Factors Controlling Rapid Stratocumulus Cloud Thinning

Abstract The relationship between the inversion stability and the liquid water path (LWP) tendency of a vertically well-mixed, adiabatic stratocumulus cloud layer is investigated in this study through the analysis of the budget equation for the LWP. The LWP budget is mainly determined by the turbulent fluxes of heat and moisture at the top and the base of the cloud layer, as well as by the source terms due to radiation and precipitation. Through substitution of the inversion stability parameter κ into the budget equation, it immediately follows that the LWP tendency will become negative for increasing values of κ due to the entrainment of increasingly dry air. Large κ values are therefore associated with strong cloud thinning. Using the steady-state solution for the LWP, an equilibrium value κeq is formulated, beyond which the stratocumulus cloud will thin. The Second Dynamics and Chemistry of Marine Stratocumulus field study (DYCOMS-II) is used to illustrate that, depending mainly on the magnitude of the moisture flux at cloud base, stratocumulus clouds can persist well within the buoyancy reversal regime.

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Radiative Impacts of Free-Tropospheric Clouds on the Properties of Marine Stratocumulus

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-12-0287.1 ◽

2013 ◽

Vol 70 (10) ◽

pp. 3102-3118 ◽

Cited By ~ 46

Author(s):

Matthew W. Christensen ◽

Gustavo G. Carrió ◽

Graeme L. Stephens ◽

William R. Cotton

Keyword(s):

Atmospheric Modeling ◽

Cloud Base ◽

Radiative Cooling ◽

Liquid Water Path ◽

Marine Stratocumulus ◽

Large Eddy ◽

Stratocumulus Clouds ◽

Cloud Optical Thickness ◽

Vertical Development ◽

Regional Atmospheric Modeling

Abstract Observations from multiple satellites and large-eddy simulations (LESs) from the Regional Atmospheric Modeling System (RAMS) are used to determine the extent to which free-tropospheric clouds (FTCs) affect the properties of stratocumulus. Overlying FTCs decrease the cloud-top radiative cooling in stratocumulus by an amount that depends on the upper-cloud base altitude, cloud optical thickness, and abundance of moisture between the cloud layers. On average, FTCs increase the downward longwave radiative flux above stratocumulus clouds (at 3.5 km) by approximately 30 W m−2. As a consequence, this forcing translates to a relative decrease in stratocumulus cooling rates by about 20%. Overall, the reduced cloud-top radiative cooling decreases the turbulent mixing, vertical development, and precipitation rate in stratocumulus clouds at night. During the day these effects are greatly reduced because the overlying clouds shade the stratocumulus from strong solar radiation, thus reducing the net radiative effect by the upper cloud. Differences in liquid water path are also observed in stratocumulus; however, the response is tied to the diurnal cycle and the time scale of interaction between the FTCs and the stratocumulus. Radiative effects by FTCs tend to be largest in the midlatitudes where the clouds overlying stratocumulus tend to be more frequent, lower, and thicker on average. In conclusion, changes in net radiation and moisture brought about by FTCs can significantly affect the dynamics of marine stratocumulus and these processes should be considered when evaluating cloud feedbacks in the climate system.

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Wind speed response of marine non-precipitating stratocumulus clouds over a diurnal cycle in cloud-system resolving simulations

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-5811-2016 ◽

2016 ◽

Vol 16 (9) ◽

pp. 5811-5839 ◽

Cited By ~ 11

Author(s):

Jan Kazil ◽

Graham Feingold ◽

Takanobu Yamaguchi

Keyword(s):

