scholarly journals Analysis of the Meridional Energy Transport by Atmospheric Overturning Circulations

2011 ◽  
Vol 68 (8) ◽  
pp. 1806-1820 ◽  
Author(s):  
Kristofer Döös ◽  
Johan Nilsson
Keyword(s):  
Mass Transport ◽  
Energy Transport ◽  
Cell Structure ◽  
Meridional Overturning Circulation ◽  
Specific Humidity ◽  
Moist Static Energy ◽  
Mean Flow ◽  
Vertical Coordinate ◽  
Meridional Overturning ◽  
Static Energy

Abstract The atmospheric meridional overturning circulation is computed using the interim European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-Interim) data. Meridional mass transport streamfunctions are calculated not only using pressure as a vertical coordinate but also using temperature, specific humidity, and geopotential height as generalized vertical coordinates. Moreover, mass transport streamfunctions are calculated using the latent, the dry static, or the moist static energy as generalized vertical coordinates. The total meridional energy transport can be obtained by integrating these streamfunctions “vertically” over their entire energy range. The time-averaged mass transport streamfunctions are also decomposed into mean-flow and eddy-induced components. The meridional mass transport streamfunctions with temperature and specific humidity as independent variables yield a two-cell structure with a tropical Hadley-like cell and a pronounced extratropical Ferrel-like cell, which carries warm and moist air poleward. These Ferrel-like cells are much stronger than the Eulerian zonal-mean Ferrel cell, a feature that can be understood by considering the residual circulation related to specific humidity or temperature. Regardless of the generalized vertical coordinate, the present meridional mass transport streamfunctions yield essentially a two-layer structure with one poleward and one equatorward branch. The strongest meridional overturning in the midlatitudes is obtained when the specific humidity or the moist static energy is used as the vertical coordinate, indicating that the specific humidity is the variable that best distinguishes between poleward- and equatorward-moving air in the lower troposphere.

Observed Long-Term Trends of the Atmospheric Circulation and of Dry and Moist Static Energies

2021 ◽  
Author(s):  
Christian Franzke ◽  
Nili Harnik
Keyword(s):  
Global Warming ◽  
Atmospheric Circulation ◽  
Zonal Wind ◽  
Energy Transport ◽  
Climate Model ◽  
Heat Fluxes ◽  
Specific Humidity ◽  
Storm Tracks ◽  
Moist Static Energy ◽  
Static Energy

<p>The atmospheric circulation response to global warming is an important problem which is theoretically still not well understood. This is a particular problem since climate model simulations provide uncertain, and at times contradictory, projections of future climate. In particular, it is still unclear how a warmer and moister atmosphere will affect the atmospheric circulation and mid-latitude storms. Here we perform a trend analysis of various atmospheric circulation measures and of the budgets of dry and moist static energy transports, which will contribute to our understanding of the role of moisture in circulation changes. Our analysis is based on the JRA-55 reanalysis data covering the period 1958 through 2018 for both winter and summer seasons. We focus our analysis on zonal mean quantities for the full latitudinal circles as well as for the Atlantic and Pacific sectors.</p><p>We find significant trends in zonal wind, eddy kinetic energy, Eady growth rate, diabatic heating rates, and specific humidity. The zonal wind changes appear to be in thermal wind balance. We also find that the increase in specific humidity is intensifying the trend in eddy moist static energy transport when compared with eddy dry static energy transport. Since band-pass filtered eddy moist static energy transports are related to storm tracks this suggests that increasing moisture in the atmosphere is contributing to the intensification and meridional shifts of storm tracks. Furthermore, our results suggest that global warming predominantly enhance heat fluxes and to a lesser extend momentum fluxes.</p>

scholarly journals Impacts of Shallow Convection on MJO Simulation: A Moist Static Energy and Moisture Budget Analysis

