Traces of Storms From the PaleoArchean Found

Sedimentology of the ∼3.3 Ga upper Mendon Formation, Barberton Greenstone Belt, South Africa

Authors:

Trower et al

Abstract:

The Mendon Formation is the uppermost unit of the 3.5–3.26 Ga Onverwacht Group in the Barberton Greenstone Belt, South Africa. It consists of a cyclic stack of komatiitic volcanic units separated by thin cherty sedimentary layers. In most areas, the uppermost Mendon Formation is a sedimentary interval characterized by black chert, banded black-and-white chert, and banded ferruginous chert, although the detailed patterns of lithofacies in different sections are more complex. Previously reported zircon U/Pb ages suggest that Mendon deposition could represent more than 70 Myr of time between ∼3334 Ma and ∼3260 Ma.

This study presents sedimentological and petrographic observations of the upper Mendon Formation from across the central part of the Barberton Greenstone Belt in order to investigate sediment sources, depositional processes, and environments of sedimentation. The dominant mode of sedimentation was quiet settling of carbonaceous grains and, in the deepest sections below storm wave base, fine ferruginous material, resulting in finely laminated black and grey chert. In situ carbonaceous laminations are rare, suggesting that benthic microbial mat growth had little direct influence on deposition. The hemipelagic background deposition was punctuated by occasional inputs of fine pyroclastic debris, formation and deposition of silica granules, and reworking by infrequent storm events. Storm deposits are represented by coarse-grained, poorly-sorted intraclast breccias, some of which include distinctive intraclasts sampling lithofacies that are not observed in situ. Despite considerable lateral variability, correlative temporal trends are resolvable in many Mendon sections: there is an upward-deepening of the overall depositional setting recorded in the oldest upper Mendon sections, consistent with the previous interpretation that Mendon time was characterized by rifting (Lowe, 1994a, 1999a). Younger Mendon cycles include thick, relatively ferruginous basal sections, interpreted to reflect the deepest water deposition. These sections are capped by black chert and silicified ashes with more evidence of disturbance and reworking by storms, reflecting gradual shoaling. This sedimentological analysis is broadly consistent with previous geochemical and tectonic analyses and provides a better picture of depositional patterns during uppermost Onverwacht time, before the distinct change in tectonic regime marked by impact spherule layer S2 and the onset of Fig Tree Group orogenesis and related siliciclastic deposition.

The Bright Storm of Uranus in 2014

Spectral analysis of Uranus' 2014 bright storm with VLT/SINFONI

Authors:

Irwin et al

Abstract:

An extremely bright storm system observed in Uranus' atmosphere by amateur observers in September 2014 triggered an international campaign to observe this feature with many telescopes across the world. Observations of the storm system in the near infrared were acquired in October and November 2014 with SINFONI on ESO's Very Large Telescope (VLT) in Chile. SINFONI is an Integral Field Unit spectrometer returning 64x64 pixel images with 2048 wavelengths. Image cubes in the H-band (1.43 - 1.87 microns) were obtained at spatial resolutions of ~0.1". The observations show that the centre of the storm feature shifts markedly with increasing altitude, moving in the retrograde direction and slightly poleward with increasing altitude. We also see a faint 'tail' of more reflective material to the immediate south of the storm, which again trails in the retrograde direction. The observed spectra were analysed with the radiative transfer and retrieval code, NEMESIS. We find that the storm is well-modelled using either two main cloud layers of a 5-layer aerosol model based on Sromovsky et al. (2011) or by the simpler two-cloud-layer model of Tice et al. (2013). The deep component appears to be due to an increase in reflectivity and altitude of the main tropospheric cloud deck at 2 - 3 bars for both models, while the upper component of the feature was modelled as being due to either a thickening of the tropospheric haze of the 2-layer model or a vertical extension of the upper tropospheric cloud of the 5-layer model, assumed to be composed of methane ice and based at the methane condensation level at 1.23 bar. During the twelve days between our sets of observations the higher-altitude component of the feature was observed to have brightened significantly and extended to even higher altitudes, while the deeper component

Do Methane Storms Drive the Dune Orientation on Titan?

