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  • 1
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    The Atmosphere over Mountainous Regions (2016)
    Lausanne : Frontiers
    Details
    Keywords: Cold air pools ; Downslope winds ; Horizontal inhomogeneity ; Hydraulic jumps ; Large eddy simulation ; mountain waves ; orographic precipitation ; Sub-mesoscale circulations ; Thermally-driven flows ; Turbulent fluxes
    Description / Table of Contents: 05 Editorial: The Atmosphere over Mountainous Regions / Miguel A. C. Teixeira, Daniel J. Kirshbaum, Haraldur Ólafsson, Peter F. Sheridan and Ivana Stiperski --- 07 Possible observation of horizontal roll vortices over the Adriatic Sea during bora / Danijel Belušić, Željko Večenaj and Margaret A. LeMone --- 14 Lee Waves on the Boundary-Layer Inversion and Their Dependence on Free-Atmospheric Stability / Johannes Sachsperger, Stefano Serafin and Vanda Grubišic’ --- 25 Non-linear Topographic Effects in Two-Layer Flows / Peter G. Baines and Edward R. Johnson --- 35 The Quasi-Steady State of the Valley Wind System / Juerg Schmidli and Richard Rotunno --- 46 Convective Boundary Layer Heights Over Mountainous Terrain—A Review of Concepts / Stephan F. J. De Wekker and Meinolf Kossmann --- 68 On the Vertical Exchange of Heat, Mass, and Momentum Over Complex, Mountainous Terrain / Mathias W. Rotach, Alexander Gohm, Moritz N. Lang, Daniel Leukauf, Ivana Stiperski and Johannes S. Wagner --- 82 Identification and Climatology of Alpine Pumping from a Regional Climate Simulation / Maximilian Graf, Meinolf Kossmann, Kristina Trusilova and Gudrun Mühlbacher --- 93 The Atmospheric Boundary Layer during Wintertime Persistent Inversions in the Grenoble Valleys / Yann Largeron and Chantal Staquet --- 112 Energetics of Slope Flows: Linear and Weakly Nonlinear Solutions of the Extended Prandtl Model / Ivan Güttler , Ivana Marinović, Željko Večenaj and Branko Grisogono --- 125 When Can a High-Resolution Simulation Over Complex Terrain be Called LES? / Joan Cuxart --- 131 Influence of the Details of Topography on Weather Forecast – Evaluation of HARMONIE Experiments in the Sochi Olympics Domain over the Caucasian Mountains / Laura Rontu, Clemens Wastl and Sami Niemelä --- 147 Effects of Landfall Location and Approach Angle of an Idealized Tropical Cyclone over a Long Mountain Range / Liping Liu, Yuh-Lang Lin and Shu-Hua Chen
    Pages: Online-Ressource (160 Seiten)
    ISBN: 9782889450169
    URL: https://doi.org/10.3389/978-2-88945-016-9
    Language: English
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  • 2
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    Synoptic Control over Orographic Precipitation Distributions during the Olympics Mountains Experiment (OLYMPEX) (2018)
    American Meteorological Society
    Details
    Publication Date: 2018-04-01
    Print ISSN: 0027-0644
    Electronic ISSN: 1520-0493
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 3
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    Assessment of Conditional Symmetric Instability from Global Reanalysis Data (2018)
    American Meteorological Society
    Details
    Publication Date: 2018-07-01
    Description: Slantwise convection, the process by which moist symmetric instability is released, has often been linked to banded clouds and precipitation, especially in frontal zones within extratropical cyclones. Studies also suggest that the latent heat release associated with slantwise convection can lead to a spinup of surface frontogenesis, which can enhance the rapid intensification of extratropical cyclones. However, most of these studies considered only local areas or short time durations. In this study, we provide a novel statistical investigation of the global climatology of the potential occurrence of slantwise convection, in terms of conditional symmetric instability, and its relationship with precipitating systems. Using the 6-hourly ERA-Interim, two different indices are calculated, namely, slantwise convective available potential energy (SCAPE) and vertically integrated extent of realizable symmetric instability (VRS), to assess the likelihood of occurrence of slantwise convection around the globe. The degree of association is quantified between these indices and the observed surface precipitation as well as the cyclone activity. The susceptibility of midlatitude cyclones to slantwise convection at different stages of their life cycle is also investigated. As compared to the nonexplosive cyclone cases, the time evolution of SCAPE and VRS within rapidly deepening cyclones exhibit higher values before, and a more significant drop after, the onset of rapid intensification, supporting the idea that the release of symmetric instability might contribute to the intensification of storms.
