Sensitivity of surface temperature to radiative forcing by contrail cirrus in a radiative-mixing model

Abstract. Earth's surface temperature sensitivity to radiative forcing (RF) by contrail cirrus and the related RF efficacy relative to CO2 are investigated in a one-dimensional idealized model of the atmosphere. The model includes energy transport by shortwave (SW) and longwave (LW) radiation and by mixing in an otherwise fixed reference atmosphere (no other feedbacks). Mixing includes convective adjustment and turbulent diffusion, where the latter is related to the vertical component of mixing by large-scale eddies. The conceptual study shows that the surface temperature sensitivity to given contrail RF depends strongly on the timescales of energy transport by mixing and radiation. The timescales are derived for steady layered heating (ghost forcing) and for a transient contrail cirrus case. The radiative timescales are shortest at the surface and shorter in the troposphere than in the mid-stratosphere. Without mixing, a large part of the energy induced into the upper troposphere by radiation due to contrails or similar disturbances gets lost to space before it can contribute to surface warming. Because of the different radiative forcing at the surface and at top of atmosphere (TOA) and different radiative heating rate profiles in the troposphere, the local surface temperature sensitivity to stratosphere-adjusted RF is larger for SW than for LW contrail forcing. Without mixing, the surface energy budget is more important for surface warming than the TOA budget. Hence, surface warming by contrails is smaller than suggested by the net RF at TOA. For zero mixing, cooling by contrails cannot be excluded. This may in part explain low efficacy values for contrails found in previous global circulation model studies. Possible implications of this study are discussed. Since the results of this study are model dependent, they should be tested with a comprehensive climate model in the future.

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Sensitivity of surface temperature to radiative forcing by cirrus and contrails in a radiative-convective model

10.5194/acp-2017-465 ◽

2017 ◽

Author(s):

Ulrich Schumann ◽

Bernhard Mayer

Keyword(s):

Surface Temperature ◽

Time Scales ◽

Temperature Sensitivity ◽

Radiative Forcing ◽

Large Scale ◽

Energy Transport ◽

Vertical Mixing ◽

Surface Cooling ◽

Local Surface Temperature ◽

Diffusion Convection

Abstract. Earth surface temperature changes induced by added thin cirrus or contrails are investigated with a radiative-convective-diffusive model, basically without climate system changes, with relaxation of the temperature profile by radiation and mixing. The conceptual study shows that the surface temperature sensitivity to cirrus depends strongly on the ratio of the time scales of energy transport by mixing and radiation, where mixing may include turbulent diffusion, convection and transports by the large-scale circulation. The time scales are derived for steady layered heating (ghost-forcing) and for a transient cirrus case. The time scales are shortest at the surface and shorter in the troposphere than in the mid-stratosphere. Heat induced by cirrus in the upper troposphere reaches the surface only for strong vertical mixing. The local surface-temperature sensitivity to adjusted radiative forcing (RF) is larger for the shortwave (SW) than the longwave (LW) cirrus forcing. For weak mixing, cirrus may cool the surface even if the cirrus causes a positive instantaneous or stratosphere-adjusted radiative forcing (RF) at the tropopause. The shorter time scales near the surface indicate a potential for dominant SW surface cooling regionally where cirrus or contrails form, while weak LW warming may dominate at larger distances.

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Cities Exacerbate Climate Warming

Urban Science ◽

10.3390/urbansci5010027 ◽

2021 ◽

Vol 5 (1) ◽

pp. 27

Author(s):

Lahouari Bounoua ◽

Kurtis Thome ◽

Joseph Nigro

Keyword(s):

Surface Temperature ◽

Land Surface ◽

Large Scale ◽

Climate Models ◽

Warming Trend ◽

Climate Mitigation ◽

Temperature Changes ◽

Surface Warming ◽

The Us

Urbanization is a complex land transformation not explicitly resolved within large-scale climate models. Long-term timeseries of high-resolution satellite data are essential to characterize urbanization within land surface models and to assess its contribution to surface temperature changes. The potential for additional surface warming from urbanization-induced land use change is investigated and decoupled from that due to change in climate over the continental US using a decadal timescale. We show that, aggregated over the US, the summer mean urban-induced surface temperature increased by 0.15 °C, with a warming of 0.24 °C in cities built in vegetated areas and a cooling of 0.25 °C in cities built in non-vegetated arid areas. This temperature change is comparable in magnitude to the 0.13 °C/decade global warming trend observed over the last 50 years caused by increased CO2. We also show that the effect of urban-induced change on surface temperature is felt above and beyond that of the CO2 effect. Our results suggest that climate mitigation policies must consider urbanization feedback to put a limit on the worldwide mean temperature increase.