Methane storms as a driver of Titan's dune orientation

Authors:

Charnay et al

Abstract:

Titan's equatorial regions are covered by eastward propagating linear dunes. This direction is opposite to mean surface winds simulated by Global Climate Models (GCMs), which are oriented westward at these latitudes, similar to trade winds on Earth. Different hypotheses have been proposed to address this apparent contradiction, involving Saturn's gravitational tides, large scale topography or wind statistics, but none of them can explain a global eastward dune propagation in the equatorial band. Here we analyse the impact of equinoctial tropical methane storms developing in the superrotating atmosphere (i.e. the eastward winds at high altitude) on Titan's dune orientation. Using mesoscale simulations of convective methane clouds with a GCM wind profile featuring superrotation, we show that Titan's storms should produce fast eastward gust fronts above the surface. Such gusts dominate the aeolian transport, allowing dunes to extend eastward. This analysis therefore suggests a coupling between superrotation, tropical methane storms and dune formation on Titan. Furthermore, together with GCM predictions and analogies to some terrestrial dune fields, this work provides a general framework explaining several major features of Titan's dunes: linear shape, eastward propagation and poleward divergence, and implies an equatorial origin of Titan's dune sand.

Are Cyclones/Hurricanes Really Getting Stronger Under Global Warming?

Validating Atmospheric Reanalysis Data Using Tropical Cyclones as Thermometers

Author:

Kossin

Abstract:

Temperatures in the upper-troposphere of the atmosphere, near the tropopause, play a key role in the evolution of tropical cyclones (TC) by controlling their potential intensity (PI), which describes the thermodynamically-based maximum TC intensity that the environment will support. Accurately identifying past trends in PI is critical for understanding the causes of observed changes in TC intensity, but calculations of PI trends using different atmospheric reanalysis products can give very different results, due largely to differences in their representation of upper-tropospheric temperatures. Without a means to verify the fidelity of the upper tropospheric temperatures, PI trends calculated from these products are very uncertain.

Here, a method is introduced to validate the upper-tropospheric temperatures in the reanalysis products by using the TCs themselves as thermometers. Using a 30-year global dataset of TC cloud-top temperatures, and three widely-utilized atmospheric reanalysis products – MERRA, ERA-Interim, and NCEP/NCAR – it is shown that storm-local upper-level temperatures in the MERRA and ERA-Interim data vary similarly to the TC cloud-top temperatures on both interannual and decadal timescales, but the NCEP/NCAR data have substantial biases that introduce an increasing trend in storm-local PI not found in the other two products. The lack of global storm-local PI trends is due to a balance between temporal increases in the mean state and the poleward migration of TCs into lower climatological PI, and has significant implications for the detection and attribution of mean TC intensity trends.

Storms Periodically Reoxygenated the Lusitanian Basin During the Sinemurian Jurassic

Spatial characterization of the late Sinemurian (Early Jurassic) palaeoenvironments in the Lusitanian Basin

Authors:

Boussaha et al

Abstract:

The upper Sinemurian of the Lusitanian Basin (Portugal) is characterized by the deposition of carbonates (dolomitic limestones, limestones), sometimes enriched in organic matter (total organic carbon up to 22%). The main goal of this study is to understand the distribution of carbonates and organic matter-rich sediments in space and time, and to characterize the context of their deposition at the basin scale. Three sections located along a proximal–distal transect in the Lusitanian Basin and dated from the oxynotum to raricostatum ammonite zones (upper Sinemurian) have been studied for their microfacies and sedimentary structures, and correlated by means of ammonite and calcareous nannofossil biostratigraphy, and sequence stratigraphy. The proximal part of the basin is dominated by carbonates whereas organic-rich sediments and marl-limestone alternations are common in the distal part. Microfacies analysis shows a trend from high- to low-energy environments, which reflects a deepening trend in most of the basin within the raricostatum ammonite Zone. A forced regression took place in the earliest Pliensbachian, which is likely related to tectono-eustasy. This particular surface can be correlated at the regional level, to several basins of the western Tethys.

The presence of black shales in the distal part of the basin and of framboidal pyrite in the proximal part is interpreted as resulting from an episode of pervasive dysoxia/anoxia at the basin scale during this time interval. The basin recorded conditions varying from dysoxic/anoxic phases in times of water column stratification, to full oxygenation in times of intense mixing by storms, attested by the presence of storm-related sedimentary structures in some carbonate-rich deposits. The occurrence of upper Sinemurian sediments rich in organic matter in other basins, in England and Spain, in the same time interval (upper Sinemurian, raricostatum ammonite Zone) suggests that palaeoclimatic and palaeogeographic conditions were prone to the development of a supraregional dysoxia/anoxia.

