Guy Dagan

Guy Dagan
Hebrew University of Jerusalem | HUJI

PhD

About

59
Publications
7,022
Reads
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720
Citations
Education
October 2012 - October 2014
Weizmann Institute of Science
Field of study
  • Atmospheric science
October 2009 - October 2012
Hebrew University of Jerusalem
Field of study
  • Atmospheric science

Publications

Publications (59)
Article
Full-text available
Global mean precipitation is expected to increase with increasing temperatures, a process which is fairly well understood. In contrast, local precipitation changes, which are key for society and ecosystems, demonstrate a large spread in predictions by climate models, can be of both signs and have much larger magnitude than the global mean change. P...
Article
Full-text available
Plain Language Summary Anthropogenic aerosols are particles suspended in the atmosphere, which were released due to anthropogenic activity. These particles have a general cooling effect on the Earth due to their interactions with radiation and with clouds. Here we show that the surface temperature in the North Atlantic Ocean is predicted to increas...
Article
Full-text available
By interacting with radiation, aerosols perturb the Earth’s energy budget and thus the global precipitation amount. It was previously shown that aerosol-radiation interactions lead to a reduction in the global-mean precipitation amount. We have further demonstrated in aqua-planet simulations that the local response to absorbing aerosols differs bet...
Article
Full-text available
Anthropogenic aerosols effect on clouds remains a persistent source of uncertainty in future climate predictions. The evolution of the environmental conditions controlling cloud properties is affected by the clouds themselves. Hence, aerosol-driven modifications of cloud properties can affect the evolution of the environmental thermodynamic conditi...
Article
Full-text available
Clouds are a key player in the global climate system, affecting the atmospheric water and energy budgets, and they are strongly coupled to the large-scale atmospheric circulation. Here we examine the co-variability of the atmospheric energy and water budget imbalances in three different global model configurations - radiative-convective equilibrium...
Preprint
Full-text available
How Earth's climate reacts to anthropogenic forcing is one of the most burning questions faced by today's scientific community. A leading source of uncertainty in estimating this sensitivity is related to the response of clouds. Under the canonical climate-change perspective of forcings and feedbacks, the effect of anthropogenic aerosols on clouds...
Article
Full-text available
Over the coming decades, it is expected that the spatial pattern of anthropogenic aerosol will change dramatically and the global aerosol composition will become relatively more absorbing. Yet, the climatic impact of this evolving spatial pattern of absorbing aerosol has received relatively little attention, in particular its impact on global-mean...
Article
Full-text available
Aerosol–cloud interactions (ACIs) are considered to be the most uncertain driver of present-day radiative forcing due to human activities. The nonlinearity of cloud-state changes to aerosol perturbations make it challenging to attribute causality in observed relationships of aerosol radiative forcing. Using correlations to infer causality can be ch...
Article
Full-text available
The Sahel rainfall has a close teleconnection with North Atlantic sea surface temperature (NASST) variability, which has separately been shown to be affected by aerosols. Therefore, changes in regional aerosols emission could potentially drive multidecadal Sahel rainfall variability. Here we combine ensembles of state‐of‐the‐art global climate mode...
Preprint
Full-text available
Over the coming decades it is expected that the spatial pattern of anthropogenic aerosol will change dramatically and that the global composition of aerosols will become relatively more absorbing. However, despite this the climatic impact of the evolving spatial pattern of absorbing aerosol has received relatively little attention, in particular th...
Article
Full-text available
Tropical deep convection can aggregate into large clusters, which can have impacts on the local humidity and precipitation. Sea surface temperature (SST) gradients have been shown to organise convection, yet there has been little work done to investigate the impact of diabatic heating perturbations in the atmosphere on the aggregation of convection...
Article
Full-text available
Sea spray aerosol (SSA) formation have a major role in the climate system, but measurements at a global-scale of this micro-scale process are highly challenging. We measured high-resolution temporal patterns of SSA number concentration over the Atlantic Ocean, Caribbean Sea, and the Pacific Ocean covering over 42,000 km. We discovered a ubiquitous...
