scholarly journals Mechanisms for Tropical Tropospheric Circulation Change in Response to Global Warming*

2012 ◽  
Vol 25 (8) ◽  
pp. 2979-2994 ◽  
Author(s):  
Jian Ma ◽  
Shang-Ping Xie ◽  
Yu Kosaka
Keyword(s):  
Global Warming ◽  
General Circulation ◽  
Vertical Motion ◽  
Circulation Model ◽  
Hadley Circulation ◽  
Walker Circulation ◽  
Hadley Cell ◽  
Circulation Change ◽  
Tropospheric Circulation ◽  
Sst Warming

Abstract The annual-mean tropospheric circulation change in global warming is studied by comparing the response of an atmospheric general circulation model (GCM) to a spatial-uniform sea surface temperature (SST) increase (SUSI) with the response of a coupled ocean–atmosphere GCM to increased greenhouse gas concentrations following the A1B scenario. In both simulations, tropospheric warming follows the moist adiabat in the tropics, and static stability increases globally in response to SST warming. A diagnostic framework is developed based on a linear baroclinic model (LBM) of the atmosphere. The mean advection of stratification change (MASC) by climatological vertical motion, often neglected in interannual variability, is an important thermodynamic term for global warming. Once MASC effect is included, LBM shows skills in reproducing GCM results by prescribing latent heating diagnosed from the GCMs. MASC acts to slow down the tropical circulation. This is most clear in the SUSI run where the Walker circulation slows down over the Pacific without any change in SST gradient. MASC is used to decelerate the Hadley circulation, but spatial patterns of SST warming play an important role. Specifically, the SST warming is greater in the Northern than Southern Hemisphere, an interhemispheric asymmetry that decelerates the Hadley cell north, but accelerates it south of the equator. The MASC and SST-pattern effects are on the same order of magnitude in our LBM simulations. The former is presumably comparable across GCMs, while SST warming patterns show variations among models in both shape and magnitude. Uncertainties in SST patterns account for intermodel variability in Hadley circulation response to global warming (especially on and south of the equator).

scholarly journals Axisymmetric Constraints on Cross-Equatorial Hadley Cell Extent

2019 ◽  
Vol 76 (6) ◽  
pp. 1547-1564 ◽  
Author(s):  
Spencer A. Hill ◽  
Simona Bordoni ◽  
Jonathan L. Mitchell
Keyword(s):  
Angular Momentum ◽  
Zonal Wind ◽  
General Circulation ◽  
Potential Temperature ◽  
Circulation Model ◽  
Hadley Circulation ◽  
Hadley Cell ◽  
Equal Area ◽  
Area Model ◽  
Hadley Cells

Abstract We consider the relevance of known constraints from each of Hide’s theorem, the angular momentum–conserving (AMC) model, and the equal-area model on the extent of cross-equatorial Hadley cells. These theories respectively posit that a Hadley circulation must span all latitudes where the radiative–convective equilibrium (RCE) absolute angular momentum satisfies or or where the RCE absolute vorticity satisfies ; all latitudes where the RCE zonal wind exceeds the AMC zonal wind; and over a range such that depth-averaged potential temperature is continuous and that energy is conserved. The AMC model requires knowledge of the ascent latitude , which needs not equal the RCE forcing maximum latitude . Whatever the value of , we demonstrate that an AMC cell must extend at least as far into the winter hemisphere as the summer hemisphere. The equal-area model predicts , always placing it poleward of . As is moved poleward (at a given thermal Rossby number), the equal-area-predicted Hadley circulation becomes implausibly large, while both and become increasingly displaced poleward of the minimal cell extent based on Hide’s theorem (i.e., of supercritical forcing). In an idealized dry general circulation model, cross-equatorial Hadley cells are generated, some spanning nearly pole to pole. All homogenize angular momentum imperfectly, are roughly symmetric in extent about the equator, and appear in extent controlled by the span of supercritical forcing.