Powerful, Destructive Tropical Cyclones Moving North and South,

Powerful, destructive tropical cyclones are now reaching their peak intensity farther from the equator and closer to the poles, according to a new study co-authored by an MIT scientist.

The results of the study, published today in the journal Nature, show that over the last 30 years, tropical cyclones — also known as hurricanes or typhoons — are moving poleward at a rate of about 33 miles per decade in the Northern Hemisphere and 38 miles per decade in the Southern Hemisphere.

"The absolute value of the latitudes at which these storms reach their maximum intensity seems to be increasing over time, in most places," says Kerry Emanuel, an MIT professor and co-author of the new paper. "The trend is statistically significant at a pretty high level."

And while the scientists who conducted the study are still investigating the atmospheric mechanisms behind this change, the trend seems consistent with a warming climate.

"It may mean the thermodynamically favorable conditions for these storms are migrating poleward," adds Emanuel, the Cecil and Ida Green Professor of Earth and Planetary Sciences at MIT.

The implications are serious, since the movement of peak intensity means regions further north and south of the equator, which have not previously had to face many landfalls by violent cyclones, may now have greater exposure to these extreme weather events. That, in turn, could lead to "potentially profound consequences to life and property," the paper states. "Any related changes to positions where storms make landfall will have obvious effects on coastal residents and infrastructure."

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Tropical Cyclones Warm Ocean, May Cause Positive Feedback Cycle

Sea surface height evidence for long-term warming effects of tropical cyclones on the ocean

Authors:

1. Wei Mei (a)
2. François Primeau (a)
3. James C. McWilliams (b)
4. Claudia Pasquero (c)

Affiliations:

a. Department of Earth System Science, University of California, Irvine, CA 92697;

b. Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA 90095; and

c. Department of Earth and Environmental Sciences, University of Milan-Bicocca, I-20126 Milan, Italy

Abstract:

Tropical cyclones have been hypothesized to influence climate by pumping heat into the ocean, but a direct measure of this warming effect is still lacking. We quantified cyclone-induced ocean warming by directly monitoring the thermal expansion of water in the wake of cyclones, using satellite-based sea surface height data that provide a unique way of tracking the changes in ocean heat content on seasonal and longer timescales. We find that the long-term effect of cyclones is to warm the ocean at a rate of 0.32 ± 0.15 PW between 1993 and 2009, i.e., ∼23 times more efficiently per unit area than the background equatorial warming, making cyclones potentially important modulators of the climate by affecting heat transport in the ocean–atmosphere system. Furthermore, our analysis reveals that the rate of warming increases with cyclone intensity. This, together with a predicted shift in the distribution of cyclones toward higher intensities as climate warms, suggests the ocean will get even warmer, possibly leading to a positive feedback.

Model Predicts Less Storms like Sandy

Model projections of atmospheric steering of Sandy-like superstorms

Authors:

1. Elizabeth A. Barnes (a,b)
2. Lorenzo M. Polvani (b,c)
3. Adam H. Sobel (b,c)

Affiliations:

a. Department of Atmospheric Science, Colorado State University, Fort Collins, CO 80523;

b. Division of Ocean and Climate Physics, Lamont-Doherty Earth Observatory, Palisades, NY 10964; and

c. Department of Applied Physics and Applied Mathematics and Department of Earth and Environmental Sciences, Columbia University, New York, NY 10027

Abstract:

Superstorm Sandy ravaged the eastern seaboard of the United States, costing a great number of lives and billions of dollars in damage. Whether events like Sandy will become more frequent as anthropogenic greenhouse gases continue to increase remains an open and complex question. Here we consider whether the persistent large-scale atmospheric patterns that steered Sandy onto the coast will become more frequent in the coming decades. Using the Coupled Model Intercomparison Project, phase 5 multimodel ensemble, we demonstrate that climate models consistently project a decrease in the frequency and persistence of the westward flow that led to Sandy’s unprecedented track, implying that future atmospheric conditions are less likely than at present to propel storms westward into the coast.

Time Lapse of Sandy Hitting Manhattan