Airflow patterns over and around a large three-dimensional hill

Wooldridge, Gene L.; Fox, R. G.; Furman, R. Wm

doi:10.1007/bf01031047

Cited by 4 publications

(2 citation statements)

References 22 publications

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“…2). The Froude number is a nondimensional value that is the ratio of inertial forces to gravitational forces and is defined as F 5 U/(Nh) (Wooldridge et al 1987;Barry 2008), where h is the height of an obstacle to the airflow and U is the mean wind speed through the approaching layer between the ground level and the height h, at a distance greater than 5h upstream of the hill; N is the Brunt-Väisälä frequency of the upstream flow, which is an indicator of atmospheric stability and is defined as N 2 5 (gu)(du/dz) (Wooldridge et al 1987), where g is gravitational acceleration, u is potential temperature, and z is height above the surface. When F , 1, vertical motion is suppressed below a critical height H c 5 h(1 2 F) but flows smoothly over the hill above this height (Snyder et al 1985), remaining attached to the terrain below as it proceeds downhill.…”

Section: ) Froude Number Analysismentioning

confidence: 99%

A Meteorological Study of the Port Hills Fire, Christchurch, New Zealand

Pretorius

Sturman

Strand

et al. 2020

Journal of Applied Meteorology and Climatology

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In February 2017, a wildfire occurred in the Port Hills on the southern boundary of Christchurch city in New Zealand. It was one of the country’s most severe fires of the last decade in terms of the scale of evacuation, infrastructure damage, and property loss. On the third day of the fire, fire behavior was unexpectedly active, and two rapid downhill fire-spread events took place, creating a dangerous situation for firefighters. The aim of this paper is to explore the atmospheric processes that influenced the fire behavior at a range of meteorological scales, from the synoptic to meso- and microscales. Meteorological and fire data analyzed include observed data together with model simulations of weather conditions at different scales: 1) the Weather Research and Forecasting (WRF) numerical weather prediction model, which provided the regional context of the fire; and 2) the California Meteorological (CALMET) diagnostic model, which was used to undertake a higher-resolution investigation of atmospheric processes near the fire. Results indicate that the fire was not strongly seasonally influenced. Instead, it appears the fire conditions were the effect of a specific combination of synoptic weather conditions and local meteorological conditions. The first rapid downhill fire-spread event was the result of airflow interaction with the intricate terrain of the Port Hills under stable nocturnal conditions. The second downhill fire-spread event bears similarities to vorticity-driven lateral spread, because the downhill component of the spread happened on a broad fire flank perpendicular to the surface wind direction and characteristic pyrocumulus convection occurred.

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Section: ) Froude Number Analysismentioning

confidence: 99%

A Meteorological Study of the Port Hills Fire, Christchurch, New Zealand

Pretorius

Sturman

Strand

et al. 2020

Journal of Applied Meteorology and Climatology

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“…According to Wooldridge et al [37], Equation (6) may also be used to find the critical height h c if Fr h is replaced by Fr (defined by Equation (3)), which is applicable when Fr < 1.…”

Section: Froude Number (Fr H ) In Terms Of the Dividing-streamline Hementioning

confidence: 99%

Analysis of Mountain Wave Effects on a Hard Landing Incident in Pico Aerodrome Using the AROME Model and Airborne Observations

Maruhashi

Serrão²,

Belo-Pereira

2019

Atmosphere

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A hard landing incident in Pico Aerodrome (LPPI) involving an Airbus A320-200 aircraft is investigated using airborne observations and forecasts of the AROME (Applications of Research to Operations at Mesoscale) model. A second flight is also analyzed. The severity of the wind shear during both flights is quantified using the intensity factor “I” that is based on aerial data and recommended by ICAO (International Civil Aviation Organization). During Flight 1, 36% of the landing phase (below 2100 ft) occurred under “severe” wind shear conditions and 16% occurred under “strong” conditions. Upstream characteristics included southwest winds, stable stratification and a Froude number close to 1. According to the AROME model, these circumstances triggered the development of vertically propagating mountain waves, with maximum vertical velocities above 400 ft/min and exceeding 200 ft/min in the flight path. These conditions, together with the severe wind shear, may have caused the incident. During the second flight, a wake with lee vortices and reversed flow developed in the region of the flight path, which is consistent with a low upstream Froude number and/or with the flow regime diagram of previous studies. During the approach phase of this flight, “severe” wind shear conditions were absent, with “strong” ones occurring 4% of the time. It predominantly displayed “light” conditions during 68% of this phase. As a result of the comparison between “I” and the AROME turbulence indicators, preliminary thresholds are proposed for these indexes. Lastly, this study provides an objective verification of AROME wind forecasts, showing a good agreement with airborne observations for wind speeds above 10 kt, but a poor skill for weaker winds.

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On atmospheric vortex streets in the wake of large islands

Etling

1989

Meteorl. Atmos. Phys.

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Airflow patterns over and around a large three-dimensional hill

Cited by 4 publications

References 22 publications

A Meteorological Study of the Port Hills Fire, Christchurch, New Zealand

A Meteorological Study of the Port Hills Fire, Christchurch, New Zealand

Analysis of Mountain Wave Effects on a Hard Landing Incident in Pico Aerodrome Using the AROME Model and Airborne Observations

On atmospheric vortex streets in the wake of large islands

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