ALBERT

Description: Recently, it has been established that interplanetary coronal mass ejections (ICMEs) can dramatically affect both trapped electron fluxes in the outer radiation belt and precipitating electron fluxes lost from the belt into the atmosphere. Precipitating electron fluxes and energies can vary over a range of timescales during these events. These variations depend on the initial energy and location of the electron population and the ICME characteristics and structures. One important factor controlling electron dynamics is the magnetic field orientation within the ejecta that is an integral part of the ICME. In this study, we examine Van Allen Probes (RBSPs) and Polar Orbiting Environmental Satellites (POESs) data to explore trapped and precipitating electron fluxes during two ICMEs. The ejecta in the selected ICMEs have magnetic cloud characteristics that exhibit the opposite sense of the rotation of the north–south magnetic field component (BZ). RBSP data are used to study trapped electron fluxes in situ, while POES data are used for electron fluxes precipitating into the upper atmosphere. The trapped and precipitating electron fluxes are qualitatively analysed to understand their variation in relation to each other and to the magnetic cloud rotation during these events. Inner magnetospheric wave activity was also estimated using RBSP and Geostationary Operational Environmental Satellite (GOES) data. In each event, the largest changes in the location and magnitude of both the trapped and precipitating electron fluxes occurred during the southward portion of the magnetic cloud. Significant changes also occurred during the end of the sheath and at the sheath–ejecta boundary for the cloud with south to north magnetic field rotation, while the ICME with north to south rotation had significant changes at the end boundary of the cloud. The sense of rotation of BZ and its profile also clearly affects the coherence of the trapped and/or precipitating flux changes, timing of variations with respect to the ICME structures, and flux magnitude of different electron populations. The differing electron responses could therefore imply partly different dominant acceleration mechanisms acting on the outer radiation belt electron populations as a result of opposite magnetic cloud rotation.

Description: In this study, the new source of O(1D) in the mesopause region due to the process OH(ν≥5)+O(3P)→OH(0≤ν′≤ν-5)+O(1D) is applied to SABER data to estimate the nighttime O(1D) distributions for the years 2003–2005. It is found that O(1D) evolutions in these years are very similar to each other. Depending on the month, monthly averaged O(1D) distributions show two to four maxima with values up to 340 cm−3 which are localized in height (at ∼92–96 km) and latitude (at ∼20–40 and ∼60–80∘ S, N). Annually averaged distributions in 2003–2005 have one weak maximum at ∼93 km and ∼65∘ S with values of 150–160 cm−3 and three pronounced maxima (with values up to 230 cm−3) at ∼95 km and ∼35∘ S, at ∼94 km and ∼40∘ N and at ∼93 km and ∼65–75∘ N, correspondingly. In general, there is slightly more O(1D) in the Northern Hemisphere than in the Southern Hemisphere. The obtained results are a useful data set for subsequent estimation of nighttime O(1D) influence on the chemistry of the mesopause region.

Description: Forecasting the thermosphere (the atmosphere's uppermost layer, from about 90 to 800 km altitude) is crucial to space-related applications, from space mission design to re-entry operations, space surveillance and more. Thermospheric dynamics is directly linked to the solar dynamics through the solar UV (ultraviolet) input, which is highly variable, and through the solar wind and plasma fluxes impacting Earth's magnetosphere. The solar input is non-periodic and non-stationary, with long-term modulations from the solar rotation and the solar cycle and impulsive components, due to magnetic storms. Proxies of the solar input exist and may be used to forecast the thermosphere, such as the F10.7 radio flux and the Mg II EUV (extreme-ultraviolet) flux. They relate to physical processes of the solar atmosphere. Other indices, such as the Ap geomagnetic index, connect with Earth's geomagnetic environment. We analyse the proxies' time series comparing them with in situ density data from the ESA (European Space Agency) GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) gravity mission, operational from March 2009 to November 2013, therefore covering the full rising phase of solar cycle 24, exposing the entire dynamic range of the solar input. We use empirical mode decomposition (EMD), an analysis technique appropriate to non-periodic, multi-scale signals. Data are taken at an altitude of 260 km, exceptionally low for a low-Earth-orbit (LEO) satellite, where density variations are the single most important perturbation to satellite dynamics. We show that the synthesized signal from optimally selected combinations of proxy basis functions, notably Mg II for the solar flux and Ap for the plasma component, shows a very good agreement with thermospheric data obtained by GOCE, during periods of low and medium solar activity. In periods of maximum solar activity, density enhancements are also well represented. The Mg II index proves to be, in general, a better proxy than the F10.7 index for modelling the solar flux because of its specific response to the UV spectrum, whose variations have the largest impact over thermospheric density.

