Radiative forcing by contrails

A parametric study of the instantaneous radiative impact of contrails is presented using three different radiative transfer models for a series of model atmospheres and cloud parameters. Contrails are treated as geometrically and optically thin plane parallel homogeneous cirrus layers in a static atmosphere. The ice water content is varied as a function of ambient temperature. The model atmospheres include tropical, mid-latitude, and subarctic summer and winter atmospheres. Optically thin contrails cause a positive net forcing at top of the atmosphere. At the surface the radiative forcing is negative during daytime. The forcing increases with the optical depth and the amount of contrail cover. At the top of the atmosphere, a mean contrail cover of 0.1% with average optical depth of 0.2 to 0.5 causes about 0.01 to 0.03 Wm⁻² daily mean instantaneous radiative forcing. Contrails cool the surface during the day and heat the surface during the night, and hence reduce the daily temperature amplitude. The net effect depends strongly on the daily variation of contrail cloud cover. The indirect radiative forcing due to particle changes in natural cirrus clouds may be of the same magnitude as the direct one due to additional cover.     

Estimating uncertainty associated with water stages from a single SAR image

It is the goal of remote sensing to infer information about objects or a natural process from a remote location. This invokes that uncertainty in measurement should be viewed as central to remote sensing. In this study, the uncertainty associated with water stages derived from a single SAR image for the Alzette (G.D. of Luxembourg) 2003 flood is assessed using a stepped GLUE procedure. Main uncertain input factors to the SAR processing chain for estimating water stages include geolocation accuracy, spatial filter window size, image thresholding value, DEM vertical precision and the number of river cross sections at which water stages are estimated. Initial results show that even with plausible parameter values uncertainty in water stages over the entire river reach is 2.8 m on average. Adding spatially distributed field water stages to the GLUE analysis following a one-at-a-time approach helps to considerably reduce SAR water stage uncertainty (0.6 m on average) thereby identifying appropriate value ranges for each uncertain SAR water stage processing factor. For the GLUE analysis a Nash-like efficiency criterion adapted to spatial data is proposed whereby acceptable SAR model simulations are required to outperform a simpler regression model based on the field-surveyed average river bed gradient. Weighted CDFs for all factors based on the proposed efficiency criterion allow the generation of reliable uncertainty quantile ranges and 2D maps that show the uncertainty associated with SAR-derived water stages. The stepped GLUE procedure demonstrated that not all field data collected are necessary to achieve maximum constraining. A possible efficient way to decide on relevant locations at which to sample in the field is proposed. It is also suggested that the resulting uncertainty ranges and flood extent or depth maps may be used to evaluate 1D or 2D flood inundation models in terms of water stages, depths or extents. For this, the extended GLUE approach, which copes with the presence of uncertainty in the observed data, may be adopted.     

Fluvial sedimentary history of Arlington Canyon,Channel Islands National Park,California

Arlington Canyon, in the northwest part of Santa Rosa Island, Channel Islands National Park, California, has been the setting for important scientific discoveries over the past half century, including the oldest human remains in North America, several vertebrate fossil sites, and purported evidence of a catastrophic extinction event at the end of the Pleistocene. The canyon is filled with alluvial sediments that date to between 16.4 and 1.1 ka (thousands of calibrated years before present), representing accumulation that occurred primarily in response to rising sea levels during the late Pleistocene and Holocene. The deposits are laterally discontinuous, exhibit a high degree of sedimentary complexity, and contain evidence of past climates and environments, including fossil bones, burned plant macrofossils, and invertebrate microfossils. Here, we show that it is critical to view the observations, data, and conclusions of scientific studies conducted in the canyon within this larger context so that localized facets of the spatially and temporally extensive alluvial deposits are not misinterpreted or misrepresented. By improving the baseline understanding of processes and drivers of sediment accumulation in Arlington Canyon, we hope to offer a solid foundation and better underpinning for future archeological, paleontological, and geochemical studies here and throughout the northern Channel Islands. Published 2019. This article is a U.S. Government work and is in the public domain in the USA.     

