Dissertations / Theses on the topic 'Atmospheric circulation Vietnam Mathematical models'

The Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO) are the most pronounced modes of extratropical atmospheric wintertime variability in the Northern Hemisphere. This thesis investigates different aspects of the AO and NAO on the in traseasonal and seasonal time scales. First, the question of how the differences between the AO and NAO are influenced by the choice of the definitions of the NAO and to what extent the AO and NAO differ from each other is investigated using the daily NCEP/NCAR reanalysis data spanning 51 boreal winters. One AO index and four different NAO indices are used in this study. It is found that the AO and NAO are quite similar to each other when both are defined using pattern-based indices, while some notable differences are observed between them when the NAO is defined using a station/gridpoint-based index. Then the predictability of the AO and NAO is examined using a simple general circulation model (SGCM). Numerical experiments are performed to determine the sensitivity of the setup processes of the AO and NAO to the details of the initial conditions. The predictive skills for the AO and NAO are compared to each other. Finally, the potential role of tropical Pacific forcing in driving the seasonal variability of the AO is explored using both observations and the SGCM. The results indicate that a negative thermal forcing over the western tropical Pacific and a positive forcing north of the equatorial mid-Pacific play important roles in producing an AO-like atmospheric response.

Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2008.
Includes bibliographical references (p. 207-221).
This thesis studies the dynamics of a rotating compressible gas sphere, driven by internal convection, as a model for the dynamics on the giant planets. We develop a new general circulation model for the Jovian atmosphere, based on the MITgcm dynamical core augmenting the nonhydrostatic model. The grid extends deep into the planet's interior allowing the model to compute the dynamics of a whole sphere of gas rather than a spherical shell (including the strong variations in gravity and the equation of state). Different from most previous 3D convection models, this model is anelastic rather than Boussinesq and thereby incorporates the full density variation of the planet. We show that the density gradients caused by convection drive the system away from an isentropic and therefore barotropic state as previously assumed, leading to significant baroclinic shear. This shear is concentrated mainly in the upper levels and associated with baroclinic compressibility effects. The interior flow organizes in large cyclonically rotating columnar eddies parallel to the rotation axis, which drive upgradient angular momentum eddy fluxes, generating the observed equatorial superrotation. Heat fluxes align with the axis of rotation, contributing to the observed flat meridional emission. We show the transition from weak convection cases with symmetric spiraling columnar modes similar to those found in previous analytic linear theory, to more turbulent cases which exhibit similar, though less regular and solely cyclonic, convection columns which manifest on the surface in the form of waves embedded within the superrotation. We develop a mechanical understanding of this system and scaling laws by studying simpler configurations and the dependence on physical properties such as the rotation period, bottom boundary location and forcing structure. These columnar cyclonic structures propagate eastward, driven by dynamics similar to that of a Rossby wave except that the restoring planetary vorticity gradient is in the opposite direction, due to the spherical geometry in the interior.
(cont.) We further study these interior dynamics using a simplified barotropic annulus model, which shows that the planetary vorticity radial variation causes the eddy angular momentum flux divergence, which drives the superrotating equatorial flow. In addition we study the interaction of the interior dynamics with a stable exterior weather layer, using a quasigeostrophic two layer channel model on a beta plane, where the columnar interior is therefore represented by a negative beta effect. We find that baroclinic instability of even a weak shear can drive strong, stable multiple zonal jets. For this model we find an analytic nonlinear solution, truncated to one growing mode, that exhibits a multiple jet meridional structure, driven by the nonlinear interaction between the eddies. Finally, given the density field from our 3D convection model we derive the high order gravitational spectra of Jupiter, which is a measurable quantity for the upcoming JUNO mission to Jupiter.
by Yohai Kaspi.
Ph.D.

