The observed relationship between Pacific SST variability and Hadley cell extent trends in reanalyses

2021 ◽  
pp. 1-49
Author(s):  
Michael Rollings ◽  
Timothy M. Merlis
Keyword(s):  
Radiative Forcing ◽  
General Circulation ◽  
Climate Models ◽  
Climate Model ◽  
Southern Oscillation ◽  
Circulation Model ◽  
Hadley Cell ◽  
Cell Width ◽  
Sst Variability

AbstractReanalysis and other observationally-based estimates suggest the tropics have expanded more than simulated by coupled climate models with historical radiative forcing. Previous research has attempted to reconcile this discrepancy by using climate model simulations with constrained tropical Pacific sea surface temperatures (SSTs) to account for the role of internal variability. Here the relationships between Hadley cell extent and internal SST variability and long-term warming are analysed using purely observational techniques. Using linearly independent components of SST variability with reanalysis datasets, the statistical relationship between Pacific variability and Hadley cell extent is quantified by timescale. There is a strong correlation between North Pacific decadal SST variability and Southern Hemisphere Hadley cell extent. Conversely, there is a weaker observed relation between the El Niño–Southern Oscillation (ENSO) and Hadley cell extent when low-frequency variability is filtered out of the ENSO signal. The observed linear sensitivity of Hadley cell width to long-termwarming agrees with coupled general circulation model experiments when accounting for uncertainties, and there is a statistically significant relationship between Northern Hemisphere Hadley cell extent and long-term warming during boreal autumn.

scholarly journals Changes in the width of the tropical belt due to simple radiative forcing changes in the GeoMIP simulations

2016 ◽  
Vol 16 (15) ◽  
pp. 10083-10095 ◽  
Author(s):  
Nicholas A. Davis ◽  
Dian J. Seidel ◽  
Thomas Birner ◽  
Sean M. Davis ◽  
Simone Tilmes
Keyword(s):  
Carbon Dioxide ◽  
Radiative Forcing ◽  
General Circulation ◽  
Climate Models ◽  
Temperature Response ◽  
Austral Summer ◽  
Hadley Cell ◽  
Solar Constant ◽  
Cell Width ◽  
Climate Forcings

Abstract. Model simulations of future climates predict a poleward expansion of subtropical arid climates at the edges of Earth's tropical belt, which would have significant environmental and societal impacts. This expansion may be related to the poleward shift of the Hadley cell edges, where subsidence stabilizes the atmosphere and suppresses precipitation. Understanding the primary drivers of tropical expansion is hampered by the myriad forcing agents in most model projections of future climate. While many previous studies have examined the response of idealized models to simplified climate forcings and the response of comprehensive climate models to more complex climate forcings, few have examined how comprehensive climate models respond to simplified climate forcings. To shed light on robust processes associated with tropical expansion, here we examine how the tropical belt width, as measured by the Hadley cell edges, responds to simplified forcings in the Geoengineering Model Intercomparison Project (GeoMIP). The tropical belt expands in response to a quadrupling of atmospheric carbon dioxide concentrations and contracts in response to a reduction in the solar constant, with a range of a factor of 3 in the response among nine models. Models with more surface warming and an overall stronger temperature response to quadrupled carbon dioxide exhibit greater tropical expansion, a robust result in spite of inter-model differences in the mean Hadley cell width, parameterizations, and numerical schemes. Under a scenario where the solar constant is reduced to offset an instantaneous quadrupling of carbon dioxide, the Hadley cells remain at their preindustrial width, despite the residual stratospheric cooling associated with elevated carbon dioxide levels. Quadrupled carbon dioxide produces greater tropical belt expansion in the Southern Hemisphere than in the Northern Hemisphere. This expansion is strongest in austral summer and autumn. Ozone depletion has been argued to cause this pattern of changes in observations and model experiments, but the results here indicate that seasonally and hemispherically asymmetric tropical expansion can be a basic response of the general circulation to climate forcings.

scholarly journals Abrupt Circulation Responses to Tropical Upper-Tropospheric Warming in a Relatively Simple Stratosphere-Resolving AGCM