Preprint
Full-text available
Aerosol-cloud interactions (ACI) are considered to be the most uncertain driver of present-day radiative forcing due to human activities. The non-linearity of cloud-state changes to aerosol perturbations make it challenging to attribute causality in observed relationships of aerosol radiative forcing. Using correlations to infer causality can also...
Article
Full-text available
Absorbing aerosol from biomass burning impacts the hydrological cycle and radiation fluxes both directly and indirectly via modifications to convective processes and cloud development. Using the ICOsahedral Non-hydrostatic modelling framework in a regional configuration with 1,500m convection-permitting resolution, we isolate the response of the A...
Article
Full-text available
Shallow clouds remain greatly significant in improving our understanding of the atmosphere. Using the Met Office Unified Model, we compare highly idealised simulations of shallow cumuli with those using more realistic domains, with open lateral boundaries and varying large-scale forcing. We find that the realistic simulations are more capable of re...
Article
Full-text available
Aerosol size distribution has major effects on warm cloud processes. Here, we use newly acquired marine aerosol size distributions (MSDs), measured in situ over the open ocean during the Tara Pacific expedition (2016-2018), to examine how the total aerosol concentration (N tot) and the shape of the MSDs change warm clouds' properties. For this, we...
Article
Full-text available
Ocean-atmosphere interactions such as sea spray aerosol (SSA) formation have a major role in the climate system, but a global-scale assessment of this micro-scale process is highly challenging. We measured high-resolution temporal patterns of SSA number concentration over the Atlantic Ocean, Caribbean Sea, and the Pacific Ocean covering 42,000 km o...
Preprint
Full-text available
Ocean-atmosphere interactions such as sea spray aerosol (SSA) formation have a major role in the climate system, but a global-scale assessment of this micro-scale process is highly challenging. We measured high-resolution temporal patterns of SSA number concentration over the Atlantic Ocean, Caribbean Sea, and the Pacific Ocean covering 42,000 km o...
Conference Paper
Full-text available
The phenomenon of convective aggregation in idealised radiative convective equilibrium simulations has the ability to change the mean state of its domain. When compared to non-aggregation conditions, these simulations usually have warmer drier mean atmospheres, with stronger precipitation in the convective areas. Many of these idealised experiments...
Preprint
Full-text available
Aerosol size distribution has major effects on warm cloud processes. Here, we use newly acquired marine aerosol size distributions (MSD), measured in-situ over the open ocean during the Tara Pacific expedition (2016–2018), to examine how the total aerosol concentration (Ntot) and the shape of the MSD change warm cloud's properties. For this, we use...
Article
Full-text available
Aerosol effects on cloud properties and the atmospheric energy and radiation budgets are studied through ensemble simulations over two month-long periods during the NARVAL campaigns (Next-generation Aircraft Remote-Sensing for Validation Studies, December 2013 and August 2016). For each day, two simulations are conducted with low and high cloud dro...
Preprint
Full-text available
By interacting with radiation, aerosols perturb the Earth's energy budget and thus the global precipitation amount. It was previously shown that aerosols lead to a reduction in the global-mean precipitation amount. We have further demonstrated in aqua-planet simulations that the local response to absorbing aerosols differs between the tropics and t...
Article
Full-text available
The atmospheric energy budget is analysed in numerical simulations of tropical cloud systems to better understand the physical processes behind aerosol effects on the atmospheric energy budget. The simulations include both shallow convective clouds and deep convective tropical clouds over the Atlantic Ocean. Two different sets of simulations, at di...
Preprint
Full-text available
Aerosol effects on cloud properties and the atmospheric energy and radiation budgets are studied through ensemble simulations over two month-long periods during the NARVAL campaigns (December 2013 and August 2016). For each day, two simulations are conducted with low and high cloud droplet number concentrations (CDNC), representing low and high aer...
