• Albrecht, B. A., M. P. Jensen, and W. J. Syrett, 1995: Marine boundary layer structure and fractional cloudiness. J. Geophys. Res., 100 , 1420914222.

    • Search Google Scholar
    • Export Citation
  • Bretherton, C. S., 1993: Understanding Albrecht's model of trade-cumulus cloud fields. J. Atmos. Sci., 50 , 22642283.

  • Detering, H. W., and D. Etling, 1985: Application of the E-ϵ turbulence model to the atmospheric boundary layer. Bound.-Layer Meteor., 33 , 113133.

    • Search Google Scholar
    • Export Citation
  • Dickinson, R. E., A. Henderson-Sellers, and P. J. Kennedy, 1993: Biosphere–Atmosphere Transfer Scheme (BATS): Version 1e as coupled to the NCAR Community Climate Model. NCAR Tech. Note NCAR/TN-387 + STR, 72 pp.

    • Search Google Scholar
    • Export Citation
  • Douglas, M., M. Nicolini, and C. Saulo, 1998: Observational evidences of a low level jet east of the Andes during January–March 1998. Meteorologica, 23 , 6372.

    • Search Google Scholar
    • Export Citation
  • Durran, D. R., and J. B. Klemp, 1982: On the effects of moisture on the Brunt–Väisälä frequency. J. Atmos. Sci., 39 , 21522158.

  • Edwards, J. M., and A. Slingo, 1996: Studies with a flexible new radiation code. I: Choosing a configuration for a large-scale model. Quart. J. Roy. Meteor. Soc., 122 , 689719.

    • Search Google Scholar
    • Export Citation
  • Fairall, C. W., E. F. Bradley, D. P. Rogers, J. B. Edson, and G. S. Young, 1996: Bulk parameterization of air–sea fluxes for Tropical Ocean–Global Atmosphere Coupled Ocean Atmosphere Research Experiment. J. Geophys. Res., 101 , 37473764.

    • 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 , 21932208.

    • Search Google Scholar
    • Export Citation
  • Giorgi, F., and G. T. Bates, 1989: The climatological skill of a regional model over complex terrain. Mon. Wea. Rev., 117 , 23252347.

  • Gordon, C. T., A. Rosati, and R. Gudgel, 2000: Tropical sensitivity of a coupled model to specified ISCCP low clouds. J. Climate, 13 , 22392260.

    • Search Google Scholar
    • Export Citation
  • Inatsu, M., H. Mukougawa, and S-P. Xie, 2002: Stationary eddy response to surface boundary forcing: Idealized GCM experiments. J. Atmos. Sci., 59 , 18981915.

    • Search Google Scholar
    • Export Citation
  • Kalnay, E., K. C. Mo, and J. Paegle, 1986: Large-amplitude, short-scale stationary Rossby waves in the Southern Hemisphere: Observations and mechanistic experiments to determine their origin. J. Atmos. Sci., 43 , 252275.

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

  • Klein, S. A., and D. L. Hartmann, 1993: The seasonal cycle of low stratiform clouds. J. Climate, 6 , 15871606.

  • Lenters, J. D., and K. H. Cook, 1995: Simulation and diagnosis of the regional summertime precipitation climatology of South America. J. Climate, 8 , 29883005.

    • Search Google Scholar
    • Export Citation
  • Lenters, J. D., and K. H. Cook, 1997: On the origin of the Bolivian high and related circulation features of the South American climate. J. Atmos. Sci., 54 , 656677.

    • Search Google Scholar
    • Export Citation
  • Ma, C-C., C. R. Mechoso, A. W. Robertson, and A. Arakawa, 1996: Peruvian stratus clouds and the tropical Pacific circulation—A coupled ocean–atmosphere GCM study. J. Climate, 9 , 16351645.

    • Search Google Scholar
    • Export Citation
  • McCaa, J. R., and C. S. Bretherton, 2004: A new parameterization for shallow cumulus convection and its application to marine subtropical cloud-topped boundary layers. Part II: Regional simulations of marine boundary layer clouds. Mon. Wea. Rev., in press.

    • Search Google Scholar
    • Export Citation
  • Mechoso, C. R., and Coauthors, 1995: The seasonal cycle over the tropical Pacific in coupled ocean–atmosphere general circulation models. Mon. Wea. Rev., 123 , 28252838.

    • Search Google Scholar
    • Export Citation
  • Mitchell, T. P., and J. M. Wallace, 1992: The annual cycle in equatorial convection and sea surface temperature. J. Climate, 5 , 11401156.