    Print ISSN: 0022-4928
    Electronic ISSN: 1520-0469
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 4
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    Initiation of Deep Convection over an Idealized Mesoscale Convergence Line (2017)
    American Meteorological Society
    Details
    Publication Date: 2017-03-01
    Description: This study performs cloud-resolving simulations of cumulus convection over an idealized surface-based convergence zone to investigate the mechanisms and sensitivities of deep convection initiation forced by mesoscale ascent. The surface convergence forms in response to a localized diurnal heating anomaly over an otherwise homogeneous and unheated surface, producing a strong boundary layer updraft over the center of the heat source. This updraft gives rise to a line of cumuli that gradually deepen and, in some cases, transition into deep convection. To statistically investigate the factors controlling this transition, a new thermal-tracking algorithm is developed to follow incipient cumulus cores as they ascend through the troposphere. This tool is used to isolate the impacts of key environmental parameters (cloud-layer lapse rate, midlevel humidity, etc.) and initial core parameters near cloud base (horizontal area, vertical velocity, etc.) on the ultimate cloud-top height. In general, the initial core size determines which thermals in a given cloud field will undergo the deepest ascent, and the sensitivity of cloud depth to initial core parameters increases in environments that are more hostile to deep convection. Diurnal midlevel moistening from detraining cumuli above the convergence line produces a small but robust enhancement in cloud-top height, particularly for smaller cores.
    Print ISSN: 0022-4928
    Electronic ISSN: 1520-0469
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 5
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    Topographic Impacts on the Spatial Distribution of Deep Convection over Southern Quebec (2016)
    American Meteorological Society
    Details
    Publication Date: 2016-03-01
    Description: Observations and numerical simulations reveal pronounced mesoscale variability in deep-convection occurrence over southern Quebec, Canada. A 22-yr climatology from the McGill radar just west of Montreal shows that deep-convection maxima exist (i) within the St. Lawrence valley surrounding Ottawa; (ii) within the Champlain valley of upstate New York, extending north to just east of Montreal; and (iii) in the lee of the Laurentian Mountains northeast of Trois-Rivières. These features are sensitive to the background low- to midlevel geostrophic wind direction, shifting northward as the southerly wind component increases. A meridional axis of suppressed convection also extends from Lake Ontario and the Adirondacks of New York north through Montreal and into the Laurentians. To physically interpret these features, a suite of quasi-idealized convection-permitting simulations is conducted. Analysis of the simulations, which broadly reproduce the observed extrema in convection occurrence, reveals that the maxima develop within pockets of moisture and mass convergence at the junctions of major river valleys and in the lee of prominent mountain ridges. In these locations, enhanced boundary layer humidity and convective available potential energy (CAPE) coincides with minimal convective inhibition (CIN). The minima occur over and downwind of water bodies, where limited surface heat fluxes reduce CAPE and increase CIN, and over the higher terrain, where reduced low-level moisture limits storm intensity.
    Print ISSN: 1558-8424
    Electronic ISSN: 1558-8432
    Topics: Geography , Physics
    Published by American Meteorological Society
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  • 6
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    Climatology of Banded Precipitation over the Contiguous United States (2016)
    American Meteorological Society
    Details
    Publication Date: 2016-11-03
    Description: A climatology of banded-precipitation features over the contiguous United States from 2003 to 2014 is constructed. A band is defined as a precipitation feature with a major axis of 100 km or greater and a ratio of major axis length to minor axis length (hereafter, aspect ratio) of 3:1 or greater. By applying an automated feature-based detection algorithm to composite radar imagery, a database of 48 916 844 precipitation features is created, of which 7 213 505 (14.8%) are bands. This algorithm produces the first climatology of precipitation bands over the contiguous United States. Banded-precipitation occurrence is broadly similar to total precipitation occurrence, with a maximum of 175 h of banded precipitation annually over the Ohio River valley. In the warm season, there is a strong diurnal signature associated with convective storm development for both the precipitation feature area and total area covered by precipitation, but little diurnal signature in aspect ratio. Strong west–east gradients in both precipitation occurrence and banded-precipitation occurrence exist, as areas west of the Rockies receive less frequent precipitation, which is much less likely to be banded. East of the Rockies, precipitation features are banded 30% of the time, versus 10%–15% west of the Rockies. Areas downwind of the Great Lakes show prominent late autumn and winter maxima in banded precipitation associated with lake-effect snowbands. Local maxima of banded-precipitation percentage occur in the Dakotas and east of the Colorado Rockies during winter. Although banded-precipitation features compose only 14.8% of all precipitation features, they contribute 21.9% of the annual precipitation occurrence over the contiguous United States.
    Print ISSN: 0027-0644
    Electronic ISSN: 1520-0493
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 7
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    The Utility of Convection-Permitting Ensembles for the Prediction of Stationary Convective Bands (2016)
    American Meteorological Society
    Details
    Publication Date: 2016-02-26
    Description: This study examines convection-permitting numerical simulations of four cases of terrain-locked quasi-stationary convective bands over the United Kingdom. For each case, a 2.2-km-grid-length, 12-member ensemble and a 1.5-km-grid-length deterministic forecast are analyzed, each with two different initialization times. Object-based verification is applied to determine whether the simulations capture the structure, location, timing, intensity, and duration of the observed precipitation. These verification diagnostics reveal that the forecast skill varies greatly between the four cases. Although the deterministic and ensemble simulations captured some aspects of the precipitation correctly in each case, they never simultaneously captured all of them satisfactorily. In general, the models predicted banded precipitation accumulations at approximately the correct time and location, but the precipitating structures were more cellular and less persistent than the coherent quasi-stationary bands that were observed. Ensemble simulations from the two different initialization times were not significantly different, which suggests a potential benefit of time-lagging subsequent ensembles to increase ensemble size. The predictive skill of the upstream larger-scale flow conditions and the simulated precipitation on the convection-permitting grids were strongly correlated, which suggests that more accurate forecasts from the parent ensemble should improve the performance of the convection-permitting ensemble nested within it.
