scholarly journals Atmosphere–Ocean Interactions and Their Footprint on Heat Transport Variability in the Northern Hemisphere

2020 ◽  
Vol 33 (9) ◽  
pp. 3691-3710
Author(s):  
Yang Liu ◽  
Jisk Attema ◽  
Wilco Hazeleger
Keyword(s):  
Heat Transport ◽  
Time Scales ◽  
Northern Hemisphere ◽  
Climate Models ◽  
Energy Transport ◽  
Historical Records ◽  
Mean Flow ◽  
Oceanic Response ◽  
Atmospheric Variations ◽  
Almost All

AbstractInteractions between the atmosphere and ocean play a crucial role in redistributing energy, thereby maintaining the energy balance of the climate system. Here, we examine the compensation between the atmosphere and ocean’s heat transport variations. Motivated by previous studies with mostly numerical climate models, this so-called Bjerknes compensation is studied using reanalysis datasets. We find that atmospheric energy transport (AMET) and oceanic energy transport (OMET) variability generally agree well among the reanalysis datasets. With multiple reanalysis products, we show that Bjerknes compensation is present at almost all latitudes from 40° to 70°N in the Northern Hemisphere from interannual to decadal time scales. The compensation rates peak at different latitudes across different time scales, but they are always located in the subtropical and subpolar regions. Unlike some experiments with numerical climate models, which attribute the compensation to the variation of transient eddy transports in response to the changes of OMET at multidecadal time scales, we find that the response of mean flow to the OMET variability leads to the Bjerknes compensation, and thus the shift of the Ferrel cell at midlatitudes at decadal time scales in winter. This cell itself is driven by the eddy momentum flux. The oceanic response to AMET variations is primarily wind driven. In summer, there is hardly any compensation and the proposed mechanism is not applicable. Given the short historical records, we cannot determine whether the ocean drives the atmospheric variations or the reverse.

scholarly journals Evidence for atmosphere-ocean meridional energy transport compensation in the past decades

2020 ◽  
Author(s):  
Wilco Hazeleger ◽  
Yang Liu ◽  
Jisk Attema
Keyword(s):  
Heat Transport ◽  
Time Scales ◽  
Climate Models ◽  
Energy Transport ◽  
Climate Modelling ◽  
Ocean Heat Transport ◽  
Ocean Reanalysis ◽  
Modelling Studies ◽  
Almost All ◽  
Atmospheric Heat

<p><span lang="EN-US">We present evidence of compensation between the atmosphere and ocean's meridional energy transport variations, also known as Bjerknes compensation. Motivated by previous studies with mostly numerical climate models, we analyze compensation using a range of atmosphere and ocean reanalysis datasets. We show that Bjerknes compensation is present at almost all latitudes from 40 degrees North to 70 degrees North in the Northern Hemisphere from interannual to decadal time scales. In contrast to results from some numerical climate models, which attribute the compensation to variations of eddy energy transports in the atmosphere in response to changes of ocean heat transport and sea ice at multi-decadal time scales, we find a response of the zonal mean of poleward energy transport to ocean heat transport variability that leads to compensation. This is apparent in a meridional shift of the Ferrel Cell at midlatitudes at decadal time scales in winter. This shift in the cell itself is driven by changes in the eddy momentum flux and related baroclinicity. The oceanic response to atmospheric heat transport variations associated by the shift is primarily wind driven. In summer, there is hardly compensation and the proposed mechanism is not at work. Interestingly, these results are robust among all reanalysis datasets and can provide a benchmark for climate modelling studies.</span></p>

scholarly journals Tropical Precipitation and Cross-Equatorial Ocean Heat Transport during the Mid-Holocene

2017 ◽  
Vol 30 (10) ◽  
pp. 3529-3547 ◽  
Author(s):  
Xiaojuan Liu ◽  
David S. Battisti ◽  
Aaron Donohoe
Keyword(s):  
Heat Transport ◽  
Northern Hemisphere ◽  
Ocean Circulation ◽  
Climate Models ◽  
Energy Transport ◽  
Hadley Cell ◽  
Upper Ocean ◽  
Ocean Heat Transport ◽  
Tropical Precipitation ◽  
Coupled Climate Models

