scholarly journals Decadal Changes of Wind Stress over the Southern Ocean Associated with Antarctic Ozone Depletion

2007 ◽  
Vol 20 (14) ◽  
pp. 3395-3410 ◽  
Author(s):  
Xiao-Yi Yang ◽  
Rui Xin Huang ◽  
Dong Xiao Wang
Keyword(s):  
Southern Ocean ◽  
Wind Stress ◽  
Zonal Wind ◽  
Ozone Depletion ◽  
Surface Wind ◽  
Southern Annular Mode ◽  
Mean Flow ◽  
Annular Mode ◽  
Surface Wind Stress ◽  
Antarctic Ozone

Abstract Using 40-yr ECMWF Re-Analysis (ERA-40) data and in situ observations, the positive trend of Southern Ocean surface wind stress during two recent decades is detected, and its close linkage with spring Antarctic ozone depletion is established. The spring Antarctic ozone depletion affects the Southern Hemisphere lower-stratospheric circulation in late spring/early summer. The positive feedback involves the strengthening and cooling of the polar vortex, the enhancement of meridional temperature gradients and the meridional and vertical potential vorticity gradients, the acceleration of the circumpolar westerlies, and the reduction of the upward wave flux. This feedback loop, together with the ozone-related photochemical interaction, leads to the upward tendency of lower-stratospheric zonal wind in austral summer. In addition, the stratosphere–troposphere coupling, facilitated by ozone-related dynamics and the Southern Annular Mode, cooperates to relay the zonal wind anomalies to the upper troposphere. The wave–mean flow interaction and the meridional circulation work together in the form of the Southern Annular Mode, which transfers anomalous wind signals downward to the surface, triggering a striking strengthening of surface wind stress over the Southern Ocean.

scholarly journals On the fast response of the Southern Ocean to changes in the zonal wind

Ocean Science ◽  
2007 ◽  
Vol 3 (3) ◽  
pp. 417-427 ◽  
Author(s):  
D. J. Webb ◽  
B. A. de Cuevas
Keyword(s):  
Southern Ocean ◽  
Wind Stress ◽  
Zonal Wind ◽  
Surface Wind ◽  
Drake Passage ◽  
Fast Response ◽  
Momentum Balance ◽  
Zonal Wind Stress ◽  
Model Studies ◽  
Barotropic Flow

Abstract. Model studies of the Southern Ocean, reported here, show that the Antarctic Circumpolar Current responds within two days to changes in the zonal wind stress at the latitudes of Drake Passage. Further investigation shows that the response is primarily barotropic and that, as one might expect, it is controlled by topography. Analysis of the results show that the changes in the barotropic flow are sufficient to transfer the changed surface wind stress to the underlying topography and that during this initial phase baroclinic processes are not involved. The model results also show that the Deacon Cell responds to changes in the wind stress on the same rapid time scale. It is shown that the changes in the Deacon Cell can also be explained by the change in the barotropic velocity field, an increase in the zonal wind stress producing an increased northward flow in shallow regions and southward flow where the ocean is deep. This new explanation is unexpected as previously the Deacon Cell has been thought of as a baroclinic feature of the ocean. The results imply that where baroclinic processes do appear to be involved in either the zonal momentum balance of the Southern Ocean or the formation of the Deacon Cell, they are part of the long term baroclinic response of the ocean's density field to the changes in the barotropic flow.

scholarly journals Southern Ocean Wind Stress in CMIP5 Models: Role of Wind Fluctuations

2020 ◽  
Vol 33 (4) ◽  
pp. 1209-1226 ◽  
Author(s):  
Xia Lin ◽  
Xiaoming Zhai ◽  
Zhaomin Wang ◽  
David R. Munday
Keyword(s):  
Southern Ocean ◽  
Time Scales ◽  
Wind Stress ◽  
Surface Wind ◽  
Coupled Model ◽  
Cmip5 Models ◽  
Coupled Models ◽  
Surface Wind Stress ◽  
Stress Changes ◽  
The Mean

