The Role of Cloud Radiative Heating in Determining the Location of the ITCZ in Aquaplanet Simulations

Abstract The relationship between the tropical circulation and cloud radiative effect is investigated. Output from the Clouds On–Off Klimate Intercomparison Experiment (COOKIE) is used to examine the impact of cloud radiative effects on circulation and climate. In aquaplanet simulations with a fixed SST pattern, the cloud radiative effect leads to an equatorward contraction of the intertropical convergence zone (ITCZ) and a reduction of the double ITCZ problem. It is shown that the cloud radiative heating in the upper troposphere increases the temperature, weakens CAPE, and inhibits the onset of convection until it is closer to the equator, where SSTs are higher. Precipitation peaks at higher values in a narrower band when the cloud radiative effects are active, compared to when they are inactive, owing to the enhancement in moisture convergence. Additionally, cloud–radiation interactions strengthen the mean meridional circulation and consequently enhance the moisture convergence. Although the mean tropical precipitation decreases, the atmospheric cloud radiative effect has a strong meridional gradient, which supports stronger poleward energy flux and speeds up the Hadley circulation. Cloud radiative heating also enhances cloud water path (liquid plus ice), which, combined with the reduction in precipitation, suggests that the cloud radiative heating reduces precipitation efficiency in these models.

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Reassessing the Effect of Cloud Type on Earth’s Energy Balance in the Age of Active Spaceborne Observations. Part I: Top of Atmosphere and Surface

Journal of Climate ◽

10.1175/jcli-d-18-0753.1 ◽

2019 ◽

Vol 32 (19) ◽

pp. 6197-6217 ◽

Cited By ~ 6

Author(s):

Tristan S. L’Ecuyer ◽

Yun Hang ◽

Alexander V. Matus ◽

Zhien Wang

Keyword(s):

Energy Balance ◽

Vertical Structure ◽

Classical Problem ◽

Cloud Base ◽

Radiative Effect ◽

Radiative Effects ◽

Solar Absorption ◽

Structure Information ◽

Cloud Radiative Effect ◽

Cloud Radiative Effects

AbstractThis study revisits the classical problem of quantifying the radiative effects of unique cloud types in the era of spaceborne active observations. The radiative effects of nine cloud types, distinguished based on their vertical structure defined by CloudSat and CALIPSO observations, are assessed at both the top of the atmosphere and the surface. The contributions from single- and multilayered clouds are explicitly diagnosed. The global, annual mean net cloud radiative effect at the top of the atmosphere is found to be −17.1 ± 4.2 W m−2 owing to −44.2 ± 2 W m−2 of shortwave cooling and 27.1 ± 3.7 W m−2 of longwave heating. Leveraging explicit cloud base and vertical structure information, we further estimate the annual mean net cloud radiative effect at the surface to be −24.8 ± 8.7 W m−2 (−51.1 ± 7.8 W m−2 in the shortwave and 26.3 ± 3.8 W m−2 in the longwave). Multilayered clouds are found to exert the strongest influence on the top-of-atmosphere energy balance. However, a strong asymmetry in net cloud radiative cooling between the hemispheres (8.6 W m−2) is dominated by enhanced cooling from stratocumulus over the southern oceans. It is found that there is no corresponding asymmetry at the surface owing to enhanced longwave emission by southern ocean clouds in winter, which offsets a substantial fraction of their impact on solar absorption in summer. Thus the asymmetry in cloud radiative effects is entirely realized as an atmosphere heating imbalance between the hemispheres.

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Radiative budget and cloud radiative effect over the Atlantic from ship based observations

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-5-2011-2012 ◽

2012 ◽

Vol 5 (2) ◽

pp. 2011-2042 ◽

Cited By ~ 3

Author(s):

J. Kalisch ◽

A. Macke

Keyword(s):

