Editorial Type:
Article
Article Type:
Research Article

On the Convective Coupling and Moisture Organization of East Pacific Easterly Waves

Adam V. Rydbeck Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado

Search for other papers by Adam V. Rydbeck in
Current site
Google Scholar
PubMed Close
and
Eric D. Maloney Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado

Search for other papers by Eric D. Maloney in
Current site
Google Scholar
PubMed Close
Print Publication:
01 Oct 2015
DOI:
https://doi.org/10.1175/JAS-D-15-0056.1
Page(s):
3850–3870
Restricted access

Abstract

Processes associated with the local amplification of easterly waves (EWs) in the east Pacific warm pool are explored. Developing EWs favor convection in the southwest and northeast quadrants of the disturbance. In nascent EWs, convection favors the southwest quadrant. As the EW life cycle progresses, convection in the northeast quadrant becomes increasingly prominent and southwest quadrant convection wanes. The EW moisture budget reveals that anomalous meridional winds acting on the mean meridional moisture gradient of the ITCZ produce moisture anomalies supportive of convection in the southwest quadrant early in the EW life cycle. As EWs mature, moisture anomalies on the poleward side of the EW begin to grow and are supported by the advection of anomalous moisture by the mean zonal wind.

In the southwest and northeast portions of the wave, where convection anomalies are favored, lower-tropospheric vorticity is generated locally through vertical stretching that supports a horizontal tilt of the wave from the southwest to the northeast. EWs with such tilts are then able to draw energy via barotropic conversion from the background cyclonic zonal wind shear present in the east Pacific. Convection anomalies associated with EWs vary strongly with changes in the background intraseasonal state. EWs during westerly and neutral intraseasonal periods are associated with robust convection anomalies. Easterly intraseasonal periods are, at times, associated with very weak EW convection anomalies because of weaker moisture and diluted CAPE variations.

Corresponding author address: Adam V. Rydbeck, Department of Atmospheric Science, Colorado State University, 1371 Campus Delivery, Fort Collins, CO 80523-1371. E-mail: arydbeck@atmos.colostate.edu

Abstract

Processes associated with the local amplification of easterly waves (EWs) in the east Pacific warm pool are explored. Developing EWs favor convection in the southwest and northeast quadrants of the disturbance. In nascent EWs, convection favors the southwest quadrant. As the EW life cycle progresses, convection in the northeast quadrant becomes increasingly prominent and southwest quadrant convection wanes. The EW moisture budget reveals that anomalous meridional winds acting on the mean meridional moisture gradient of the ITCZ produce moisture anomalies supportive of convection in the southwest quadrant early in the EW life cycle. As EWs mature, moisture anomalies on the poleward side of the EW begin to grow and are supported by the advection of anomalous moisture by the mean zonal wind.

In the southwest and northeast portions of the wave, where convection anomalies are favored, lower-tropospheric vorticity is generated locally through vertical stretching that supports a horizontal tilt of the wave from the southwest to the northeast. EWs with such tilts are then able to draw energy via barotropic conversion from the background cyclonic zonal wind shear present in the east Pacific. Convection anomalies associated with EWs vary strongly with changes in the background intraseasonal state. EWs during westerly and neutral intraseasonal periods are associated with robust convection anomalies. Easterly intraseasonal periods are, at times, associated with very weak EW convection anomalies because of weaker moisture and diluted CAPE variations.

Corresponding author address: Adam V. Rydbeck, Department of Atmospheric Science, Colorado State University, 1371 Campus Delivery, Fort Collins, CO 80523-1371. E-mail: arydbeck@atmos.colostate.edu
Save
Cover Journal of the Atmospheric Sciences
Journal of the Atmospheric Sciences

  • Aiyyer, A., and J. Molinari, 2008: MJO and tropical cyclogenesis in the Gulf of Mexico and eastern Pacific: Case study and idealized numerical modeling. J. Atmos. Sci., 65, 2691–2704, doi:10.1175/2007JAS2348.1.

    • Search Google Scholar
    • Export Citation

  • Aiyyer, A., A. Mekonnen, and C. J. Schreck, 2012: Projection of tropical cyclones on wavenumber–frequency-filtered equatorial waves. J. Climate, 25, 3653–3658, doi:10.1175/JCLI-D-11-00451.1.

    • Search Google Scholar
    • Export Citation

  • Avila, L. A., and J. L. Guiney, 2000: Eastern North Pacific hurricane season of 1998. Mon. Wea. Rev., 128, 2990–3000, doi:10.1175/1520-0493(2000)128<2990:ENPHSO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Avila, L. A., R. J. Pasch, J. L. Beven, J. L. Franklin, M. B. Lawrence, S. R. Stewart, and J.-G. Jiing, 2003: Eastern North Pacific hurricane season of 2001. Mon. Wea. Rev., 131, 249–262, doi:10.1175/1520-0493(2003)131<0249:ASNPHS>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Back, L. E., and C. S. Bretherton, 2009: A simple model of climatological rainfall and vertical motion patterns over the tropical oceans. J. Climate, 22, 6477–6497, doi:10.1175/2009JCLI2393.1.

