Finite-Amplitude Lagrangian-Mean Wave Activity Diagnostics Applied to the Baroclinic Eddy Life Cycle

2012 ◽  
Vol 69 (10) ◽  
pp. 3013-3027 ◽  
Author(s):  
Abraham Solomon ◽  
Gang Chen ◽  
Jian Lu
Keyword(s):  
Life Cycle ◽  
Second Life ◽  
Wave Breaking ◽  
General Circulation ◽  
Early Stage ◽  
Potential Temperature ◽  
Circulation Model ◽  
Finite Amplitude ◽  
Wave Activity ◽  
Life Cycles

Abstract Lagrangian-mean wave activity diagnostics are applied to the nonlinear baroclinic eddy life cycle in a simple general circulation model of the atmosphere. The growth of these instabilities through baroclinic conversion of potential temperature gradients and their subsequent barotropic decay can exhibit two distinct life cycles. One life cycle results in equatorward propagation of the growing eddy, anticyclonic wave breaking, and a poleward shift of the mean jet. The second life cycle is distinguished by limited equatorward propagation and cyclonic wave breaking on the poleward flank of the jet. Using a conservative finite-amplitude, Lagrangian-mean wave activity (negative pseudomomentum) to quantify wave growth and propagation reveals more details about the life cycles than could be discerned from eddy kinetic energy (EKE) or other Eulerian metrics. It is shown that the distribution of pseudomomentum relative to the latitude of the axis of the jet can be used to provide a clear distinction between the two life cycles at an early stage in their development and, hence, a prediction for the subsequent shift of the jet. This suggests that the distribution of pseudomomentum may provide some predictability for the atmospheric annular modes.

scholarly journals A Multivariate Empirical Orthogonal Function Method to Construct Nitrate Maps in the Southern Ocean

2018 ◽  
Vol 35 (7) ◽  
pp. 1505-1519 ◽  
Author(s):  
Yu-Chiao Liang ◽  
Matthew R. Mazloff ◽  
Isabella Rosso ◽  
Shih-Wei Fang ◽  
Jin-Yi Yu
Keyword(s):  
Southern Ocean ◽  
General Circulation ◽  
Model Simulation ◽  
Potential Temperature ◽  
Circulation Model ◽  
Empirical Orthogonal Functions ◽  
Cluster Method ◽  
Sampling Strategies ◽  
Data Sampling ◽  
Mean Square Errors

AbstractThe ability to construct nitrate maps in the Southern Ocean (SO) from sparse observations is important for marine biogeochemistry research, as it offers a geographical estimate of biological productivity. The goal of this study is to infer the skill of constructed SO nitrate maps using varying data sampling strategies. The mapping method uses multivariate empirical orthogonal functions (MEOFs) constructed from nitrate, salinity, and potential temperature (N-S-T) fields from a biogeochemical general circulation model simulation Synthetic N-S-T datasets are created by sampling modeled N-S-T fields in specific regions, determined either by random selection or by selecting regions over a certain threshold of nitrate temporal variances. The first 500 MEOF modes, determined by their capability to reconstruct the original N-S-T fields, are projected onto these synthetic N-S-T data to construct time-varying nitrate maps. Normalized root-mean-square errors (NRMSEs) are calculated between the constructed nitrate maps and the original modeled fields for different sampling strategies. The sampling strategy according to nitrate variances is shown to yield maps with lower NRMSEs than mapping adopting random sampling. A k-means cluster method that considers the N-S-T combined variances to identify key regions to insert data is most effective in reducing the mapping errors. These findings are further quantified by a series of mapping error analyses that also address the significance of data sampling density. The results provide a sampling framework to prioritize the deployment of biogeochemical Argo floats for constructing nitrate maps.

scholarly journals Idealised simulations of the deep atmosphere of hot Jupiters

2019 ◽  
Vol 632 ◽  
pp. A114 ◽  
Author(s):  
F. Sainsbury-Martinez ◽  
P. Wang ◽  
S. Fromang ◽  
P. Tremblin ◽  
T. Dubos ◽  
...  
Keyword(s):  
General Circulation ◽  
Potential Temperature ◽  
Circulation Model ◽  
Final State ◽  
Vertical Advection ◽  
Atmospheric Circulations ◽  
Hot Jupiters ◽  
Heating And Cooling ◽  
Natural Outcome

