Editorial Type:
Article
Article Type:
Research Article

Characteristics of an African Easterly Wave Observed during NAMMA

Robert Cifelli Cooperative Institute for Research in the Atmosphere, Colorado State University, and NOAA/Earth System Research Laboratory, Boulder, Colorado

Search for other papers by Robert Cifelli in
Current site
Google Scholar
PubMed Close
,
Timothy Lang Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado

Search for other papers by Timothy Lang in
Current site
Google Scholar
PubMed Close
,
Steven A. Rutledge Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado

Search for other papers by Steven A. Rutledge in
Current site
Google Scholar
PubMed Close
,
Nick Guy Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado

Search for other papers by Nick Guy in
Current site
Google Scholar
PubMed Close
,
Edward J. Zipser Department of Meteorology, University of Utah, Salt Lake, Utah

Search for other papers by Edward J. Zipser in
Current site
Google Scholar
PubMed Close
,
Jon Zawislak Department of Meteorology, University of Utah, Salt Lake, Utah

Search for other papers by Jon Zawislak in
Current site
Google Scholar
PubMed Close
, and
Robert Holzworth Department of Atmospheric Science, University of Washington, Seattle, Washington

Search for other papers by Robert Holzworth in
Current site
Google Scholar
PubMed Close
Print Publication:
01 Jan 2010
Collections:
TCSP NAMMA
DOI:
https://doi.org/10.1175/2009JAS3141.1
Page(s):
3–25
Restricted access

Abstract

The evolution of an African easterly wave is described using ground-based radar and ancillary datasets from three locations in West Africa: Niamey, Niger (continental), Dakar, Senegal (coastal), and Praia, Republic of Cape Verde (oceanic). The data were collected during the combined African Monsoon Multidisciplinary Analyses (AMMA) and NASA AMMA (NAMMA) campaigns in August–September 2006.

Two precipitation events originated within the wave circulation and propagated with the wave across West Africa. Mesoscale convective systems (MCSs) associated with these events were identified at all three sites ahead of, within, and behind the 700-mb wave trough. An additional propagating event was indentified that originated east of the wave and moved through the wave circulation. The MCS activity associated with this event did not show any appreciable change resulting from its interaction with the wave. The MCS characteristics at each site were different, likely due to a combination of life cycle effects and changes in relative phasing between the propagating systems and the position of low-level convergence and thermodynamic instability associated with the wave. At the ocean and coastal sites, the most intense convection occurred ahead of the wave trough where both high CAPE and low-level convergence were concentrated. At the continental site, convection was relatively weak owing to the fact that the wave dynamics and thermodynamics were not in sync when the systems passed through Niamey. The only apparent effect of the wave on MCS activity at the continental site was to extend the period of precipitation activity during one of the events that passed through coincident with the 700-mb wave trough. Convective organization at the land sites was primarily in the form of squall lines and linear MCSs oriented perpendicular to the low-level shear. The organization at the oceanic site was more complicated, transitioning from linear MCSs to widespread stratiform cloud with embedded convection. The precipitation activity was also much longer lived at the oceanic site due to the wave becoming nearly stationary near the Cape Verdes, providing an environment supportive of deep convection for an extended period.

Corresponding author address: Robert Cifelli, R/PSD2, 325 Broadway, Boulder, CO 80305. Email: rob.cifelli@noaa.gov

This article included in the TCSP NAMMA special collection.

Abstract

The evolution of an African easterly wave is described using ground-based radar and ancillary datasets from three locations in West Africa: Niamey, Niger (continental), Dakar, Senegal (coastal), and Praia, Republic of Cape Verde (oceanic). The data were collected during the combined African Monsoon Multidisciplinary Analyses (AMMA) and NASA AMMA (NAMMA) campaigns in August–September 2006.

