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Robert Wood - One of the best experts on this subject based on the ideXlab platform.
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studying the vertical variation of cloud droplet effective radius using ship and space borne remote sensing data
Journal of Geophysical Research, 2008Co-Authors: Ruiyue Chen, Robert Wood, Ralph Ferraro, Fulung ChangAbstract:[1] The albedo of marine stratocumuli depends upon cloud liquid water content, droplet effective radius (re), and how these parameters vary with height. Using satellite data and shipborne data from the East Pacific Investigation of Climate (EPIC) Stratocumulus Study, this study investigates the cloud re vertical variation for drizzling and nondrizzling clouds. Visible/near-infrared retrievals from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) are used to estimate the vertical profile of re. MODIS re observations and collocated shipborne scanning C-band precipitation radar data show that re generally increases with height in nondrizzling clouds, consistent with aircraft observations. It is found that in clouds with precipitation rates greater than a few hundredths of a mm h−1 the vertical gradient of re is significantly less than that in nondrizzling clouds and can become negative when the Drizzle is heavier than approximately 0.1 mm h−1. High values of re at drizzling cloud base are consistent with estimates of the ratio of liquid water in the Drizzle drops to that in the cloud droplets. C-band derived cloud base precipitation rates are found to be better correlated with re at cloud base than with re at cloud top, suggesting that passive remote sensing may be useful for Drizzle detection.
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Drizzle in stratiform boundary layer clouds part i vertical and horizontal structure
Journal of the Atmospheric Sciences, 2005Co-Authors: Robert WoodAbstract:Abstract Detailed observations of stratiform boundary layer clouds on 12 days are examined with specific reference to Drizzle formation processes. The clouds differ considerably in mean thickness, liquid water path (LWP), and droplet concentration. Cloud-base precipitation rates differ by a factor of 20 between cases. The lowest precipitation rate is found in the case with the highest droplet concentration even though this case had by far the highest LWP, suggesting that Drizzle can be severely suppressed in polluted clouds. The vertical and horizontal structure of cloud and Drizzle liquid water and bulk microphysical parameters are examined in detail. In general, the highest concentration of r > 20 μm Drizzle drops is found toward the top of the cloud, and the mean volume radius of the Drizzle drops increases monotonically from cloud top to base. The resulting precipitation rates are largest at the cloud base but decrease markedly only in the upper third of the cloud. Below cloud, precipitation rates dec...
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Drizzle in Stratiform Boundary Layer Clouds. Part I: Vertical and Horizontal Structure
Journal of the Atmospheric Sciences, 2005Co-Authors: Robert WoodAbstract:Detailed observations of stratiform boundary layer clouds on 12 days are examined with specific reference to Drizzle formation processes. The clouds differ considerably in mean thickness, liquid water path (LWP), and droplet concentration. Cloud-base precipitation rates differ by a factor of 20 between cases. The lowest precipitation rate is found in the case with the highest droplet concentration even though this case had by far the highest LWP, suggesting that Drizzle can be severely suppressed in polluted clouds. The vertical and horizontal structure of cloud and Drizzle liquid water and bulk microphysical parameters are examined in detail. In general, the highest concentration of r 20 m Drizzle drops is found toward the top of the cloud, and the mean volume radius of the Drizzle drops increases monotonically from cloud top to base. The resulting precipitation rates are largest at the cloud base but decrease markedly only in the upper third of the cloud. Below cloud, precipitation rates decrease markedly with distance below base due to evaporation, and are broadly consistent in most cases with the results from a simple sedimentation– evaporation model. Evidence is presented that suggests evaporating Drizzle is cooling regions of the subcloud layer, which could result in dynamical feedbacks. A composite power spectrum of the horizontal spatial series of precipitation rate is found to exhibit a power-law scaling from the smallest observable scales to close to the maximum observable scale (30 km). The exponent is considerably lower (1.1–1.2) than corresponding exponents for LWP variability obtained in other studies (1.5–2), demonstrating that there is relatively more variability of Drizzle on small scales. Singular measures analysis shows that Drizzle fields are much more intermittent than the cloud liquid water content fields, consistent with a Drizzle production process that depends strongly upon liquid water content. The adiabaticity of the clouds, which can be modeled as a simple balance between Drizzle loss and turbulent replenishment, is found to decrease if the time scale for Drizzle loss is shorter than roughly 5–10 eddy turnover time scales. Finally, the data are compared with three simple scalings derived from recent observations of Drizzle in subtropical stratocumulus clouds.
