Numerical Study of the Diurnal Cycle along the Central Oregon Coast during Summertime Northerly Flow

Bielli, Soline; Barbour, Philip L.; Samelson, R. M.; Skyllingstad, Eric D.; Wilczak, James M.

doi:10.1175/1520-0493(2002)130<0992:nsotdc>2.0.co;2

Cited by 19 publications

(25 citation statements)

References 20 publications

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“…7c). The meridional wind component is approximately in geostrophic balance above the turbulent boundary layer as found by previous studies of the CLLCJ and its Northern Hemisphere counterpart, the California coastal jet (e.g., Bielli et al 2002;Muñ oz and Garreaud 2005). However, a careful inspection shows that, within the boundary layer top inversion, the meridional wind is slightly supergeostrophic.…”

Section: Classification and Characteristics Of Cllcjsupporting

confidence: 81%

Some Insights into the Characteristics and Dynamics of the Chilean Low-Level Coastal Jet

Jiang

Wang

O’Neill

2010

Monthly Weather Review

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The characteristics and dynamics of the Chilean low-level coastal jet (CLLCJ) are examined here through diagnosing real-time mesoscale model forecasts in support of the Variability of the American Monsoon System (VAMOS) Ocean-Cloud-Atmosphere Land Study (VOCALS) and additional sensitivity simulations. The forecasted surface winds over the southeast Pacific compare favorably with available observations. According to the forecasts and sensitivity simulations, the Southeast Pacific high pressure system (SEPH) plays a primary role in driving the CLLCJ. The Andes significantly intensify the CLLCJ mainly through interacting with the SEPH and anchoring a baroclinic zone along the Chilean coast. The land-sea differential heating also enhances the CLLCJ by strengthening the coastal baroclinic zone. Based on the location of the SEPH center, the CLLCJ can be separated into two types: a strong-forcing jet, with the SEPH close to the central Chilean coastline; and a weak-forcing jet, with the SEPH centered far away from the coastline. The former is much more intense and associated with stronger interaction between the SEPH and the Andes.The CLLCJ is slightly supergeostrophic within the marine boundary layer top inversion, where weak easterlies develop, and subgeostrophic in the turbulent boundary layer below, where westerlies are present. The inversion easterlies induce strong subsidence along the coast, which contributes to the formation of the coastal low and the coastal baroclinic zone.

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Section: Classification and Characteristics Of Cllcjsupporting

confidence: 81%

Some Insights into the Characteristics and Dynamics of the Chilean Low-Level Coastal Jet

Jiang

Wang

O’Neill

2010

Monthly Weather Review

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“…Previous studies have shown that coastal regions are favorable for the formation of LLJs because of the contrasts in temperature, moisture availability, roughness, and albedo. Other such case studies have been previously conducted for the LLJ events that occurred along the California coast (e.g., Meitin and Stuart 1977;Sjostedt et al 1990;Dorman and Winant 1995;Bielli et al 2002). In the present case, eliminating the water surfaces produces the smallest changes in the mass and wind fields among the three sensitivity simulations, except for the more stable PBL over the ocean, as expected (cf.…”

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confidence: 80%

Low-Level Jets over the Mid-Atlantic States: Warm-Season Climatology and a Case Study

Zhang

Weaver

2006

Journal of Applied Meteorology and Climatology

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Although considerable research has been conducted to study the characteristics of the low-level jets (LLJs) over the Great Plains states, little is known about the development of LLJs over the Mid-Atlantic states. In this study, the Mid-Atlantic LLJ and its associated characteristics during the warm seasons of 2001 and 2002 are documented with both the wind profiler data and the daily real-time model forecast products. A case study with three model sensitivity simulations is performed to gain insight into the three-dimensional structures and evolution of an LLJ and the mechanisms by which it developed. It is found that the Mid-Atlantic LLJ, ranging from 8 to 23 m s Ϫ1, appeared at an average altitude of 670 m and on 15-25 days of each month. About 90% of the 160 observed LLJ events occurred between 0000 and 0600 LST, and about 60% had southerly to westerly directions. Statistically, the real-time forecasts capture most of the LLJ events with nearly the right timing, intensity, and altitude, although individual forecasts may not correspond to those observed. For a selected southwesterly LLJ case, both the observations and the control simulation exhibit a pronounced diurnal cycle of horizontal winds in the lowest 1.5 km. The simulation shows that the Appalachian Mountains tend to produce a sloping mixed layer with northeasterly thermal winds during the daytime and reversed thermal winds after midnight. With additional thermal contrast effects associated with the Chesapeake Bay and the Atlantic Ocean, the daytime low-level winds vary significantly from the east coast to the mountainous regions. The LLJ after midnight tends to be peaked preferentially around 77.5°W near the middle portion of the sloping terrain, and it decreases eastward as a result of the opposite thermal gradient across the coastline from the mountain-generated thermal gradient. Although the Mid-Atlantic LLJ is much weaker and less extensive than that over the Great Plains states, it has a width of 300-400 km (to its half-peak value) and a length scale of more than 1500 km, following closely the orientation of the Appalachians. Sensitivity simulations show that eliminating the surface heat fluxes produces the most significant impact on the development of the LLJ, then topography and the land-sea contrast, with its area-averaged intensity reduced from 12 m s Ϫ1 to about 6, 9, and 10 m s Ϫ1, respectively.

