Importance of Accurate Liquid Water Path for Estimation of Solar Radiation in Warm Boundary Layer Clouds: An Observational Study

2003 ◽  
Vol 16 (18) ◽  
pp. 2997-3009 ◽  
Author(s):  
Manajit Sengupta ◽  
Eugene E. Clothiaux ◽  
Thomas P. Ackerman ◽  
Seiji Kato ◽  
Qilong Min
Keyword(s):  
Boundary Layer ◽  
Solar Radiation ◽  
Observational Study ◽  
Liquid Water ◽  
Liquid Water Path ◽  
Water Path ◽  
Boundary Layer Clouds

scholarly journals Improving the Representation of Low Clouds and Drizzle in the ECMWF Model Based on ARM Observations from the Azores

2014 ◽  
Vol 142 (2) ◽  
pp. 668-685 ◽  
Author(s):  
Maike Ahlgrimm ◽  
Richard Forbes
Keyword(s):  
Boundary Layer ◽  
Liquid Water ◽  
Surface Radiation ◽  
Shortwave Radiation ◽  
Cloud Base ◽  
Liquid Water Path ◽  
Water Path ◽  
Boundary Layer Clouds ◽  
Low Cloud ◽  
Ecmwf Model

Abstract In this study, the representation of marine boundary layer clouds is investigated in the ECMWF model using observations from the Atmospheric Radiation Measurement (ARM) mobile facility deployment to Graciosa Island in the North Atlantic. Systematic errors in the occurrence of clouds, liquid water path, precipitation, and surface radiation are assessed in the operational model for a 19-month-long period. Boundary layer clouds were the most frequently observed cloud type but were underestimated by 10% in the model. Systematic but partially compensating surface radiation errors exist and can be linked to opposing cloud cover and liquid water path errors in broken (shallow cumulus) and overcast (stratocumulus) low-cloud regimes, consistent with previously reported results from the continental ARM Southern Great Plains (SGP) site. Occurrence of precipitation is overestimated by a factor of 1.5 at cloud base and by a factor of 2 at the surface, suggesting deficiencies in both the warm-rain formation and subcloud evaporation parameterizations. A single-column version of the ECMWF model is used to test combined changes to the parameterizations of boundary layer, autoconversion/accretion, and rain evaporation processes at Graciosa. Low-cloud occurrence, liquid water path, radiation biases, and precipitation occurrence are all significantly improved when compared to the ARM observations. Initial results from the modified parameterizations in the full model show improvement in the global top-of-the-atmosphere shortwave radiation, suggesting the reduced errors in the comparison at Graciosa are more widely applicable to boundary layer cloud around the globe.

scholarly journals An Algorithm for the Retrieval of Droplet Number Concentration and Geometrical Thickness of Stratiform Marine Boundary Layer Clouds Applied to MODIS Radiometric Observations

2005 ◽  
Vol 44 (1) ◽  
pp. 28-38 ◽  
Author(s):  
Lothar Schüller ◽  
Ralf Bennartz ◽  
Jürgen Fischer ◽  
Jean-Louis Brenguier
Keyword(s):  
Boundary Layer ◽  
Liquid Water ◽  
Dispersion Model ◽  
Cloud Model ◽  
Number Concentration ◽  
Trade Wind ◽  
Liquid Water Path ◽  
Water Path ◽  
Airborne Measurements ◽  
Boundary Layer Clouds

