• Avila, L. A., R. J. Pasch, and J.-G. Jiing, 2000: Atlantic tropical systems of 1996 and 1997: Years of contrasts. Mon. Wea. Rev., 128, 36953706, https://doi.org/10.1175/1520-0493(2000)128<3695:ATSOAY>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Bain, C. L., K. D. Williams, S. F. Milton, and J. T. Heming, 2014: Objective tracking of African easterly waves in Met Office models. Quart. J. Roy. Meteor. Soc., 140, 4757, https://doi.org/10.1002/qj.2110.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Berry, G. J., and C. D. Thorncroft, 2012: African easterly wave dynamics in a mesoscale numerical model: The upscale role of convection. J. Atmos. Sci., 69, 12671283, https://doi.org/10.1175/JAS-D-11-099.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Berry, G. J., C. Thorncroft, and T. Hewson, 2007: African easterly waves during 2004—Analysis using objective techniques. Mon. Wea. Rev., 135, 12511267, https://doi.org/10.1175/MWR3343.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Bessafi, M., and M. C. Wheeler, 2006: Modulation of South Indian Ocean tropical cyclones by the Madden–Julian oscillation and convectively coupled equatorial waves. Mon. Wea. Rev., 134, 638656, https://doi.org/10.1175/MWR3087.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Brammer, A., and C. D. Thorncroft, 2015: Variability and evolution of African easterly wave structures and their relationship with tropical cyclogenesis over the eastern Atlantic. Mon. Wea. Rev., 143, 49754995, https://doi.org/10.1175/MWR-D-15-0106.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Brammer, A., C. D. Thorncroft, and J. P. Dunion, 2018: Observations and predictability of a nondeveloping tropical disturbance over the eastern Atlantic. Mon. Wea. Rev., 146, 30793096, https://doi.org/10.1175/MWR-D-18-0065.1.

    • Crossref
    • 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, https://doi.org/10.1175/1520-0469(1972)029<0077:TOASOE>2.0.CO;2.

    • Crossref
    • 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, 67676776, https://doi.org/10.1175/2008JCLI2523.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Cheng, Y.-M., C. D. Thorncroft, and G. N. Kiladis, 2019: Two contrasting African easterly wave behaviors. J. Atmos. Sci., 76, 17531768, https://doi.org/10.1175/JAS-D-18-0300.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Diedhiou, A., S. Janicot, A. Vitard, 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 reanalyzes. Climate Dyn., 15, 795822, https://doi.org/10.1007/s003820050316.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Dunkerton, T. J., M. T. Montgomery, and Z. Wang, 2009: Tropical cyclogenesis in a tropical wave critical layer: Easterly waves. Atmos. Chem. Phys., 9, 55875646, https://doi.org/10.5194/acp-9-5587-2009.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Elless, T. J., and R. D. Torn, 2018: African easterly wave forecast verification and its relation to convective errors within the ECMWF ensemble prediction system. Wea. Forecasting, 33, 461477, https://doi.org/10.1175/WAF-D-17-0130.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Elless, T. J., and R. D. Torn, 2019: Investigating the factors that contribute to African easterly wave intensity forecast uncertainty in the ECMWF ensemble prediction system. Mon. Wea. Rev., 147, 16791698, https://doi.org/10.1175/MWR-D-18-0071.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Emanuel, K. A., D. J. Neelin, and C. Bretherton, 1994: On large-scale circulations in convecting atmosphere. Quart. J. Roy. Meteor. Soc., 120, 11111143, https://doi.org/10.1002/qj.49712051902.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Frank, W. M., and P. E. Roundy, 2006: The role of tropical waves in tropical cyclogenesis. Mon. Wea. Rev., 134, 23972417, https://doi.org/10.1175/MWR3204.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Gruber, A., 1974: The wavenumber-frequency spectra of satellite-measured brightness in the tropics. J. Atmos. Sci., 31, 16751680, https://doi.org/10.1175/1520-0469(1974)031<1675:TWFSOS>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hall, N. M., G. N. Kiladis, and C. D. Thorncroft, 2006: Three-dimensional structure and dynamics of African easterly waves. Part II: Dynamical modes. J. Atmos. Sci., 63, 22312245, https://doi.org/10.1175/JAS3742.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hankes, I., Z. Wang, G. Zhang, and C. Fritz, 2015: Merger of African easterly waves and formation of Cape Verde storms. Quart. J. Roy. Meteor. Soc., 141, 13061319, https://doi.org/10.1002/qj.2439.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hersbach, H., and Coauthors, 2020: The ERA5 global reanalysis. Quart. J. Roy. Meteor. Soc., 146, 19992049, https://doi.org/10.1002/qj.3803.

