A case study of boundary layer ventilation by convection and coastal processes

Dacre, Helen; Gray, Suzanne L.; Belcher, Stephen E.

doi:10.1029/2006jd007984

Cited by 36 publications

(45 citation statements)

References 28 publications

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“…Over LIS, residual layers have frequently been found in summer months, when land-sea temperature contrasts are larger [41] and observed as reservoirs for boundary layer trace gas pollutants during air quality episodes along the East Coast [42]. In the study conducted here, data further suggested that the residual layer facilitated the long-range transport achieved by the plume through its advection into the lower troposphere and over the marine boundary layer, thus, detaching it from surface interactions in a similar fashion to that described by Dacre et al [15] and Fochesatto et al [43].…”

Section: Physical Structure Of the Plume Layersupporting

confidence: 84%

“…In this, decoupling of the continental airmass, usually through the formation of a residual layer following the diurnal fluctuation of the daytime boundary layer, is the ventilation mechanism for the plume's release. Very similar scenarios have recently detailed in the coastal atmospheric study by Dacre et al [15] and observed during previous field campaigns in the North Atlantic, as reported by Gong et al [52]. As these and other related studies have pointed out, the coastal IBL structure can play a significant role in low-altitude regional transport, particularly over the GOM [3,9,13,14,52].…”

Section: /21~daysupporting

confidence: 83%

“…Numerous efforts have described such scenarios, including Owen et al [11] who found that along the North American Atlantic coast, "exported continental plumes produce pollutant layers in a statically stable atmosphere with weak vertical mixing". Dacre et al [15] added that these polluted coastal layers are generally shallow residual layers of the continental boundary layer which are eventually advected into the lower marine troposphere. The authors continue that this advection can be a function of local mesoscale processes, such as the sea-breeze and coastal land-sea flow patterns, which, in their study, facilitated shallow ventilation and boundary layer trace gas transport over the Atlantic and North Sea.…”

Section: Introductionmentioning

confidence: 99%

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Meteorological Influences on Trace Gas Transport along the North Atlantic Coast during ICARTT 2004

et al. 2014

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An analysis of coastal meteorological mechanisms facilitating the transit pollution plumes emitted from sources in the Northeastern U.S. was based on observations from the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) 2004 field campaign. Particular attention was given to the relation of these plumes to coastal transport patterns in lower tropospheric layers throughout the Gulf of Maine (GOM), and their contribution to large-scale pollution outflow from the North American continent. Using measurements obtained during a series of flights of the National Oceanic & Atmospheric Administration (NOAA) WP-3D and the National Aeronautics and Space Administration (NASA) DC-8, a unique quasi-Lagrangian case study was conducted for a freshly emitted plume emanating from the New York City source region in late July 2004. The development of this plume stemmed from the OPEN ACCESSAtmosphere 2014, 5 974 accumulation of boundary layer pollutants within a coastal residual layer, where weak synoptic conditions allowed for its advection into the marine troposphere and transport by a mean southwesterly flow. Upon entering the GOM, analysis showed that the plume layer vertical structure evolved into an internal boundary layer form, with signatures of steep vertical gradients in temperature, moisture and wind speed often resulting in periodic turbulence. This structure remained well-defined during the plume study, allowing for the detachment of the plume layer from the surface and minimal plume-sea surface exchange. In contrast, shear driven turbulence within the plume layer facilitated lateral mixing with other low-level plumes during its transit. This turbulence was periodic and further contributed to the high spatial variability in trace gas mixing ratios. Further influences of the turbulent mixing were observed in the impact of the plume inland as observed by the Atmospheric Investigation, Regional Modeling, Analysis and Prediction (AIRMAP) air quality network. This impact was seen as extreme elevations of surface ozone and CO levels, equaling the highest observed that summer.

