scholarly journals On the contribution of fast and slow responses to precipitation changes caused by aerosol perturbations

2021 ◽  
Vol 21 (13) ◽  
pp. 10179-10197
Author(s):  
Shipeng Zhang ◽  
Philip Stier ◽  
Duncan Watson-Parris
Keyword(s):  
Large Scale ◽  
Energy Transport ◽  
Hadley Cell ◽  
Radiative Heating ◽  
Specific Humidity ◽  
Radiative Cooling ◽  
Tropical Rainfall ◽  
Absorbing Aerosols ◽  
Global Mean ◽  
Fast Responses

Abstract. Changes in global-mean precipitation are strongly constrained by global radiative cooling, while regional rainfall changes are less constrained because energy can be transported. Absorbing and non-absorbing aerosols have different effects on both global-mean and regional precipitation, due to the distinct effects on energetics. This study analyses the precipitation responses to large perturbations in black carbon (BC) and sulfate (SUL) by examining the changes in atmospheric energy budget terms on global and regional scales, in terms of fast (independent of changes in sea surface temperature, SST) and slow responses (mediated by changes in SST). Changes in atmospheric radiative cooling/heating are further decomposed into contributions from clouds, aerosols, and clear–clean sky (without clouds or aerosols). Both cases show a decrease in global-mean precipitation, which is dominated by fast responses in the BC case and slow responses in the SUL case. The geographical patterns are distinct too. The intertropical convergence zone (ITCZ), accompanied by tropical rainfall, shifts northward in the BC case, while it shifts southward in the SUL case. For both cases, energy transport terms from the slow response dominate the changes in tropical rainfall, which are associated with the northward (southward) shift of the Hadley cell in response to the enhanced southward (northward) cross-equatorial energy flux caused by increased BC (SUL) emission. The extra-tropical precipitation decreases in both cases. For the BC case, fast responses to increased atmospheric radiative heating contribute most to the reduced rainfall, in which absorbing aerosols directly heat the mid-troposphere, stabilise the column, and suppress precipitation. Unlike BC, non-absorbing aerosols decrease surface temperatures through slow processes, cool the whole atmospheric column, and reduce specific humidity, which leads to decreased radiative cooling from the clear–clean sky, which is consistent with the reduced rainfall. Examining the changes in large-scale circulation and local thermodynamics qualitatively explains the responses of precipitation to aerosol perturbations, whereas the energetic perspective provides a method to quantify their contributions.

scholarly journals On the Contribution of Fast and Slow Responses to Precipitation Changes Caused by Aerosol Perturbations

2021 ◽  
Author(s):  
Shipeng Zhang ◽  
Philip Stier ◽  
Duncan Watson-Parris
Keyword(s):  
Large Scale ◽  
Energy Transport ◽  
Hadley Cell ◽  
Radiative Heating ◽  
Specific Humidity ◽  
Radiative Cooling ◽  
Tropical Rainfall ◽  
Absorbing Aerosols ◽  
Global Mean ◽  
Fast Responses

Abstract. Changes in global-mean precipitation are strongly constrained by global radiative cooling, while regional rainfall changes are less constrained because energy can be transported. Absorbing and non-absorbing aerosols have different effects on both global-mean and regional precipitation, due to the distinct effects on energetics. This study analyses the precipitation responses to large perturbations in black carbon (BC) and sulphate (SUL) respectively by examining the changes in atmospheric energy budget terms on global and regional scales, in terms of fast (independent of changes in sea surface temperature (SST)) and slow responses (mediated by changes in SST). Changes in atmospheric radiative cooling/heating are further decomposed into contributions from clouds, aerosols, and clear-clean sky (without clouds or aerosols). Both cases show a decrease in global-mean precipitation, dominated by fast responses in the BC case while slow responses in the SUL case. The geographical patterns are distinct too. The intertropical convergence zone (ITCZ), accompanied with tropical rainfall, shifts northward in the BC case, while southward in the SUL case. For both cases, energy transport terms from the slow response dominates the changes in tropical rainfall, which are associated with the northward (southward) shift of Hadley cell in response to the enhanced southward (northward) cross-equatorial energy flux caused by increased BC (SUL) emission. The extra-tropical precipitation decreases in both cases. For the BC case, fast responses to increased atmospheric radiative heating contribute most to the reduced rainfall, in which absorbing aerosols directly heat the mid-troposphere, stabilise the column, and suppress precipitation. Unlike BC, non-absorbing aerosols decrease surface temperatures through slow processes, cool the whole atmospheric column, and reduce specific humidity, which leads to decreased radiative cooling from the clean-clear sky, and is consistent with the reduced rainfall. Examining the changes in large-scale circulation and local thermodynamics qualitatively explains the responses of precipitation to aerosol perturbations, whereas the energetic perspective provides a method to quantify their contributions.