Regional Tropical Precipitation Change Mechanisms in ECHAM4/OPYC3 under Global Warming*

2006 ◽  
Vol 19 (17) ◽  
pp. 4207-4223 ◽  
Author(s):  
Chia Chou ◽  
J. David Neelin ◽  
Jien-Yi Tu ◽  
Cheng-Ta Chen
Keyword(s):  
Global Warming ◽  
Greenhouse Gases ◽  
General Circulation Model ◽  
General Circulation ◽  
Vertical Motion ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Additional Contribution ◽  
Tropical Precipitation ◽  
Precipitation Anomalies

Abstract Mechanisms of global warming impacts on regional tropical precipitation are examined in a coupled atmosphere–ocean general circulation model (ECHAM4/OPYC3). The pattern of the regional tropical precipitation changes, once established, tends to persist, growing in magnitude as greenhouse gases increase. The sulfate aerosol induces regional tropical precipitation anomalies similar to the greenhouse gases but with opposite sign, thus reducing the early signal. Evidence for two main mechanisms, the upped-ante and the anomalous gross moist stability (M′) mechanisms (previously proposed in an intermediate complexity model), is found in this more comprehensive coupled general circulation model. Preferential moisture increase occurs in convection zones. The upped-ante mechanism signature of dry advection from nonconvective regions is found in tropical drought regions on the margins of convection zones. Here advection in both the atmospheric boundary layer and lower free troposphere are found to be important, with an additional contribution from horizontal temperature transport in some locations. The signature of the M′ mechanism—moisture convergence due to increased moisture in regions of large mean vertical motion—enhances precipitation within strong convective regions. Ocean dynamical feedbacks can be assessed by net surface flux, the main example being the El Niño–like shift of the equatorial Pacific convection zone. Cloud–radiative feedbacks are found to oppose precipitation anomalies over ocean regions.

scholarly journals Pacific Influences on Tropical Atlantic Teleconnections to the Southern Hemisphere High Latitudes

2016 ◽  
Vol 29 (18) ◽  
pp. 6425-6444 ◽  
Author(s):  
Graham R. Simpkins ◽  
Yannick Peings ◽  
Gudrun Magnusdottir
Keyword(s):  
Climate Variability ◽  
Southern Hemisphere ◽  
Rossby Wave ◽  
General Circulation ◽  
Wave Train ◽  
Circulation Model ◽  
Hadley Circulation ◽  
Walker Circulation ◽  
Tropical Atlantic ◽  
Dynamical Mechanism

Abstract Several recent studies have connected Antarctic climate variability to tropical Atlantic sea surface temperatures (SST), proposing a Rossby wave response from the Atlantic as the primary dynamical mechanism. In this investigation, reanalysis data and atmospheric general circulation model experiments are used to further diagnose these dynamical links. Focus is placed on the possible mediating role of Pacific processes, motivated by the similar spatial characteristics of Southern Hemisphere (SH) teleconnections associated with tropical Atlantic and Pacific SST variability. During austral winter (JJA), both reanalyses and model simulations reveal that Atlantic teleconnections represent a two-mechanism process, whereby increased tropical Atlantic SST promotes two conditions: 1) an intensification of the local Atlantic Hadley circulation (HC), driven by enhanced interaction between SST anomalies and the ITCZ, that increases convergence at the descending branch, establishing anomalous vorticity forcing from which a Rossby wave emanates, expressed as a pattern of alternating positive and negative geopotential height anomalies across the SH extratropics (the so-called HC-driven components); and 2) perturbations to the zonal Walker circulation (WC), driven primarily by an SST-induced amplification, that creates a pattern of anomalous upper-level convergence across the central/western Pacific, from which an ENSO-like Rossby wave train can be triggered (the so-called WC-driven components). While the former are found to dominate, the WC-driven components play a subsidiary yet important role. Indeed, it is the superposition of these two separate but interrelated mechanisms that gives the overall observed response. By demonstrating an additional Pacific-related component to Atlantic teleconnections, this study highlights the need to consider Atlantic–Pacific interactions when diagnosing tropical-related climate variability in the SH extratropics.

scholarly journals Understanding Hadley Cell Expansion versus Contraction: Insights from Simplified Models and Implications for Recent Observations

2013 ◽  
Vol 26 (12) ◽  
pp. 4304-4321 ◽  
Author(s):  
Neil F. Tandon ◽  
Edwin P. Gerber ◽  
Adam H. Sobel ◽  
Lorenzo M. Polvani
Keyword(s):  
Global Warming ◽  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Circulation Model ◽  
Hadley Cell ◽  
Thermal Forcing ◽  
Narrow Region ◽  
Definition Of ◽  
The Tropics