Context. The anomalously large radii of hot Jupiters has long been a mystery. However, by combining both theoretical arguments and 2D models, a recent study has suggested that the vertical advection of potential temperature leads to a hotter adiabatic temperature profile in the deep atmosphere than the profile obtained with standard 1D models. Aims. In order to confirm the viability of that scenario, we extend this investigation to 3D, time-dependent models. Methods. We use a 3D general circulation model DYNAMICO to perform a series of calculations designed to explore the formation and structure of the driving atmospheric circulations, and detail how it responds to changes in both the upper and deep atmospheric forcing. Results. In agreement with the previous, 2D study, we find that a hot adiabat is the natural outcome of the long-term evolution of the deep atmosphere. Integration times of the order of 1500 yr are needed for that adiabat to emerge from an isothermal atmosphere, explaining why it has not been found in previous hot Jupiter studies. Models initialised from a hotter deep atmosphere tend to evolve faster toward the same final state. We also find that the deep adiabat is stable against low-levels of deep heating and cooling, as long as the Newtonian cooling timescale is longer than ~3000 yr at 200 bar. Conclusions. We conclude that steady-state vertical advection of potential temperature by deep atmospheric circulations constitutes a robust mechanism to explain the inflated radii of hot Jupiters. We suggest that future models of hot Jupiters be evolved for a longer time than currently done, and when possible that models initialised with a hot deep adiabat be included. We stress that this mechanism stems from the advection of entropy by irradiation-induced mass flows and does not require a (finely tuned) dissipative process, in contrast with most previously suggested scenarios.

The Dynamical Response to Snow Cover Perturbations in a Large Ensemble of Atmospheric GCM Integrations

2009 ◽  
Vol 22 (5) ◽  
pp. 1208-1222 ◽  
Author(s):  
Christopher G. Fletcher ◽  
Steven C. Hardiman ◽  
Paul J. Kushner ◽  
Judah Cohen
Keyword(s):  
Snow Cover ◽  
General Circulation ◽  
Circulation Model ◽  
Wave Activity ◽  
Dynamical Response ◽  
Mean Flow ◽  
Surface Cooling ◽  
Fall Season ◽  
Annular Mode ◽  
Northern Annular Mode

Abstract Variability in the extent of fall season snow cover over the Eurasian sector has been linked in observations to a teleconnection with the winter northern annular mode pattern. Here, the dynamics of this teleconnection are investigated using a 100-member ensemble of transient integrations of the GFDL atmospheric general circulation model (AM2). The model is perturbed with a simple persisted snow anomaly over Siberia and is integrated from October through December. Strong surface cooling occurs above the anomalous Siberian snow cover, which produces a tropospheric form stress anomaly associated with the vertical propagation of wave activity. This wave activity response drives wave–mean flow interaction in the lower stratosphere and subsequent downward propagation of a negative-phase northern annular mode response back into the troposphere. A wintertime coupled stratosphere–troposphere response to fall season snow forcing is also found to occur even when the snow forcing itself does not persist into winter. Finally, the response to snow forcing is compared in versions of the same model with and without a well-resolved stratosphere. The version with the well-resolved stratosphere exhibits a faster and weaker response to snow forcing, and this difference is tied to the unrealistic representation of the unforced lower-stratospheric circulation in that model.

scholarly journals The Emergence of Shallow Easterly Jets within QBO Westerlies

2018 ◽  
Vol 75 (1) ◽  
pp. 21-40 ◽  
Author(s):  
Peter Hitchcock ◽  
Peter H. Haynes ◽  
William J. Randel ◽  
Thomas Birner
Keyword(s):  
Potential Vorticity ◽  
General Circulation ◽  
Circulation Model ◽  
Shear Zones ◽  
Wave Activity ◽  
Mean Flow ◽  
Quasi Biennial Oscillation ◽  
Westerly Jet ◽  
Eddy Fluxes ◽  
Biennial Oscillation

A configuration of an idealized general circulation model has been obtained in which a deep, stratospheric, equatorial, westerly jet is established that is spontaneously and quasi-periodically disrupted by shallow easterly jets. Similar to the disruption of the quasi-biennial oscillation (QBO) observed in early 2016, meridional fluxes of wave activity are found to play a central role. The possible relevance of two feedback mechanisms to these disruptions is considered. The first involves the secondary circulation produced in the shear zones on the upper and lower flanks of the easterly jet. This is found to play a role in maintaining the aspect ratio of the emerging easterly jet. The second involves the organization of the eddy fluxes by the mean flow: the presence of a weak easterly anomaly within a tall, tropical, westerly jet is demonstrated to produce enhanced and highly focused wave activity fluxes that reinforce and strengthen the easterly anomalies. The eddies appear to be organized by the formation of strong potential vorticity gradients on the subtropical flanks of the easterly anomaly. Similar wave activity and potential vorticity structures are found in the ERA-Interim for the observed QBO disruption, indicating this second feedback was active then.

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.

Parameterization of PBL Processes in an Atmospheric General Circulation Model: Description and Preliminary Assessment

2009 ◽  
Vol 137 (3) ◽  
pp. 1061-1082 ◽  
Author(s):  
Celal S. Konor ◽  
Gabriel Cazes Boezio ◽  
Carlos R. Mechoso ◽  
Akio Arakawa
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Atmospheric General Circulation Model ◽  
Potential Temperature ◽  
Circulation Model ◽  
Surface Fluxes ◽  
Shortwave Radiation ◽  
Model Description ◽  
Atmospheric General Circulation ◽  
Seasonal And Diurnal Variations

