• Anderson, B. T., J. O. Roads, S. C. Chen, and H. M. H. Juang, 2000: Regional simulation of the low level monsoon winds over the Gulf of California and southwestern United States. J. Geophys. Res., 105 , 1795517969.

    • Search Google Scholar
    • Export Citation
  • Anthes, R. A., Y-H. Kuo, D. Baumhefner, R. M. Errico, and T. W. Bettge, 1985: Predictability of mesoscale atmospheric motions. Advances in Geophysics, Vol. 28B, Academic Press, 159–202.

  • Berbery, E. H., 2001: Mesoscale moisture analysis of the North American monsoon. J. Climate, 14 , 121137.

  • Berbery, E. H., and M. S. Fox-Rabinovitz, 2003: Multiscale diagnosis of the North American monsoon system using a variable-resolution GCM. J. Climate, 16 , 19291947.

    • Search Google Scholar
    • Export Citation
  • Brenner, I. S., 1974: A surge of maritime tropical air—Gulf of California to the southwestern United States. Mon. Wea. Rev., 102 , 375389.

    • Search Google Scholar
    • Export Citation
  • Burpee, R. W., 1972: The origin and structure of easterly waves in the lower troposphere of North Africa. J. Atmos. Sci., 29 , 7790.

  • Burpee, R. W., 1974: Characteristics of North African easterly waves during the summers of 1968 and 1969. J. Atmos. Sci., 31 , 15561570.

    • Search Google Scholar
    • Export Citation
  • Davies, H. C., and R. E. Turner, 1977: Updating prediction models by dynamical relaxation: An examination of the technique. Quart. J. Roy. Meteor. Soc., 103 , 225245.

    • Search Google Scholar
    • Export Citation
  • Douglas, M. W., 1995: The summertime low-level jet over the Gulf of California. Mon. Wea. Rev., 123 , 23342347.

  • Douglas, M. W., and J. C. Leal, 2003: Summertime surges over the Gulf of California: Aspects of their climatology, mean structure, and evolution from radiosonde, NCEP reanalysis, and rainfall data. Wea. Forecasting, 18 , 5574.

    • Search Google Scholar
    • Export Citation
  • Douglas, M. W., R. A. Maddox, K. Howard, and S. Reyes, 1993: The Mexican monsoon. J. Climate, 6 , 16651678.

  • Douglas, M. W., A. Valdez-Manzanilla, and R. G. Cueto, 1998: Diurnal variation and horizontal extent of the low-level jet over the northern Gulf of California. Mon. Wea. Rev., 126 , 20172025.

    • 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
  • Dudhia, J., 1993: A nonhydrostatic version of the Penn State–NCAR Mesoscale Model: Validation tests and simulation of an Atlantic cyclone and cold front. Mon. Wea. Rev., 121 , 14931513.

    • Search Google Scholar
    • Export Citation
  • Fuller, R. D., and D. J. Stensrud, 2000: The relationship between tropical easterly waves and surges over the Gulf of California during the North American Monsoon. Mon. Wea. Rev., 128 , 29832989.

    • Search Google Scholar
    • Export Citation
  • Gochis, D. J., W. J. Shuttleworth, and Z-L. Yang, 2002: Sensitivity of the modeled North American monsoon regional climate to convective parameterization. Mon. Wea. Rev., 130 , 12821298.

    • Search Google Scholar
    • Export Citation
  • Gutzler, D. S., and Coauthors, 2005: The North American Monsoon Model Assessment Project: Integrating numerical modeling into a field-based process study. Bull. Amer. Meteor. Soc., 86 , 14231429.

    • Search Google Scholar
    • Export Citation
  • Hales, J. E., 1972: Surges of maritime tropical air northward over the Gulf of California. Mon. Wea. Rev., 100 , 298306.

  • Hales, J. E., 1974: Southwestern United States summer monsoon source—Gulf of Mexico or Pacific Ocean. J. Appl. Meteor., 13 , 331342.

    • Search Google Scholar
    • Export Citation
  • Higgins, R. W., and W. Shi, 2000: Dominant factors responsible for interannual variability of the summer monsoon in the southwestern United States. J. Climate, 13 , 759776.

    • Search Google Scholar
    • Export Citation
  • Higgins, R. W., Y. Yao, and X. L. Wang, 1997: Influence of the North American monsoon system on the U.S. summer precipitation regime. J. Climate, 10 , 26002622.