    • Search Google Scholar
    • Export Citation
  • Nogues-Paegle, J., and Coauthors, cited, 2000: American low level jets: A scientific prospectus and implementation plan. [Available online at http://www.met.utah.edu/jnpaegle/research/ALLS. html.].

    • Search Google Scholar
    • Export Citation
  • Nordeng, T. E., 1995: Extended versions of the convective parameterisation scheme at ECMWF and their impact upon the mean climate and transient activity of the model in the Tropics. ECMWF Research Department Tech. Memo. 206, 41 pp.

    • Search Google Scholar
    • Export Citation
  • Okajima, H., S-P. Xie, and A. Numaguti, 2003: Interhemispheric coherence of tropical climate variability: Effect of climatological ITCZ. J. Meteor. Soc. Japan, in press.

    • Search Google Scholar
    • Export Citation
  • Philander, S. G. H., D. Gu, D. Halpern, G. Lambert, N-C. Lau, T. Li, and R. C. Pacanowski, 1996: The role of low-level stratus clouds in keeping the ITCZ mostly north of the equator. J. Climate, 9 , 29562972.

    • Search Google Scholar
    • Export Citation
  • Reynolds, R. W., and T. M. Smith, 1994: Improved global sea surface temperature analyses using optimum interpolation. J. Climate, 7 , 929948.

    • Search Google Scholar
    • Export Citation
  • Small, R. J., S-P. Xie, and Y. Wang, 2003: Numerical simulation of atmospheric response to Pacific tropical instability waves. J. Climate, 16 , 37233741.

    • Search Google Scholar
    • Export Citation
  • Stone, P. H., and R. M. Chervin, 1984: The influence of ocean surface temperature gradient and continentality on the Walker circulation. Part II: Prescribed global changes. Mon. Wea. Rev., 112 , 15241534.

    • Search Google Scholar
    • Export Citation
  • Sun, Z., and L. Rikus, 1999: Improved application of exponential sum fitting transmissions to inhomogeneous atmosphere. J. Geophys. Res., 104 , 62916303.

    • Search Google Scholar
    • Export Citation
  • Tiedtke, M., 1989: A comprehensive mass flux scheme for cumulus parameterization in large-scale models. Mon. Wea. Rev., 117 , 17791800.

    • Search Google Scholar
    • Export Citation
  • Walsh, K., 1994: On the influence of the Andes on the general circulation of the Southern Hemisphere. J. Climate, 7 , 10191025.

  • Wang, Y., 2001: An explicit simulation of tropical cyclones with a triply nested movable mesh primitive equation model: TCM3. Part I: Model description and control experiment. Mon. Wea. Rev., 129 , 13701394.

    • Search Google Scholar
    • Export Citation
  • Wang, Y., 2002: An explicit simulation of tropical cyclones with a triply nested movable mesh primitive equation model: TCM3. Part II: Model refinement and sensitivity to cloud microphysics. Mon. Wea. Rev., 130 , 30223036.

    • Search Google Scholar
    • Export Citation
  • Wang, Y., O. L. Sen, and B. Wang, 2003: A highly resolved regional climate model (IPRC-RegCM) and its simulation of the 1998 severe precipitation event over China. Part I: Model description and verification of simulation. J. Climate, 16 , 17211738.

    • 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
  • Wentz, F. J., C. Gentemann, D. Smith, and D. Chelton, 2000: Satellite measurements of sea surface temperature through clouds. Science, 288 , 847850.

    • Search Google Scholar
    • Export Citation
  • Wyant, M. C., C. S. Bretherton, H. A. Rand, and D. E. Stevens, 1997: Numerical simulations and a conceptual model of the subtropical marine stratocumulus to trade cumulus transition. J. Atmos. Sci., 54 , 168192.

    • Search Google Scholar
    • Export Citation
  • Xie, P., and P. A. Arkin, 1996: Analyses of global monthly precipitation using gauge observations, satellite estimates, and numerical model predictions. J. Climate, 9 , 840858.

    • Search Google Scholar
    • Export Citation
  • Xie, S-P., 1996: Westward propagation of latitudinal asymmetry in a coupled ocean–atmosphere model. J. Atmos. Sci., 53 , 32363250.

  • Xie, S-P., and K. Saito, 2001: Formation and variability of a northerly ITCZ in a hybrid coupled AGCM: Continental forcing and ocean–atmospheric feedback. J. Climate, 14 , 12621276.

    • Search Google Scholar
    • Export Citation
  • Xie, S-P., W. T. Liu, Q. Liu, and M. Nonaka, 2001: Far-reaching effects of the Hawaiian Islands on the Pacific Ocean–atmosphere system. Science, 292 , 20572060.

