Using SAR Remote Sensing, Field Observations, and Models to Better Understand Coastal Flows in the Gulf of Alaska

Winstead, Nathaniel S.; Colle, Brian A.; Bond, Nicholas A.; Young, George S.; Olson, Joseph B.; Loescher, Kenneth; Monaldo, F.; Thompson, D. R.; Pichel, William G.

doi:10.1175/bams-87-6-787

Cited by 23 publications

(21 citation statements)

References 39 publications

(40 reference statements)

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“…Some hybrid jets were detached 10-15 km from the coast, while others had sharp wind speed boundaries (shock jets), which does not conform to the gradual offshore weakening of barrier jets observed in other studies (Parish 1982). Olson et al (2007, hereafter OL07) detailed the structure and dynamics of a classical and hybrid jet sampled during the Southern Alaskan Regional Jets Experiment (SARJET; Winstead et al 2006). The classical jet had maximum winds Ͼ30 m s Ϫ1 at the coast between 600 and 800 m above mean sea level (MSL) and an offshore extent of ϳ60 km, whereas the hybrid jet of ϳ30 m s Ϫ1 was displaced 30-40 km offshore at 500 m above MSL (OL07, their Figs.…”

Section: Introductionmentioning

confidence: 93%

Three-Dimensional Idealized Simulations of Barrier Jets along the Southeast Coast of Alaska

Olson

Colle

2009

Monthly Weather Review

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Three-dimensional idealized simulations using the fifth-generation Pennsylvania State University-NCAR Mesoscale Model (MM5) down to 6-km grid spacing were performed in order to understand how different ambient conditions (wind speed and direction, stability, and inland cold pool) and terrain characteristics impact barrier jets along the southeastern Alaskan coast. The broad inland terrain of western North America is important in Alaskan jet development, since it rotates the impinging flow cyclonically (more coast parallel) well upstream of the coast, thus favoring more low-level flow blocking while also adding momentum and width to the barrier jet. Near the steep coastal terrain, the largest wind speed enhancement factor (1.9-2.0) in the terrain-parallel direction relative to the ambient onshore-directed wind speed occurs at relatively low Froude numbers (Fr ϳ 0.3-0.4). These low Froude numbers are associated with (10-15 m s Ϫ1 ) ambient wind speeds and wind directions orientated 30°-45°from terrain-parallel. For simulations with an inland cold pool and nearly coast-parallel flow, strong gap outflows develop through the coastal mountain gaps, shifting the largest wind speed enhancement to Fr Ͻ 0.2. The widest barrier jets occur with ambient winds oriented nearly terrain-parallel with strong static stability. The gap outflows shift the position of the jet maximum farther offshore from the coast and increase the jet width. The height of the jet maxima is typically located at the top of the shallow gap outflow (ϳ500 m MSL), but without strong gap outflows, the jet heights are located at the top of the boundary layer, which is higher (lower) for large (small) frictionally induced vertical wind shear and weak (strong) static stability.

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Section: Introductionmentioning

confidence: 93%

Three-Dimensional Idealized Simulations of Barrier Jets along the Southeast Coast of Alaska

Olson

Colle

2009

Monthly Weather Review

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“…The frequency of observation varies according to location and is generally low compared to coarse-resolution satellite sensors and site measurements. A major advantage of SAR data in connection with offshore wind resource assessment is the ability to resolve mesoscale wind variations caused by topography in near-coastal areas (Alpers et al 2009;Winstead et al 2006;Young and Winstead 2005).…”

Section: Introductionmentioning

confidence: 99%

Wind Class Sampling of Satellite SAR Imagery for Offshore Wind Resource Mapping

Badger

Nielsen

et al. 2010

Journal of Applied Meteorology and Climatology

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High-resolution wind fields retrieved from satellite synthetic aperture radar (SAR) imagery are combined for mapping of wind resources offshore where site measurements are costly and sparse. A new sampling strategy for the SAR scenes is introduced, based on a method for statistical-dynamical downscaling of largescale wind conditions using a set of wind classes that describe representative wind situations. One or more SAR scenes are then selected to represent each wind class and the classes are weighted according to their frequency of occurrence. The wind class methodology was originally developed for mesoscale modeling of wind resources. Its performance in connection with sampling of SAR scenes is tested against two sets of random SAR samples and meteorological observations at three sites in the North Sea during 2005-08. Predictions of the mean wind speed and the Weibull scale parameter are within 5% from the mast observations whereas the deviation on power density and the Weibull shape parameter is up to 7%. These results are promising and may be improved further through a better population of the wind classes. Advantages of the wind class sampling method over random sampling include, in principle, selection of the most representative SAR scenes such that wind resources can be predicted from a lower number of SAR samples. Furthermore, the wind class weightings can be adjusted to represent any time period.

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“…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). Prefrontal low-level blocking has been observed to aid rapid weakening of a cold front as it approached the Pacific Cascades (Bond et al 2005), and topographic barrier jets have been observed by synthetic aperture radar in the Gulf of Alaska (Winstead et al 2006). In addition to these observational studies, there are multiple theoretical experiments that describe the inverse relationship between the Froude number and the degree of frontal retardation (e.g., Egger and Hoinka 1992).…”

Section: Introductionmentioning

confidence: 99%

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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Using SAR Remote Sensing, Field Observations, and Models to Better Understand Coastal Flows in the Gulf of Alaska

Abstract: A synergistic approach using synthetic aperture radar, mesoscale modeling, and aircraft observations has improved our understanding of barrier jets in the Gulf of Alaska.

Cited by 23 publications

References 39 publications

Three-Dimensional Idealized Simulations of Barrier Jets along the Southeast Coast of Alaska

Three-Dimensional Idealized Simulations of Barrier Jets along the Southeast Coast of Alaska

Wind Class Sampling of Satellite SAR Imagery for Offshore Wind Resource Mapping

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

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