2012 ◽  
Vol 25 (12) ◽  
pp. 4097-4115 ◽  
Author(s):  
Shuguang Wang ◽  
Edwin P. Gerber ◽  
Lorenzo M. Polvani
Keyword(s):  
Climate Change ◽  
General Circulation ◽  
Climate Models ◽  
Climate Model ◽  
Polar Vortex ◽  
Circulation Model ◽  
Hadley Cell ◽  
Critical Threshold ◽  
Intergovernmental Panel ◽  
Upper Troposphere

Abstract The circulation response of the atmosphere to climate change–like thermal forcing is explored with a relatively simple, stratosphere-resolving general circulation model. The model is forced with highly idealized physics, but integrates the primitive equations at resolution comparable to comprehensive climate models. An imposed forcing mimics the warming induced by greenhouse gasses in the low-latitude upper troposphere. The forcing amplitude is progressively increased over a range comparable in magnitude to the warming projected by Intergovernmental Panel on Climate Change coupled climate model scenarios. For weak to moderate warming, the circulation response is remarkably similar to that found in comprehensive models: the Hadley cell widens and weakens, the tropospheric midlatitude jets shift poleward, and the Brewer–Dobson circulation (BDC) increases. However, when the warming of the tropical upper troposphere exceeds a critical threshold, ~5 K, an abrupt change of the atmospheric circulation is observed. In the troposphere the extratropical eddy-driven jet jumps poleward nearly 10°. In the stratosphere the polar vortex intensifies and the BDC weakens as the intraseasonal coupling between the troposphere and the stratosphere shuts down. The key result of this study is that an abrupt climate transition can be effected by changes in atmospheric dynamics alone, without need for the strong nonlinearities typically associated with physical parameterizations. It is verified that the abrupt climate shift reported here is not an artifact of the model’s resolution or numerics.

scholarly journals Changes in theWidth of the Tropical Belt due to Simple Radiative Forcing Changes in the GeoMIP Simulations

2016 ◽  
Author(s):  
Nicholas Davis ◽  
Dian J. Seidel ◽  
Thomas Birner ◽  
Sean M. Davis ◽  
Simone Tilmes
Keyword(s):  
Carbon Dioxide ◽  
Radiative Forcing ◽  
General Circulation ◽  
Climate Models ◽  
Temperature Response ◽  
Austral Summer ◽  
Hadley Cell ◽  
Solar Constant ◽  
Cell Width ◽  
Climate Forcings

Abstract. Model simulations of future climates predict a poleward expansion of subtropical arid climates at the edges of earth's tropical belt, which would have significant environmental and societal impacts. This expansion may be related to the poleward shift of the Hadley cell edges, where subsidence stabilizes the atmosphere and suppresses precipitation. Understanding the primary drivers of tropical expansion is hampered by the myriad forcing agents in most model projections of future climate. While many previous studies have examined the response of idealized models to simplified climate forcings and the response of comprehensive climate models to more complex climate forcings, none have examined how comprehensive climate models respond to simplified climate forcings. To shed light on robust processes associated with tropical expansion, here we examine how the tropical belt width, as measured by the Hadley cell edges, responds to simplified forcings in the Geoengineering Model Intercomparison Project (GeoMIP). The tropical belt expands in response to a quadrupling of atmospheric carbon dioxide concentrations and contracts in response to a reduction in the solar constant, with a range of a factor of three in the response among nine models. Models with more surface warming and an overall stronger temperature response to quadrupled carbon dioxide exhibit greater tropical expansion, a robust result in spite of intermodel differences in the mean Hadley cell width, parameterizations, and numerical schemes. Under a scenario where the solar constant is reduced to offset an instantaneous quadrupling of carbon dioxide, the Hadley cells remain at their preindustrial width, despite the residual stratospheric cooling associated with elevated carbon dioxide levels. Quadrupled carbon dioxide produces greater tropical belt expansion in the Southern Hemisphere than in the Northern Hemisphere. This expansion is strongest in austral summer and autumn. Ozone depletion has been argued to cause this pattern of changes in observations and model experiments, but the results here indicate that seasonally- and hemispherically-asymmetric tropical expansion can be a basic response of the general circulation to climate forcings.

scholarly journals Interhemispheric differences of mesosphere/lower thermosphere winds and tides investigated from three whole atmosphere models and meteor radar observations

