Dispersion in Neptune’s zonal wind velocities from NIR Keck AO observations in July 2009     

Patrick J. Fitzpatrick  Imke de Pater  Statia Luszcz-Cook  Michael H. Wong  Heidi B. Hammel 《Astrophysics and Space Science》2014,350(1):65-88

We report observations of Neptune made in H-(1.4–1.8 μm) and K’-(2.0–2.4 μm) bands on 14 and 16 July 2009 from the 10-m W.M. Keck II Telescope using the near-infrared camera NIRC2 coupled to the Adaptive Optics (AO) system. We track the positions of 54 bright atmospheric features over a few hours to derive their zonal and latitudinal velocities, and perform radiative transfer modeling to measure the cloud-top pressures of 50 features seen simultaneously in both bands. We observe one South Polar Feature (SPF) on 14 July and three SPFs on 16 July at ～65?°S. The SPFs observed on both nights are different features, consistent with the high variability of Neptune’s storms. There is significant dispersion in Neptune’s zonal wind velocities about the smooth Voyager wind profile fit of Sromovsky et al. (Icarus, 105:140, 1993), much greater than the upper limit we expect from vertical wind shear, with the largest dispersion seen at equatorial and southern mid-latitudes. Comparison of feature pressures vs. residuals in zonal velocity from the smooth Voyager wind profile also directly reveals the dominance of mechanisms over vertical wind shear in causing dispersion in the zonal winds. Vertical wind shear is not the primary cause of the difference in dispersion and deviation in zonal velocities between features tracked in H-band on 14 July and those tracked in K’-band on 16 July. Dispersion in the zonal velocities of features tracked over these short time periods is dominated by one or more mechanisms, other than vertical wind shear, that can cause changes in the dispersion and deviation in the zonal velocities on timescales of hours to days.  相似文献   

Particle Retention in a Submerged Meadow and Its Variation Near the Leading Edge     

Elizabeth Follett  Heidi Nepf 《Estuaries and Coasts》2018,41(3):724-733

The retention of particles within meadows of submerged aquatic vegetation impacts the fate of organic matter, pollen, and larvae. Because flow conditions near the leading edge differ from those over the bulk of the canopy, particle retention is likely to differ as well. In particular, near the leading edge of a wide meadow, flow deceleration generates a vertical updraft, which impacts particle fate. In the fully developed region of the meadow, shear layer vortices at the top of the meadow may also influence particle fate. In this study, the retention of particles was measured along the length of a 10-m model meadow (height h?=?0.1 m) and was connected to the evolving flow field. Two particle sizes, with settling velocity w _s50?=?0.00075?,?0.018 m s^?1, were released at two heights within the model meadow \( \left(\frac{Z_{rel}}{h}=0.31,0.81\right). \) The retention of particles was measured using microscope slides distributed along the flume bed. Retention increased with distance from the leading edge, associated with the decrease in vertical updraft. Retention was also greater for the particles with higher settling velocity. In the fully developed region of the meadow, particle retention was lower for particles influenced by the shear layer vortices at the top of the meadow (\( \frac{Z_{rel}}{h}=0.81 \)).  相似文献   

Seasonal controls on sediment transport and deposition in Lake Ohau,South Island,New Zealand: Implications for a high‐resolution Holocene palaeoclimate reconstruction          下载免费PDF全文

Heidi A. Roop  Gavin B. Dunbar  Richard Levy  Marcus J. Vandergoes  Alexander L. Forrest  Sharon L. Walker  Jennifer Purdie  Phaedra Upton  James Whinney 《Sedimentology》2015,62(3):826-844

Laminated sediments in Lake Ohau, Mackenzie Basin, New Zealand, offer a potential high‐resolution climate record for the past 17 kyr. Such records are particularly important due to the relative paucity of detailed palaeoclimate data from the Southern Hemisphere mid‐latitudes. This paper presents outcomes of a study of the sedimentation processes of this temperate lake setting. Hydrometeorological, limnological and sedimentological data were collected over a 14 month period between 2011 and 2013. These data indicate that seasonality in the hydrometeorological system in combination with internal lake dynamics drives a distinct seasonal pattern of sediment dispersal and deposition on a basin‐wide scale. Sedimentary layers that accumulate proximal to the lake inflow at the northern end of the lake form in response to discrete inflow events throughout the year and display an event stratigraphy. In contrast, seasonal change in the lake system controls accumulation of light (winter) and dark (summer) laminations at the distal end of the lake, resulting in the preservation of varves. This study documents the key processes influencing sediment deposition throughout Lake Ohau and provides fundamental data for generating a high‐resolution palaeoclimate record from this temperate lake.  相似文献   

Probabilities of future VEI ≥ 2 eruptions at the Central American Volcanic Arc: a statistical perspective based on the past centuries’ eruption record     

Yvonne Dzierma  Heidi Wehrmann 《International Journal of Earth Sciences》2014,103(7):2029-2042

