The Impact of the Appalachian Mountains on Cyclonic Weather Systems. Part I: A Climatology

O'Handley, Christopher; Bosart, Lance F.

doi:10.1175/1520-0493(1996)124<1353:tiotam>2.0.co;2

Cited by 31 publications

(19 citation statements)

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“…A similar low-level, prefrontal wind maximum was observed adjacent to the steep terrain along the central California coast (Doyle 1997) and just west of the Sierra Nevada (Marwitz 1987). Other observations of fronts decelerated by upstream flow blocked by topography have been made in the European Alps (e.g., Kurz 1990), the Appalachian Mountains (O'Handley and Bosart 1996), the coastal mountains of western Canada (Doyle and Bond 2001), the Wasatch mountains of northern Utah (Cox et al 2005), and the Pacific Northwest (Braun et al 1999;Yu and Bond 2002). Precipitation distribution in the Alps and Apennines has also been related to both the degree of flow blocking by topography (e.g., Medina and Houze 2003) and the amount of entrainment of moist low-level air into unblocked flow aloft (e.g., Bousquet and Smull 2006).…”

Section: Introductionsupporting

confidence: 68%

Effect of the Andes Cordillera on Precipitation from a Midlatitude Cold Front

Barrett

Garreaud

Falvey

2009

Monthly Weather Review

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The effects of the Andes Cordillera, the major mountain range in South America, on precipitation patterns of baroclinic systems approaching from the southeast Pacific remain largely unstudied. This study focuses on a case in late May 2008 when an upper-level trough and surface cold front produced widespread precipitation in central Chile. The primary goal was to analyze the physical mechanisms responsible for the structure and evolution of the precipitation.Weather Research and Forecasting (WRF) model simulations indicate that as an upper-level trough approached central Chile, midtropospheric flow below 700 hPa was blocked by the high topography and deflected poleward in the form of a barrier jet. This northerly jet had wind maxima in excess of 15 m s 21 , was centered around 925 hPa, and extended westward 200 km from the mountains. It intersected the cold front, which approached from the south near the coast, thereby increasing convergence along the frontal surface, slowing its equatorward progress, and enhancing rainfall over central Chile. Another separate region of heavy precipitation formed over the upwind slopes of the cordillera. A trajectory analysis confirmed that the barrier jet moved low-level parcels from their origin in the moist southeast Pacific boundary layer to the coast. When model topography was reduced to twenty percent of its original height, the cold front advanced more rapidly to the northeast, generated less precipitation in central Chile between 338 and 368S, and produced minimal orographic precipitation on the upwind Andean slopes. Based on these findings, the high topography appears responsible for not only orographic precipitation but also for substantially increasing precipitation totals over the central coast and valley.

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Section: Introductionsupporting

confidence: 68%

Effect of the Andes Cordillera on Precipitation from a Midlatitude Cold Front

Barrett

Garreaud

Falvey

2009

Monthly Weather Review

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“…In the velocity composite, average speeds of cold fronts change from 6 m s −1 far to the north to 3-4 m s −1 directly to the north of the Alpine crest and finally to 7-9 m s −1 near the southern summits. Taking into account that there is no restriction to a specific direction in the present study, the retardation for the most common northwesterly direction seems to be similar to that of O'Handley and Bosart (1996).…”

Section: Discussion Of the Climatologymentioning

confidence: 99%

“…They both found the majority of cold fronts to slow down considerably, e.g. O'Handley and Bosart (1996) noted a mean frontal deceleration of 40%. Several case studies revealed further details about cold fronts in the Alpine region (e.g.…”

Section: J Jenkner Et Almentioning

confidence: 95%

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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“…In particular, deflections have been well documented for typhoons passing over Taiwan's CMR and the Cordillera Central of northern Luzon in the Philippines (e.g., Brand and Blelloch, 1974;Wang, 1980), TC's passing over Madagascar and La Reunion mountains (Rakotomavo et al, 2011), and hurricanes passing over the Cordillera Central of Hispañola (Bender et al, 1987) and the Sierra Madre Mountains of Mexico (Zehnder, 1993;Zehnder and Reeder, 1997). Similar track deflections have also been observed with mid-latitude cyclones passing over the Appalachians (e.g., O'Handley and Bosart, 1996). Effects of orography on TC tracks have been studied extensively for typhoons passing over Taiwan's CMR and the Cordillera Central of northern Luzon in the Philippines.…”

Section: Introductionmentioning

confidence: 56%

Effects of Landfall Location and Approach Angle of an Idealized Tropical Cyclone over a Long Mountain Range

2016

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Effects of landfall location and approach angle on track deflection associated with a tropical cyclone (TC) passing over an idealized and Central Appalachian Mountain is investigated by a series of idealized numerical experiments. When the TC landfalls on the central portion of the mountain range, it is deflected to the south upstream, passes over the mountain anticyclonically, and then moves westward downstream. The TC motion is steered by the positive vorticity tendency (VT) which is dominated by horizontal vorticity advection upstream and downstream, but with additional influence from the stretching and residual terms, which are mainly associated with diabatic heating and frictional effects. The track deflection mechanism upstream and downstream is similar to the dry flow in previous study, but is very different in the vicinity of the mountain. When the TC landfalls near the northern (southern) tip, it experiences less (more) southward deflection due to stronger (weaker) vorticity advection around the tip. When the TC approaches the mountain range from the southeast and landfalls on the northern tip, center, or southern tip, the track deflections are similar to those embedded in an easterly flow but with weaker orographic blocking. These results are similar to the cases simulated in the dry flow in previous study, except that there is no track discontinuity due to the weaker orographic blocking associated with strong TC convection. When a TC moves along the north-south mountain range from the south, it tends to deflect toward the mountain and then crosses over to the other side at later time. In these cases, the positive VT is influenced by all horizontal vorticity advection, vorticity stretching (diabatic heating), and residual (friction) terms due to longer and stronger interaction with the mountain range. The vorticity stretching is mainly caused by diabatic heating in the moist flow, instead of by lee slope vorticity stretching in the previous study for dry flow.

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The Impact of the Appalachian Mountains on Cyclonic Weather Systems. Part I: A Climatology

Cited by 31 publications

References 0 publications

Effect of the Andes Cordillera on Precipitation from a Midlatitude Cold Front

Effect of the Andes Cordillera on Precipitation from a Midlatitude Cold Front

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

Effects of Landfall Location and Approach Angle of an Idealized Tropical Cyclone over a Long Mountain Range

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