    • Search Google Scholar
    • Export Citation

  • Bretherton, C. S., M. E. Peters, and L. E. Back, 2004: Relationships between water vapor path and precipitation over the tropical oceans. J. Climate, 17, 1517–1528, doi:10.1175/1520-0442(2004)017<1517:RBWVPA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Carlson, T. N., 1969: Synoptic histories of three African disturbances that developed into Atlantic hurricanes. Mon. Wea. Rev., 97, 256–276, doi:10.1175/1520-0493(1969)097<0256:SHOTAD>2.3.CO;2.

    • Search Google Scholar
    • Export Citation

  • Crosbie, E., and Y. Serra, 2014: Intraseasonal modulation of synoptic-scale disturbances and tropical cyclone genesis in the eastern North Pacific. J. Climate, 27, 5724–5745, doi:10.1175/JCLI-D-13-00399.1.

    • Search Google Scholar
    • Export Citation

  • Davis, C., C. Snyder, and A. C. Didlake Jr., 2008: A vortex-based perspective of eastern Pacific tropical cyclone formation. Mon. Wea. Rev., 136, 2461–2477, doi:10.1175/2007MWR2317.1.

    • Search Google Scholar
    • Export Citation

  • Dee, D. P., and Coauthors, 2011: The ERA-Interim reanalysis: Configuration and performance of the data assimilation system. Quart. J. Roy. Meteor. Soc., 137, 553–597, doi:10.1002/qj.828.

    • Search Google Scholar
    • Export Citation

  • Dunn, G. E., 1940: Cyclogenesis in the tropical Atlantic. Bull. Amer. Meteor. Soc., 21, 215–229.

  • Frank, N. L., 1969: The “Inverted V” cloud pattern—An easterly wave? Mon. Wea. Rev., 97, 130–140, doi:10.1175/1520-0493(1969)097<0130:TVCPEW>2.3.CO;2.

    • Search Google Scholar
    • Export Citation

  • Gu, G., and C. Zhang, 2002: Cloud components of the Intertropical Convergence Zone. J. Geophys. Res., 107, 4565, doi:10.1029/2002JD002089.

    • Search Google Scholar
    • Export Citation

  • Gu, G., R. F. Adler, G. J. Huffman, and S. Curtis, 2004: African easterly waves and their association with precipitation. J. Geophys. Res., 109, D04101, doi:10.1029/2003JD003967.

    • Search Google Scholar
    • Export Citation

  • Hartmann, D. L., and E. D. Maloney, 2001: The Madden–Julian oscillation, barotropic dynamics, and North Pacific tropical cyclone formation. Part II: Stochastic barotropic modeling. J. Atmos. Sci., 58, 2559–2570, doi:10.1175/1520-0469(2001)058<2559:TMJOBD>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Holloway, C. E., and J. D. Neelin, 2009: Moisture vertical structure, column water vapor, and tropical deep convection. J. Atmos. Sci., 66, 1665–1683, doi:10.1175/2008JAS2806.1.

    • Search Google Scholar
    • Export Citation

  • Hoover, B. T., 2015: Identifying a barotropic growth mechanism in east Pacific tropical cyclogenesis using adjoint-derived sensitivity gradients. J. Atmos. Sci., 72, 1215–1234, doi:10.1175/JAS-D-14-0053.1.

    • Search Google Scholar
    • Export Citation

  • Jiang, X., and D. E. Waliser, 2008: Northward propagation of the subseasonal variability over the eastern Pacific warm pool. Geophys. Res. Lett., 35, L09814, doi:10.1029/2008GL033723.

    • Search Google Scholar
    • Export Citation

  • Jordan, C., 1958: Mean soundings for the West Indies area. J. Meteor., 15, 91–97, doi:10.1175/1520-0469(1958)015<0091:MSFTWI>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Kiladis, G. N., C. D. Thorncroft, and N. M. J. Hall, 2006: Three-dimensional structure and dynamics of African easterly waves. Part I: Observations. J. Atmos. Sci., 63, 2212–2230, doi:10.1175/JAS3741.1.

