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The role of dynamic and diabatic processes in the generation of cut-off lows over Northwest Africa

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Summary

The present observational study addresses the role of dynamic and diabatic processes leading to the generation of four deep upper-level troughs/cut-offs, involved in two extreme precipitation episodes over West Africa during the cool season. The elongated potential vorticity (PV) streamers associated with the observed troughs form as a result of an equatorward transport of high-PV air downstream of a large ridge over the central North Atlantic. Strong deformation along the eastern side of the ridge leads to a thinning of the PV streamers. In some situations the tips of the streamers break up and form distinct and long-lived stationary cut-offs near West Africa, in particular if the presence of another PV ridge downstream allows a complete isolation from the midlatitude westerlies. In other situations a prior anticyclonic wave-breaking event over Europe leads to an advection of high-PV towards the Iberian Peninsula that merges with the streamer and impedes a complete cut-off.

The observations presented here suggest that the rapid amplification of the PV ridges over the North Atlantic and thus the subsequent streamer formation are related to upstream latent heating through non-conservative diabatic reduction of upper-level PV and through the strong divergent outflow near the tropopause that support large negative isentropic PV advection. The intense latent heat release is promoted by cyclo- and frontogenesis, and the transport of warm, moist air by a low-level jet ahead of the surface cold front (often called a warm conveyor belt; WCB). Diabatic PV tendencies are highest where the WCB rises over the surface warm front to the northeast or east of the cyclone centre. In most cases the distinct heating occurs in connection with a strong upper-level jet and a rapid deepening of the involved surface cyclone. More quantitative dynamical and statistical studies of the suggested relation are needed to better understand the relative contributions of single factors to the large and synoptic scale evolution that leads to PV streamers/cut-offs near West Africa.

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References

  • C Appenzeller HC Davies (1992) ArticleTitleStructure of stratospheric intrusions into the troposphere Nature 358 570–572 Occurrence Handle10.1038/358570a0

    Article  Google Scholar 

  • C Appenzeller HC Davies WA Norton (1996) ArticleTitleFragmentation of stratospheric intrusions J Geophys Res 101 1435–1456 Occurrence Handle10.1029/95JD02674

    Article  Google Scholar 

  • J Benedict S Lee SB Feldstein (2004) ArticleTitleSynoptic view of the North Atlantic Oscillation J Atmos Sci 61 121–144 Occurrence Handle10.1175/1520-0469(2004)061<0121:SVOTNA>2.0.CO;2

    Article  Google Scholar 

  • Browning K (1990) Organization of clouds and precipitation in extratropical cyclones. In: Extratropical cyclones: The Erik H. Palmén Memorial Volume (Newton C, Holopainen E, eds), pp 129–153. Boston: Amer Meteor Soc

  • Cammas J-P, Keyser D, Lackmann GM, Molinari J (1994) Diabatic redistribution of potential vorticity accompanying the development of an outflow jet within a strong extratropical cyclone. In: Preprints, Int. Symp. on the Life Cycles of Extratropical Cyclones, Vol. II, pp 403–409. Bergen: Geophysical Institute, University of Bergen

  • S Eckhardt A Stohl H Wernli P James C Forster N Spichtinger (2004) ArticleTitleA 15-year climatology of warm conveyor belts J Clim 17 218–237 Occurrence Handle10.1175/1520-0442(2004)017<0218:AYCOWC>2.0.CO;2

    Article  Google Scholar 

  • KA Emanuel M Fantini AJ Thorpe (1987) ArticleTitleBaroclinic instability in an environment of small stability to slantwise moist convection. Part I: two-dimensional models J Atmos Sci 44 1559–1573 Occurrence Handle10.1175/1520-0469(1987)044<1559:BIIAEO>2.0.CO;2

    Article  Google Scholar 

  • AH Fink P Knippertz (2003) ArticleTitleAn extreme precipitation event in southern Morocco in spring 2002 and some hydrological implications Weather 58 377–387 Occurrence Handle10.1256/wea.256.02

    Article  Google Scholar 

  • BJ Hoskins ME McIntyre AW Robertson (1985) ArticleTitleOn the use and significance of isentropic potential vorticity maps Q J Roy Meteor Soc 111 877–946 Occurrence Handle10.1256/smsqj.47001

    Article  Google Scholar 

  • JW Hurrell (1995) ArticleTitleDecadal trends in the North Atlantic Oscillation and relationships to regional temperature and precipitation Science 269 676–679 Occurrence Handle10.1126/science.269.5224.676

    Article  Google Scholar 

  • H Iskenderian (1995) ArticleTitleA 10-year climatology of northern hemisphere tropical cloud plumes and their composite flow patterns J Clim 8 1630–1637 Occurrence Handle10.1175/1520-0442(1995)008<1630:AYCONH>2.0.CO;2

