Potential Vorticity, Easterly Waves, and Eastern Pacific Tropical Cyclogenesis

John Molinari Department of Earth and Atmospheric Science, State University of New York at Albany, Albany, New York

Search for other papers by John Molinari in
Current site
Google Scholar
PubMed
Close
,
David Knight Department of Earth and Atmospheric Science, State University of New York at Albany, Albany, New York

Search for other papers by David Knight in
Current site
Google Scholar
PubMed
Close
,
Michael Dickinson Department of Earth and Atmospheric Science, State University of New York at Albany, Albany, New York

Search for other papers by Michael Dickinson in
Current site
Google Scholar
PubMed
Close
,
David Vollaro Department of Earth and Atmospheric Science, State University of New York at Albany, Albany, New York

Search for other papers by David Vollaro in
Current site
Google Scholar
PubMed
Close
, and
Steven Skubis Department of Earth and Atmospheric Science, State University of New York at Albany, Albany, New York

Search for other papers by Steven Skubis in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

A significant sign reversal in the meridional potential vorticity gradient was found during the summer of 1991 on the 310-K isentropic surface (near 700 mb) over the Caribbean Sea. The Charney–Stern necessary condition for instability of the mean flow is met in this region. It is speculated that the sign reversal permits either invigoration of African waves or actual generation of easterly waves in the Caribbean.

During the same season, a correlation existed between the strength of the negative potential vorticity gradient in the Caribbean and subsequent cyclogenesis in the eastern Pacific. The meridional PV gradient, convective heating measured by outgoing longwave radiation data, and eastern Pacific cyclogenesis all varied on the timescale of the Madden–Julian oscillation (MJO). It is hypothesized that upstream wave growth in the dynamically unstable region provides the connection between the MJO (or any other convective forcing) and the associated enhanced downstream tropical cyclogenesis.

Corresponding author address: Dr. John Molinari, Department of Earth and Atmospheric Science, SUNY at Albany, Earth Science 351, Albany, NY 12222.

Abstract

A significant sign reversal in the meridional potential vorticity gradient was found during the summer of 1991 on the 310-K isentropic surface (near 700 mb) over the Caribbean Sea. The Charney–Stern necessary condition for instability of the mean flow is met in this region. It is speculated that the sign reversal permits either invigoration of African waves or actual generation of easterly waves in the Caribbean.

During the same season, a correlation existed between the strength of the negative potential vorticity gradient in the Caribbean and subsequent cyclogenesis in the eastern Pacific. The meridional PV gradient, convective heating measured by outgoing longwave radiation data, and eastern Pacific cyclogenesis all varied on the timescale of the Madden–Julian oscillation (MJO). It is hypothesized that upstream wave growth in the dynamically unstable region provides the connection between the MJO (or any other convective forcing) and the associated enhanced downstream tropical cyclogenesis.

Corresponding author address: Dr. John Molinari, Department of Earth and Atmospheric Science, SUNY at Albany, Earth Science 351, Albany, NY 12222.

Save
  • Avila, L. A., 1991: Eastern North Pacific hurricane season of 1990. Mon. Wea. Rev.,119, 2034–2046.

  • ——, and R. J. Pasch, 1992: Atlantic tropical systems of 1991. Mon. Wea. Rev.,120, 2688–2696.

  • Betts, A. K., 1975: Parametric interpretation of trade wind cumulus budget studies. J. Atmos. Sci.,32, 1934–1945.

  • Bister, M., and K. A. Emanuel, 1997: The genesis of Hurricane Guillermo: TEXMEX analyses and a modeling study. Mon. Wea. Rev.,125, 2662–2682.

  • Boer, G. J., 1995: Analyzed and forecast large-scale tropical divergent flow. Mon. Wea. Rev.,123, 3539–3553.

  • Bosart, L. F., and J. A. Bartlo, 1991: Tropical storm formation in a baroclinic environment. Mon. Wea. Rev.,119, 1979–2013.

  • Burpee, R. W., 1972: The origin and structure of easterly waves in the lower troposphere of North Africa. J. Atmos. Sci.,29, 77–90.

  • Carlson, T. N., 1969: Some remarks on African disturbances and their progress over the tropical Atlantic. Mon. Wea. Rev.,97, 716–726.

  • Charney, J. G., and M. E. Stern, 1962: On the stability of internal baroclinic jets in a rotating atmosphere. J. Atmos. Sci.,19, 159–172.

  • Chen, S. S., R. A. Houze, and B. E. Mapes, 1996: Multiscale variability of deep convection in relation to large-scale circulation in TOGA COARE. J. Atmos. Sci.,53, 1380–1409.

  • Codazzi, A., 1841: Resumen de la Geografia de Venezuela. Reprinted 1940, R. M. Baralt and R. Diaz, Eds., Taller de Artes Graficas, Escuela Tecnica Industrial, 303 pp. [Available from State University of New York at Albany, 1400 Washington Avenue, Albany, NY 12222.].

  • Duchon, C. E., 1979: Lanczos filtering in one and two dimensions. J. Appl. Meteor.,18, 1016–1022.

  • Eliassen, A., 1983: The Charney–Stern theorem on barotropic–baroclinic instability. Pure Appl. Geophys.,121, 563–573.

  • Ferreira, R. N., and W. H. Schubert, 1997: Barotropic aspects of ITCZ breakdown. J. Atmos. Sci.,54, 261–285.