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Drizzle in stratiform boundary layer clouds part ii microphysical aspects
Journal of the Atmospheric Sciences, 2005Co-Authors: Robert WoodAbstract:Abstract This is the second of two observational papers examining Drizzle in stratiform boundary layer clouds. Part I details the vertical and horizontal structure of cloud and Drizzle parameters, including some bulk microphysical variables. In this paper, the focus is on the in situ size-resolved microphysical measurements, particularly of Drizzle drops (r > 20 μm). Layer-averaged size distributions of Drizzle drops within cloud are shown to be well represented using either a truncated exponential or a truncated lognormal size distribution. The size-resolved microphysical measurements are used to estimate autoconversion and accretion rates by integration of the stochastic collection equation (SCE). These rates are compared with a number of commonly used bulk parameterizations of warm rain formation. While parameterized accretion rates agree well with those derived from the SCE initialized with observed spectra, the autoconversion rates seriously disagree in some cases. These disagreements need to be addr...
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reflectivity and rain rate in and below drizzling stratocumulus
Quarterly Journal of the Royal Meteorological Society, 2004Co-Authors: Kimberly K Comstock, Sandra E Yuter, Robert Wood, Christopher S BrethertonAbstract:Ship-based radar measurements obtained during the East Pacific Investigation of Climate 2001 stratocumulus (Sc) cruise are used to derive characteristics of the rainfall from drizzling Sc. Reflectivity to rain rate (Z–R) relationships are determined from shipboard raindrop-size distribution measurements obtained from observations using filter-paper, and compared to Z–R relationships derived from aircraft probe data from below north-east Atlantic drizzling Sc and stratus. A model for the evaporation and sedimentation of Drizzle is combined with reflectivity profiles from a millimetre-wavelength cloud radar to derive information on the mean raindrop radius and Drizzle drop concentrations at cloud base, and to show how Z–R relationships change with height below the cloud base. The Z–R relationships are used in conjunction with shipborne C-band radar reflectivity data to estimate areal average precipitation with uncertainties at cloud base and at the surface. In the Sc Drizzle Z–R relationship, Z = aRb (where a and b are constants), the estimated exponent b = 1.1 to 1.4 is lower than commonly observed in deep convective rain (b = 1.5). Analyses indicate that variations in Sc rain rates and reflectivities are influenced both by fluctuations in Drizzle drop concentration and in mean radius, but that number concentration contributes more to the modulation of rain rate in Sc. Rain rates derived using the scanning C-band radar are found to be spatially variable, with much of the accumulation originating from a small fraction of the drizzling area. The observations also suggest that rain rate in marine Sc is strongly dependent on cloud liquid-water path, and inversely correlated with cloud droplet concentration. Copyright © 2004 Royal Meteorological Society
Roy Rasmussen - One of the best experts on this subject based on the ideXlab platform.