Description: We present multi-period modulation of energetic electron flux observed by the BeiDa Imaging Electron Spectrometer (BD-IES) on board a Chinese navigation satellite on 13 October 2015. Electron flux oscillations were observed at a dominant period of ∼190 s in consecutive energy channels from ∼50 to ∼200 keV. Interestingly, flux modulations at a secondary period of ∼400 s were also unambiguously observed. The oscillating signals at different energy channels were observed in sequence, with a time delay of up to ∼900 s. This time delay far exceeds the oscillating periods, by which we speculate that the modulations were caused by localized ultra-low-frequency (ULF) waves. To verify the wave–particle interaction scenario, we revisit the classic drift-resonance theory. We adopt the calculation method therein to derive the electron energy change in a multi-period ULF wave field. Then, based on the modeled energy change, we construct the flux variations to be observed by a virtual spacecraft. The predicted particle signatures well agree with the BD-IES observations. We demonstrate that the particle energy change might be underestimated in the conventional theories, as the Betatron acceleration induced by the curl of the wave electric field was often omitted. In addition, we show that azimuthally localized waves would notably extend the energy width of the resonance peak, whereas the drift-resonance interaction is only efficient for particles at the resonant energy in the original theory.

Description: Nature Geoscience 6, 828 (2013). doi:10.1038/ngeo1931 Authors: Shang-Ping Xie, Bo Lu & Baoqiang Xiang Spatial variations in ocean warming have been linked to regional changes in tropical cyclones, precipitation and monsoons. But development of reliable regional climate projections for climate change mitigation and adaptation remains challenging. The presence of anthropogenic aerosols, which are highly variable in space and time, is thought to induce spatial patterns of climate response that are distinct from those of well-mixed greenhouse gases. Using CMIP5 climate simulations that consider aerosols and greenhouse gases separately, we show that regional responses to changes in greenhouse gases and aerosols are similar over the ocean, as reflected in similar spatial patterns of ocean temperature and precipitation. This similarity suggests that the climate response to radiative changes is relatively insensitive to the spatial distribution of these changes. Although anthropogenic aerosols are largely confined to the Northern Hemisphere, simulations that include aerosol forcing predict decreases in temperature and westerly wind speed that reach the pristine Southern Hemisphere oceans. Over land, the climate response to aerosol forcing is more localized, but larger scale spatial patterns are also evident. We suggest that the climate responses induced by greenhouse gases and aerosols share key ocean–atmosphere feedbacks, leading to a qualitative resemblance in spatial distribution.

Description: Nature Geoscience 6, 856 (2013). doi:10.1038/ngeo1928 Authors: Chloé Michaut, Yanick Ricard, David Bercovici & R. Steve J. Sparks Eruptions at active silicic volcanoes are often cyclical. For example, at the Soufrière Hills volcano in Montserrat, Mount Pinatubo in the Philippines, and Sakurajima in Japan, episodes of intense activity alternate with repose intervals over periods between several hours and a day. Abrupt changes in eruption rates have been explained with the motion of a plug of magma that alternatively sticks or slides along the wall of the volcanic conduit. However, it is unclear how the static friction that prevents the plug from sliding is periodically overcome. Here we use two-phase flow equations to model a gas-rich, viscous magma ascending through a volcanic conduit. Our analyses indicate that magma compaction yields ascending waves comprised of low- and high-porosity bands. However, magma ascent to lower pressures also causes gas expansion. We find that the competition between magma compaction and gas expansion naturally selects pressurized gas waves with specific periods. At the surface, these waves can induce cyclical eruptive behaviour with periods between 1 and 100 hours, which compares well to the observations from Soufrière Hills, Mount Pinatubo and Sakurajima. We find that the period is insensitive to volcano structure, but increases weakly with magma viscosity. We conclude that observations of a shift to a longer eruption cycle imply an increase in magma viscosity and thereby enhanced volcanic hazard.

