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.

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.

scholarly journals The sensitivity of the large-scale atmosphere circulation to changes in surface temperature gradients in the Northern Hemisphere

2017 ◽  
Author(s):  
Sonja Molnos ◽  
Stefan Petri ◽  
Jascha Lehmann ◽  
Erik Peukert ◽  
Dim Coumou
Keyword(s):  
Temperature Gradient ◽  
Surface Temperature ◽  
Northern Hemisphere ◽  
Large Scale ◽  
Planetary Waves ◽  
Hadley Cell ◽  
Temperature Fields ◽  
Storm Tracks ◽  
Meridional Temperature Gradient ◽  
Jet Streams

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, jet streams, storm tracks and planetary waves. Associated impacts cover a broad range, including changes in the frequency and nature of weather extremes and shifts of fertile habitats with implications for biodiversity and agriculture. Dynamical theories have been proposed that link the shift of the poleward edge of the Northern Hadley cell to changes in the meridional temperature gradient. Moreover, model simulations have been carried out to analyse the cause of observed and projected changes in the large-scale atmosphere circulation. However, the question of the underlying drivers and particularly the possible role of global warming is still debated. Here, we use a statistical-dynamical atmosphere model (SDAM) to analyse the sensitivity of the Northern Hemisphere Hadley cell, storm tracks, jet streams and planetary waves to changes in temperature fields by systematically altering the zonal and meridional temperature gradient as well as the global mean surface temperature.

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

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

<p>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 CO<sub>2</sub> 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°C) and a greatly reduced meridional temperature gradient (by ~30% in SST). However, reproducing these large-scale climate features at reasonable CO<sub>2</sub> 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.</p><p>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 CO<sub>2</sub> concentrations between x1 to x9 preindustrial levels.</p><p>Preliminary results indicate that all models that provide data for at least 3 different CO<sub>2</sub> 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.</p>

scholarly journals Summer Westerly Jet in Northern Hemisphere during the Mid-Holocene: A Multi-Model Study

Atmosphere ◽  
2020 ◽  
Vol 11 (11) ◽  
pp. 1193
Author(s):  
Chuchu Xu ◽  
Mi Yan ◽  
Liang Ning ◽  
Jian Liu
Keyword(s):  
Temperature Gradient ◽  
Northern Hemisphere ◽  
Hadley Cell ◽  
Dynamic Processes ◽  
Jet Stream ◽  
Meridional Temperature Gradient ◽  
The North ◽  
Westerly Jet ◽  
Poleward Shift ◽  
Thermodynamic Processes

The upper-level jet stream, a narrow band of maximum wind speed in the mid-latitude westerlies, exerts a considerable influence on the global climate by modulating the transport and distribution of momentum, heat and moisture. In this study by using four high-resolution models in the Paleoclimate Modelling Intercomparison Project phase 3, the changes of position and intensity of the northern hemisphere westerly jet at 200 hPa in summer during the mid-Holocene (MH), as well as the related mechanisms, are investigated. The four models show similar performance on the westerly jet. At the hemispheric scale, the simulated westerly jet has a poleward shift during the MH compared to the preindustrial period. The warming in arctic and cooling in the tropics during the MH are caused by the orbital changes of the earth and the precipitation changes, and it could lead to the weakened meridional temperature gradient and pressure gradient, which might account for the poleward shift of the westerly jet from the thermodynamic perspective. From the dynamic perspective, two maximum centers of eddy kinetic energy are simulated over the North Pacific and North Atlantic with the north deviation, which could cause the northward movement of the westerly jet. The weakening of the jet stream is associated with the change of the Hadley cell and the meridional temperature gradient. The largest weakening is over the Pacific Ocean where both the dynamic and the thermodynamic processes have weakening effects. The smallest weakening is over the Atlantic Ocean, and it is induced by the offset effects of dynamic processes and thermodynamic processes. The weakening over the Eurasia is mainly caused by the dynamic processes.

scholarly journals The Effect of Vertical Baroclinicity Concentration on Atmospheric Macroturbulence Scaling Relations

