Climatology of drizzle in marine boundary layer clouds based on 1 year of data from CloudSat and Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO)

Leon, D.; Wang, Zhien; Liu, Dong

doi:10.1029/2008jd009835

Cited by 129 publications

(147 citation statements)

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“…Here, lightly and heavily drizzling clouds are defined as low clouds with column maximum radar reflectivity in the range of −15 dBZ ≤ Z max < 0 dBZ and Z max ≥ 0 dBZ, respectively. The regions with the largest contributions of low and drizzling clouds are again the NEP, SEP and SEA with drizzling low-cloud fractions up to almost 40 %, which is in reasonable agreement with previous satellite-based estimates (Leon et al, 2008).…”

Section: Variability Of Marine Low Clouds and Their Morphologiessupporting

confidence: 81%

Climatology of stratocumulus cloud morphologies: microphysical properties and radiative effects

2014

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Abstract. An artificial neural network cloud classification scheme is combined with A-train observations to characterize the physical properties and radiative effects of marine low clouds based on their morphology and type of mesoscale cellular convection (MCC) on a global scale. The cloud morphological categories are (i) organized closed MCC, (ii) organized open MCC and (iii) cellular but disorganized MCC.Global distributions of the frequency of occurrence of MCC types show clear regional signatures. Organized closed and open MCCs are most frequently found in subtropical regions and in midlatitude storm tracks of both hemispheres. Cellular but disorganized MCC are the predominant type of marine low clouds in regions with warmer sea surface temperature such as in the tropics and trade wind zones. All MCC types exhibit a pronounced seasonal cycle.The physical properties of MCCs such as cloud fraction, radar reflectivity, drizzle rates and cloud top heights as well as the radiative effects of MCCs are found highly variable and a function of the type of MCC. On a global scale, the cloud fraction is largest for closed MCC with mean cloud fractions of about 90 %, whereas cloud fractions of open and cellular but disorganized MCC are only about 51 % and 40 %, respectively. Probability density functions (PDFs) of cloud fractions are heavily skewed and exhibit modest regional variability.PDFs of column maximum radar reflectivities and inferred cloud base drizzle rates indicate fundamental differences in the cloud and precipitation characteristics of different MCC types. Similarly, the radiative effects of MCCs differ substantially from each other in terms of shortwave reflectance and transmissivity. These differences highlight the importance of low-cloud morphologies and their associated cloudiness on the shortwave cloud forcing.

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Section: Variability Of Marine Low Clouds and Their Morphologiessupporting

confidence: 81%

Climatology of stratocumulus cloud morphologies: microphysical properties and radiative effects

2014

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“…As noted in Part 1, average MBL depth increases offshore and the basic structure is similar, albeit offset lower, to a September-October 2000 average (Wood and Bretherton, 2004), a July 2006-June 2007 average (Leon et al, 2008), and an October 2008 average (Zuidema et al, 2009). The deepest MBL (∼1600 m) occurs at 20 • S, 100 • W. MBL height is very low near the continent and the contours parallel the coastline, an aspect that is consistent with the alongshore observations in Rahn and Garreaud (2009a).…”

Section: Mean Statementioning

confidence: 85%

Marine boundary layer over the subtropical southeast Pacific during VOCALS-REx – Part 2: Synoptic variability

Rahn

Garreaud

2010

Atmos. Chem. Phys.

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Abstract. In the second part of this work we study the day-to-day variability of the marine atmospheric boundary layer (MBL) over the subtropical southeast Pacific using primarily results from a numerical simulation that covered the whole VOCALS-REx period (October-November 2008). In situ and satellite-derived observations of the MBL height in the offshore region indicate rapid, significant variations (from 500 m to 1700 m a.s.l. over a few days) during October. These MBL changes are connected with the passage of midlatitude troughs that altered the large-scale environment over the VOCALS-REx region. In contrast, the synoptic forcing and MBL changes were less prominent during November. Modelled and observed MBL depth at Point Omega (20 • S, 85 • W) compare quite well during October (but the simulation is on average 200 m lower) while in November the simulation does not perform as well.In the prognostic local MBL height equation the height change, the horizontal MBL height advection, and the large scale vertical velocity at MBL top are calculated explicitly from the simulation. The entrainment velocity is calculated as the residual of the other terms in the equation. While the vertical velocity and residual terms are opposing and generally have the largest magnitude on average, it is the variability in the advection that explains most of the large changes in the MBL depth. Examination of several cases during VOCALS-REx suggests that the advective term is in turn largely controlled by changes in wind direction, driven by midlatitude activity, acting on a MBL that generally slopes down toward the coast. In one phase, the subtropical anticyclone is reinforced and extends toward the Chilean coast, leading to easterly wind that advects low MBL heights from the coast as far as Point Omega. The opposite phase occurs after the passage of an extratropical cyclone over southern Chile, leading to southwesterly wind that advects a deeper MBL towards subtropical latitudes.