Boundary Layer ◽

Wind Speed ◽

Large Scale ◽

Layer Growth ◽

Radiative Properties ◽

Cloud Base ◽

Latent Heat Release ◽

Marine Stratocumulus ◽

Stratocumulus Clouds ◽

Boundary Layer Growth

Abstract. Observed and projected trends in large-scale wind speed over the oceans prompt the question: how do marine stratocumulus clouds and their radiative properties respond to changes in large-scale wind speed? Wind speed drives the surface fluxes of sensible heat, moisture, and momentum and thereby acts on cloud liquid water path (LWP) and cloud radiative properties. We present an investigation of the dynamical response of non-precipitating, overcast marine stratocumulus clouds to different wind speeds over the course of a diurnal cycle, all else equal. In cloud-system resolving simulations, we find that higher wind speed leads to faster boundary layer growth and stronger entrainment. The dynamical driver is enhanced buoyant production of turbulence kinetic energy (TKE) from latent heat release in cloud updrafts. LWP is enhanced during the night and in the morning at higher wind speed, and more strongly suppressed later in the day. Wind speed hence accentuates the diurnal LWP cycle by expanding the morning–afternoon contrast. The higher LWP at higher wind speed does not, however, enhance cloud top cooling because in clouds with LWP ⪆ 50 g m−2, longwave emissions are insensitive to LWP. This leads to the general conclusion that in sufficiently thick stratocumulus clouds, additional boundary layer growth and entrainment due to a boundary layer moistening arises by stronger production of TKE from latent heat release in cloud updrafts, rather than from enhanced longwave cooling. We find that large-scale wind modulates boundary layer decoupling. At nighttime and at low wind speed during daytime, it enhances decoupling in part by faster boundary layer growth and stronger entrainment and in part because shear from large-scale wind in the sub-cloud layer hinders vertical moisture transport between the surface and cloud base. With increasing wind speed, however, in decoupled daytime conditions, shear-driven circulation due to large-scale wind takes over from buoyancy-driven circulation in transporting moisture from the surface to cloud base and thereby reduces decoupling and helps maintain LWP. The total (shortwave + longwave) cloud radiative effect (CRE) responds to changes in LWP and cloud fraction, and higher wind speed translates to a stronger diurnally averaged total CRE. However, the sensitivity of the diurnally averaged total CRE to wind speed decreases with increasing wind speed.

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

Atmospheric Measurement Techniques ◽

10.5194/amt-13-1485-2020 ◽

2020 ◽

Vol 13 (3) ◽

pp. 1485-1499 ◽

Cited By ~ 1

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.

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Precipitation susceptibility in marine stratocumulus and shallow cumulus from airborne measurements

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-11395-2016 ◽

2016 ◽

Vol 16 (17) ◽

pp. 11395-11413 ◽

Cited By ~ 11

Author(s):

Eunsil Jung ◽

Bruce A. Albrecht ◽

Armin Sorooshian ◽

Paquita Zuidema ◽

Haflidi H. Jonsson

Keyword(s):

Marine Boundary Layer ◽

Qualitative Behavior ◽

Liquid Water Path ◽

Cumulus Clouds ◽

Marine Stratocumulus ◽

Airborne Measurements ◽

Boundary Layer Clouds ◽

Shallow Cumulus ◽

Stratocumulus Clouds ◽

Field Campaigns

Abstract. Precipitation tends to decrease as aerosol concentration increases in warm marine boundary layer clouds at fixed liquid water path (LWP). The quantitative nature of this relationship is captured using the precipitation susceptibility (So) metric. Previously published works disagree on the qualitative behavior of So in marine low clouds: So decreases monotonically with increasing LWP or cloud depth (H) in stratocumulus clouds (Sc), while it increases and then decreases in shallow cumulus clouds (Cu). This study uses airborne measurements from four field campaigns on Cu and Sc with similar instrument packages and flight maneuvers to examine if and why So behavior varies as a function of cloud type. The findings show that So increases with H and then decreases in both Sc and Cu. Possible reasons for why these results differ from those in previous studies of Sc are discussed.

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Meteorological and Aerosol Effects on Marine Stratocumulus

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-15-0101.1 ◽

2016 ◽

Vol 73 (2) ◽

pp. 807-820 ◽

Cited By ~ 1

Author(s):

Zhe Li ◽

Huiwen Xue ◽

Jen-Ping Chen ◽

Wei-Chyung Wang

Keyword(s):

Precipitation Amount ◽

Wrf Model ◽

Cloud Fraction ◽

Cloud Base ◽

Liquid Water Path ◽

Marine Stratocumulus ◽

Diurnal Cycles ◽

Microphysical Properties ◽

Southeastern Pacific ◽

Lower Cloud

Abstract This study investigates the effects of meteorological conditions and aerosols on marine stratocumulus in the southeastern Pacific using the Weather Research and Forecasting (WRF) Model. Two regimes with different temperature and moisture conditions in the finest model domain are investigated. The western regime is around 87°–79°W, while the eastern regime is around 79°–71°W. In both regimes, cloud fraction, liquid water path (LWP), cloud thickness, and precipitation show significant diurnal cycles. Cloud fraction can be 0.83 during the night and down to 0.29 during the day in the western regime. The diurnal cycles in the eastern regime have smaller amplitudes but are still very strong. Stratocumulus properties also differ in the two regimes. Compared to the western regime, the eastern regime has lower temperature, higher relative humidity, and a more coupled boundary layer, leading to higher cloud fraction (by 0.11) and lower cloud-base height. The eastern regime also has lower inversion height that causes lower cloud-top height and thinner clouds and, hence, lower LWP and less precipitation. Cloud microphysical properties are very sensitive to aerosols in both regimes. Increasing aerosols greatly increase cloud number concentration, decrease cloud effective radius, and suppress precipitation. Cloud macrophysical properties (cloud fraction, LWP) are not sensitive to aerosols in either regime, most notably in the eastern regime where precipitation amount is less. The changes in cloud fraction and LWP caused by changes in aerosol concentrations are smaller than the changes in the diurnal cycle and the spatial variability between the two regimes.