    Article  Google Scholar 

  • Jones SC, collaborators (2003) The extratropical transition of tropical cyclones: forecast challenges, current understanding, and future directions. Wea Forecast 18: 1052–1092

    Google Scholar 

  • GN Kiladis (1998) ArticleTitleObservations of Rossby waves linked to convection over the eastern tropical Pacific J Atmos Sci 55 321–339 Occurrence Handle10.1175/1520-0469(1998)055<0321:OORWLT>2.0.CO;2

    Article  Google Scholar 

  • GN Kiladis KM Weickmann (1992) ArticleTitleCirculation anomalies associated with tropical convection during northern winter Mon Wea Rev 120 1900–1923 Occurrence Handle10.1175/1520-0493(1992)120<1900:CAAWTC>2.0.CO;2

    Article  Google Scholar 

  • GN Kiladis KM Weickmann (1997) ArticleTitleHorizontal structure and seasonality of large-scale circulations associated withsubmonthly tropical convection Mon Wea Rev 125 1997–2013 Occurrence Handle10.1175/1520-0493(1997)125<1997:HSASOL>2.0.CO;2

    Article  Google Scholar 

  • P Knippertz (2004) ArticleTitleA simple identification scheme for upper-level troughs and its application to winter precipitation variability in Northwest Africa J Clim 17 1411–1418 Occurrence Handle10.1175/1520-0442(2004)017<1411:ASISFU>2.0.CO;2

    Article  Google Scholar 

  • P Knippertz (2005) ArticleTitleTropical-extratropical interactions associated with an Atlantic tropical plume and subtropical jet streak Mon Wea Rev 133 2759–2776 Occurrence Handle10.1175/MWR2999.1

    Article  Google Scholar 

  • P Knippertz JE Martin (2005) ArticleTitleTropical plumes and extreme precipitation in subtropical and tropical West Africa Q J Roy Meteor Soc 131 2337–2365 Occurrence Handle10.1256/qj.04.148

    Article  Google Scholar 

  • P Knippertz U Ulbrich F Marques J Corte-Real (2003) ArticleTitleDecadal changes in the link El Niño, NAO and European/North African rainfall Int J Climatol 23 1293–1311 Occurrence Handle10.1002/joc.944

    Article  Google Scholar 

  • B Liebmann DL Hartmann (1984) ArticleTitleAn observational study of tropical–midlatitude interaction on intraseasonal time scales during winter J Atmos Sci 41 3333–3350 Occurrence Handle10.1175/1520-0469(1984)041<3333:AOSOTI>2.0.CO;2

    Article  Google Scholar 

  • JE Martin JA Otkin (2004) ArticleTitleThe rapid growth and decay of an extratropical cyclone over the Central Pacific Ocean Wea Forecast 19 358–376 Occurrence Handle10.1175/1520-0434(2004)019<0358:TRGADO>2.0.CO;2

    Article  Google Scholar 

  • AC Massacand H Wernli HC Davies (2001) ArticleTitleInfluence of upstream diabatic heating upon an Alpine event of heavy precipitation Mon Wea Rev 129 2822–2828 Occurrence Handle10.1175/1520-0493(2001)129<2822:IOUDHU>2.0.CO;2

    Article  Google Scholar 

  • JP McGuirk DJ Ulsh (1990) ArticleTitleEvolution of tropical plumes in VAS water vapor imagery Mon Wea Rev 118 1758–1766 Occurrence Handle10.1175/1520-0493(1990)118<1758:EOTPIV>2.0.CO;2

    Article  Google Scholar 

  • SE Nicholson J Kim (1997) ArticleTitleThe relationship of the El Niño-southern oscillation to African rainfall Int J Climatol 17 117–135 Occurrence Handle10.1002/(SICI)1097-0088(199702)17:2<117::AID-JOC84>3.0.CO;2-O

    Article  Google Scholar 

  • R Nieto L Gimeno L de la Torre P Ribera D Gallego R García-Herrera JA García M Nuñez A Redaño J Lorente (2005) ArticleTitleClimatological features of cut-off low systems in the northern hemisphere J Clim 18 3085–3103 Occurrence Handle10.1175/JCLI3386.1

    Article  Google Scholar 

  • JL Pelly BJ Hoskins (2003) ArticleTitleA new perspective on blocking J Atmos Sci 60 743–755 Occurrence Handle10.1175/1520-0469(2003)060<0743:ANPOB>2.0.CO;2

