Abstract
The zonal flow associated with cut-off lows (COLs) comprises two jet streaks of different spatial extents. The smaller scale jet streak, located north of the COLs, forms as a result of meridional divergence of vorticity advection and it is quasi-stationary, relative to the COLs. It dissipates as the COLs do the same. The larger scale jet streak gives rise to anticyclonic and equatorward Rossby wave breaking (RWB) as it propagates southeasterly to the base of the ridge, south of the COL and then northeasterly beyond that point. As the jet streak propagates it brings with it the anticyclonic barotropic shear that causes the Rossby waves to break. Its propagation is caused by zonal momentum advection by the zonal flow from jet streak entrance to its exit. As it propagates, its northwesterly/southeasterly orientation changes to one that is more zonal to become south-westerly/northeasterly at the end of the COL life cycle. This change in orientation is due to meridional advection of zonal momentum,where the meridional flow advects momentum southward (northward) at the jet streak entrance (exit). The jet streaks form a split jet structure and the winds between the streaks is decelerated by vorticity advection convergence. Because the flow and COL (and RWB) life cycle are coupled, understanding the dynamics that underlie the changes in the COL ambient flow contributes to resolving the outstanding RWB/COL causality problem.
![](http://media.springernature.com/m312/springer-static/image/art%3A10.1007%2Fs00382-020-05401-4/MediaObjects/382_2020_5401_Fig1_HTML.png)
![](http://media.springernature.com/m312/springer-static/image/art%3A10.1007%2Fs00382-020-05401-4/MediaObjects/382_2020_5401_Fig2_HTML.png)
![](http://media.springernature.com/m312/springer-static/image/art%3A10.1007%2Fs00382-020-05401-4/MediaObjects/382_2020_5401_Fig3_HTML.png)
![](http://media.springernature.com/m312/springer-static/image/art%3A10.1007%2Fs00382-020-05401-4/MediaObjects/382_2020_5401_Fig4_HTML.png)
![](http://media.springernature.com/m312/springer-static/image/art%3A10.1007%2Fs00382-020-05401-4/MediaObjects/382_2020_5401_Fig5_HTML.png)
![](http://media.springernature.com/m312/springer-static/image/art%3A10.1007%2Fs00382-020-05401-4/MediaObjects/382_2020_5401_Fig6_HTML.png)
![](http://media.springernature.com/m312/springer-static/image/art%3A10.1007%2Fs00382-020-05401-4/MediaObjects/382_2020_5401_Fig7_HTML.png)
Similar content being viewed by others
References
Abatzoglou JT (2016) Contribution of cutoff lows to precipitation across the United States. J Appl Meteo Clim 55:893–899
Barnes MA, Ndarana T, Landman WA (2020) Cut-off lows in the southern Hemisphere and their extension to the surface. Clim Dyn (submitted)
Bell FG (1994) Floods and landslides in Natal and notably the Greater Durban Region, September 1987: a Retrospective view. Environ Eng Geosci XXXI:59–74
Bowley KA, Gyakum JR, Atallah EH (2019) A new perspective toward cataloging Northern Hemisphere Rossby Wave breaking on the dynamic Tropopause. Mon Wea Rev 147(409):431
Brown TJ, Hall BL (1999) The use of t values in climatological composite analyses. J Clim 12:2941–2944
Dee DP, Uppala SM, Simmons AJ, Berrisford P, Poli P, Kobayashi S, Andrae U, Balmaseda MA, Balsamo G, Bauer P, Bechtold P, Beljaars AC, van de Berg L, Bidlot J, Bormann N, Delsol C, Dragani R, Fuentes M, Geer AJ, Haimberger L, Healy SB, Hersbach H, Hlm EV, Isaksen L, Kllberg P, Khler M, Matricardi M, McNally AP, MongeSanz BM, Morcrette J, Park B, Peubey C, de Rosnay P, Tavolato C, Thpaut J, Vitart F (2011) The ERA Interim reanalysis: con guration and performance of the data assimilation system. Q J R Meteorol Soc 137:553–597