Two precipitation events originated within the wave circulation and propagated with the wave across West Africa. Mesoscale convective systems (MCSs) associated with these events were identified at all three sites ahead of, within, and behind the 700-mb wave trough. An additional propagating event was indentified that originated east of the wave and moved through the wave circulation. The MCS activity associated with this event did not show any appreciable change resulting from its interaction with the wave. The MCS characteristics at each site were different, likely due to a combination of life cycle effects and changes in relative phasing between the propagating systems and the position of low-level convergence and thermodynamic instability associated with the wave. At the ocean and coastal sites, the most intense convection occurred ahead of the wave trough where both high CAPE and low-level convergence were concentrated. At the continental site, convection was relatively weak owing to the fact that the wave dynamics and thermodynamics were not in sync when the systems passed through Niamey. The only apparent effect of the wave on MCS activity at the continental site was to extend the period of precipitation activity during one of the events that passed through coincident with the 700-mb wave trough. Convective organization at the land sites was primarily in the form of squall lines and linear MCSs oriented perpendicular to the low-level shear. The organization at the oceanic site was more complicated, transitioning from linear MCSs to widespread stratiform cloud with embedded convection. The precipitation activity was also much longer lived at the oceanic site due to the wave becoming nearly stationary near the Cape Verdes, providing an environment supportive of deep convection for an extended period.

Corresponding author address: Robert Cifelli, R/PSD2, 325 Broadway, Boulder, CO 80305. Email: rob.cifelli@noaa.gov

This article included in the TCSP NAMMA special collection.

Save
Cover Journal of the Atmospheric Sciences
Journal of the Atmospheric Sciences

  • Anagnostou, E. N., C. A. Morales, and T. Dinku, 2001: The use of TRMM Precipitation Radar observations in determining ground radar calibration biases. J. Atmos. Oceanic Technol., 18 , 616–628.

    • Search Google Scholar
    • Export Citation

  • Aspliden, C. I., Y. Tourre, and J. B. Sabine, 1976: Some climatological aspects of West African disturbance lines during GATE. Mon. Wea. Rev., 104 , 1029–1035.

    • Search Google Scholar
    • Export Citation

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

  • Berry, G. J., and C. Thorncroft, 2005: Case study of an intense African easterly wave. Mon. Wea. Rev., 133 , 752–766.

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

    • Search Google Scholar
    • Export Citation

  • Burpee, R. W., 1974: Characteristics of North African easterly waves during the summers of 1968 and 1969. J. Atmos. Sci., 31 , 1556–1570.

    • Search Google Scholar
    • Export Citation

  • Carlson, T. N., 1969a: Synoptic histories of three African disturbances that developed into Atlantic hurricanes. Mon. Wea. Rev., 97 , 256–276.

    • Search Google Scholar
    • Export Citation

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

    • Search Google Scholar
    • Export Citation

  • Chen, T-C., S-Y. Wang, and A. J. Clark, 2008: North Atlantic hurricanes contributed by African easterly waves north and south of the African easterly jet. J. Climate, 21 , 6767–6776.

    • Search Google Scholar
    • Export Citation

  • Cheng, C-P., and R. A. Houze Jr., 1979: The distribution of convective and mesoscale precipitation in GATE radar echo patterns. Mon. Wea. Rev., 107 , 1370–1381.

    • Search Google Scholar
    • Export Citation

  • Chong, M., P. Amayenc, G. Scialom, and J. Testud, 1987: A tropical squall line observed during the COPT 81 experiment in West Africa. Part I: Kinematic structure inferred from dual-Doppler radar data. Mon. Wea. Rev., 115 , 670–694.

    • Search Google Scholar
    • Export Citation

  • Cifelli, R., S. W. Nesbitt, S. A. Rutledge, W. A. Petersen, and S. Yuter, 2007: Radar characteristics of precipitation features in the EPIC and TEPPS regions of the east Pacific. Mon. Wea. Rev., 135 , 1576–1595.

    • Search Google Scholar
    • Export Citation

  • Diedhiou, A., S. Janicot, A. Viltard, P. de Felice, and H. Laurent, 1999: Easterly wave regimes and associated convection over West Africa and tropical Atlantic: Results from the NCEP/NCAR and ECMWF reanalyses. Climate Dyn., 15 , 795–822.

    • Search Google Scholar
    • Export Citation

  • Duvel, J. P., 1990: Convection over tropical Africa and the Atlantic Ocean during northern summer. Part II: Modulation by easterly waves. Mon. Wea. Rev., 118 , 1855–1868.