Cloud Type ◽

Radiative Effects ◽

Radiative Fluxes ◽

Stratus Clouds ◽

Solar Cooling ◽

Cloud Radiative Effect ◽

Single Column ◽

Single Column Model ◽

Cloud Radiative Effects ◽

The Mean

Abstract. The aim of this study is to determine cloud-type resolved cloud radiative budgets and cloud radiative effects from surface measurements of broadband radiative fluxes over the Atlantic Ocean. Furthermore, based on simultaneous observations of the state of the cloudy atmosphere a radiative closure study has been performed by means of the ECHAM5 single column model in order to identify the models ability to realistically reproduce the effects of clouds on the climate system. An extensive data base of radiative and atmospheric measurements has been established along five meridional cruises of the German research icebreaker POLARSTERN. Besides pyranometer and pyrgeometer for downward broadband solar and thermal radiative fluxes, a sky imager and a microwave radiometer have been utilized to determine cloud fraction and cloud type on the one hand and temperature and humidity profiles as well as liquid water path for warm non-precipitating clouds on the other hand. Averaged over all cruise tracks we obtain a total net (solar + thermal) radiative flux of 144 W m−2 that is dominated by the solar component. In general, the solar contribution is large for cirrus clouds and small for stratus clouds. No significant meridional dependencies were found for the surface radiation budgets and cloud effects. The strongest surface longwave cloud effects were shown in the presence of low level clouds. Clouds with a high optical density induce strong negative solar radiative effects under high solar altitudes. The mean surface net cloud radiative effect is −34 W m−2. For the purpose of quickly estimating the mean surface longwave, shortwave and net cloud effects in moderate, subtropical and tropical climate regimes a new parameterisation was created, considering the total cloud amount and the solar zenith angle. The ECHAM5 single column model provides a surface net cloud effect that is more cooling by 16 W m−2 compared to the radiation observations. This overestimation in solar cooling is mostly caused by the shortwave impact of convective clouds. The latter show a large overestimation in solar cooling of up to 112 W m−2. Mean cloud radiative effects of cirrus and stratus clouds were simulated close to the observations.

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Radiative budget and cloud radiative effect over the Atlantic from ship-based observations

Atmospheric Measurement Techniques ◽

10.5194/amt-5-2391-2012 ◽

2012 ◽

Vol 5 (10) ◽

pp. 2391-2401 ◽

Cited By ~ 10

Author(s):

J. Kalisch ◽

A. Macke

Keyword(s):

Cloud Type ◽

Radiative Effects ◽

Radiative Fluxes ◽

Stratus Clouds ◽

Solar Cooling ◽

Cloud Radiative Effect ◽

Single Column ◽

Single Column Model ◽

Cloud Radiative Effects ◽

The Mean

Abstract. The aim of this study is to determine cloud-type resolved cloud radiative budgets and cloud radiative effects from surface measurements of broadband radiative fluxes over the Atlantic Ocean. Furthermore, based on simultaneous observations of the state of the cloudy atmosphere, a radiative closure study has been performed by means of the ECHAM5 single column model in order to identify the model's ability to realistically reproduce the effects of clouds on the climate system. An extensive database of radiative and atmospheric measurements has been established along five meridional cruises of the German research icebreaker Polarstern. Besides pyranometer and pyrgeometer for downward broadband solar and thermal radiative fluxes, a sky imager and a microwave radiometer have been utilized to determine cloud fraction and cloud type on the one hand and temperature and humidity profiles as well as liquid water path for warm non-precipitating clouds on the other hand. Averaged over all cruise tracks, we obtain a total net (solar + thermal) radiative flux of 144 W m−2 that is dominated by the solar component. In general, the solar contribution is large for cirrus clouds and small for stratus clouds. No significant meridional dependencies were found for the surface radiation budgets and cloud effects. The strongest surface longwave cloud effects were shown in the presence of low level clouds. Clouds with a high optical density induce strong negative solar radiative effects under high solar altitudes. The mean surface net cloud radiative effect is −33 W m−2. For the purpose of quickly estimating the mean surface longwave, shortwave and net cloud effects in moderate, subtropical and tropical climate regimes, a new parameterisation was created, considering the total cloud amount and the solar zenith angle. The ECHAM5 single column model provides a surface net cloud effect that is more cooling by 17 W m−2 compared to the radiation observations. This overestimation in solar cooling is mostly caused by the shortwave impact of convective clouds. The latter show a large overestimation in solar cooling of up to 114 W m−2. Mean cloud radiative effects of cirrus and stratus clouds were simulated close to the observations.

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The Impact of Cloud Radiative Effects on the Tropical Tropopause Layer Temperatures

Atmosphere ◽

10.3390/atmos9100377 ◽

2018 ◽

Vol 9 (10) ◽

pp. 377 ◽

Cited By ~ 4

Author(s):

Qiang Fu ◽

Maxwell Smith ◽

Qiong Yang

Keyword(s):

