scholarly journals Energy exchanges in Saturn's polar regions from Cassini observations: Part I: Eddy-zonal flow interactions

2021 ◽  
Author(s):  
Peter L Read ◽  
Arrate Antuñano ◽  
Greg Colyer ◽  
Simon Cabanes ◽  
Teresa del Rio-Gaztelurrutia ◽  
...  
Keyword(s):  
Zonal Flow ◽  
Polar Regions ◽  
Flow Interactions ◽  
Energy Exchanges

Multiple Timescales of the Southern Annular Mode

2021 ◽  
Author(s):  
Qiuyan Zhang ◽  
Yang Zhang ◽  
Zhaohua Wu
Keyword(s):  
Seasonal Variability ◽  
Low Frequency ◽  
Austral Summer ◽  
Zonal Flow ◽  
Southern Annular Mode ◽  
Multiple Timescales ◽  
Annular Mode ◽  
Flow Interactions ◽  
The Cross ◽  
Sst Anomalies

<p>Using the ensemble empirical mode decomposition (EEMD) method, this study systematically investigates the multiple timescales of the Southern Annular Mode (SAM) and identifies their relative contributions to the low-frequency persistence of SAM. Analyses show that the subseasonal sustaining of SAM mainly depends on the contribution of longer-timescale variabilities, especially the cross-seasonal variability. When subtracting the cross-seasonal variability from the SAM, the positive covariance between the eddy and zonal flow, which is suggested the positive eddy feedback in SAM, disappears. Composite analysis shows that only with strong cross-seasonal variability, the meridional shift of zonal wind, eddy momentum forcing and baroclinicity anomalies can be maintained for more than 20 days, mainly resulting from the longer-timescale (especially the cross-seasonal timescale) eddy-zonal flow interactions. This study further suggests that the dipolar sea surface temperature (SST) anomalies in the mid latitude of Southern Hemisphere (SH) is a possible cause for the cross-seasonal variability. Analysis shows that about half of the strong cross-seasonal timescale events are accompanied by evident dipolar SST anomalies, which mostly occur in austral summer. The cross-seasonal dependence of the eddy-zonal flow interactions suggests the longer-timescale (especially the cross-seasonal timescale) contribution cannot be neglected in subseasonal prediction of SAM.</p>

scholarly journals On the Self-Maintenance of Midlatitude Jets

2006 ◽  
Vol 63 (8) ◽  
pp. 2109-2122 ◽  
Author(s):  
Walter A. Robinson
Keyword(s):  
Zonal Flow ◽  
Equilibrium Temperature ◽  
Intrinsic Variability ◽  
Annular Modes ◽  
Global Circulation ◽  
Flow Interactions ◽  
Level Model ◽  
Poleward Shift ◽  
Temperature Contrast ◽  
Two Level Model

Abstract In this paper an atmospheric jet is considered self-maintaining if the overall effect of baroclinic eddies is to preserve or enhance its westerly shear with height. Observations suggest that the wintertime jets in Earth’s atmosphere are self-maintaining. This has implications for the intrinsic variability of these jets—the annular modes—and for how the extratropics respond to tropical warming. The theory of quasigeostrophic eddy–zonal flow interactions is employed to determine how a jet can be self-maintaining. Whether or not a jet is self-maintaining is found to depend sensitively on the meridional distribution of the absorption of wave activity. The eddy driving of the jet in a simple two-level model of the global circulation is examined. It is found that, with approximately wintertime settings of parameters (a radiative equilibrium equator–pole temperature contrast of 60 K), the midlatitude jets in this model are self-maintaining. The jet is not self-maintaining, however, when the radiative equilibrium equator-to-pole temperature contrast is reduced below a critical value (∼24 K temperature contrast). Eddy amplitudes are also greatly reduced, in this case. The transition to a self-maintaining jet, as the radiative equilibrium temperature contrast is increased, suggests a set of feedback mechanisms that involve the strength of the baroclinicity in the jet center and where baroclinic eddies are absorbed in the subtropics. A barotropic eastward force applied to the model Tropics causes a poleward shift in the latitudes of greatest eddy absorption and induces a transition from a non-self-maintaining to a self-maintaining jet. Self-maintaining behavior ultimately disappears, as the equator–pole thermal contrast, and thus the eddies, are strengthened. The flow is then highly disturbed and no longer dominated by wavelike baroclinic eddies.