    • Search Google Scholar
    • Export Citation
  • Higgins, R. W., K. C. Mo, and Y. Yao, 1998: Interannual variability of the U.S. summer precipitation regime with emphasis on the southwestern monsoon. J. Climate, 11 , 25822606.

    • Search Google Scholar
    • Export Citation
  • Higgins, R. W., W. Shi, and C. Hain, 2004: Relationships between Gulf of California moisture surges and precipitation in the southwestern United States. J. Climate, 17 , 29832997.

    • Search Google Scholar
    • Export Citation
  • Hong, S-Y., and H-L. Pan, 1996: Nonlocal boundary layer vertical diffusion in a medium-range forecast model. Mon. Wea. Rev., 124 , 23222339.

    • Search Google Scholar
    • Export Citation
  • Kain, J. S., and J. M. Fritsch, 1990: A one-dimensional entraining/detraining plume model and its application in convective parameterization. J. Atmos. Sci., 47 , 27842802.

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

  • McCollum, D. M., R. A. Maddox, and K. W. Howard, 1995: Case study of a severe mesoscale convective system in central Arizona. Wea. Forecasting, 10 , 643668.

    • Search Google Scholar
    • Export Citation
  • Mlawer, E. J., S. J. Taubman, P. D. Iacono, and S. A. Clough, 1997: Radiative transfer for inhomogenous atmosphere: RRTM, a validated correlated-k model for the longwave. J. Geophys. Res., 102 , 1666316682.

    • Search Google Scholar
    • Export Citation
  • Mo, K. C., and E. H. Berbery, 2004: Low-level jets and the summer precipitation regimes over North America. J. Geophys. Res., 109 .D06117, doi:10.1029/2003JD004106.

    • Search Google Scholar
    • Export Citation
  • Mo, K. C., J-K. Schemm, H. M. H. Juang, R. W. Higgins, and Y. Song, 2005: Impact of model resolution on the prediction of summer precipitation over the United States and Mexico. J. Climate, 18 , 39103927.

    • Search Google Scholar
    • Export Citation
  • Mock, C. J., 1996: Climatic controls and spatial variations of precipitation in the western United States. J. Climate, 9 , 11111125.

  • NOAA, 1988: Storm Data. Vol. 30, No. 8, 66 pp. [Available from National Climatic Data Center, Environmental Data and Information Service, NOAA, Asheville, NC 28801.].

  • Paegle, J., Q. Yang, and M. Wang, 1997: Predictability in limited area and global models. Meteor. Atmos. Phys., 63 , 5369.

  • Reed, R. J., D. C. Norquist, and E. E. Recker, 1977: The structure and properties of African wave disturbances as observed during phase III of GATE. Mon. Wea. Rev., 105 , 317333.

    • Search Google Scholar
    • Export Citation
  • Saleeby, S. M., and W. R. Cotton, 2004: Simulations of the North American monsoon system. Part I: Model analysis of the 1993 monsoon season. J. Climate, 17 , 19972018.

    • Search Google Scholar
    • Export Citation
  • Schmitz, J. T., and S. L. Mullen, 1996: Water vapor transport associated with the summertime North American monsoon as depicted by ECMWF analyses. J. Climate, 9 , 16211634.

    • Search Google Scholar
    • Export Citation
  • Stensrud, D. J., R. L. Gall, S. L. Mullen, and K. W. Howard, 1995: Model climatology of the Mexican monsoon. J. Climate, 8 , 17751794.

    • Search Google Scholar
    • Export Citation
  • Stensrud, D. J., R. L. Gall, and M. K. Nordquist, 1997: Surges over the Gulf of California during the Mexican monsoon. Mon. Wea. Rev., 125 , 417437.

    • Search Google Scholar
    • Export Citation
  • Tang, M., and E. R. Reiter, 1984: Plateau monsoons of the Northern Hemisphere: A comparison between North America and Tibet. Mon. Wea. Rev., 112 , 617637.

    • Search Google Scholar
    • Export Citation
  • Tribbia, J. J., and D. P. Baumhefner, 2004: Scale interactions and atmospheric predictability: An updated perspective. Mon. Wea. Rev., 132 , 703713.

