Accumulation mode aerosol, pockets of open cells, and particle nucleation in the remote subtropical Pacific marine boundary layer

Petters, M. D.; Snider, Jefferson R.; Stevens, Björn; Vali, Gabor; Faloona, I. C.; Russell, Lynn M.

doi:10.1029/2004jd005694

Cited by 106 publications

(106 citation statements)

References 50 publications

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“…The open-cell structures are called Pockets of Open Cells (POCs) or rifts (Sharon et al, 2006). Their origin is not fully understood, but significant differences in aerosol and cloud microphysical properties between POCs and the surrounding clouds are typically observed Petters et al, 2006;Sharon et al, 2006;Wood et al, 2008Wood et al, , 2011a. VanZanten and Stevens (2005), Sharon et al (2006), and Wood et al (2011a) found that POCs are characterized by enhanced drizzle, although drizzle itself seem insufficient for transition from closed-to open-cell circulations Wood et al (2011a).…”

Section: Published By Copernicus Publications On Behalf Of the Europementioning

confidence: 99%

Limited-are a modelling of stratocumulus over South-Eastern Pacific

et al. 2012

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Abstract. This paper presents application of the Weather Research and Forecasting (WRF) model to limited-area modeling of atmospheric processes over the subtropical southeastern Pacific, with the emphasis on the stratocumulustopped boundary layer. The simulations cover a domain from the VAMOS (Variability of the American Monsoon Systems) Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) field project conducted in the subtropical south-eastern Pacific in October and November 2008. We focus on a day where the UK's BAe-146 research aircraft encountered Pockets of Open Cells (POCs) at the very western edge of its flight track, rather than on the entire campaign as investigated in previous limited-area modeling studies. Model results are compared to aircraft observations with the main conclusion that the simulated stratocumulus-topped boundary layer is significantly too shallow. This appears to be a combination of an already too shallow boundary layer in the dataset used to provide initial and lateral boundary conditions, and the inability of the WRF model to increase the boundary-layer height. Several sensitivity simulations, applying different subgrid-scale parameterizations available in the model, a larger computational domain and longer simulations, as well as a different dataset providing initial and lateral boundary conditions were all tried to improve the simulation. These changes appeared to have a rather small effect on the results.The model does simulate the formation of mesoscale cloud-free regions that one might consider similar to Pockets of Open Cells observed in nature. However, formation of these regions does not seem to be related to drizzle-induced transition from open-to closed-cell circulations as simulated by LES models. Instead, the cloud-free regions appear to result from mesoscale variations of the lower-tropspheric vertical velocity. Areas of negative vertical velocity with minima (a few cm s −1 ) near the boundary layer top seem to induce direct evaporation of the cloud layer. It remains to be seen in LES studies whether the mechanism seen in the model is realistic or if it is simply an artifact of interactions between resolved and parameterized processes.

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Section: Published By Copernicus Publications On Behalf Of the Europementioning

confidence: 99%

Limited-are a modelling of stratocumulus over South-Eastern Pacific

et al. 2012

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“…We estimate the random error on the cloud forcing is less than ±10 Wm −2 , which is due to measurement, interpolation and radiation transfer calculation errors. Cloud radar reflectivity was obtained using a Kband millimeter wavelength cloud radar (Moran et al, 1998). CCN were measured with two identical in situ CCN counters (Roberts and Nenes, 2005).…”

Section: Observations and Model Descriptionmentioning

confidence: 99%

An Arctic CCN-limited cloud-aerosol regime

et al. 2011

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Abstract. On average, airborne aerosol particles cool the Earth's surface directly by absorbing and scattering sunlight and indirectly by influencing cloud reflectivity, life time, thickness or extent. Here we show that over the central Arctic Ocean, where there is frequently a lack of aerosol particles upon which clouds may form, a small increase in aerosol loading may enhance cloudiness thereby likely causing a climatologically significant warming at the ice-covered Arctic surface. Under these low concentration conditions cloud droplets grow to drizzle sizes and fall, even in the absence of collisions and coalescence, thereby diminishing cloud water. Evidence from a case study suggests that interactions between aerosol, clouds and precipitation could be responsible for attaining the observed low aerosol concentrations.

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“…Bretherton et al, 2004;Comstock et al, 2005;Stevens et al, 2005;Petters et al, 2006;Wood et al, 2008Wood et al, , 2011a; and references therein). Very briefly, local dynamical processes leading to enhanced drizzle formation in Sc clouds remove moisture and cloud condensation nuclei (CCN) from the boundary layer, thus suppressing recovery of the cloud from the moisture sink of drizzle.…”

Section: Introductionmentioning

confidence: 99%

Gravity‐wave‐induced perturbations in marine stratocumulus

Allen

Vaughan

Toniazzo

et al. 2012

Quart J Royal Meteoro Soc

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We discuss the role of atmospheric gravity waves in modulating cloud radiative and dynamical properties over the southeast Pacific. Satellite imagery and satelliteretrieved cloud properties during October 2008 illustrate three distinct episodes of horizontal propagation of gravity wave trains across the large-scale stratocumulus (Sc) cloud deck capping the local marine boundary layer. In one period, 7-9 October 2008, the waves modulated cloud-top-height by up to 400 m peak-to-trough, propagating perpendicular to the synoptic boundary layer flow with phase speed 15.3 m s −1 , period ∼1 h and horizontal wavelength 55 km. The gravity waves were observed to be non-dispersive. These waves were first evident in the cloud deck near 30• S, 85• W during a 24 h period beginning at midday on 7 October 2008, and propagated northeastward toward the Peruvian coast for the following 48 h. During this time they induced both reversible and non-reversible changes in cloud-radiative and cloud-dynamic properties, such that areas of clear sky developed in the troughs of passing wave-fronts. These pockets of open cells persisted long after the passage of the gravity waves, advecting northwestward with the background wind. Using the analysis fields of the European Centre for Medium-Range Weather Forecasts in conjunction with infrared and microwave satellite imagery, we show that these gravity waves emerged from a disturbed subtropical jet stream. The radiant of the waves was coincident in all cases with centres of large negative residuals in nonlinear balance, suggesting that geostrophic readjustment of sharply divergent flows associated with the disturbed jet provided a source for the wave energy. Conversely, gravity waves were not observed in more quiescent jet conditions. This case study highlights the important and irreversible effects that gravity waves propagating in the troposphere can have on cloud radiative properties (and hence surface radiation budgets) over a very wide area. It also highlights the importance of synoptic influence on Sc-covered marine boundary layers.

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Accumulation mode aerosol, pockets of open cells, and particle nucleation in the remote subtropical Pacific marine boundary layer

Cited by 106 publications

References 50 publications

Limited-are a modelling of stratocumulus over South-Eastern Pacific

Limited-are a modelling of stratocumulus over South-Eastern Pacific

An Arctic CCN-limited cloud-aerosol regime

Gravity‐wave‐induced perturbations in marine stratocumulus

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