Role of the Low-Frequency Deformation Field on the Explosive Growth of Extratropical Cyclones at the Jet Exit. Part II: Baroclinic Critical Region

G. Rivière Centre National de Recherches Météorologiques, Météo-France, Toulouse, France

Search for other papers by G. Rivière in
Current site
Google Scholar
PubMed
Close
and
A. Joly Centre National de Recherches Météorologiques, Météo-France, Toulouse, France

Search for other papers by A. Joly in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

Midlatitude cyclones tend to develop strongly in specific locations relative to the large-scale flow, such as jet-exit zones. Here, the approach developed in Part I that highlights the role of large-scale deformation in constraining the location of such events is continued. The atmospheric flow is decomposed into a high- and low-frequency part separating large and synoptic scales. A new low-frequency diagnostic has been introduced, called effective deformation Δm. It is defined as σ2mζ2m, where σm is the low-frequency deformation magnitude and ζm is the low-frequency vorticity.

While Part I focused on large-scale conditions inducing an intermediate phase of barotropic growth, the present paper concentrates on other configurations that rather prevent this phase from happening. This large-scale circulation is characterized by the presence of a strong zonal upper-level jet and a lower-level jet that are meridionally quite far from each other over the Atlantic but close to one another in the eastern Atlantic region. As high-frequency disturbances are trapped by the effective deformation of the low-frequency jets, the increasing closeness of the two jets associated with that of the two effective deformation fields computed in the lower and upper levels defines a region called the baroclinic critical region where upper high-frequency disturbances and surface cyclones may strongly interact baroclinically. The increased baroclinic energy collection resulting from this constrained configuration change is outlined. An analysis of the explosive growth of the Christmas wind storms of 1999 and of mid-December 2004 provides different realizations of this configuration and associated mechanism.

Corresponding author address: Dr. G. Rivière, Météo-France, CNRM/GMAP/RECYF, 42 av. G. Coriolis, 31057 Toulouse CEDEX, France. Email: gwendal.riviere@cnrm.meteo.fr

Abstract

Midlatitude cyclones tend to develop strongly in specific locations relative to the large-scale flow, such as jet-exit zones. Here, the approach developed in Part I that highlights the role of large-scale deformation in constraining the location of such events is continued. The atmospheric flow is decomposed into a high- and low-frequency part separating large and synoptic scales. A new low-frequency diagnostic has been introduced, called effective deformation Δm. It is defined as σ2mζ2m, where σm is the low-frequency deformation magnitude and ζm is the low-frequency vorticity.

While Part I focused on large-scale conditions inducing an intermediate phase of barotropic growth, the present paper concentrates on other configurations that rather prevent this phase from happening. This large-scale circulation is characterized by the presence of a strong zonal upper-level jet and a lower-level jet that are meridionally quite far from each other over the Atlantic but close to one another in the eastern Atlantic region. As high-frequency disturbances are trapped by the effective deformation of the low-frequency jets, the increasing closeness of the two jets associated with that of the two effective deformation fields computed in the lower and upper levels defines a region called the baroclinic critical region where upper high-frequency disturbances and surface cyclones may strongly interact baroclinically. The increased baroclinic energy collection resulting from this constrained configuration change is outlined. An analysis of the explosive growth of the Christmas wind storms of 1999 and of mid-December 2004 provides different realizations of this configuration and associated mechanism.

Corresponding author address: Dr. G. Rivière, Météo-France, CNRM/GMAP/RECYF, 42 av. G. Coriolis, 31057 Toulouse CEDEX, France. Email: gwendal.riviere@cnrm.meteo.fr

Save
  • Cai, M., and M. Mak, 1990: On the basic dynamics of regional cyclogenesis. J. Atmos. Sci., 47 , 14171442.

  • Davies, H. C., and C. H. Bishop, 1994: Eady edge waves and rapid development. J. Atmos. Sci., 51 , 19301946.

  • Hare, S. H., and I. N. James, 2001: Baroclinic developments in jet entrances and exits. I: Linear normal modes. Quart. J. Roy. Meteor. Soc., 127 , 12931303.

    • Search Google Scholar
    • Export Citation
  • Hello, G., and P. Arbogast, 2004: Two different methods to correct the initial conditions applied to the storm of 27 December 1999 over southern France. Meteor. Appl., 11 , 4157.

    • Search Google Scholar
    • Export Citation
  • Hoskins, B. J., M. E. McIntyre, and A. W. Robertson, 1985: On the use and significance of isentropic potential vorticity maps. Quart. J. Roy. Meteor. Soc., 111 , 877946.

    • Search Google Scholar
    • Export Citation
  • James, I. N., 1987: Suppression of baroclinic instability in horizontally sheared flows. J. Atmos. Sci., 44 , 37103720.

  • Petterssen, S., and S. J. Smebye, 1971: On the development of extratropical cyclones. Quart. J. Roy. Meteor. Soc., 97 , 457482.

  • Rivière, G., and A. Joly, 2006: Role of the low-frequency deformation field on the explosive growth of extratropical cyclones at the jet exit. Part I: Barotropic critical region. J. Atmos. Sci., 63 , 19651981.

    • Search Google Scholar
    • Export Citation
  • Rivière, G., B. L. Hua, and P. Klein, 2003: Perturbation growth in terms of barotropic alignment properties. Quart. J. Roy. Meteor. Soc., 129 , 26132635.

    • Search Google Scholar
    • Export Citation
  • Rivière, G., B. L. Hua, and P. Klein, 2004: Perturbation growth in terms of baroclinic alignment properties. Quart. J. Roy. Meteor. Soc., 130 , 16551673.

    • Search Google Scholar
    • Export Citation
  • Ulbrich, U., A. H. Fink, M. Klawa, and J. G. Pinto, 2001: Three extreme storms over Europe in December 1999. Weather, 56 , 7080.

  • Wang, C-C., and J. C. Rogers, 2001: A composite study of explosive cyclogenesis in different sectors of the North Atlantic. Part I: Cyclone structure and evolution. Mon. Wea. Rev., 129 , 14811499.

    • Search Google Scholar
    • Export Citation
  • Warrenfeltz, L. L., and R. L. Elsberry, 1989: Superposition effects in rapid cyclogenesis—Linear model studies. J. Atmos. Sci., 46 , 789802.

    • Search Google Scholar
    • Export Citation
  • Wernli, H., S. Dirren, M. A. Liniger, and M. Zillig, 2002: Dynamical aspects of the life cycle of the winter storm “Lothar” (24–26 December 1999). Quart. J. Roy. Meteor. Soc., 128 , 405429.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 257 45 5
PDF Downloads 148 33 1