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Drivers of (non-)linear Eocene surface warming in the DeepMIP ensemble

10.5194/egusphere-egu21-14127 ◽

2021 ◽

Author(s):

Sebastian Steinig ◽

Jiang Zhu ◽

Ran Feng ◽

Keyword(s):

Temperature Gradient ◽

Heat Transport ◽

Climate Sensitivity ◽

Radiative Forcing ◽

Large Scale ◽

Surface Albedo ◽

Early Eocene ◽

Meridional Heat Transport ◽

Surface Warming ◽

Global Mean

The early Eocene greenhouse represents the warmest interval of the Cenozoic and therefore provides a unique opportunity to understand how the climate system operates under elevated atmospheric CO2 levels similar to those projected for the end of the 21st century. Early Eocene geological records indicate a large increase in global mean surface temperatures compared to present day (by ~14&#176;C) and a greatly reduced meridional temperature gradient (by ~30% in SST). However, reproducing these large-scale climate features at reasonable CO2 levels still poses a challenge for current climate models. Recent modelling studies indicate an important role for shortwave (SW) cloud feedbacks to drive increases in climate sensitivity with global warming, which helps to close the gap between simulated and reconstructed Eocene global warmth and temperature gradient. Nevertheless, the presence of such state-dependent feedbacks and their relative strengths in other models remain unclear.In this study, we perform a systematic investigation of the simulated surface warming and the underlying mechanisms in the recently published DeepMIP ensemble. The DeepMIP early Eocene simulations use identical paleogeographic boundary conditions and include six models with suitable output: CESM1.2_CAM5, GFDL_CM2.1, HadCM3B_M2.1aN, IPSLCM5A2, MIROC4m and NorESM1_F. We advance previous energy balance analysis by applying the approximate partial radiative perturbation (APRP) technique to quantify the individual contributions of surface albedo, cloud and non-cloud atmospheric changes to the simulated Eocene top-of-the-atmosphere SW flux anomalies. We further compare the strength of these planetary albedo feedbacks to changes in the longwave atmospheric emissivity and meridional heat transport in the warm Eocene climate. Particular focus lies in the sensitivity of the feedback strengths to increasing global mean temperatures in experiments at a range of atmospheric CO2 concentrations between x1 to x9 preindustrial levels.Preliminary results indicate that all models that provide data for at least 3 different CO2 levels show an increase of the equilibrium climate sensitivity at higher global mean temperatures. This is associated with an increase of the overall strength of the positive SW cloud feedback with warming in those models. This nonlinear behavior seems to be related to both a reduction and optical thinning of low-level clouds, albeit with intermodel differences in the relative importance of the two mechanisms. We further show that our new APRP results can differ significantly from previous estimates based on cloud radiative forcing alone, especially in high-latitude areas with large surface albedo changes. We also find large intermodel variability and state-dependence in meridional heat transport modulated by changes in the atmospheric latent heat transport. Ongoing work focuses on the spatial patterns of the climate feedbacks and the implications for the simulated meridional temperature gradients.

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The Large-Scale Dynamical Response of Clouds to Aerosol Forcing

Journal of Climate ◽

10.1175/jcli-d-17-0050.1 ◽

2017 ◽

Vol 30 (21) ◽

pp. 8783-8794 ◽

Cited By ~ 7

Author(s):

Brian Soden ◽

Eui-Seok Chung

Keyword(s):