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the common occurrence of highly supercooled Drizzle and rain near the coastal regions of the western united states
Journal of Geophysical Research, 2013Co-Authors: Daniel Rosenfeld, Roy Rasmussen, Frank Mcdonough, Rei Chemke, Paul J Demott, Ryan C Sullivan, Jennifer M Comstock, B Schmid, J M Tomlinson, Haf JonssonAbstract:The formation of highly supercooled rain was documented by aircraft observations in clouds at a wide range of conditions near the coastal region of the western United States. Several case studies are described in detail using combined cloud and aerosol measurements to document both the highly super-cooled condition and the relatively pristine aerosol conditions under which it forms. The case studies include: (1) Marine convective clouds over the coastal waters of northern California, as measured by cloud physics probes flown on a Gulfstream-1 aircraft during the CALWATER campaign in February and early March 2011. The clouds had extensive Drizzle in their tops, which extended downward to the 0°C isotherm as supercooled rain. Ice multiplication was observed only in mature parts of the clouds where cloud water was already depleted. (2) Orographically triggered convective clouds in marine air mass over the foothills of the Sierra Nevada to the east of Sacramento, as measured in CALWATER. Supercooled rain was observed down to -21°C. No indications for ice multiplication were evident. (3) Orographic layer clouds over Yosemite National Park, also measured in CALWATER. The clouds had extensive Drizzle at -21°C, which intensified with little freezing lower in the cloud, and (4) Supercooled Drizzlemore » drops in layer clouds near Juneau, Alaska, as measured by the Wyoming King Air as part of a FAA project to study aircraft icing in this region. Low concentrations of CCN was a common observation in all these clouds, allowing for the formation of clouds with small concentration of large drops that coalesced into supercooled Drizzle and raindrops. Another common observation was the absence of ice nuclei and/or ice crystals in measurable concentrations was associated with the persistent supercooled Drizzle and rain. Average ice crystal concentrations were 0.007 l-1 at the top of convective clouds at -12°C and 0.03 l-1 in the case of layer clouds at -21°C. In combination these two conditions provide ideal conditions for the formation of highly supercooled Drizzle and rain. These results help explain the anomalously high incidences of aircraft icing at cold temperatures in U.S. west coast clouds (Bernstein et al., 2004) and highlight the need to include aerosol effects when simulating aircraft icing with cloud models. These case studies can also serve as benchmarks for explicit cloud microphysics models attempting to simulate the formation of precipitation in these types of pristine conditions.« less
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freezing Drizzle detection with wsr 88d radars
Journal of Applied Meteorology and Climatology, 2009Co-Authors: Kyoko Ikeda, Roy Rasmussen, Edward A Brandes, Frank McdonoughAbstract:Abstract This study describes a freezing Drizzle detection algorithm based on the Weather Surveillance Radar-1988 Doppler (WSR-88D) measured radar reflectivity. Although radar returns from freezing Drizzle and light snow are similar—<5 dBZ and spatially uniform—freezing Drizzle can be identified using feature parameters computed from radar reflectivity, such as local and global standard deviations and reflectivity texture weighted with a fuzzy-logic scheme. Algorithm results agree well with surface precipitation reports. The proposed algorithm can serve as one component of automated decision-support schemes for icing hazard detection and/or hydrometeor identification.
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observations of freezing Drizzle in extratropical cyclonic storms during improve 2
Journal of the Atmospheric Sciences, 2007Co-Authors: Kyoko Ikeda, Roy Rasmussen, William D Hall, Gregory ThompsonAbstract:Abstract Observations of supercooled Drizzle aloft within two storms impacting the Oregon Cascades during the second Improvement of Microphysical Parameterization through Observational Verification Experiment (IMPROVE-2) field project are presented. The storms were characterized by a structure and evolution similar to the split-front model of synoptic storms. Both storms were also characterized by strong cross-barrier flow. An analysis of aircraft and radar data indicated the presence of supercooled Drizzle during two distinct storm periods: 1) the intrafrontal period immediately following the passage of an upper cold front and 2) the postfrontal period. The conditions associated with these regions of supercooled Drizzle included 1) temperatures between −3° and −19°C, 2) ice crystal concentrations between 1 and 2 L−1, and 3) bimodal cloud droplet distributions of low concentration [cloud condensation nuclei (CCN) concentration between 20 and 30 cm−3 and cloud drop concentration <35 cm−3]. Unique to this s...
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New Ground Deicing Hazard Associated with Freezing Drizzle Ingestion by Jet Engines
Journal of Aircraft, 2006Co-Authors: Roy Rasmussen, Chuck Wade, Frank Hage, Scott Landolt, Matt Tryhane, Allan Ramsay, Jeff Cole, R K Moore, David Fleming, Amor DavisAbstract:Anew ground deicing hazard is described, consisting of the accretion of freezing Drizzle onto jet engine fan blades and cowlings, and subsequent shedding of the accreted ice during takeoff leading to damage to jet engine fan blades. Cases of damage to aircraft from hazardous surface icing conditions at Denver, Colorado and Oslo, Norway are described., The two cases at Denver cost United Airlines over $2 million in damage to 12 B737-300 engines. The hazard is identified as heavy freezing Drizzle through examination of National Weather Service observations of upper level temperature and humidity, satellite, radar, and freezing rain sensor data. The official National Weather Service observation during these cases, however, was either light snow and mist or light freezing Drizzle. The reason for this misreport and underestimate of intensity lies in the current reporting rules for determining freezing Drizzle intensity by visibility and not by precipitation rate. Theoretical relationships are presented that show that the variation in Drizzle size distribution and the difference in determining visibility from day and night is the cause of the poor correlation of Drizzle rate with visibility.
