Cut-off low systems
A cut-off low (COL) corresponds to a closed low in the upper troposphere that has become completely detached (cut off) from the basic westerly current usually being advected equatorward of the mid-latitude westerlies (Gimeno et al., 2007a). These systems are slow moving and often stay over the same region for several days, therefore capable of considerably affecting the weather conditions felt at the surface. Moreover, these features play a significant role in the tropospheric ozone balance through dissipation and mixing of stratospheric ozone. Because these structures require information from the upper troposphere they were only described after the use of upper air soundings became available, i.e. after the 2nd World War (e.g. Douglas, 1947; Hsieh, 1949). Afterwards the interest on these events has decreased considerably, partially due to the inexistence of long and reliable climatologies.
In recent years there has been a significant increase on studies of polar and mid-latitude COLs (less of subtropical ones) focusing different perspectives, namely; a) modelling of COL case studies and tropopause folds (e.g. Ebel et al., 1991; Langford et al., 1996), b) impact of COLs on tropospheric ozone (e.g. Vaughan y Price, 1989; Oltmans et al., 1992; Ancellet et al., 1994; Barsby y Diab, 1995; Cuevas et al., 2000; Kentarchos et al., 2000; Baray et al. 2003), c) mesoscale analysis of the life cycle of a COL (e.g. Ravetta and Ancellet, 2000; Gouget et al., 2000). Furthermore, COL climatologies based on (painstaking) visual inspection of thousands of charts (e.g. Price and Vaughan, 1992; Kentarchos et al., 1998, 1999) are now being substituted by much faster objective procedures (e.g. Nieto et al, 2005) allowing new directions of COLs related studies.
The climate change group of IDL has done some work on these systems namely helping to analyse the precipitation and cloudiness associated with COLs located over Iberia (Nieto et al., 2007a). Additionally we have looked in detail on how these systems are related with the occurrence of blocking systems over Europe (Nieto et al., 2007b) and with the decay of the Polar vortex (Gimeno et al., 2007b). The group has also contributed significantly with a new long-term climatology for the entire Northern Hemisphere using different Reanalyses datasets and methodological approaches (Nieto et al., 2008).
Figure 1. Diagram of the typical synoptic situation of a cut-off low showing the different stages of its life cycle using the geopotential field at 200 hPa.
- Ancellet, G., M. Beekmann and A. Papayannis, 1994: Impact of a cut-off lows development transport of ozone in the free troposphere. Journal of Geophysical Research, 99, 3451-3468.
- Baray, J.L , S. Baldy, R.D. Diab and J.P. Cammas, 2003: Dynamical study of a tropical cut-off low over South Africa and its impact on tropospheric ozone. Atmospheric Environment., 37, 1475–1488.
- Barsby, J. and R.D. Diab, 1995: Total ozone and synoptic weather relationships over southern Africa and sorrounding oceans. Journal Geophysical. Research, 100, 3023-3032.
- Cuevas, E., Diamantino V. Henriques and J.M. Sancho, 2000: Stratosphere-Troposphere Exchange events over North Atlantic subtropical region. Proceedings 2ª Asamblea Hispano-Portuguesa de Geodesia y Geofísica, Lagos (Portugal), 8-12 febrero 2000, pp 451-452.
- Douglas, C.K.M. (1947). “Cold Pools”. Meteorological Magazine, 76, 225-231.
- Ebel, A., H. Hass, H.J. Jakobs, M. Laule, M. Memmesheimer and A. Oberreuter, 1991: Simulation of ozone intrusion caused by tropopause fold and COL. Atmospheric Environment, 25A, 2131-2144.
- Gimeno L , Trigo RM, Ribera P, García JA (2007a) Special Issue on Cut-off Low systems (COL), Meteorology and Atmospheric Physics, 96, 1-2 (doi: 10.1007/s00703-006-0216-5) (Published)
- Gimeno L, Nieto R and Trigo R. (2007b) Decay of the Northern Hemisphere stratospheric polar vortex and the occurrence of cut-off low systems. Meteorology & Atmospheric Physics 96, 21-28 ; doi:10.1007/s00703-006-0218-3.
- Gouget, H., G. Vaughan, A. Marenco and H.G.J. Smit, 2000: Decay of a cut off-low and contribution to stratosphere-troposphere exchange. Quarterly Journal of the Royal Meteorological Society, 126, 1117-1141.
- Hsieh, Y.P. (1949) “An investigation of a selected cold vortex over North America”, Journal of Meteorology, 6, 401-410.
- Kentarchos, A. and T.D. Davies, 1998: A climatology of cut-off lows at 200 hPa in the Northern Hemisphere, 1990-1994. International Journal of. Climatology, 18, 379-390.
- Kentarchos, A., G.J. Roelofs, J. Lelieveld and E. Cuevas, 2000: On the origin of elevated surface ozone concentrations at Izaña Observatory during the last days of March1996: a model study. Geophysical Research Letters, Vol 27, 22, 3699-3702.
- Langford, A., C. Masters, M. Proffitt, E. Hsie and A. Tuck, 1996: Ozone measurenments in a tropopause fold associated with a cut-off low system. Geophysical Research Letters, 23, 2501-2504 (and correction in Geophysical Research Letters , 24, 109-110.
- Nieto R., L. Gimeno, L. de la Torre, P. Ribera, D. Gallego, R. García-Herrera, J.A. García, M. Núñez, A. Redaño and J.Lorente, 2005: Climatological features of Cut-off low systems in the Northern Hemisphere. Journal of Climate, 18, 3085-3113.
- Nieto R, Gimeno L, Añel JA, de la Torre L, Gallego D, Barriopedro D, Gallego MC, Gordillo A, Redaño A and Delgado G. (2007a) Analysis of the precipitation and cloudiness associated with COLs occurrence in the Iberian Peninsula. Meteorology & Atmospheric Physics 96, 103-119 ; doi:10.1007/s00703-006-0223-6.
- Nieto R, Gimeno L, de la Torre L, Ribera P, Barriopedro D, García-Herrera R, Serrano A, Gordillo A, Redaño A y Lorente J. (2007b) Interannual variability of cut-off low systems over the European sector: the role of blocking and the northern hemisphere circulation modes. Meteorology & Atmospheric Physics 96, 85-101 ; doi:10.1007/s00703-006-0222-7.
- Nieto R, Sprenger M, Wernil H, Trigo R.M., Gimeno L. (2008). Identification and Climatology of Cutoff Lows near the Tropopause. Annals of the New York Academy of Sciences, 1146, 256–290, doi: 10.1196/annals.1446.016
- Oltmans, S., H. Levy II, J.M. Harris, J.T. Merrill, J.L. Moody, J. Lathrop, E. Cuevas, M. Trainer, M.S. O'Neill, J.M. Prospero, H. Vömel and B.J. Johnson, 1996: Summer and Spring Ozone Profiles Over the North Atlantic from Ozononesonde Measurements. Journal of Geophysical Research, 101, D22, 29179-29200.
- Price, J.D. and G. Vaughan, 1992: Statistical studies of cut-off low systems. Annales Geophysicae, 10, 96-102.
- Ravetta, F. and G. Ancellet, 2000: Identification of dynamical processes at the tropopause during the decay of a cut-off low using high resolution airbone lidar ozone measurements. Monthly Weather Review, 128, 3252-3267.
- Vaughan, G. and J.D. Price, 1989: Ozone transport into the troposphere in a cut-off low event. Ozone In The Free Atmosphere, A Deepak, Virginia, USA, 415-418.