Abstract This paper presents the basic features of a newly developed planetary boundary layer (PBL) parameterization, and the performance assessment of a version of the University of California, Los Angeles (UCLA), Atmospheric General Circulation Model (AGCM) to which the parameterization is incorporated. The UCLA AGCM traditionally uses a framework in which a sigma-type vertical coordinate for the PBL shares a coordinate surface with the free atmosphere at the PBL top. This framework facilitates an explicit representation of processes concentrated near the PBL top, which is crucially important especially for predicting PBL clouds. In the new framework, multiple layers are introduced between the PBL top and earth’s surface, allowing for predictions of the vertical profiles of potential temperature, total water mixing ratio, and horizontal winds within the PBL. The vertically integrated “bulk” turbulent kinetic energy (TKE) is also predicted for the PBL. The PBL-top mass entrainment is determined through an equation including the effects of TKE and the radiative and evaporative cooling processes concentrated near the PBL top. The surface fluxes are determined from an aerodynamic formula in which the velocity scale depends both on the square root of TKE and the grid-scale PBL velocity at the lowermost model layer. The turbulent fluxes within the PBL are determined through an approach that includes the effects of both large convective and small diffusive eddies. AGCM simulations with the new formulation of PBL are analyzed with a focus on the seasonal and diurnal variations. The simulated seasonal cycle of stratocumulus over the eastern oceans is realistic, as are the diurnal cycles of the PBL depth and precipitation over land. The simulated fluxes of latent heat, momentum, and shortwave radiation at the ocean surface and baroclinic activity in the middle latitudes show significant improvements over the previous versions of the AGCM based on the single-layer PBL.

The Role of Linear Interference in the Annular Mode Response to Extratropical Surface Forcing

2010 ◽  
Vol 23 (22) ◽  
pp. 6036-6050 ◽  
Author(s):  
Karen L. Smith ◽  
Christopher G. Fletcher ◽  
Paul J. Kushner
Keyword(s):  
Rossby Wave ◽  
General Circulation ◽  
Classical Problem ◽  
Circulation Model ◽  
Wave Activity ◽  
Surface Cooling ◽  
Annular Mode ◽  
Positive Tendency ◽  
Phase Wave ◽  
Wave Response

Abstract The classical problem of predicting the atmospheric circulation response to extratropical surface forcing is revisited in the context of the observed connection between autumnal snow cover anomalies over Siberia and wintertime anomalies of the northern annular mode (NAM). Previous work has shown that in general circulation model (GCM) simulations in which autumnal Siberian snow forcing is prescribed, a vertically propagating Rossby wave train is generated that propagates into the stratosphere, drives dynamical stratospheric warming, and induces a negative NAM response that couples to the troposphere. Important questions remain regarding the dynamics of the response to this surface cooling. It is shown that previously unexplained aspects of the evolution of the response in a comprehensive GCM can be explained by examining the time evolution of the phasing, and hence the linear interference, between the Rossby wave response and the background climatological stationary wave. When the wave response and background wave are in phase, wave activity into the stratosphere is amplified and the zonal-mean stratosphere–troposphere NAM response displays a negative tendency; when they are out of phase, wave activity into the stratosphere is reduced and the NAM response displays a positive tendency. The effects of linear interference are probed further in a simplified GCM, where an imposed lower tropospheric cooling is varied in position, strength, and sign. As in the comprehensive GCM, linear interference strongly influences the response over a realistic range of forcing strengths. The transition from linear to nonlinear behavior is shown to depend simply on forcing strength.

scholarly journals Atmospheric Blocking: The Impact of Topography in an Idealized General Circulation Model

2020 ◽  
Author(s):  
Veeshan Narinesingh ◽  
James F. Booth ◽  
Spencer K. Clark ◽  
Yi Ming
Keyword(s):  
High Pressure ◽  
General Circulation ◽  
Storm Track ◽  
Circulation Model ◽  
Wave Activity ◽  
Stationary Waves ◽  
Atmospheric Blocking ◽  
The Pacific ◽  
The Impact ◽  
Wave Activity Flux

Abstract. Atmospheric blocking can have important impacts on weather hazards, but the fundamental dynamics of blocking are not yet fully understood. As such, this work investigates the influence of topography on atmospheric blocking in terms of dynamics, spatial frequency, duration and displacement. Using an idealized GCM, an aquaplanet integration, and integrations with topography are analyzed. Block-centered composites show midlatitude aquaplanet blocks exhibit similar wave activity flux behavior to those observed in reality, whereas high-latitude blocks do not. The addition of topography significantly increases blocking and determines distinct regions where blocks are most likely to occur. These regions are found near high-pressure anomalies in the stationary waves and near storm track exit regions. Focusing on block duration, blocks originating near topography are found to last longer than those that are formed without or far from topography but have qualitatively similar evolutions in terms of nearby geopotential height anomalies and wave activity fluxes in composites. Integrations with two mountains have greater amounts of blocking compared to the single mountain case, however, the longitudinal spacing between the mountains is important for how much blocking occurs. Comparison between integrations with longitudinally long and short ocean basins show that more blocking occurs when storm track exits spatially overlap with high-pressure maxima in stationary waves. These results have real-world implications, as they help explain the differences in blocking between the Northern and Southern Hemisphere, and the differences between the Pacific and Atlantic regions in the Northern Hemisphere.

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