Abstract Algorithms are now currently used for the retrieval of cloud optical thickness and droplet effective radius from multispectral radiance measurements. This paper extends their application to the retrieval of cloud droplet number concentration, cloud geometrical thickness, and liquid water path in shallow convective clouds, using an algorithm that was previously tested with airborne measurements of cloud radiances and validated against in situ measurements of the same clouds. The retrieval is based on a stratified cloud model of liquid water content and droplet spectrum. Radiance measurements in visible and near-infrared channels of the Moderate Resolution Imaging Spectroradiometer (MODIS), which is operated from the NASA platforms Terra and Aqua, are analyzed. Because of uncertainties in the simulation of the continental surface reflectance, the algorithm is presently limited to the monitoring of the microphysical structure of boundary layer clouds over the ocean. Two MODIS scenes of extended cloud fields over the North Atlantic Ocean trade wind region are processed. A transport and dispersion model (the Hybrid Single-Particle Lagrangian Integrated Trajectory Model, HYSPLIT4) is also used to characterize the origin of the air masses and hence their aerosol regimes. One cloud field formed in an air mass that was advected from southern Europe and North Africa. It shows high values of the droplet concentration when compared with the second cloud system, which developed in a more pristine environment. The more pristine case also exhibits a higher geometrical thickness and, thus, liquid water path, which counterbalances the expected cloud albedo increase of the polluted case. Estimates of cloud liquid water path are then compared with retrievals from the Special Sensor Microwave Imager (SSM/I). SSM/I-derived liquid water paths are in good agreement with the MODIS-derived values.

Measurement of Vertical Liquid Water Path by Means of an Airborne Radiometer and the Shortwave Albedo of Marine Low-Level Clouds during WENPEX in Japan

1995 ◽  
Vol 34 (2) ◽  
pp. 471-481 ◽  
Author(s):  
Y. Fujiyoshi ◽  
Y. Ishizaka ◽  
T. Takeda ◽  
T. Hayasaka ◽  
M. Tanaka
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Liquid Water ◽  
Microwave Radiometer ◽  
Cloud Droplet ◽  
Precipitable Water ◽  
Horizontal Distribution ◽  
Liquid Water Path ◽  
Water Path ◽  
Boundary Layer Clouds

Abstract Special observations were made over the southwest island area of the East China Sea from 12 to 27 January 1991 as part of the World Climate Research Program in Japan (WENPEX—Western North Pacific Cloud–Radiation Experiment). Two aircraft were used to determine the air truth of the total vertical liquid water path (LWP) using a microwave radiometer. One airplane was fitted with a 37-GHz radiometer and flew above planetary boundary layer clouds. The other flew inside the clouds with a cloud droplet spectrometer. These aircraft flew simultaneously along the same flight path when planetary boundary layer clouds were formed over the warm sea during an outbreak of cold air. The result of the air truth of the LWPradiometer indicates that the 37-GHZ microwave radiometer gives an estimation of the LWP accurate to 100 mg cm−2. The shortwave cloud albedo was related to the LWPradiometer. The albedo increases with the LWP, independent of cloud type, when measured just above the cloud tops. The measured albedo is nearly the same as the calculated albedo when the LWPradiometer is larger than 60 mg cm−2 but much smaller than the calculated albedo when the LWPradiometer is less than 40 mg cm−2. Cloud-top irregularity is suggested to be the primary cause of this discrepancy. The degree of inhomogeneity of the horizontal distribution of liquid water appears to be correlated with the amount of precipitable water in the planetary boundary layer.

Reconciling and Validating the Cloud Thickness and Liquid Water Path Tendencies Proposed by R. Wood and J. J. van der Dussen et al.

2015 ◽  
Vol 72 (5) ◽  
pp. 2033-2040 ◽  
Author(s):  
Mohamed S. Ghonima ◽  
Joel R. Norris ◽  
Thijs Heus ◽  
Jan Kleissl
Keyword(s):  
Boundary Layer ◽  
Liquid Water ◽  
Mixed Boundary ◽  
Liquid Water Path ◽  
Water Path ◽  
Large Eddy ◽  
Heat And Moisture ◽  
Cloud Thickness ◽  
Detailed Derivation ◽  
Good Agreement

Abstract A detailed derivation of stratocumulus cloud thickness and liquid water path tendencies as a function of the well-mixed boundary layer mass, heat, and moisture budget equations is presented. The derivation corrects an error in the cloud thickness tendency equation derived by R. Wood to make it consistent with the liquid water path tendency equation derived by J. J. van der Dussen et al. The validity of the tendency equations is then tested against the output of large-eddy simulations of a typical stratocumulus-topped boundary layer case and is found to be in good agreement.