Maximum Temperature ◽

Radiative Effects ◽

Heating Rates ◽

Tropical Tropopause Layer ◽

Tropical Tropopause ◽

Cloud Radiative Effect ◽

Single Column ◽

Cloud Radiative Effects ◽

Cold Point ◽

The Impact

A single-column radiative-convective model (RCM) is a useful tool to investigate the physical processes that determine the tropical tropopause layer (TTL) temperature structures. Previous studies on the TTL using the RCMs, however, omitted the cloud radiative effects. In this study, we examine the impact of cloud radiative effects on the simulated TTL temperatures using an RCM. We derive the cloud radiative effects based on satellite observations, which show heating rates in the troposphere but cooling rates in the stratosphere. We find that the cloud radiative effect warms the TTL by as much as 2 K but cools the lower stratosphere by as much as −1.5 K, resulting in a thicker TTL. With (without) considering cloud radiative effects, we obtain a convection top of ≈167 hPa (≈150 hPa) with a temperature of ≈213 K (≈209 K), and a cold point at ≈87 hPa (≈94 hPa) with a temperature of ≈204 K (≈204 K). Therefore, the cloud radiative effects widen the TTL by both lowering the convection-top height and enhancing the cold-point height. We also examine the impact of TTL cirrus radiative effects on the RCM-simulated temperatures. We find that the TTL cirrus warms the TTL with a maximum temperature increase of ≈1.3 K near 110 hPa.

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Regional and Seasonal Influence of Cloud Radiative Effects on CMIP6 Model Climate Sensitivity

10.5194/egusphere-egu2020-12467 ◽

2020 ◽

Author(s):

Bithi De ◽

George Tselioudis

Keyword(s):

Climate Sensitivity ◽

Significant Contribution ◽

Coupled Model ◽

Radiative Effect ◽

Radiative Effects ◽

Seasonal Influence ◽

Equilibrium Climate Sensitivity ◽

Cloud Radiative Effect ◽

Cloud Radiative Effects ◽

The Relationship

Recent analyses of Coupled Model&#160;Intercomparison&#160;Project phase 6&#160;(CMIP6)&#160;models&#160;have shown&#160;higher&#160;climate sensitivities than&#160;previously reported,&#160;and this&#160;increase&#160;has been preliminary attributed to&#160;the simulation of anomalous Shortwave&#160;Cloud Radiative Effect (SWCRE)&#160;over the southern midlatitude regions. In this work, we further&#160;explore how the seasonal and annual SWCRE over different regions of the globe influence the model climate sensitivities. Our study suggests a significant contribution of SWCRE on climate sensitivities in both northern and southern midlatitudes; and the relationship remains robust across the seasons. Additionally, we assess the underlying physics of the inter-model spread to diagnose model biases.&#160;The results will contribute to quantify the severity of the Equilibrium Climate Sensitivity, as simulated by the CMIP6 models.

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Monte Carlo-based subgrid parameterization of vertical velocity and stratiform cloud microphysics in ECHAM5.5-HAM2

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-5477-2013 ◽

2013 ◽

Vol 13 (2) ◽

pp. 5477-5507

Author(s):

J. Tonttila ◽

P. Räisänen ◽

H. Järvinen

Keyword(s):

Monte Carlo ◽

Vertical Velocity ◽

Cloud Droplet ◽

Cloud Microphysics ◽

Radiative Effects ◽

Cloud Droplets ◽

Microphysical Properties ◽

Cloud Radiative Effects ◽

Cloud Activation ◽

The Impact

Abstract. A new method for parameterizing the subgrid variations of vertical velocity and cloud droplet number concentration (CDNC) is presented for GCMs. These parameterizations build on top of existing parameterizations that create stochastic subgrid cloud columns inside the GCM grid-cells, which can be employed by the Monte Carlo independent column approximation approach for radiative transfer. The new model version adds a description for vertical velocity in individual subgrid columns, which can be used to compute cloud activation and the subgrid distribution of the number of cloud droplets explicitly. This provides a consistent way for simulating the cloud radiative effects with two-moment cloud microphysical properties defined in subgrid-scale. The primary impact of the new parameterizations is to decrease the CDNC over polluted continents, while over the oceans the impact is smaller. This promotes changes in the global distribution of the cloud radiative effects and might thus have implications on model estimation of the indirect radiative effect of aerosols.

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The Surface Longwave Cloud Radiative Effect from Space Lidar Observations

10.5194/egusphere-egu21-2064 ◽

2021 ◽

Author(s):

Assia Arouf

Keyword(s):

