scholarly journals On clocks and clouds

2014 ◽  
Vol 14 (13) ◽  
pp. 6729-6738 ◽  
Author(s):  
M. K. Witte ◽  
P. Y. Chuang ◽  
G. Feingold
Keyword(s):  
Vertical Direction ◽  
Trade Wind ◽  
Cumulus Cloud ◽  
Initial Value ◽  
Cumulus Clouds ◽  
Mature Phase ◽  
Cloud Properties ◽  
Large Eddy ◽  
Multiple Pulses

Abstract. Cumulus clouds exhibit a life cycle that consists of (a) the growth phase (increasing size, most notably in the vertical direction); (b) the mature phase (growth ceases; any precipitation that develops is strongest during this period); and (c) the dissipation phase (cloud dissipates because of precipitation and/or entrainment; no more dynamical support). Although radar can track clouds over time and give some sense of the age of a cloud, most aircraft in situ measurements lack temporal context. We use large eddy simulations of trade wind cumulus cloud fields from cases during the Barbados Oceanographic and Meteorological Experiment (BOMEX) and Rain In Cumulus over the Ocean (RICO) campaigns to demonstrate a potential cumulus cloud "clock." We find that the volume-averaged total water mixing ratio rt is a useful cloud clock for the 12 clouds studied. A cloud's initial rt is set by the subcloud mixed-layer mean rt and decreases monotonically from the initial value due primarily to entrainment. The clock is insensitive to aerosol loading, environmental sounding and extrinsic cloud properties such as lifetime and volume. In some cases (more commonly for larger clouds), multiple pulses of buoyancy occur, which complicate the cumulus clock by replenishing rt. The clock is most effectively used to classify clouds by life phase.

scholarly journals On clocks and clouds

2013 ◽  
Vol 13 (9) ◽  
pp. 23461-23490
Author(s):  
M. K. Witte ◽  
P. Y. Chuang ◽  
G. Feingold
Keyword(s):  
Vertical Direction ◽  
Trade Wind ◽  
Cumulus Cloud ◽  
Initial Value ◽  
Cumulus Clouds ◽  
Mature Phase ◽  
Cloud Properties ◽  
Large Eddy ◽  
Multiple Pulses

Abstract. Cumulus clouds exhibit a life cycle that consists of: (a) the growth phase (increasing size, most notably in the vertical direction); (b) the mature phase (growth ceases; any precipitation that develops is strongest during this period); and (c) the dissipation phase (cloud dissipates because of precipitation and/or entrainment; no more dynamical support). Although radar can track clouds over time and give some sense of the age of a cloud, most aircraft in situ measurements lack temporal context. We use large eddy simulations of trade wind cumulus cloud fields from cases during the Barbados Oceanographic and Meteorological Experiment (BOMEX) and Rain In Cumulus over the Ocean (RICO) campaigns to demonstrate a potential cumulus cloud "clock". We find that the volume-averaged total water mixing ratio rt is a useful cloud clock for the 12 clouds studied. A cloud's initial rt is set by the subcloud mixed-layer mean rt and decreases monotonically from the initial value due primarily to entrainment. The clock is insensitive to aerosol loading, environmental sounding and extrinsic cloud properties such as lifetime and volume. In some cases (more commonly for larger clouds), multiple pulses of buoyancy occur, which complicate the cumulus clock by replenishing rt. The clock is most effectively used to classify clouds by life phase.

scholarly journals Satellite-observed relationships between aerosol and trade-wind cumulus cloud properties over the Indian Ocean

2011 ◽  
Vol 38 (1) ◽  
pp. n/a-n/a ◽  
Author(s):  
Sagnik Dey ◽  
Larry Di Girolamo ◽  
Guangyu Zhao ◽  
Alexandra L. Jones ◽  
Greg M. McFarquhar
Keyword(s):  
Indian Ocean ◽  
Trade Wind ◽  
Cumulus Cloud ◽  
Cloud Properties ◽  
The Indian Ocean

scholarly journals Improvement of airborne retrievals of cloud droplet number concentration of trade wind cumulus using a synergetic approach

