scholarly journals Evaluation of the aerosol indirect effect in marine stratocumulus clouds: Droplet number, size, liquid water path, and radiative impact

2005 ◽  
Vol 110 (D8) ◽  
Author(s):  
Cynthia H. Twohy
Keyword(s):  
Liquid Water ◽  
Indirect Effect ◽  
Liquid Water Path ◽  
Marine Stratocumulus ◽  
Aerosol Indirect Effect ◽  
Water Path ◽  
Radiative Impact ◽  
Stratocumulus Clouds

scholarly journals Relationship between drizzle rate, liquid water path and droplet concentration at the scale of a stratocumulus cloud system

2008 ◽  
Vol 8 (16) ◽  
pp. 4641-4654 ◽  
Author(s):  
O. Geoffroy ◽  
J.-L. Brenguier ◽  
I. Sandu
Keyword(s):  
Liquid Water ◽  
Field Experiments ◽  
Liquid Water Path ◽  
Marine Stratocumulus ◽  
Data Set ◽  
Water Path ◽  
Droplet Concentration ◽  
Stratocumulus Clouds ◽  
Shallow Clouds ◽  
The One

Abstract. The recent ACE-2, EPIC and DYCOMS-II field experiments showed that the drizzle precipitation rate of marine stratocumulus scales with the cloud geometrical thickness or liquid water path, and the droplet concentration, when averaged over a domain typical of a GCM grid. This feature is replicated here with large-eddy-simulations using state-of-the-art bulk parameterizations of precipitation formation in stratocumulus clouds. The set of numerical simulations shows scaling relationships similar to the ones derived from the field experiments, especially the one derived from the DYCOMS-II data set. This result suggests that the empirical relationships were not fortuitous and that they reflect the mean effect of cloud physical processes. Such relationships might be more suited to GCM parameterizations of precipitation from shallow clouds than bulk parameterizations of autoconversion, that were initially developed for cloud resolving models.

scholarly journals Model intercomparison of indirect aerosol effects

2006 ◽  
Vol 6 (1) ◽  
pp. 1579-1617 ◽  
Author(s):  
J. E. Penner ◽  
J. Quaas ◽  
T. Storelvmo ◽  
T. Takemura ◽  
O. Boucher ◽  
...  
Keyword(s):  
Liquid Water ◽  
Indirect Effect ◽  
Radiative Forcing ◽  
Cloud Fraction ◽  
Liquid Water Path ◽  
Aerosol Indirect Effect ◽  
Water Path ◽  
Series Of Experiments ◽  
Aerosol Effects ◽  
Indirect Forcing

Abstract. Modeled differences in predicted effects are increasingly used to help quantify the uncertainty of these effects. Here, we examine modeled differences in the aerosol indirect effect in a series of experiments that help to quantify how and why model-predicted aerosol indirect forcing varies between models. The experiments start with an experiment in which aerosol concentrations, the parameterization of droplet concentrations and the autoconversion scheme are all specified and end with an experiment that examines the predicted aerosol indirect forcing when only aerosol sources are specified. Although there are large differences in the predicted liquid water path among the models, the predicted aerosol indirect effect for the first experiment is rather similar. Changes to the autoconversion scheme can lead to large changes in the liquid water path of the models and to the response of the liquid water path to changes in aerosols. Nevertheless, these changes do not necessarily lead to large changes in the radiative forcing. The parameterization of cloud fraction within models is not sensitive to the aerosol concentration, and, therefore, the response of the modeled cloud fraction within the present models appears to be smaller than that which would be associated with model ''noise''. The prediction of aerosol concentrations, given a fixed set of sources, leads to some of the largest differences in the predicted aerosol indirect radiative forcing among the models. Thus, this aspect of modeling requires significant improvement in order to improve the prediction of aerosol indirect effects.

scholarly journals Relationship between drizzle rate, liquid water path and droplet concentration at the scale of a stratocumulus cloud system

2008 ◽  
Vol 8 (1) ◽  
pp. 3921-3959 ◽  
Author(s):  
O. Geoffroy ◽  
J.-L. Brenguier ◽  
I. Sandu
Keyword(s):  
Liquid Water ◽  
Field Experiments ◽  
Liquid Water Path ◽  
Marine Stratocumulus ◽  
Data Set ◽  
Water Path ◽  
Droplet Concentration ◽  
Stratocumulus Clouds ◽  
Shallow Clouds ◽  
The One