    Article  Google Scholar 

  • DJ Posselt JE Martin (2004) ArticleTitleThe effect of latent heat release on the evolution of a warm occluded thermal structure Mon Wea Rev 132 578–599 Occurrence Handle10.1175/1520-0493(2004)132<0578:TEOLHR>2.0.CO;2

    Article  Google Scholar 

  • GA Postel MH Hitchman (1999) ArticleTitleClimatology of Rossby wave breaking along the subtropical tropopause J Atmos Sci 56 359–373 Occurrence Handle10.1175/1520-0469(1999)056<0359:ACORWB>2.0.CO;2

    Article  Google Scholar 

  • PJ Roebber (1984) ArticleTitleStatistical analysis and updated climatology of explosive cyclogenesis Mon Wea Rev 112 1577–1589 Occurrence Handle10.1175/1520-0493(1984)112<1577:SAAUCO>2.0.CO;2

    Article  Google Scholar 

  • F Sanders JR Gyakum (1980) ArticleTitleSynoptic-dynamic climatology of the “bomb” Mon Wea Rev 108 1589–1606 Occurrence Handle10.1175/1520-0493(1980)108<1589:SDCOT>2.0.CO;2

    Article  Google Scholar 

  • MA Shapiro H Wernli NA Bond R Langland (2001) ArticleTitleThe influence of the 1997–99 El Niño Southern Oscillation on extratropical baroclinic life cycles over the eastern North Pacific Q J Roy Meteor Soc 127 331–342

    Google Scholar 

  • MT Stoelinga (1996) ArticleTitleA potential vorticity-based study of therole of diabatic heating and friction in a numericallysimulated baroclinic cyclone Mon Wea Rev 124 849–874 Occurrence Handle10.1175/1520-0493(1996)124<0849:APVBSO>2.0.CO;2

    Article  Google Scholar 

  • C Thorncroft SC Jones (2000) ArticleTitleThe extratropical transitions of hurricanes Felix and Iris in 1995 Mon Wea Rev 128 947–972 Occurrence Handle10.1175/1520-0493(2000)128<0947:TETOHF>2.0.CO;2

    Article  Google Scholar 

  • CD Thorncroft BJ Hoskins ME McIntyre (1993) ArticleTitleTwo paradigms of baroclinic-wave life-cycle behavior Q J Roy Meteor Soc 119 17–55 Occurrence Handle10.1002/qj.49711950903

    Article  Google Scholar 

  • Trenberth KE (1992) Global analyses from ECMWF and atlas of 1000 to 10 hPa circulation statistics. NCAR Tech Note, NCAR/TN-373 + STR, National Center for Atmospheric Research, Boulder, CO. NTIS PB92-218718/AS, 191 pp

  • Uccellini LW (1999) Processes contributing to the rapid development of extratropical cyclones. In: The life cycles of extratropical cyclones (Shapiro MA, Gronas S, eds), pp 81–105. Boston: Amer Meteor Soc

  • LW Uccellini PJ Kocin (1987) ArticleTitleThe interaction of jet streak circulations during heavy snow events along the east coast of the United States Wea Forecast 2 289–308 Occurrence Handle10.1175/1520-0434(1987)002<0289:TIOJSC>2.0.CO;2

    Article  Google Scholar 

  • LW Uccellini PJ Kocin RA Petersen CH Wash KF Brill (1984) ArticleTitleThe Presidents’ Day cyclone of 18–19 February 1979: synoptic overview and analysis of the subtropical jet streak influencing the pre-cyclogenesis period Mon Wea Rev 112 31–55 Occurrence Handle10.1175/1520-0493(1984)112<0031:TPDCOF>2.0.CO;2

    Article  Google Scholar 

  • PJ Webster JR Holton (1982) ArticleTitleCross-equatorial response tomiddle-latitude forcing in a zonally varying basic state J Atmos Sci 39 722–733 Occurrence Handle10.1175/1520-0469(1982)039<0722:CERTML>2.0.CO;2

    Article  Google Scholar 

  • H Wernli (1997) ArticleTitleA Lagrangian-based analysis of extratropical cyclones. II: a detailed case study Q J Roy Meteor Soc 123 1677–1706 Occurrence Handle10.1002/qj.49712354211

    Article  Google Scholar 

  • Wernli H, Sprenger M (2006) Identification and ERA-15 climatology of potential vorticity streamers and cutoffs near the extratropical tropopause. J Atmos Sci (in press)

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  1. Department of Atmospheric and Oceanic Sciences, University of Wisconsin–Madison, Madison, Wisconsin, USA

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  1. P. Knippertz
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Knippertz, P., Martin, J. The role of dynamic and diabatic processes in the generation of cut-off lows over Northwest Africa. Meteorol. Atmos. Phys. 96, 3–19 (2007). https://doi.org/10.1007/s00703-006-0217-4

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