Spatio-temporal Patterns of the Precipitation Response to Aerosol Perturbations from an Energetic Perspective

2020 ◽  
Author(s):  
Shipeng Zhang ◽  
Philip Stier ◽  
Duncan Watson-Parris ◽  
Guy Dagan
Keyword(s):  
Energy Transport ◽  
Spatial Scales ◽  
Heat Fluxes ◽  
Radiative Cooling ◽  
Regional Patterns ◽  
Geographical Patterns ◽  
Clear Sky ◽  
Spatio Temporal ◽  
Absorbing Aerosols ◽  
Global Mean

<p>Absorbing and non-absorbing aerosols have distinct effects on both global-mean and regional precipitation. Local changes of precipitation in response to aerosol perturbations are more complex than global-mean changes, which are strongly constrained by global energy budget. This work examines the changes of atmospheric energetic budget terms to study effects of large perturbations in black carbon (BC) and sulphate (SUL) on precipitation. Both cases show decrease of global-mean precipitation but with different geographical patterns. Decreased atmospheric radiative cooling contributes to the majority of decreased global-mean precipitation. It is caused by increased aerosols absorption in BC case but decreased cooling from clean-clear sky (without clouds and aerosols) in SUL case. Fast responses, which are independent of changes in sea surface temperature (SST), dominate the precipitation changes in the BC case, not only for global mean but also for regional patterns. Slow responses, which are mediated by changes in SST, dominate the precipitation responses in SUL case, both globally and regionally.</p><p> </p><p>Relationships between temporal responses of local precipitation and diabatic cooling and precipitation are also examined for both BC and SUL perturbations. Both cases show remarkable similar pattern of correlations despite of essentially different patterns of changes in precipitation and diabatic cooling. Strong positive correlations are found over mid-latitude land and this is mainly due to the changes from surface sensible heat fluxes. Negative correlations are found over tropical oceans, mainly contributed by (longwave) radiative cooling from clouds and clean-clear sky. Further analysis shows this similarity is caused by the natural variability which is independent from external forcing. It indicates that the temporal relationship between changes in local precipitation and diabatic cooling is forcer-independent. This correlation is examined as a function of increasing spatial scales, which demonstrates the scale at which the dominating energetic term on regional precipitation shifts from energy transport to atmospheric diabatic cooling.</p>

scholarly journals The Large-Scale Dynamical Response of Clouds to Aerosol Forcing

2017 ◽  
Vol 30 (21) ◽  
pp. 8783-8794 ◽  
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.

scholarly journals Exploring the sensitivity of Northern Hemisphere atmospheric circulation to different surface temperature forcing using a statistical–dynamical atmospheric model

2019 ◽  
Vol 26 (1) ◽  
pp. 1-12 ◽  
Author(s):  
Sonja Totz ◽  
Stefan Petri ◽  
Jascha Lehmann ◽  
Erik Peukert ◽  
Dim Coumou
Keyword(s):  
Temperature Gradient ◽  
Large Scale ◽  
Planetary Waves ◽  
Hadley Cell ◽  
Storm Tracks ◽  
Meridional Temperature Gradient ◽  
Jet Streams ◽  
Global Mean Temperature ◽  
Mean Temperature ◽  
Global Mean

Abstract. Climate and weather conditions in the mid-latitudes are strongly driven by the large-scale atmosphere circulation. Observational data indicate that important components of the large-scale circulation have changed in recent decades, including the strength and the width of the Hadley cell, jets, storm tracks and planetary waves. Here, we use a new statistical–dynamical atmosphere model (SDAM) to test the individual sensitivities of the large-scale atmospheric circulation to changes in the zonal temperature gradient, meridional temperature gradient and global-mean temperature. We analyze the Northern Hemisphere Hadley circulation, jet streams, storm tracks and planetary waves by systematically altering the zonal temperature asymmetry, the meridional temperature gradient and the global-mean temperature. Our results show that the strength of the Hadley cell, storm tracks and jet streams depend, in terms of relative changes, almost linearly on both the global-mean temperature and the meridional temperature gradient, whereas the zonal temperature asymmetry has little or no influence. The magnitude of planetary waves is affected by all three temperature components, as expected from theoretical dynamical considerations. The width of the Hadley cell behaves nonlinearly with respect to all three temperature components in the SDAM. Moreover, some of these observed large-scale atmospheric changes are expected from dynamical equations and are therefore an important part of model validation.