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freezing Drizzle formation in stably stratified layer clouds part ii the role of giant nuclei and aerosol particle size distribution and solubility
Journal of the Atmospheric Sciences, 2005Co-Authors: Istvan Geresdi, Roy RasmussenAbstract:Abstract This paper investigates how the characteristics of aerosol particles (size distribution and solubility) as well as the presence of giant nuclei affect Drizzle formation in stably stratified layer clouds. A new technique was developed to simulate the evolution of water drops from wet aerosol particles and implemented into a detailed microphysical model. The detailed microphysical model was incorporated into a one-dimensional parcel model and a two-dimensional version of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5). Sensitivity experiments were performed with the parcel model using a constant updraft speed and with the two-dimensional model by simulating flow over a bell-shaped mountain. The results showed that 1) stably stratified clouds with weak updrafts (<10 cm s−1) can form Drizzle relatively rapidly for maritime size distributions with any aerosol particle solubility, and for continental size distributions with hi...
Pavlos Kollias - One of the best experts on this subject based on the ideXlab platform.
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a new criterion to improve operational Drizzle detection with ground based remote sensing
Journal of Atmospheric and Oceanic Technology, 2019Co-Authors: Claudia Acquistapace, Ulrich Lohnert, Maximilian Maahn, Pavlos KolliasAbstract:AbstractLight shallow precipitation in the form of Drizzle is one of the mechanisms for liquid water removal, affecting cloud lifetime and boundary layer dynamics and thermodynamics. The early form...
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relationship between turbulence and Drizzle in continental and marine low stratiform clouds
Journal of the Atmospheric Sciences, 2018Co-Authors: Paloma Borque, Pavlos Kollias, Edward P Luke, Fan YangAbstract:AbstractTurbulence and Drizzle-rate measurements from a large dataset of marine and continental low stratiform clouds are presented. Turbulence peaks at cloud base over land and near cloud top over...
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optimizing observations of Drizzle onset with millimeter wavelength radars
Atmospheric Measurement Techniques, 2016Co-Authors: Claudia Acquistapace, Pavlos Kollias, Stefan Kneifel, Ulrich Lohnert, Maximilian Maahn, Matthias BauerpfundsteinAbstract:Abstract. Cloud Doppler radars are increasingly used to study cloud and precipitation microphysical processes. Typical bulk cloud properties such as liquid or ice content are usually derived using the first three standard moments of the radar Doppler spectrum. Recent studies demonstrated the value of higher moments for the reduction of retrieval uncertainties and for providing additional insights into microphysical processes. Large effort has been undertaken, e.g., within the Atmospheric Radiation Measurement (ARM) program to ensure high quality of radar Doppler spectra. However, a systematic approach concerning the accuracy of higher moment estimates and sensitivity to basic radar system settings, such as spectral resolution, integration time and beam width, are still missing. In this study, we present an approach on how to optimize radar settings for radar Doppler spectra moments in the specific context of Drizzle detection. The process of Drizzle development has shown to be particularly sensitive to higher radar moments such as skewness. We collected radar raw data (I/Q time series) from consecutive zenith-pointing observations for two liquid cloud cases observed at the cloud observatory JOYCE in Germany. The I/Q data allowed us to process Doppler spectra and derive their moments using different spectral resolutions and integration times during identical time intervals. This enabled us to study the sensitivity of the spatiotemporal structure of the derived moments to the different radar settings. The observed signatures were further investigated using a radar Doppler forward model which allowed us to compare observed and simulated sensitivities and also to study the impact of additional hardware-dependent parameters such as antenna beam width. For the observed cloud with Drizzle onset we found that longer integration times mainly modify spectral width (Sw) and skewness (Sk), leaving other moments mostly unaffected. An integration time of 2 s seems to be an optimal compromise: both observations and simulations revealed that a 10 s integration time – as it is widely used for European cloud radars – leads to a significant turbulence-induced increase of Sw and reduction of Sk compared to 2 s integration time. This can lead to significantly different microphysical interpretations with respect to Drizzle water content and effective radius. A change from 2 s to even shorter integration times (0. 4 s) has much smaller effects on Sw and Sk. We also find that spectral resolution has a small impact on the moment estimations, and thus on the microphysical interpretation of the Drizzle signal. Even the coarsest spectral resolution studied, 0. 08 ms−1, seems to be appropriate for calculation moments of drizzling clouds. Moreover, simulations provided additional insight into the microphysical interpretation of the skewness signatures observed: in low (high)-turbulence conditions, only Drizzle larger than 20 µm (40 µm) can generate Sk values above the Sk noise level (in our case 0.4). Higher Sk values are also obtained in simulations when smaller beam widths are adopted.