Article
Full-text available
Previous study of shallow convection has generally suffered from having to balance domain size with resolution, resulting in high-resolution studies which do not capture large-scale behaviour of the cloud fields. In this work we hope to go some way towards addressing this by carrying out cloud-resolving simulations on large domains. Simulations of...
Article
Full-text available
The atmospheric energy budget is analysed in numerical simulations of tropical cloud systems. This is done in order to better understand the physical processes behind aerosol effects on the atmospheric energy budget. The simulations include both shallow convective clouds and deep convective tropical clouds over the Atlantic Ocean. Two different set...
Article
Full-text available
Plain Language Summary Predicting precipitation changes due to climate change is of great importance for society. We propose that the present‐day characteristic scale of the hydrological cycle (for which precipitation roughly equals evaporation) predicts the spatial scale of future precipitation changes under global warming. For smaller scales than...
Article
Full-text available
The effects of aerosol on warm convective cloud cores are evaluated using single cloud and cloud field simulations. Three core definitions are examined: positive vertical velocity (Wcore), supersaturation (RHcore), and positive buoyancy (Bcore). As presented in Part 1 (Heiblum et al., 2019), the property Bcore⊆RHcore⊆Wcore is seen during growth of...
Article
Full-text available
The properties of a warm convective cloud are determined by the competition between the growth and dissipation processes occurring within it. One way to observe and follow this competition is by partitioning the cloud to core and margin regions. Here we look at three core definitions, namely positive vertical velocity (Wcore), supersaturation (RHco...
Article
Full-text available
Plain Language Summary Precipitation, as the Earth's only natural source of fresh water, is of great importance for society. Climate change, besides changing the mean surface temperature and its distribution, is expected to change the precipitation's temporal and spatial distribution and, to a lesser extent, the global mean precipitation. One impor...
Article
Full-text available
Previous study of shallow convection has generally suffered from having to balance domain size with resolution, resulting in high resolution studies which do not capture large scale behaviour of the cloud fields. In this work we hope to go some way towards addressing this by carrying out cloud resolving simulations on large domains. Simulations of...
Article
Full-text available
Aerosol effects on convective clouds and associated precipitation constitute an important open-ended question in climate research. Previous studies have linked an increase in aerosol concentration to a delay in the onset of rain, invigorated clouds and stronger rain rates. Here, using observational data, we show that the aerosol effect on convectiv...
Article
Shallow convection is a subgrid process in cloud-resolving models for which their grid box is larger than the size of small cumulus clouds (Cu). At the same time such Cu substantially affect radiation properties and thermodynamic parameters of the low atmosphere. The main microphysical parameters used for calculation of radiative properties of Cu i...
Article
Full-text available
Clouds control much of the Earth's energy and water budgets. Aerosols, suspended in the atmosphere, interact with clouds and affect their properties. Recent studies have suggested that the aerosol effect on warm convective cloud systems evolve in time and eventually approach a steady state for which the overall effects of aerosols can be considered...
Article
Full-text available
Physical insights into processes governing temporal organization and evolution of cloud-fields are of great importance for climate research. Here, using large eddy simulations with a bin- microphysics scheme, we show that warm convective cloud fields exhibit oscillations with two distinct periods (~10 and ~90 min, for the case studied here). The sh...
Article
Full-text available
The properties of a warm convective cloud are determined by the competition between the growth and dissipation processes occurring within it. One way to observe and follow this competition is by partitioning the cloud to core and margin regions. Here we look at three core definitions: positive vertical velocity (Wcore), supersaturation (RHcore), an...
Article
Full-text available
The effects of aerosol on warm convective cloud cores are evaluated using single cloud and cloud field simulations. As presented in Part I, the Bcore⊆RHcore⊆Wcore property is seen during growth of warm convective clouds. We show that this property is kept irrespective of aerosol concentration. During dissipation core fractions gen...
Article
The large uncertainty in estimating the global aerosol radiative forcing (ARF) is one of the major challenges the climate community faces for climate projection. While the global-mean ARF may affect global quantities such as surface temperature, its spatial distribution may result in local thermodynamical and, thus, dynamical changes. Future change...
