Radiative–Dynamical Feedbacks in Low Liquid Water Path Stratiform Clouds

Petters, Jonathan; Harrington, Jerry Y.; Clothiaux, Eugene E.

doi:10.1175/jas-d-11-0169.1

Cited by 27 publications

(31 citation statements)

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“…Overall, we find increased mixing and en- trainment in the simulations with radiation. Both the mixing and the resulting vertical velocities are due to a destabilization of the atmosphere which results from thermal cooling as, e.g., also found by Sommerai (1976), Fu et al (1995), Petters et al (2012) and Lilly (1988). Clouds also become deeper in vertical extent and contain more liquid water if thermal radiation is accounted for.…”

Section: Discussionmentioning

confidence: 76%

“…Furthermore, they found an increased liquid water content and enhanced droplet growth. Destabilization and enhanced turbulence caused by the vertical differential heating and cooling was found in addition by Sommerai (1976), Fu et al (1995), Petters et al (2012) and Lilly (1988). Larson et al (2001) showed that thermal cooling, on the one hand, enhances condensation and thus increases liquid water content; on the other hand, radiation causes more entrainment and therefore a decrease in liquid water content.…”

Section: Introductionmentioning

confidence: 94%

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Effects of 3-D thermal radiation on the development of a shallow cumulus cloud field

et al. 2017

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Abstract. We investigate the effects of thermal radiation on cloud development in large-eddy simulations (LESs) with the UCLA-LES model. We investigate single convective clouds (driven by a warm bubble) at 50 m horizontal resolution and a large cumulus cloud field at 50 and 100 m horizontal resolutions. We compare the newly developed 3-D Neighboring Column Approximation with the independent column approximation and a simulation without radiation and their respective impact on clouds. Thermal radiation causes strong local cooling at cloud tops accompanied by a modest warming at the cloud bottom and, in the case of the 3-D scheme, also cloud side cooling. 3-D thermal radiation causes systematically larger cooling when averaged over the model domain. In order to investigate the effects of local cooling on the clouds and to separate these local effects from a systematically larger cooling effect in the modeling domain, we apply the radiative transfer solutions in different ways. The direct effect of heating and cooling at the clouds is applied (local thermal radiation) in a first simulation. Furthermore, a horizontal average of the 1-D and 3-D radiation in each layer is used to study the effect of local cloud radiation as opposed to the domain-averaged effect. These averaged radiation simulations exhibit a cooling profile with stronger cooling in the cloudy layers. In a final setup, we replace the radiation simulation by a uniform cooling of 2.6 K day −1 . To focus on the radiation effects themselves and to avoid possible feedbacks, we fixed surface fluxes of latent and sensible heat and omitted the formation of rain in our simulations.Local thermal radiation changes cloud circulation in the single cloud simulations, as well as in the shallow cumulus cloud field, by causing stronger updrafts and stronger subsiding shells. In our cumulus cloud field simulation, we find that local radiation enhances the circulation compared to the averaged radiation applications. In addition, we find that thermal radiation triggers the organization of clouds in two different ways. First, local interactive radiation leads to the formation of cell structures; later on, larger clouds develop. Comparing the effects of 3-D and 1-D thermal radiation, we find that organization effects of 3-D local thermal radiation are usually stronger than the 1-D counterpart. Horizontally averaged radiation causes more clouds and deeper clouds than a no radiation simulation but, in general less-organized clouds than in the local radiation simulations. Applying a constant cooling to the simulations leads to a similar development of the cloud field as in the case of averaged radiation, but less water condenses overall in the simulation. Generally, clouds contain more liquid water if radiation is accounted for. Furthermore, thermal radiation enhances turbulence and mixing as well as the size and lifetime of clouds. Local thermal radiation produces larger clouds with longer lifetimes.The cloud fields in the 100 and 50 m resolution simulations develop similarly...

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Section: Discussionmentioning

confidence: 76%

Section: Introductionmentioning

confidence: 94%

Effects of 3-D thermal radiation on the development of a shallow cumulus cloud field

et al. 2017

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“…The representation of liquid stratiform clouds in current climate models is relatively poor, leading to large uncertainties in climate predictions (Randall et al, 2007). Radiative, dynamic and feedback processes involved in liquid clouds still need to be studied (e.g., Petters et al, 2012;Bennartz et al, 2013;Boucher et al, 2013) and thus require accurate measurement instrumentation. In-situ measurements may be directly used for model validations, or to improve and validate remote sensing, radar and lidar retrieval algorithms.…”

Section: Introductionmentioning

confidence: 99%

Quantitative evaluation of seven optical sensors for cloud microphysical measurements at the Puy-de-Dôme Observatory, France