AbstractThe Southern Ocean (SO) surface wind stress is a major atmospheric forcing for driving the Antarctic Circumpolar Current and the global overturning circulation. Here the effects of wind fluctuations at different time scales on SO wind stress in 18 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) are investigated. It is found that including wind fluctuations, especially on time scales associated with synoptic storms, in the stress calculation strongly enhances the mean strength, modulates the seasonal cycle, and significantly amplifies the trends of SO wind stress. In 11 out of the 18 CMIP5 models, the SO wind stress has strengthened significantly over the period of 1960–2005. Among them, the strengthening trend of SO wind stress in one CMIP5 model is due to the increase in the intensity of wind fluctuations, while in all the other 10 models the strengthening trend is due to the increasing strength of the mean westerly wind. These discrepancies in SO wind stress trend in CMIP5 models may explain some of the diverging behaviors in the model-simulated SO circulation. Our results suggest that to reduce the uncertainty in SO responses to wind stress changes in the coupled models, both the mean wind and wind fluctuations need to be better simulated.

The impact of topography and eddy parameterization on the simulated Southern Ocean circulation response to changes in surface wind stress

2020 ◽  
Author(s):  
Hailu Kong ◽  
Malte F. Jansen
Keyword(s):  
Southern Ocean ◽  
Wind Stress ◽  
Ocean Circulation ◽  
Surface Wind ◽  
Flat Bottom ◽  
Coarse Resolution ◽  
Surface Wind Stress ◽  
Stress Changes ◽  
The Impact ◽  
Meso Scale

AbstractIt remains uncertain how the Southern Ocean circulation responds to changes in surface wind stress, and whether coarse resolution simulations, where meso-scale eddy fluxes are parameterized, can adequately capture the response. We address this problem using two idealized model setups mimicking the Southern Ocean: a flat bottom channel, and a channel with moderately complex topography. Under each topographic configuration and varying wind stress, we compare several coarse resolution simulations, configured with different eddy parameterizations, against an eddy-resolving simulation. We find that: (1) without topography, sensitivity of the Antarctic Circumpolar Current (ACC) to wind stress is overestimated by coarse resolution simulations, due to an underestimate of the sensitivity of the eddy diffusivity; (2) in the presence of topography, stationary eddies dominate over transient eddies in counteracting the direct response of the ACC and overturning circulation to wind stress changes; (3) coarse resolution simulations with parameterized eddies capture this counteracting effect reasonably well, largely due to their ability to resolve stationary eddies. Our results highlight the importance of topography in modulating the response of the Southern Ocean circulation to changes in surface wind stress. The interaction between meso-scale eddies and stationary meanders induced by topography requires more attention in future development and testing of eddy parameterizations.

scholarly journals Southern “Annular Modes” Simulated by a Climate Model—Patterns, Mechanisms, and Uses

2007 ◽  
Vol 64 (9) ◽  
pp. 3113-3131 ◽  
Author(s):  
I. G. Watterson
Keyword(s):  
Zonal Wind ◽  
Climate Model ◽  
Southern Annular Mode ◽  
Momentum Equation ◽  
Mean Flow ◽  
Annular Mode ◽  
Annular Modes ◽  
Daily Data ◽  
Physically Based ◽  
Mean Climate