Über den schwermineralgehalt der von P. Sabban untersuchten heidesandproben

Zusammenfassung P. Sabban hat in einer 1897 erschienen Arbeit von 76 Sanden aus der südwestlichen Mecklenburgischen Heide genaue Zahlenwerte über Korngrße und Schwermineralgehalt nebst geologischen Vorkommensangaben veröffentlicht, ohne jedoch diese Datensammlung irgendwie weiter auszuwerten. Eine solche Auswertung auf statistischer Grundlage ist hier durchgeführt. Die Sande bestehen im wesentlichen aus 2 Korngrößen: 0,5–0,15 mm (d) und < 0,15 mm (e). Am häufigsten sind Sande mit d:e = 1:l. Der Schwermineralgehalt (s) ist im Mittel 0,95%.s sinkt mit steigendemd. Alle Sande mitd/e > 2 1/2 habens < 1. Bei den 47 als jüngstes Übergewehtes bezeichneten Sanden sind die Typen mitd > e häufiger. Diese zeigen ein geringeress (0,S). Die selteneren mitd <e haben ein mittlerss von 1,3. Im Mittel hat die ganze Gruppe gleichens-Gehalt wie die Dünen- und Heidesande. Es dürfte sich um eine Windsortierung handeln, bei welcher ein feinkörnigerer Anteil mit relativ höherem Schwermineralgehalt ausgeblasen wurde. Die sicher wassersortierten Talsande der Niederung um Dömitz und Boizenburg haben niedriges-Werte (0,3–0,8), die übergewehten Sande auf dem alten Diluvialplateau bei Lübthen höheres-Werte und feineres Korn. Nebenbei wird vergleichsweise aus Messungen des Verfassers die Schwermineralmenge des Strandsandes von Warnemünde als in Übereinstimmung stehend mit derjenigen des Geschiebemergels, von dem jener genetisch abzuleiten ist, nachgewiesen.     

Crustal thinning beneath the Rwenzori region, Albertine rift, Uganda, from receiver-function analysis

The Rwenzori mountains in western Uganda, with a maximum elevation of more than 5,000 m, are located within the Albertine rift valley. We have deployed a temporary seismic network on the Ugandan side of the mountain range to study the seismic velocity structure of the crust and upper mantle beneath this section of the rift. We present results from a receiver-function study revealing a simple crustal structure along the eastern rift flank with a more or less uniform crustal thickness of about 30 km. The complexity of inner-crustal structures increases drastically within the Rwenzori block. We apply different inversion techniques to obtain reliable results for the thickness of the crust. The observations expose a significantly thinner crust beneath the Rwenzori range with thickness values ranging from about 20–28 km beneath northern and central parts of the mountains. Our study therefore indicates the absence of a crustal root beneath the Rwenzori block. Beneath the Lake Edward and Lake George basins we detect the top of a layer of significantly reduced S-wave velocity at 15 km depth. This low-velocity layer may be attributed to the presence of partial melt beneath a region of recent volcanic activity.     

Zur optischen Anisotropie der Kohle

Coal macerals are often, as is well known, optically anisotropic. Recent charcoal, carboniferous fusinite and carboniferous vitrinite were measured: 1. with a special goniometer, 2. in a microscope with vertical illumination between crossed polarizers, 3. with a mica compensator. The measurements with the special goniometer and photomultiplier gave characteristic curves. The minimum of these curves is the Brewster angle, which is constant for a particular material. The value of the Brewster angle is different parallel and perpendicular to the direction of the seam respectively. While the sample is rotating (360°) in a microscope between the crossed polarizers the value of reflectivity changes in a characteristically symmetrical manner. There is good agreement with the goniometer measurement. To study the influence of absorption similar curves were produced for quartz, turmaline and vitrain. It was possible to find the retardation in a layer of vitrain by means of a very sensitive elliptical compensator. The absolute value of this retardation is extremely small, its mathematical sign coincides with the results of the other experiments.

