Numerical studies by the authors and others of the 1994 Piedmont flood show that the orographically modified flow was a critical element for the production of extraordinary rainfall. To uncover the precise mechanism of orographic rainfall occurring in full-physics MM5 simulations of the 1994 Piedmont flood, the authors carried out simulations with the same real-data initial and boundary conditions, but with the real orography replaced by an idealized one. With excellent agreement between real and idealized orography on the rainfall rate versus time in the Piedmont area, analysis of the idealized-orography simulation provides a clear picture of the model's mechanism of orographically induced rainfall. As noted in previous studies of the 1994 Piedmont case, a moist saturated airflow has a reduced effective static stability and tends to flow over the mountains, while an unsaturated airstream is stable and tries to flow around (toward the left in the Northern Hemisphere). In the 1994 Piedmont case, t...

/pdf/mechanisms-of-intense-alpine-rainfall-292frf7jib.pdf

Mechanisms of Intense Alpine Rainfall

Numerical model simulations of idealized and observed flows are used to investigate thedynamics of low-level jet streams that form in stratified flow downstream of the vertex of largeelliptical barriers such as the southern tip of Greenland, hereafter referred to as ‘‘tip jets’’. Thetip jet dynamics are governed by conservation of Bernouli function as parcels accelerate downthe pressure gradient during orographic descent. In some circumstances, the Greenland tip jetis influenced by baroclinic effects such as differential horizontal (cross-stream) thermal advectionand/or vertical shear. In contrast, in the barotropic situation upstream flow is diverted aroundand over the obstacle into laminar (Bernouli conservation) and turbulent (Bernouli deficit)regimes, respectively. In both situations, a downstream geostrophic balance is achieved, characterizedby baroclinicity and vertical shear associated with the surface-based tip-jet front. Thestrength of the tip-jet is most sensitive to changes in the basic state dimensionless mountainheight (Nh/U) and Rossby number, underscoring the importance of the orographic deflectionof airstreams and Lagrangian accelerations on the slope. Enhanced surface-based forcing of theocean circulation occurs in the region of the tip jet core through large air–sea energy exchange(upward surface-heat fluxes >800W m −2 ), and at the tip jet flank through localized surfacestress forcing. DOI: 10.1034/j.1600-0870.1996.00014.x

Flow response to large-scale topography: the Greenland tip jet

The role of mesoscale orography along the central California coast in the development and evolution of a coastal jet and rainband is investigated using a high-resolution, triply nested, nonhydrostatic numerical model. Comparison of the model simulations, which use horizontal grid increments of 5 and 2 km on the inner computational meshes, with a coastal mesoscale observation network indicates that the finescale structure of the jet and rainband dynamics are adequately simulated, although phase and orientation errors occur. The observed and simulated near-surface winds have maximum speeds that exceed 22 m s−1 and a direction nearly parallel to the coastline and topography. Force balance analysis indicates that blocking in the lowest 500 m and flow over the coastal range above this layer contribute to mesoscale pressure perturbations, including pressure ridging upstream of the coastal mountains, which forces the ageostrophic dynamics of the coastal jet. Pressure perturbations associated with the to...

The Influence of Mesoscale Orography on a Coastal Jet and Rainband

Numerical simulations of nonrotating flow with uniform basic wind and stability past long three-dimensional (3D) ridges are compared to the corresponding two-dimensional (2D) limit to reveal the importance of 3D effects. For mountain heights smaller than the threshold for breaking waves, the low-level flow over the interior of the ridge is well described by 2D theory when the horizontal aspect ratio β is roughly 10 or greater. By contrast, in flows with wave breaking significant discrepancies between 2D and 3D results remain apparent even for β = 12. It is found that the onset of wave breaking and the transition to the high-drag state is accompanied in 3D by an abrupt increase in deflection of the low-level flow around the ridge. The increased flow deflection is produced at least in part by upstream-propagating columnar disturbances forced by the transition to the high-drag state. The deflection of the incident flow reduces the amplitude of the mountain wave aloft relative to 2D and acts as a neg...

/pdf/three-dimensional-effects-in-high-drag-state-flows-over-long-2skq21ndwy.pdf

Three-Dimensional Effects in High-Drag-State Flows over Long Ridges.

In this study, the interaction of cold fronts with idealized coastal terrain typical of the western United States and Canada is considered. Two issues are examined. First, what are the factors that determine the strength of the coastal winds, and second, what are the orographic effects on the frontal evolution? To address these issues, the authors utilize a two-dimensional, Boussinesq terrain-following coordinate numerical model in which a uniform prescribed flow is forced to move over a plateau. The resultant across-mountain velocities are characterized by a zone of strongly decelerated flow upstream of the windward slope and a train of inertia-gravity waves downstream. A barrier-jet oriented parallel to the mountain is produced by the Coriolis force. The variations of the magnitude of the upstream deceleration and the barrier jet over a wide range of Froude numbers and Rossby numbers are described. Steady, linear theory applied to flow over a plateau shows that the upstream deceleration is dete...

https://journals.ametsoc.org/doi/pdf/10.1175/1520-0469%281999%29056%3C0517%3AEOCOOL%3E2.0.CO%3B2

Effects of Coastal Orography on Landfalling Cold Fronts. Part I: Dry, Inviscid Dynamics

A theoretical and modelling study is undertaken of an airstream of uniform flow ( U ) and stratification ( N ) impinging normally upon a two-dimensional bell-shaped ridge of half-width ( L ) and height ( H ) that is located on an  f -plane. The associated Rossby number ( R o =  U/fL ) and inverse Froude Number ( F =  NH/U ) are taken to be such that the effects of both the earth's rotation and non-linear processes can significantly influence the nature of the flow response. It is shown that within this intermediate meso-α/ β scale sub-domain of ( R o ,  F ) parameter space there are several distinctive signatures to the flow response, and each signature is associated with the generation of appreciable buoyancy wave energy. As R o decreases across the sub-domain, the source for this wave energy changes continuously from the con-ventional direct orographic forcing of vertically propagating waves (for  R o > 1), to that linked with the cusping of a leeward train of low-level near-inertial waves (for  R o ∼ 1), and thereafter to the forcing induced by the adjustment that accompanies the scale contraction of balanced flow (for  R o < 1). In effect this change highlights the various pathways to regime transition within the intermediate domain. DOI: 10.1034/j.1600-0870.1995.t01-2-00008.x

Flow over a mesoscale ridge: pathways to regime transition

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

J. Trüb

Author Tools

Chat about Author

Papers

Flow over a mesoscale ridge: pathways to regime transition