2021 ◽  
Author(s):  
Gunter Stober ◽  
Ales Kuchar ◽  
Dimitry Pokhotelov ◽  
Huixin Liu ◽  
Han-Li Liu ◽  
...  
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
Climate Model ◽  
Lower Thermosphere ◽  
Winter Season ◽  
General Circulation Models ◽  
Meteor Radar ◽  
Radar Observations ◽  
Seasonal Characteristics

Abstract. Long-term and continuous observations of mesospheric/lower thermospheric winds are rare, but they are important to investigate climatological changes at these altitudes on time scales of several years, covering a solar cycle and longer. Such long time series are a natural heritage of the mesosphere/lower thermosphere climate, and they are valuable to compare climate models or long term runs of general circulation models (GCMs). Here we present a climatological comparison of wind observations from six meteor radars at two conjugate latitudes to validate the corresponding mean winds and atmospheric diurnal and semidiurnal tides from three GCMs, namely Ground-to-Topside Model of Atmosphere and Ionosphere for Aeronomy (GAIA), Whole Atmosphere Community Climate Model Extension (Specified Dynamics) (WACCM-X(SD)) and Upper Atmosphere ICOsahedral Non-hydrostatic (UA-ICON) model. Our results indicate that there are interhemispheric differences in the seasonal characteristics of the diurnal and semidiurnal tide. There also are some differences in the mean wind climatologies of the models and the observations. Our results indicate that GAIA shows a reasonable agreement with the meteor radar observations during the winter season, whereas WACCM-X(SD) shows a better agreement with the radars for the hemispheric zonal summer wind reversal, which is more consistent with the meteor radar observations. The free running UA-ICON tends to show similar winds and tides compared to WACCM-X(SD).

scholarly journals The Effect of a Well-Resolved Stratosphere on Surface Climate: Differences between CMIP5 Simulations with High and Low Top Versions of the Met Office Climate Model

2012 ◽  
Vol 25 (20) ◽  
pp. 7083-7099 ◽  
Author(s):  
S. C. Hardiman ◽  
N. Butchart ◽  
T. J. Hinton ◽  
S. M. Osprey ◽  
L. J. Gray
Keyword(s):  
General Circulation ◽  
Climate Model ◽  
Southern Oscillation ◽  
Coupled Model ◽  
Circulation Model ◽  
Climate Simulation ◽  
Reanalysis Dataset ◽  
Quasi Biennial Oscillation ◽  
Surface Climate ◽  
The Impact

Abstract The importance of using a general circulation model that includes a well-resolved stratosphere for climate simulations, and particularly the influence this has on surface climate, is investigated. High top model simulations are run with the Met Office Unified Model for the Coupled Model Intercomparison Project Phase 5 (CMIP5). These simulations are compared to equivalent simulations run using a low top model differing only in vertical extent and vertical resolution above 15 km. The period 1960–2002 is analyzed and compared to observations and the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis dataset. Long-term climatology, variability, and trends in surface temperature and sea ice, along with the variability of the annular mode index, are found to be insensitive to the addition of a well-resolved stratosphere. The inclusion of a well-resolved stratosphere, however, does improve the impact of atmospheric teleconnections on surface climate, in particular the response to El Niño–Southern Oscillation, the quasi-biennial oscillation, and midwinter stratospheric sudden warmings (i.e., zonal mean wind reversals in the middle stratosphere). Thus, including a well-represented stratosphere could improve climate simulation on intraseasonal to interannual time scales.

scholarly journals Preindustrial-to-present-day radiative forcing by tropospheric ozone from improved simulations with the GISS chemistry-climate GCM

2003 ◽  
Vol 3 (5) ◽  
pp. 1675-1702 ◽  
Author(s):  
D. T. Shindell ◽  
G. Faluvegi ◽  
N. Bell
Keyword(s):  
Tropospheric Ozone ◽  
Radiative Forcing ◽  
General Circulation ◽  
Climate Model ◽  
Circulation Model ◽  
Tropospheric Chemistry ◽  
True Value ◽  
Tropopause Region ◽  
Dynamics Simulations ◽  
Goddard Institute