  • Hopsch, S. B., C. D. Thorncroft, and K. R. Tyle, 2010: Analysis of African easterly wave structures and their role in influencing tropical cyclogenesis. Mon. Wea. Rev., 138, 13991419, https://doi.org/10.1175/2009MWR2760.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Janiga, M. A., and C. D. Thorncroft, 2013: Regional differences in the kinematic and thermodynamic structure of African easterly waves. Quart. J. Roy. Meteor. Soc., 139, 15981614, https://doi.org/10.1002/qj.2047.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Janiga, M. A., and C. D. Thorncroft, 2016: The influence of African easterly waves on convection over tropical Africa and the east Atlantic. Mon. Wea. Rev., 144, 171192, https://doi.org/10.1175/MWR-D-14-00419.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Kiladis, G. N., C. D. Thorncroft, and N. M. Hall, 2006: Three-dimensional structure and dynamics of African easterly waves. Part I: Observations. J. Atmos. Sci., 63, 22122230, https://doi.org/10.1175/JAS3741.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Kiladis, G. N., M. C. Wheeler, P. T. Haertel, K. H. Straub, and P. E. Roundy, 2009: Convectively coupled equatorial waves. Rev. Geophys., 47, RG2003, https://doi.org/10.1029/2008RG000266.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Knapp, K. R., and Coauthors, 2011: Globally gridded satellite (GridSat) observations for climate studies. Bull. Amer. Meteor. Soc., 92, 893907, https://doi.org/10.1175/2011BAMS3039.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Landsea, C. W., and J. L. Franklin, 2013: Atlantic hurricane database uncertainty and presentation of a new database format. Mon. Wea. Rev., 141, 35763592, https://doi.org/10.1175/MWR-D-12-00254.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Leppert, K. D., II, D. J. Cecil, and W. A. Petersen, 2013a: Relation between tropical easterly waves, convection, and tropical cyclogenesis: A Lagrangian perspective. Mon. Wea. Rev., 141, 26492668, https://doi.org/10.1175/MWR-D-12-00217.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Leppert, K. D., II, W. A. Petersen, and D. J. Cecil, 2013b: Electrically active convection in tropical easterly waves and implications for tropical cyclogenesis in the Atlantic and East Pacific. Mon. Wea. Rev., 141, 542556, https://doi.org/10.1175/MWR-D-12-00174.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Liebmann, B., G. N. Kiladis, L. M. V. Carvalho, C. Jones, C. S. Vera, I. Bladé, and D. Allured, 2009: Origin of convectively coupled Kelvin waves over South America. J. Climate, 22, 300315, https://doi.org/10.1175/2008JCLI2340.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Mantripragada, R. S. S., C. J. Schreck III, and A. Aiyyer, 2021: Energetics of interactions between African easterly waves and convective coupled Kelvin waves. Mon. Wea. Rev., 149, 38213835, https://doi.org/10.1175/MWR-D-21-0003.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Mayta, V. C., G. N. Kiladis, J. Dias, P. L. S. Dias, and M. Gehne, 2021: Convectively coupled Kelvin waves over tropical South America. J. Climate, 34, 65316547, https://doi.org/10.1175/JCLI-D-20-0662.1.