2013 ◽  
Vol 26 (8) ◽  
pp. 2417-2431 ◽  
Author(s):  
Qiongqiong Cai ◽  
Guang J. Zhang ◽  
Tianjun Zhou
Keyword(s):  
Boundary Layer ◽  
Deep Convection ◽  
Lower Troposphere ◽  
Longwave Radiation ◽  
Reanalysis Data ◽  
Specific Humidity ◽  
Moist Static Energy ◽  
Shallow Convection ◽  
Budget Analysis ◽  
Static Energy

Abstract The role of shallow convection in Madden–Julian oscillation (MJO) simulation is examined in terms of the moist static energy (MSE) and moisture budgets. Two experiments are carried out using the NCAR Community Atmosphere Model, version 3.0 (CAM3.0): a “CTL” run and an “NSC” run that is the same as the CTL except with shallow convection disabled below 700 hPa between 20°S and 20°N. Although the major features in the mean state of outgoing longwave radiation, 850-hPa winds, and vertical structure of specific humidity are reasonably reproduced in both simulations, moisture and clouds are more confined to the planetary boundary layer in the NSC run. While the CTL run gives a better simulation of the MJO life cycle when compared with the reanalysis data, the NSC shows a substantially weaker MJO signal. Both the reanalysis data and simulations show a recharge–discharge mechanism in the MSE evolution that is dominated by the moisture anomalies. However, in the NSC the development of MSE and moisture anomalies is weaker and confined to a shallow layer at the developing phases, which may prevent further development of deep convection. By conducting the budget analysis on both the MSE and moisture, it is found that the major biases in the NSC run are largely attributed to the vertical and horizontal advection. Without shallow convection, the lack of gradual deepening of upward motion during the developing stage of MJO prevents the lower troposphere above the boundary layer from being preconditioned for deep convection.

scholarly journals Trends in continental temperature and humidity directly linked to ocean warming

2018 ◽  
Vol 115 (19) ◽  
pp. 4863-4868 ◽  
Author(s):  
Michael P. Byrne ◽  
Paul A. O’Gorman
Keyword(s):  
Relative Humidity ◽  
Land Surface ◽  
Moisture Transport ◽  
Climate Change Impacts ◽  
Atmospheric Dynamics ◽  
Specific Humidity ◽  
Climate Projections ◽  
Moist Static Energy ◽  
Temperature And Humidity ◽  
Static Energy

In recent decades, the land surface has warmed substantially more than the ocean surface, and relative humidity has fallen over land. Amplified warming and declining relative humidity over land are also dominant features of future climate projections, with implications for climate-change impacts. An emerging body of research has shown how constraints from atmospheric dynamics and moisture budgets are important for projected future land–ocean contrasts, but these ideas have not been used to investigate temperature and humidity records over recent decades. Here we show how both the temperature and humidity changes observed over land between 1979 and 2016 are linked to warming over neighboring oceans. A simple analytical theory, based on atmospheric dynamics and moisture transport, predicts equal changes in moist static energy over land and ocean and equal fractional changes in specific humidity over land and ocean. The theory is shown to be consistent with the observed trends in land temperature and humidity given the warming over ocean. Amplified land warming is needed for the increase in moist static energy over drier land to match that over ocean, and land relative humidity decreases because land specific humidity is linked via moisture transport to the weaker warming over ocean. However, there is considerable variability about the best-fit trend in land relative humidity that requires further investigation and which may be related to factors such as changes in atmospheric circulations and land-surface properties.