2017 ◽  
Vol 74 (5) ◽  
pp. 1651-1667 ◽  
Author(s):  
Janni Yuval ◽  
Yohai Kaspi
Keyword(s):  
Relaxation Time ◽  
Temperature Gradient ◽  
Potential Energy ◽  
Vertical Structure ◽  
Temperature Gradients ◽  
Lapse Rate ◽  
Meridional Temperature Gradient ◽  
Available Potential Energy ◽  
The Mean ◽  
Mean State

Abstract Motivated by the expectation that under global warming upper-level meridional temperature gradients will increase while lower-level temperature gradients will decrease, the relations between the vertical structure of baroclinicity and eddy fields are investigated. The sensitivity of eddies and the relation between the mean available potential energy and eddy quantities are studied for cases where the vertical structure of the lapse rate and meridional temperature gradient are modified. To investigate this systematically, an idealized general circulation model with a Newtonian cooling scheme that has a very short relaxation time for the mean state and a long relaxation time for eddies is used. This scheme allows for any chosen zonally mean state to be obtained with good precision. The results indicate that for similar change in the lapse rate or meridional temperature gradient, eddies are more sensitive to changes in baroclinicity where it is already large. Furthermore, when the vertical structure of the lapse rate or the meridional temperature gradient is modified, there is no universal linear relation between the mean available potential energy and eddy quantities.

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.

Overshooting warming targets – temperature reversibility and implications for impacts, adaptation needs and near-term mitigation

2021 ◽  
Author(s):  
Carl-Friedrich Schleussner ◽  
Quentin Lejeune ◽  
Philippe Ciais ◽  
Thomas Gasser ◽  
Joeri Rogelj ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Global Warming ◽  
Large Scale ◽  
Carbon Dioxide Removal ◽  
Global Mean Temperature ◽  
Mean Temperature ◽  
Removal Technologies ◽  
Near Term ◽  
The Impact ◽  
Global Mean

<p>Limiting global mean temperature increase to politically agreed temperature limits such as the 1.5°C threshold in the Paris Agreement becomes increasingly challenging. This has given rise to a class of overshoot emissions pathways in the mitigation literature that limit warming to such thresholds only after allowing for a temporary overshoot. However, substantial biogeophysical uncertainties remain regarding the large-scale deployment of Carbon Dioxide Removal technologies required to potentially reverse global warming. Additionally, beyond global mean temperature very little is known about the benefits of declining temperatures on impacts and adaptation needs. Here we will provide an overview of the current state of understanding regarding the reversibility of global warming, as well as impacts and adaptation needs under overshoot pathways.</p><p>We highlight the characteristics of the overshoot scenarios from the literature, and especially those that are compatible with identified sustainability limits for Carbon Dioxide Removal deployment. We will compare those characteristics with uncertainties arising from the Earth System’s response which may complicate the efforts to achieve a decrease in Global Mean Temperature after peak warming is reached. This part will include latest results of the permafrost carbon feedback under stylized overshoot scenarios. Eventually, we will summarise the state-of-the-art knowledge and present new results regarding the impacts of overshoot scenarios for non-linear and time-lagged responses such as sea-level rise, permafrost and glaciers. This will allow for a preliminary assessment of the impact and adaptation benefits of early mitigation compatible with a no or low overshoot pathways.</p>

Re-examining inferences from Hadley cell theory on tropical expansion under global warming throughout the seasonal cycle

2020 ◽  
Author(s):  
Spencer Hill ◽  
Jonathan Mitchell ◽  
Simona Bordoni
Keyword(s):  
Global Warming ◽  
Temperature Gradient ◽  
Large Scale ◽  
Climate Models ◽  
Numerical Models ◽  
Global Climate Models ◽  
Hadley Cell ◽  
Critical Examination ◽  
Cell Width ◽  
Hadley Cells

