scholarly journals ITCZ Width Controls on Hadley Cell Extent and Eddy-Driven Jet Position and Their Response to Warming

2019 ◽  
Vol 32 (4) ◽  
pp. 1151-1166 ◽  
Author(s):  
Oliver Watt-Meyer ◽  
Dargan M. W. Frierson
Keyword(s):  
Global Warming ◽  
Surface Temperature ◽  
Atmospheric Model ◽  
Hadley Cell ◽  
Lower Latitude ◽  
Tropical Precipitation ◽  
Highly Sensitive ◽  
Poleward Shift ◽  
The Impact ◽  
Zonal Momentum

The impact of global warming–induced intertropical convergence zone (ITCZ) narrowing onto the higher-latitude circulation is examined in the GFDL Atmospheric Model, version 2.1 (AM2.1), run over zonally symmetric aquaplanet boundary conditions. A striking reconfiguration of the deep tropical precipitation from double-peaked, off-equatorial ascent to a single peak at the equator occurs under a globally uniform +4 K sea surface temperature (SST) perturbation. This response is found to be highly sensitive to the SST profile used to force the model. By making small (≤1 K) perturbations to the surface temperature in the deep tropics, varying control simulation precipitation patterns with both single and double ITCZs are generated. Across the climatologies, narrower regions of ascent correspond to more equatorward Hadley cell edges and eddy-driven jets. Under the global warming perturbation, the experiments in which there is narrowing of the ITCZ show significantly less expansion of the Hadley cell and somewhat less poleward shift of the eddy-driven jet than those without ITCZ narrowing. With a narrower ITCZ, the ascending air has larger zonal momentum, causing more westerly upper-tropospheric subtropical wind. In turn, this implies 1) the subtropical jet will become baroclinically unstable at a lower latitude and 2) the critical (zero wind) line will shift equatorward, allowing midlatitude eddies to propagate farther equatorward. Both of these mechanisms modify the Hadley cell edge position, and the latter affects the jet position.

Sensitivities and Mechanisms of the Zonal Mean Atmospheric Circulation Response to Tropical Warming

2013 ◽  
Vol 70 (8) ◽  
pp. 2487-2504 ◽  
Author(s):  
Lantao Sun ◽  
Gang Chen ◽  
Jian Lu
Keyword(s):  
Global Warming ◽  
El Niño ◽  
El Nino ◽  
Atmospheric Model ◽  
Hadley Cell ◽  
Upper Troposphere ◽  
Future Global Warming ◽  
Large Ensembles ◽  
Poleward Shift ◽  
Mean Circulation

Abstract Although El Niño and global warming are both characterized by warming in the tropical upper troposphere, the latitudinal changes of the Hadley cell edge and midlatitude eddy-driven jet are opposite in sign. Using an idealized dry atmospheric model, the zonal mean circulation changes are investigated with respect to different patterns of tropical warming. Generally speaking, an equatorward shift in circulation takes place in the presence of enhanced tropical temperature gradient or narrow tropical warming, similar to the changes associated with El Niño events. In contrast, the zonal mean atmospheric circulations expand or shift poleward in response to upper-tropospheric warming or broad tropical warming, resembling the changes under future global warming. The mechanisms underlying these opposite changes in circulation are investigated by comparing the dry dynamical responses to a narrow tropical warming and a broad warming as analogs for El Niño and global warming. When running the idealized model in a zonally symmetric configuration in which the eddy feedback is disabled, both the narrow and broad warmings give rise to an equatorward shift of the subtropical jet. The eddy adjustment is further examined using large ensembles of transient response to a sudden switch-on of the forcing. For both narrow and broad tropical warmings, the jets move equatorward initially. In the subsequent adjustment, the initial equatorward shift is further enhanced and sustained by the low-level baroclinicity under the narrow tropical warming, whereas the initial equatorward shift transitions to a poleward shift associated with altered irreversible mixing of potential vorticity in the upper troposphere in the case of broad warming.

scholarly journals A Link between the Hiatus in Global Warming and North American Drought

2015 ◽  
Vol 28 (9) ◽  
pp. 3834-3845 ◽  
Author(s):  
Thomas L. Delworth ◽  
Fanrong Zeng ◽  
Anthony Rosati ◽  
Gabriel A. Vecchi ◽  
Andrew T. Wittenberg
Keyword(s):  
Global Warming ◽  
North America ◽  
Surface Temperature ◽  
North American ◽  
Radiative Forcing ◽  
Tropical Pacific ◽  
Global Warming Hiatus ◽  
Warming Hiatus ◽  
The Impact ◽  
The Tropical Pacific