    Print ISSN: 0027-0644
    Electronic ISSN: 1520-0493
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 8
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    The Mississippi Valley Convection Minimum on Summer Afternoons: Observations and Numerical Simulations (2015)
    American Meteorological Society
    Details
    Publication Date: 2015-12-29
    Description: Analysis of 15 years of composite radar images over the continental United States reveals a distinct minimum of deep-convection occurrence over the interior lower Mississippi Valley on summer afternoons, relative to surrounding areas. To understand the mechanisms behind this convection signature, quasi-idealized numerical simulations with the Weather Research and Forecasting (WRF) Model are performed. The simulations, which broadly reproduce the valley convection minimum, suggest that convective inhibition is maximized, and low-level ascent minimized, over the flat valley terrain. By contrast, weaker inhibition and stronger mechanically forced ascent over the hills flanking the valley combine to initiate convection more readily. Although the orography of the region is unremarkable, it has a stronger influence on the regional convection pattern than do variations in land use.
    Print ISSN: 0027-0644
    Electronic ISSN: 1520-0493
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 9
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    Verification of 24-h Quantitative Precipitation Forecasts over the Pacific Northwest from a High-Resolution Ensemble Kalman Filter System (2017)
    American Meteorological Society
    Details
    Publication Date: 2017-05-19
    Description: Environment and Climate Change Canada (ECCC) has recently developed an experimental high-resolution EnKF (HREnKF) regional ensemble prediction system, which it tested over the Pacific Northwest of North America for the first half of February 2011. The HREnKF has 2.5-km horizontal grid spacing and assimilates surface and upper-air observations every hour. To determine the benefits of the HREnKF over less expensive alternatives, its 24-h quantitative precipitation forecasts are compared with those from a lower-resolution (15 km) regional ensemble Kalman filter (REnKF) system and to ensembles directly downscaled from the REnKF using the same grid as the HREnKF but with no additional data assimilation (DS). The forecasts are verified against rain gauge observations and gridded precipitation analyses, the latter of which are characterized by uncertainties of comparable magnitude to the model forecast errors. Nonetheless, both deterministic and probabilistic verification indicates robust improvements in forecast skill owing to the finer grids of the HREnKF and DS. The HREnKF exhibits a further improvement in performance over the DS in the first few forecast hours, suggesting a modest positive impact of data assimilation. However, this improvement is not statistically significant and may be attributable to other factors.
    Print ISSN: 0882-8156
    Electronic ISSN: 1520-0434
    Topics: Geography , Physics
    Published by American Meteorological Society
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  • 10
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    Climatology of Size, Shape, and Intensity of Precipitation Features over Great Britain and Ireland (2017)
    American Meteorological Society
    Details
    Publication Date: 2017-05-24
    Description: A climatology of precipitation features (or objects) from the Great Britain and Ireland radar-derived precipitation mosaic from 2006 to 2015 is constructed, with features defined as contiguous areas of nonzero precipitation rates. Over the 10 years, there are 54 811 747 nonunique precipitating features over 100 km2 in area, with a median precipitation feature area of 249 km2, median major axis length of 29.2 km, median aspect ratio of 2.0:1, median feature mean precipitation rate of 0.49 mm h−1, and median feature maximum precipitation rate of 2.4 mm h−1. Small-scale precipitating systems are most common, but larger systems exceeding 10 000 km2 contribute close to 70% of the annual precipitation across the study region. Precipitation feature characteristics are sensitive to changes in annual and diurnal environment, with feature intensities peaking during the afternoon in summer and the largest precipitation features occurring during winter. Precipitation intensities less than 5 mm h−1 comprise 97.3% of all precipitation occurrences and contribute 83.6% of the total precipitation over land. Banded precipitation features (defined as precipitation features with aspect ratio at least 3:1 and major axis length at least 100 km) comprise 3% of all precipitation features by occurrence, but contribute 23.7% of the total precipitation. Mesoscale banded features (defined as banded precipitation features with major axis length at least 100 km and total area not exceeding 10 000 km2) and mesoscale convective banded features (defined as banded precipitation features with at least 100 km2 of precipitation rates exceeding 10 mm h−1) are most prevalent in southwestern England, with mesoscale convective banded features contributing up to 2% of precipitation.
    Print ISSN: 1525-755X
    Electronic ISSN: 1525-7541
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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