2019 ◽  
Vol 12 (3) ◽  
pp. 1635-1658 ◽  
Author(s):  
Kevin Wolf ◽  
André Ehrlich ◽  
Marek Jacob ◽  
Susanne Crewell ◽  
Martin Wirth ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Cloud Droplet ◽  
Number Concentration ◽  
Cloud Base ◽  
Trade Wind ◽  
Liquid Water Path ◽  
Cloud Properties ◽  
Research Aircraft ◽  
Cloud Droplet Number Concentration

Abstract. In situ measurements of cloud droplet number concentration N are limited by the sampled cloud volume. Satellite retrievals of N suffer from inherent uncertainties, spatial averaging, and retrieval problems arising from the commonly assumed strictly adiabatic vertical profiles of cloud properties. To improve retrievals of N it is suggested in this paper to use a synergetic combination of passive and active airborne remote sensing measurement, to reduce the uncertainty of N retrievals, and to bridge the gap between in situ cloud sampling and global averaging. For this purpose, spectral solar radiation measurements above shallow trade wind cumulus were combined with passive microwave and active radar and lidar observations carried out during the second Next Generation Remote Sensing for Validation Studies (NARVAL-II) campaign with the High Altitude and Long Range Research Aircraft (HALO) in August 2016. The common technique to retrieve N is refined by including combined measurements and retrievals of cloud optical thickness τ, liquid water path (LWP), cloud droplet effective radius reff, and cloud base and top altitude. Three approaches are tested and applied to synthetic measurements and two cloud scenarios observed during NARVAL-II. Using the new combined retrieval technique, errors in N due to the adiabatic assumption have been reduced significantly.

Aerosol effects on shallow cumulus cloud fields in idealised and realistic simulations

2020 ◽  
Author(s):  
George Spill ◽  
Philip Stier ◽  
Paul Field ◽  
Guy Dagan
Keyword(s):  
Large Scale ◽  
Trade Wind ◽  
Quasi Equilibrium ◽  
Cumulus Cloud ◽  
Shallow Convection ◽  
Shallow Cumulus ◽  
Synoptic Conditions ◽  
Large Eddy ◽  
Transient Forcing ◽  
Periodic Domains

<p>Shallow cumulus clouds interact with their environment in myriad significant ways, and yet their behavour is still poorly understood, and is responsible for much uncertainty in climate models. Improving our understanding of these clouds is therefore an important part of improving our understanding of the climate system as a whole.</p><p>Modelling studies of shallow convection have traditionally made use of highly idealised simulations using large-eddy models, which allow for high resolution, detailed simulations. However, this idealised nature, with periodic boundaries and constant forcing, and the quasi-equilibrium cloud fields produced, means that they do not capture the effect of transient forcing and conditions found in the real atmosphere, which contains shallow cumulus cloud fields unlikely to be in equilibrium.<span> </span></p><p>Simulations with more realistic nested domains and forcings have previously been shown to have significant persistent responses differently to aerosol perturbations, in contrast to many large eddy simulations in which perturbed runs tend to reach a similar quasi-equilibrium.<span> </span></p><p>Here, we further this investigation by using a single model to present a comparison of familiar idealised simulations of trade wind cumuli in periodic domains, and simulations with a nested domain, whose boundary conditions are provided by a global driving model, able to simulate transient synoptic conditions.<span> </span></p><p>The simulations are carried out using the Met Office Unified Model (UM), and are based on a case study from the Rain In Cumulus over the Ocean (RICO) field campaign. Large domains of 500km are chosen in order to capture large scale cloud field behaviour. A double-moment interactive microphysics scheme is used, along with prescribed aerosol profiles based on RICO observations, which are then perturbed.</p><p>We find that the choice between realistic nested domains with transient forcing and idealised periodic domains with constant forcing does indeed affect the nature of the response to aerosol perturbations, with the realistic simulations displaying much larger persistent changes in domain mean fields such as liquid water path and precipitation rate.<span> </span></p>

scholarly journals Large-eddy simulation of organized precipitating trade wind cumulus clouds

2013 ◽  
Vol 13 (1) ◽  
pp. 1855-1889 ◽  
Author(s):  
A. Seifert ◽  
T. Heus
Keyword(s):  
Large Eddy Simulation ◽  
Trade Wind ◽  
Shallow Convection ◽  
Cumulus Clouds ◽  
Eddy Simulation ◽  
Cold Pools ◽  
Cloud Clusters ◽  
Large Eddy ◽  
Sensitivity Studies ◽  
The Individual