    • 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, 54055421, https://doi.org/10.1175/JCLI3920.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Mekonnen, A., C. D. Thorncroft, A. R. Aiyyer, and G. N. Kiladis, 2008: Convectively coupled Kelvin waves over tropical Africa during the boreal summer: Structure and variability. J. Climate, 21, 66496667, https://doi.org/10.1175/2008JCLI2008.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Mounier, F., G. Kiladis, and S. Janicot, 2007: Analysis of the dominant mode of convectively coupled Kelvin waves in the West African monsoon. J. Climate, 20, 14871503, https://doi.org/10.1175/JCLI4059.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Nolan, D. S., 2007: What is the trigger for tropical cyclogenesis? Aust. Meteor. Mag., 56, 241266.

  • Núñez Ocasio, K. M., J. L. Evans, and G. S. Young, 2020: A wave-relative framework analysis of AEW–MCS interactions leading to tropical cyclogenesis. Mon. Wea. Rev., 148, 46574671, https://doi.org/10.1175/MWR-D-20-0152.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Núñez Ocasio, K. M., A. Brammer, J. L. Evans, G. S. Young, and Z. L. Moon, 2021: Favorable monsoon environment over eastern Africa for subsequent tropical cyclogenesis of African easterly waves. J. Atmos. Sci., 78, 29112925, https://doi.org/10.1175/JAS-D-20-0339.1.

    • Search Google Scholar
    • Export Citation
  • Peng, M. S., B. Fu, T. Li, and D. E. Stevens, 2012: Developing versus nondeveloping disturbances for tropical cyclone formation. Part I: North Atlantic. Mon. Wea. Rev., 140, 10471066, https://doi.org/10.1175/2011MWR3617.1.

    • Crossref
    • 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, 317333, https://doi.org/10.1175/1520-0493(1977)105<0317:TSAPOA>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Russell, J. O., and A. Aiyyer, 2020: The potential vorticity structure and dynamics of African easterly waves. J. Atmos. Sci., 77, 871890, https://doi.org/10.1175/JAS-D-19-0019.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Russell, J. O., A. Aiyyer, J. D. White, and W. Hannah, 2017: Revisiting the connection between African easterly waves and Atlantic tropical cyclogenesis. Geophys. Res. Lett., 44, 587595, https://doi.org/10.1002/2016GL071236.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Russell, J. O., A. Aiyyer, and J. D. White, 2020: African easterly wave dynamics in convection-permitting simulations: Rotational stratiform instability as a conceptual model. J. Adv. Model. Earth Syst., 12, e2019MS001706, https://doi.org/10.1029/2019MS001706.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Schreck, C. J., 2015: Kelvin waves and tropical cyclogenesis: A global survey. Mon. Wea. Rev., 143, 39964011, https://doi.org/10.1175/MWR-D-15-0111.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Schreck, C. J., 2016: Convectively coupled Kelvin waves and tropical cyclogenesis in a semi-Lagrangian framework. Mon. Wea. Rev., 144, 41314139, https://doi.org/10.1175/MWR-D-16-0237.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Straub, K. H., and G. N. Kiladis, 2002: Observations of a convectively coupled Kelvin wave in the eastern Pacific ITCZ. J. Atmos. Sci., 59, 3053, https://doi.org/10.1175/1520-0469(2002)059<0030:OOACCK>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Straub, K. H., and G. N. Kiladis, 2003: Extratropical forcing of convectively coupled Kelvin waves during austral winter. J. Atmos. Sci., 60, 526543, https://doi.org/10.1175/1520-0469(2003)060<0526:EFOCCK>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Takayabu, Y. N., 1994: Large-scale cloud disturbances associated with equatorial waves. Part I: Spectral features of the cloud disturbances. J. Meteor. Soc. Japan, 72, 433449, https://doi.org/10.2151/jmsj1965.72.3_433.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Tang, B., and K. Emanuel, 2012: A ventilation index for tropical cyclones. Bull. Amer. Meteor. Soc., 93, 19011912, https://doi.org/10.1175/BAMS-D-11-00165.1.