Abstract Both high-latitude (HLM) and low-latitude modes (LLM) of variability of zonal wind in the Southern Hemisphere have been identified. Through an analysis of a simulation for 1871–2200 by the CSIRO Mark 3 climate model, the extent to which these might both be described as “annular modes,” based on their statistical patterns, physical mechanisms, and usefulness in climate study, is assessed. The modes are determined as EOF1 and EOF2 of vertically integrated zonal and monthly mean zonal wind, for 1871–1970. These match well those from ECMWF Re-Analysis (ERA) data and also from the earlier Mark 2 model. The mode index time series relate to largely annular patterns of local wind and surface pressure anomalies [with HLM giving the familiar southern annular mode (SAM)], and other simulated quantities. While modes calculated from 90° sectors are only moderately correlated (mostly in the polar region) for HLM, the link increases with time scale. There is little such relationship for LLM. A momentum equation analysis using daily data confirms that both zonal modes are driven by eddies, but only HLM features a positive eddy–mean flow feedback. Variation in feedback and surface damping through the seasonal cycle relate well to that in index autocorrelation, with the HLM being more persistent in summer. Stratospheric winds feature a long-lived component that tends to lead the HLM. The HLM drives sea surface temperature anomalies that persist for months, and coupling with the ocean increases variability on longer time scales. The annular variability in the warmer climate of the twenty-second century is barely changed, but the mean climate change in the far south projects strongly on the HLM. The LLM features some statistical annularity and may have some uses. However, only the HLM can be considered to be a physically based mode—the zonal-wind equivalent to the one southern annular mode.

Observations of SST-Induced Perturbations of the Wind Stress Field over the Southern Ocean on Seasonal Timescales

2003 ◽  
Vol 16 (14) ◽  
pp. 2340-2354 ◽  
Author(s):  
Larry W. O'Neill ◽  
Dudley B. Chelton ◽  
Steven K. Esbensen
Keyword(s):  
Southern Ocean ◽  
Wind Stress ◽  
Surface Wind ◽  
Wind Stress Curl ◽  
Latitude Range ◽  
Surface Wind Stress ◽  
Secondary Circulations ◽  
Vertical Turbulent Mixing ◽  
Wind Stress Field ◽  
Sst Fronts

Abstract The surface wind stress response to sea surface temperature (SST) over the latitude range 30°–60°S in the Southern Ocean is described from the National Aeronautics and Space Administration's QuikSCAT scatterometer observations of wind stress and Reynolds analyses of SST during the 2-yr period August 1999 to July 2001. While ocean–atmosphere coupling at midlatitudes has previously been documented from several case studies, this is the first study to quantify this relation over the entire Southern Ocean. The spatial structures of the surface wind perturbations with wavelengths shorter than 10° latitude by 30° longitude are closely related to persistent spatial variations of the SST field on the same scales. The wind stress curl and divergence are shown to be linearly related, respectively, to the crosswind and downwind components of the SST gradient. The curl response has a magnitude only about half that of the divergence response. This observed coupling is consistent with the hypothesis that SST modification of marine atmospheric boundary layer (MABL) stability affects vertical turbulent mixing of momentum, inducing perturbations in the surface winds. The nonequivalence between the responses of the curl and divergence to the crosswind and downwind SST gradients suggests that secondary circulations in the MABL may also play an important role by producing significant perturbations in the surface wind field near SST fronts that are distinct from the vertical turbulent transfer of momentum. The importance of the wind stress curl in driving Ekman vertical velocity in the open ocean implies that the coupling between winds and SST may have important feedback effects on upper ocean processes near SST fronts.

scholarly journals Overturning response to a surface wind stress doubling in an eddying and a non-eddying ocean

2021 ◽  
Author(s):  
Veit Lüschow ◽  
Jochem Marotzke ◽  
Jin-Song von Storch
Keyword(s):  
Wind Stress ◽  
Surface Wind ◽  
Relative Vorticity ◽  
Ocean Model ◽  
Meridional Overturning Circulation ◽  
Western Boundary ◽  
Boundary Current ◽  
Mean Flow ◽  
Surface Wind Stress ◽  
Stress Changes