Abstract. Trade wind cumulus clouds often organize in along-wind cloud streets and across-wind mesoscale arcs. We present a benchmark large-eddy simulation which resolves the individual clouds as well as the mesoscale organization on scales of O(10 km). Different methods to quantify organization of cloud fields are applied and discussed. Using perturbed physics large-eddy simulations experiments the processes leading to the formation of cloud clusters and the mesoscale arcs are revealed. We find that both cold pools as well as the sub-cloud layer moisture field are crucial to understand the organization of precipitating shallow convection. Further sensitivity studies show that microphysical assumptions can have a pronounced impact on the onset of cloud organization.

scholarly journals Shallow cumulus cloud feedback in large eddy simulations – bridging the gap to storm-resolving models

2021 ◽  
Vol 21 (5) ◽  
pp. 3275-3288
Author(s):  
Jule Radtke ◽  
Thorsten Mauritsen ◽  
Cathy Hohenegger
Keyword(s):  
Cloud Cover ◽  
Horizontal Resolution ◽  
Cloud Fraction ◽  
Cloud Feedback ◽  
Cloud Base ◽  
Trade Wind ◽  
Cumulus Cloud ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Carry Over

Abstract. The response of shallow trade cumulus clouds to global warming is a leading source of uncertainty in projections of the Earth's changing climate. A setup based on the Rain In Cumulus over the Ocean field campaign is used to simulate a shallow trade wind cumulus field with the Icosahedral Nonhydrostatic Large Eddy Model in a control and a perturbed 4 K warmer climate, while degrading horizontal resolution from 100 m to 5 km. As the resolution is coarsened, the base-state cloud fraction increases substantially, especially near cloud base, lateral mixing is weaker, and cloud tops reach higher. Nevertheless, the overall vertical structure of the cloud layer is surprisingly robust across resolutions. In a warmer climate, cloud cover reduces, alone constituting a positive shortwave cloud feedback: the strength correlates with the amount of base-state cloud fraction and thus is stronger at coarser resolutions. Cloud thickening, resulting from more water vapour availability for condensation in a warmer climate, acts as a compensating feedback, but unlike the cloud cover reduction it is largely resolution independent. Therefore, refining the resolution leads to convergence to a near-zero shallow cumulus feedback. This dependence holds in experiments with enhanced realism including precipitation processes or warming along a moist adiabat instead of uniform warming. Insofar as these findings carry over to other models, they suggest that storm-resolving models may exaggerate the trade wind cumulus cloud feedback.

On the size dependence of cumulus cloud spacing

2021 ◽  
Author(s):  
Thirza van Laar ◽  
Roel Neggers
Keyword(s):  
Spatial Organization ◽  
Size Dependence ◽  
Nearest Neighbor ◽  
Trade Wind ◽  
Grey Zone ◽  
Cumulus Cloud ◽  
Cumulus Clouds ◽  
Horizontal Size ◽  
Earth’S Climate ◽  
Convective Cells

<p>The spatial variability of Trade wind cumulus cloud fields has been found to be of great importance for understanding their role in Earth's climate system. In this study the focus is on the spacing between individual cumulus clouds. The main objective is to establish how inter-cloud spacing depends on cloud size, information that is crucial for understanding cloud-radiation interaction and spatial organization, and for informing grey zone parametrizations. To this end, a large-domain high resolution ICON LES simulation of marine shallow cumulus cloud fields is used. The domain is located at the subtropical Atlantic and the simulations are performed for the time of the recent NARVAL South campaign (December 2013). The simulations are compared with MODIS satellite imagery and research flight measurements, showing a good agreement between observations and the simulation, on both cloud size statistics and the vertical structure of the boundary layer.  </p><p>To determine the size and locations of the clouds, a cluster analysis was applied to the data. The inter-cloud, or nearest neighbor spacing (NNS), is addressed using four different expressions, classic definitions but also novel ones. For all definitions the spacing increases with cloud size, but the dependence is strongly influenced by the used definition. The classic definition, the spacing between clouds of any size, shows a well-defined logarithmic dependence on cloud size. The logarithmic relation can be explained by the abundance of closely-spaced small clouds. The small distances between these clouds form an upper bound for the NNS for the larger cloud sizes. In contrast, the spacing between clouds of a similar size increases exponentially with size. We argue that the exponential size-dependence reflects the mesoscale dynamics that drive the horizontal size of large convective cells, of which the cumulus clouds are the visible parts.  </p>

scholarly journals Statistical analysis of an LES shallow cumulus cloud ensemble using a cloud tracking algorithm

