Sensitivities of Orographic Precipitation to Terrain Geometry and Upstream Conditions in Idealized Simulations

Watson, Campbell D.; Lane, Todd P.

doi:10.1175/jas-d-11-0198.1

Cited by 24 publications

(16 citation statements)

References 33 publications

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“…These results are in agreement with those of Watson and Lane (2012) who showed that in a linear regime, i.e. Nh/u <<1, there is limited sensitivity of terrain-induced flows to upstream wind direction because small changes do not cause a regime transition.…”

Section: Discussionsupporting

confidence: 93%

Trapped mountain waves during a light aircraft accident

Parker¹,

Lane

2013

AMOJ

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On 31 July 2007 a fatal light aircraft crash occurred near Clonbinane, Victoria, Australia and the official investigation concluded that mountain wave turbulence was the likely cause. This study uses three-dimensional numerical modelling and linear wave theory to examine the dynamics of mountain waves during this turbulence event and their role in generating turbulence. Analysis of the observed environment and three-dimensional idealised simulations elucidate the occurrence of trapped mountain waves and their role in creating regions of enhanced turbulence in the vicinity of the aircraft accident. Specifically, these waves perturb layers of low dynamic stability in the upstream flow, promoting turbulence in those layers. A simple ensemble of these three-dimensional simulations is also used to assess the robustness of the model solutions and demonstrate the utility of highresolution ensembles for explicit mountain wave turbulence prediction.

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Section: Discussionsupporting

confidence: 93%

Trapped mountain waves during a light aircraft accident

Parker¹,

Lane

2013

AMOJ

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“…This funneling is similar to that produced by concave ridges (Schneidereit and Sch€ ar 2000;Gheusi and Davies 2004;Jiang 2006;Watson and Lane 2012) and strongly enhances the precipitation downstream of the GSL. Latent heating from condensation and fusion likely serves as an additional nonlinear feedback mechanism for enhancing the crossband circulation and precipitation during the event.…”

Section: Discussionmentioning

confidence: 63%

“…Mountain ranges farther to the west (i.e., the Stansbury and Cedar Mountains) broaden the horizontal scale of the discontinuous concavity. In idealized simulations, Watson and Lane (2012) show that outer portions of a concave ridge deflect flow inward to yield flow deceleration, convergence, and enhanced upward motions. A comparison of the low-level flows in WAS and DT supports this conceptual model.…”

Section: E Downstream Orographic Influencesmentioning

confidence: 98%

“…For example, concavities in the Alps are associated with climatological precipitation maxima (Frei and Sch€ ar 1998) low-level convergence and precipitation enhancement during some precipitation events (Schneidereit and Sch€ ar 2000;Gheusi and Davies 2004). In stratified moist flow, idealized numerical modeling studies produce enhanced convergence and precipitation within terrain concavities compared to linear or convex ridges (Jiang 2006;Watson and Lane 2012).…”

Section: E Downstream Orographic Influencesmentioning

confidence: 99%

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Orographic Influences on a Great Salt Lake–Effect Snowstorm

Alcott

Steenburgh

2013

Monthly Weather Review

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Although several mountain ranges surround the Great Salt Lake (GSL) of northern Utah, the extent to which orography modifies GSL-effect precipitation remains largely unknown. Here the authors use observational and numerical modeling approaches to examine the influence of orography on the GSL-effect snowstorm of 27 October 2010, which generated 6-10 mm of precipitation (snow-water equivalent) in the Salt Lake Valley and up to 30 cm of snow in the Wasatch Mountains. The authors find that the primary orographic influences on the event are 1) foehnlike flow over the upstream orography that warms and dries the incipient low-level air mass and reduces precipitation coverage and intensity; 2) orographically forced convergence that extends downstream from the upstream orography, is enhanced by blocking windward of the Promontory Mountains, and affects the structure and evolution of the lake-effect precipitation band; and 3) blocking by the Wasatch and Oquirrh Mountains, which funnels the flow into the Salt Lake Valley, reinforces the thermally driven convergence generated by the GSL, and strongly enhances precipitation. The latter represents a synergistic interaction between lake and downstream orographic processes that is crucial for precipitation development, with a dramatic decrease in precipitation intensity and coverage evident in simulations in which either the lake or the orography are removed. These results help elucidate the spectrum of lake-orographic processes that contribute to lake-effect events and may be broadly applicable to other regions where lake effect precipitation occurs in proximity to complex terrain.

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“…Cannon et al (2012) found from idealized numerical simulations that embedded convection over tall and wide mountains causes competing effects (enhanced condensation in updrafts and enhanced evaporation through turbulent mixing and compensating subsidence) and leads to little net change in precipitation, while, for short and narrow mountains, convective updrafts strongly enhance the precipitation efficiency. Watson andLane (2012, 2014) undertook idealized, highresolution simulations and found that a concave ridge generates substantially more precipitation than the straight and convex ridges. A number of real-world simulations have focused on the island of Hawaii (e.g., Rasmussen et al 1989;Reisner and Smolarkiewicz 1994), where the 4-km mountain peak is found to create blocking with a large nondimensional mountain height.…”

mentioning

confidence: 99%

Understanding Orographic Effects on Surface Observations at Macquarie Island

Zhan

Belušić

Huang

et al. 2016

Journal of Applied Meteorology and Climatology

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The meteorological observations on Macquarie Island have become of increasing value for efforts to understand the unique nature of atmospheric processes over the Southern Ocean. While the island is of modest elevation (peak altitude of 410 m), the orographic effects on observations on this island are still not clear. High-resolution numerical simulations [Weather Research and Forecasting (WRF) Model] with and without terrain have been used to identify orographic effects for four cases representing common synoptic patterns at Macquarie Island: a cold front, a warm front, postfrontal drizzle, and a midlatitude cyclone. Although the simulations cannot capture every possible feature of the precipitation, preliminary results show that clouds and precipitation can readily be perturbed by the island with the main enhancement of precipitation normally in the lee in accordance with the nondimensional mountain height being much less than 1. The weather station is located at the far north end of the island and is only in the lee to southerly and southwesterly winds, which are normally associated with drizzle. The station is on the upwind side for strong northwesterly winds, which are most common and can bring heavier frontal precipitation. Overall the orographic effect on the precipitation record is not found to be significant, except for the enhancement of drizzle found in southwesterly winds. Given the strong winds over the Southern Ocean and the shallow height of the island, the 3D nondimensional mountain height is smaller than 1 in 93.5% of the soundings. As a result, boundary layer flow commonly passes over the island, with the greatest impact in the lee.

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Sensitivities of Orographic Precipitation to Terrain Geometry and Upstream Conditions in Idealized Simulations

Cited by 24 publications

References 33 publications

Trapped mountain waves during a light aircraft accident

Trapped mountain waves during a light aircraft accident

Orographic Influences on a Great Salt Lake–Effect Snowstorm

Understanding Orographic Effects on Surface Observations at Macquarie Island

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