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separating cloud and Drizzle radar moments during precipitation onset using doppler spectra
Journal of Atmospheric and Oceanic Technology, 2013Co-Authors: Edward P Luke, Pavlos KolliasAbstract:The retrieval of cloud, Drizzle, and turbulence parameters using radar Doppler spectra is challenged by the convolution of microphysical and dynamical influences and the overall uncertainty introduced by turbulence. A new technique that utilizes recorded radar Doppler spectra from profiling cloud radars is presented here. The technique applies to areas in clouds where Drizzle is initially produced by the autoconversion process and is detectedby apositiveskewnessin the radarDopplerspectrum.Usingthe Gaussian-shape propertyof cloud Doppler spectra, the cloud-only radar Doppler spectrum is estimated and used to separate the cloud and Drizzle contributions. Once separated, the cloud spectral peak can be used to retrieve vertical air motion and eddy dissipation rates, while the Drizzle peak can be used to estimate the three radar moments of the Drizzle particle size distribution. The technique works for nearly 50% of spectra found near cloud top, with efficacy diminishing to roughly 15% of spectra near cloud base. The approach has been tested on a large dataset collected in the Azores during the Atmospheric Radiation Measurement Program (ARM) Mobile Facility deployment on Graciosa Island from May 2009 through December 2010. Validation of the proposed technique is achieved using the cloud base as a natural boundary between radar Doppler spectra with and without cloud droplets. The retrieval algorithm has the potential to characterize the dynamical and microphysical conditionsat cloud scale during the transition from cloud to precipitation. This has significant implications for improving the understanding of Drizzle onset in liquid clouds and for improving model parameterization schemes of autoconversion of cloud water into Drizzle.
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cloud radar doppler spectra in drizzling stratiform clouds 2 observations and microphysical modeling of Drizzle evolution
Journal of Geophysical Research, 2011Co-Authors: Pavlos Kollias, Wanda Szyrmer, Jasmine Remillard, Edward P LukeAbstract:sites is presented. The evolution of the Doppler spectra moments is consistent with the onset and growth of Drizzle particles and can be used to assist modeling studies of Drizzle onset and growth. Time‐height radar observations are used to exhibit the coherency of the Doppler spectra shape parameters and demonstrate their potential to improve the interpretation and use of radar observations. In addition, a simplified microphysical approach to modeling the vertical evolution of the Drizzle particle size distribution in warm stratiform clouds is described and used to analyze the observations. The formation rate of embryonic Drizzle droplets due to the autoconversion process is not calculated explicitly; however, accretion and evaporation processes are explicitly modeled. The microphysical model is used as input to a radar Doppler spectrum forward model, and synthetic radar Doppler spectra moments are generated. Three areas of interest are studied in detail: early Drizzle growth near the cloud top, growth by accretion of the well‐developed Drizzle, and Drizzle depletion below the cloud base due to evaporation. The modeling results are in good agreement with the continental and maritime observations. This demonstrates that steady state one‐dimensional explicit microphysical models coupled with a forward model and comprehensive radar Doppler spectra observations offer a powerful method to explore the vertical evolution of the Drizzle particle size distribution.
Graham Feingold - One of the best experts on this subject based on the ideXlab platform.