    • Search Google Scholar
    • Export Citation

  • Fink, A. H., and A. Reiner, 2003: Spatiotemporal variability of the relation between African easterly waves and West African squall lines in 1998 and 1999. J. Geophys. Res., 108 , 4332. doi:10.1029/2002JD002816.

    • Search Google Scholar
    • Export Citation

  • Fortune, M., 1980: Properties of African squall lines inferred from time-lapse satellite imagery. Mon. Wea. Rev., 108 , 153–168.

  • Fuentes, J. D., B. Geerts, T. Dejene, P. D’Odorico, and E. Joseph, 2008: Vertical attributes of precipitation systems in West Africa and adjacent Atlantic Ocean. Theor. Appl. Climatol., 92 , 181–193.

    • Search Google Scholar
    • Export Citation

  • Futyan, J. M., and A. D. Del Genio, 2007: Deep convective system evolution over Africa and the tropical Atlantic. J. Climate, 20 , 5041–5060.

    • Search Google Scholar
    • Export Citation

  • Gamache, J. F., and R. A. Houze Jr., 1983: Water budget of a mesoscale convective system in the tropics. J. Atmos. Sci., 40 , 1835–1850.

    • Search Google Scholar
    • Export Citation

  • Geerts, B., and T. Dejene, 2005: Regional and diurnal variability of the vertical structure of precipitation systems in Africa based on spaceborne radar data. J. Climate, 18 , 893–916.

    • 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

  • Houze Jr., R. A., 1977: Structure and dynamics of a tropical squall-line system. Mon. Wea. Rev., 105 , 1540–1567.

  • Houze Jr., R. A., and C-P. Cheng, 1977: Radar characteristics of tropical convection observed during GATE: Mean properties and trends over the summer season. Mon. Wea. Rev., 105 , 964–980.

    • Search Google Scholar
    • Export Citation

  • Houze Jr., R. A., and E. N. Rappaport, 1984: Air motions and precipitation structure of an early summer squall line over the eastern tropical Atlantic. J. Atmos. Sci., 41 , 553–574.

    • Search Google Scholar
    • Export Citation

  • Hudlow, M. D., 1979: Mean rainfall patterns for the three phases of GATE. J. Appl. Meteor., 18 , 1656–1669.

  • Janicot, S., and Coauthors, 2008: Large-scale overview of the summer monsoon over West Africa during the AMMA field experiment in 2006. Ann. Geophys., 26 , 2569–2595.

    • Search Google Scholar
    • Export Citation

  • Keenan, T. D., and R. E. Carbone, 1992: A preliminary morphology of precipitation systems in tropical northern Australia. Quart. J. Roy. Meteor. Soc., 118 , 283–326.

    • 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.

    • Search Google Scholar
    • Export Citation

  • Laing, A. G., R. Carbone, V. Levizzani, and J. Tuttle, 2008: The propagation and diurnal cycles of deep convection in northern tropical Africa. Quart. J. Roy. Meteor. Soc., 134 , 93–109.

    • Search Google Scholar
    • Export Citation

  • Landsea, C. W., 1993: A climatology of intense (or major) Atlantic hurricanes. Mon. Wea. Rev., 121 , 1703–1713.

  • Lang, T. J., S. W. Nesbitt, and L. D. Carey, 2009: On the correction of partial beam blockage in polarimetric radar data. J. Atmos. Oceanic Technol., 26 , 943–957.

    • Search Google Scholar
    • Export Citation

  • Leary, C. A., 1984: Precipitation structure of the cloud clusters in a tropical easterly wave. Mon. Wea. Rev., 112 , 313–325.

  • LeMone, M. A., E. J. Zipser, and S. B. Trier, 1998: The role of environmental shear and thermodynamic conditions in determining the structure and evolution of mesoscale convective systems during TOGA COARE. J. Atmos. Sci., 55 , 3493–3518.

    • Search Google Scholar
    • Export Citation

  • López, R. E., 1978: Internal structure and development processes of C-scale aggregates of cumulus clouds. Mon. Wea. Rev., 106 , 1488–1494.