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Section: Physical Structure Of the Plume Layersupporting

confidence: 84%

Section: /21~daysupporting

confidence: 83%

Section: Introductionmentioning

confidence: 99%

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Meteorological Influences on Trace Gas Transport along the North Atlantic Coast during ICARTT 2004

et al. 2014

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“…Both forms of convective activity can lead to ventilation of the boundary layer and rapid vertical transport on a time-scale of hours into the free troposphere (e.g. Gimson, 1997;Dacre et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Boundary‐layer ventilation by baroclinic life cycles

Sinclair

Gray

Belcher

2008

Quart J Royal Meteoro Soc

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Ventilation of the boundary layer has an important effect on local and regional air quality and is a prerequisite for long-range pollution transport. Once in the free troposphere, pollutants can alter the chemical composition of the troposphere and impact on the Earth's radiative forcing. Idealised baroclinic life cycles, LC1 and LC2, have been simulated in a three-dimensional dry hemispheric model in the presence of boundary-layer turbulent fluxes. A passive tracer is added to the simulations to represent pollution emitted at, or near, the surface. A simple conveyor-belt diagnostic is developed to objectively identify regions of the boundary layer that can be ventilated by either warm or cold conveyor belts. Transport of pollutants within and above the boundary layer is examined on synoptic scales. Three different physical mechanisms are found to interact with each other to ventilate pollutants out of the boundary layer. These mechanisms are turbulent mixing within the boundary layer, horizontal advection due to Ekman convergence and divergence within the boundary layer, and advection by the warm conveyor belt. The mass of tracer ventilated by the two life cycles is remarkably similar given the differences in frontal structure, suggesting that the large-scale baroclinicity is an effective constraint on ventilation.

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“…In this paper, the term "coastal outflow layer" will be used to describe the decoupling of pollution from the surface via the formation of an internal stable BL which occurs when there is horizontal transport from land to sea and the land BL is deeper than the MBL (as is typically the case on nonfrontal summer days) (Dacre et al, 2007). The coastal outflow layer lies above the MBL (H MBL ) but below the maximum height that the continental BL reaches during its diurnal cycle (H max ).…”

Section: L Peake Et Al: Coastal Outflowmentioning

confidence: 99%

Meteorological factors controlling low-level continental pollutant outflow across a coast

et al. 2014

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Abstract. Coastal outflow describes the horizontal advection of pollutants from the continental boundary layer (BL) across a coastline. The outflow can ventilate polluted continental BLs and thus regulate air quality in highly populated coastal regions. This paper investigates the factors controlling coastal outflow and quantifies their importance as a ventilation mechanism. Tracers in the Met Office Unified Model (MetUM) are used to examine the magnitude and variability of coastal outflow over the eastern United States during summer 2004. Over the 4 week period examined, ventilation of tracer from the continental BL via coastal outflow occurs with the same magnitude as vertical ventilation via convection and advection. The relative importance of tracer decay rate, cross-coastal advection rate, and a parameter based on the relative continental and marine BL heights on coastal outflow is assessed by reducing the problem to a time-dependent box model. The ratio of the advection rate and decay rate is a dimensionless parameter which determines whether tracers are long-lived or short-lived. Long-and short-lived tracers exhibit different behaviours with respect to coastal outflow. Short-lived tracers exhibit large diurnal variability in coastal outflow but long-lived tracers do not. For short-lived tracers, increasing the advection rate increases the diurnally averaged magnitude of coastal outflow, but this has the opposite effect for very long-lived tracers. By using the box-model solutions to interpret the MetUM simulations, a land width is determined which represents the distance inland over which emissions contribute significantly to coastal outflow. A land width of between 100 and 400 km is found to be representative for a tracer with a lifetime of 24 h.

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A case study of boundary layer ventilation by convection and coastal processes

Cited by 36 publications

References 28 publications

Meteorological Influences on Trace Gas Transport along the North Atlantic Coast during ICARTT 2004

Meteorological Influences on Trace Gas Transport along the North Atlantic Coast during ICARTT 2004

Boundary‐layer ventilation by baroclinic life cycles

Meteorological factors controlling low-level continental pollutant outflow across a coast

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