Cloud-Top Entrainment Instability Observed in AMTEX

Mahrt, L.; Paumier, James O.

doi:10.1175/1520-0469(1982)039<0622:cteioi>2.0.co;2

Cited by 28 publications

(16 citation statements)

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“…From observations (Mahrt and Paumier, 1982;Nicholls and Turton, 1986), however, it is found that even if the instability criterion of Randall (1980b) and Deardorff (1980a) is met, the cloud often does not entrain more rapidly than usual. Nicholls and Turton (1986) have argued that it is necessary to include the fact that mixing takes place between various fractions of inversion air and cloudy air (Mahrt and Paumier, 1982). This is in contrast to the assumption of Randall (1980b) and DeardorR (1980a) that the mixed parcel remains just saturated, and thus take into account only one mixing ratio.…”

Section: Entrainment Instabilitymentioning

confidence: 96%

“…This cloud top entrainment instability (Randall, 1980b;Deardot%, 1980a;Manton, 1980;Hanson, 1982Hanson, , 1987Mahrt and Paumier, 1982;Randall, 1984b;Nicholls and Turton, 1986) leads to large entrainment rates and is thought to be one of the mechanisms at play in breaking up a solid cloud deck. From observations (Mahrt and Paumier, 1982;Nicholls and Turton, 1986), however, it is found that even if the instability criterion of Randall (1980b) and Deardorff (1980a) is met, the cloud often does not entrain more rapidly than usual. Nicholls and Turton (1986) have argued that it is necessary to include the fact that mixing takes place between various fractions of inversion air and cloudy air (Mahrt and Paumier, 1982).…”

Section: Entrainment Instabilitymentioning

confidence: 99%

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Current problems in the stratocumulus-topped atmospheric boundary layer

Driedonks

Duynkerke

1989

Boundary-Layer Meteorol

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Abstmct. Extended sheets of stratocumulus (SC) in the upper part of the atmospheric boundary layer (ABL) often occur under appropriate meteorological conditions. These cloud decks are important both in climate studies and in weather forecasting. We review the current knowledge of the turbulent structure of the ABL capped by a cloud deck, in the light of recent observations and model studies. The most important physical processes determining this structure are longwave radiative cooling at cloud top, shortwave radiative warming by absorption in the cloud, surface buoyancy flux, and wind shear in the ABL. As a result, turbulence can cause entrainment against the buoyancy jump at cloud top. In cases where only longwave radiative fluxes and surface buoyancy tluxes are important, the turbulent structure is relatively well understood. When shortwave radiative fluxes and/or wind shear are also important, the resulting turbulent structure may change considerably. A decoupling of the cloud from the sub-cloud layer or of the top of the cloud from the rest of the ABL is then regularly observed. In no cases are the details of the entrainment at cloud top understood well enough to derive a relatively simple formulation that is consistent with observations. Cloud-top entrainment instability may lead to the break-up of a cloud deck (but also to cloud deepening). The role of mesoscale circulations in determining fractional cloudiness is not yet well understood.

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Section: Entrainment Instabilitymentioning

confidence: 96%

Section: Entrainment Instabilitymentioning

confidence: 99%

Current problems in the stratocumulus-topped atmospheric boundary layer

Driedonks

Duynkerke

1989

Boundary-Layer Meteorol

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“…Because of the varying strength of roll vortices and thermals, the vertical displacement of the aircraft from the undulating capping inversion is expected to change considerably along the horizontal flight path near Zi . This further complicates the analysis of data near Zj (e.g., Jensen and Lenschow, 1978;Mahrt and Paumier, 1982). At 0.9Z, of El, the aircraft encounters dry air with a 38% mean relative humidity (RH, BV = 269.6 K), which fluctuates between the mixed-layer air (0, = 268.5 K, RH = 71%) and the inversion top air (0, = 273 K, RH = 14%).…”