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Stratocumulus to cumulus transition by Drizzle
Journal of Advances in Modeling Earth Systems, 2017Co-Authors: Takanobu Yamaguchi, Graham Feingold, Jan KazilAbstract:The stratocumulus to cumulus transition (SCT) is typically considered to be a slow, multi-day process, caused primarily by dry air entrainment associated with overshooting cumulus, with minor influence of Drizzle. This study revisits the role of Drizzle in the SCT with large eddy simulations coupled with a two-moment bulk microphysics scheme that includes a budget on aerosol (Na) and cloud droplet number concentrations (Nc). We show a strong precipitation-induced modulation of the SCT by Drizzle initiated in penetrative cumulus under stratocumulus. Lagrangian SCT simulations are initiated with various, moderate Na (100-250 cm-3), which produce little to no Drizzle from the stratocumulus. As expected, Drizzle formation in cumuli is regulated by cloud depth and Nc, with stronger dependence on cloud depth, so that, for the current case, Drizzle is generated in all simulations once cumulus clouds become sufficiently deep. The Drizzle generated in the cumuli washes out stratocumulus cloud water and much of the aerosol, and a cumulus state appears for approximately 10 hours. With additional simulations with a fixed Nc (100 cm-3), we show that prediction of Nc is necessary for this fast SCT since it is a result of a positive feedback of collision-coalescence induced aerosol depletion that enhances Drizzle formation. A fixed Nc does not permit this feedback, and thus results in weak influence of Drizzle on the SCT. Simulations with fixed droplet concentrations that bracket the time varying aerosol/drop concentrations are therefore not representative of the role of Drizzle in the SCT.
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joint retrievals of cloud and Drizzle in marine boundary layer clouds using ground based radar lidar and zenith radiances
Atmospheric Measurement Techniques, 2015Co-Authors: Mark D Fielding, Graham Feingold, Robin J Hogan, J C Chiu, Edwin W Eloranta, Ewan J Oconnor, M P CadedduAbstract:Abstract. Active remote sensing of marine boundary-layer clouds is challenging as Drizzle drops often dominate the observed radar reflectivity. We present a new method to simultaneously retrieve cloud and Drizzle vertical profiles in drizzling boundary-layer clouds using surface-based observations of radar reflectivity, lidar attenuated backscatter, and zenith radiances under conditions when precipitation does not reach the surface. Specifically, the vertical structure of droplet size and water content of both cloud and Drizzle is characterised throughout the cloud. An ensemble optimal estimation approach provides full error statistics given the uncertainty in the observations. To evaluate the new method, we first perform retrievals using synthetic measurements from large-eddy simulation snapshots of cumulus under stratocumulus, where cloud water path is retrieved with an error of 31 g m−2. The method also performs well in non-drizzling clouds where no assumption of the cloud profile is required. We then apply the method to observations of marine stratocumulus obtained during the Atmospheric Radiation Measurement MAGIC deployment in the Northeast Pacific. Here, retrieved cloud water path agrees well with independent three-channel microwave radiometer retrievals, with a root mean square difference of 10–20 g m−2.
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marine stratocumulus aerosol cloud relationships in the mase ii experiment precipitation susceptibility in eastern pacific marine stratocumulus
Journal of Geophysical Research, 2009Co-Authors: Graham Feingold, Armin Sorooshian, Haflidi H Jonsson, Richard C Flagan, John H SeinfeldAbstract:Observational data on aerosol-cloud-Drizzle relationships in marine stratocumulus are presented from the second Marine Stratus/Stratocumulus Experiment (MASE-II) carried out in July 2007 over the eastern Pacific near Monterey, California. Observations, carried out in regions of essentially uniform meteorology with localized aerosol enhancements due to ship exhaust (“ship tracks”), demonstrate, in accord with those from numerous other field campaigns, that increased cloud drop number concentration Nc and decreased cloud top effective radius r_e are associated with increased subcloud aerosol concentration. Modulation of Drizzle by variations in aerosol levels is levels is clearly evident. Variations of cloud base Drizzle rate R_(cb) are found to be consistent with the proportionality, R_(cb) / H^3/N_c, where H is cloud depth. Simultaneous aircraft and A-Train satellite observations are used to quantify the precipitation susceptibility of clouds to aerosol perturbations in the eastern Pacific region.
