Multidecadal and interannual changes of stationary Rossby waves

Freitas, Ana Carolina Vasques; Rao, V. Brahmananda

doi:10.1002/qj.894

Cited by 6 publications

(3 citation statements)

References 59 publications

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“…This is consistent with studies showing a weakening in the meridional circulation, and consequent large-scale observed changes in the wintertime subtropical jet (e.g. Frederiksen and Frederiksen 2007;Freitas and Rao 2011). This is a seemingly stronger signal than for the vertically integrated mass streamfunction "Intensity" defined by Nguyen et al (2013).…”

Section: Slow-external Modessupporting

confidence: 86%

Projections of Southern Hemisphere atmospheric circulation interannual variability

2016

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Section: Slow-external Modessupporting

confidence: 86%

Projections of Southern Hemisphere atmospheric circulation interannual variability

2016

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“…The differences in each one of the cases can be more clearly seen and properly analyzed in a superimposed map [35]. Thus, the contours in red are for weak HC cases, superimposed on the contours in blue for strong HC cases.…”

Section: Latitudementioning

confidence: 94%

Changes in the Austral Winter Hadley Circulation and the Impact on Stationary Rossby Waves Propagation

Freitas¹,

Ambrizzi²

2012

Advances in Meteorology

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The present study investigates how changes in the Hadley Cell (HC) intensity impact the stationary Rossby waves energy propagation in the Southern Hemisphere (SH) extratropics. Composites for weak and strong HC Intensity Index (HCI) were used in this analysis. The results for weak HC cases showed a wave train emanating from the subtropical central-west Indian Ocean in an arc-like route, with zonal wavenumber three in the polar jet waveguide, and reaching the north of South America. For strong HC cases, the wave train is also trapped inside the polar jet waveguide with zonal wavenumber four, emanating from subtropical central-east Indian Ocean and reaching the subtropical west coast of Africa. A weaker zonally oriented wave train with zonal wavenumber five has been found in the subtropical region with opposite polarity for weak and strong HC cases. Over the South America, the results show that an HC weakening can lead to a very cold and rainy winter in the southwest of the continent and a mild warm and dry winter on Brazilian states of Minas Gerais and Bahia. A pattern almost opposite was observed when the CH strengthens.

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“…Several studies have shown that, in the late 1970s and early 1980s, a major shift occurred in the structure of large-scale circulation in both hemispheres (e.g., Freitas and Rao, 2011;Frederiksen and Frederiksen, 2005;2007 -hereafter FF05, FF07, respectively). In the Southern Hemisphere (SH), FF05 and FF07 found that there were quite large changes in thermal structure and atmospheric circulation, between the periods of 1949-1968 and 1975-1994.…”

Section: Introductionmentioning

confidence: 99%

Assessing the impacts of changes in the Hadley Circulation on stationary Rossby wave propagation

Freitas

O’Kane

Frederiksen

et al. 2013

Piantadosi, J., Anderssen, R.S. And Boland J. (Eds) MODSIM2013, 20th International Congress on Modelling and Simulation

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The Hadley Cell (HC) plays a key role in the climate system. Generally defined as the zonal mean meridional mass circulation in the atmosphere bounded roughly by 30ºS and 30ºN, with warmer air rising in the tropics and colder air sinking in the subtropics, this circulation transports momentum flux to the subtropics and heat from the tropics to the subtropics and to high latitudes through extra-tropical baroclinic eddies broadly organized into storm tracks and stationary Rossby waves. Through anomalous upper tropospheric divergence, modifications in the HC are connected to changes in the generation of Rossby waves that propagate into the extra-tropics. Thus, tropical variability affects the extra-tropical atmospheric circulation. Changes in the location, intensity or seasonality of major climatological features of the general circulation, such as the HC or Rossby waves, can have important implications for regional climates by modifying patterns of temperature and precipitation. Several studies have identified that, in the late 1970s and early 1980s, a major shift occurred in the structure of large-scale circulation in both hemispheres, including a weakening of HC. Thus, in this paper we investigate how the changes in the HC, which occurred in the mid-1970s, have affected the stationary Rossby wave energy propagation in the Southern Hemisphere (SH) extratropics. We have employed the CSIRO Mk-3L general circulation model in a simulation with observed sea surface temperatures (SSTs) and time evolving historical carbon dioxide concentrations. Our focus is on the performance of the model in simulating the climatology for the twenty year periods 1949-68 and 1975-94 and on comparisons with the corresponding observations. We find that the model is quite skilful in reproducing the broad features of the important inter-decadal changes that occurred in the mid-1970s. We have also analysed the Rossby Wave Source (RWS) and mid-latitude circulation responses at upper levels associated with tropical variability. The RWS forcing is found to be located directly over the high latitude downward branch of the local HC, which is associated with upper-level convergence zones. The vortex stretching term is the largest contribution to the total RWS and the term of absolute vorticity advection by the divergent flow is mainly associated with the anticyclonic anomaly sources in the subtropics. The results also show that the weakening of the HC, which occurred in the period 1975-1994, leads to higher pressure developing over southern Australia, especially over southwestern Australia, contributing to rainfall reductions in these regions.

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Multidecadal and interannual changes of stationary Rossby waves

Cited by 6 publications

References 59 publications

Projections of Southern Hemisphere atmospheric circulation interannual variability

Projections of Southern Hemisphere atmospheric circulation interannual variability

Changes in the Austral Winter Hadley Circulation and the Impact on Stationary Rossby Waves Propagation

Assessing the impacts of changes in the Hadley Circulation on stationary Rossby wave propagation

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