Abstract. The recent ACE-2, EPIC and DYCOMS-II field experiments showed that the drizzle precipitation rate of marine stratocumulus scales with the cloud geometrical thickness or liquid water path, and the droplet concentration, when averaged over a domain typical of a GCM grid. This feature is replicated here with large-eddy-simulations using state-of-the-art bulk parameterizations of precipitation formation in stratocumulus clouds. The set of numerical simulations shows scaling relationships similar to the ones derived from the field experiments, especially the one derived from the DYCOMS-II data set. This result suggests that the empirical relationships were not fortuitous and that they reflect the mean effect of cloud physical processes. Such relationships might be more suited to GCM parameterizations of precipitation from shallow clouds than bulk parameterizations of autoconversion, that were initially developed for cloud resolving models.

scholarly journals Ground-based observations of cloud and drizzle liquid water path in stratocumulus clouds

2020 ◽  
Vol 13 (3) ◽  
pp. 1485-1499 ◽  
Author(s):  
Maria P. Cadeddu ◽  
Virendra P. Ghate ◽  
Mario Mech
Keyword(s):  
Liquid Water ◽  
Microwave Radiometer ◽  
Precipitable Water ◽  
Cloud Base ◽  
Radiative Cooling ◽  
Liquid Water Path ◽  
Cell Systems ◽  
Water Path ◽  
Closed Cell ◽  
Stratocumulus Clouds

Abstract. The partition of cloud and drizzle water path in precipitating clouds plays a key role in determining the cloud lifetime and its evolution. A technique to quantify cloud and drizzle water path by combining measurements from a three-channel microwave radiometer (23.8, 30, and 90 GHz) with those from a vertically pointing Doppler cloud radar and a ceilometer is presented. The technique is showcased using 1 d of observations to derive precipitable water vapor, liquid water path, cloud water path, drizzle water path below the cloud base, and drizzle water path above the cloud base in precipitating stratocumulus clouds. The resulting cloud and drizzle water path within the cloud are in good qualitative agreement with the information extracted from the radar Doppler spectra. The technique is then applied to 10 d each of precipitating closed and open cellular marine stratocumuli. In the closed-cell systems only ∼20 % of the available drizzle in the cloud falls below the cloud base, compared to ∼40 % in the open-cell systems. In closed-cell systems precipitation is associated with radiative cooling at the cloud top <-100Wm-2 and a liquid water path >200 g m−2. However, drizzle in the cloud begins to exist at weak radiative cooling and liquid water path >∼150 g m−2. Our results collectively demonstrate that neglecting scattering effects for frequencies at and above 90 GHz leads to overestimation of the total liquid water path of about 10 %–15 %, while their inclusion paves the path for retrieving drizzle properties within the cloud.

scholarly journals The Spiderweb Structure of Stratocumulus Clouds

Atmosphere ◽  
2020 ◽  
Vol 11 (7) ◽  
pp. 730
Author(s):  
Georgios Matheou ◽  
Anthony B. Davis ◽  
João Teixeira
Keyword(s):  
Liquid Water ◽  
Evaporative Cooling ◽  
Liquid Water Content ◽  
Entrainment Rate ◽  
Liquid Water Path ◽  
Integral Boundary ◽  
Water Path ◽  
Large Eddy ◽  
Stratocumulus Clouds ◽  
Distinctive Structure

Stratocumulus clouds have a distinctive structure composed of a combination of lumpy cellular structures and thin elongated regions, resembling canyons or slits. The elongated slits are referred to as “spiderweb” structure to emphasize their interconnected nature. Using very high resolution large-eddy simulations (LES), it is shown that the spiderweb structure is generated by cloud-top evaporative cooling. Analysis of liquid water path (LWP) and cloud liquid water content shows that cloud-top evaporative cooling generates relatively shallow slits near the cloud top. Most of liquid water mass is concentrated near the cloud top, thus cloud-top slits of clear air have a large impact on the entire-column LWP. When evaporative cooling is suppressed in the LES, LWP exhibits cellular lumpy structure without the elongated low-LWP regions. Even though the spiderweb signature on the LWP distribution is negligible, the cloud-top evaporative cooling process significantly affects integral boundary layer quantities, such as the vertically integrated turbulent kinetic energy, mean liquid water path, and entrainment rate. In a pair of simulations driven only by cloud-top radiative cooling, evaporative cooling nearly doubles the entrainment rate.