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“…The presence of strong diurnal variations in the coastal ocean along the U.S. west coast, and in particular around the coastal capes, has been found by both observational and modeling studies (Beardsley et al 1987;Burk and Thompson 1996;Kindle et al 2002;Bielli et al 2002;Perlin et al 2004;Haack et al 2008). The combination of orographic and diurnal effects is likely the source of the reported variability in the coastal region, but the exact mechanism responsible for the diurnal variations has yet to be determined.…”

Section: Diurnal Variationsmentioning

confidence: 84%

“…Alternative compression bulges are often found on the windward side of the coastal promontories (Beardsley et al 1987;Winant et al 1988;Rogerson 1999;Samelson 1992). The intensity of these mesoscale phenomena, their spatial extents, and their effects on the coastal ocean circulation, however, show some uncertainty and variability in the nearshore area (;100 km), where coastal topography, the diurnal cycle, and the underlying sea surface temperature field complicate the analysis (Enriquez and Friehe 1995;Dorman et al 2000;Bielli et al 2002;Haack et al 2001Haack et al , 2008.…”

Section: Introductionmentioning

confidence: 99%

Coastal Atmospheric Circulation around an Idealized Cape during Wind-Driven Upwelling Studied from a Coupled Ocean–Atmosphere Model

Perlin

Skyllingstad

Samelson

2011

Monthly Weather Review

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The study analyzes atmospheric circulation around an idealized coastal cape during summertime upwellingfavorable wind conditions simulated by a mesoscale coupled ocean-atmosphere model. The domain resembles an eastern ocean boundary with a single cape protruding into the ocean in the center of a coastline. The model predicts the formation of an orographic wind intensification area on the lee side of the cape, extending a few hundred kilometers downstream and seaward. Imposed initial conditions do not contain a low-level temperature inversion, which nevertheless forms on the lee side of the cape during the simulation, and which is accompanied by high Froude numbers diagnosed in that area, suggesting the presence of the supercritical flow. Formation of such an inversion is likely caused by average easterly winds resulting on the lee side that bring warm air masses originating over land, as well as by air warming during adiabatic descent on the lee side of the topographic obstacle. Mountain leeside dynamics modulated by differential diurnal heating is thus suggested to dominate the wind regime in the studied case.The location of this wind feature and its strong diurnal variations correlate well with the development and evolution of the localized lee side trough over the coastal ocean. The vertical extent of the leeside trough is limited by the subsidence inversion aloft. Diurnal modulations of the ocean sea surface temperatures (SSTs) and surface depth-averaged ocean current on the lee side of the cape are found to strongly correlate with wind stress variations over the same area.Wind-driven coastal upwelling develops during the simulation and extends offshore about 50 km upwind of the cape. It widens twice as much on the lee side of the cape, where the coldest nearshore SSTs are found. The average wind stress-SST coupling in the 100-km coastal zone is strong for the region upwind of the cape, but is notably weaker for the downwind region, estimated from the 10-day-average fields. The study findings demonstrate that orographic and diurnal modulations of the near-surface atmospheric flow on the lee side of the cape notably affect the air-sea coupling on various temporal scales: weaker wind stress-SST coupling results for the long-term averages, while strong correlations are found on the diurnal scale.

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Numerical Study of the Diurnal Cycle along the Central Oregon Coast during Summertime Northerly Flow

Cited by 19 publications

References 20 publications

Some Insights into the Characteristics and Dynamics of the Chilean Low-Level Coastal Jet

Some Insights into the Characteristics and Dynamics of the Chilean Low-Level Coastal Jet

Low-Level Jets over the Mid-Atlantic States: Warm-Season Climatology and a Case Study

Coastal Atmospheric Circulation around an Idealized Cape during Wind-Driven Upwelling Studied from a Coupled Ocean–Atmosphere Model

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