  • Fjörtoff, R., 1950: Application of integral theorems in deriving criteria of stability for laminar flows and for the baroclinic circular vortex. Geofis. Publ.,17(6), 1–52.

  • Frank, N. L., 1970: Atlantic tropical systems of 1969. Mon. Wea. Rev.,98, 307–314.

  • Gruber, A., 1974: Wavenumber–frequency spectra of satellite-measured brightness in the tropics. J. Atmos. Sci.,31, 1675–1680.

  • ——, and A. F. Krueger, 1984: The status of the NOAA outgoing longwave radiation data set. Bull. Amer. Meteor. Soc.,65, 958–962.

  • Haynes, P. H., and M. E. McIntyre, 1987: On the evolution of vorticity and potential vorticity in the presence of diabatic heating and frictional or other forces. J. Atmos. Sci.,44, 828–841.

  • Hendon, H. H., 1986: Streamfunction and velocity potential representation of equatorially trapped waves. J. Atmos. Sci.,43, 3038–3042.

  • Krishnamurti, T. N., C. E. Levy, and H.-L. Pan, 1975: On simultaneous surges in the trades. J. Atmos. Sci.,32, 2367–2370.

  • Lanczos, C., 1956: Applied Analysis. Prentice-Hall, 539 pp.

  • Liebmann, B., and H. H. Hendon, 1990: Synoptic-scale disturbances near the equator. J. Atmos. Sci.,47, 1463–1479.

  • ——, ——, and J. D. Glick, 1994: The relationship between tropical cyclones of the western Pacific and Indian Oceans and the Madden–Julian oscillation. J. Meteor. Soc. Japan,72, 401–411.

  • Madden, R. A., and P. R. Julian, 1971: Description of a 40–50 day oscillation in the zonal wind in the tropical Pacific. J. Atmos. Sci.,28, 702–708.

  • ——, and ——, 1994: Observations of the 40–50 day tropical oscillation—A review. Mon. Wea. Rev.,122, 814–837.

  • Molinari, J., S. Skubis, and D. Vollaro, 1995: External influences on hurricane intensity. Part III: Potential vorticity evolution. J. Atmos. Sci.,52, 3593–3606.

  • Montgomery, M. T., and B. F. Farrell, 1993: Tropical cyclone formation. J. Atmos. Sci.,50, 285–310.

  • Nakazawa, T., 1986: Intraseasonal variations of OLR in the tropics during the FGGE year. J. Meteor. Soc. Japan,64, 17–33.

  • Nitta, T., and S. Esbensen, 1974: Heat and moisture budget analyses using BOMEX data. Mon. Wea. Rev.,102, 17–28.

  • ——, and Y. Takabayu, 1985: Global analysis of the lower tropospheric disturbances in the tropics during the northern summer of the FGGE year. Part II: Regional characteristics of the disturbances. Pure Appl. Geophys.,123, 272–292.

  • Rappaport, E. N., and M. Mayfield, 1992: Eastern North Pacific hurricane season of 1991. Mon. Wea. Rev.,120, 2697–2708.

  • Reed, R. J., A. Hollingsworth, W. A. Heckley, and F. Delsol, 1988: An evaluation of the performance of the ECMWF operational system in analyzing and forecasting easterly wave disturbances over Africa and the tropical Atlantic. Mon. Wea. Rev.,116, 824–865.

  • Schubert, W. H., P. E. Ciesielski, D. E. Stevens, and H. Kuo, 1991: Potential vorticity modeling of the ITCZ and the Hadley circulation. J. Atmos. Sci.,48, 1493–1509.

  • Shapiro, L. J., 1977: Tropical storm formation from easterly waves: A criterion for development. J. Atmos. Sci.,34, 1007–1021.

  • ——, 1980: The effect of nonlinearities on the evolution of barotropic easterly waves in a non-uniform environment. J. Atmos. Sci.,37, 2631–2643.

  • ——, 1986: The three-dimensional structure of synoptic-scale disturbances over the tropical Atlantic. Mon. Wea. Rev.,114, 1876–1891.

  • Thorncroft, C. D., and B. J. Hoskins, 1994a: An idealized study of African easterly waves. Part I: A linear view. Quart. J. Roy. Meteor. Soc.,120, 953–982.

  • ——, and ——, 1994b: An idealized study of African easterly waves. Part II: A nonlinear view. Quart. J. Roy. Meteor. Soc.,120, 983–1016.

  • Turk, M., D. Vollaro, and J. Molinari, 1995: Large-scale aspects of active and inactive periods of eastern Pacific tropical cyclogenesis. Preprints, 21st Conf. on Hurricanes and Tropical Meteorology, Miami, FL, Amer. Meteor. Soc., 106–107.

  • Zehnder, J. A., 1993: The influence of large-scale topography on barotropic vortex motion. J. Atmos. Sci.,50, 2519–2532.

  • ——, and R. L. Gall, 1991: On a mechanism for orographic triggering of tropical cyclones in the eastern North Pacific. Tellus,43A, 25–36.

  • Zehr, R. M., 1992: Tropical cyclogenesis in the western north Pacific. NOAA Tech. Rep. NESDIS 61, 181 pp. [Available from the National Technical Information Service, U.S. Department of Commerce, Sills Bldg., 5285 Port Royal Road, Springfield, VA 22161.].

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 783 236 21
PDF Downloads 574 123 5