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Am Schluß möchte ich meinem Mitarbeiter, Herrn Diplom-Physiker Peter Buchta, meinen Dank aussprechen. Er hat nicht nur die meisten hier zugrunde liegenden Messungen ausgeführt und die erläuternden Figuren gezeichnet, sondern auch durch ständige Diskussion zum Inhalt dieser Arbeit beigetragen. Zu danken habe ich ferner Frau Prof. Th. Mackowsky vom Kohleforschungs-Institut Essen-Kray sowie Herrn Dr. H. Jacob von der Bundesanstalt für Bodenforschung, Hannover, für die Überlassung spezieller Kohleproben. Mein besonderer Dank gilt der Deutschen Forschungsgemeinschaft, die durch eine Sach-Beihilfe die Durchführung der Experimente ermöglicht hat.     

Minimum friction velocity and heat transfer in the rough surface layer of a convective boundary layer

A simple model is deduced for the surface layer of a convective boundary layer for zero mean wind velocity over homogeneous rough ground. The model assumes large-scale convective circulation driven by surface heat flux with a flow pattern as it would be obtained by conditional ensemble averages. The surface layer is defined here such that in this layer horizontal motions dominate relative to vertical components. The model is derived from momentum and heat balances for the surface layer together with closures based on the Monin-Obukhov theory. The motion in the surface layer is driven by horizontal gradients of hydrostatic pressure. The balances account for turbulent fluxes at the surface and fluxes by convective motions to the mixed layer. The latter are the dominant ones. The model contains effectively two empirical coefficients which are determined such that the model's predictions agree with previous experimental results for the horizontal turbulent velocity fluctuations and the temperature fluctuations. The model quantitatively predicts the decrease of the minimum friction velocity and the increase of the temperature difference between the mixed layer and the ground with increasing values of the boundary layer/roughness height ratio. The heat transfer relationship can be expressed in terms of the common Nusselt and Rayleigh numbers, Nu and Ra, as Nu ~ Ra^{% MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaSGbaeaaca% aIXaaabaGaaGOmaaaaaaa!3779!\[{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}\]}. Previous results of the form Nu ~ Ra^{% MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaSGbaeaaca% aIXaaabaGaaG4maaaaaaa!377A!\[{1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-\nulldelimiterspace} 3}\]} are shown to be restricted to Rayleigh-numbers less than a certain value which depends on the boundary layer/roughness height ratio.     

Numerical simulation of turbulent convective flow over wavy terrain

By means of a large-eddy simulation, the convective boundary layer is investigated for flows over wavy terrain. The lower surface varies sinusoidally in the downstream direction while remaining constant in the other. Several cases are considered with amplitude up to 0.15H and wavelength ofH to 8H, whereH is the mean fluid-layer height. At the lower surface, the vertical heat flux is prescribed to be constant and the momentum flux is determined locally from the Monin-Obukhov relationship with a roughness lengthz _o=10^–4 H. The mean wind is varied between zero and 5w _*, wherew _* is the convective velocity scale. After rather long times, the flow structure shows horizontal scales up to 4H, with a pattern similar to that over flat surfaces at corresponding shear friction. Weak mean wind destroys regular spatial structures induced by the surface undulation at zero mean wind. The surface heating suppresses mean-flow recirculation-regions even for steep surface waves. Short surface waves cause strong drag due to hydrostatic and dynamic pressure forces in addition to frictional drag. The pressure drag increases slowly with the mean velocity, and strongly with /H. The turbulence variances increase mainly in the lower half of the mixed layer forU/w _*>2.     

Patterns of disaster commemoration in long‐term recovery

The postdisaster landscape is replete with memorials that help communities collectively remember destructive events and recover psychologically. Although commemoration is intrinsic to all stages of recovery, little research from the disaster‐science field engages memorial texts across disasters. Meanwhile, a rich body of work on memorials and their functions exists in the cultural geographic tradition. Drawing from this literature, the current study examines a sample of U.S.‐based memorials to discern patterns within the postdisaster commemorative landscape. This research leverages discourse analysis to interrogate the meanings and mechanics of postdisaster memory work. Findings revealing that disasters catalyze remembrances that remake places, postdisaster memorial texts construct wide‐ranging degrees of intimacy, and memorials distilling survivor memories impel community recovery differently than memorials that reconstruct imagined pasts. These identified patterns in postdisaster commemoration enable further systematic exploration of memory work in the long‐term recovery process.