Cloud Cover ◽

Temporal Variations ◽

Radiative Effect ◽

Cloud Properties ◽

Cloud Radiative Effect ◽

Long Time ◽

The One ◽

Natural Climate ◽

The Impact ◽

Lidar Observations

Clouds exert important effects on Earth's surface energy balance through their effects on longwave (LW) and shortwave (SW) radiation. Indeed, clouds radiatively warm the surface in the LW domain by emitting LW radiation back to the ground. The surface LW cloud radiative effect (CRE) quantifies this warming effect. To study the impact of clouds on the interanual natural climate variability, we need to observe them on a long time scale over all kinds of surfaces. The CALIPSO space lidar provides these observations by sampling the atmosphere along its track over all kinds of surfaces for over than 14 years (2006-2020).In this work, we propose new estimates of the surface LW CRE from space-based lidar observations only. Indeed, we show from 1D atmospheric column radiative transfer calculations, that surface LW CRE at sea level linearly decreases with the cloud altitude. Thus, these computations allow to establish simple relationships between the surface LW CRE, and five cloud properties observed by the CALIPSO space lidar: the opaque cloud cover and altitude, the thin cloud cover, altitude, and emissivity. Over the 2008&#8211;2011, CALIPSO-based retrieval (27.7 W m-2) is 1.2 W m-2 larger than the one derived from combined space radar, lidar, and radiometer observations. Over the 2008&#8211;2018 period, the global mean CALIPSO-based retrieval (27.5 W m-2) is 0.1 W m-2 larger than the one derived from CERES space radiometer. Our estimates show that globally, opaque clouds warm the surface by 23.3 W m-2 and thin clouds contribute only by 4.2 W m-2. At high latitudes North and South over oceans, the largest surface LW opaque CRE occurs in fall (40.4 W m-2, 31.6 W m-2) due to the formation of additional opaque low clouds after sea ice melting over a warmer ocean.To quantify the cloud property that drives the temporal variations of the surface LW CRE, the surface LW CRE needs to be related by simple relationships to a finite number of cloud properties such as cloud opacity, cloud altitude and cloud cover. This study allows a decomposition and attribution approach of the surface LW CRE variations and shows that they are driven by the variations occurring in the opaque cloud properties. Moreover, opaque cloud cover drives over than 73% of global surface LW CRE interannual variations.

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Toward a Consistent Definition between Satellite and Model Clear-Sky Radiative Fluxes

Journal of Climate ◽

10.1175/jcli-d-19-0381.1 ◽

2020 ◽

Vol 33 (1) ◽

pp. 61-75 ◽

Cited By ~ 3

Author(s):

Norman G. Loeb ◽

Fred G. Rose ◽

Seiji Kato ◽

David A. Rutan ◽

Wenying Su ◽

...

Keyword(s):

Tropical Pacific ◽

Radiative Effect ◽

The West ◽

Model Calculations ◽

Radiative Fluxes ◽

Clear Sky ◽

Cloud Radiative Effect ◽

Adjustment Factors ◽

The Impact ◽

Global Mean

AbstractA new method of determining clear-sky radiative fluxes from satellite observations for climate model evaluation is presented. The method consists of applying adjustment factors to existing satellite clear-sky broadband radiative fluxes that make the observed and simulated clear-sky flux definitions more consistent. The adjustment factors are determined from the difference between observation-based radiative transfer model calculations of monthly mean clear-sky fluxes obtained by ignoring clouds in the atmospheric column and by weighting hourly mean clear-sky fluxes with imager-based clear-area fractions. The global mean longwave (LW) adjustment factor is −2.2 W m−2 at the top of the atmosphere and 2.7 W m−2 at the surface. The LW adjustment factors are pronounced at high latitudes during winter and in regions with high upper-tropospheric humidity and cirrus cloud cover, such as over the west tropical Pacific, and the South Pacific and intertropical convergence zones. In the shortwave (SW), global mean adjustment is 0.5 W m−2 at TOA and −1.9 W m−2 at the surface. It is most pronounced over sea ice off of Antarctica and over heavy aerosol regions, such as eastern China. However, interannual variations in the regional SW and LW adjustment factors are small compared to those in cloud radiative effect. After applying the LW adjustment factors, differences in zonal mean cloud radiative effect between observations and climate models decrease markedly between 60°S and 60°N and poleward of 65°N. The largest regional improvements occur over the west tropical Pacific and Indian Oceans. In contrast, the impact of the SW adjustment factors is much smaller.

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The efficacy of aerosol–cloud radiative perturbations from near-surface emissions in deep open-cell stratocumuli

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-17475-2018 ◽

2018 ◽

Vol 18 (23) ◽

pp. 17475-17488 ◽

Cited By ~ 9

Author(s):

Anna Possner ◽

Hailong Wang ◽

Robert Wood ◽

Ken Caldeira ◽

Thomas P. Ackerman

Keyword(s):