    • Search Google Scholar
    • Export Citation

  • Krishnamurti, T. N., and D. Baumhefner, 1966: Structure of a tropical disturbance based on solutions of a multilevel baroclinic model. J. Appl. Meteor., 5, 396–406, doi:10.1175/1520-0450(1966)005<0396:SOATDB>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Lau, K.-H., and N.-C. Lau, 1992: The energetics and propagation dynamics of tropical summertime synoptic-scale disturbances. Mon. Wea. Rev., 120, 2523–2539, doi:10.1175/1520-0493(1992)120<2523:TEAPDO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Lee, H.-T., 2014: Climate Algorithm Theoretical Basis Document (C-ATBD): Outgoing longwave radiation (OLR)—Daily. NOAA’s Climate Data Record (CDR) program. NOAA Tech Rep. CDRP-ATBD-0526, 46 pp. [Available online at http://www1.ncdc.noaa.gov/pub/data/sds/cdr/CDRs/Outgoing%20Longwave%20Radiation%20-%20Daily/AlgorithmDescription.pdf.]

  • Malkus, J. S., and H. Riehl, 1964: Cloud structure and distributions over the tropical Pacific Ocean. Tellus, 16A, 275–287, doi:10.1111/j.2153-3490.1964.tb00167.x.

    • Search Google Scholar
    • Export Citation

  • Maloney, E. D., and D. L. Hartmann, 2000: Modulation of eastern North Pacific hurricanes by the Madden–Julian oscillation. J. Climate, 13, 1451–1460, doi:10.1175/1520-0442(2000)013<1451:MOENPH>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Maloney, E. D., and D. L. Hartmann, 2001: The Madden–Julian oscillation, barotropic dynamics, and North Pacific tropical cyclone formation. Part I: Observations. J. Atmos. Sci., 58, 2545–2558, doi:10.1175/1520-0469(2001)058<2545:TMJOBD>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Maloney, E. D., and J. T. Kiehl, 2002: Intraseasonal eastern Pacific precipitation and SST variations in a GCM coupled to a slab ocean model. J. Climate, 15, 2989–3007, doi:10.1175/1520-0442(2002)015<2989:IEPPAS>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Maloney, E. D., and S. K. Esbensen, 2003: The amplification of east Pacific Madden–Julian oscillation convection and wind anomalies during June–November. J. Climate, 16, 3482–3497, doi:10.1175/1520-0442(2003)016<3482:TAOEPM>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Maloney, E. D., and S. K. Esbensen, 2005: A modeling study of summertime east Pacific wind-induced ocean–atmosphere exchange in the intraseasonal oscillation. J. Climate, 18, 568–584, doi:10.1175/JCLI-3280.1.

    • Search Google Scholar
    • Export Citation

  • Maloney, E. D., and S. K. Esbensen, 2007: Satellite and buoy observations of intraseasonal variability in the tropical northeast Pacific. Mon. Wea. Rev., 135, 3–19, doi:10.1175/MWR3271.1.

    • Search Google Scholar
    • Export Citation

  • Maloney, E. D., D. B. Chelton, and S. K. Esbensen, 2008: Subseasonal SST variability in the tropical eastern North Pacific during boreal summer. J. Climate, 21, 4149–4167, doi:10.1175/2007JCLI1856.1.

    • Search Google Scholar
    • Export Citation

  • Molinari, J., and D. Vollaro, 2000: Planetary- and synoptic-scale influences on eastern Pacific tropical cyclogenesis. Mon. Wea. Rev., 128, 3296–3307, doi:10.1175/1520-0493(2000)128<3296:PASSIO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Nitta, T., and Y. Takayabu, 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, doi:10.1007/BF00877023.

    • Search Google Scholar
    • Export Citation

  • NOAA, 2014: Outgoing longwave radiation—Daily. National Climatic Data Center, accessed 23 June 2014. [Available online at http://www.ncdc.noaa.gov/cdr/operationalcdrs.html.]

  • Palmer, C. E., 1952: Reviews of modern meteorology—5. Tropical meteorology. Quart. J. Roy. Meteor. Soc., 78, 126–164, doi:10.1002/qj.49707833603.

    • Search Google Scholar
    • Export Citation

  • Pasch, R. J., and Coauthors, 2009: Eastern North Pacific hurricane season of 2006. Mon. Wea. Rev., 137, 3–20, doi:10.1175/2008MWR2508.1.

    • Search Google Scholar
    • Export Citation

  • Peters, O., and J. D. Neelin, 2006: Critical phenomena in atmospheric precipitation. Nat. Phys., 2, 393–396, doi:10.1038/nphys314.

  • Petersen, W. A., R. Cifelli, D. J. Boccippio, S. A. Rutledge, and C. Fairall, 2003: Convection and easterly wave structures observed in the eastern Pacific warm pool during EPIC-2001. J. Atmos. Sci., 60, 1754–1773, doi:10.1175/1520-0469(2003)060<1754:CAEWSO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Raymond, D. J., 2000: Thermodynamic control of tropical rainfall. Quart. J. Roy. Meteor. Soc., 126, 889–898, doi:10.1002/qj.49712656406.

