titan’s atmosphere is in eastward super-rotation, suggesting that this momentum may be delivered to the surface. Here we assess the influence of equatorial tropical methane storms—which develop at high altitudes during the equinox—on Titan’s dune orientation, using mesoscale simulations of convective methane clouds with a GCM wind profile that includes super-rotation. We find that these storms produce fast eastward gust fronts above the surface that exceed the normal westward surface winds. These episodic gusts generated by tropical storms are expected to dominate aeolian transport, leading to eastward propagation of dunes. We therefore suggest a coupling between super-rotation, tropical methane storms and dune formation on Titan. This framework, applied to GCM predictions and analogies to some terrestrial dune fields, explains the linear shape, eastward propagation and poleward divergence of Titan’s dunes, and implies an equatorial origin of dune sand.
Nature Geoscience. doi:10.1038/ngeo2412
Authors: F. Javier Martín-Torres, María-Paz Zorzano, Patricia Valentín-Serrano, Ari-Matti Harri, Maria Genzer, Osku Kemppinen, Edgard G. Rivera-Valentin, Insoo Jun, James Wray, Morten Bo Madsen, Walter Goetz, Alfred S. McEwen, Craig Hardgrove, Nilton Renno, Vincent F. Chevrier, Michael Mischna, Rafael Navarro-González, Jesús Martínez-Frías, Pamela Conrad, Tim McConnochie, Charles Cockell, Gilles Berger, Ashwin R. Vasavada, Dawn Sumner & David Vaniman
Water is a requirement for life as we know it. Indirect evidence of transient liquid water has been observed from orbiter on equatorial Mars, in contrast with expectations from large-scale climate models. The presence of perchlorate salts, which have been detected at Gale crater on equatorial Mars by the Curiosity rover, lowers the freezing temperature of water. Moreover, perchlorates can form stable hydrated compounds and liquid solutions by absorbing atmospheric water vapour through deliquescence. Here we analyse relative humidity, air temperature and ground temperature data from the Curiosity rover at Gale crater and find that the observations support the formation of night-time transient liquid brines in the uppermost 5 cm of the subsurface that then evaporate after sunrise. We also find that changes in the hydration state of salts within the uppermost 15 cm of the subsurface, as measured by Curiosity, are consistent with an active exchange of water at the atmosphere–soil interface. However, the water activity and temperature are probably too low to support terrestrial organisms. Perchlorates are widespread on the surface of Mars and we expect that liquid brines are abundant beyond equatorial regions where atmospheric humidity is higher and temperatures are lower.
Nature Geoscience. doi:10.1038/ngeo2405
Authors: Cheng Li & Andrew P. Ingersoll