Emission Line ◽

Radiative Properties ◽

Radiative Effect ◽

Radiative Effects ◽

Near Surface ◽

Open Cell ◽

Detection And Attribution ◽

Cloud Radiative Effects ◽

Ship Tracks ◽

Cloud Radiative Properties

Abstract. Aerosol–cloud radiative effects are determined and quantified in simulations of deep open-cell stratocumuli observed during the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) campaign off the west coast of Chile. The cloud deck forms in a boundary layer 1.5 km deep, with cell sizes reaching 50 km in diameter. Global databases of ship tracks suggest that these linear structures are seldom found in boundary layers this deep. Here, we quantify the changes in cloud radiative properties to a continuous aerosol point source moving along a fixed emission line releasing 1017 particles per second. We show that a spatially coherent cloud perturbation is not evident along the emission line. Yet our model simulates an increase in domain-mean all-sky albedo of 0.05, corresponding to a diurnally averaged cloud radiative effect of 20 W m−2, given the annual mean solar insolation at the VOCALS-REx site. Therefore, marked changes in cloud radiative properties in precipitating deep open cells may be driven by anthropogenic near-surface aerosol perturbations, such as those generated by ships. Furthermore, we demonstrate that these changes in cloud radiative properties are masked by the naturally occurring variability within the organised cloud field. A clear detection and attribution of cloud radiative effects to a perturbation in aerosol concentrations becomes possible when sub-filtering of the cloud field is applied, using the spatio-temporal distribution of the aerosol perturbation. Therefore, this work has implications for the detection and attribution of effective cloud radiative forcing in marine stratocumuli, which constitutes one of the major physical uncertainties within the climate system. Our results suggest that ships may sometimes have a substantial radiative effect on marine clouds and albedo, even when ship tracks are not readily visible.

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Subtropical clouds stabilize near-Snowball Earth states

10.5194/egusphere-egu2020-10617 ◽

2020 ◽

Author(s):

Christoph Braun ◽

Aiko Voigt ◽

Johannes Hörner ◽

Joaquim G. Pinto

Keyword(s):

Sea Ice ◽

General Circulation ◽

General Circulation Models ◽

Snowball Earth ◽

Radiative Effects ◽

Albedo Feedback ◽

The Earth ◽

Cloud Radiative Effects ◽

Planetary Albedo ◽

The Impact

Atmospheric general circulation models developed for the Earth system include comprehensive parameterizations of clouds. Applying them to exoplanet atmospheres provides an opportunity to advance understanding of clouds, atmosphere dynamics, and their coupling in the context of planetary climate dynamics and habitability.Here, we study a deep-time extreme climate of Earth as an example of the cold limit of the habitable zone. Geological evidence indicates near-global ice cover during the Neoproterozoic (1000 &#8211; 541 Million years ago) associated with considerable hysteresis of atmospheric CO2. The Snowball Earth hypothesis provides a straightforward interpretation of Neoproterozoic proxies based on a runaway of the sea-ice albedo feedback. However, the Snowball Earth hypothesis relies on the existence of local habitats to explain the survival of photosynthetic marine species on an entirely ice-covered planet. The Jormungand hypothesis may resolve this issue by considering a weakening of the sea-ice albedo feedback by exposure of dark bare sea ice when sea ice enters the subtropics. This potentially allows the Earth system to stabilize in a climate state - the Jormungand state - with near-global ice cover. Around the equator, a narrow strip of ocean remains ice-free, where life would have easily survived during the pan-glaciations.The weakening of the sea-ice albedo feedback is based on the change of the meridional structure of planetary albedo with a moving sea-ice edge. While previous work focused on the contribution of surface albedo to planetary albedo, we here focus on the impact of subtropical and tropical cloudiness on planetary albedo. Enhanced cloudiness generally weakens the sea-ice albedo feedback and thus decreases the climate sensitivity of the Jormungand state, i.e. it stabilizes the Jormungand state. We analyze the impact of cloudiness on the stability of the Jormungand state in the general circulation models CAM3 and ICON-AES with idealized aquaplanet setups. While CAM3 shows significant CO2-hysteresis of the Jormungand state, ICON-AES exhibits no stable Jormungand state. Consistently, CAM3 exhibits stronger cloudiness than ICON-AES, especially in the subtropics. An analysis with a one-dimensional energy balance model shows that the Jormungand hysteresis strongly depends on the sensitivity of the planetary albedo to an advance of sea ice into the subtropics. Accordingly, we demonstrate that the absence of cloud-radiative effects within vertical columns in the subtropics drastically decreases the Jormungand hysteresis in CAM3.Overall, the magnitude of the Jormungand hysteresis is tightly linked to the representation of cloud-radiative effects in general circulation models. Our results highlight the important role of uncertainties associated with cloud-radiative effects for climate feedbacks on planet Earth in the context of extreme climates, such as they have occurred in Earth&#8217;s deep past or might be found on Earth-like planets. In consequence, this also stresses the need and challenges of accounting for adequate cloud modeling for planetary climates.

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