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Title: About the horizontal variability of effective radius in stratocumulus clouds: HORIZONTAL VARIABILITY OF R E IN STRATOCUMULUS CLOUDS

Authors:
 [1];  [1];  [1]
  1. Department of Atmospheric Sciences, The Hebrew University of Jerusalem, Jerusalem Israel
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1402200
Grant/Contract Number:
2010446
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Journal of Geophysical Research: Atmospheres
Additional Journal Information:
Journal Volume: 121; Journal Issue: 16; Related Information: CHORUS Timestamp: 2017-10-23 17:23:08; Journal ID: ISSN 2169-897X
Publisher:
Wiley Blackwell (John Wiley & Sons)
Country of Publication:
United States
Language:
English

Citation Formats

Magaritz-Ronen, L., Khain, A., and Pinsky, M.. About the horizontal variability of effective radius in stratocumulus clouds: HORIZONTAL VARIABILITY OF R E IN STRATOCUMULUS CLOUDS. United States: N. p., 2016. Web. doi:10.1002/2016JD024977.
Magaritz-Ronen, L., Khain, A., & Pinsky, M.. About the horizontal variability of effective radius in stratocumulus clouds: HORIZONTAL VARIABILITY OF R E IN STRATOCUMULUS CLOUDS. United States. doi:10.1002/2016JD024977.
Magaritz-Ronen, L., Khain, A., and Pinsky, M.. 2016. "About the horizontal variability of effective radius in stratocumulus clouds: HORIZONTAL VARIABILITY OF R E IN STRATOCUMULUS CLOUDS". United States. doi:10.1002/2016JD024977.
@article{osti_1402200,
title = {About the horizontal variability of effective radius in stratocumulus clouds: HORIZONTAL VARIABILITY OF R E IN STRATOCUMULUS CLOUDS},
author = {Magaritz-Ronen, L. and Khain, A. and Pinsky, M.},
abstractNote = {},
doi = {10.1002/2016JD024977},
journal = {Journal of Geophysical Research: Atmospheres},
number = 16,
volume = 121,
place = {United States},
year = 2016,
month = 8
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1002/2016JD024977

