Thermodynamic structure and entrainment of stratocumulus over the Southern Ocean

Boers, R.; Krummel, Paul B.; Siems, Steven T.; Hess, Glenn

doi:10.1029/98jd00529

Cited by 13 publications

(7 citation statements)

References 34 publications

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“…The most common estimate for mid-latitude MBL entrainment for clear and cloudy conditions, however, is 3Á4 mm s (1 (e.g. Kritz, 1983;Ayers and Galbally, 1995;Boers et al, 1998;Stevens et al, 2003;Sandu et al, 2009). In most cases, the uncertainty associated with these estimates is of the order of 25Á60%.…”

Section: Entrainment Velocitymentioning

confidence: 97%

“…Kritz, 1983). The primary capping inversion that separates MBL processes from the free troposphere is usually found 1000Á1900 m above sea level (Ayers and Galbally, 1995;Boers et al, 1998;Russell et al, 1998;Lenschow et al, 1999). When present, cloud base usually lies between 400 and 800 m, and the overlying cloud layer is often less than 500 m thick (Russell et al, 1998;Lenschow et al, 1999).…”

Section: Entrainment Velocitymentioning

confidence: 97%

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Constraining annual and seasonal radon-222 flux density from the Southern Ocean using radon-222 concentrations in the boundary layer at Cape Grim

Zahorowski

Griffiths

Chambers

et al. 2013

Tellus B: Chemical and Physical Meteorology

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Radon concentrations measured between 2001 and 2008 in marine air at Cape Grim, a baseline site in north-western Tasmania, are used to constrain the radon flux density from the Southern Ocean. A method is described for selecting hourly radon concentrations that are least perturbed by land emissions and dilution by the free troposphere. The distribution of subsequent radon flux density estimates is representative of a large area of the Southern Ocean, an important fetch region for Southern Hemisphere climate and air pollution studies. The annual mean flux density (0.27 mBq m−2 s−1) compares well with the mean of the limited number of spot measurements previously conducted in the Southern Ocean (0.24 mBq m−2 s−1), and to some spot measurements made in other oceanic regions. However, a number of spot measurements in other oceanic regions, as well as most oceanic radon flux density values assumed for modelling studies and intercomparisons, are considerably lower than the mean reported here. The reported radon flux varies with seasons and, in summer, with latitude. It also shows a quadratic dependence on wind speed and significant wave height, as postulated and measured by others, which seems to support our assumption that the selected least perturbed radon concentrations were in equilibrium with the oceanic radon source. By comparing the least perturbed radon observations in 2002–2003 with corresponding ‘TransCom’ model intercomparison results, the best agreement is found when assuming a normally distributed radon flux density with σ=0.075 mBq m−2 s−1

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Section: Entrainment Velocitymentioning

confidence: 97%

Section: Entrainment Velocitymentioning

confidence: 97%

Constraining annual and seasonal radon-222 flux density from the Southern Ocean using radon-222 concentrations in the boundary layer at Cape Grim

Zahorowski

Griffiths

Chambers

et al. 2013

Tellus B: Chemical and Physical Meteorology

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show abstract

“…We suggest that the absence of this post-sunrise ozone destruction may not have been apparent in current photochemical models when compared with observations because of the underestimation of the diurnally averaged entrainment rate of air from the free troposphere into the marine boundary layer [Boers et at., 1998], which is the major source of ozone for the remote MBL.…”