scholarly journals The Role of Eddy Diffusivity Profiles on Stratocumulus Liquid Water Path Biases

2007 ◽  
Vol 135 (7) ◽  
pp. 2786-2793 ◽  
Author(s):  
Stephan R. de Roode
Keyword(s):  
Boundary Layer ◽  
Liquid Water ◽  
Sensible Heat Flux ◽  
Eddy Diffusivity ◽  
Specific Humidity ◽  
Entrainment Rate ◽  
Liquid Water Path ◽  
Water Path ◽  
Wide Range ◽  
Heat And Moisture

Abstract Results from simulations of the stratocumulus-topped boundary layer with one-dimensional versions of general simulation models typically exhibit a wide range of spread in the modeled liquid water path (LWP). These discrepancies are often attributed to differences in the modeled entrainment rate. Results from a large eddy simulation of the First International Satellite Cloud Climatology Project Regional Experiment I stratocumulus case are analyzed. The diagnosed eddy diffusivities for heat and moisture are found to differ by about a factor of 3. Moreover, both have a much larger magnitude than the ones typically applied in boundary layer parameterization schemes. Motivated by these results mean state solutions are analyzed for the specific case in which the vertical fluxes of heat and moisture are prescribed, whereas eddy diffusivity profiles are systematically varied by multiplication with a constant factor. The solutions demonstrate that any value, ranging from zero to a maximum adiabatic value, can be obtained for the LWP. In the subtropical parts over the ocean where horizontally extended stratocumulus fields persist, the surface sensible heat flux is typically small, whereas surface evaporation and entrainment of relatively dry air from above the surface can result in significant moisture fluxes. If the eddy diffusivity values are small, then the mean specific humidity will tend to decrease quite rapidly with height in order to support the humidity flux. This results in erroneous low humidity values in the upper part of the boundary layers causing low LWP values.

scholarly journals Evaluation of stratocumulus cloud prediction in the Met Office forecast model during VOCALS-REx

2010 ◽  
Vol 10 (21) ◽  
pp. 10541-10559 ◽  
Author(s):  
S. J. Abel ◽  
D. N. Walters ◽  
G. Allen
Keyword(s):  
Boundary Layer ◽  
Diurnal Cycle ◽  
Liquid Water ◽  
Large Scale ◽  
Marine Boundary Layer ◽  
Coastal Region ◽  
Forecast Model ◽  
Good Representation ◽  
Liquid Water Path ◽  
Water Path

Abstract. Observations in the subtropical southeast Pacific obtained during the VOCALS-REx field experiment are used to evaluate the representation of stratocumulus cloud in the Met Office forecast model and to identify key areas where model biases exist. Marked variations in the large scale structure of the cloud field were observed during the experiment on both day-to-day and on diurnal timescales. In the remote maritime region the model is shown to have a good representation of synoptically induced variability in both cloud cover and marine boundary layer depth. Satellite observations show a strong diurnal cycle in cloud fraction and liquid water path in the stratocumulus with enhanced clearances of the cloud deck along the Chilean and Peruvian coasts on certain days. The model accurately simulates the phase of the diurnal cycle but is unable to capture the coastal clearing of cloud. Observations along the 20° S latitude line show a gradual increase in the depth of the boundary layer away from the coast. This trend is well captured by the model (typical low bias of 200 m) although significant errors exist at the coast where the model marine boundary layer is too shallow and moist. Drizzle in the model responds to changes in liquid water path in a manner that is consistent with previous ship-borne observations in the region although the intensity of this drizzle is likely to be too high, particularly in the more polluted coastal region where higher cloud droplet number concentrations are typical. Another mode of variability in the cloud field that the model is unable to capture are regions of pockets of open cellular convection embedded in the overcast stratocumulus deck and an example of such a feature that was sampled during VOCALS-REx is shown.

scholarly journals Manipulating marine stratocumulus cloud amount and albedo: a process-modelling study of aerosol-cloud-precipitation interactions in response to injection of cloud condensation nuclei

