scholarly journals Network approach to patterns in stratocumulus clouds

2017 ◽  
Vol 114 (40) ◽  
pp. 10578-10583 ◽  
Author(s):  
Franziska Glassmeier ◽  
Graham Feingold
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Global Climate Models ◽  
Scale Invariant ◽  
Entropy Maximization ◽  
Large Eddy ◽  
Radiative Impact ◽  
Stratocumulus Clouds ◽  
Cell Merging ◽  
Earth’S Climate

Stratocumulus clouds (Sc) have a significant impact on the amount of sunlight reflected back to space, with important implications for Earth’s climate. Representing Sc and their radiative impact is one of the largest challenges for global climate models. Sc fields self-organize into cellular patterns and thus lend themselves to analysis and quantification in terms of natural cellular networks. Based on large-eddy simulations of Sc fields, we present a first analysis of the geometric structure and self-organization of Sc patterns from this network perspective. Our network analysis shows that the Sc pattern is scale-invariant as a consequence of entropy maximization that is known as Lewis’s Law (scaling parameter: 0.16) and is largely independent of the Sc regime (cloud-free vs. cloudy cell centers). Cells are, on average, hexagonal with a neighbor number variance of about 2, and larger cells tend to be surrounded by smaller cells, as described by an Aboav–Weaire parameter of 0.9. The network structure is neither completely random nor characteristic of natural convection. Instead, it emerges from Sc-specific versions of cell division and cell merging that are shaped by cell expansion. This is shown with a heuristic model of network dynamics that incorporates our physical understanding of cloud processes.

scholarly journals Stratocumulus Clouds in Southeastern Pacific Simulated by Eight CMIP5–CFMIP Global Climate Models

2014 ◽  
Vol 27 (8) ◽  
pp. 3000-3022 ◽  
Author(s):  
Jia-Lin Lin ◽  
Taotao Qian ◽  
Toshiaki Shinoda
Keyword(s):  
Cloud Cover ◽  
Large Scale ◽  
Climate Models ◽  
Global Climate ◽  
Cloud Feedback ◽  
Global Climate Models ◽  
Temperature Structure ◽  
Model Intercomparison ◽  
Stratocumulus Clouds ◽  
Intercomparison Project

Abstract This study examines the stratocumulus clouds and associated cloud feedback in the southeast Pacific (SEP) simulated by eight global climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5) and Cloud Feedback Model Intercomparison Project (CFMIP) using long-term observations of clouds, radiative fluxes, cloud radiative forcing (CRF), sea surface temperature (SST), and large-scale atmosphere environment. The results show that the state-of-the-art global climate models still have significant difficulty in simulating the SEP stratocumulus clouds and associated cloud feedback. Comparing with observations, the models tend to simulate significantly less cloud cover, higher cloud top, and a variety of unrealistic cloud albedo. The insufficient cloud cover leads to overly weak shortwave CRF and net CRF. Only two of the eight models capture the observed positive cloud feedback at subannual to decadal time scales. The cloud and radiation biases in the models are associated with 1) model biases in large-scale temperature structure including the lack of temperature inversion, insufficient lower troposphere stability (LTS), and insufficient reduction of LTS with local SST warming, and 2) improper model physics, especially insufficient increase of low cloud cover associated with larger LTS. The two models that arguably do best at simulating the stratocumulus clouds and associated cloud feedback are the only ones using cloud-top radiative cooling to drive boundary layer turbulence.

scholarly journals Data Length Requirements for Observational Estimates of Land–Atmosphere Coupling Strength

2015 ◽  
Vol 16 (4) ◽  
pp. 1615-1635 ◽  
Author(s):  
Kirsten L. Findell ◽  
Pierre Gentine ◽  
Benjamin R. Lintner ◽  
Benoit P. Guillod
Keyword(s):  
Time Series ◽  
Coupling Strength ◽  
Climate Models ◽  
Negative Impact ◽  
Global Climate ◽  
Global Climate Models ◽  
Mean Values ◽  
Single Realization ◽  
Earth’S Climate ◽  
Multiple Metrics

Abstract Multiple metrics have been developed in recent years to characterize the strength of land–atmosphere coupling in regional and global climate models. Evaluation of these metrics against observations has proven challenging because of limited observations and/or metric definitions based on model experimental designs that are not replicable with observations. Additionally, because observations are limited in time, with only a single realization of the earth’s climate available, metrics of land–atmosphere coupling strength typically assume stationarity and ergodicity, so that an observed time series (or set of time series) can be used in place of an ensemble mean of multiple realizations. The present study evaluates the observational data requirements necessary for robust quantification of a suite of land–atmosphere coupling metrics previously described in the literature. It is demonstrated that the amount of data required to obtain robust estimates of metrics assessing relationships between variables is greater than that necessary to constrain means of directly measured observables. Moreover, while the addition of unbiased noise does not significantly alter the mean of a directly observable quantity, inclusion of such noise degrades metrics based on connections between variables, yielding a unidirectional and negative impact on metric strength estimates. This analysis suggests that longer records of surface observations are required to correctly estimate land–atmosphere coupling strength than are required to estimate mean values of the observed quantities.

scholarly journals The Atmospheric Pathway of the Cloud-Radiative Impact on the Circulation Response to Global Warming: Important and Uncertain