Atmospheric Circulation ◽

Radiative Forcing ◽

Large Scale ◽

Energy Transport ◽

Hadley Cell ◽

Dynamical Response ◽

Aerosol Radiative Forcing ◽

Aerosol Forcing ◽

Meridional Displacement ◽

Cloud Response

Radiative kernels are used to quantify the instantaneous radiative forcing of aerosols and the aerosol-mediated cloud response in coupled ocean–atmosphere model simulations under both historical and future emission scenarios. The method is evaluated using matching pairs of historical climate change experiments with and without aerosol forcing and accurately captures the spatial pattern and global-mean effects of aerosol forcing. It is shown that aerosol-driven changes in the atmospheric circulation induce additional cloud changes. Thus, the total aerosol-mediated cloud response consists of both local microphysical changes and nonlocal dynamical changes that are driven by hemispheric asymmetries in aerosol forcing. By comparing coupled and fixed sea surface temperature (SST) simulations with identical aerosol forcing, the relative contributions of these two components are isolated, exploiting the ability of prescribed SSTs to also suppress changes in the atmospheric circulation. The radiative impact of the dynamical cloud changes is found to be comparable in magnitude to that of the microphysical cloud changes and acts to further amplify the interhemispheric asymmetry of the aerosol radiative forcing. The dynamical cloud response is closely linked to the meridional displacement of the Hadley cell, which, in turn, is driven by changes in the cross-equatorial energy transport. In this way, the dynamical cloud changes act as a positive feedback on the meridional displacement of the Hadley cell, roughly doubling the projected changes in cross-equatorial energy transport compared to that from the microphysical changes alone.

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Large Increase in Incident Shortwave Radiation due to the Ozone Hole Offset by High Climatological Albedo over Antarctica

Journal of Climate ◽

10.1175/jcli-d-16-0842.1 ◽

2017 ◽

Vol 30 (13) ◽

pp. 4883-4890 ◽

Cited By ~ 6

Author(s):

G. Chiodo ◽

L. M. Polvani ◽

M. Previdi

Keyword(s):

Surface Temperature ◽

Ozone Depletion ◽

Climate Model ◽

Stratospheric Ozone ◽

Surface Energy Budget ◽

Ozone Hole ◽

Radiative Heating ◽

Shortwave Radiation ◽

Stratospheric Ozone Depletion ◽

Continental Scale

Despite increasing scientific scrutiny in recent years, the direct impact of the ozone hole on surface temperatures over Antarctica remains uncertain. Here, this question is explored by using the Community Earth System Model–Whole Atmosphere Community Climate Model (CESM-WACCM), contrasting two ensembles of runs with and without stratospheric ozone depletion. It is found that, during austral spring, the ozone hole leads to a surprisingly large increase in surface downwelling shortwave (SW) radiation over Antarctica of 3.8 W m−2 in clear sky and 1.8 W m−2 in all sky. However, despite this large increase in incident SW radiation, no ozone-induced surface warming is seen in the model. It is shown that the lack of a surface temperature response is due to reflection of most of the increased downward SW, resulting in an insignificant change to the net SW radiative heating. To first order, this reflection is simply due to the high climatological surface albedo of the Antarctic snow (97% in visible SW), resulting in a net zero ozone-induced surface SW forcing. In addition, it is shown that stratospheric ozone depletion has a negligible effect on longwave (LW) radiation and other components of the surface energy budget. These results suggest a minimal role for ozone depletion in forcing Antarctic surface temperature trends on a continental scale.

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Time-Varying Climate Sensitivity from Regional Feedbacks

Journal of Climate ◽

10.1175/jcli-d-12-00544.1 ◽

2013 ◽

Vol 26 (13) ◽

pp. 4518-4534 ◽

Cited By ~ 199

Author(s):

Kyle C. Armour ◽

Cecilia M. Bitz ◽

Gerard H. Roe

Keyword(s):

Surface Temperature ◽

Climate Sensitivity ◽

Time Variation ◽

Radiative Forcing ◽

Global Climate ◽

Regional Climate ◽

Climate Feedback ◽

Climate Feedbacks ◽

Geographic Pattern ◽

Surface Warming

Abstract The sensitivity of global climate with respect to forcing is generally described in terms of the global climate feedback—the global radiative response per degree of global annual mean surface temperature change. While the global climate feedback is often assumed to be constant, its value—diagnosed from global climate models—shows substantial time variation under transient warming. Here a reformulation of the global climate feedback in terms of its contributions from regional climate feedbacks is proposed, providing a clear physical insight into this behavior. Using (i) a state-of-the-art global climate model and (ii) a low-order energy balance model, it is shown that the global climate feedback is fundamentally linked to the geographic pattern of regional climate feedbacks and the geographic pattern of surface warming at any given time. Time variation of the global climate feedback arises naturally when the pattern of surface warming evolves, actuating feedbacks of different strengths in different regions. This result has substantial implications for the ability to constrain future climate changes from observations of past and present climate states. The regional climate feedbacks formulation also reveals fundamental biases in a widely used method for diagnosing climate sensitivity, feedbacks, and radiative forcing—the regression of the global top-of-atmosphere radiation flux on global surface temperature. Further, it suggests a clear mechanism for the “efficacies” of both ocean heat uptake and radiative forcing.