Linkage of Arctic Sea Ice and Energy Transport

2021 ◽  
Author(s):  
Ines Höschel ◽  
Dörthe Handorf ◽  
Christoph Jacobi ◽  
Johannes Quaas
Keyword(s):  
Sea Ice ◽  
Large Scale ◽  
Energy Transport ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Moist Static Energy ◽  
Large Scale Circulation ◽  
Arctic Sea ◽  
Rossby Wave Propagation ◽  
Static Energy

<p>The loss of Arctic sea ice as a consequence of global warming is changing the forcing of the atmospheric large-scale circulation.  Areas not covered with sea ice anymore may act as an additional heat source.  Associated changes in Rossby wave propagation can initiate tropospheric and stratospheric pathways of Arctic - Mid-latitude linkages.  These pathways have the potential to impact on the large-scale energy transport into the Arctic.  On the other hand, studies show that the large-scale circulation contributes to Arctic warming by poleward transport of moist static energy. This presentation shows results from research within the Transregional Collaborative Research Center “ArctiC Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms (AC)3” funded by the Deutsche Forschungsgemeinschaft.  Using the ERA interim and ERA5 reanalyses the meridional moist static energy transport during high ice and low ice periods is compared.  The investigation discriminates between contributions from planetary and synoptic scale.  Special emphasis is put on the seasonality of the modulations of the large-scale energy transport.</p>

scholarly journals Moisture Modes and the Eastward Propagation of the MJO

2013 ◽  
Vol 70 (1) ◽  
pp. 187-192 ◽  
Author(s):  
Adam Sobel ◽  
Eric Maloney
Keyword(s):  
Growth Rate ◽  
Moisture Gradient ◽  
Moist Static Energy ◽  
Mean Flow ◽  
Considerable Uncertainty ◽  
Low Level ◽  
Zonal Advection ◽  
The Mean ◽  
Frictional Convergence ◽  
Static Energy

Abstract The authors discuss modifications to a simple linear model of intraseasonal moisture modes. Wind–evaporation feedbacks were shown in an earlier study to induce westward propagation in an eastward mean low-level flow in this model. Here additional processes, which provide effective sources of moist static energy to the disturbances and which also depend on the low-level wind, are considered. Several processes can act as positive sources in perturbation easterlies: zonal advection (if the mean zonal moisture gradient is eastward), modulation of synoptic eddy drying by the MJO-scale wind perturbations, and frictional convergence. If the sum of these is stronger than the wind–evaporation feedback—as observations suggest may be the case, though with considerable uncertainty—the model produces unstable modes that propagate weakly eastward relative to the mean flow. With a small amount of horizontal diffusion or other scale-selective damping, the growth rate is greatest at the largest horizontal scales and decreases monotonically with wavenumber.

scholarly journals Simple Estimates of Polar Amplification in Moist Diffusive Energy Balance Models

2018 ◽  
Vol 31 (15) ◽  
pp. 5811-5824 ◽  
Author(s):  
Timothy M. Merlis ◽  
Matthew Henry
Keyword(s):  
Energy Balance ◽  
General Circulation ◽  
Energy Transport ◽  
Circulation Model ◽  
Thermodynamic Quantity ◽  
Solar Radiation Management ◽  
Moist Static Energy ◽  
Polar Amplification ◽  
Energy Balance Models ◽  
Static Energy

Diffusive energy balance models (EBMs) that use moist static energy, rather than temperature, as the thermodynamic variable to determine the energy transport provide an idealized framework to understand the pattern of radiatively forced surface warming. These models have a polar amplified warming pattern that is quantitatively similar to general circulation model simulations. Even without surface albedo changes or other spatially varying feedbacks, they simulate polar amplification that results from increased poleward energy transport with warming. Here, two estimates for polar amplification are presented that do not require numerical solution of the EBM governing equation. They are evaluated relative to the results of numerical moist EBM solutions. One estimate considers only changes in a moist thermodynamic quantity (assuming that the increase in energy transport results in a spatially uniform change in moist static energy in the warmed climate) and has more polar amplification than the EBM solution. The other estimate uses a new solution of a truncated form of the moist EBM equation, which allows for a temperature change that is consistent with both the dry and latent energy transport changes, as well as radiative changes. The truncated EBM solution provides an estimate for polar amplification that is nearly identical to that of the numerical EBM solution and only depends on the EBM parameters and climatology of temperature. This solution sheds light on the dependence of polar amplification on the climatological temperature distribution and offers an estimate of the residual polar warming in solar radiation management geoengineered climates.