Thesis: Ph. D., Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 175-180).
This thesis explores the buoyancy-driven circulation in the Red Sea, using a combination of observations, as well as numerical modeling and analytical method. The first part of the thesis investigates the formation mechanism and spreading of Red Sea Overflow Water (RSOW) in the Red Sea. The preconditions required for open-ocean convection, which is suggested to be the formation mechanism of RSOW, are examined. The RSOW is identified and tracked as a layer with minimum potential vorticity and maximum chlorofluorocarbon-12. The pathway of the RSOW is also explored using numerical simulation. If diffusivity is not considered, the production rate of the RSOW is estimated to be 0.63 Sv using Walin's method. By comparing this 0.63 Sv to the actual RSOW transport at the Strait of Bab el Mandeb, it is implied that the vertical diffusivity is about 3.4 x10-5 m 2 s-1. The second part of the thesis studies buoyancy-forced circulation in an idealized Red Sea. Buoyancy-loss driven circulation in marginal seas is usually dominated by cyclonic boundary currents on f-plane, as suggested by previous observations and numerical modeling. This thesis suggests that by including [beta]-effect and buoyancy loss that increases linearly with latitude, the resultant mean Red Sea circulation consists of an anticyclonic gyre in the south and a cyclonic gyre in the north. In mid-basin, the northward surface flow crosses from the western boundary to the eastern boundary. The observational support is also reviewed. The mechanism that controls the crossover of boundary currents is further explored using an ad hoc analytical model based on PV dynamics. This ad hoc analytical model successfully predicts the crossover latitude of boundary currents. It suggests that the competition between advection of planetary vorticity and buoyancy-loss related term determines the crossover latitude. The third part of the thesis investigates three mechanisms that might account for eddy generation in the Red Sea, by conducting a series of numerical experiments. The three mechanisms are: i) baroclinic instability; ii) meridional structure of surface buoyancy losses; iii) cross-basin wind fields.
by Ping Zhai.
Ph. D.

Thesis (M.S.)--Joint Program in Oceanography/ Applied Ocean Science and Engineering, Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution, 2006.
"September 2006." Bibliography: p. 97-106.

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2012.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 221-236).
This thesis focuses on ocean circulation and atmospheric forcing in the Atlantic Ocean at the Last Glacial Maximum (LGM, 18-21 thousand years before present). Relative to the pre-industrial climate, LGM atmospheric CO₂ concentrations were about 90 ppm lower, ice sheets were much more extensive, and many regions experienced significantly colder temperatures. In this thesis a novel approach to dynamical reconstruction is applied to make estimates of LGM Atlantic Ocean state that are consistent with these proxy records and with known ocean dynamics. Ocean dynamics are described with the MIT General Circulation Model in an Atlantic configuration extending from 35°S to 75°N at 1° resolution. Six LGM proxy types are used to constrain the model: four compilations of near sea surface temperatures from the MARGO project, as well as benthic isotope records of [delta]¹⁸O and [delta]¹³C compiled by Marchal and Curry; 629 individual proxy records are used. To improve the fit of the model to the data, a least-squares fit is computed using an algorithm based on the model adjoint (the Lagrange multiplier methodology). The adjoint is used to compute improvements to uncertain initial and boundary conditions (the control variables). As compared to previous model-data syntheses of LGM ocean state, this thesis uses a significantly more realistic model of oceanic physics, and is the first to incorporate such a large number and diversity of proxy records. A major finding is that it is possible to find an ocean state that is consistent with all six LGM proxy compilations and with known ocean dynamics, given reasonable uncertainty estimates. Only relatively modest shifts from modern atmospheric forcing are required to fit the LGM data. The estimates presented herein succesfully reproduce regional shifts in conditions at the LGM that have been inferred from proxy records, but which have not been captured in the best available LGM coupled model simulations. In addition, LGM benthic [delta]¹⁸O and [delta]¹³C records are shown to be consistent with a shallow but robust Atlantic meridional overturning cell, although other circulations cannot be excluded.
by Holly Janine Dail.
Ph.D.

This thesis examines the development and validation of Canadian Land Surface Scheme (CLASS) for various wetland landscapes individually, along with an evaluation of modelled results over a heterogeneous surface with airborne observations. A further statistical analysis of the effects of land surface classification procedures over the study area and their influence on modelled results is performed. CLASS is tested over individual wetland types: bog, fen and marsh in a stand-alone (non-GCM coupled) mode. Atmospheric conditions are provided for the eight site locations from tower measured data, while each surface is parameterized within the model from site specific measurements. Resulting model turbulent and radiative flux output is then statistically evaluated against observed tower data. Findings show that while CLASS models vascular dominated wetland areas (fen and marsh) quite well, non-vascular wetlands (bogs) are poorly represented, even with improved soil descriptions. At times when the water table is close to the surface, evaporation is greatly overestimated, whereas lowered water tables generate a vastly underestimated latent heat flux. Because CLASS does not include a moisture transfer scheme applicable for non-vascular vegetation, the description of this vegetation type as either a vascular plant or bare soil appears inappropriate.
CLASS was then tuned for a specific bog location found in the Hudson Bay Lowland (HBL) during the Northern Wetlands Study (NOWES). With bog surfaces better described within the model, testing of CLASS over a highly heterogeneous 169 km2 HBL region is then undertaken. The model is first modified for lake and pond surfaces and then separate runs for bog, fen, lake and tree/shrub categories is undertaken. Using a GIS, the test region under which airborne flux measurements are available is divided into 104 grid cells and proportions of each surface type are calculated within each cell. Findings indicate that although the modelled grid average radiation and flux values are reasonably well reproduced (4% error for net radiation, 10% for latent heat flux and 30% for sensible heat flux), spatial agreement between modelled and observed grid cells is disappointing. (Abstract shortened by UMI.)