Article
Full-text available
Better representation of cloud–aerosol interactions is crucial for an improved understanding of natural and anthropogenic effects on climate. Recent studies have shown that the overall aerosol effect on warm convective clouds is non-monotonic. Here, we reduce the system's dimensions to its center of gravity (COG), enabling distillation and simplifi...
Article
Full-text available
Cloud feedbacks could influence significantly the overall response of the climate system to global warming. Here we study the response of warm convective clouds to a uniform temperature change under constant relative humidity (RH) conditions. We show that an increase in temperature drives competing effects at the cloud scale: a reduction in the the...
Article
Full-text available
10 Better representation of cloud-aerosol interactions is crucial for an improved 11 understanding of natural and anthropogenic effects on climate. Recent studies have 12 shown that the overall effect can be viewed as a competition between processes with 13 opposing trends. Here, we reduce the system's dimensions to its center of gravity 14 (COG),...
Article
Full-text available
Understanding aerosol effects on deep convective clouds and the derived effects on the radiation budget and rain patterns can largely contribute to estimations of climate uncertainties. The challenge is difficult in part because key microphysical processes in the mixed and cold phases are still not well understood. For deep convective clouds with a...
Article
Full-text available
Large eddy simulations (LESs) with bin microphysics are used here to study cloud fields’ sensitivity to changes in aerosol loading and the time evolution of this response. Similarly to the known response of a single cloud, we show that the mean field properties change in a nonmonotonic trend, with an optimum aerosol concentration for which the fiel...
Article
Full-text available
Convective cloud formation and evolution strongly depend on environmental temperature and humidity profiles. The forming clouds change the profiles that created them by redistributing heat and moisture. Here we show that the evolution of the field’s thermodynamic properties depends heavily on the concentration of aerosol, liquid or solid particles...
Preprint
Full-text available
Understanding aerosol effects on deep convective clouds and the derived effects on the radiation budget and rain patterns can largely contribute to estimations of climate uncertainties. The challenge is difficult in part because key microphysical processes in the mixed and cold phases are still not well understood. For deep convective clouds with a...
Article
Full-text available
Cloud-aerosol interactions are considered as one of the largest sources of uncertainties in the study of climate change. Here, another possible cloud-aerosol effect on climate is proposed. A series of Large Eddy Simulations (LES) with bin microphysics reveal a sensitivity of the total atmospheric water vapor amount to aerosol concentration. Under p...
Article
Full-text available
Large Eddy Simulations (LES) with bin microphysics are used here to study cloud fields' sensitivity to changes in aerosol properties and the time evolution of this response. Similarly to the known response of a single cloud, we show that the mean field properties change in a non-monotonic trend, with an optimum aerosol concentration for which the f...
Article
In Part I of this work a 3-D cloud tracking algorithm and phase space of center of gravity altitude versus cloud liquid water mass (CvM space) were introduced and described in detail. We showed how new physical insight can be gained by following cloud trajectories in the CvM space. Here this approach is used to investigate aerosol effects on cloud...
Article
We study the evolution of warm convective cloud fields using large eddy simulations of continental and trade cumulus. Individual clouds are tracked a posteriori from formation to dissipation using a 3-D cloud-tracking algorithm, and results are presented in the phase space of center of gravity altitude versus cloud liquid water mass (CvM space). Th...
Article
Full-text available
Cloud droplet mobility is referred to here as a measure of the droplets’ ability to move with ambient air. We claim that an important part of the aerosol effect on convective clouds is driven by changes in droplet mobility. We show that the mass-weighted average droplet terminal velocity, defined here as the ‘effective terminal velocity’(η) and its...
Article
Full-text available
Warm rain production as the end result of all clouds' processes is highly affected by aerosol loading and properties. Here an axisymmetric bin microphysics cloud model is used to study the aerosol's effects on the competition and synergy between processes in a single convective cloud, to provide a baseline for studies of aerosol effects on cloud fi...