Abstract Summertime insolation intensified in the Northern Hemisphere during the mid-Holocene, resulting in enhanced monsoonal precipitation. In this study, the authors examine the changes in the annual-mean tropical precipitation as well as changes in atmospheric circulation and upper-ocean circulation in the mid-Holocene compared to the preindustrial climate, as simulated by 12 coupled climate models from PMIP3. In addition to the predominant zonally asymmetric changes in tropical precipitation, there is a small northward shift in the location of intense zonal-mean precipitation (mean ITCZ) in the mid-Holocene in the majority (9 out of 12) of the coupled climate models. In contrast, the shift is southward in simulations using an atmospheric model coupled to a slab ocean. The northward mean ITCZ shift in the coupled simulations is due to enhanced northward ocean heat transport across the equator [OHT(EQ)], which demands a compensating southward atmospheric energy transport across the equator, accomplished by shifting the Hadley cell and hence the mean ITCZ northward. The increased northward OHT(EQ) is primarily accomplished by changes in the upper-ocean gyre circulation in the tropical Pacific acting on the zonally asymmetric climatological temperature distribution. The gyre intensification results from the intensification of the monsoonal winds in the Northern Hemisphere and the weakening of the winds in the Southern Hemisphere, both of which are forced directly by the insolation changes.

scholarly journals Synthesis and evaluation of historical meridional heat transport from midlatitudes towards the Arctic

2020 ◽  
Vol 11 (1) ◽  
pp. 77-96
Author(s):  
Yang Liu ◽  
Jisk Attema ◽  
Ben Moat ◽  
Wilco Hazeleger
Keyword(s):  
Climate Variability ◽  
Heat Transport ◽  
Climate Models ◽  
Energy Transport ◽  
Reanalysis Data ◽  
Arctic Climate ◽  
The Arctic ◽  
Global Ocean ◽  
Data Sets ◽  
Sea Ice Concentration

Abstract. Meridional energy transport (MET), both in the atmosphere (AMET) and ocean (OMET), has significant impact on the climate in the Arctic. In this study, we quantify AMET and OMET at subpolar latitudes from six reanalysis data sets. We investigate the differences between the data sets and we check the coherence between MET and the Arctic climate variability at interannual timescales. The results indicate that, although the mean transport in all data sets agrees well, the spatial distributions and temporal variations of AMET and OMET differ substantially among the reanalysis data sets. For the ocean, only after 2007, the low-frequency signals in all reanalysis products agree well. A further comparison with observed heat transport at 26.5∘ N and the subpolar Atlantic, and a high-resolution ocean model hindcast confirms that the OMET estimated from the reanalysis data sets are consistent with the observations. For the atmosphere, the differences between ERA-Interim and the Japanese 55-year Reanalysis (JRA-55) are small, while the Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2) differs from them. An extended analysis of linkages between Arctic climate variability and AMET shows that atmospheric reanalyses differ substantially from each other. Among the chosen atmospheric products, ERA-Interim and JRA-55 results are most consistent with those from coupled climate models. For the ocean, the Ocean Reanalysis System 4 (ORAS4) and Simple Ocean Data Assimilation version 3 (SODA3) agree well on the relation between OMET and sea ice concentration (SIC), while the GLobal Ocean reanalyses and Simulations version 3 (GLORYS2V3) deviates from those data sets. The regressions of multiple fields in the Arctic on both AMET and OMET suggest that the Arctic climate is sensitive to changes of meridional energy transport at subpolar latitudes in winter. Given the good agreement on the diagnostics among assessed reanalysis products, our study suggests that the reanalysis products are useful for the evaluation of energy transport. However, assessments of products with the AMET and OMET estimated from reanalysis data sets beyond interannual timescales should be conducted with great care and the robustness of results should be evaluated through intercomparison, especially when studying variability and interactions between the Arctic and midlatitudes.

Eddy Formation in the Tropical Atlantic Induced by Abrupt Changes in the Meridional Overturning Circulation

2009 ◽  
Vol 39 (11) ◽  
pp. 3021-3031 ◽  
Author(s):  
Marlos Goes ◽  
David P. Marshall ◽  
Ilana Wainer
Keyword(s):  
Reynolds Number ◽  
Time Scales ◽  
Northern Hemisphere ◽  
Meridional Overturning Circulation ◽  
Shear Instability ◽  
Tropical Atlantic ◽  
Mean Flow ◽  
Overturning Circulation ◽  
Meridional Overturning ◽  
The Impact

Abstract The variability of the meridional overturning circulation (MOC) in the upper tropical Atlantic basin is investigated using a reduced-gravity model in a simplified domain. Four sets of idealized numerical experiments are performed: (i) switch-on of the MOC until a fixed value when a constant northward flow is applied along the western boundary; (ii) MOC with a variable flow; (iii) MOC in a quasi-steady flow; and (iv) shutdown of the MOC in the Northern Hemisphere. Results from experiments (i) show that eddies are generated at the equatorial region by shear instability and detached northward; eddies are responsible for an enhancement of the mean flow and the variability of the MOC. Results from experiments (ii) show a transitional behavior of the MOC related to the eddy generation in interannual–decadal time scales as the Reynolds number varies due to the variations in the MOC. In experiments (iii), a critical Reynolds number Rec around 30 is found, above which eddies are generated. Experiments (iv) demonstrate that even after the collapse of MOC in the Northern Hemisphere, eddies can still be generated and carry energy across the equator into the Northern Hemisphere; these eddies act to attenuate the impact of the MOC shutdown on short time scales. The results described here may be particularly pertinent to ocean general circulation models in which the Reynolds number lies close to the bifurcation point separating the laminar and turbulent regimes.