Abstract Portions of western North America have experienced prolonged drought over the last decade. This drought has occurred at the same time as the global warming hiatus—a decadal period with little increase in global mean surface temperature. Climate models and observational analyses are used to clarify the dual role of recent tropical Pacific changes in driving both the global warming hiatus and North American drought. When observed tropical Pacific wind stress anomalies are inserted into coupled models, the simulations produce persistent negative sea surface temperature anomalies in the eastern tropical Pacific, a hiatus in global warming, and drought over North America driven by SST-induced atmospheric circulation anomalies. In the simulations herein the tropical wind anomalies account for 92% of the simulated North American drought during the recent decade, with 8% from anthropogenic radiative forcing changes. This suggests that anthropogenic radiative forcing is not the dominant driver of the current drought, unless the wind changes themselves are driven by anthropogenic radiative forcing. The anomalous tropical winds could also originate from coupled interactions in the tropical Pacific or from forcing outside the tropical Pacific. The model experiments suggest that if the tropical winds were to return to climatological conditions, then the recent tendency toward North American drought would diminish. Alternatively, if the anomalous tropical winds were to persist, then the impact on North American drought would continue; however, the impact of the enhanced Pacific easterlies on global temperature diminishes after a decade or two due to a surface reemergence of warmer water that was initially subducted into the ocean interior.

scholarly journals Thermodynamics of climate change: generalized sensitivities

2010 ◽  
Vol 10 (2) ◽  
pp. 3699-3715 ◽  
Author(s):  
V. Lucarini ◽  
K. Fraedrich ◽  
F. Lunkeit
Keyword(s):  
Climate Change ◽  
Global Warming ◽  
Surface Temperature ◽  
Entropy Production ◽  
Theoretical Approach ◽  
Climate Model ◽  
Co2 Concentration ◽  
Energy Cycle ◽  
Lorenz Energy Cycle ◽  
The Impact

Abstract. Using a recent theoretical approach, we study how the impact of global warming of the thermodynamics of the climate system by performing experiments with a simplified yet Earth-like climate model. In addition to the globally averaged surface temperature, the intensity of the Lorenz energy cycle, the Carnot efficiency, the material entropy production and the degree of irreversibility of the system are linear with the logarithm of the CO2 concentration. These generalized sensitivities suggest that the climate becomes less efficient, more irreversible, and features higher entropy production as it becomes warmer.

Cloud-Radiative Impacts On Tropical Circulation Change in GFDL AM4.1

2020 ◽  
Author(s):  
Juho Iipponen ◽  
Leo Donner
Keyword(s):  
Walker Circulation ◽  
Atmospheric Model ◽  
Hadley Cell ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Tropical Circulation ◽  
The North ◽  
Microphysical Properties ◽  
Tropospheric Circulation ◽  
Gross Moist Stability ◽  
The Impact

<pre>We use the Geophysical Fluid Dynamics Laboratory (GFDL) state-of-the-art AM4.1 atmospheric model to assess the impact of clouds on the change in tropical circulation. Slab-ocean experiments where cloud microphysical properties are locked to either the pre-industrial or 4xCO<sub>2</sub> conditions allow us to cleanly separate the circulation changes into a part caused by the cloud radiative effects (CREs), and to a part caused by the CO<sub>2</sub> changes. The CO<sub>2</sub>-induced SST changes are shown to dominate the response in the boundary layer, but are rivaled by the impacts of CREs in the mid to upper troposphere. The reduction in the east-to-west sea level pressure difference over the Pacific is solely caused by the increasing CO<sub>2</sub> and SST, but they only account for about half of the change in the mid-tropospheric Walker circulation. The weakening of the free-tropospheric circulation is shown to be mostly caused by the near-equal contributions the CO<sub>2</sub> and CREs make to the changes in dry-static and gross moist stability. Also, concerning the <span>meridional</span> circulation, we show that the response in the strength of the southern branch of the Hadley cell is largely due to CREs, while they have a much smaller impact in the north.</pre>

scholarly journals Amazonian Deforestation: Impact of Global Warming on the Energy Balance and Climate