2019 ◽  
Vol 32 (10) ◽  
pp. 3051-3067 ◽  
Author(s):  
Aiko Voigt ◽  
Nicole Albern ◽  
Georgios Papavasileiou
Keyword(s):  
Global Warming ◽  
Climate Models ◽  
Global Climate ◽  
Regional Climate ◽  
Regional Climate Change ◽  
Global Climate Models ◽  
Radiative Heating ◽  
Substantial Part ◽  
Radiative Impact ◽  
High Level

Abstract Previous work showed that the poleward expansion of the annual-mean zonal-mean atmospheric circulation in response to global warming is strongly modulated by changes in clouds and their radiative heating of the surface and atmosphere. Here, a hierarchy and an ensemble of global climate models are used to study the circulation impact of changes in atmospheric cloud-radiative heating in the absence of changes in sea surface temperature (SST), which is referred to as the atmospheric pathway of the cloud-radiative impact. For the MPI-ESM model, the atmospheric pathway is responsible for about half of the total cloud-radiative impact, and in fact half of the total circulation response. Changes in atmospheric cloud-radiative heating are substantial in both the lower and upper troposphere. However, because SST is prescribed the atmospheric pathway is dominated by changes in upper-tropospheric cloud-radiative heating, which in large part results from the upward shift of high-level clouds. The poleward circulation expansion via the atmospheric pathway and changes in upper-tropospheric cloud-radiative heating are qualitatively robust across three global models, yet their magnitudes vary by a factor of 3. A substantial part of these magnitude differences are related to the upper-tropospheric radiative heating by high-level clouds in the present-day climate. A comparison with observations highlights the model deficits in representing the radiative heating by high-level clouds and indicates that reducing these deficits can contribute to improved predictions of regional climate change.

scholarly journals Comparing multiple model-derived aerosol optical properties to collocated ground-based and satellite measurements

2016 ◽  
Author(s):  
Ilissa B. Ocko ◽  
Paul A. Ginoux
Keyword(s):  
Climate Models ◽  
Climate Modeling ◽  
Global Climate ◽  
Measurement Techniques ◽  
Single Scattering ◽  
Global Climate Models ◽  
Multiple Model ◽  
Anthropogenic Aerosols ◽  
Earth’S Climate ◽  
Aerosol Properties

Abstract. Anthropogenic aerosols are a key factor governing Earth’s climate, and play a central role in human-caused climate change. However, because of aerosols’ complex physical, optical, and dynamical properties, aerosols are one of the most uncertain aspects of climate modeling. Fortunately, aerosol measurement networks over the past few decades have led to the establishment of long-term observations for numerous locations worldwide. Further, the availability of datasets from several different measurement techniques (such as ground-based and satellite instruments) can help scientists increasingly improve modeling efforts. This study explores the value of evaluating several model-simulated aerosol properties with data from collocated instruments. We compare optical depth (total, scattering, and absorption), single scattering albedo, Ångström exponent, and extinction vertical profiles in two prominent global climate models to seasonal observations from collocated instruments (AERONET and CALIOP) at seven polluted and biomass burning regions worldwide. We find that models may accurately reproduce one variable while totally failing at another; data from collocated instruments can reveal underlying aerosol-governing physics; column properties may wash out important vertical distinctions; and "improved" models does not mean all aspects are improved. We conclude that it is important to make use of all available data (parameters and instruments) when evaluating aerosol properties derived by models.

scholarly journals Atmospheric black carbon can exhibit enhanced light absorption at high relative humidity

2013 ◽  
Vol 13 (11) ◽  
pp. 29413-29445 ◽  
Author(s):  
Y. Wei ◽  
Q. Zhang ◽  
J. E. Thompson
Keyword(s):  
Black Carbon ◽  
Light Absorption ◽  
Climate Models ◽  
Global Climate ◽  
Global Climate Models ◽  
Absorption Enhancement ◽  
High Humidity ◽  
Hygroscopic Growth ◽  
Enhanced Absorption ◽  
Earth’S Climate

Abstract. Some estimates suggest atmospheric soot (a.k.a. black carbon, BC) warms Earth's climate by roughly 50% the magnitude of increased carbon dioxide. However, one uncertainty in the climate-forcing estimate for BC is the degree to which sunlight absorption is influenced by particle mixing state. Here we show that hygroscopic growth of atmospheric aerosol particles sampled at Houston, TX leads to an enhancement in both light scattering and absorption. Measurements suggest light absorption increases roughly three-four fold at high ambient humidity for coated soot particles. However, when the fraction of coated BC particles was reduced, the absorption enhancement was also reduced, suggesting coatings are crucial for the effect to occur. In addition, the extent to which MAC was increased at high humidity varied considerably over time, even for BC that consistently presented as being coated. This suggests the chemical composition of the coating and/or source of BC may also be an important parameter to constrain MAC enhancement at high humidity. Nonetheless, the results are largely consistent with previous laboratory and model results predicting absorption enhancement. We conclude that the enhanced absorption increases the warming effect of soot aerosol aloft, and global climate models should include parameterizations for RH effects to accurately describe absorptive heating by BC.

Extreme Events in High Resolution CMCC Regional and Global Climate Models

2011 ◽  
Author(s):  
Enrico Scoccimarro ◽  
Silvio Gualdi ◽  
Antonella Sanna ◽  
Edoardo Bucchignani ◽  
Myriam Montesarchio
Keyword(s):  
High Resolution ◽  
Extreme Events ◽  
Climate Models ◽  
Global Climate ◽  
Global Climate Models
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