Observations of Moist Adiabatic Ascent in Northeast Colorado Cumulus Congestus Clouds

Heymsfield, Andrew J.; Johnson, Peter N.; Dye, J. E.

doi:10.1175/1520-0469(1978)035<1689:oomaai>2.0.co;2

Cited by 125 publications

(65 citation statements)

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“…In this study, we also find that weaker updrafts are associated with stronger entrainment-detrainment using in situ measurements of relative humidity, equivalent potential temperature, droplet concentration, and LWC (not shown). Previous studies (e.g., Heymsfield et al, 1978;Wang and Geerts, 2013) suggest updraft cores unaffected by entrainment may exist in some convective clouds.…”

Section: Discussionmentioning

confidence: 89%

“…In the analysis above, the downdrafts observed in HiCu and COPE are stronger than those observed in ICE-T. This may be partly because the ambient relative humidity is low in HiCu and COPE compared to ICE-T, resulting in a strong evaporation-cooling effect when the ambient air mixes with cloud parcels through lateral entrainmentdetrainment (Heymsfield et al, 1978). Entrainment has impacts on updrafts as well.…”

Section: Discussionmentioning

confidence: 93%

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Characteristics of vertical air motion in isolated convective clouds

et al. 2016

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Abstract. The vertical velocity and air mass flux in isolated convective clouds are statistically analyzed using aircraft in situ data collected from three field campaigns: High-Plains Cumulus (HiCu) conducted over the midlatitude High Plains, COnvective Precipitation Experiment (COPE) conducted in a midlatitude coastal area, and Ice in Clouds Experiment-Tropical (ICE-T) conducted over a tropical ocean. The results show that small-scale updrafts and downdrafts ( < 500 m in diameter) are frequently observed in the three field campaigns, and they make important contributions to the total air mass flux. The probability density functions (PDFs) and profiles of the observed vertical velocity are provided. The PDFs are exponentially distributed. The updrafts generally strengthen with height. Relatively strong updrafts (> 20 m s −1 ) were sampled in COPE and ICE-T. The observed downdrafts are stronger in HiCu and COPE than in ICE-T. The PDFs of the air mass flux are exponentially distributed as well. The observed maximum air mass flux in updrafts is of the order 10 4 kg m −1 s −1 . The observed air mass flux in the downdrafts is typically a few times smaller in magnitude than that in the updrafts. Since this study only deals with isolated convective clouds, and there are many limitations and sampling issues in aircraft in situ measurements, more observations are needed to better explore the vertical air motion in convective clouds.

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Section: Discussionmentioning

confidence: 89%

Section: Discussionmentioning

confidence: 93%

Characteristics of vertical air motion in isolated convective clouds

et al. 2016

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“…In this case f E (z) is unity except in the upper third of each thermal where it is 0.5, and in the central third of the thermal where it is interpolated from 0.5 to unity. This parametrizes the adiabatic cores seen in aircraft observations by Heymsfield et al (1978). Finally, E is an entrainment parameter that is adjusted to obtain a match of the passive tracer profile between the EMM and a 3-D model at all levels (see subsection 3(b)).…”

Section: The Model (A) Overviewmentioning

confidence: 99%

Anvil glaciation in a deep cumulus updraught over Florida simulated with the Explicit Microphysics Model. I: Impact of various nucleation processes

Phillips

Andronache

Sherwood

et al. 2005

Quart J Royal Meteoro Soc

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SUMMARYSimulations of a cumulonimbus cloud observed in the Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE) with an advanced version of the Explicit Microphysics Model (EMM) are presented. The EMM has size-resolved aerosols and predicts the time evolution of sizes, bulk densities and axial ratios of ice particles. Observations by multiple aircraft in the troposphere provide inputs to the model, including observations of the ice nuclei and of the entire size distribution of condensation nuclei.Homogeneous droplet freezing is found to be the source of almost all of the ice crystals in the anvil updraught of this particular model cloud. Most of the simulated droplets that freeze to form anvil crystals appear to be nucleated by activation of aerosols far above cloud base in the interior of the cloud ('secondary' or 'in-cloud' droplet nucleation). This is partly because primary droplets formed at cloud base are invariably depleted by accretion before they can reach the anvil base in the updraught, which promotes an increase with height of the average supersaturation in the updraught aloft. More than half of these aerosols, activated far above cloud base, are entrained into the updraught of this model cloud from the lateral environment above about 5 km above mean sea level. This confirms the importance of remote sources of atmospheric aerosol for anvil glaciation.Other nucleation processes impinge indirectly upon the anvil glaciation by modifying the concentration of supercooled droplets in the upper levels of the mixed-phase region. For instance, the warm-rain process produces a massive indirect impact on the anvil crystal concentration, because it determines the mass of precipitation forming in the updraught. It competes with homogeneous freezing as a sink for cloud droplets. The effects from turbulent enhancement of the warm-rain process and from other nucleation processes on the anvil ice properties are assessed.

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“…Hereafter, the occurrence of the shell in other numerical cases is discussed, along with various properties of the shell (section 5), including the relevance of the shell to the dynamics of the cloud and the cloud layer. A connection will be made here with the off-center position of the cloud core as seen by Heymsfield et al (1978) and the "humidity halos" that are found by, for example, Perry and Hobbs (1996), Lu et al (2003), and Laird (2005), and adjoin clouds. These halos are shown to be caused by lateral mixing and yield an increase in humidity of the environmental air especially at the downshear side of the cloud.…”

Section: Introductionmentioning

confidence: 99%

Subsiding Shells around Shallow Cumulus Clouds

Heus

Jonker

2008

Journal of the Atmospheric Sciences

185

160

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In this study large-eddy simulations (LES) are used to gain more knowledge on the shell of subsiding air that is frequently observed around cumulus clouds. First, a detailed comparison between observational and numerical results is presented to better validate LES as a tool for studies of microscale phenomena. It is found that horizontal cloud profiles of vertical velocity, humidity, and temperature are in good agreement with observations. They show features similar to the observations, including the presence of the shell of descending air around the cloud. Second, the availability of the complete 3D dataset in LES has been exploited to examine the role of lateral mixing in the exchange of cloud and environmental air. The origin of the subsiding shell is examined by analyzing the individual terms of the vertical momentum equation. Buoyancy is found to be the driving force for this shell, and it is counteracted by the pressure-gradient force. This shows that evaporative cooling at the cloud edge, induced by lateral mixing of cloudy and environmental air, is the responsible mechanism behind the descending shell. For all clouds, and especially the smaller ones, the negative mass flux generated by the subsiding shell is significant. This suggests an important role for lateral mixing throughout the entire cloud layer. The role of the shell in these processes is further explored and described in a conceptual three-layer model of the cloud.

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Observations of Moist Adiabatic Ascent in Northeast Colorado Cumulus Congestus Clouds

Cited by 125 publications

References 0 publications

Characteristics of vertical air motion in isolated convective clouds

Characteristics of vertical air motion in isolated convective clouds

Anvil glaciation in a deep cumulus updraught over Florida simulated with the Explicit Microphysics Model. I: Impact of various nucleation processes

Subsiding Shells around Shallow Cumulus Clouds

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