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The distribution of cloud and precipitation properties across oceanic extratropical cyclone cold fronts is examined using four years of combined CloudSat radar and CALIPSO lidar retrievals. The global annual mean cloud and precipi...
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The distribution of cloud and precipitation properties across oceanic extratropical cyclone cold fronts is examined using four years of combined CloudSat radar and CALIPSO lidar retrievals. The global annual mean cloud and precipitation distributions show that low-level clouds are ubiquitous in the postfrontal zone while higher-level cloud frequency and precipitation peak in the warm sector along the surface front. Increases in temperature and moisture within the cold front region are associated with larger high-level but lower mid-/low-level cloud frequencies and precipitation decreases in the cold sector. This behavior seems to be related to a shift from stratiform to convective clouds and precipitation. Stronger ascent in the warm conveyor belt tends to enhance cloudiness and precipitation across the cold front. A strong temperature contrast between the warm and cold sectors also encourages greater post-cold-frontal cloud occurrence. While the seasonal contrasts in environmental temperature, moisture, and ascent strength are enough to explain most of the variations in cloud and precipitation across cold fronts in both hemispheres, they do not fully explain the differences between Northern and Southern Hemisphere cold fronts. These differences are better explained when the impact of the contrast in temperature across the cold front is also considered. In addition, these large-scale parameters do not explain the relatively large frequency in springtime postfrontal precipitation.
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The bone histology of non-avian dinosaurs is enlightening for understanding many aspects of the growth and development of these long-extinct animals. The rate of bone apposition and remodelling in the shaft of long bones appears t...
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The bone histology of non-avian dinosaurs is enlightening for understanding many aspects of the growth and development of these long-extinct animals. The rate of bone apposition and remodelling in the shaft of long bones appears to be accelerated in some groups and decelerated in others. We propose a developmental model to illustrate these fundamental aspects of long bone diaphyseal histology at different growth stages. We developed the model based on an ontogenetic series of long bones of the sauropod dinosaur Apatosaurus. The model describes the histology and microanatomy based on three fronts that move radially: the apposition front, the Haversian substitution front, and the resorption front. When applied to additional sauropod dinosaurs, differences and similarities observed in the microstructure of the different taxa could be explained with the model. The benefit of this model is that it is not limited to Sauropoda but appears to be applicable to a broad range of terrestrial amniote long bones and thus could provide unique insights into life history and evolutionary patterns of bone development
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A detailed analysis of the Southland Front, a shelf-break system off the southeast coast of South Island, New Zealand is presented. The position, temperature, temperature range and width of the front are determined using a new sta...
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A detailed analysis of the Southland Front, a shelf-break system off the southeast coast of South Island, New Zealand is presented. The position, temperature, temperature range and width of the front are determined using a new statistical front detection algorithm and 21 years worth of Advanced Very High Resolution Radiometer satellite sea surface temperature (SST) data. Overall, the front is strongest (highest SST gradients) in the summer and winter, and the across front gradient decreases northward in all seasons, consistent with an equatorward decrease in stability and divergence of isobaths. The surface expression of the front moves further offshore during the winter months and is found closest inshore in the summer. Seasonality of the front is strongly controlled by the annual cycle of subtropical and subantarctic water mass temperatures. Both the temperature and strength of the front are interannually variable, and correlated with the El Ni?o-Southern Oscillation (ENSO); they both decrease during El Ni?o, and increase during La Ni?a events. ENSO indices lead changes in the fronts temperature by up to 6 months. Conversely, the gradient may change up to 6 months in advance of peak ENSO indices. The strength and sign of correlations is seasonally dependent.
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In this study two commonly used automated methods to detect atmospheric fronts in the lower troposphere are compared in various synoptic situations. The first method is a thermal approach, relying on the gradient of equivalent pot...
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In this study two commonly used automated methods to detect atmospheric fronts in the lower troposphere are compared in various synoptic situations. The first method is a thermal approach, relying on the gradient of equivalent potential temperature (TH), while the second method is based on temporal changes in the 10 m wind (WND). For a comprehensive objective comparison of the outputs of these methods of frontal identification, both schemes are firstly applied to an idealised strong baroclinic wave simulation in the absence of topography. Then, two case-studies (one in the Northern Hemisphere (NH) and one in the Southern Hemisphere (SH)) were conducted to contrast fronts detected by the methods. Finally, we obtain global winter and summer frontal occurrence climatologies (derived from ERA-Interim for 1979-2012) and compare the structure of these. TH is able to identify cold and warm fronts in strong baroclinic cases that are in good agreement with manual analyses. WND is particularly suited for the detection of strongly elongated, meridionally oriented moving fronts, but has very limited ability to identify zonally oriented warm fronts. We note that the areas of the main TH frontal activity are shifted equatorwards compared to the WND patterns and are located upstream of regions of main WND front activity. The number of WND fronts in the NH shows more interseasonal variations than TH fronts, decreasing by more than 50% from winter to summer. In the SH there is a weaker seasonal variation of the number of observed WND fronts, however TH front activity reduces from summer (DJF) to winter (JJA). The main motivation is to give an overview of the performance of these methods, such that researchers can choose the appropriate one for their particular interest.
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Ocean front plays an important role in marine fishery production and biogeochemical cycling. This letter proposes a multiscale deep framework to meet the need for automatic ocean front detection and fine-grained location. The fram...