scholarly journals Aerosol Impacts on the Diurnal Cycle of Marine Stratocumulus

2008 ◽  
Vol 65 (8) ◽  
pp. 2705-2718 ◽  
Author(s):  
Irina Sandu ◽  
Jean-Louis Brenguier ◽  
Olivier Geoffroy ◽  
Odile Thouron ◽  
Valery Masson
Keyword(s):  
Boundary Layer ◽  
Diurnal Cycle ◽  
Liquid Water ◽  
Large Scale ◽  
Cloud Microphysics ◽  
Cloud Base ◽  
Liquid Water Path ◽  
Marine Stratocumulus ◽  
Water Path ◽  
The Impact

Abstract Recent large-eddy simulation (LES) studies of the impact of aerosol on the dynamics of nocturnal marine stratocumulus revealed that, depending on the large-scale forcings, an aerosol-induced increase of the droplet concentration can lead to either an increase or a decrease of the liquid water path, hence contrasting with the cloud thickening that is expected from a reduction of the precipitation efficiency. In this study, the aerosol impacts on cloud microphysics are examined in the context of the boundary-layer diurnal cycle using 36-h LES simulations of pristine and polluted clouds. These simulations corroborate previous findings that during nighttime aerosol-induced liquid water path changes are sensitive to the large-scale forcings via enhancement of cloud-top entrainment such that, ultimately, the liquid water path may be reduced when the free-tropospheric-entrained air is drier. During the day, however, enhanced entrainment, inhibition of drizzle evaporation below cloud base, and reduced sensible heat flux from the surface lead to a more pronounced decoupling of the boundary layer, which significantly amplifies the liquid water path reduction of the polluted clouds. At night the sign of the liquid water path difference between pristine and polluted clouds depends upon large-scale forcings, while during the day the liquid water path of polluted clouds is always smaller than the one of the pristine clouds. Suggestions are made on how observational studies could be designed for validation of these simulations.

scholarly journals Comparison of a global-climate model to a cloud-system resolving model for the long-term response of thin stratocumulus clouds to preindustrial and present-day aerosol conditions

2009 ◽  
Vol 9 (5) ◽  
pp. 21317-21369 ◽  
Author(s):  
S. S. Lee ◽  
J. E. Penner
Keyword(s):  
Liquid Water ◽  
Environmental Conditions ◽  
General Circulation ◽  
Global Climate Model ◽  
Cloud System ◽  
Percentage Increase ◽  
Liquid Water Path ◽  
Cumulus Clouds ◽  
Water Path ◽  
Stratocumulus Clouds

Abstract. The response of a case of thin, warm marine-boundary-layer (MBL) clouds to preindustrial (PI) and present-day (PD) conditions is simulated by a cloud-system resolving model (CSRM). Here, both the aerosol conditions and environmental conditions match those of a general circulation model (GCM). The environmental conditions are characterized by the initial condition and the large-scale forcings of humidity and temperature, as well as the surface fluxes. The response of the CSRM is compared to that simulated by GCM. The percentage increase of liquid-water path (LWP) due to a change from the PI to PD conditions is ~3 times larger in the CSRM than that in the GCM due to the formation of cumulus clouds. The formation of cumulus clouds is controlled by a larger increase in the surface latent-heat (LH) flux in the PD environment than in the PI environment rather than by the change in aerosols. However, the aerosol increase from the PI to PD level determines the LWP response in the stratocumulus clouds, while the impacts of changes in environmental conditions are negligible for stratocumulus clouds. The conversion of cloud liquid to rain through autoconversion and accretion plays a negligible role in the CSRM in the response to aerosols, whereas it plays a role that is as important as condensation in the GCM. Supplementary simulations show that increasing aerosols increase the sensitivity of the cloud responses to the PI and PD environmental conditions and that aerosol effects on clouds depend on the cloud type; the liquid water path (LWP) of warm cumulus clouds is more sensitive to aerosols than the LWP of stratocumulus clouds.

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