Abstract This study seeks a deeper understanding of the causes of Hadley Cell (HC) expansion, as projected under global warming, and HC contraction, as observed under El Niño. Using an idealized general circulation model, the authors show that a thermal forcing applied to a narrow region around the equator produces “El Niño–like” HC contraction, while a forcing with wider meridional extent produces “global warming–like” HC expansion. These circulation responses are sensitive primarily to the thermal forcing’s meridional structure and are less sensitive to its vertical structure. If the thermal forcing is confined to the midlatitudes, the amount of HC expansion is more than three times that of a forcing of comparable amplitude that is spread over the tropics. This finding may be relevant to recently observed trends of rapid tropical widening. The shift of the HC edge is explained using a very simple model in which the transformed Eulerian mean (TEM) circulation acts to diffuse heat meridionally. In this context, the HC edge is defined as the downward maximum of residual vertical velocity in the upper troposphere ; this corresponds well with the conventional Eulerian definition of the HC edge. In response to a positive thermal forcing, there is anomalous diabatic cooling, and hence anomalous TEM descent, on the poleward flank of the thermal forcing. This causes the HC edge () to shift toward the descending anomaly, so that a narrow forcing causes HC contraction and a wide forcing causes HC expansion.

A Closer Comparison of Early and Late-Winter Atmospheric Trends in the Northern Hemisphere

2005 ◽  
Vol 18 (16) ◽  
pp. 3204-3216 ◽  
Author(s):  
Yongyun Hu ◽  
Ka Kit Tung ◽  
Jiping Liu
Keyword(s):  
Northern Hemisphere ◽  
General Circulation ◽  
Polar Vortex ◽  
Circulation Model ◽  
Hadley Circulation ◽  
Reanalysis Data ◽  
Hadley Cell ◽  
The Arctic ◽  
Late Winter ◽  
Positive Trend

Abstract Decadal trends are compared in various fields between Northern Hemisphere early winter, November–December (ND), and late-winter, February–March (FM), months using reanalysis data. It is found that in the extratropics and polar region the decadal trends display nearly opposite tendencies between ND and FM during the period from 1979 to 2003. Dynamical trends in late winter (FM) reveal that the polar vortex has become stronger and much colder and wave fluxes from the troposphere to the stratosphere are weaker, consistent with the positive trend of the Arctic Oscillation (AO) as found in earlier studies, while trends in ND appear to resemble a trend toward the low-index polarity of the AO. In the Tropics, the Hadley circulation shows significant intensification in both ND and FM, with stronger intensification in FM. Unlike the Hadley cell, the Ferrel cell shows opposite trends between ND and FM, with weakening in ND and strengthening in FM. Comparison of the observational results with general circulation model simulations is also discussed.

scholarly journals Effects of Climatological Model Biases on the Projection of Tropical Climate Change

2015 ◽  
Vol 28 (24) ◽  
pp. 9909-9917 ◽  
Author(s):  
Zhen-Qiang Zhou ◽  
Shang-Ping Xie
Keyword(s):  
Climate Change ◽  
Global Warming ◽  
General Circulation ◽  
Climate Models ◽  
Circulation Model ◽  
Walker Circulation ◽  
Tropical Climate ◽  
Equatorial Pacific ◽  
Model Biases ◽  
Tropical Climate Change

Abstract Climate models suffer from long-standing biases, including the double intertropical convergence zone (ITCZ) problem and the excessive westward extension of the equatorial Pacific cold tongue. An atmospheric general circulation model is used to investigate how model biases in the mean state affect the projection of tropical climate change. The model is forced with a pattern of sea surface temperature (SST) increase derived from a coupled simulation of global warming but uses an SST climatology derived from either observations or a coupled historical simulation. The comparison of the experiments reveals that the climatological biases have important impacts on projected changes in the tropics. Specifically, during February–April when the climatological ITCZ displaces spuriously into the Southern Hemisphere, the model overestimates (underestimates) the projected rainfall increase in the warmer climate south (north) of the equator over the eastern Pacific. Furthermore, the global warming–induced Walker circulation slowdown is biased weak in the projection using coupled model climatology, suggesting that the projection of the reduced equatorial Pacific trade winds may also be underestimated. This is related to the bias that the climatological Walker circulation is too weak in the model, which is in turn due to a too-weak mean SST gradient in the zonal direction. The results highlight the importance of improving the climatological simulation for more reliable projections of regional climate change.

scholarly journals The Response of the Tropospheric Circulation to Water Vapor–Like Forcings in the Stratosphere

2011 ◽  
Vol 24 (21) ◽  
pp. 5713-5720 ◽  
Author(s):  
Neil F. Tandon ◽  
Lorenzo M. Polvani ◽  
Sean M. Davis
Keyword(s):  
Water Vapor ◽  
General Circulation ◽  
Significant Contribution ◽  
Circulation Model ◽  
Hadley Cell ◽  
Model Resolution ◽  
Stratospheric Water Vapor ◽  
Forcing Function ◽  
Tropospheric Circulation ◽  
Opposite Response