    • Search Google Scholar
    • Export Citation

  • Mathon, V., H. Laurent, and T. Label, 2002: Mesoscale convective system rainfall in the Sahel. J. Appl. Meteor., 41 , 1081–1092.

  • McTaggart-Cowan, R., G. D. Deane, L. F. Bosart, C. A. Davis, and T. J. Galarneau, 2008: Climatology of tropical cyclogenesis in the North Atlantic (1948–2004). Mon. Wea. Rev., 136 , 1284–1304.

    • Search Google Scholar
    • Export Citation

  • Mekonnen, A., C. D. Thorncroft, and A. R. Aiyyer, 2006: Analysis of convection and its association with African easterly waves. J. Climate, 19 , 5405–5421.

    • Search Google Scholar
    • Export Citation

  • Mohr, C. G., L. J. Miller, R. L. Vaughan, and H. W. Frank, 1986: The merger of mesoscale datasets into a common Cartesian format for efficient and systematic analyses. J. Atmos. Oceanic Technol., 3 , 143–161.

    • Search Google Scholar
    • Export Citation

  • Nesbitt, S. W., R. Cifelli, and S. A. Rutledge, 2006: Storm morphology and rainfall characteristics of TRMM precipitation features. Mon. Wea. Rev., 134 , 2702–2721.

    • Search Google Scholar
    • Export Citation

  • Nzeukou, A., H. Sauvageot, A. D. Ochou, and C. M. F. Kebe, 2004: Raindrop size distribution and radar parameters at Cape Verde. J. Appl. Meteor., 43 , 90–105.

    • Search Google Scholar
    • Export Citation

  • Omotosho, J. B., 1985: The separate contributions of squall lines, thunderstorms and the monsoon to the total rainfall in Nigeria. J. Climatol., 5 , 543–552.

    • Search Google Scholar
    • Export Citation

  • Patterson, V. L., M. D. Hudlow, P. J. Pytlowaney, F. P. Richards, and J. D. Hoff, 1979: GATE radar rainfall processing system. NOAA Tech. Memo. EDIS 26, 34 pp. [Available from the National Technical Information Service, Sills Building, 5285 Port Royal Rd., Springfield, VA 22161].

    • Search Google Scholar
    • Export Citation

  • Pytharoulis, I., and C. Thorncroft, 1999: The low-level structure of African easterly waves in 1995. Mon. Wea. Rev., 127 , 2266–2280.

    • Search Google Scholar
    • Export Citation

  • Redelsperger, J. L., C. D. Thorncroft, A. Diedhiou, T. Lebel, D. J. Parker, and J. Polcher, 2006: African Monsoon Multidisciplinary Analysis: An international research project and field campaign. Bull. Amer. Meteor. Soc., 87 , 1739–1746.

    • 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.

    • Search Google Scholar
    • Export Citation

  • 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.

    • Search Google Scholar
    • Export Citation

  • Rickenbach, T., and S. A. Rutledge, 1998: Convection in TOGA COARE: Horizontal scale, morphology, and rainfall production. J. Atmos. Sci., 55 , 2715–2729.

    • Search Google Scholar
    • Export Citation

  • Rickenbach, T., R. Nieto Ferreira, N. Guy, and E. Williams, 2009: Radar-observed squall line propagation and the diurnal cycle of convection in Niamey, Niger during the 2006 African Monsoon and Multidisciplinary Analyses intensive observing period. J. Geophys. Res., 114 , D03107. doi:10.1029/2008JD010871.

    • Search Google Scholar
    • Export Citation

  • Rodger, C. J., J. B. Brundell, and R. L. Dowden, 2005: Location accuracy of VLF World-Wide Lightning Location (WWLL) network: Post-algorithm upgrade. Ann. Geophys., 23 , 277–290.

    • Search Google Scholar
    • Export Citation

  • Ross, R. S., and T. N. Krishnamurti, 2007: Low-level African easterly wave activity and its relation to Atlantic tropical cyclogenesis in 2001. Mon. Wea. Rev., 135 , 3950–3964.