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Ocean front plays an important role in marine fishery production and biogeochemical cycling. This letter proposes a multiscale deep framework to meet the need for automatic ocean front detection and fine-grained location. The framework mainly focuses on bringing a well-trained deep learning model into front detection and location on the global satellite sea surface temperature image. First, a multiscale scanner is designed to divide the ocean into small areas of different scales. Then, we introduce the deep model to determine that a front has occurred, and translate the global image into binary ones of various grained. Here, an overlapping scanning way is suggested to locate the front in a small region. Finally, all the binary images are scale-weighted fused into one image, which presents the center and periphery with different brightness levels. Experimental illustrations on three typical areas of the ocean are featured with six scanning scales to show the effectiveness and practical use of the proposed framework. Moreover, the comparison experiments with the traditional method also show its advantages.
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The geographical position of the Arctic front and two branches of the Polar front over Europe was determined during the period 1995-2015 using calculated grid fields of the thermal frontal parameter in the troposphere layer of 850...
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The geographical position of the Arctic front and two branches of the Polar front over Europe was determined during the period 1995-2015 using calculated grid fields of the thermal frontal parameter in the troposphere layer of 850-700 hPa. It was revealed that the geographical position of climatological fronts changed both in the cold and warm periods of the year in comparison with climate data. The most recent standard reference period of 1961-1990 recommended by WMO (WMO, 2017) was used for comparison. It is shown that in January there was a shift of the northern and southern branches of the Polar front to the north compared to the reference climate period, and in July the convergence of both branches of the Polar front in the middle latitudes was observed. The Arctic front was characterized by a northern location compared to the climate in both January and July. It is revealed that the main areas of frontogenesis in the cold period of the year were the sea surface, namely. the southern regions of the Norwegian Sea, the central part of the Baltic Sea, and the western half of the Mediterranean Sea. In the summer, more active atmospheric fronts were over the continent in the area of the mountain systems such as the south of the Scandinavian mountains, the north of the Alps and Pyrenees, the Urals, and the lower Volga region. The Arctic front intensified over the Barents and Norwegian Seas in all seasons of the year.
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The subarctic-subtropical transition area of the western North Pacific is an important summer feeding grounds of sei whales. The oceanographic structure and circulation of this area are largely determined by strong oceanic fronts ...
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The subarctic-subtropical transition area of the western North Pacific is an important summer feeding grounds of sei whales. The oceanographic structure and circulation of this area are largely determined by strong oceanic fronts and associated geostrophic currents, namely the Polar Front (PF), Subarctic Front (SAF) and Kuroshio Extension Front (KEF). The relationship between the distribution of sei whales and oceanographic fronts was investigated using a generalized additive model (GAM), and the cetacean sighting survey data and oceanographic observations in July from 2000 to 2007 were used in the analysis. The number of individual sei whales was used as the response variable while the distances from the PF, SAF, and KEF to the whales were used as explanatory variables along with the longitude values. Sei whales were concentrated north and south of the SAF and the areas from 250 to 300 km north and from 100 to 200 km south of the SAF were estimated as high-density areas of sei whales. The entire inter-frontal zone between the PF and SAF featured an elevated concentration of sei whales, and the area south of the PF and along the SAF was identified as an important feeding ground of sei whales in July from 2000 to 2007.
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This study introduces a detailed and objective classification for midlatitude maritime fronts. The classification is based on a principal component analysis (PCA) to determine the dominant patterns of variability between fronts. H...
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This study introduces a detailed and objective classification for midlatitude maritime fronts. The classification is based on a principal component analysis (PCA) to determine the dominant patterns of variability between fronts. Here, fronts are defined as three-dimensional frontal volumes, which are detected in the ERA-Interim dataset for a large number of locations in the Atlantic, Pacific and Indian oceans during both winter and summer. In addition to the well-established distinction between warm and cold fronts, the PCA exposes several new dimensions of variability: (i) front intensity, (ii) surface fluxes and (iii) along-front transports, linked to the intensity of the associated conveyor belts. These new dimensions of variability are regionally and seasonally robust and a lagged composite analysis demonstrates that each of the new front types evolves in a dynamically characteristic way. Further, the new front types can be related to established ones like katafronts and anafronts. The new front types are finally redefined based on simple parameter thresholds to simplify their application in future studies.
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Many fronts over the UK do not fit the traditional conceptual model of a single maximum of vertical shear of the horizontal wind sloped over the cold air. A 2-year climatology of 296 cold, warm, and occluded fronts from a mesosphe...
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Many fronts over the UK do not fit the traditional conceptual model of a single maximum of vertical shear of the horizontal wind sloped over the cold air. A 2-year climatology of 296 cold, warm, and occluded fronts from a mesosphere–stratosphere–troposphere radar near Aberystwyth, Wales, reveals that 74% of warm fronts were associated with multiple linear bands representing maxima of vertical wind shear, radar return signal power, or both. In contrast, 51% of cold fronts lacked any such maxima. Similarly, the warm frontal segments of occluded fronts exhibited more banding than the cold frontal segments. Copyright ? 2011 Royal Meteorological Society
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Models describing microscopic or mesoscopic phenomena in physics are inherently discrete, where the lattice spacing between fundamental components, such as in the case of atomic sites, is a fundamental physical parameter. The effe...
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Models describing microscopic or mesoscopic phenomena in physics are inherently discrete, where the lattice spacing between fundamental components, such as in the case of atomic sites, is a fundamental physical parameter. The effect of spatial discreteness over front propagation phenomenon in an overdamped one-dimensional periodic lattice is studied. We show here that the study of front propagation leads in a discrete description to different conclusions that in the case of its, respectively, continuous description, and also that the results of the discrete model, can be inferred by effective continuous equations with a supplementary spatially periodic term that we have denominated Peierls-Nabarro drift, which describes the bifurcation diagram of the front speed, the appearance of particle-type solutions and their snaking bifurcation diagram. Numerical simulations of the discrete equation show quite good agreement with the phenomenological description. This journal is
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