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“…Drizzle with wide ranging intensities and areal extent is a common feature in stratocumulus-topped boundary layers, especially in remote marine environments (Brost et al, 1982;Nicholls and Leighton, 1986;Frisch et al, 1995;Vali et al, 1998;Yuter et al, 2000;Pawlowska and Brenguier, 2003;Bretherton et al, 2004;Comstock et al, 2004;vanZanten et al, 2005;Leon et al, 2008;Kubar et al, 2009). Over parts of the eastern subtropical/tropical oceans dominated by stratocumulus, including the southeastern Pacific, the intensity and frequency of drizzle tends to increase westwards from the coast (Leon et al, 2008;Kubar et al, 2009;Bretherton et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

“…Over parts of the eastern subtropical/tropical oceans dominated by stratocumulus, including the southeastern Pacific, the intensity and frequency of drizzle tends to increase westwards from the coast (Leon et al, 2008;Kubar et al, 2009;Bretherton et al, 2010). The westward increase in drizzle coincides with changes in both aerosol concentrations and macrophysical properties of the stratocumulus deck (e.g., George and Wood, 2010;Bretherton et al, 2010;Allen et al, 2011), thereby raising the question: to what extent does the westward increase in drizzle reflect changes in cloud macrophysical properties, changes in cloud microphysical properties, and changes in aerosol (e.g., Wood et al, 2009)? Of the drizzle falling from stratocumulus, a significant fraction evaporates before reaching the surface vanZanten et al, 2005;Wood, 2005).…”

Section: Introductionmentioning

confidence: 99%

Does precipitation susceptibility vary with increasing cloud thickness in marine stratocumulus?

et al. 2012

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Abstract.The relationship between precipitation rate and accumulation mode aerosol concentration in marine stratocumulus-topped boundary layers is investigated by applying the precipitation susceptibility metric to aircraft data obtained during the VOCALS Regional Experiment. A new method to calculate the precipitation susceptibility that incorporates non-precipitating clouds is introduced. The mean precipitation rate R over a segment of the data is expressed as the product of a drizzle fraction f and a drizzle intensity I (mean rate for drizzling columns). The susceptibility S x is then defined as the fractional decrease in precipitation variable x={R,f ,I } per fractional increase in the concentration of aerosols with dry diameter >0.1 µm, with cloud thickness h held fixed. The precipitation susceptibility S R is calculated using data from both precipitating and nonprecipitating cloudy columns to quantify how aerosol concentrations affect the mean precipitation rate of all clouds of a given h range and not just the mean precipitation of clouds that are precipitating. S R systematically decreases with increasing h, and this is largely because S f decreases with h while S I is approximately independent of h. In a general sense, S f can be thought of as the effect of aerosols on the probability of precipitation, while S I can be thought of as the effect of aerosols on the intensity of precipitation. Since thicker clouds are likely to precipitate regardless of ambient aerosol concentration, we expect S f to decrease with increasing h. The results are broadly insensitive to the choice of horizontal averaging scale. Similar susceptibilities are found for both cloud base and near-surface drizzle rates. The analysis is repeated with cloud liquid water path held fixed instead of cloud thickness. Simple power law relationships relating precipitation rate to aerosol concentration or cloud droplet concentration do not capture this observed behavior.

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Climatology of drizzle in marine boundary layer clouds based on 1 year of data from CloudSat and Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO)

Cited by 129 publications

References 73 publications

Climatology of stratocumulus cloud morphologies: microphysical properties and radiative effects

Climatology of stratocumulus cloud morphologies: microphysical properties and radiative effects

Marine boundary layer over the subtropical southeast Pacific during VOCALS-REx – Part 2: Synoptic variability

Does precipitation susceptibility vary with increasing cloud thickness in marine stratocumulus?

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