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Turbulence in The Marine Boundary Layer and Air Motions Below Stratocumulus Clouds at the ARM Eastern North Atlantic Site

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-21-0087.1 ◽

2021 ◽

Author(s):

Virendra P. Ghate ◽

Maria P. Cadeddu ◽

Xue Zheng ◽

Ewan O’Connor

Keyword(s):

Boundary Layer ◽

North Atlantic ◽

Vertical Velocity ◽

Marine Boundary Layer ◽

Cloud Layer ◽

Similar Amount ◽

Marine Stratocumulus ◽

Stratocumulus Clouds ◽

Eastern North Atlantic ◽

Rain Rates

AbstractMarine stratocumulus clouds are intimately coupled to the turbulence in the boundary layer and drizzle is known to be ubiquitous within them. Six years of data collected at the Atmospheric Radiation Measurement (ARM)’s Eastern North Atlantic site are utilized to characterize turbulence in the marine boundary layer and air motions below stratocumulus clouds. Profiles of variance of vertical velocity binned by wind direction (wdir) yielded that the boundary layer measurements are affected by the island when the wdir is between 90° and 310° (measured clockwise from North where air is coming from). Data collected during the marine conditions (wdir<90 or wdir>310) showed that the variance of vertical velocity was higher during the winter months than during the summer months due to higher cloudiness, wind speeds, and surface fluxes. During marine conditions the variance of vertical velocity and cloud fraction exhibited a distinct diurnal cycle with higher values during the nighttime than during the daytime. Detailed analysis of 32 cases of drizzling marine stratocumulus clouds showed that for a similar amount of radiative cooling at the cloud top, within the sub-cloud layer 1) drizzle increasingly falls within downdrafts with increasing rain rates, 2) the strength of the downdrafts increases with increasing rain rates, and 3) the correlation between vertical air motion and rain rate is highest in the middle of the sub-cloud layer. The results presented herein have implications for climatological and model evaluation studies conducted at the ENA site, along with efforts of accurately representing drizzle-turbulence interactions in a range of atmospheric models.

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

Atmospheric Chemistry and Physics ◽

10.5194/acp-8-4641-2008 ◽

2008 ◽

Vol 8 (16) ◽

pp. 4641-4654 ◽

Cited By ~ 46

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.

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On the Parameterization of Convective Downdrafts for Marine Stratocumulus Clouds

Monthly Weather Review ◽

10.1175/mwr-d-19-0292.1 ◽

2020 ◽

Vol 148 (5) ◽

pp. 1931-1950 ◽

Cited By ~ 2

Author(s):

Elynn Wu ◽

Handa Yang ◽

Jan Kleissl ◽

Kay Suselj ◽

Marcin J. Kurowski ◽

...

Keyword(s):

Mass Flux ◽

Turbulent Transport ◽

Eddy Diffusivity ◽

Moisture Profile ◽

Marine Stratocumulus ◽

Eddy Simulation ◽

Single Column ◽

Stratocumulus Clouds ◽

Heat And Moisture Transport ◽

Heat And Moisture

Abstract The role of nonlocal transport on the development and maintenance of marine stratocumulus (Sc) clouds in coarse-resolution models is investigated, with a special emphasis on the downdraft contribution. A new parameterization of cloud-top-triggered downdrafts is proposed and validated against large-eddy simulation (LES) for two Sc cases. The applied nonlocal mass-flux scheme is part of the stochastic multiplume eddy-diffusivity/mass-flux (EDMF) framework decomposing the turbulent transport into local and nonlocal contributions. The complementary local turbulent transport is represented with the Mellor–Yamada–Nakanishi–Niino (MYNN) scheme. This EDMF version has been implemented in the Weather Research and Forecasting (WRF) single-column model (SCM) and tested for three model versions: without mass flux, with updrafts only, and with both updrafts and downdrafts. In the LES, the downdraft and updraft contributions to the total heat and moisture transport are comparable and significant. The WRF SCM results show a good agreement between the parameterized downdraft turbulent transport and LES. While including updrafts greatly improves the modeling of Sc clouds over the simulation without mass flux, the addition of downdrafts is less significant, although it helps improve the moisture profile in the planetary boundary layer.

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Aerosol Impacts on the Diurnal Cycle of Marine Stratocumulus

Journal of the Atmospheric Sciences ◽

10.1175/2008jas2451.1 ◽

2008 ◽

Vol 65 (8) ◽

pp. 2705-2718 ◽

Cited By ~ 69

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.

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