<p>Simulations of global warming in numerical models ranging from full-complexity atmosphere-ocean global climate models (GCMs) to highly idealized, dry, atmospheric GCMs almost invariably feature poleward expansion of the annual-mean Hadley cell extent.  The attendant widening of the subtropical dry zones underlying the Hadley cell descending branches makes understanding this response of the large-scale circulation to climate change of paramount societal and ecological importance.  Two theories, one that neglects the role of large-scale eddy process and one that does not, yield similar but ultimately distinct dependencies of the Hadley cell width on planetary parameters, including those such as the equator-to-pole temperature gradient that also robustly change under global warming.  A common approach, therefore, is to use the responses of these parameters diagnosed from GCM simulations to make arguments about their influence on the Hadley cell widening.  This talk offers a critical examination of that approach.</p><p>The approach's key flaw is that the quantities such as the equator-to-pole temperature gradient that appear in the theoretical scalings refer to their values in the *absence* of any large-scale overturning circulation, Hadley cells or eddies, i.e. in the hypothetical state of latitude-by-latitude radiative convective equilibrium (RCE).  This RCE state is what "forces" the Hadley cells, and once the Hadley cells emerge they modify (among others) the equator-to-pole temperature gradient.  Using these theories to understand the Hadley cell response to increased CO2 therefore requires analyzing the responses of the hypothetical RCE state to the increased CO2, which we do via single column model simulations.  In addition, we present a new scaling for the Hadley cell extent applicable to the solsticial seasons that, unlike the existing scalings, does not depend sensitively on the presence or absence of large-scale eddies, which we use in conjunction with solsticial RCE simulations to clarify arguments regarding tropical expansion over the course of the annual cycle in addition to the annual mean.  The implications for these refined theoretical arguments on results from prior studies and on constraining future Hadley cell expansion are discussed.</p>

The Tropospheric Response to Tropical and Subtropical Zonally Asymmetric Torques: Analytical and Idealized Numerical Model Results

2012 ◽  
Vol 69 (1) ◽  
pp. 214-235 ◽  
Author(s):  
Tiffany A. Shaw ◽  
William R. Boos
Keyword(s):  
Temperature Gradient ◽  
Northern Hemisphere ◽  
General Circulation ◽  
Large Scale ◽  
Critical Line ◽  
Circulation Model ◽  
General Circulation Models ◽  
Kelvin Wave ◽  
Meridional Temperature Gradient ◽  
Poleward Shift

Abstract The tropospheric response to prescribed tropical and subtropical zonally asymmetric torques, which can be considered as idealizations of vertical momentum transfers by orographic gravity waves or convection, is investigated. The linear analytical Gill model response to westward upper-tropospheric torques is compared to the response to a midtropospheric heating, which is a familiar point of reference. The response to an equatorial torque projects onto a Kelvin wave response to the east that is of opposite sign to the response to the east of the heating at upper levels. In contrast, the torque and heating both produce Rossby gyres of the same sign to the west of the forcing and the zonal-mean streamfunction responses are identical. When the forcings are shifted into the Northern Hemisphere, the streamfunction responses have opposite signs: there is upwelling in the Southern (Northern) Hemisphere in response to the torque (heating). The nonlinear response to westward torques was explored in idealized general circulation model experiments. In the absence of a large-scale meridional temperature gradient, the response to an equatorial torque was confined to the tropics and was qualitatively similar to the linear solutions. When the torque was moved into the subtropics, the vorticity budget response was similar to a downward control–type balance in the zonal mean. In the presence of a meridional temperature gradient, the response to an equatorial torque involved a poleward shift of the midlatitude tropospheric jet and Ferrel cell. The response in midlatitudes was associated with a poleward shift of the regions of horizontal eddy momentum flux convergence, which coincided with a shift in the upper-tropospheric critical line for baroclinic waves. The shift in the critical line was caused (in part) by the zonal wind response to the prescribed torque, suggesting a possible cause of the response in midlatitudes. Overall, this hierarchy of analytical and numerical results highlights robust aspects of the response to tropical and subtropical zonally asymmetric torques and represents the first step toward understanding the response in fully comprehensive general circulation models.

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.

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