Section: Discussionmentioning

confidence: 99%

“…The differences for any particular hour are not symmetrically distributed, and there is a tendency during an individual run of baseline conditions for the ozone concentration to decrease in summer, and to a lesser extent, increase in winter with increasing time from the start of the baseline conditions[Zahorowski et al, 1996]. This leads to a net negative bias in the 24 hour average difference in summer.We have looked at 10 variations on the definition of baseline and other associated statistics such as the diurnal timing of commencement of baseline and found that this sunrise ozone decrease is robust to these definitions as is the midday summer decrease, but other apparent features vary with the definitions.Diagnostic and Explanatory ModelThe inversion capped MBL is not a permanent feature over the southern ocean, but is a transient feature that persists for about two-thirds of the time breaking up and reforming on a near weekly basis with the passage of frontal systems through this region[Boers et al, 1998]. Hence, what we observe is not an equilibrium boundary layer but one constantly reforming and approaching equilibrium.…”

mentioning

confidence: 99%

Mid‐latitude marine boundary‐layer ozone destruction at visible sunrise observed at Cape Grim, Tasmania, 41°S

Galbally¹,

Bentley²,

Meyer³

2000

Geophysical Research Letters

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Abstract. An analysis is made of 13 years of observations of ozone concentrations in the remote marine boundary layer at Cape Grim, Tasmania 41øS. These data reveal a decrease in ozone concentration in the first few hours following sunrise at a rate of around 0.1 ppb h -z in mid-summer and in mid-winter. This ozone destruction phenomenon causes an asymmetry in the daily ozone loss rate with enhanced destruction following sunrise, is statistically distinguishable from the 03 -HOx destruction cycle that peaks at midday, and occurs at similar rates in mid-summer and in midwinter.The cause of this sunrise ozone decrease is examined using the conservation equation for ozone. We speculate that ozone destruction at sunrise arises due to halogen chemistry. The absence of sunrise ozone decrease in models of marine boundary-layer photochemistry means that the ozone destruction rate in the remote marine boundary layer is underestimated by perhaps a factor of two.

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“…ity probability distribution functions, not those derived from the truncated distributions. The range of values reported by Boers et al [1998], in their analysis of airborne gust probe data from marine stratocumulus clouds are in good agreement with the range of values we report in section 2.2.2. There is also consistency with the parameterizations of VanZanten et al [1999], who conducted numerical studies of turbulence in a cloud-topped boundary layer.…”

Section: Sensitivity To Vertical Velocitymentioning

confidence: 99%

Aerosol activation in marine stratocumulus clouds: 2. Köhler and parcel theory closure studies

et al. 2003

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[1] Aerosol properties and vertical velocities relevant to cloud droplet concentrations in marine stratocumulus clouds are presented. Data were collected at a coastal surface site, and on an aircraft that flew north (upwind) of the surface site during the CLOUDYCOLUMN portion of the second Aerosol Characterization Experiment (ACE-2). In a closure study we compare observations, from five study days, and predictions based on Köhler and parcel theory. Measured and predicted cloud condensation nuclei (CCN) do agree after accounting for differences between the mobility equivalent (D me ) and sphere equivalent (D se ) diameters, but only when considering results from two study days unaffected by continental pollution. After applying the D me À D se correction, cloud droplet concentration closure was also achieved, or nearly achieved, on three study days. Discrepancies between predicted and measured CCN, or between predicted and measured droplet concentration, were always in the direction of predicted values being larger than that measured. Although theoretical studies do specify scenarios where droplet concentration and CCN overestimation can occur, the observed disparities may also be due to multiple and poorly characterized experimental biases.

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Thermodynamic structure and entrainment of stratocumulus over the Southern Ocean

Abstract: The boundary layer is mostly buoyancy-driven, with shear-generated turbulence at most only half of the buoyancy-generated turbulence.

Cited by 13 publications

References 34 publications

Constraining annual and seasonal radon-222 flux density from the Southern Ocean using radon-222 concentrations in the boundary layer at Cape Grim

Constraining annual and seasonal radon-222 flux density from the Southern Ocean using radon-222 concentrations in the boundary layer at Cape Grim

Mid‐latitude marine boundary‐layer ozone destruction at visible sunrise observed at Cape Grim, Tasmania, 41°S

Aerosol activation in marine stratocumulus clouds: 2. Köhler and parcel theory closure studies

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