Both physical circulation and biogeochemical characteristics are unique in the Southern Ocean (SO) region, and are fundamentally different from those of the northern hemisphere. Moreover, according to previous research, the oceanic response to the trend of the Southern Annual Mode (SAM) has profound impacts on the future oceanic uptake of carbon dioxide in the SO. In other words, the climate and circulation of the SO are strongly coupled to the overlying atmospheric variability. However, while we have understanding on the SO physical circulation and have the ability to predict the future changes of the SO climate and physical processes, the link between the SO physical processes, the air-sea carbon flux, and correlated climate variability remains unknown. Even though scientists have been studying the spatial and temporal variability of the SO carbon flux and the associated biogeochemical processes, the spatial patterns and the magnitudes of the air-sea carbon flux do not agree between models and observations. Therefore, in this study, we utilized a modified version of a general circulation model (GCM) to performed realistic simulations of the SO carbon on seasonal to interannual timescales, and focused on the crucial physical and biogeochemical processes that control the carbon flux. The spatial pattern and the seasonal cycle of the air-sea carbon dioxide flux is calculated, and is broadly consistent with the climatological observations. The variability of air-sea carbon flux is mainly controlled by the gas exchange rate and the partial pressure of carbon dioxide, which is in turn controlled by the compensating changes in temperature and dissolved inorganic carbon. We investigated the seasonal variability of dissolved inorganic carbon based on different regional processes. Furthermore, we also investigated the dynamical adjustment of the surface carbon flux in response to the different gas exchange parameterizations, and conclude that parameterization has little impact on spatially integrated carbon flux. Our simulation well captured the SO carbon cycle variability on seasonal to interannual timescales, and we will improve our model by employ a better scheme of nutrient cycle, and consider more nutrients as well as ecological processes in our future study.

Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 209-215).
Observations from a three-year field program on the inner shelf south of Martha's Vineyard, MA and a numerical model are used to describe the effect of stratification on inner shelf circulation, transport, and sediment resuspension height. Thermal stratification above the bottom mixed layer is shown to cap the height to which sediment is resuspended. Stratification increases the transport driven by cross-shelf wind stresses, and this effect is larger in the response to offshore winds than onshore winds. However, a one-dimensional view of the dynamics is not sufficient to explain the relationship between circulation and stratification. An idealized, cross-shelf transect in a numerical model (ROMS) is used to isolate the effects of stratification, wind stress magnitude, surface heat flux, cross-shelf density gradient, and wind direction on the inner shelf response to the cross-shelf component of the wind stress. In well mixed and weakly stratified conditions, the cross-shelf density gradient can be used to predict the transport efficiency of the cross-shelf wind stress. In stratified conditions, the presence of an along-shelf wind stress component makes the inner shelf response to cross-shelf wind stress strongly asymmetric.
by Rachel Mandy Horwitz.
Ph.D.

Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2008.
Includes bibliographical references (p. [221]-232).
Marine ecosystems reflect the physical structure of their environment and the biological processes they carry out. This leads to spatial heterogeneity and temporal variability, some of which is imposed externally and some of which emerges from the ecological mechanisms themselves. The main focus of this thesis is on the formation of spatial patterns in the distribution of zooplankton arising from social interactions between individuals. In the Southern Ocean, krill often assemble in swarms and schools, the dynamics of which have important ecological consequences. Mathematical and numerical models are employed to study the interplay of biological and physical processes that contribute to the observed patchiness. The evolution of social behavior is simulated in a theoretical framework that includes zooplankton population dynamics, swimming behavior, and some aspects of the variability inherent to fluid environments. First, I formulate a model of resource utilization by a stage-structured predator population with density-dependent reproduction. Second, I incorporate the predator-prey dynamics into a spatially-explicit model, in which aggregations develop spontaneously as a result of linear instability of the uniform distribution. In this idealized ecosystem, benefits related to the local abundance of mates are offset by the cost of having to share resources with other group members. Third, I derive a weakly nonlinear approximation for the steady-state distributions of predator and prey biomass that captures the spatial patterns driven by social tendencies. Fourth, I simulate the schooling behavior of zooplankton in a variable environment; when turbulent flows generate patchiness in the resource field, schools can forage more efficiently than individuals.
(cont.) Taken together, these chapters demonstrate that aggregation/ schooling can indeed be the favored behavior when (i) reproduction (or other survival measures) increases with density in part of the range and (ii) mixing of prey into patches is rapid enough to offset the depletion. In the final two chapters, I consider sources of temporal variability in marine ecosystems. External perturbations amplified by nonlinear ecological interactions induce transient ex-cursions away from equilibrium; in predator-prey dynamics the amplitude and duration of these transients are controlled by biological processes such as growth and mortality. In the Southern Ocean, large-scale winds associated with ENSO and the Southern Annular Mode cause convective mixing, which in turn drives air-sea fluxes of carbon dioxide and oxygen. Whether driven by stochastic fluctuations or by climatic phenomena, variability of the biogeochemical/physical environment has implications for ecosystem dynamics.
by Ariane Verdy.
Ph.D.

Thesis (S.M.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2006.
Includes bibliographical references (p. 69-74).
Interactions between physical and biological processes in the Southern Ocean have significant impacts on local ecosystems as well as on global climate. In this thesis, I present evidence that the Southern Ocean circulation affects the variability of zooplankton and sea surface temperature, both of which are involved in air-sea exchanges of carbon dioxide. First, I examine the formation of spatial patterns in the distribution of Antarctic krill (Euphausia superba) resulting from social behavior. Turbulence of the flow is found to provide favorable conditions for the evolution social behavior in an idealized biological-physical model. Second, I analyze observations of sea surface temperature variability in the region of the Antarctic circumpolar current. Results suggest that propagating anomalies can be explained as a linear response to local atmospheric forcing by the Southern Annular Mode and remote forcing by El-Nifio southern oscillation, in the presence of advection by a mean flow.
by Ariane Verdy.
S.M.

Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), February 2013.
"February 2013." Cataloged from PDF version of thesis.
Includes bibliographical references (p. 175-184).
Efforts to monitor the ocean for signs of climate change are hampered by ever-present noise, in the form of stochastic ocean variability, and detailed knowledge of the character of this noise is necessary for estimating the significance of apparent trends. Typically, uncertainty estimates are made by a variety of ad hoc methods, often based on numerical model results or the variability of the data set being analyzed. We provide a systematic approach based on the four-dimensional frequency-wavenumber spectrum of low-frequency ocean variability. This thesis presents an empirical model of the spectrum of ocean variability for periods between about 20 days and 15 years and wavelengths of about 200-10,000 km, and describes applications to ocean circulation trend detection, observing system design, and satellite data processing. The horizontal wavenumber-frequency part of the model spectrum is based on satellite altimetry, current meter data, moored temperature records, and shipboard ADCP data. The spectrum is dominated by motions along a "nondispersive line". The observations considered are consistent with a universal [omega] -² power law at the high end of the frequency range, but inconsistent with a universal wavenumber power law. The model spectrum is globally varying and accounts for changes in dominant phase speed, period, and wavelength with location. The vertical structure of the model spectrum is based on numerical model results, current meter data, and theoretical considerations. We find that the vertical structure of kinetic energy is surface intensified relative to the simplest theoretical predictions. We present a theory for the interaction of linear Rossby waves with rough topography; rough topography can explain both the observed phase speeds and vertical structure of variability. The improved description of low-frequency ocean variability presented here will serve as a useful tool for future oceanographic studies.
by Cimarron James Lemuel Wortham, IV.
Ph.D.

Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 187-195).
Large-scale thermal forcing and freshwater fluxes play an essential role in setting temperature and salinity in the ocean. A number of recent estimates of the global oceanic freshwater balance as well as the global oceanic surface net heat flux are used to investigate the effects of heat- and freshwater forcing at the ocean surface. Such forcing induces changes in both density and density-compensated temperature and salinity changes ('spice'). The ratio of the relative contributions of haline and thermal forcing in the mixed layer is maintained by large-scale surface fluxes, leading to important consequences for mixing in the ocean interior. In a stratified ocean, mixing processes can be either along lines of constant density (isopycnal) or across those lines (diapycnal). The contribution of these processes to the total mixing rate in the ocean can be estimated from the large-scale forcing by evaluating the production of thermal variance, salinity variance and temperature-salinity covariance. Here, I use new estimates of surface fluxes to evaluate these terms and combine them to generate estimates of the production of density and spice variance under the assumption of a linear equation of state. As a consequence, it is possible to estimate the relative importance of isopycnal and diapycnal mixing in the ocean. While isopycnal and diapycnal processes occur on very different length scales, I find that the surface-driven production of density and spice variance requires an approximate equipartition between isopycnal and diapycnal mixing in the ocean interior. In addition, consideration of the full nonlinear equation of state reveals that surface fluxes require an apparent buoyancy gain (expansion) of the ocean, which allows an estimate of the amount of contraction on mixing due to cabbeling in the ocean interior.
by Julian J. Schanze.
Ph.D.

The OSU global coupled atmosphere/ocean general circulation model (A/O GCM) has been used to simulate the present (lxCO₂) climate and to investigate a CO₂-induced (2xCO₂) climate change. Previous analysis of the lxCO₂ simulation showed distinct errors in the simulated sea surface temperature (SST) and sea ice which were attributed primarily to the atmospheric GM (AGCM). Analysis of the 2xCO₂ simulation showed that the CO₂-induced warming penetrated into the ocean; this caused a delay in the equilibration of the climate system with an estimated e-folding time of 50-75 years. The present study has two objectives. The principal objective is to answer the question: By what pathways and through which physical processes does the simulated ocean general circulation produce the penetration of the CO₂-induced warming into the ocean? The secondary objective is to evaluate the performance of the oceanic GCM (OGCM) in the lxCO₂ simulation. The comparison of the simulated lxCO₂ internal oceanic fields with the corresponding observations shows that although they are basically similar, there are distinct errors. Further analysis shows that these errors were generated by the OGCM during its spin-up integration prior to its coupling with the AGCM. This study thus shows that it is not sufficient to compare the simulated SST with the observed SST to evaluate the performance of the OGCM. It is also necessary to compare the simulated internal oceanic quantities with the corresponding observed quantities. The global mean analysis of the CO₂-induced climate changes shows that the ocean gains heat at a rate of 3 W/m² due to the CO₂ doubling. This heat penetrates downward into the ocean predominantly through the reduction in the convective overturning. The zonal mean analysis shows that the surface warming increased from the tropics toward the mid-latitudes of both hemispheres and penetrated gradually to the deeper ocean. The oceanic warming penetrated to a greater depth in the subtropics and mid-latitudes than in the equatorial region. A zonal mean heat budget analysis shows that the CO₂-induced warming of the ocean occurs predominantly through the downward transport of heat, with the meridional heat flux being only of secondary importance. In the tropics the penetration of the CO₂-induced heating is minimized by the upwelling of cold water. In the subtropics the heating is transported downward more readily by the downwelling existing there. In the high latitudes the suppressed convection plays the dominant role in the downward penetration of the CO₂-induced heating.
Graduation date: 1987

Dissertation submitted to the Faculty of Science, University of the Witwatersraild, Johannesburg for the Degree of Master of Science.
Six general circulation model simulations of present-day southern African climate are assessed, Each of these models are early-generation equilibrium climate models linked to simple mixed-slab oceans. Simulations of surface air temperature over the subcontinent are sensitive to the grid-scale parameterisation of convection in summer. At high latitudes, large simulation errors are caused by errors in the specification of sea-ice albedo feedbacks. Increased spatial resolution and the inclusion of a gravity wave drag term in the momentum equations results in a markedly-improved simulated mean sea level pressure distribution. Tho models successfully simulate the pattern of rainfall seasonality over the Subcontinent, although grid-point simulation of precipitation is unreliable. Treatment of convection, cloud radiative feedbacks and the oceans by this generation of models is simplistic, and consequently there is a large degree of uncertainty associated with predictions of future climate under doubled-carbon dioxide conditions. For this reason, more reliable estimates of future conditions will be achieved using only those models which reproduce present climate most accurately. Early-generation general circulation models suggest a warming of 4°C to 5°C for the southern African region as a whole throughout the year. Over the subcontinent, warming is expected to be least in the tropics, and greatest in the dry subtropical regions in winter. Estimated changes in mean sea level pressure indicate a southward shlft of all pressure systems, with a weakening of the subtropical high pressure belt and mid-latitude westerlies. Little agreement exists between the models concerning predictions of regional precipitation change. However, broad scale changes in precipitation patterns are in accordance with predicted circulation changes over the subcontinent. Generally wetter conditions may be expected in the tropics throughout the year and over the summer rainfall region during summer. Decreased winter rainfall may be expected over the winter rainfall region of the south-western Cape. However, estimated precipitation changes are grid-point specific and therefore must riot be over-interpreted. The present climate validation has resulted in more reliable estimates of future conditions for the southern African region. This approach should be extended to recent slrnulations which include more comprehensive treatment of important physical processes.
Andrew Chakane 2018