    • Search Google Scholar
    • Export Citation

  • Raymond, D. J., C. López-Carrillo, and L. López Cavazos, 1998: Case-studies of developing east Pacific easterly waves. Quart. J. Roy. Meteor. Soc., 124, 2005–2034, doi:10.1002/qj.49712455011.

    • Search Google Scholar
    • Export Citation

  • 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, 317–333, doi:10.1175/1520-0493(1977)105<0317:TSAPOA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Riehl, H., 1945: Waves in the easterlies and the polar front in the tropics. Dept. of Meteorology, University of Chicago Misc. Rep. 17, 79 pp.

  • Riehl, H., 1948: On the formation of west Atlantic hurricanes. Dept. of Meteorology, University of Chicago Misc. Rep. 24, 67 pp.

  • Riehl, H., 1954: Tropical Meteorology. McGraw-Hill, 392 pp.

  • Rydbeck, A. V., and E. D. Maloney, 2014: Energetics of east Pacific easterly waves during intraseasonal events. J. Climate, 27, 7603–7621, doi:10.1175/JCLI-D-14-00211.1.

    • Search Google Scholar
    • Export Citation

  • Rydbeck, A. V., E. D. Maloney, S.-P. Xie, J. Hafner, and J. Shaman, 2013: Remote forcing versus local feedback of east Pacific intraseasonal variability during boreal summer. J. Climate, 26, 3575–3596, doi:10.1175/JCLI-D-12-00499.1.

    • Search Google Scholar
    • Export Citation

  • Sahany, S., J. D. Neelin, K. Hales, and R. B. Neale, 2012: Temperature–moisture dependence of the deep convective transition as a constraint on entrainment in climate models. J. Atmos. Sci., 69, 1340–1358, doi:10.1175/JAS-D-11-0164.1.

    • Search Google Scholar
    • Export Citation

  • Serra, Y. L., and R. A. Houze Jr., 2002: Observations of variability on synoptic timescales in the east Pacific ITCZ. J. Atmos. Sci., 59, 1723–1743, doi:10.1175/1520-0469(2002)059<1723:OOVOST>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Serra, Y. L., G. N. Kiladis, and M. F. Cronin, 2008: Horizontal and vertical structure of easterly waves in the Pacific ITCZ. J. Atmos. Sci., 65, 1266–1284, doi:10.1175/2007JAS2341.1.

    • Search Google Scholar
    • Export Citation

  • Serra, Y. L., G. N. Kiladis, and K. Hodges, 2010: Tracking and mean structure of easterly waves over the Intra-Americas Sea. J. Climate, 23, 4823–4840, doi:10.1175/2010JCLI3223.1.

    • Search Google Scholar
    • Export Citation

  • Simpson, R. H., N. Frank, D. Shideler, and H. M. Johnson, 1968: Atlantic tropical disturbances, 1967. Mon. Wea. Rev., 96, 251–259, doi:10.1175/1520-0493(1968)096<0251:ATD>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Small, R. J., S.-P. Xie, E. D. Maloney, S. P. de Szoeke, and T. Miyama, 2011: Intraseasonal variability in the far-east Pacific: Investigation of the role of air–sea coupling in a regional coupled model. Climate Dyn., 36, 867–890, doi:10.1007/s00382-010-0786-2.

    • Search Google Scholar
    • Export Citation

  • Sobel, A. H., and C. S. Bretherton, 2000: Modeling tropical precipitation in a single column. J. Climate, 13, 4378–4392, doi:10.1175/1520-0442(2000)013<4378:MTPIAS>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Sobel, A. H., S. E. Yuter, C. S. Bretherton, and G. N. Kiladis, 2004: Large-scale meteorology and deep convection during TRMM KWAJEX. Mon. Wea. Rev., 132, 422–444, doi:10.1175/1520-0493(2004)132<0422:LMADCD>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Tai, K.-S., and Y. Ogura, 1987: An observational study of easterly waves over the eastern Pacific in the northern summer using FGGE data. J. Atmos. Sci., 44, 339–361, doi:10.1175/1520-0469(1987)044<0339:AOSOEW>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Wolding, B. O., and E. D. Maloney, 2015: Objective diagnostics and the Madden–Julian oscillation. Part II: Application to moist static energy and moisture budgets. J. Climate, 28, 7786–7808.

  • Yanai, M., 1961: A detailed analysis of typhoon formation. J. Meteor. Soc. Japan, 39, 187–214.

  • Yanai, M., and T. Nitta, 1967: Computation of vertical motion and vorticity budget in a Caribbean easterly wave. J. Meteor. Soc. Japan, 45, 444–466.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 353 176 7
PDF Downloads 237 100 3