The Atmospheric Energy Constraint on Global-Mean Precipitation Change

2014 ◽  
Vol 27 (2) ◽  
pp. 757-768 ◽  
Author(s):  
Angeline G. Pendergrass ◽  
Dennis L. Hartmann
Keyword(s):  
Water Vapor ◽  
Temperature Increase ◽  
Longwave Radiation ◽  
Surface Fluxes ◽  
Lapse Rate ◽  
Specific Humidity ◽  
Radiative Cooling ◽  
Rate Of Increase ◽  
Precipitation Increase ◽  
Global Mean

Abstract Models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) robustly predict that the rate of increase in global-mean precipitation with global-mean surface temperature increase is much less than the rate of increase of water vapor. The goal of this paper is to explain in detail the mechanisms by which precipitation increase is constrained by radiative cooling. Changes in clear-sky atmospheric radiative cooling resulting from changes in temperature and humidity in global warming simulations are in good agreement with the multimodel, global-mean precipitation increase projected by GCMs (~1.1 W m−2 K−1). In an atmosphere with fixed specific humidity, radiative cooling from the top of the atmosphere (TOA) increases in response to a uniform temperature increase of the surface and atmosphere, while atmospheric cooling by exchange with the surface decreases because the upward emission of longwave radiation from the surface increases more than the downward longwave radiation from the atmosphere. When a fixed relative humidity (RH) assumption is made, however, uniform warming causes a much smaller increase of cooling at the TOA, and the surface contribution reverses to an increase in net cooling rate due to increased downward emission from water vapor. Sensitivity of precipitation changes to lapse rate changes is modest when RH is fixed. Carbon dioxide reduces TOA emission with only weak effects on surface fluxes, and thus suppresses precipitation. The net atmospheric cooling response and thereby the precipitation response to CO2-induced warming at fixed RH are mostly contributed by changes in surface fluxes. The role of clouds is discussed. Intermodel spread in the rate of precipitation increase across the CMIP5 simulations is attributed to differences in the atmospheric cooling.

scholarly journals Thermodynamic and Dynamic Mechanisms for Hydrological Cycle Intensification over the Full Probability Distribution of Precipitation Events

2019 ◽  
Vol 76 (2) ◽  
pp. 497-516 ◽  
Author(s):  
Gang Chen ◽  
Jesse Norris ◽  
J. David Neelin ◽  
Jian Lu ◽  
L. Ruby Leung ◽  
...  
Keyword(s):  
Probability Distribution ◽  
Moisture Transport ◽  
Large Scale ◽  
Hydrological Cycle ◽  
Dynamic Effect ◽  
Hadley Cell ◽  
Precipitation Extremes ◽  
Specific Humidity ◽  
Wide Range ◽  
Full Probability

Abstract Precipitation changes in a warming climate have been examined with a focus on either mean precipitation or precipitation extremes, but changes in the full probability distribution of precipitation have not been well studied. This paper develops a methodology for the quantile-conditional column moisture budget of the atmosphere for the full probability distribution of precipitation. Analysis is performed on idealized aquaplanet model simulations under 3-K uniform SST warming across different horizontal resolutions. Because the covariance of specific humidity and horizontal mass convergence is much reduced when conditioned onto a given precipitation percentile range, their conditional averages yield a clear separation between the moisture (thermodynamic) and circulation (dynamic) effects of vertical moisture transport on precipitation. The thermodynamic response to idealized climate warming can be understood as a generalized “wet get wetter” mechanism, in which the heaviest precipitation of the probability distribution is enhanced most from increased gross moisture stratification, at a rate controlled by the change in lower-tropospheric moisture rather than column moisture. The dynamic effect, in contrast, can be interpreted by shifts in large-scale atmospheric circulations such as the Hadley cell circulation or midlatitude storm tracks. Furthermore, horizontal moisture advection, albeit of secondary role, is important for regional precipitation change. Although similar mechanisms are at play for changes in both mean precipitation and precipitation extremes, the thermodynamic contributions of moisture transport to increases in high percentiles of precipitation tend to be more widespread across a wide range of latitudes than increases in the mean, especially in the subtropics.

scholarly journals The effect of coherent stirring on the advection–condensation of water vapour

2017 ◽  
Vol 473 (2202) ◽  
pp. 20170196 ◽  
Author(s):  
Yue-Kin Tsang ◽  
Jacques Vanneste
Keyword(s):  
Water Vapour ◽  
Large Scale ◽  
Passive Scalar ◽  
Hadley Cell ◽  
Moisture Distribution ◽  
Specific Humidity ◽  
Initial Time ◽  
Small Scale ◽  
Kinematic Models ◽  
Scale Turbulence

Atmospheric water vapour is an essential ingredient of weather and climate. The key features of its distribution can be represented by kinematic models which treat it as a passive scalar advected by a prescribed flow and reacting through condensation. Condensation acts as a sink that maintains specific humidity below a prescribed, space-dependent saturation value. To investigate how the interplay between large-scale advection, small-scale turbulence and condensation controls moisture distribution, we develop simple kinematic models which combine a single circulating flow with a Brownian-motion representation of turbulence. We first study the drying mechanism of a water-vapour anomaly released inside a vortex at an initial time. Next, we consider a cellular flow with a moisture source at a boundary. The statistically steady state attained shows features reminiscent of the Hadley cell such as boundary layers, a region of intense precipitation and a relative humidity minimum. Explicit results provide a detailed characterization of these features in the limit of strong flow.

