• Ayers, J. K., P. Minnis, P. W. Heck, A. D. Rapp, D. F. Young, W. L. Smith Jr., and L. Nguyen, 2002: A one-year climatology of cloud properties derived from GOES-8 over the southeastern Pacific for PACS. Preprints, 11th Conf. on Cloud Physics, Ogden, UT, Amer. Meteor. Soc., CD-ROM, P2.10.

  • Benjamin, S. G., and T. N. Carlson, 1986: Some effects of the surface heating and topography on the regional severe storm environment. Part I: Three-dimensional simulations. Mon. Wea. Rev., 114 , 9751001.

    • Search Google Scholar
    • Export Citation
  • Blackadar, A. K., 1976: High resolution models of the planetary boundary layer. Advances in Environmental Sciences and Engineering, Vol. 1, J. R. Pfafflin and E. N. Ziegler, Eds., Gordon and Breach, 50–85.

    • Search Google Scholar
    • Export Citation
  • Bridger, A. F. C., W. C. Brick, and P. F. Lester, 1993: The structure of the marine inversion layer off the central California coast: Mesoscale conditions. Mon. Wea. Rev., 121 , 335351.

    • Search Google Scholar
    • Export Citation
  • Dudhia, J., 1989: Numerical study of convection observed during the Winter Monsoon Experiment using a mesoscale two-dimensional model. J. Atmos. Sci., 46 , 30773107.

    • Search Google Scholar
    • Export Citation
  • Garreaud, R. D., and J. Rutllant, 2003: Coastal lows along the subtropical west coast of South America: Numerical simulation of a typical case. Mon. Wea. Rev., 131 , 891908.

    • Search Google Scholar
    • Export Citation
  • Garreaud, R. D., J. Rutllant, J. Quintana, J. Carrasco, and P. Minnis, 2001: CIMAR-5: A snapshot of the lower troposphere over the subtropical southeast Pacific. Bull. Amer. Meteor. Soc., 82 , 21932207.

    • Search Google Scholar
    • Export Citation
  • Garreaud, R. D., J. Rutllant, and H. Fuenzalida, 2002: Coastal lows along the subtropical west coast of South America: Mean structure and evolution. Mon. Wea. Rev., 130 , 7588.

    • Search Google Scholar
    • Export Citation
  • Gayno, G. A., 1994: Development of a high-order, fog-producing boundary layer suitable for use in numerical weather prediction. M.S. thesis, Department of Meteorology, The Pennsylvania State University, 104 pp.

  • Grell, G. A., J. Dudhia, and D. R. Stauffer, 1994: A description of the fifth-generation Penn State University/NCAR Mesoscale Model (MM5). NCAR Tech. Note NCAR/TN-398+STR, 122 pp.

  • Halpern, D., and Coauthors, 2002: An Atlas of Monthly Mean Distributions of SSMI Wind Speed, AVHRR Sea Surface Temperature, TMI Sea Surface Temperature, QuickSCAT Ocean Vector Wind, SeaWiFS Chlorophill-a, and TOPEX/POSEIDON Sea Surface Topography during 2001. JPL Publication 02–23, NASA, 210 pp.

  • Josey, S. A., E. C. Kent, and P. K. Taylor, 2002: Wind stress forcing of the ocean in the SOC climatology: Comparisons with the NCEP–NCAR, ECMWF, UWM/COADS, and Hellerman and Rosenstein datasets. J. Phys. Oceanogr., 32 , 19932019.

    • Search Google Scholar
    • Export Citation
  • Kain, J. S., and J. M. Fritsch, 1983: Convective parameterization for mesoscale models: The Kain–Fritsch scheme. The Representation of Cumulus Convection in Numerical Models, Meteor. Monogr., No. 46, Amer. Meteor. Soc., 165–170.

  • Kalnay, E., and Coauthors, 1996: The NCEP/NCAR 40-Year Reanalysis Project. Bull. Amer. Meteor. Soc., 77 , 437471.

  • Klein, S. A., 1997: Synoptic variability of low-cloud properties and meteorological parameters in the subtropical trade wind boundary layer. J. Climate, 10 , 20182039.

    • Search Google Scholar
    • Export Citation
  • Minnis, P., and E. F. Harrison, 1984: Diurnal variability of regional cloud and clear-sky radiative parameters derived from GOES data. Part II: November 1978 cloud distribution. J. Climate Appl. Meteor., 23 , 10121031.

    • Search Google Scholar
    • Export Citation
  • Minnis, P., and Coauthors, 2001: Cloud coverage during FIRE ACE derived from AVHRR data. J. Geophys. Res., 106 , 1521515233.

  • Muñoz, R., and R. Garreaud, 2004: Dynamics of the low level jet off the west coast of subtropical South America. Mon. Wea. Rev., submitted.

    • Search Google Scholar
    • Export Citation
  • Parish, T. R., 2000: Forcing of the summertime low-level jet along the California coast. J. Appl. Meteor., 39 , 24212433.

  • Reynolds, R. W., and D. C. Marsico, 1993: An improved real-time global sea surface temperature analysis. J. Climate, 6 , 114119.

  • Rousseeuw, P. J., 1987: Silhouettes: A graphical aid to the interpretation and validation of cluster analysis. J. Comput. Appl. Math., 20 , 5365.

    • Search Google Scholar
    • Export Citation
  • Rutllant, J., 1993: Coastal lows and associated southerly winds in north-central Chile. Preprints, Fourth Int. Conf. on Southern Hemisphere Meteorology, Hobart, Australia, Amer. Meteor. Soc., 268–269.

  • Rutllant, J., 1994: On the generation of coastal lows in central Chile. IAEA/UNESCO Internal Report IC/94/167, International Centre for Theoretical Physics, 15 pp.