AbstractIn this paper, the overturning responses to wind stress changes of an eddying and a non-eddying ocean are compared. Differences are found in the deep overturning cell in the low-latitude North Atlantic with substantial implications for the deep western boundary current (DWBC). In an ocean-only twin experiment with one eddying and one non-eddying configuration of the MPI ocean model, two different forcings are being applied: the standard NCEP forcing and the NCEP forcing with 2x surface wind stress. The response to the wind stress doubling in the Atlantic meridional overturning circulation is similar in the eddying and the non-eddying configuration, showing an increase by about 4 Sv (~25%, 1 Sv = 106 m3s−1). In contrast, the DWBC responds with a speedup in the non-eddying and a slowdown in the eddying configuration. This paper demonstrates that the DWBC slowdown in the eddying configuration is largely balanced by eddy vorticity fluxes. Because those fluxes are not resolved and also not captured by an eddy parameterization in the non-eddying configuration, such a DWBC slowdown is likely not to occur in non-eddying ocean models which therefore might not capture the whole range of overturning responses. Furthermore, evidence is provided that the balancing effect of the eddies is not a passive reaction to a remotely triggered DWBC slowdown. Instead, deep eddies which are sourced from the upper ocean provide an excess input of relative vorticity which then actively forces the DWBC mean flow to slow down.

scholarly journals Evolution of the eastward shift in the quasi-stationary minimum of the Antarctic total ozone column

2016 ◽  
Author(s):  
Asen Grytsai ◽  
Gennadi Milinevsky ◽  
Andrew Klekociuk ◽  
Oleksandr Evtushevsky
Keyword(s):  
Ozone Depletion ◽  
Total Ozone ◽  
Regional Climate ◽  
Southern Annular Mode ◽  
Reanalysis Data ◽  
Austral Spring ◽  
Annular Mode ◽  
Antarctic Ozone ◽  
The Antarctic ◽  
Ozone Column

Abstract. The quasi-stationary pattern of the Antarctic total ozone has changed during the last four decades, demonstrating an eastward shift in the zonal ozone minimum. In this work, the association between the longitudinal shift of the zonal ozone minimum and changes in meteorological fields in austral spring (September–November) for 1979–2014 is analyzed. Regressive, correlative and anomaly composite analyses are applied to reanalysis data. Patterns of the Southern Annular Mode and quasi-stationary zonal waves 1 and 3 in the meteorological fields show relationships with interannual variability in the longitude of the zonal ozone minimum. On decadal time scales, consistent longitudinal shifts of the zonal ozone minimum and zonal wave 3 pattern in the middle troposphere temperature at the southern mid-latitudes are shown. As known, Antarctic ozone depletion in spring is strongly projected on the Southern Annular Mode in summer and impacts tropospheric climate. The results of this study suggest that changes in zonal ozone asymmetry accompanying the ozone depletion could be associated with regional climate changes in the Southern Hemisphere in spring.

scholarly journals On the fast response of the Southern Ocean to changes in the zonal wind

2006 ◽  
Vol 3 (3) ◽  
pp. 471-501 ◽  
Author(s):  
D. J. Webb ◽  
B. A. de Cuevas
Keyword(s):  
Southern Ocean ◽  
Wind Stress ◽  
Zonal Wind ◽  
Surface Wind ◽  
Drake Passage ◽  
Fast Response ◽  
Momentum Balance ◽  
Zonal Wind Stress ◽  
Model Studies ◽  
Barotropic Flow

Abstract. Model studies of the Southern Ocean, reported here, show that the Antarctic Circumpolar Current responds within two days to changes in the zonal wind stress at the latitudes of Drake Passage. Further investigation shows that the response is primarily barotropic and that, as one might expect, it is controlled by topography. Analysis of the results show that the changes in the barotropic flow are sufficient to transfer the changed surface wind stress to the underlying topography and that during this initial phase baroclinic processes are not involved. The model results also show that the Deacon Cell responds to changes in the wind stress on the same rapid time scale. It is shown that the changes in the Deacon Cell can also be explained by the change in the barotropic velocity field, an increase in the zonal wind stress producing an increased northward flow in shallow regions and southward flow where the ocean is deep. This new explanation is unexpected as previously the Deacon Cell has been thought of as a baroclinic feature of the ocean. The results imply that where baroclinic processes do appear to be involved in either the zonal momentum balance of the Southern Ocean or the formation of the Deacon Cell, they are part of the long term baroclinic response of the ocean's density field to the changes in the barotropic flow.