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

2017 ◽  
Vol 17 (22) ◽  
pp. 13833-13848 ◽  
Author(s):  
Ulrich Schumann ◽  
Bernhard Mayer
Keyword(s):  
Surface Temperature ◽  
Temperature Sensitivity ◽  
Radiative Forcing ◽  
Large Scale ◽  
Energy Transport ◽  
Vertical Component ◽  
Circulation Model ◽  
Surface Energy Budget ◽  
Radiative Heating ◽  
Surface Warming

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.

Tropical Tropospheric-Only Responses to Absorbing Aerosols

2012 ◽  
Vol 25 (7) ◽  
pp. 2471-2480 ◽  
Author(s):  
Geeta G. Persad ◽  
Yi Ming ◽  
V. Ramaswamy
Keyword(s):  
Black Carbon ◽  
General Circulation Model ◽  
General Circulation ◽  
Large Scale ◽  
Substantial Reduction ◽  
Circulation Model ◽  
Cloud Amount ◽  
Radiative Heating ◽  
Physically Based ◽  
Absorbing Aerosols

Abstract Absorbing aerosols affect the earth’s climate through direct radiative heating of the troposphere. This study analyzes the tropical tropospheric-only response to a globally uniform increase in black carbon, simulated with an atmospheric general circulation model, to gain insight into the interactions that determine the radiative flux perturbation. Over the convective regions, heating in the free troposphere hinders the vertical development of deep cumulus clouds, resulting in the detrainment of more cloudy air into the large-scale environment and stronger cloud reflection. A different mechanism operates over the subsidence regions, where heating near the boundary layer top causes a substantial reduction in low cloud amount thermodynamically by decreasing relative humidity and dynamically by lowering cloud top. These findings, which align well with previous general circulation model and large-eddy simulation calculations for black carbon, provide physically based explanations for the main characteristics of the tropical tropospheric adjustment. The implications for quantifying the climate perturbation posed by absorbing aerosols are discussed.

scholarly journals Exploring the sensitivity of the large-scale atmosphere circulation to changes in surface temperature gradients using a Statistical-Dynamical Atmosphere Model

2018 ◽  
Author(s):  
Sonja Totz ◽  
Stefan Petri ◽  
Jascha Lehmann ◽  
Erik Peukert ◽  
Dim Coumou
Keyword(s):  
Temperature Gradient ◽  
Large Scale ◽  
Planetary Waves ◽  
Temperature Gradients ◽  
Hadley Cell ◽  
Storm Tracks ◽  
Meridional Temperature Gradient ◽  
Global Mean Temperature ◽  
Temperature Asymmetry ◽  
Global Mean

Abstract. Climate and weather conditions in the mid-latitudes are strongly driven by the large-scale atmosphere circulation. Observational data indicates that important components of the large-scale circulation have changed in recent decades including the strength of the Hadley cell, jets, storm tracks and planetary waves. Here, we use a statistical-dynamical atmosphere model (SDAM) to analyse the sensitivity of the Northern Hemisphere dynamical components to changes in temperature fields by systematically altering the zonal temperature asymmetry and meridional temperature gradient as well as the global mean temperature. Our results show that the strength of the Hadley cell, storm tracks and jet streams depends almost linearly on both the global mean temperature and the meridional temperature gradient whereas the zonal temperature asymmetry has little or no influence. The magnitude of planetary waves is clearly affected by all three temperature components. The width of the Hadley cell behaves nonlinearly with respect to all three temperature components. Under global warming the temperature gradients are expected to change: Enhanced warming is expected in the Arctic, largely near the surface, and at the equator at high altitudes, altering the meridional temperature gradient. Further, land-ocean contrasts will change due to enhanced land warming. Also there is a pronounced seasonality to these warming patterns. Using SDAMs to disentangle and separately analyse the effect of individual temperature changes can help to understand observed and projected changes in large-scale atmosphere dynamics. Moreover, some of these observed large-scale atmospheric changes are expected from dynamical equations and therefore an important part of model validation.

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