2011 ◽  
Vol 11 (1) ◽  
pp. 885-916 ◽  
Author(s):  
H. Wang ◽  
P. J. Rasch ◽  
G. Feingold
Keyword(s):  
Boundary Layer ◽  
Liquid Water ◽  
Marine Boundary Layer ◽  
Cloud Condensation Nuclei ◽  
Cloud Amount ◽  
Number Concentration ◽  
Condensation Nuclei ◽  
Liquid Water Path ◽  
Water Path ◽  
Injection Method

Abstract. We use a cloud-system-resolving model to study marine-cloud brightening. We examine how injected aerosol particles that act as cloud condensation nuclei (CCN) are transported within the marine boundary layer and how the additional particles in clouds impact cloud microphysical processes, and feedback on dynamics. Results show that the effectiveness of cloud brightening depends strongly on meteorological and background aerosol conditions. Cloud albedo enhancement is very effective in a weakly precipitating boundary layer and in CCN-limited conditions preceded by heavy and/or persistent precipitation. The additional CCN help sustain cloud water by weakening the precipitation substantially in the former case and preventing the boundary layer from collapse in the latter. For a given amount of injected CCN, the injection method (i.e., number and distribution of sprayers) is critical to the spatial distribution of these CCN. Both the areal coverage and the number concentration of injected particles are key players but neither one always emerges as more important than the other. The same amount of injected material is much less effective in either strongly precipitating clouds or polluted clouds, and it is ineffective in a relatively dry boundary layer that supports clouds of low liquid water path. In the polluted case and "dry" case, the CCN injection increases drop number concentration but lowers supersaturation and liquid water path. As a result, the cloud experiences very weak albedo enhancement, regardless of the injection method.

scholarly journals Ultra-clean and smoky marine boundary layers frequently occur in the same season over the southeast Atlantic

2020 ◽  
Vol 20 (4) ◽  
pp. 2341-2351 ◽  
Author(s):  
Sam Pennypacker ◽  
Michael Diamond ◽  
Robert Wood
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Biomass Burning ◽  
Liquid Water ◽  
Marine Boundary Layer ◽  
Liquid Water Path ◽  
Accumulation Mode ◽  
Water Path ◽  
Aerosol Cloud ◽  
Ascension Island

Abstract. We study 41 d with daily median surface accumulation mode aerosol particle concentrations below 50 cm−3 (ultra-clean conditions) observed at Ascension Island (ASI; 7.9∘ S, 14.4∘ W) between June 2016 and October 2017 as part of the Layered Atlantic Smoke Interactions with Clouds (LASIC) campaign. Interestingly, these days occur during a period of great relevance for aerosol–cloud–radiation interactions, the southeast Atlantic (SEATL) biomass-burning season (approximately June–October). That means that these critical months can feature both the highest surface aerosol numbers, from smoke intrusion into the marine boundary layer, as well as the lowest. While carbon monoxide and refractory black carbon concentrations on ultra-clean days do not approach those on days with heavy smoke, they also frequently exceed background concentrations calculated in the non-burning season from December 2016 to April 2017. This is evidence that even what become ultra-clean boundary layers can make contact with and entrain from an overlying SEATL smoke layer before undergoing a process of rapid aerosol removal. Because many ultra-clean and polluted boundary layers observed at Ascension Island during the biomass burning season follow similar isobaric back trajectories, the variability in this entrainment is likely more closely tied to the variability in the overlying smoke rather than large-scale horizontal circulation through the boundary layer. Since exceptionally low accumulation mode aerosol numbers at ASI do not necessarily indicate the relative lack of other trace pollutants, this suggests the importance of regional variations in what constitutes an “ultra-clean” marine boundary layer. Finally, surface drizzle rates, frequencies and accumulation – as well as retrievals of liquid water path – all consistently tend toward higher values on ultra-clean days. This implicates enhanced coalescence scavenging in low clouds as the key driver of ultra-clean events in the southeast Atlantic marine boundary layer. These enhancements occur against and are likely mediated by the backdrop of a seasonal increase in daily mean cloud fraction and daily median liquid water path over ASI, peaking in September and October in both LASIC years. Therefore the seasonality in ultra-clean day occurrence seems directly linked to the seasonality in SEATL cloud properties. These results highlight the importance of two-way aerosol–cloud interactions in the region.