FEATURES OF WIND FIELD OVER THE SEA SURFACE IN THE COASTAL AREA BASED ON SAR OBSERVATIONS

2017 ◽  
Author(s):  
Anna Monzikova ◽  
Anna Monzikova ◽  
Vladimir Kudryavtsev Vladimir ◽  
Vladimir Kudryavtsev Vladimir ◽  
Alexander Myasoedov ◽  
...  
Keyword(s):  
Wind Stress ◽  
Surface Wind ◽  
Quantitative Description ◽  
Energy Resource ◽  
Resource Assessment ◽  
Internal Boundary Layer ◽  
Offshore Wind ◽  
Internal Boundary ◽  
Sar Images ◽  
Surface Wind Stress

“Wind-shadowing” effects in the Gulf of Finland coastal zone are analyzed using high resolution Envisat Synthetic Aperture Radar (SAR) measurements and model simulations. These effects are related to the internal boundary layer (IBL) development due to abrupt change the surface roughness at the sea-land boundary. Inside the "shadow" areas the airflow accelerates and the surface wind stress increases with the fetch. Such features can be revealed in SAR images as dark areas adjacent to the coastal line. Quantitative description of these effects is important for offshore wind energy resource assessment. It is found that the surface wind stress scaled by its equilibrium value (far from the coast) is universal functions of the dimensionless fetch Xf/G. Wind stress reaches an equilibrium value at the distance Xf/G of about 0.4.

scholarly journals Southern Annular Mode Dynamics in Observations and Models. Part II: Eddy Feedbacks

2013 ◽  
Vol 26 (14) ◽  
pp. 5220-5241 ◽  
Author(s):  
Isla R. Simpson ◽  
Theodore G. Shepherd ◽  
Peter Hitchcock ◽  
John F. Scinocca
Keyword(s):  
Negative Feedback ◽  
Planetary Wave ◽  
Southern Annular Mode ◽  
Summer Season ◽  
Substantial Contribution ◽  
Mean Flow ◽  
Annular Mode ◽  
Planetary Scale ◽  
Zonal Wavenumber ◽  
Climatological Circulation

Abstract Many global climate models (GCMs) have trouble simulating southern annular mode (SAM) variability correctly, particularly in the Southern Hemisphere summer season where it tends to be too persistent. In this two-part study, a suite of experiments with the Canadian Middle Atmosphere Model (CMAM) is analyzed to improve the understanding of the dynamics of SAM variability and its deficiencies in GCMs. Here, an examination of the eddy–mean flow feedbacks is presented by quantification of the feedback strength as a function of zonal scale and season using a new methodology that accounts for intraseasonal forcing of the SAM. In the observed atmosphere, in the summer season, a strong negative feedback by planetary-scale waves, in particular zonal wavenumber 3, is found in a localized region in the southwest Pacific. It cancels a large proportion of the positive feedback by synoptic- and smaller-scale eddies in the zonal mean, resulting in a very weak overall eddy feedback on the SAM. CMAM is deficient in this negative feedback by planetary-scale waves, making a substantial contribution to its bias in summertime SAM persistence. Furthermore, this bias is not alleviated by artificially improving the climatological circulation, suggesting that climatological circulation biases are not the cause of the planetary wave feedback deficiency in the model. Analysis of the summertime eddy feedbacks in the models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) confirms that this is indeed a common problem among GCMs, suggesting that understanding this planetary wave feedback and the reason for its deficiency in GCMs is key to improving the fidelity of simulated SAM variability in the summer season.

Sign in / Sign up

Export Citation Format

Share Document