Abstract. Improved estimates of the radiative forcing from tropospheric ozone increases since the preindustrial have been calculated with the tropospheric chemistry model used at the Goddard Institute for Space Studies (GISS) within the GISS general circulation model (GCM). The chemistry in this model has been expanded to include simplified representations of peroxyacetylnitrates and non-methane hydrocarbons in addition to background NOx-HOx-Ox-CO-CH4 chemistry. The GCM has improved resolution and physics in the boundary layer, improved resolution near the tropopause, and now contains a full representation of stratospheric dynamics. Simulations of present-day conditions show that this coupled chemistry-climate model is better able to reproduce observed tropospheric ozone, especially in the tropopause region, which is critical to climate forcing. Comparison with preindustrial simulations gives a global annual average radiative forcing due to tropospheric ozone increases of 0.30 W/m2 with standard assumptions for preindustrial emissions. Locally, the forcing reaches more than 0.8 W/m2 in parts of the northern subtropics during spring and summer, and is more than 0.6 W/m2 through nearly all the Northern subtropics and mid-latitudes during summer. An alternative preindustrial simulation with soil NOx emissions reduced by two-thirds and emissions of isoprene, paraffins and alkenes from vegetation increased by 50% gives a forcing of 0.33 W/m2. Given the large uncertainties in preindustrial ozone amounts, the true value may lie well outside this range.

scholarly journals The 1986–1989 ENSO cycle in a chemical climate model

2006 ◽  
Vol 6 (12) ◽  
pp. 4669-4685 ◽  
Author(s):  
S. Brönnimann ◽  
M. Schraner ◽  
B. Müller ◽  
A. Fischer ◽  
D. Brunner ◽  
...  
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Climate Models ◽  
Climate Model ◽  
Circulation Model ◽  
Enso Cycle ◽  
Atlantic Sector ◽  
Ensemble Simulations ◽  
Chemical Climate ◽  
Middle Stratosphere

Abstract. A pronounced ENSO cycle occurred from 1986 to 1989, accompanied by distinct dynamical and chemical anomalies in the global troposphere and stratosphere. Reproducing these effects with current climate models not only provides a model test but also contributes to our still limited understanding of ENSO's effect on stratosphere-troposphere coupling. We performed several sets of ensemble simulations with a chemical climate model (SOCOL) forced with global sea surface temperatures. Results were compared with observations and with large-ensemble simulations performed with an atmospheric general circulation model (MRF9). We focus our analysis on the extratropical stratosphere and its coupling with the troposphere. In this context, the circulation over the North Atlantic sector is particularly important. Relative to the La Niña winter 1989, observations for the El Niño winter 1987 show a negative North Atlantic Oscillation index with corresponding changes in temperature and precipitation patterns, a weak polar vortex, a warm Arctic middle stratosphere, negative and positive total ozone anomalies in the tropics and at middle to high latitudes, respectively, as well as anomalous upward and poleward Eliassen-Palm (EP) flux in the midlatitude lower stratosphere. Most of the tropospheric features are well reproduced in the ensemble means in both models, though the amplitudes are underestimated. In the stratosphere, the SOCOL simulations compare well with observations with respect to zonal wind, temperature, EP flux, meridional mass streamfunction, and ozone, but magnitudes are underestimated in the middle stratosphere. With respect to the mechanisms relating ENSO to stratospheric circulation, the results suggest that both, upward and poleward components of anomalous EP flux are important for obtaining the stratospheric signal and that an increase in strength of the Brewer-Dobson circulation is part of that signal.

scholarly journals Climate Model Biases in the Width of the Tropical Belt

2016 ◽  
Vol 29 (5) ◽  
pp. 1935-1954 ◽  
Author(s):  
Nicholas Davis ◽  
Thomas Birner
Keyword(s):  
Seasonal Cycle ◽  
Climate Models ◽  
Climate Model ◽  
Large Fraction ◽  
Horizontal Resolution ◽  
Hadley Cell ◽  
Second Phase ◽  
Cell Width ◽  
Mean Width ◽  
The Mean