scholarly journals Large eddy simulation of ship tracks in the collapsed marine boundary layer: a case study from the Monterey area ship track experiment

2015 ◽  
Vol 15 (10) ◽  
pp. 5851-5871 ◽  
Author(s):  
A. H. Berner ◽  
C. S. Bretherton ◽  
R. Wood
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Liquid Water ◽  
Satellite Images ◽  
Sensitivity Study ◽  
Liquid Water Path ◽  
Water Path ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Ship Tracks

Abstract. For the first time, a large eddy simulation (LES) coupled to a bulk aerosol scheme is used to simulate an aircraft-sampled ship track. The track was formed by the M/V Sanko Peace on 13 June 1994 in a shallow drizzling boundary layer with high winds but very low background aerosol concentrations (10 cm−3). A Lagrangian framework is used to simulate the evolution of a short segment of track as it is advected away from the ship for 8 h (a downwind distance exceeding 570 km). Using aircraft observations for initialization, good agreement is obtained between the simulated and observed features of the ambient boundary layer outside the track, including the organization of the cloud into mesoscale rolls. After 8 h, a line of aerosol is injected to start the ship track. The simulation successfully reproduces the significant albedo enhancement and suppression of drizzle observed within the track. The aerosol concentration within the track dilutes as it broadens due to turbulent mixing. A sensitivity study shows the broadening rate strongly depends on the alignment between the track and the wind-aligned boundary layer rolls, as satellite images of ship tracks suggest. Entrainment is enhanced within the simulated track, but the observed 100 m elevation of the ship track above the surrounding layer is not simulated, possibly because the LES quickly sharpens the rather weak observed inversion. Liquid water path within the simulated track increases with time even as the ambient liquid water path is decreasing. The albedo increase in the track from liquid water and cloud fraction enhancement (second indirect effect) eventually exceeds that from cloud droplet number increases (first indirect or Twomey effect). In a sensitivity study with a higher initial ambient aerosol concentration, stronger ship track aerosol source, and much weaker drizzle, there is less liquid water inside the track than outside for several hours downwind, consistent with satellite estimates for such situations. In that case, the Twomey effect dominates throughout, although, as seen in satellite images, the albedo enhancement of the track is much smaller.

scholarly journals Large Eddy Simulation of the Diurnal Cycle in Southeast Pacific Stratocumulus

2009 ◽  
Vol 66 (2) ◽  
pp. 432-449 ◽  
Author(s):  
Peter Caldwell ◽  
Christopher S. Bretherton
Keyword(s):  
Boundary Layer ◽  
Diurnal Cycle ◽  
Liquid Water ◽  
Cloud Base ◽  
Liquid Water Path ◽  
Water Path ◽  
Diurnal Cycles ◽  
Eddy Simulation ◽  
Droplet Concentration ◽  
Large Eddy

Abstract This paper describes a series of 6-day large eddy simulations of a deep, sometimes drizzling stratocumulus-topped boundary layer based on forcings from the East Pacific Investigation of Climate (EPIC) 2001 field campaign. The base simulation was found to reproduce the observed mean boundary layer properties quite well. The diurnal cycle of liquid water path was also well captured, although good agreement appears to result partially from compensating errors in the diurnal cycles of cloud base and cloud top due to overentrainment around midday. At all times of the day, entrainment is found to be proportional to the vertically integrated buoyancy flux. Model stratification matches observations well; turbulence profiles suggest that the boundary layer is always at least somewhat decoupled. Model drizzle appears to be too sensitive to liquid water path and subcloud evaporation appears to be too weak. Removing the diurnal cycle of subsidence had little effect on simulated liquid water path. Simulations with changed droplet concentration and drizzle susceptibility showed large liquid water path differences at night, but differences were quite small at midday. Droplet concentration also had a significant impact on entrainment, primarily through droplet sedimentation feedback rather than through drizzle processes.

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