2013 ◽  
Vol 52 (3) ◽  
pp. 521-530 ◽  
Author(s):  
E. C. Moraes ◽  
Sergio H. Franchito ◽  
V. Brahmananda Rao
Keyword(s):  
Global Warming ◽  
Energy Balance ◽  
Surface Temperature ◽  
Radiation Flux ◽  
Tropical Region ◽  
Net Radiation ◽  
Climatic Impact ◽  
Intergovernmental Panel ◽  
Emissions Scenarios ◽  
The Impact

AbstractA coupled biosphere–atmosphere statistical–dynamical model is used to study the relative roles of the impact of the land change caused by tropical deforestation and global warming on energy balance and climate. Three experiments were made: 1) deforestation, 2) deforestation + 2 × CO2, and 3) deforestation + CO2, CH4, N2O, and O3 for 2100. In experiment 1, the climatic impact of the Amazonian deforestation is studied. In experiment 2, the effect of doubling CO2 is included. In experiment 3, the concentrations of the greenhouse gases (GHGs) correspond to the A1FI scenario from the Intergovernmental Panel on Climate Change Special Report on Emissions Scenarios. The results showed that the percentage of the warming caused by deforestation relative to the warming when the increase in GHG concentrations is included is higher than 60% in the tropical region. On the other hand, with the increase in GHG concentrations, a reduction in the decrease of evapotranspiration and precipitation in the tropical region occurs when compared with the deforestation case. Because of an increase in the net longwave flux at the surface, there is a reduction in the decrease of the surface net radiation flux when compared with the case of only deforestation. This leads to an increase in the surface temperature. Although the changes are higher at 5°S, the percentage of them when the increase in GHG concentrations is included together with deforestation relative to the case of only deforestation is higher at 5°N (higher than 50% for the surface temperature and higher than 90% for the foliage and air foliage temperatures) in both experiments 2 and 3.

scholarly journals Exploiting the Abrupt 4 × CO2 Scenario to Elucidate Tropical Expansion Mechanisms

2019 ◽  
Vol 32 (3) ◽  
pp. 859-875 ◽  
Author(s):  
Rei Chemke ◽  
Lorenzo M. Polvani
Keyword(s):  
Surface Temperature ◽  
Phase Speed ◽  
Static Stability ◽  
Hadley Cell ◽  
Lapse Rate ◽  
Minor Role ◽  
Tropopause Height ◽  
Cell Edge ◽  
Dry Zone ◽  
Poleward Shift

Future emissions of greenhouse gases into the atmosphere are projected to result in significant circulation changes. One of the most important changes is the widening of the tropical belt, which has great societal impacts. Several mechanisms (changes in surface temperature, eddy phase speed, tropopause height, and static stability) have been proposed to explain this widening. However, the coupling between these mechanisms has precluded elucidating their relative importance. Here, the abrupt quadrupled-CO2 simulations of phase 5 of the Coupled Model Intercomparison Project (CMIP5) are used to examine the proposed mechanisms. The different time responses of the different mechanisms allow us to disentangle and evaluate them. As suggested by earlier studies, the Hadley cell edge is found to be linked to changes in subtropical baroclinicity. In particular, its poleward shift is accompanied by an increase in subtropical static stability (i.e., a decrease in temperature lapse rate) with increased CO2 concentrations. These subtropical changes also affect the eddy momentum flux, which shifts poleward together with the Hadley cell edge. Transient changes in tropopause height, eddy phase speed, and surface temperature, however, were found not to accompany the poleward shift of the Hadley cell edge. The widening of the Hadley cell, together with the increase in moisture content, accounts for most of the expansion of the dry zone. Eddy moisture fluxes, on the other hand, are found to play a minor role in the expansion of the dry zone.

scholarly journals Global Influence of Tropical Pacific Variability with Implications for Global Warming Slowdown

2017 ◽  
Vol 30 (7) ◽  
pp. 2679-2695 ◽  
Author(s):  
Chuan-Yang Wang ◽  
Shang-Ping Xie ◽  
Yu Kosaka ◽  
Qinyu Liu ◽  
Xiao-Tong Zheng
Keyword(s):  
Global Warming ◽  
Surface Temperature ◽  
Time Scale ◽  
Decadal Variability ◽  
Temperature Response ◽  
Tropical Pacific ◽  
Tropospheric Temperature ◽  
Decadal Time Scale ◽  
The Impact ◽  
Global Mean