    • Search Google Scholar
    • Export Citation

  • Rowell, D. P., and J. R. Milford, 1993: On the generation of African squall lines. J. Climate, 6 , 1181–1193.

  • Rutledge, S. A., and R. A. Houze Jr., 1987: A diagnostic modeling study of the trailing stratiform region of a midlatitude squall line. J. Atmos. Sci., 44 , 2640–2656.

    • Search Google Scholar
    • Export Citation

  • Sauvageot, H., and J. P. Lacaux, 1995: The shape of averaged drop size distributions. J. Atmos. Sci., 52 , 1070–1083.

  • Schumacher, C., and R. A. Houze Jr., 2006: Stratiform precipitation production over sub-Saharan Africa and the tropical east Atlantic as observed by TRMM. Quart. J. Roy. Meteor. Soc., 132 , 2235–2255.

    • Search Google Scholar
    • Export Citation

  • Seo, H., M. Jochum, R. Murtugudde, A. J. Miller, and J. O. Roads, 2008: Precipitation from African easterly waves in a coupled model of the tropical Atlantic. J. Climate, 21 , 1417–1431.

    • Search Google Scholar
    • Export Citation

  • Steiner, M., R. A. Houze Jr., and S. E. Yuter, 1995: Climatological characterization of three-dimensional storm structure from operational radar and rain gauge data. J. Appl. Meteor., 34 , 1978–2007.

    • Search Google Scholar
    • Export Citation

  • Thompson Jr., R. M., S. W. Payne, E. E. Recker, and R. J. Reed, 1979: Structure and properties of synoptic-scale wave disturbances in the intertropical convergence zone of the eastern Atlantic. J. Atmos. Sci., 36 , 53–72.

    • Search Google Scholar
    • Export Citation

  • Thorncroft, C. D., and K. Hodges, 2001: African easterly wave variability and its relationship to Atlantic tropical cyclone activity. J. Climate, 14 , 1166–1179.

    • Search Google Scholar
    • Export Citation

  • Thorncroft, C. D., N. M. J. Hall, and G. N. Kiladis, 2008: Three-dimensional structure and dynamics of African easterly waves. Part III: Genesis. J. Atmos. Sci., 65 , 3596–3607.

    • Search Google Scholar
    • Export Citation

  • Wei, T., and R. A. Houze Jr., 1987: The GATE squall line of 9–10 August 1974. Adv. Atmos. Sci., 4 , 85–92.

  • Weisman, M. L., and J. B. Klemp, 1986: Characteristics of convective storms. Mesoscale Meteorology and Forecasting, P. S. Ray, Ed., Amer. Meteor. Soc., 331–358.

    • Search Google Scholar
    • Export Citation

  • WMO, 1975: Report on the field phase of GATE: Meteorological atlas. GATE Rep 17, World Meteorological Association, 23 pp.

  • Yuter, S. E., and R. A. Houze Jr., 1995: Three-dimensional kinematic and microphysical evolution of Florida cumulonimbus. Part II: Frequency distributions of vertical velocity, reflectivity, and differential reflectivity. Mon. Wea. Rev., 123 , 1941–1963.

    • Search Google Scholar
    • Export Citation

  • Zawislak, J., and E. J. Zipser, 2009: Observations of seven African easterly waves in the east Atlantic during 2006. J. Atmos. Sci., in press.

    • Search Google Scholar
    • Export Citation

  • Zipser, E., 1977: Mesoscale and convective-scale downdrafts as distinct components of squall-line structure. Mon. Wea. Rev., 105 , 1568–1589.

    • Search Google Scholar
    • Export Citation

  • Zipser, E. J., D. J. Cecil, C. Liu, S. W. Nesbitt, and D. P. Yorty, 2006: Where are the most intense thunderstorms on earth? Bull. Amer. Meteor. Soc., 87 , 1057–1071.

    • Search Google Scholar
    • Export Citation

  • Zipser, E. J., and Coauthors, 2009: The Saharan air layer and the fate of African easterly waves—NASA’s AMMA field study of tropical cyclogenesis. Bull. Amer. Meteor. Soc., 90 , 1137–1156.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 935 531 247
PDF Downloads 238 94 4