Due to the wide range of physical scales involved, clouds cannot be fully resolved in models of the global climate, and so are parameterized. The resultant model deficiencies in simulating important cloud processes within the current climate are strongly implicated in the large uncertainty in model predictions of future climate changes. Previous work has highlighted the uncertainties in predictions of future climate related to thermodynamic cloud changes, understanding of which requires detailed observations of small-scale cloud microphysics. In this thesis, we argue that understanding the linkages between mid-latitude clouds and the general circulation of the atmosphere can advance efforts to constrain their response to climate forcing. We make this argument with three main methods of analysis: 1) observations, 2) state-of-the-art general circulation models, and 3) experiments with an idealized model of the global climate. First, we perform a comprehensive investigation of the observed inter-annual relationships between clouds, their radiative effects, and key indices of the large-scale atmospheric circulation. Using reanalysis data and satellite retrievals, we find a relationship between the edge of the Hadley circulation (HC) and the high cloud field that is largely robust against season and ocean basin. In contrast, shifts of the mid-latitude eddy-driven jet latitude, which had been the focus of previous work on the coupling between mid-latitude clouds and circulation, only correlate with the high cloud field in the wintertime North Atlantic. In that season and basin, poleward shifts of the circulation are associated with anomalous shortwave cloud radiative warming. During all seasons in the Southern Hemisphere, however, poleward shifts of the circulation are associated with anomalous shortwave cloud radiative cooling. Second, we examine Coupled Model Intercomparison Project phase 5 (CMIP5) model output to evaluate the models' simulation of the inter-annual co-variability between the Southern Hemisphere HC extent and the shortwave cloud radiative effect. In the control climate runs, during years when the HC edge is anomalously poleward, most models reduce their cloud cover in the lower mid-latitudes (approximately 30$^\circ$S - 45$^\circ$S) and allow more sunlight to warm the region, although we find no such shortwave radiative warming in observations. We correlate these biases in the co-variability between the HC extent and shortwave cloud radiative anomalies with model biases in the climatological HC extent. Models whose climatological HCs are unrealistically equatorward compared to the observations exhibit weaker climatological subsidence in the lower mid-latitudes and exhibit larger increases in subsidence there with poleward HC extent shifts than models with more realistic climatological HCs. This behavior, based on control climate variability, has important implications for the model response to forcing. In 4$\times$CO$_2$-forced runs, models with unrealistically equatorward HCs in the control climatology exhibit a stronger shortwave cloud radiative warming response in the lower mid-latitudes and tend to have larger values of equilibrium climate sensitivity than models with more realistic HCs in the control climatology. The above correlative analyses suggest that uncertainty in the linkages between mid-latitude clouds and the general circulation of the atmosphere contributes to uncertainty in the model response to forcing. Finally, we use simulations of the global climate in an idealized aquaplanet model to show that the biases in the climatological Southern Hemisphere circulation do indeed contribute to much of the model spread in the cloud-circulation coupling. We find that for the same 1$^\circ$ latitude poleward shift, simulations with narrower climatological HCs exhibit stronger mid-latitude shortwave cloud radiative warming anomalies than simulations with wider climatological HCs. The shortwave cloud radiative warming anomalies result predominantly from a subsidence warming of the planetary boundary layer, which decreases low-level cloud fraction and is stronger for narrower HCs because of a tighter mean meridional circulation. A comparison of the spread across aquaplanet simulations with that across CMIP5 models suggests that about half of the model uncertainty in the mid-latitude cloud-circulation coupling stems from this impact of the circulation on the large-scale temperature structure of the boundary layer, and thus can be removed by improving the representation of the climatological circulation in models. Therefore, a more realistic representation of the Hadley circulation in models can improve their representation of the linkage between mid-latitude clouds and the atmospheric circulation in the current climate and increase overall confidence in predictions of future climate.