A probabilistic eruption forecast is provided for seven historically active volcanoes along the Central American Volcanic Arc (CAVA), as a pivotal empirical contribution to multi-disciplinary volcanic hazards assessment. The eruption probabilities are determined with a Kaplan–Meier estimator of survival functions, and parametric time series models are applied to describe the historical eruption records. Aside from the volcanoes that are currently in a state of eruptive activity (Santa María, Fuego, and Arenal), the highest probabilities for eruptions of VEI ≥ 2 occur at Concepción and Cerro Negro in Nicaragua, which are likely to erupt to 70–85 % within the next 10 years. Poás and Irazú in Costa Rica show a medium to high eruption probability, followed by San Miguel (El Salvador), Rincón de la Vieja (Costa Rica), and Izalco (El Salvador; 24 % within the next 10 years).  相似文献   

Using Multiple Grids in Markov Mesh Facies Modeling     

Odd Kolbjørnsen  Marita Stien  Heidi Kjønsberg  Bjørn Fjellvoll  Petter Abrahamsen 《Mathematical Geosciences》2014,46(2):205-225

A multigrid Markov mesh model for geological facies is formulated by defining a hierarchy of nested grids and defining a Markov mesh model for each of these grids. The facies probabilities in the Markov mesh models are formulated as generalized linear models that combine functions of the grid values in a sequential neighborhood. The parameters in the generalized linear model for each grid are estimated from the training image. During simulation, the coarse patterns are first laid out, and by simulating increasingly finer grids we are able to recreate patterns at different scales. The method is applied to several tests cases and results are compared to the training image and the results of a commercially available snesim algorithm. In each test case, simulation results are compared qualitatively by visual inspection, and quantitatively by using volume fractions, and an upscaled permeability tensor. When compared to the training image, the method produces results that only have a few percent deviation from the values of the training image. When compared with the snesim algorithm the results in general have the same quality. The largest computational cost in the multigrid Markov mesh is the estimation of model parameters from the training image. This is of comparable CPU time to that of creating one snesim realization. The simulation of one realization is typically ten times faster than the estimation.  相似文献   

A review of multiple natural hazards and risks in Germany     

Heidi Kreibich  Philip Bubeck  Michael Kunz  Holger Mahlke  Stefano Parolai  Bijan Khazai  James Daniell  Tobia Lakes  Kai Schröter 《Natural Hazards》2014,74(3):2279-2304

Although Germany is not among the most hazard-prone regions of the world, it does experience various natural hazards that have caused considerable economic and human losses in the past. Moreover, risk due to natural hazards is expected to increase in several regions of Germany if efficient risk management is not able to accommodate global changes. The most important natural hazards, in terms of past human and economic damage they caused, are storms, floods, extreme temperatures and earthquakes. They all show a pronounced spatial and temporal variability. In the present article, a review of these natural hazards, associated risks and their management in Germany is provided. This review reveals that event and risk analyses, as well as risk management, predominantly focus on one single hazard, generally not considering the cascading and conjoint effects in a full multi-hazard and risks approach. However, risk management would need integrated multi-risk analyses to identify, understand, quantify and compare different natural hazards and their impacts, as well as their interactions.  相似文献   

Estimating the Instantaneous Drag–Wind Relationship for a Horizontally Homogeneous Canopy     

Ying Pan  Marcelo Chamecki  Heidi M. Nepf 《Boundary-Layer Meteorology》2016,160(1):63-82

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LAMOST Experiment for Galactic Understanding and Exploration （LEGUE） The survey＇s science plan     

Li-Cai Deng  Heidi Jo Newberg  Chao Liu  Jeffrey L. Carlin  Timothy C. Beers  Li Chen  Hsu-Tai Lee  Carl J. Grillmair  Puragra Guhathakurta  Zhan-Wen Han  Jin-Liang Hou  Sebastien Lepine  Jing Li  Xiao-Wei Liu  Kai-Ke Pan  J. A. Sellwood  Bo Wang  Hong-Chi Wang  Fan Yang  Brian Yanny  Hao-Tong Zhang  Yue-Yang Zhang  Zheng Zheng  Zi Zhu 《天体物理学报》2012,(7):735-754

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An algorithm for preferential selection of spectroscopic targets in LEGUE     

Jeffrey L. Carlin  Sebastien Lepine  Heidi Jo Newberg  Li-Cai Deng  Timothy C. Beers  Yu-Qin Chen  Norbert Christlie  Xiao-Ting Fu  Shuang Gao  Carl J. Grillmair  PuragraGuhathakurta  Zhan-Wen Han  Jin-Liang Hou  Hsu-Tai Lee  Jing Li  Chao Liu  Xiao-Wei Liu  Kai-Ke Pan  J. A. Sellwood  Hong-Chi Wang  Fan Yang  Brian Yanny  Yue-Yang Zhan  Zheng Zheng  Zi Zhu 《天体物理学报》2012,(7):755-771

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The LEGUE high latitude bright survey design for the LAMOST pilot survey     

Yue-Yang Zhang  Jeffrey L. Carlin  Fan Yang  Chao Liu  Li-Cai Deng  Heidi Jo Newberg  Hao-Tong Zhang  Sebastien Lepine  Yan Xu  Shuang Gao  Norbert Chfi＇ stlieb  Zhan-Wen Han  Jin-Liang Hou  Hsu-Tai Lee  Xiao-Wei Liu  Kai-Ke Pan  Hong-Chi Wang 《天体物理学报》2012,(7):792-804

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