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on the relationship among cloud turbulence droplet formation and Drizzle as viewed by doppler radar microwave radiometer and lidar
Journal of Geophysical Research, 1999Co-Authors: Graham Feingold, Bjorn Stevens, Shelby A Frisch, William R CottonAbstract:Cloud radar, microwave radiometer, and lidar remote sensing data acquired during the Atlantic Stratocumulus Transition Experiment (ASTEX) are analyzed to address the relationship between (1) drop number concentration and cloud turbulence as represented by vertical velocity and vertical velocity variance and (2) Drizzle formation and cloud turbulence. Six cases, each of about 12 hours duration, are examined; three of these cases are characteristic of nondrizzling boundary layers and three of drizzling boundary layers. In all cases, microphysical retrievals are only performed when Drizzle is negligible (radar reflectivity 0.5) between radar reflectivity and in-cloud vertical velocity variance, although one of the boundary layers that experienced Drizzle exhibited a negative correlation between these parameters. However, in the subcloud region, all boundary layers that experienced Drizzle exhibit a negative correlation between radar reflectivity and vertical velocity variance.
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exploratory cloud resolving simulations of boundary layer arctic stratus clouds part i warm season clouds
Atmospheric Research, 1998Co-Authors: Peter Q Olsson, Jerry Y Harrington, Graham Feingold, William R Cotton, Sonia M KreidenweisAbstract:Two-dimensional simulations of arctic stratus clouds (ASC) were conducted using a sophisticated cloud-resolving model with explicit microphysics and a two-stream radiative transfer model. The effects of varying cloud condensation nuclei (CCN) concentrations upon the subsequent cloud and its microphysical, radiative and dynamical structure were studied. In this study CCN concentrations were varied within the ranges found in warm-season arctic boundary layers (ABLs) to produce non-drizzling and weakly drizzling stratus decks. Experiments that included all model physics, no-Drizzle, and no shortwave radiation were conducted to elucidate the effects of microphysics and radiation on the simulated stratus. Both simulations that did and that did not include the effects of Drizzle showed that the higher CCN concentrations produced a cloud with larger reflectivity and absorptivity, but also produced eddies that were weaker than with lower CCN concentrations. Simulations that included the effects of Drizzle showed a similar response to changes in CCN concentrations. Simulations with no Drizzle produced more vigorous eddies than their drizzling counterparts because cooling due to evaporation below cloud tends to stabilize the ABL. The simulations without the effects of short-wave radiation produced very vigorous eddies that penetrated more deeply into the ABL. In this case, the simulation with higher CCN concentrations produced the most vigorous eddies. This resulted from a subtle interplay of microphysics, radiation, and dynamics.
M P Cadeddu - One of the best experts on this subject based on the ideXlab platform.
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ground based observations of cloud and Drizzle liquid water path in stratocumulus clouds
Atmospheric Measurement Techniques, 2020Co-Authors: M P Cadeddu, Mario MechAbstract: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 - 100 W m - 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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joint retrievals of cloud and Drizzle in marine boundary layer clouds using ground based radar lidar and zenith radiances
Atmospheric Measurement Techniques, 2015Co-Authors: Mark D Fielding, Graham Feingold, Robin J Hogan, J C Chiu, Edwin W Eloranta, Ewan J Oconnor, M P CadedduAbstract:Abstract. Active remote sensing of marine boundary-layer clouds is challenging as Drizzle drops often dominate the observed radar reflectivity. We present a new method to simultaneously retrieve cloud and Drizzle vertical profiles in drizzling boundary-layer clouds using surface-based observations of radar reflectivity, lidar attenuated backscatter, and zenith radiances under conditions when precipitation does not reach the surface. Specifically, the vertical structure of droplet size and water content of both cloud and Drizzle is characterised throughout the cloud. An ensemble optimal estimation approach provides full error statistics given the uncertainty in the observations. To evaluate the new method, we first perform retrievals using synthetic measurements from large-eddy simulation snapshots of cumulus under stratocumulus, where cloud water path is retrieved with an error of 31 g m−2. The method also performs well in non-drizzling clouds where no assumption of the cloud profile is required. We then apply the method to observations of marine stratocumulus obtained during the Atmospheric Radiation Measurement MAGIC deployment in the Northeast Pacific. Here, retrieved cloud water path agrees well with independent three-channel microwave radiometer retrievals, with a root mean square difference of 10–20 g m−2.