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  • The equation of radiative energy balance in a homogeneous plane-parallel cloud accounts for the photon transport in the vertical direction only. From this equation, the absorption can be evaluated as a difference between the net radiative fluxes measured on the cloud top and bottom. Real clouds exhibit extreme horizontal variability of their optical and, hence, radiative properties. So the radiative energy balance equation for inhomogeneous clouds includes an extra term to describe the net energy transport in the horizontal directions (radiative horizontal transport). This study investigates the horizontal transport in nonhomogeneous stratocumulus clouds and its influence on the accuracy ofmore » absorption estimates. Using a realistic fractal model of marine stratocumulus clouds and Monte Carlo method, it is shown that the magnitude of horizontal transport (1) is comparable with those of albedo, transmittance, and absorptance and (2) depends strongly on the fractal dimension of cloud optical depth. Because of the horizontal transport, there is no unique dependence between optical and radiative properties of given pixel. The neglect of the horizontal transport is a major source of uncertainty in absorption estimates. Two possible ways of improving the inhomogeneous cloud absorption estimates from field measurements are discussed.« less
  • The spectral dependence of the radiative horizontal transport (the horizontal transport of radiative energy) E and its effect on the accuracy of spectral and broadband absorption retrieval in the near-infrared (IR) wavelength range was investigated using a large-eddy simulation (LES) cloud model with explicit microphysics and a three-dimensional Monte Carlo radiative transfer model. Two typical types of marine clouds representing inhomogeneous overcast and broken stratocumulus clouds have been simulated. We demonstrate that (i) the basic statistics (e.g., variance and correlation function) of the horizontal transport are wavelength dependent and (ii) the estimates of spectral and broadband absorption with a givenmore » accuracy (e.g., rmse ~4%) may require the use of different spatial resolutions.« less
  • Numerical simulations described in previous studies showed that adding cloud condensation nuclei to marine stratocumulus can prevent their breakup from closed into open cells. Additional analyses of the same simulations show that the suppression of rain is well described in terms of cloud drop effective radius (re). Rain is initiated when re near cloud top is around 12-14 um. Cloud water starts to get depleted when column-maximum rain intensity (Rmax) exceeds 0.1 mm h-1. This happens when cloud-top re reaches 14 um. Rmax is mostly less than 0.1 mm h-1 at re<14 um, regardless of the cloud water path, butmore » increases rapidly when re exceeds 14 um. This is in agreement with recent aircraft observations and theoretical observations in convective clouds so that the mechanism is not limited to describing marine stratocumulus. These results support the hypothesis that the onset of significant precipitation is determined by the number of nucleated cloud drops and the height (H) above cloud base within the cloud that is required for cloud drops to reach re of 14 um. In turn, this can explain the conditions for initiation of significant drizzle and opening of closed cells providing the basis for a simple parameterization for GCMs that unifies the representation of both precipitating and non-precipitating clouds as well as the transition between them. Furthermore, satellite global observations of cloud depth (from base to top), and cloud top re can be used to derive and validate this parameterization.« less
  • The influence of clear air entrainment on the droplet effective radius of cloudy air parcels is investigated theoretically and experimentally by using data collected in 16 warm maritime tropical cumuli during the Joint Hawaii Warm Rain Project (1985). The theoretical study consists of calculations of the droplet spectrum, droplet effective radius, and liquid water content performed by an entraining cloud parcel model for different entrainment-mixing scenarios. The numerical simulation results are interpreted by means of an analytic equation of the droplet effective radius expressed as a function of both the liquid water content and the droplet concentration. In the experimentmore » study, the behavior of the effective radius is examined at all scales as a function of the liquid water content, used as a dilution degree indicator. At a given cloud level, in the abscence of secondary droplet activation, the effective radius of the droplet spectrum of small-scale parcels (10-Hz data) is roughly independent of the liquid water content and appears unaffected by entrainment. In contrast, if secondary droplet activation occurs in diluted ascending cloud parcels, a wide range of effective radius values is observed for a given liquid water content as a result of the induced variation of the droplet concentration. Further, mean cloud pass effective radii increase with increasing mean pass liquid water contents and mean pass height above cloud base. The results limit the validity of the classical cloud effective radius parameterizations used in the radiative transfer calculations in climate models and some suggestions to improve these parameterizations are presented.« less
  • The angular distribution of scattered radiation deep within a cloud layer was measured in marine stratocumulus clouds modified by the emissions from ships. These observations, obtained at 13 discrete wavelengths between 0.5 and 2.3 [mu]m, were acquired as the University of Washington C-131A aircraft flew through a pair of roughly parallel ship track signatures produced in clouds off the coast of southern California on July 10, 1987. In the first of these ship tracks, the nadir (upwelling) intensity increased from 40 to 110 W m[sup [minus]2] [mu]m[sup [minus]1] sr[sup [minus]1] at 0.744 [mu]m. The second ship track produced a lessmore » dramatic, but more uniform, increase in the upwelling intensity. In contrast, the nadir intensity at 2.20 [mu]m decreased from 1 to 0.13 W m[sup [minus]2] [mu]m[sup [minus]1] sr[sup [minus]1] in the first ship track and to 0.6 W m[sup [minus]2] [mu]m[sup [minus]1] sr[sup [minus]1] in the second ship track. The relative angular distribution of the intensity field at each wavelength was used to determine the similarity parameter, and hence single scattering albedo, of the cloud using the diffusion domain method. Besides the spectral similarity parameter, these measurements provide a good estimate of the optical depth of the cloud layer both above and below the aircraft. Results of this analysis are presented for a 120-km section of marine stratocumulus cloud including both ship tracks. This analysis shows that the total optical thickness of the cloud layer increased in the ship tracks, in contrast to the similarity parameter which decreased. The decrease in absorption was a direct consequence of the reduction in cloud droplet size that occurred within the ship tracks. 34 refs., 11 figs., 2 tabs.« less