    • Search Google Scholar
    • Export Citation
  • Xu, K-M., and D. A. Randall, 1996: A semiempirical cloudiness parameterization for use in climate models. J. Atmos. Sci., 53 , 30843102.

    • Search Google Scholar
    • Export Citation
  • Yu, J-Y., and C. R. Mechoso, 1999: Links between annual variations of Peruvian stratocumulus clouds and of SST in the eastern equatorial Pacific. J. Climate, 12 , 33053318.

    • Search Google Scholar
    • Export Citation
  • Yuter, S. E., Y. Serra, and R. A. Houze Jr., 2000: The 1997 Pan American climate studies tropical eastern Pacific process study. Part II: Stratocumulus region. Bull. Amer. Meteor. Soc., 81 , 483490.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 294 81 8
PDF Downloads 152 69 4

Effects of the Andes on Eastern Pacific Climate: A Regional Atmospheric Model Study

View More View Less
  • 1 International Pacific Research Center, School of Ocean and Earth Science and Technology, University of Hawaii at Manoa, Honolulu, Hawaii
  • | 2 International Pacific Research Center and Department of Meteorology, University of Hawaii at Manoa, Honolulu, Hawaii
Restricted access

Abstract

A regional atmospheric model is used to study the effects of the narrow and steep Andes on the eastern Pacific climate. In the Southern Hemisphere cold season (i.e., August–October 1999), the model reproduces key climatic features, including the intertropical convergence zone (ITCZ) north of the equator and an extensive low-level cloud deck capped by a temperature inversion to the south. Blocking the warm easterly winds from South America, the Andes help maintain the divergence and temperature inversion and, hence, the stratocumulus cloud deck over the southeast Pacific off South America. In an experiment where the Andean mountains are removed, the warm advection from the South American continent lowers the inversion height and reduces the low-level divergence offshore, leading to a significant reduction in cloud amount and an increase in solar radiation that reaches the sea surface.

In March and early April 1999, the model simulates a double ITCZ in response to the seasonal warming on and south of the equator, in agreement with satellite observations. Under the same sea surface temperature forcing, the removal of the Andes prolongs the existence of the southern ITCZ for 3 weeks. Without the mountains, the intrusion of the easterlies from South America enhances the convergence in the lower atmosphere, and the transient disturbances travel freely westward from the continent. Both effects of the Andes removal favor deep convection south of the equator.

The same sensitivity experiments are repeated with orography used in T42 global models, and the results confirm that an underrepresentation of the Andes reduces the stratus clouds in the cold season and prolongs the southern ITCZ in the warm season, with both acting to weaken the latitudinal asymmetry of eastern Pacific climate. The implications of these results for coupled modeling of climatic asymmetry are discussed.

Corresponding author address: Dr. Haiming Xu, IPRC/SOEST, University of Hawaii at Manoa, 2525 Correa Road, Honolulu, HI 96822. Email: hxu@hawaii.edu

Abstract

A regional atmospheric model is used to study the effects of the narrow and steep Andes on the eastern Pacific climate. In the Southern Hemisphere cold season (i.e., August–October 1999), the model reproduces key climatic features, including the intertropical convergence zone (ITCZ) north of the equator and an extensive low-level cloud deck capped by a temperature inversion to the south. Blocking the warm easterly winds from South America, the Andes help maintain the divergence and temperature inversion and, hence, the stratocumulus cloud deck over the southeast Pacific off South America. In an experiment where the Andean mountains are removed, the warm advection from the South American continent lowers the inversion height and reduces the low-level divergence offshore, leading to a significant reduction in cloud amount and an increase in solar radiation that reaches the sea surface.

In March and early April 1999, the model simulates a double ITCZ in response to the seasonal warming on and south of the equator, in agreement with satellite observations. Under the same sea surface temperature forcing, the removal of the Andes prolongs the existence of the southern ITCZ for 3 weeks. Without the mountains, the intrusion of the easterlies from South America enhances the convergence in the lower atmosphere, and the transient disturbances travel freely westward from the continent. Both effects of the Andes removal favor deep convection south of the equator.

The same sensitivity experiments are repeated with orography used in T42 global models, and the results confirm that an underrepresentation of the Andes reduces the stratus clouds in the cold season and prolongs the southern ITCZ in the warm season, with both acting to weaken the latitudinal asymmetry of eastern Pacific climate. The implications of these results for coupled modeling of climatic asymmetry are discussed.

Corresponding author address: Dr. Haiming Xu, IPRC/SOEST, University of Hawaii at Manoa, 2525 Correa Road, Honolulu, HI 96822. Email: hxu@hawaii.edu

Save