2012 ◽  
Vol 12 (2) ◽  
pp. 1101-1119 ◽  
Author(s):  
J. T. Dawe ◽  
P. H. Austin
Keyword(s):  
Thermodynamic Properties ◽  
Cloud Base ◽  
Cumulus Cloud ◽  
Cumulus Clouds ◽  
Base Area ◽  
Eddy Simulation ◽  
Cloud Properties ◽  
Shallow Cumulus ◽  
Cloud Height ◽  
Upper Level

Abstract. A technique for the tracking of individual clouds in a Large Eddy Simulation (LES) is presented. We use this technique on an LES of a shallow cumulus cloud field based upon the Barbados Oceanographic and Meteorological Experiment (BOMEX) to calculate statistics of cloud height, lifetime, and other physical properties for individual clouds in the model. We also examine the question of nature versus nurture in shallow cumulus clouds: do properties at cloud base determine the upper-level properties of the clouds (nature), or are cloud properties determined by the environmental conditions they encounter (nurture). We find that clouds which ascend through an environment that has been pre-moistened by previous cloud activity are no more likely to reach the inversion than clouds that ascend through a drier environment. Cloud base thermodynamic properties are uncorrelated with upper-level cloud properties, while mean fractional entrainment and detrainment rates display moderate correlations with cloud properties up to the inversion. Conversely, cloud base area correlates well with upper-level cloud area and maximum cloud height. We conclude that cloud thermodynamic properties are primarily influenced by entrainment and detrainment processes, cloud area and height are primarily influenced by cloud base area, and thus nature and nurture both play roles in the dynamics of BOMEX shallow cumulus clouds.

Validation of trade wind cumulus cloud properties derived from meteorological satellites

2005 ◽  
Author(s):  
Iliana Genkova ◽  
Guangyu Zhao ◽  
Gabriela Seiz ◽  
Eric Snodgrass ◽  
Marile Colon ◽  
...  
Keyword(s):  
Trade Wind ◽  
Cumulus Cloud ◽  
Cloud Properties

scholarly journals Optically thin clouds in the trades

2021 ◽  
Author(s):  
Theresa Mieslinger ◽  
Bjorn Stevens ◽  
Tobias Kölling ◽  
Manfred Brath ◽  
Martin Wirth ◽  
...  
Keyword(s):  
Cloud Cover ◽  
Climate Models ◽  
Trade Wind ◽  
Cumulus Cloud ◽  
Total Cloud Cover ◽  
Clear Sky ◽  
Cloud Radiative Effect ◽  
Large Eddy ◽  
Lidar Measurements ◽  
Cloud Mask

Abstract. We develop a new method to describe the total cloud cover including optically thin clouds in trade wind cumulus cloud fields. Climate models as well as Large Eddy Simulations commonly underestimate the cloud cover, while estimates from observations largely disagree on the cloud cover in the trades. Currently, trade wind clouds contribute significantly to the uncertainty in climate sensitivity estimates derived from model perturbation studies. To simulate clouds well and especially how they change in a future climate we have to know how cloudy it is. In this study we develop a method to quantify the cloud cover from a clear-sky perspective. Using well-known radiative transfer relations we retrieve the clear-sky contribution in high-resolution satellite observations of trade cumulus cloud fields during EUREC4A. Knowing the clear-sky part, we can investigate the remaining cloud-related contributions consisting of areas detected by common cloud masking algorithms and those undetected areas related to optically thin clouds. We find that the cloud-mask cloud cover underestimates the total cloud cover by a factor of 2. Lidar measurements on board the HALO aircraft support our findings by showing a high abundance of optically thin clouds during EUREC4A. Mixing the undetected optically thin clouds into the clear-sky signal can cause an underestimation of the cloud radiative effect of up to −32 %. We further discuss possible artificial correlations in aersol-cloud cover interaction studies that might arise from undetected optically thin clouds. Our analysis suggests that the known underestimation of trade wind cloud cover and simultaneous overestiamtion of cloud brightness in models is even higher than assumed so far.

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