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Relative Humidity in the Troposphere with AIRS

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-13-0363.1 ◽

2014 ◽

Vol 71 (7) ◽

pp. 2516-2533 ◽

Cited By ~ 12

Author(s):

Alexander Ruzmaikin ◽

Hartmut H. Aumann ◽

Evan M. Manning

Keyword(s):

Relative Humidity ◽

Surface Temperature ◽

Radiative Forcing ◽

General Circulation ◽

Large Scale ◽

Statistical Significance ◽

General Circulation Models ◽

Positive Trend ◽

Drying Time ◽

Clear Sky

Abstract New global satellite data from the Atmospheric Infrared Sounder (AIRS) are applied to study the tropospheric relative humidity (RH) distribution and its influence on outgoing longwave radiation (OLR) for January and July in 2003, 2007, and 2011. RH has the largest maxima over 90% in the equatorial tropopause layer in January. Maxima in July do not arise above 60%. Seasonal variations of about 20% in zonally averaged RH are observed in the equatorial region of the low troposphere, in the equatorial tropopause layer, and in the polar regions. The seasonal variability in the recent decade has increased by about 5% relative to that in 1973–88, indicating a positive trend. The observed RH profiles indicate a moist bias in the tropical and subtropical regions typically produced by the general circulation models. The new data and method of evaluating the statistical significance of bimodality confirm bimodal probability distributions of RH at large tropospheric scales, notably in the ascending branch of the Hadley circulation. Bimodality is also seen at 500–300 hPa in mid- and high latitudes. Since the drying time of the air is short compared with the mixing time of moist and dry air, the bimodality reflects the large-scale distribution of sources of moisture and the atmospheric circulation. Analysis of OLR dependence on surface temperature shows a 0.2 W m−2 K−1 difference in sensitivities between clear-sky and all-sky OLR, indicating a positive longwave cloud radiative forcing. Diagrams of the clear-sky OLR as functions of percentiles of surface temperature and relative humidity in the tropics are designed to provide a new measure of the supergreenhouse effect.

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Satellite Perspectives of Sea Surface Temperature Diurnal Warming on Atmospheric Moistening and Radiative Heating During MJO

Journal of Climate ◽

10.1175/jcli-d-20-0350.1 ◽

2020 ◽

pp. 1-56

Author(s):

Kyle Itterly ◽

Patrick Taylor ◽

J. Brent Roberts

Keyword(s):

Surface Temperature ◽

Sea Surface Temperature ◽

Large Scale ◽

Active Phase ◽

Radiative Heating ◽

Sea Surface ◽

Integrated Analysis ◽

Moist Static Energy ◽

Diurnal Warming ◽

Static Energy

AbstractDiurnal air-sea coupling affects climate modes such as the Madden-Julian Oscillation (MJO) via the regional moist static energy budget. Prior to MJO initiation, large-scale subsidence increases (decreases) surface shortwave insolation (winds). These act in concert to significantly warm the uppermost layer of the ocean over the course of a single day and the ocean mixed layer over the course of 1-2 weeks. Here, we provide an integrated analysis of multiple surface, top-of-atmosphere, and atmospheric column observations to assess the covariability related to regions of strong diurnal sea surface temperature (dSST) warming over 44 MJO events between 2000-2018 to assess their role in MJO initiation. Combining satellite observations of evaporation and precipitation with reanalysis moisture budget terms, we find 30-50% enhanced moistening over high dSST regions during late afternoon using either ERA5 or MERRA-2 despite large model biases. Diurnally developing moisture convergence, only modestly weaker evaporation, and diurnal minimum precipitation act to locally enhance moistening over broad regions of enhanced diurnal warming, which rectifies onto the larger scale. Field campaign ship and sounding data corroborate that strong dSST periods are associated with reduced middle tropospheric humidity and larger diurnal amplitudes of surface warming, evaporation, instability, and column moistening. Further, we find greater daytime increases in low cloud cover and evidence of enhanced radiative destabilization for the top 50th dSST percentile. Together, these results support that dSST warming acts in concert with large-scale dynamics to enhance moist static energy during the suppressed to active phase transition of the MJO.

