Racoro Extended-Term Aircraft Observations of Boundary Layer Clouds

Vogelmann, Andrew M.; McFarquhar, Greg M.; Ogren, J. A.; Turner, David D.; Comstock, J. M.; Feingold, Graham; Long, Charles; Jonsson, Haflidi H.; Bucholtz, Anthony; Collins, D. R.; Diskin, G. S.; Gerber, H.; Lawson, R. Paul; Woods, Roy K.; Andrews, Elisabeth; Yang, Hyunseok; Chiu, J. Christine; Hartsock, Daniel; Hubbe, J. M.; Lo, Chaomei; Marshak, Alexander; Monroe, Justin; McFarlane, Sally A.; Schmid, Beat; Tomlinson, Jason; Toto, Tami

doi:10.1175/bams-d-11-00189.1

Cited by 94 publications

(100 citation statements)

References 56 publications

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“…This type of cloud favors the entrainment mixing feedback, in which polluted clouds tend to have lower LWC because of enhanced droplet evaporation. The differences between the results shown here and the study of Vogelmann et al (2012) suggest that the entrainment mixing process is not dominant over the Amazon. Possible reasons include abundant water vapor, thicker clouds, stronger convection and updrafts, and low vertical wind shear.…”

Section: Comparing the Main Drivers Of Bulk Microphysical Properties contrasting

confidence: 96%

“…The meteorological and cloud morphology conditions in the Amazon also seem to enable the high sensitivity values found. A previous study by Vogelmann et al (2012) found relatively invariant N d as a function of N a . Beyond instrumental and methodological differences, this study also focused on shallow (200 to 500 m thickness) broken clouds with weak updrafts over Oklahoma.…”

Section: Comparing the Main Drivers Of Bulk Microphysical Properties mentioning

confidence: 73%

“…High humidity of the surrounding air induces weaker LWC and N d depletion by the entrainment mixing process (see, for instance, Korolev et al, 2016) because of slower evaporation. Stronger convection induces deeper clouds that have a relatively low areato-volume ratio as compared to the clouds reported in Vogelmann et al (2012). Therefore, the entrainment at cloud edges are not as dominant.…”

Section: Comparing the Main Drivers Of Bulk Microphysical Properties mentioning

confidence: 84%

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Sensitivities of Amazonian clouds to aerosols and updraft speed

et al. 2017

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Abstract. The effects of aerosol particles and updraft speed on warm-phase cloud microphysical properties are studied in the Amazon region as part of the ACRIDICON-CHUVA experiment. Here we expand the sensitivity analysis usually found in the literature by concomitantly considering cloud evolution, putting the sensitivity quantifications into perspective in relation to in-cloud processing, and by considering the effects on droplet size distribution (DSD) shape. Our in situ aircraft measurements over the Amazon Basin cover a wide range of particle concentration and thermodynamic conditions, from the pristine regions over coastal and forested areas to the southern Amazon, which is highly polluted from biomass burning. The quantitative results show that particle concentration is the primary driver for the vertical profiles of effective diameter and droplet concentration in the warm phase of Amazonian convective clouds, while updraft speeds have a modulating role in the latter and in total condensed water. The cloud microphysical properties were found to be highly variable with altitude above cloud base, which we used as a proxy for cloud evolution since it is a measure of the time droplets that were subject to cloud processing. We show that DSD shape is crucial in understanding cloud sensitivities. The aerosol effect on DSD shape was found to vary with altitude, which can help models to better constrain the indirect aerosol effect on climate.

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Section: Comparing the Main Drivers Of Bulk Microphysical Properties contrasting

confidence: 96%

Section: Comparing the Main Drivers Of Bulk Microphysical Properties mentioning

confidence: 73%

Section: Comparing the Main Drivers Of Bulk Microphysical Properties mentioning

confidence: 84%

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Sensitivities of Amazonian clouds to aerosols and updraft speed

et al. 2017

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“…In addition, a nearly global survey of the effective radii in marine and continental shallow warm clouds (Han et al, 1994) indicated mean r eff values of 11.8 and 8.5 µm, respectively. Nevertheless, small r eff values, in the range of 3.5-5.5 µm, have been reported for in situ measurements of continental boundary layer cumulus clouds (Han et al, 1995;Vogelmann et al, 2012). These values coincide well with the findings of Deng et al (2009), who reported an average r eff of 3.86 µm, with an average LWC of 0.16 g m −3 , from in situ measurements of Cu clouds in Beijing.…”

Section: Introductionsupporting

confidence: 87%

On transition-zone water clouds

et al. 2014

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Abstract.A recent field campaign was conducted to measure the properties of thin, warm convective clouds forming under conditions of weak updrafts. During the campaign, shortlived clouds (on the order of minutes) with droplets' effective radius of 1-2 µm and low liquid water path (∼ 500 mg m −2 ) were measured. These low values are puzzling, since in most studies an effective radius of 4 µm is reported to serve as the lower bound for clouds. A theoretical cloud model designed to resolve the droplet-activation process suggested conditions that favor the formation of such clouds. Here we show that these clouds, which mark the transition from haze to cloud, are highly sensitive to the magnitude of the initial perturbation that initiated them. We define these clouds as "transition-zone clouds". The existence of such clouds poses a key challenge for the analysis of atmospheric observations and models, since they "further smooth" the transition from dry aerosol through haze pockets to cumulus clouds.

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“…As mentioned above, this approach has been founded on an assumption of gamma distribution for the cloud droplet spectrum. Although a large number of observations have provided support to this assumption (Mason 1971;Sedunov 1974;Cotton and Anthes 1989;Pruppacher and Klett 1997), some other observations have shown exceptional examples (Deng et al 2009). Following our previous work, here we seek a general method for obtaining the relative dispersion and at the same time eliminate the assumption of gamma distribution with an aim of widening the application of this method.…”

Section: Introductionmentioning

confidence: 99%

Skewness of cloud droplet spectrum and an improved estimation for its relative dispersion

Liu

2016

Meteorol Atmos Phys

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The relative dispersion of the cloud droplet spectrum is a very important parameter in describing and modeling cloud microphysical processes. Based on the definition of skewness as well as theoretical and data analyses, a linear fitting relationship (a = 2.91e-0.59) between skewness (a) and relative dispersion (e) is established and a new method is developed to estimate the relative dispersion of the cloud droplet spectrum. The new method does not depend on any assumption of a particular distribution for the cloud droplet spectrum and has broader applicability than the previous methods. Comparisons of the three methods for the relative dispersion with the observed data supported the following conclusions. (1) The skewness of the cloud droplet spectrum is asymmetrically distributed. An assumption of zero skewness in quantifying the relative dispersion inevitably results in relatively large deviations from the observations. Errors of the estimated relative dispersion due to the omission of the skewness term are not solely related to the skewness, but rather to the product of the skewness and relative dispersion. (2) The use of the assumption that the cloud droplet spectrum takes a gamma distribution is similar to the assumption that the skewness is twice the relative dispersion. This leads to a better accuracy in estimating the relative dispersion than that with zero skewness assumption. (3) Comparisons with observations show that the new method is more accurate than the one under gamma distribution assumption and is the best among all the three methods. (4) It is believed that finding a better correlation between the skewness and the relative dispersion would further reduce the deviations for the estimated relative dispersion.

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Racoro Extended-Term Aircraft Observations of Boundary Layer Clouds

Cited by 94 publications

References 56 publications

Sensitivities of Amazonian clouds to aerosols and updraft speed

Sensitivities of Amazonian clouds to aerosols and updraft speed

On transition-zone water clouds

Skewness of cloud droplet spectrum and an improved estimation for its relative dispersion

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