The impact of internal tropical Pacific variability on global mean surface temperature (GMST) is quantified using a multimodel ensemble. A tropical Pacific index (TPI) is defined to track tropical Pacific sea surface temperature (SST) variability. The simulated GMST is highly correlated with TPI on the interannual time scale but this correlation weakens on the decadal time scale. The time-scale dependency is such that the GMST regression equation derived from the observations, which are dominated by interannual variability, would underestimate the magnitude of decadal GMST response to tropical Pacific variability. The surface air temperature response to tropical Pacific variability is strong in the tropics but weakens in the extratropics. The regression coefficient of GMST against TPI shows considerable intermodel variations, primarily because of differences in high latitudes. The results have important implications for the planned intercomparison of pacemaker experiments that force Pacific variability to follow the observed evolution. The model dependency of the GMST regression suggests that in pacemaker experiments—model performance in simulating the recent “slowdown” in global warming—will vary substantially among models. It also highlights the need to develop observational constraints and to quantify the TPI effect on the decadal variability of GMST. Compared to GMST, the correlation between global mean tropospheric temperature and TPI is high on both interannual and decadal time scales because of a common structure in the tropical tropospheric temperature response that is upward amplified and meridionally broad.

scholarly journals The Precipitation Response to an Idealized Subtropical Continent

2016 ◽  
Vol 29 (12) ◽  
pp. 4543-4564 ◽  
Author(s):  
Elizabeth A. Maroon ◽  
Dargan M. W. Frierson ◽  
Sarah M. Kang ◽  
Jacob Scheff
Keyword(s):  
General Circulation ◽  
Hadley Circulation ◽  
General Circulation Models ◽  
Atmospheric Model ◽  
Opposite Hemisphere ◽  
Clear Sky ◽  
Tropical Precipitation ◽  
Precipitation Response ◽  
Atmospheric General Circulation Models ◽  
The Impact

Abstract A subtropical continent is added to two aquaplanet atmospheric general circulation models (AGCMs) to better understand the influence of land on tropical circulation and precipitation. The first model, the gray-radiation moist (GRaM) AGCM, has simplified physics, while the second model, the GFDL Atmospheric Model version 2.1 (AM2.1), is a fully comprehensive AGCM. Both models have a continent that is 60° wide in longitude from 10° to 30°N, in an otherwise slab-ocean-covered world. The precipitation response varies with cloudy- and clear-sky feedbacks and depends on continental albedo. In GRaM simulations with a continent, precipitation in the Northern Hemisphere decreases mostly as a result of decreased evaporation. In AM2.1 simulations, precipitation also shifts southward via Hadley circulation changes due to increasing albedo, but the radiative impact of clouds and moisture creates a more complex response. Results are similar when a seasonal cycle of insolation is included in AM2.1 simulations. The impact of a large, bright subtropical continent is to shift precipitation to the opposite hemisphere. In these simulations, the hemisphere of greater tropical precipitation is better predicted by the hemisphere with greater atmospheric energy input, as has been shown in previous literature, rather than the hemisphere that has higher surface temperature.

scholarly journals Seasonal Dependency of Tropical Precipitation Change under Global Warming

2020 ◽  
Vol 33 (18) ◽  
pp. 7897-7908 ◽  
Author(s):  
Yu-Fan Geng ◽  
Shang-Ping Xie ◽  
Xiao-Tong Zheng ◽  
Chuan-Yang Wang
Keyword(s):  
Global Warming ◽  
Deep Convection ◽  
Atmospheric Model ◽  
Precipitation Change ◽  
Dynamic Component ◽  
Tropical Precipitation ◽  
Eastern Equatorial Pacific ◽  
Warming Pattern ◽  
Sst Warming ◽  
Dynamic Components

AbstractTropical precipitation change under global warming varies with season. The present study investigates the characteristics and cause of the seasonality in rainfall change. Diagnostically, tropical precipitation change is decomposed into thermodynamic and dynamic components. The thermodynamic component represents the wet-get-wetter effect and its seasonality is due mostly to that in the mean vertical velocity, especially in the monsoon regions. The dynamic component includes the warmer-get-wetter effect due to the spatial variations in sea surface temperature (SST) warming, while the seasonality is due to that of the climatological SST and can be largely reproduced by an atmospheric model forced with the monthly climatological SST plus the annual-mean SST warming pattern. In the eastern equatorial Pacific where the SST warming is locally enhanced; for example, rainfall increases only during the March–May season when the climatological SST is high enough for deep convection. To the extent that the seasonality of tropical precipitation change over oceans arises mostly from that of the climatological SST, the results support the notion that reducing model biases in climatology improves regional rainfall projections.

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