et al. 2015

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Abstract.Clouds have an important role in Earth's radiative budget. Since the late 1970s, considerable instrumental developments have been made in order to quantify cloud microphysical and optical properties, for both airborne and groundbased applications. Intercomparison studies have been carried out in the past to assess the reliability of cloud microphysical properties inferred from various measurement techniques. However, observational uncertainties still exist, especially for droplet size distribution measurements and need to be reduced.In this work, we discuss results from an intercomparison campaign, performed at the Puy de Dôme in May 2013. During this campaign, a unique set of cloud instruments was operating simultaneously in ambient air conditions and in a wind tunnel. A Particle Volume Monitor (PVM-100), a Forward Scattering Spectrometer Probe (FSSP), a Fog Monitor (FM-100), and a Present Weather Detector (PWD) were sampling on the roof of the station. Within a wind tunnel located underneath the roof, two Cloud Droplet Probes (CDPs) and a modified FSSP (SPP-100) were operating. The main objectives of this paper are (1) to study the effects of wind direction and speed on ground-based cloud observations, (2) to quantify the cloud parameters discrepancies observed by the different instruments, and (3) to develop methods to improve the quantification of the measurements.The results revealed that all instruments showed a good agreement in their sizing abilities, both in terms of amplitude and variability. However, some of them, especially the FM-100, the FSSP and the SPP, displayed large discrepancies in their capability to assess the magnitude of the total number concentration of the cloud droplets. As a result, the total liquid water content can differ by up to a factor of 5 between the probes. The use of a standardization procedure, based on data of integrating probes (PVM-100 or visibilimeter) and extinction coefficient comparison substantially enhanced the instrumental agreement. During this experiment, the total concentration agreed in variations with the visibilimeter, except for the FSSP, so a corrective factor can be applied and it ranges from 0.44 to 2.2. This intercomparison study highlights the necessity to have an instrument which provides a bulk measurement of cloud microphysical or optical properties during cloud ground-based campaigns. Moreover, the FM and FSSP orientation was modified with an angle ranging from 30 to 90 • angle with wind speeds from 3 to 7 m s −1 . The results show that the induced number concentration loss is between 29 and 98 % for the FSSP and between 15 and 68 % for the FM-100. In particular, FSSP experiments showed strong discrepancies when the wind speed was lower than 3 m s −1 and/or when the angle between the wind direction and the orientation of the instruments is greater than 30• . An inadequate orientation of the FSSP towards the wind direction leads to an underestimation of the measured effective diameter.

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“…From 09:30 UTC to 15:30 UTC, the base case LWP decreases from 67 g m −2 to 18 g m −2 as solar insolation increases. After 14:00 UTC the cloud layer has thinned such that it is optically thin in the longwave (LW) (Garrett and Zhao, 2006;Petters et al, 2012), and LW radiative cooling from the cloud top begins to decrease slightly with time.…”

Section: Results From Experimental Simulationsmentioning

confidence: 99%

“…The impact of aerosol on stratiform cloud has been of particular interest and has been extensively studied with models (e.g. Jiang et al, 2002;Ackerman et al, 2004;Lu and Seinfeld, 2005;Wood, 2007;Bretherton et al, 2007;Sandu et al, 2008;Hill et al, 2008;Petters et al, 2012), remote sensing (e.g. Nakajima et al, 1991;Han et al, 1998;Sekiguchi et al, 2003;Kaufman et al, 2005;Quaas et al, 2006;Painemal and Zuidema, 2010) and in-situ observations (e.g.…”

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confidence: 99%

A comparative study of the response of modeled non-drizzling stratocumulus to meteorological and aerosol perturbations

et al. 2013

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The impact of changes in aerosol and cloud droplet concentration (N_a and N_d) on the radiative forcing of stratocumulus-topped boundary layers (STBLs) has been widely studied. How these impacts compare to those due to variations in meteorological context has not been investigated in a systematic fashion for non-drizzling overcast stratocumulus. In this study we examine the impact of observed variations in meteorological context and aerosol state on daytime, non-drizzling overcast stratiform evolution, and determine how resulting changes in cloud properties compare.

Using large-eddy simulation (LES) we create a model base case of daytime southeast Pacific coastal stratocumulus, spanning a portion of the diurnal cycle (early morning to near noon) and constrained by observations taken during the VOCALS (VAMOS Ocean-Atmosphere-Land Study) field campaign. We perturb aerosol and meteorological properties around this base case to investigate the stratocumulus response. We determine perturbations in the cloud top jumps in potential temperature θ and total water mixing ratio q_t from ECMWF Re-analysis Interim data, and use a set of N_d values spanning the observable range. To determine the cloud response to these meteorological and aerosol perturbations, we compute changes in liquid water path (LWP), bulk optical depth (τ) and cloud radiative forcing (CRF).

We find that realistic variations in the thermodynamic jump properties can elicit a response in the cloud properties of τ and shortwave (SW) CRF that are on the same order of magnitude as the response found due to realistic changes in aerosol state (i.e N_d). In response to increases in N_d, the cloud layer in the base case thinned due to increases in evaporative cooling and entrainment rate. This cloud thinning somewhat mitigates the increase in τ resulting from increases in N_d. On the other hand, variations in θ and q_t jumps did not substantially modify N_d. The cloud layer thickens in response to an increase in the θ jump and thins in response to an increase in the q_t jump, both resulting in a τ and SW CRF response comparable to those found from perturbations in N_d. Longwave CRF was not substantially altered by the perturbations we tested.

We find that realistic variations in meteorological context can elicit a response in CRF and τ on the same order of magnitude as, and at times larger than, that response found due to realistic changes in aerosol state. We estimate the limits on variability of cloud top jump properties required for accurate observation of aerosol SW radiative impacts on stratocumulus, and find strict constraints: less than 1 K and 1 g kg⁻¹ in the early morning hours, and order 0.1 K and 0.1 g kg⁻¹ close to solar noon. These constraints suggest that accurately observing aerosol radiative impacts in st...

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Radiative–Dynamical Feedbacks in Low Liquid Water Path Stratiform Clouds

Cited by 27 publications

References 50 publications

Effects of 3-D thermal radiation on the development of a shallow cumulus cloud field

Effects of 3-D thermal radiation on the development of a shallow cumulus cloud field

Quantitative evaluation of seven optical sensors for cloud microphysical measurements at the Puy-de-Dôme Observatory, France

A comparative study of the response of modeled non-drizzling stratocumulus to meteorological and aerosol perturbations

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