scholarly journals The Response of the ITCZ to Extratropical Thermal Forcing: Idealized Slab-Ocean Experiments with a GCM

2008 ◽  
Vol 21 (14) ◽  
pp. 3521-3532 ◽  
Author(s):  
Sarah M. Kang ◽  
Isaac M. Held ◽  
Dargan M. W. Frierson ◽  
Ming Zhao
Keyword(s):  
Mixed Layer ◽  
Energy Transport ◽  
Meridional Overturning Circulation ◽  
Convection Scheme ◽  
Thermal Forcing ◽  
Tropical Precipitation ◽  
Model Configuration ◽  
Mixed Layer Ocean ◽  
Meridional Overturning ◽  
The Tropics

Abstract Using a comprehensive atmospheric GCM coupled to a slab mixed layer ocean, experiments are performed to study the mechanism by which displacements of the intertropical convergence zone (ITCZ) are forced from the extratropics. The northern extratropics are cooled and the southern extratropics are warmed by an imposed cross-equatorial flux beneath the mixed layer, forcing a southward shift in the ITCZ. The ITCZ displacement can be understood in terms of the degree of compensation between the imposed oceanic flux and the resulting response in the atmospheric energy transport in the tropics. The magnitude of the ITCZ displacement is very sensitive to a parameter in the convection scheme that limits the entrainment into convective plumes. The change in the convection scheme affects the extratropical–tropical interactions in the model primarily by modifying the cloud response. The results raise the possibility that the response of tropical precipitation to extratropical thermal forcing, important for a variety of problems in climate dynamics (such as the response of the tropics to the Northern Hemisphere ice sheets during glacial maxima or to variations in the Atlantic meridional overturning circulation), may be strongly dependent on cloud feedback. The model configuration described here is suggested as a useful benchmark helping to quantify extratropical–tropical interactions in atmospheric models.

Annular Mode Variability of the Atmospheric Meridional Energy Transport and Circulation

2015 ◽  
Vol 72 (5) ◽  
pp. 2070-2089 ◽  
Author(s):  
Ray Yamada ◽  
Olivier Pauluis
Keyword(s):  
Energy Transport ◽  
Energy Levels ◽  
Storm Track ◽  
Momentum Balance ◽  
Moist Static Energy ◽  
Residual Circulation ◽  
Meridional Transport ◽  
Annular Modes ◽  
Poleward Shift ◽  
Static Energy

Abstract Month-to-month variability in the meridional atmospheric energy transport is analyzed in the Modern-Era Retrospective Analysis for Research and Applications (MERRA) reanalysis for 1979–2012. The meridional transport of moist static energy (MSE) is composited onto the high and low phases of the northern and southern annular modes (NAM and SAM). While the high phase of the NAM and SAM is known to involve a poleward shift in the midlatitude storm track and jet, it is shown here that the distribution of poleward MSE transport shifts equatorward. This change is explained by examining the variability of the underlying meridional circulation. In particular, changes in the mass transport averaged on dry and moist static energy levels are considered. These circulations have an advantage over the conventional Eulerian circulation for explaining the total energy transport. They are computed using the statistical transformed Eulerian-mean (STEM) formulation, which provides a decomposition of the circulation into Eulerian-mean and eddy-driven components. The equatorward shift in the MSE transport is largely explained by a poleward shift of the Ferrel cell, while changes in the eddy-driven circulation have a comparatively small effect on the energy transport. The changes in the residual circulation and jet are shown to be consistent through momentum balance arguments. Mean-eddy feedback mechanisms that drive and sustain the annular modes are discussed at the end as a possible explanation for why the changes in the eddy-driven circulation are weak compared to the changes in the Eulerian circulation.

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.

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