Abstract An idealized, dry general circulation model is used to examine the response of the tropospheric circulation to thermal forcings that mimic changes in stratospheric water vapor (SWV). It is found that SWV-like cooling in the stratosphere produces a poleward-shifted, strengthened jet and an expanded, weakened Hadley cell. This response is shown to be almost entirely driven by cooling located in the extratropical lower stratosphere; when cooling is limited to the tropical stratosphere, it generates a much weaker and qualitatively opposite response. It is demonstrated that these circulation changes arise independently of any changes in tropopause height, are insensitive to the detailed structure of the forcing function, and are robust to model resolution. The responses are quantitatively of the same order as those due to well-mixed greenhouse gases, suggesting a potentially significant contribution of SWV to past and future changes in the tropospheric circulation.

scholarly journals Estimating the Continental Response to Global Warming Using Pattern-Scaled Sea Surface Temperatures and Sea Ice

2016 ◽  
Vol 29 (24) ◽  
pp. 9125-9139 ◽  
Author(s):  
Adeline Bichet ◽  
Paul J. Kushner ◽  
Lawrence Mudryk
Keyword(s):  
Global Warming ◽  
Sea Ice ◽  
General Circulation ◽  
Circulation Model ◽  
Tropical Indian Ocean ◽  
Sea Surface ◽  
Climate Projections ◽  
Western Boundary ◽  
Sea Ice Concentration ◽  
Continental Climate

Abstract Better constraining the continental climate response to anthropogenic forcing is essential to improve climate projections. In this study, pattern scaling is used to extract, from observations, the patterned response of sea surface temperature (SST) and sea ice concentration (SICE) to anthropogenically dominated long-term global warming. The SST response pattern includes a warming of the tropical Indian Ocean, the high northern latitudes, and the western boundary currents. The SICE pattern shows seasonal variations of the main locations of sea ice loss. These SST–SICE response patterns are used to drive an ensemble of an atmospheric general circulation model, the National Center for Atmospheric Research (NCAR) Community Atmosphere Model, version 5 (CAM5), over the period 1980–2010 along with a standard AMIP ensemble using observed SST—SICE. The simulations enable attribution of a variety of observed trends of continental climate to global warming. On the one hand, the warming trends observed in all seasons across the entire Northern Hemisphere extratropics result from global warming, as does the snow loss observed over the northern midlatitudes and northwestern Eurasia. On the other hand, 1980–2010 precipitation trends observed in winter over North America and in summer over Africa result from the recent decreasing phase of the Pacific decadal oscillation and the recent increasing phase of the Atlantic multidecadal oscillation, respectively, which are not part of the global warming signal. The method holds promise for near-term decadal climate prediction but as currently framed cannot distinguish regional signals associated with oceanic internal variability from aerosol forcing and other sources of short-term forcing.

scholarly journals Summertime precipitation in Hokkaido and Kyushu, Japan in response to global warming

2021 ◽  
Author(s):  
Daichi Takabatake ◽  
Masaru Inatsu
Keyword(s):  
Global Warming ◽  
Tropical Cyclones ◽  
General Circulation ◽  
Dynamical Downscaling ◽  
Circulation Model ◽  
Policy Decision ◽  
Moisture Flux ◽  
Specific Humidity ◽  
Future Climate Change ◽  
Moisture Flux Convergence

Abstract We analyzed a large ensemble dataset called the database for Policy Decision Making for Future climate change (d4PDF), which contains 60-km resolution atmospheric general circulation model output and 20-km resolution dynamical downscaling for the Japanese domain. The increase in moisture and precipitation, and their global warming response in June–July–August were described focusing on the differences between Hokkaido and Kyushu. The results suggested that the specific humidity increased almost following the Clausius Clapeyron relation, but the change in stationary circulation suppressed the precipitation increase, except for in western Kyushu. The + 4 K climate in Hokkaido would be as hot and humid as the present climate in Kyushu. The circulation change related to the southward shift of the jet stream and an eastward shift of the Bonin high weakened the moisture flux convergence via a stationary field over central Japan including eastern Kyushu. The transient eddy activity counteracted the increase in humidity, so that the moisture flux convergence and precipitation did not change much over Hokkaido. Because the contribution of tropical cyclones to the total precipitation was at most 10%, the decrease in the number of tropical cyclones did not explain the predicted change in precipitation.

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