Editorial Type:
Article
Article Type:
Research Article

Western Pacific Warm Pool Region Sensitivity to Convective Triggering byBoundary Layer Thermals in the NOGAPS Atmospheric GCM

James A. Ridout Naval Research Laboratory, Monterey, California

Search for other papers by James A. Ridout in
Current site
Google Scholar
PubMed Close
and
Carolyn A. Reynolds Naval Research Laboratory, Monterey, California

Search for other papers by Carolyn A. Reynolds in
Current site
Google Scholar
PubMed Close
Print Publication:
01 Jul 1998
DOI:
https://doi.org/10.1175/1520-0442(1998)011<1553:WPWPRS>2.0.CO;2
Page(s):
1553–1573
Restricted access

Abstract

The sensitivity of the atmospheric general circulation model of the Navy Operational Global Atmospheric Prediction System to a parameterization of convective triggering by atmospheric boundary layer thermals is investigated. The study focuses on the western Pacific warm pool region and examines the results of seasonal integrations of the model for the winter of 1987/88. A parameterization for thermal triggering of deep convection is presented that is based on a classification of the unstable boundary layer. Surface-based deep convection is allowed only for boundary layer regimes associated with the presence of thermals. The regime classification is expressed in terms of a Richardson number that reflects the relative significance of buoyancy and shear in the boundary layer. By constraining deep convection to conditions consistent with the occurrence of thermals (high buoyancy to shear ratios), there is a significant decrease in precipitation over the southern portion of the northeast trade wind zone in the tropical Pacific and along the ITCZ. This decrease in precipitation allows for an increased flux of moisture into the region south of the equator corresponding to the warmest portion of the Pacific warm pool. Improvements in the simulated distribution of precipitation, precipitable water, and low-level winds in the tropical Pacific are demonstrated. Over the western Pacific, the transition from free convective conditions associated with thermals to forced convective conditions is found to be primarily due to variations in mixed layer wind speed. Low-level winds thus play the major role in regulating the ability of thermals to initiate deep convection. The lack of coupling with the ocean in these simulations may possibly produce a distorted picture in this regard.

Corresponding author address: Dr. James A. Ridout, NRL-Monterey, 7 Grace Hopper Ave., Stop 2, Monterey, CA 93943-5502.

Abstract

The sensitivity of the atmospheric general circulation model of the Navy Operational Global Atmospheric Prediction System to a parameterization of convective triggering by atmospheric boundary layer thermals is investigated. The study focuses on the western Pacific warm pool region and examines the results of seasonal integrations of the model for the winter of 1987/88. A parameterization for thermal triggering of deep convection is presented that is based on a classification of the unstable boundary layer. Surface-based deep convection is allowed only for boundary layer regimes associated with the presence of thermals. The regime classification is expressed in terms of a Richardson number that reflects the relative significance of buoyancy and shear in the boundary layer. By constraining deep convection to conditions consistent with the occurrence of thermals (high buoyancy to shear ratios), there is a significant decrease in precipitation over the southern portion of the northeast trade wind zone in the tropical Pacific and along the ITCZ. This decrease in precipitation allows for an increased flux of moisture into the region south of the equator corresponding to the warmest portion of the Pacific warm pool. Improvements in the simulated distribution of precipitation, precipitable water, and low-level winds in the tropical Pacific are demonstrated. Over the western Pacific, the transition from free convective conditions associated with thermals to forced convective conditions is found to be primarily due to variations in mixed layer wind speed. Low-level winds thus play the major role in regulating the ability of thermals to initiate deep convection. The lack of coupling with the ocean in these simulations may possibly produce a distorted picture in this regard.

Corresponding author address: Dr. James A. Ridout, NRL-Monterey, 7 Grace Hopper Ave., Stop 2, Monterey, CA 93943-5502.

Save
Cover Journal of Climate
Journal of Climate

  • Beljaars, A. C. M., 1994: The parameterization of surface fluxes in large-scale models under free convection. Quart. J. Roy. Meteor. Soc.,122, 255–270.

  • ——, and A. A. M. Holtslag, 1991: Flux parameterization over land surfaces for atmospheric models. J. Appl. Meteor.,30, 327–341.

  • Bjerknes, J., 1969: Atmospheric teleconnections from the equatorial Pacific. Mon. Wea. Rev.,97, 163–172.

  • Charnock, H., 1955: Wind stress on a water surface. Quart. J. Roy. Meteor. Soc.,81, 639–640.

  • Davies, R., 1982: Documentation of the solar radiation parameterization in the GLAS climate model. NASA Tech. Memo 83961, 57 pp. [NTIS N82-30779/4.].

  • Deardorff, J. W., 1972: Numerical investigation of neutral and unstable planetary boundary layers. J. Atmos. Sci.,29, 91–115.

  • Ding, Y. H., A. Sumi, and X. S. Shen, 1995: Structures of the mixed layer and estimates of sea surface fluxes during TOGA-COARE IOP. Part I: Structures of the mixed layer. J. Meteor. Soc. Japan,73, 569–583.

  • Gates, W. L., 1992: AMIP: The Atmospheric Model Intercomparison Project. Bull. Amer. Meteor. Soc.,73, 1962–1970.

  • Grossman, R. L., 1982: An analysis of vertical velocity spectra obtained in the BOMEX fair-weather, trade-wind boundary layer. Bound.-Layer Meteor.,23, 323–357.