  • Rutllant, J., and V. Montecino, 2002: Multiscale upwelling forcing cycles and biological response off north-central Chile. Rev. Chilena Hist. Natural., 75 , 217231.

    • Search Google Scholar
    • Export Citation
  • Rutllant, J., I. Masotti, J. Calderón, and S. Vega, 2004: A comparison of spring coastal upwelling off central Chile at the extremes of the 1996–1997 ENSO cycle. Cont. Shelf Res., 24 , 773787.

    • Search Google Scholar
    • Export Citation
  • Shaffer, G., S. Hormazábal, O. Pizarro, and S. Salinas, 1999: Seasonal and interannual variability of currents and temperature over the slope off central Chile. J. Geophys. Res., 104 , 2995129961.

    • Search Google Scholar
    • Export Citation
  • Shafran, P. C., N. L. Seaman, and G. A. Gayno, 2000: Evaluation of numerical predictions of boundary layer structure during the Lake Michigan Ozone Study (LMOS). J. Appl. Meteor., 39 , 412426.

    • Search Google Scholar
    • Export Citation
  • Wang, Y., S-P. Xie, H. Xu, and B. Wang, 2004: Regional model simulations of marine boundary layer clouds over the southeast Pacific off South America. Part I: Control experiment. Mon. Wea. Rev., 132 , 274296.

    • Search Google Scholar
    • Export Citation
  • Wilks, D. S., 1995: Statistical Methods in the Atmospheric Sciences: An Introduction. Academic Press, 467 pp.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 6 6 6
PDF Downloads 3 3 3

The Low-Level Jet off the West Coast of Subtropical South America: Structure and Variability

View More View Less
  • 1 Department of Geophysics, Universidad de Chile, Santiago, Chile
Restricted access

Abstract

The subtropical anticyclone over the southeast Pacific drives low-level southerly flow along the west coast of South America. In turn, the alongshore flow induces coastal upwelling that supports a wealth of fishery resources. Within this region, satellite data, marine reports, and coastal observations indicate the existence of a southerly coastal jet (i.e., a maximum of wind speed) off central Chile (26°–36°S). The mean features and variability of this southerly jet is documented in this work using 4 yr of satellite-derived sea surface winds, complemented by satellite-derived cloud amount fields and atmospheric reanalysis. Furthermore, analysis of in situ data and model results of a well-defined jet event during October 2000 allows a preliminary description of the jet’s three-dimensional structure and a comparison with the northerly jet off the coast of California.

Southerly jet events off central Chile occur year-round, but they are more frequent during spring–summer (over 60% of the time). The jet is characterized by an elongated maximum of surface wind speed (∼10 m s−1) with its axis at about 150 km off the coast and a cross-shore scale of about 500 km. The two Quick Scatterometer (QuikSCAT) fields per day (a.m. and p.m. passes) allow a rough estimate of the amplitude of the diurnal cycle of the surface winds, which appears to be remarkably small in the region of the jet. The jet events are associated with the passage of a midlatitude ridge over the southeast Pacific strengthening the subtropical anticyclone. Upstream and over the jet region the coastal deck of stratocumulus clouds tends to dissipate in contrast to an increase in cloudiness downstream of the jet. In the case study the jet core resides at the top of the marine boundary layer (MBL)/inversion layer. Weak offshore flow prevails above the jet axis, and even weaker onshore flow prevails in the MBL. Consistent with its subtropical location the jet is embedded in a region of large-scale subsidence; nevertheless a mesoscale area of mean upward motion is simulated just downstream of the jet core.

Corresponding author address: Dr. René Garreaud, Departamento de Geofísica, Universidad de Chile, Blanco Encalada 2002, Santiago, Chile. Email: rgarreau@dgf.uchile.cl

Abstract

The subtropical anticyclone over the southeast Pacific drives low-level southerly flow along the west coast of South America. In turn, the alongshore flow induces coastal upwelling that supports a wealth of fishery resources. Within this region, satellite data, marine reports, and coastal observations indicate the existence of a southerly coastal jet (i.e., a maximum of wind speed) off central Chile (26°–36°S). The mean features and variability of this southerly jet is documented in this work using 4 yr of satellite-derived sea surface winds, complemented by satellite-derived cloud amount fields and atmospheric reanalysis. Furthermore, analysis of in situ data and model results of a well-defined jet event during October 2000 allows a preliminary description of the jet’s three-dimensional structure and a comparison with the northerly jet off the coast of California.

Southerly jet events off central Chile occur year-round, but they are more frequent during spring–summer (over 60% of the time). The jet is characterized by an elongated maximum of surface wind speed (∼10 m s−1) with its axis at about 150 km off the coast and a cross-shore scale of about 500 km. The two Quick Scatterometer (QuikSCAT) fields per day (a.m. and p.m. passes) allow a rough estimate of the amplitude of the diurnal cycle of the surface winds, which appears to be remarkably small in the region of the jet. The jet events are associated with the passage of a midlatitude ridge over the southeast Pacific strengthening the subtropical anticyclone. Upstream and over the jet region the coastal deck of stratocumulus clouds tends to dissipate in contrast to an increase in cloudiness downstream of the jet. In the case study the jet core resides at the top of the marine boundary layer (MBL)/inversion layer. Weak offshore flow prevails above the jet axis, and even weaker onshore flow prevails in the MBL. Consistent with its subtropical location the jet is embedded in a region of large-scale subsidence; nevertheless a mesoscale area of mean upward motion is simulated just downstream of the jet core.

Corresponding author address: Dr. René Garreaud, Departamento de Geofísica, Universidad de Chile, Blanco Encalada 2002, Santiago, Chile. Email: rgarreau@dgf.uchile.cl

Save