Dong L, Colucci SJ (2015) The role of non-quasigeostrophic forcing in Southern Hemisphere blocking onsets. Mon Weather Rev 143:1455–1471
Dyson L (2015) A heavy rainfall sounding climatology over Gauteng South Africa, using self-organising maps. Clim Dyn 45:3051–3065
Edmon HJ, Hoskins BJ, McIntyre ME (1980) Eliassen-Palm cross sections for the troposphere. J Atmos Sci 37:2600–2616
Favre A, Hewitson B, Lennard C, Cerezo-Mota R, Tadross M (2013) Cut-off lows in the South Africa region and their contribution to precipitation. Clim Dyn 41:2331–2351
Fuenzalida HA, Sánchez R, Garreaud RD (2005) A climatology of cutoff lows in the Southern Hemisphere. J Geophys Res Atmos 110:1–10
Gan MA, Piva E (2013) Energetics of a southeastern Pacific cut-off low. Atmos Sci Lett 14:272–280
Gan MA, Piva ED (2016) Energetics of southeastern Pacific cutoff lows. Clim Dyn 46:3453–3462
Godoy AA, Possia NE, Campetella CM, Skabar YG (2011) A cut-off low in southern South America; dynamic and thermodynamic processes. Revista Brasileira de Meteorologia 26:503–514
Holton JR, Hakim GJ (2013) An introduction to dynamic meteorology, 5th edn. Elsevier Academic Press, p 553
Holton JR, Hakim GJ (2014) An Introduction to Dynamic Meteorology. 5th edn. Elsevier Academic Press, p 553
Hoskins BJ, Mcintyre ME, Robertson AW (1985) On the use and significance of isentropic potential vorticity maps. Q J R Meteor Soc 111:877–946
Keyser D, Shapiro MA (1986) A review of the structure and dynamics of upper level frontal zones. Mon Wea Rev 114:452–499
Kunz T, Fraedrich K, Lunkeit F (2009) Response of idealized baroclinic wave life cycles to stratospheric flow conditions. J Atmos Sci 66:2288–2302
Kunkel D, Hoor P, Wirth V (2016) The tropopause inversion layer in baroclinic life-cycle experiments: the role of diabatic processes atmos. Chem Phys 16:541–560
Lang AA, Martin JE (2012) The structure and evolution of lower stratospheric frontal zones. Part 1: examples in northwesterly and southwesterly flow. Q J R Meteorol Soc 138:1350–1365
Martin JE (2014) Quasi-geostrophic diagnosis of the influence of vorticity advection on the development of upper level jet-front systems. Q J R Meteorol Soc 140:2658–2671
Nakamura M, Plumb RA (1994) The effects of flow asymmetry on the direction of Rossby wave breaking. J Atmos Sci 51:2031–2045
Ndarana T, Waugh DW (2010) The link between cut-off lows and Rossby wave breaking in the Southern Hemisphere. Q J R Meteor Soc 136:869–885
Ndarana T, Bopape M, Waugh D, Dyson D (2018) The Influence of the lower stratosphere on ridging Atlantic Ocean anticyclones over South Africa. J Clim 31:6175–6187
Ndarana T, Mpati S, Bopape M, Engelbrecht F, Chikoore H (2020) The flow and moisture fluxes associated with ridging South Atlantic Ocean anticyclones during the subtropical southern African summer. Submitted Int J Climatol
Nieto R et al (2005) Climatological features of cutoff low systems in the Northern Hemisphere. J Clim 18:3085–3103
Orlanski I, Katzfey J (1991) The life cycle of a cyclone wave in the Southern Hemisphere. 1. Eddy energy budget. J Atmos Sci 48:1972–1998
Orlanski I, Sheldon JP (1995) Stages in the energetics of baroclinic systems. Tellus 47A:605–628
Palmén E, Newtown CW (1979) Atmospheric circulation systems, their structure and physical interpretation. Academic Press, Cambridge
Pelmén E, Newtown CW (1969) Atmospheric circulation systems, their structure and physical interpretation. Academic Press
Peters D, Waugh DW (2003) Rossby wave breaking in the Southern Hemisphere wintertime upper troposphere. Mon Wea Rev 131:2623–2634