Extracting the Buoyancy-Driven Atlantic Meridional Overturning Circulation

2020 ◽  
Vol 33 (11) ◽  
pp. 4697-4714
Author(s):  
Sarah M. Larson ◽  
Martha W. Buckley ◽  
Amy C. Clement
Keyword(s):  
Heat Transport ◽  
Time Scales ◽  
Northern Hemisphere ◽  
Gulf Stream ◽  
Coupled Model ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Low Pass ◽  
Meridional Overturning ◽  
Fully Coupled

AbstractVariations in the Atlantic meridional overturning circulation (AMOC) driven by buoyancy forcing are typically characterized as having a low-frequency time scale, interhemispheric structure, cross-equatorial heat transport, and linkages to the strength of Northern Hemisphere gyre circulations and the Gulf Stream. This study first tests whether these attributes ascribed to the AMOC are reproduced in a coupled model that is mechanically decoupled and, hence, is only buoyancy coupled. Overall, the mechanically decoupled model reproduces these attributes, with the exception that in the subpolar gyre, buoyancy drives AMOC variations on interannual to multidecadal time scales, yet only the multidecadal variations penetrate into the subtropics. A stronger AMOC is associated with a strengthening of the Northern Hemisphere gyre circulations, Gulf Stream, and northward oceanic heat transport throughout the basin. We then determine whether the characteristics in the mechanically decoupled model can be recovered by low-pass filtering the AMOC in a fully coupled version of the same model, a common approach used to isolate the buoyancy-driven AMOC. A major conclusion is that low-pass filtering the AMOC in the fully coupled model reproduces the buoyancy-driven AMOC pattern and most of the associated attributes, but not the statistics of the temporal variability. The strength of the AMOC–Gulf Stream connection is also not reproduced. The analyses reveal caveats that must be considered when choosing indexes and filtering techniques to estimate the buoyancy-driven AMOC. Results also provide insight on the latitudinal dependence of time scales and drivers of ocean circulation variability in coupled models, with potential implications for measurement and detection of the buoyancy-driven AMOC in the real world.

scholarly journals The Partitioning of Meridional Heat Transport from the Last Glacial Maximum to CO2 Quadrupling in Coupled Climate Models

2020 ◽  
Vol 33 (10) ◽  
pp. 4141-4165 ◽  
Author(s):  
Aaron Donohoe ◽  
Kyle C. Armour ◽  
Gerard H. Roe ◽  
David S. Battisti ◽  
Lily Hahn
Keyword(s):  
Heat Transport ◽  
Last Glacial Maximum ◽  
Climate Models ◽  
Energy Transport ◽  
Glacial Maximum ◽  
Meridional Heat Transport ◽  
Last Glacial ◽  
Coupled Climate Models ◽  
The Last Glacial Maximum ◽  
The Last Glacial

AbstractMeridional heat transport (MHT) is analyzed in ensembles of coupled climate models simulating climate states ranging from the Last Glacial Maximum (LGM) to quadrupled CO2. MHT is partitioned here into atmospheric (AHT) and implied oceanic (OHT) heat transports. In turn, AHT is partitioned into dry and moist energy transport by the meridional overturning circulation (MOC), transient eddy energy transport (TE), and stationary eddy energy transport (SE) using only monthly averaged model output that is typically archived. In all climate models examined, the maximum total MHT (AHT + OHT) is nearly climate-state invariant, except for a modest (4%, 0.3 PW) enhancement of MHT in the Northern Hemisphere (NH) during the LGM. However, the partitioning of MHT depends markedly on the climate state, and the changes in partitioning differ considerably among different climate models. In response to CO2 quadrupling, poleward implied OHT decreases, while AHT increases by a nearly compensating amount. The increase in annual-mean AHT is a smooth function of latitude but is due to a spatially inhomogeneous blend of changes in SE and TE that vary by season. During the LGM, the increase in wintertime SE transport in the NH midlatitudes exceeds the decrease in TE resulting in enhanced total AHT. Total AHT changes in the Southern Hemisphere (SH) are not significant. These results suggest that the net top-of-atmosphere radiative constraints on total MHT are relatively invariant to climate forcing due to nearly compensating changes in absorbed solar radiation and outgoing longwave radiation. However, the partitioning of MHT depends on detailed regional and seasonal factors.