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Stratospheric aerosol radiative forcing simulated by the chemistry climate model EMAC using aerosol CCI satellite data

10.5194/acp-2018-330 ◽

2018 ◽

Author(s):

Christoph Brühl ◽

Jennifer Schallock ◽

Klaus Klingmüller ◽

Charles Robert ◽

Christine Bingen ◽

...

Keyword(s):

Optical Depth ◽

Radiative Forcing ◽

General Circulation ◽

Asian Summer Monsoon ◽

Michelson Interferometer ◽

Circulation Model ◽

Volcanic Eruptions ◽

Radiative Heating ◽

Tropospheric Aerosol ◽

Atmospheric Sounding

Abstract. This paper presents decadal simulations of stratospheric and tropospheric aerosol by the chemistry general circulation model EMAC constrained with satellite observations in the framework of the ESA-Aerosol-CCI project like GOMOS (Global Ozone Monitoring by Occultation of Stars) and (A)ATSR ((Advanced) Along Track Scanning Radiometer) on ENVISAT (European Environmental Satellite), and IASI (Infrared Atmospheric Sounding Interferometer) on Metop (Meteorological Operational Satellite). The EMAC simulations with modal interactive aerosol and observations by GOMOS show that sulfate particles from about 230 volcanic eruptions identified mostly from MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) SO2 limb measurements dominate the interannual variability of aerosol extinction in the lower stratosphere, and of radiative forcing at the tropopause. To explain the observations, desert dust and organic and black carbon, transported to the lowermost stratosphere by the Asian summer monsoon and tropical convection, are also important. This holds also for radiative heating by aerosol in the lowermost stratosphere. Comparison with (A)ATSR total aerosol optical depth at different wavelengths and IASI dust optical depth shows that the model is able to represent stratospheric and tropospheric aerosol in a consistent way.

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Seasonal Variation of Cloud Systems over ARM SGP

Journal of the Atmospheric Sciences ◽

10.1175/2007jas2394.1 ◽

2008 ◽

Vol 65 (7) ◽

pp. 2107-2129 ◽

Cited By ~ 10

Author(s):

Xiaoqing Wu ◽

Sunwook Park ◽

Qilong Min

Keyword(s):

Liquid Water ◽

Radiative Forcing ◽

General Circulation ◽

Large Scale ◽

General Circulation Models ◽

Heat Fluxes ◽

Radiative Heating ◽

Dominant Factor ◽

Cloud Systems ◽

Second Peak

Abstract Increased observational analyses provide a unique opportunity to perform years-long cloud-resolving model (CRM) simulations and generate long-term cloud properties that are very much in demand for improving the representation of clouds in general circulation models (GCMs). A year 2000 CRM simulation is presented here using the variationally constrained mesoscale analysis and surface measurements. The year-long (3 January–31 December 2000) CRM surface precipitation is highly correlated with the Atmospheric Radiation Measurement (ARM) observations with a correlation coefficient of 0.97. The large-scale forcing is the dominant factor responsible for producing the precipitation in summer, spring, and fall, but the surface heat fluxes play a more important role during winter when the forcing is weak. The CRM-simulated year-long cloud liquid water path and cloud (liquid and ice) optical depth are also in good agreement (correlation coefficients of 0.73 and 0.64, respectively) with the ARM retrievals over the Southern Great Plains (SGP). The simulated cloud systems have 50% more ice water than liquid water in the annual mean. The vertical distributions of ice and liquid water have a single peak during spring (March–May) and summer (June–August), but a second peak occurs near the surface during winter (December–February) and fall (September–November). The impacts of seasonally varied cloud water are very much reflected in the cloud radiative forcing at the top-of-atmosphere (TOA) and the surface, as well as in the vertical profiles of radiative heating rates. The cloudy-sky total (shortwave and longwave) radiative heating profile shows a dipole pattern (cooling above and warming below) during spring and summer, while a second peak of cloud radiative cooling appears near the surface during winter and fall.

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