  • Harshvardhan, R. Davies, D. A. Randall, and T. G. Corsetti, 1987: A fast radiation parameterization for atmospheric circulation models. J. Geophys. Res.,92, 1009–1016.

  • Hogan, T. F., and T. E. Rosmond, 1991: The description of the Navy Operational Global Atmospheric Prediction System’s Spectral Forecast Model. Mon. Wea. Rev.,119, 1786–1815.

  • ——, and L. R. Brody, 1993: Sensitivity studies of the navy’s Global Forecast Model parameterizations and evaluation of improvements to NOGAPS. Mon. Wea. Rev.,121, 2373–2395.

  • Holtslag, A. A. M., E. I. F. De Bruijn, and H.-L. Pan, 1990: A high resolution air mass transformation model for short-range weather forecasting. Mon. Wea. Rev.,118, 1561–1575.

  • Huang, R., and F. Sun, 1992: Impacts of the tropical western Pacific on the East Asian summer monsoon. J. Meteor. Soc. Japan,70, 243–256.

  • Kain, J. S., and J. M. Fritsch, 1992: The role of the convective “trigger function” in numerical forecasts of mesoscale convective systems. Meteor. Atmos. Phys.,49, 93–106.

  • Kuettner, J. P., 1959: The band structure of the atmosphere. Tellus,11, 267–294.

  • ——, 1971: Cloud bands in the earth’s atmosphere—Observations and theory. Tellus,23, 404–426.

  • Lau, K.-M., J. H. Kim, and Y. Sud, 1996: Intercomparison of hydrologic processes in AMIP GCMs. Bull. Amer. Meteor. Soc.,77, 2209–2227.

  • LeMone, M. A., and W. T. Pennell, 1976: The relationship of trade wind cumulus distribution to subcloud layer fluxes and structure. Mon. Wea. Rev.,104, 524–539.

  • Lin, X., and R. H. Johnson, 1996: Kinematic and thermodynamic characteristics of the flow over the western Pacific warm pool during TOGA COARE. J. Atmos. Sci.,53, 695–715.

  • Liu, G., J. A. Curry, and R.-S. Sheu, 1995: Classification of clouds over the western equatorial Pacific Ocean using combined infrared and microwave satellite data. J. Geophys. Res.,100, 13 811–13 826.

  • Louis, J. F., M. Tiedtke, and J. F. Geleyn, 1982: A short history of the operational PBL-parameterization at ECMWF. Workshop on Boundary Layer Parameterization, Reading, United Kingdom, ECMWF, 59–79.

  • McPhaden, M. J., and J. Picaut, 1990: El Niño–Southern Oscillation displacements of the western equatorial Pacific warm pool. Science,250, 1385–1388.

  • Mechoso, C. R., and Coauthors, 1995: The seasonal cycle over the tropical Pacific in coupled ocean–atmosphere general circulation models. Mon. Wea. Rev.,123, 2825–2838.

  • Moorthi, S., and M. J. Suarez, 1992: Relaxed Arakawa–Schubert: A parameterization of moist convection for general circulation models. Mon. Wea. Rev.,120, 978–1002.

  • Newell, R. E., 1979: Climate and the ocean. Amer. Sci.,67, 405–416.

  • Ramanathan, V., and W. Collins, 1991: Thermodynamic regulation of ocean warming by cirrus clouds deduced from observations of the 1987 El Niño. Nature,351, 27–32.

  • Ridout, J. A., B. Chertock, and R. Gelaro, 1994: The response of a GCM to a change in cloud solar forcing: Model feedbacks and comparison with satellite data. J. Geophys. Res.,99, 18 555–18 576.

  • Rogers, R. F., and J. M. Fritsch, 1996: A general framework for convective trigger functions. Mon. Wea. Rev.,124, 2438–2452.

  • Scorer, R., 1972: Clouds of the World. Stackpole Books, 176 pp.

  • Slingo, J., 1987: The development and verification of a cloud prediction scheme for the ECMWF model. Quart. J. Roy. Meteor. Soc.,113, 899–927.

  • Smith, S. D., 1980: Wind stress and heat flux over the ocean in gale force winds. J. Phys. Oceanogr.,10, 709–726.

  • ——, 1988: Coefficients for sea surface wind stress, heat flux, and wind profiles as a function of wind speed and temperature. J. Geophys. Res.,93, 15 467–15 472.

  • Stull, R. B., 1988: An Introduction to Boundary Layer Meteorology. Kluwer Academic, 666 pp.

  • ——, 1994: A convective transport theory of surface fluxes. J. Atmos. Sci.,51, 3–22.

  • Tiedtke, M., 1989: A comprehensive mass flux scheme for cumulus parameterization in large-scale models. Mon. Wea. Rev.,117, 1779–1800.

  • Troen, I., and L. Mahrt, 1986: A simple model of the atmospheric boundary layer; sensitivity to surface evaporation. Bound.-Layer Meteor.,37, 129–148.

  • Waliser, D. E., 1996: Formation and limiting mechanisms for very high sea surface temperature: Linking the dynamics and the thermodynamics. J. Climate,9, 161–188.

  • Webster, P. J., and R. Lukas, 1992: TOGA COARE: The Coupled Ocean–Atmosphere Response Experiment. Bull. Amer. Meteor. Soc.,73, 1377–1416.

  • Yanai, M., S. Esbensen, and J. H. Chu, 1973: Determination of the bulk properties of tropical cloud clusters from large-scale heat and moisture budgets. J. Atmos. Sci.,30, 611–627.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 1069 589 38
PDF Downloads 172 49 0