Aerosol lofting from sea breeze during the Indian Ocean Experiment

Verma, Sunita; Boucher, Oliviér; Venkataraman, Chandra; Reddy, M. Shekar; Müller, Detlef; Chazette, Patrick; Crouzille, B.

doi:10.1029/2005jd005953

Cited by 34 publications

(38 citation statements)

References 34 publications

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“…The first evidence of this diurnal behavior was already gathered during the pre-INDOEX FFP campaign in 1998, when rapid increases of an order of magnitude in the aerosol concentrations in all size categories were seen corresponding with the onset of the land breeze in the evening in the coastal city of Trivandrum (Murugavel and Kamra, 1999). Similar to the daytime sea breeze effects, simulations with a mesoscale model (Simpson and Raman, 2005) reproduce this mechanism, and the basic features are also present in the zoom region of a global model (Verma et al, 2006), confirming this as an important mechanism in controlling the pollutant outflow in the regional MBL. The split layers in the SAW-ABC will have important implications for the large scale effects, for instance due to differences in the impact of warming by absorbing aerosols located near the surface (which would tend to substantially increase atmospheric instability) compared to warming in the residual layer (which can strengthen the MBL inversion cap).…”

Section: Outflow Channels and Layersmentioning

confidence: 58%

“…The convergence of the sea breeze with the NE monsoon winds results in strong upwelling in the boundary layer. Verma et al (2006) computed that both the mean horizontal velocity of the sea breeze (3.4 m/s) and the ascent rate are about twice as large in March as in February 1999. For March, the mean ascent rate computed with the global model is about 0.25 Pa/s, which is equivalent to about 12 h for transport from the surface to 1 km (about 100 hPa pressure difference); interestingly, in some cases up to an order of magnitude more rapid ascent is computed with the mesoscale model, though the reasons for these differences (other than the higher resolution of the mesoscale model) are not known.…”

Section: Outflow Channels and Layersmentioning

confidence: 99%

“…Despite the potential contributions to the elevated layers from various mechanisms, recent strong support for the primary role of the land-sea breeze in producing these elevated layers has been provided by simulations with a mesoscale model (Simpson and Raman, 2006) and with a global model which includes a zoom feature allowing the resolution to be increased to better than 0.5 • in the horizontal over the zoom region (Verma et al, 2006) the land-sea breeze circulation, whereas it is not represented in the lower resolutions typically used in global models. Several features emerge from these two studies taken together.…”

Section: Outflow Channels and Layersmentioning

confidence: 99%

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Atmospheric pollutant outflow from southern Asia: a review

2010

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Abstract. Southern Asia, extending from Pakistan and Afghanistan to Indonesia and Papua New Guinea, is one of the most heavily populated regions of the world. Biofuel and biomass burning play a disproportionately large role in the emissions of most key pollutant gases and aerosols there, in contrast to much of the rest of the Northern Hemisphere, where fossil fuel burning and industrial processes tend to dominate. This results in polluted air masses which are enriched in carbon-containing aerosols, carbon monoxide, and hydrocarbons. The outflow and long-distance transport of these polluted air masses is characterized by three distinct seasonal circulation patterns: the winter monsoon, the summer monsoon, and the monsoon transition periods. During winter, the near-surface flow is mostly northeasterly, and the regional pollution forms a thick haze layer in the lower troposphere which spreads out over millions of square km between southern Asia and the Intertropical Convergence Zone (ITCZ), located several degrees south of the equator over the Indian Ocean during this period. During summer, the heavy monsoon rains effectively remove soluble gases and aerosols. Less soluble species, on the other hand, are lifted to the upper troposphere in deep convective clouds, and are then transported away from the region by strong upper tropospheric winds, particularly towards northern Africa and the Mediterranean in the tropical easterly jet. Part of the pollution can reach the tropical tropopause layer, the gateway to the stratosphere. During the monsoon transition periods, the flow across the Indian Ocean is primarily zonal, and strong pollution plumes originating from both southeastern Asia and from Africa spread across the central Indian Ocean. This paper provides a review of the current state of knowledge based on the many observational and modeling studies over the last decades that have examined the southern AsianCorrespondence to: M. G. Lawrence (mark.lawrence@mpic.de) atmospheric pollutant outflow and its large scale effects. An outlook is provided as a guideline for future research, pointing out particularly critical issues such as: resolving discrepancies between top down and bottom up emissions estimates; assessing the processing and aging of the pollutant outflow; developing a better understanding of the observed elevated pollutant layers and their relationship to local sea breeze and large scale monsoon circulations; and determining the impacts of the pollutant outflow on the Asian monsoon meteorology and the regional hydrological cycle, in particular the mountain cryospheric reservoirs and the fresh water supply, which in turn directly impact the lives of over a billion inhabitants of southern Asia.

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Section: Outflow Channels and Layersmentioning

confidence: 58%

Section: Outflow Channels and Layersmentioning

confidence: 99%

Section: Outflow Channels and Layersmentioning

confidence: 99%

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Atmospheric pollutant outflow from southern Asia: a review

2010

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“…from the Indian coast (Verma et al, 2006). Within the MBL the high humidity typically enables faster photochemical processing (via higher OH radical concentrations, e.g., Real et al (2008)) and soluble species also experience deposition to the surface.…”

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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“…This layer of air above the MBL can become decoupled from the surface, and is subject to higher wind speeds and negligible deposition, enabling more efficient long-range transport than within the MBL. Verma [7] and Raman [8] show that pollutants are frequently observed in layers above the top of the MBL. This study uses the Met Office Unified Model with passive tracers to quantify coastal outflow and investigate the meteorological processes that control it.…”

Section: Introductionmentioning

confidence: 99%

Coastal influences on pollution transport

Peake¹,

Dacre²,

Methven³

2011

WIT Transactions on Ecology and the Environment

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The ventilation of pollutants from the boundary layer into the free troposphere is an important process in controlling regional air quality. Coastal outflow is the horizontal ventilation of pollutants across a coastline from a layer within the continental boundary layer to above the marine boundary layer. It has been shown using the Met Office Unified Model that the ventilation by coastal outflow occurs with a similar order of magnitude to ventilation by convection, and that it possesses a diurnal cycle induced by the boundary layer height cycle over land. Pollutants with short lifetimes (typically several hours) exhibit the greatest diurnal variability in export by coastal outflow. Ventilation by coastal outflow by pollutants with longer lifetimes are less dependent on the boundary layer height over land and more dependent on the large scale cross-coastal wind strength. A simple model developed to simulate coastal outflow shows that increasing the pollutant lifetime, wind speed or convective boundary layer height increases export of tracer by coastal outflow. Above a threshold windspeed, coastal outflow is reduced due to tracer being exported across a coastline before being able to be mixed to a height greater than the marine boundary layer. Convection slightly decreases export by coastal outflow, although this effect is small.

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Aerosol lofting from sea breeze during the Indian Ocean Experiment

Cited by 34 publications

References 34 publications

Atmospheric pollutant outflow from southern Asia: a review

Atmospheric pollutant outflow from southern Asia: a review

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

Coastal influences on pollution transport

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