Frontal Interaction with the Appalachian Mountains. Part I: A Climatology

Schumacher, Philip N.; Knight, David J.; Bosart, Lance F.

doi:10.1175/1520-0493(1996)124<2453:fiwtam>2.0.co;2

Cited by 20 publications

(21 citation statements)

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“…The reason probably is a different orientation of the mean mountain axis. Schumacher et al (1996) find that 45% of cold fronts passing the Appalachians are not slowed down considerably. Since the Alps are a much higher obstacle, the proportion of nearly unaltered propagation probably is much lower.…”

Section: Discussion Of the Climatologymentioning

confidence: 88%

“…Throughout the year Flocas noted two main paths of fronts merging over the Alps: one from central France and one from the Pyrenees and the Mediterranean. O' Handley and Bosart (1996) and Schumacher et al (1996) conducted two climatological studies of cold fronts approaching the Appalachian Mountains in North America. They both found the majority of cold fronts to slow down considerably, e.g.…”

Section: J Jenkner Et Almentioning

confidence: 99%

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Detection and climatology of fronts in a high‐resolution model reanalysis over the Alps

Jenkner

Sprenger

Schwenk

et al. 2009

Meteorological Applications

103

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The identification of low-level thermal fronts is particularly challenging in high-resolution model fields over complex terrain. Firstly, direct model output often contains numerical noise which spuriously influences the highfrequency variability of thermal parameters. Secondly, the boundary layer interferes via convection and consequently leaves its thermal marks on low levels. Here, an automated objective method for the detection of frontal lines is introduced which is designed to be insusceptible to consequences of small grid spacings. To this end, existing algorithms are readopted and combined in a novel way. The overall technique subdivides into a basic detection of fronts and a supplemental division into local fronts and synoptic fronts. The fundamental parts of the detection are: (1) a smoothing of the initial fields, (2) a definition of the frontal strength, and, (3) a localisation with the thermal front parameter. The local fronts are identified by means of a classification of open and closed thermal contours. The resulting data comprise the spatial outline of the frontal structures in a binary field as well as their type and movement. The novel methodology is applied to a 3 year high-resolution reanalysis over central Europe computed with the COSMO model using a grid spacing of 7 km. Grid-point based climatologies are derived for the Alpine region. Frequencies of occurrence and characteristics of motion are analysed for different frontal types. The novel climatology also provides quantitative evidence of dynamical properties such as the retardation of cold fronts ahead of mountains and the dissolution of warm fronts over mountains.

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Section: Discussion Of the Climatologymentioning

confidence: 88%

Section: J Jenkner Et Almentioning

confidence: 99%

Detection and climatology of fronts in a high‐resolution model reanalysis over the Alps

Jenkner

Sprenger

Schwenk

et al. 2009

Meteorological Applications

103

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“…During IPEX IOP3, a landfalling occluded front weakened and deformed as it approached the Sierra Nevada, similar to that observed previously near the Sierra Nevada by Hoffman (1995), Reynolds and Kuciauskas (1988), and Blazek (2000), as well as upstream of the Appalachians (Schumacher et al 1996). Ultimately, there was little evidence that the baroclinity associated with the surface-based occlusion was able to penetrate into the lowlands to the lee of the Sierra Nevada as the upper-level trough continued to move downstream.…”

Section: A Storm Evolution Over the Western United Statesmentioning

confidence: 99%

Terrain Influences on Synoptic Storm Structure and Mesoscale Precipitation Distribution during IPEX IOP3

Shafer

Steenburgh

Cox

et al. 2006

Monthly Weather Review

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The influence of topography on the evolution of a winter storm over the western United States and distribution of precipitation over northern Utah are examined using data collected during the third intensive observing period (IOP3) of the Intermountain Precipitation Experiment (IPEX). The analysis is based on high-density surface observations collected by the MesoWest cooperative networks, special radiosonde observations, wind profiler observations, Next-Generation Weather Radar (NEXRAD) data, and conventional data. A complex storm evolution was observed, beginning with frontal distortion and low-level frontolysis as a surface occluded front approached the Sierra Nevada. As the low-level occluded front weakened, the associated upper-level trough moved over the Sierra Nevada and overtook a lee trough. The upper-level trough, which was forward sloping and featured more dramatic moisture than temperature gradients, then moved across Nevada with a weak surface reflection as a pressure trough.Over northern Utah, detailed observations revealed the existence of a midlevel trough beneath the forward-sloping upper-level trough. This midlevel trough appeared to form along a high-potential-vorticity banner that developed over the southern Sierra Nevada and moved downstream over northern Utah. A surface trough moved over northern Utah 3 h after the midlevel trough and delineated two storm periods. Ahead of the surface trough, orographic precipitation processes dominated and produced enhanced mountain precipitation. This period also featured lowland precipitation enhancement upstream of the northern Wasatch Mountains where a windward convergence zone was present. Precipitation behind the surface trough was initially dominated by orographic processes, but soon thereafter featured convective precipitation that was not fixed to the terrain. Processes responsible for the complex vertical trough structure and precipitation distribution over northern Utah are discussed.

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“…Two methods of approximating the constant static stability have appeared frequently in the literature. In one method, the Brunt-Väisälä frequency is averaged between the ground and some height aloft to yield a constant N (e.g., Mass and Ferber 1990;Schumacher et al 1996;Bénech et al 1998;Medina and Houze 2003;Jiang et al 2005). We refer to this as the averaging method.…”

Section: Introductionmentioning

confidence: 99%

Estimating Topographic Blocking Using a Froude Number When the Static Stability Is Nonuniform

Reinecke

Durran

2008

Journal of the Atmospheric Sciences

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A parameter widely used to predict topographic flow blocking is the nondimensional mountain height or, synonymously, the inverse Froude number. Predictions using this parameter are based on the morphology of flows with uniform upstream static stability and wind speed, which rarely occur in the real world. The appropriateness of applying this theory in the presence of nontrivial background stability is therefore investigated using a numerical model. Two methods were considered to estimate the low-level stability, averaging the Brunt-Väisälä frequency below the crest and using the bulk change in between the ground and crest level.No single best method emerged for estimating the upstream static stability and thereby mapping the simulations with inversions onto the set of solutions with constant stratification. Instead, the best method depended on the application at hand. To predict the onset of flow stagnation, averaging the low-level stability worked best, while to predict low-level flow diversion the bulk estimate of low-level stability was most appropriate. These results are consistent across a range of inversion thicknesses and strengths. In addition, it is shown that variations in static stability above the mountain crest have little impact on flow blocking.

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Frontal Interaction with the Appalachian Mountains. Part I: A Climatology

Cited by 20 publications

References 0 publications

Detection and climatology of fronts in a high‐resolution model reanalysis over the Alps

Detection and climatology of fronts in a high‐resolution model reanalysis over the Alps

Terrain Influences on Synoptic Storm Structure and Mesoscale Precipitation Distribution during IPEX IOP3

Estimating Topographic Blocking Using a Froude Number When the Static Stability Is Nonuniform

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