Abstract Earth’s arid subtropics are situated at the edges of the tropical belt, which encircles the planet along the equator and covers half of its surface area. The climate of the tropical belt is strongly influenced by the Hadley cells, with their subsidence and easterly trade winds both sustaining the aridity at the belt’s edges. The understanding of Earth’s past, present, and future climates is contingent on understanding the dynamics influencing this region. An important but unanswered question is how realistically climate models reproduce the mean state of the tropical belt. This study augments the existing literature by examining the mean width and seasonality of the tropical belt in climate models from phase 5 of CMIP (CMIP5) and experiments from the second phase of the Chemistry–Climate Model Validation (CCMVal-2) activity of the Stratospheric Processes and Their Role in Climate (SPARC) project. While the models overall reproduce the structure of the tropical belt width’s seasonal cycle, they underestimate its amplitude and cannot consistently reproduce the seasonal cycle lag between the Northern Hemisphere Hadley cell edge and subtropical jet latitudes found in observations. Additionally, up to 50% of the intermodel variation in mean tropical belt width can be attributed to model horizontal resolution, with finer resolution leading to a narrower tropical belt. Finer resolution is associated with an equatorward shift and intensification of subtropical eddy momentum flux convergence, which via the Coriolis torque explains essentially all of the grid-size bias and a large fraction of the total intermodel variation in Hadley cell width.

scholarly journals Microphysical simulations of sulfur burdens from stratospheric sulfur geoengineering

2012 ◽  
Vol 12 (10) ◽  
pp. 4775-4793 ◽  
Author(s):  
J. M. English ◽  
O. B. Toon ◽  
M. J. Mills
Keyword(s):  
Radiative Forcing ◽  
General Circulation ◽  
Climate Model ◽  
Three Dimensional ◽  
Circulation Model ◽  
Injection Rate ◽  
Sulfur Chemistry ◽  
Aerosol Mass ◽  
Tropospheric Aerosol ◽  
So2 Gas

Abstract. Recent microphysical studies suggest that geoengineering by continuous stratospheric injection of SO2 gas may be limited by the growth of the aerosols. We study the efficacy of SO2, H2SO4 and aerosol injections on aerosol mass and optical depth using a three-dimensional general circulation model with sulfur chemistry and sectional aerosol microphysics (WACCM/CARMA). We find increasing injection rates of SO2 in a narrow band around the equator to have limited efficacy while broadening the injecting zone as well as injecting particles instead of SO2 gas increases the sulfate burden for a given injection rate, in agreement with previous work. We find that injecting H2SO4 gas instead of SO2 does not discernibly alter sulfate size or mass, in contrast with a previous study using a plume model with a microphysical model. However, the physics and chemistry in aircraft plumes, which are smaller than climate model grid cells, need to be more carefully considered. We also find significant perturbations to tropospheric aerosol for all injections studied, particularly in the upper troposphere and near the poles, where sulfate burden increases by up to 100 times. This enhanced burden could have implications for tropospheric radiative forcing and chemistry. These results highlight the need to mitigate greenhouse gas emissions rather than attempt to cool the planet through geoengineering, and to further study geoengineering before it can be seriously considered as a climate intervention option.

scholarly journals Prognostic parameterization of cloud ice with a single category in the aerosol-climate model ECHAM(v6.3.0)-HAM(v2.3)

2017 ◽  
Author(s):  
Remo Dietlicher ◽  
David Neubauer ◽  
Ulrike Lohmann
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
Climate Model ◽  
Traditional Approach ◽  
Circulation Model ◽  
Cloud Microphysics ◽  
High Temporal Resolution ◽  
Conversion Rates ◽  
Single Category ◽  
Cloud Ice

Abstract. A new scheme for stratiform cloud microphysics has been implemented in the ECHAM6-HAM2 general circulation model. It features a widely used description of cloud water with two categories for cloud droplets and rain drops. The unique aspect of the scheme is the break with the traditional approach to describe cloud ice analogously. Here we parameterize cloud ice with a single, prognostic category as it has been done in regional models and most recently also in the global model CAM5. A single category does not rely on heuristic conversion rates from one category to another. At the same time it is conceptually easier and closer to first principles. This work shows that a single category is a viable approach to describe cloud ice in climate models. Prognostic representation of sedimentation is achieved by a nested approach for sub-stepping the microphysics scheme. This yields good results in terms of numerical stability and accuracy as compared to simulations with high temporal resolution. The improvement of the representation of cloud ice in ECHAM6-HAM2 is twofold. Not only are we getting rid of heuristic conversion rates but we also find that the prognostic treatment of sedimenting ice allows to unbiasedly represent the ice formation pathway from nucleation over growth by deposition and collisions to sedimentation.

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