    • Search Google Scholar
    • Export Citation
  • Wilks, D. S., 1995: Statistical Methods in the Atmospheric Sciences: An Introduction. International Geophysics Series, Vol. 59, Academic Press, 467 pp.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 229 128 6
PDF Downloads 191 104 0

Impact of Tropical Easterly Waves on the North American Monsoon

View More View Less
  • 1 Cooperative Institute for Mesoscale Meteorological Studies, University of Oklahoma, and NOAA/National Severe Storms Laboratory, Norman, Oklahoma
  • | 2 NOAA/National Severe Storms Laboratory, Norman, Oklahoma
Restricted access

Abstract

The North American monsoon (NAM) is a prominent summertime feature over northwestern Mexico and the southwestern United States. It is characterized by a distinct shift in midlevel winds from westerly to easterly as well as a sharp, marked increase in rainfall. This maximum in rainfall accounts for 60%–80% of the annual precipitation in northwestern Mexico and nearly 40% of the yearly rainfall over the southwestern United States. Gulf surges, or coastally trapped disturbances that occur over the Gulf of California, are important mechanisms in supplying the necessary moisture for the monsoon and are hypothesized in previous studies to be initiated by the passage of a tropical easterly wave (TEW). Since the actual number of TEWs varies from year to year, it is possible that TEWs are responsible for producing some of the interannual variability in the moisture flux and rainfall seen in the NAM.

To explore the impact of TEWs on the NAM, four 1-month periods are chosen for study that represent a reasonable variability in TEW activity. Two continuous month-long simulations are produced for each of the selected months using the Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model. One simulation is a control run that uses the complete boundary condition data, whereas a harmonic analysis is used to remove TEWs with periods of approximately 3.5 to 7.5 days from the model boundary conditions in the second simulation. These simulations with and without TEWs in the boundary conditions are compared to determine the impact of the waves on the NAM. Fields such as meridional moisture flux, rainfall totals, and surge occurrences are examined to define similarities and differences between the model runs. Results suggest that the removal of TEWs not only reduces the strength of gulf surges, but also rearranges rainfall over the monsoon region. Results further suggest that TEWs influence rainfall over the Southern Plains of the United States, with TEWs leading to less rainfall in this region. While these results are only suggestive, since rainfall is the most difficult model forecast parameter, it may be that TEWs alone can explain part of the inverse relationship between NAM and Southern Plains rainfall.

Corresponding author address: David J. Stensrud, National Severe Storms Laboratory, National Weather Center, Room 4368, 120 David L. Boren Blvd., Norman, OK 73072. Email: David.Stensrud@noaa.gov

Abstract

The North American monsoon (NAM) is a prominent summertime feature over northwestern Mexico and the southwestern United States. It is characterized by a distinct shift in midlevel winds from westerly to easterly as well as a sharp, marked increase in rainfall. This maximum in rainfall accounts for 60%–80% of the annual precipitation in northwestern Mexico and nearly 40% of the yearly rainfall over the southwestern United States. Gulf surges, or coastally trapped disturbances that occur over the Gulf of California, are important mechanisms in supplying the necessary moisture for the monsoon and are hypothesized in previous studies to be initiated by the passage of a tropical easterly wave (TEW). Since the actual number of TEWs varies from year to year, it is possible that TEWs are responsible for producing some of the interannual variability in the moisture flux and rainfall seen in the NAM.

To explore the impact of TEWs on the NAM, four 1-month periods are chosen for study that represent a reasonable variability in TEW activity. Two continuous month-long simulations are produced for each of the selected months using the Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model. One simulation is a control run that uses the complete boundary condition data, whereas a harmonic analysis is used to remove TEWs with periods of approximately 3.5 to 7.5 days from the model boundary conditions in the second simulation. These simulations with and without TEWs in the boundary conditions are compared to determine the impact of the waves on the NAM. Fields such as meridional moisture flux, rainfall totals, and surge occurrences are examined to define similarities and differences between the model runs. Results suggest that the removal of TEWs not only reduces the strength of gulf surges, but also rearranges rainfall over the monsoon region. Results further suggest that TEWs influence rainfall over the Southern Plains of the United States, with TEWs leading to less rainfall in this region. While these results are only suggestive, since rainfall is the most difficult model forecast parameter, it may be that TEWs alone can explain part of the inverse relationship between NAM and Southern Plains rainfall.

Corresponding author address: David J. Stensrud, National Severe Storms Laboratory, National Weather Center, Room 4368, 120 David L. Boren Blvd., Norman, OK 73072. Email: David.Stensrud@noaa.gov

Save