scholarly journals The Polar Radiant Energy in the Far InfraRed Experiment: A New Perspective on Polar Longwave Energy Exchanges

2021 ◽  
pp. 1-46
Author(s):  
Tristan S. L’Ecuyer ◽  
Brian J. Drouin ◽  
James Anheuser ◽  
Meredith Grames ◽  
David Henderson ◽  
...  
Keyword(s):  
Thermal Emission ◽  
Radiant Energy ◽  
Far Infrared ◽  
Temporal Variations ◽  
Infrared Emission ◽  
The Arctic ◽  
Energy Budgets ◽  
Polar Regions ◽  
Spectral Variation ◽  
Energy Exchanges

AbstractThe Earth’s climate is strongly influenced by energy deficits at the poles that emit more thermal energy than they receive from the sun. Energy exchanges between the surface and atmosphere influence the local environment while heat transport from lower latitudes drives midlatitude atmospheric and oceanic circulations. In the Arctic, in particular, local energy imbalances induce strong seasonality in surface-atmosphere heat exchanges and an acute sensitivity to forced climate variations. Despite these important local and global influences, the largest contributions to the polar atmospheric and surface energy budgets have not been fully characterized. The spectral variation of far-infrared radiation that makes up 60% of polar thermal emission has never been systematically measured impeding progress toward consensus in predicted rates of Arctic warming, sea ice decline, and ice sheet melt.Enabled by recent advances in sensor miniaturization and CubeSat technology, the Polar Radiant Energy in the Far InfraRed Experiment (PREFIRE) mission will document, for the first time, the spectral, spatial, and temporal variations of polar far-infrared emission. Selected under NASA’s Earth Ventures Instrument (EVI) program, PREFIRE will utilize new light weight, low-power, ambient temperature detectors capable of measuring at wavelengths up to 50 micrometers to quantify Earth’s far-infrared spectrum. Estimates of spectral surface emissivity, water vapor, cloud properties, and the atmospheric greenhouse effect derived from these measurements offer the potential to advance our understanding of the factors that modulate thermal fluxes in the cold, dry conditions characteristic of the polar regions.

scholarly journals Annular Variability and Eddy–Zonal Flow Interactions in a Simplified Atmospheric GCM. Part I: Characterization of High- and Low-Frequency Behavior

2009 ◽  
Vol 66 (10) ◽  
pp. 3075-3094 ◽  
Author(s):  
Sarah Sparrow ◽  
Michael Blackburn ◽  
Joanna D. Haigh
Keyword(s):  
Low Frequency ◽  
Circulation Model ◽  
Zonal Flow ◽  
Life Cycles ◽  
Quasi Equilibrium ◽  
Global Circulation Model ◽  
Low Frequencies ◽  
Flow Interactions ◽  
Slow Evolution ◽  
Frequency Behavior

Abstract Experiments have been performed using a simplified, Newtonian forced, global circulation model to investigate how variability of the tropospheric jet can be characterized by examining the combined fluctuations of the two leading modes of annular variability. Eddy forcing of this variability is analyzed in the phase space of the leading modes using the vertically integrated momentum budget. The nature of the annular variability and eddy forcing depends on the time scale. At low frequencies the zonal flow and baroclinic eddies are in quasi equilibrium and anomalies propagate poleward. The eddies are shown primarily to reinforce the anomalous state and are closely balanced by the linear damping, leaving slow evolution as a residual. At high frequencies the flow is strongly evolving and anomalies are initiated on the poleward side of the tropospheric jet and propagate equatorward. The eddies are shown to drive this evolution strongly: eddy location and amplitude reflect the past baroclinicity, while eddy feedback on the zonal flow may be interpreted in terms of wave breaking associated with baroclinic life cycles in lateral shear.

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