Northern hemisphere atmospheric response to changes of atlantic ocean SST on decadal time scales: a GCM experiment

1990 ◽  
Vol 4 (3) ◽  
pp. 157-174 ◽  
Author(s):  
Andreas Hense ◽  
Rita Glowienka-Hense ◽  
Hans von Storch ◽  
Ursula Stähler
Keyword(s):  
Atlantic Ocean ◽  
Time Scales ◽  
Northern Hemisphere ◽  
Atmospheric Response

Eddy-mediated Hadley cell expansion due to axisymmetric angular momentum adjustment to greenhouse gas forcings

2021 ◽  
Author(s):  
Nicholas A. Davis ◽  
Thomas Birner
Keyword(s):  
Angular Momentum ◽  
Greenhouse Gas ◽  
Cell Expansion ◽  
Energy Transport ◽  
Baroclinic Instability ◽  
Temperature Response ◽  
Equilibrium Temperature ◽  
Hadley Cell ◽  
Mean Flow ◽  
Fully Coupled

AbstractThe poleward expansion of the Hadley cells is one of the most robust modeled responses to increasing greenhouse gas concentrations. There are many proposed mechanisms for expansion, and most are consistent with modeled changes in thermodynamics, dynamics, and clouds. The adjustment of the eddies and the mean flow to greenhouse gas forcings, and to one another, complicates any effort toward a deeper understanding. Here we modify the Gray Radiation AND Moist Aquaplanet (GRANDMA) model to uncouple the eddy and mean flow responses to forcings. When eddy forcings are held constant, the purely axisymmetric response of the Hadley cell to a greenhouse gas-like forcing is an intensification and poleward tilting of the cell with height in response to an axisymmetric increase in angular momentum in the subtropics. The angular momentum increase drastically alters the circulation response compared to axisymmetric theories, which by nature neglect this adjustment. Model simulations and an eddy diffusivity framework demonstrate that the axisymmetric increase in subtropical angular momentum – the direct manifestation of the radiative-convective equilibrium temperature response – drives a poleward shift of the eddy stresses which leads to Hadley cell expansion. Prescribing the eddy response to the greenhouse gas-like forcing shows that eddies damp, rather than drive, changes in angular momentum, moist static energy transport, and momentum transport. Expansion is not driven by changes in baroclinic instability, as would otherwise be diagnosed from the fully-coupled simulation. These modeling results caution any assessment of mechanisms for circulation change within the fully-coupled wave-mean flow system.

Opuntia ficus-indica (prickly pear).

2021 ◽  
Author(s):  
Nick Pasiecznik
Keyword(s):  
Vitamin C ◽  
Large Scale ◽  
Time Lag ◽  
Prickly Pear ◽  
Invasive Weeds ◽  
Historical Records ◽  
Opuntia Ficus Indica ◽  
Actual Risk ◽  
Invasive Spread ◽  
Almost All

Abstract O. ficus-indica is highly valued as a fruit-producing cactus, also yielding 'leaves' that are used as a vegetable and browsed by livestock. It has been introduced widely from its native Mexico to almost all countries where the climate is suitable. The fruit is very rich in vitamin C and is exploited commercially in many areas. Many countries, especially in Asia, have recently established large-scale commercial plantations. However, O. ficus-indica, like several other species of Opuntia, have been known to spread and become invasive weeds. Historical records, however, appear to indicate a time-lag of about 100 years between introduction and the beginnings of invasive spread thus the actual risk may be low.

scholarly journals Oceanic Overturning and Heat Transport: The Role of Background Diffusivity

2019 ◽  
Vol 32 (3) ◽  
pp. 701-716 ◽  
Author(s):  
Magnus Hieronymus ◽  
Jonas Nycander ◽  
Johan Nilsson ◽  
Kristofer Döös ◽  
Robert Hallberg
Keyword(s):  
Heat Transport ◽  
Large Scale ◽  
Energy Transport ◽  
Climate Model ◽  
Potential Temperature ◽  
Meridional Heat Transport ◽  
Sea Ice Extent ◽  
Antarctic Sea Ice ◽  
Meridional Overturning

The role of oceanic background diapycnal diffusion for the equilibrium climate state is investigated in the global coupled climate model CM2G. Special emphasis is put on the oceanic meridional overturning and heat transport. Six runs with the model, differing only by their value of the background diffusivity, are run to steady state and the statistically steady integrations are compared. The diffusivity changes have large-scale impacts on many aspects of the climate system. Two examples are the volume-mean potential temperature, which increases by 3.6°C between the least and most diffusive runs, and the Antarctic sea ice extent, which decreases rapidly as the diffusivity increases. The overturning scaling with diffusivity is found to agree rather well with classical theoretical results for the upper but not for the lower cell. An alternative empirical scaling with the mixing energy is found to give good results for both cells. The oceanic meridional heat transport increases strongly with the diffusivity, an increase that can only partly be explained by increases in the meridional overturning. The increasing poleward oceanic heat transport is accompanied by a decrease in its atmospheric counterpart, which keeps the increase in the planetary energy transport small compared to that in the ocean.

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