Description: Nature Geoscience 6, 866 (2013). doi:10.1038/ngeo1933 Authors: Suzanne M. Carbotte, Milena Marjanović, Helene Carton, John C. Mutter, Juan Pablo Canales, Mladen R. Nedimović, Shuoshuo Han & Michael R. Perfit The global mid-ocean ridge is segmented in its seafloor morphology and magmatic systems, but the origin of and relationships between this tectonic and magmatic segmentation are poorly understood. At fast-spreading ridges, tectonic segmentation is observed on a fine scale, but it is unclear whether this partitioning also occurs in the magmatic system. Fine-scale tectonic segmentation could have a deep origin, arising from the distribution of upwelling mantle melt, or a shallow origin, linked to offset intruding dikes from long, more continuous crustal reservoirs. Here we use seismic reflection data from the fast-spreading East Pacific Rise, between 8° 20′ N and 10° 10′ N, which includes a unique area where two documented volcanic eruptions have occurred, to image the crustal magma bodies in high resolution. We find that the magma reservoirs form 5- to 15-km-long segments that coincide with the fine-scale tectonic segmentation at the seafloor and that three lens segments fed the recent eruptions. Transitions in composition, volume and morphology of erupted lavas coincide with disruptions in the lens that define magmatic segments. We conclude that eruptions at the East Pacific Rise are associated with the vertical ascent of magma from lenses that are mostly physically isolated, leading to the eruption of distinct lavas at the surface that coincide with fine-scale tectonic segmentation.

Description: Nature Geoscience 6, 871 (2013). doi:10.1038/ngeo1911 Authors: Judith A. Coggon, Ambre Luguet, Geoffrey M. Nowell & Peter W. U. Appel Partial melting of the Earth’s mantle is a key process in the generation of crustal material and the formation of continents. Crustal samples record the generation of crust up to 4.4 billion years (Gyr) ago, yet the complementary record in the mantle extends to only 3.3 Gyr ago, with sparse evidence for differentiation occurring 3.9–4.1 Gyr ago. Here we use the Pt–Os isotope chronometer to show that a Hadean record of mantle depletion is preserved in Earth’s oldest known ultramafic rocks, the Ujaragssuit Nunât intrusion of southwest Greenland. We identify two distinct age populations at approximately 4.1 and 2.9 Gyr. We suggest that the younger age population records a regional metamorphic event and the older one records mantle depletion. We also identify individual sample ages of up to 4.36 Gyr old, thus extending the record of large mantle-melting events into the Hadean. Furthermore, the preservation of Hadean model ages in Os-rich mantle-derived rocks supports the theory that re-enrichment of Os in the mantle during the Late Heavy Bombardment—after expected partitioning into the Earth’s core—occurred at least 0.2 Gyr earlier than previously thought. This also implies that the Earth could have been habitable by 4.1 Gyr ago.

Description: Nature Geoscience 6, 875 (2013). doi:10.1038/ngeo1903 Authors: Jun Wu & Peter R. Buseck A significant fraction of Earth’s carbon resides in the mantle, but the mode of carbon storage presents a long-standing problem. The mantle contains fluids rich in carbon dioxide and methane, carbonate-bearing melts, carbonate minerals, graphite, diamond and carbides, as well as dissolved carbon atoms in metals. However, it is uncertain whether these can sufficiently account for the total amount of carbon thought to be stored in the mantle and the volume of carbon degassed from the mantle at volcanoes. Moreover, such carbon hosts should significantly affect the physical and chemical behaviour of the mantle, including its melting temperature, electrical conductivity and oxidation state. Here we use in situ transmission electron microscopy to measure the storage of carbon within common mantle mineral analogues—nickel-doped lanthanum chromate perovskite and titanium dioxide—in laboratory experiments at high pressure and temperature. We detect elevated carbon concentrations at defect sites in the nanocrystals, maintained at high pressures within annealed carbon nanocages. Specifically, our experiments show that small stacking faults within the mantle analogue materials are effective carbon sinks at mantle conditions, potentially providing an efficient mechanism for carbon storage in the mantle. Furthermore, this carbon can be readily released under lower pressure conditions, and may therefore help to explain carbon release in volcanic eruptions.

Description: Nature Geoscience 6, 885 (2013). doi:10.1038/ngeo1922 Authors: Lars Möller, Todd Sowers, Michael Bock, Renato Spahni, Melanie Behrens, Jochen Schmitt, Heinrich Miller & Hubertus Fischer