Pinheiro HR, Hodges KI, Gan MA, Ferreira NJ (2017) A new perspective of the climatological features of upper level cutoff lows in the Southern Hemisphere. Clim Dyn 48:541–559
Pinheiro HR, Hodges KI, Gan MA (2019) Sensitivity of identifying cutoff lows in the Southern Hemisphere using multiple criteria: implications for numbers, seasonality and intensity. Clim Dyn 53:6699–6713
Plumb RA (1986) Three-dimensional propagation of transient quasi-geostrophic eddies and its relationship with the eddy forcing of the time-mean flow. J Atmos Sci 43:1657–1678
Porcù F, Carrassi A, Medaglia CM, Prodi F, Mugnai A (2007) A study on cut-off low vertical structure and precipitation in the Mediterranean region. Meteorol Atmos Phys 96:121–140
Price JD, Vaughan G (1993) The potential for stratosphere-troposphere exchange in cut-off low systems. Q J R Meteorol Soc 119:343–365
Pyle ME, Keyser D, Bosart LF (2004) A diagnostic study of jet streaks: kinematic signatures and relationship to coherent Tropopause disturbances. Mon Wea Rev 132:297–319
Reboita MS, Nieto R, Gimeno L, Da Rocha RP, Ambrizzi T, Garreaud R, Krger LF (2010) Climatological features of cutoff low systems in the Southern Hemisphere. J Geophys Res Atmos 115:D17104
Reyers M, Shao Y (2019) Cut off lows off the coast of the Atacama Desert under present day condition and in the Last Glacial Maximum. Global Planet Change 181:102–983
Riviére G, Orlanski I (2007) Characteristics of the Atlantic storm track eddy activity and its relation with the North Atlantic Oscillation. J Atmos Sci 64:241–266
Shapiro MA (1982) Mesoscale weather systems of the central United States. CIRES Univ. of Colorado/NOAA, Boulder, p 78
Singleton AT, Reason CJC (2006) A numerical model study of an intense cut-off low pressure system over South Africa. Mon Wea Rev 135:1128–1150
Singleton AT, Reason CJC (2007) Variability in the characteristics of cut-off low pressure systems over subtropical Southern Africa. Int J Climatol 27:295–310
Stander JH, Dyson L, Engelbrecht CJ (2016) A snow forecasting decision tree for significant snowfall over the interior of South Africa. S Afr J Sci 112(9/10):1–10
Takaya K, Nakamura H (2001) A formulation of a phase-independent wave-activity flux for stationary and migratory quasigeostrophic eddies on a zonally varying basic flow. J Atmos Sci 58:608–627
Tennant W (2004) Considerations when using pre-1979 NCEP/NCAR reanalysis in the southern hemisphere. Geophys Res Lett 31:L11112
Thorncroft CD, Hoskins BJ, McIntyre ME (1993) Two paradigms of baroclinic-wave life-cycle behaviour. Q J R Meteor Soc 119:17–55
Wang S, Polvani LM (2011) Double tropopause formation in idealized baroclinic life cycles: the key role of an initial tropopause inversion layer. J Geophys Res 116:D05108
Waugh DW, Polvani LM (2000) Climatology of intrusions into the tropical upper troposphere. Geophys Res Lett 27:3857–3860
Acknowledgements
The authors would like to thank Prof Darryn Waugh for commenting on the contents of the paper and the two anonymous reviewers who provided valuable constructive criticism of the paper.
Funding
This research was supported by Water Research Commission (Grant K5-2829).
Author information
Authors and Affiliations
Corresponding author
Additional information
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
About this article
Cite this article
Ndarana, T., Rammopo, T.S., Chikoore, H. et al. A quasi-geostrophic diagnosis of the zonal flow associated with cut-off lows over South Africa and surrounding oceans. Clim Dyn 55, 2631–2644 (2020). https://doi.org/10.1007/s00382-020-05401-4
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00382-020-05401-4