Section: Spectral Distributionsmentioning

confidence: 99%

“…Therefore, the evaporative-cooling influenced roll circulations, which also carry q-8 highly negatively correlated air parcels (Figures 12 and 13), transfer sensible heat upward (C,, > 0) and moisture downward (C,, < 0). It is generally known that cloud-top entrainment instability is characterized by an upward buoyancy flux at the cloud top, which can generate turbulent kinetic energy and enhance entrainment near the cloud top (e.g., Randall;Deardorff, 1980;Mahrt and Paumier, 1982). However, at E2, A& (the jump of equivalent potential temperature across Zi from above to below) is positive and ~'0: > 0 is not consistent with the jump criterion of instability.…”

Section: Spectral Distributionsmentioning

confidence: 99%

Heat fluxes and roll circulations over the western Gulf Stream during an intense cold-air outbreak

Chou

Ferguson

1991

Boundary-Layer Meteorol

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Turbulence and heat fluxes in the marine atmospheric boundary layer (MABL) far the roll vortex regime, observed during the Genesis of Atlantic Lows Experiment (GALE) over the western Gulf Stream, have been studied. The spqctral analysis suggests that cloud streets (roll vortices) are vertically organized convection in the MABL having the same roll scale for both the cloud layer and subcloud layer, and that the roll spacing is about three times the MABL depth. The roll circu~tions contribute signi~cantly to the sensible (temperature) and latent heat (moisture) fluxes with importance increasing upward. Near the MABL top, these fluxes are primarily due to roll vortices which transfer both sensible heat and moisture upward in the lower half of the convective MABL. Near the MABL top, the roll circulations transfer sensible heat downward and moisture upward in the clear thermalstreet region, but roll vortices influenced by evaporative cooling can transfer sensible heat upward and moisture downward in the cloud-street region. Near the cloud-top, the upward buoyancy Rux due to evaporative cooling is highly related to the roll circulations near the inversion.For the lower half of the MABL, the normalized temperature flux decreases upward more rapidly than the humidity flux, which is mainly because Potential temperature (8) increases slightly upward while humidity (q) decreases slightly upward above the unstable surface layer. The gradient production (associated with the 6 gradient) is a source for the temperature flux in the unstable surface layer but changes to a sink in the mixed layer, while the gradient production (associated with the q gradient) acts as a source for the humidity ilux in both the unstable surface and mixed layers. The results suggest that the entrainment at the MABL top might affect the budgets of temperature and humidity fluxes in the lower MABL, but not in the unstable surface layer.

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“…The influence of coastal waters on low-level atmospheric circulation has been investigated in several recent studies (Sweet et al, 1981;Mahrt and Paumier, 1982;Hsu, 1984;Huang and Raman, 1992;Riordan and Lin, 1992). For example, Hsu (1984) showed that the SST gradient across an oceanic frontal feature induces a cross-front pressure gradient which induces a crossfront atmospheric component of flow.…”

Section: Introductionmentioning

confidence: 99%

Interaction between surface wind and ocean circulation in the Carolina Capes in a coupled low-order model

Xie¹,

Pietrafesa²,

Raman³

1997

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Interactions between surface winds and ocean currents over an east-coast continental shelf are studied using a simple mathematical model. The model physics include crossshelf advection of sea surface temperature (SST) by Ekman drift, upwelling due to Ekman transport divergence, differential heating of the low-level atmosphere by a cross-shelf SST gradient. and the Coriolis effect. Additionally, the effects of diabatic cooling of surface waters due to air-sea heat exchange and of the vertical density stratification on the thickness of the upper ocean Ekman layer are considered. The model results are qualitatively consistent with observed wind-driven coastal Ocean circulation and surface wind signatures induced by SST. This simple model also demonstrates that two-way air-sea interaction plays a significant role in the subtidal frequency variability of coastal ocean circulation and mesoscale variability of surface wind fields over coastal waters.

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Cloud-Top Entrainment Instability Observed in AMTEX

Cited by 28 publications

References 0 publications

Current problems in the stratocumulus-topped atmospheric boundary layer

Current problems in the stratocumulus-topped atmospheric boundary layer

Heat fluxes and roll circulations over the western Gulf Stream during an intense cold-air outbreak

Interaction between surface wind and ocean circulation in the Carolina Capes in a coupled low-order model

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