    • Crossref
    • 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, 35963607, https://doi.org/10.1175/2008JAS2575.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ventrice, M. J., and C. D. Thorncroft, 2013: The role of convectively coupled atmospheric Kelvin waves on African easterly wave activity. Mon. Wea. Rev., 141, 19101924, https://doi.org/10.1175/MWR-D-12-00147.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ventrice, M. J., C. D. Thorncroft, and M. A. Janiga, 2012a: Atlantic tropical cyclogenesis: A three-way interaction between an African easterly wave, diurnally varying convection, and a convectively coupled atmospheric Kelvin wave. Mon. Wea. Rev., 140, 11081124, https://doi.org/10.1175/MWR-D-11-00122.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ventrice, M. J., C. D. Thorncroft, and C. Schreck, 2012b: Impacts of convectively coupled Kelvin waves on environmental conditions for Atlantic tropical cyclogenesis. Mon. Wea. Rev., 140, 21982214, https://doi.org/10.1175/MWR-D-11-00305.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Wang, Z., M. T. Montgomery, and T. J. Dunkerton, 2010: Genesis of pre-Hurricane Felix (2007). Part I: The role of the easterly wave critical layer. J. Atmos. Sci., 67, 17111729, https://doi.org/10.1175/2009JAS3420.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Wheeler, M., and G. Kiladis, 1999: Convectively coupled equatorial waves: Analysis of clouds and temperature in the wavenumber–frequency domain. J. Atmos. Sci., 56, 374399, https://doi.org/10.1175/1520-0469(1999)056<0374:CCEWAO>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Wu, L., and M. Takahashi, 2017: Contributions of tropical waves to tropical cyclone genesis over the western North Pacific. Climate Dyn., 50, 46354649, https://doi.org/10.1007/s00382-017-3895-3.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Yanai, M., S. Esbensen, and J.-H. Chu, 1973: Determination of bulk properties of tropical cloud clusters from large-scale heat and moisture budgets. J. Atmos. Sci., 30, 611627, https://doi.org/10.1175/1520-0469(1973)030<0611:DOBPOT>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Zawislak, J., 2020: Global survey of precipitation properties observed during tropical cyclogenesis and their differences compared to nondeveloping disturbances. Mon. Wea. Rev., 148, 15851606, https://doi.org/10.1175/MWR-D-18-0407.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Zawislak, J., and E. J. Zipser, 2014: A multisatellite investigation of the convective properties of developing and nondeveloping tropical disturbances. Mon. Wea. Rev., 142, 46244645, https://doi.org/10.1175/MWR-D-14-00028.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 1058 732 44
Full Text Views 354 290 18
PDF Downloads 368 283 19

The Influence of Convectively Coupled Kelvin Waves on African Easterly Waves in a Wave-Following Framework

Quinton A. LawtonaRosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida

Search for other papers by Quinton A. Lawton in
Current site
Google Scholar
PubMed
Close
,
Sharanya J. MajumdaraRosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida

Search for other papers by Sharanya J. Majumdar in
Current site
Google Scholar
PubMed
Close
,
Krista DottererbUniversity at Albany, State University of New York, Albany, New York

Search for other papers by Krista Dotterer in
Current site
Google Scholar
PubMed
Close
,
Christopher ThorncroftbUniversity at Albany, State University of New York, Albany, New York

Search for other papers by Christopher Thorncroft in
Current site
Google Scholar
PubMed
Close
, and
Carl J. Schreck IIIcCooperative Institute for Satellite Earth System Studies, North Carolina State University, Asheville, North Carolina

Search for other papers by Carl J. Schreck III in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

While considerable attention has been given to how convectively coupled Kelvin waves (CCKWs) influence the genesis of tropical cyclones (TCs) in the Atlantic Ocean, less attention has been given to their direct influence on African easterly waves (AEWs). This study builds a climatology of AEW and CCKW passages from 1981 to 2019 using an AEW-following framework. Vertical and horizontal composites of these passages are developed and divided into categories based on AEW position and CCKW strength. Many of the relationships that have previously been found for TC genesis also hold true for non-developing AEWs. This includes an increase in convective coverage surrounding the AEW center in phase with the convectively enhanced (“active”) CCKW crest, as well as a buildup of relative vorticity from the lower to upper troposphere following this active crest. Additionally, a new finding is that CCKWs induce specific humidity anomalies around AEWs that are qualitatively similar to those of relative vorticity. These modifications to specific humidity are more pronounced when AEWs are at lower latitudes and interacting with stronger CCKWs. While the influence of CCKWs on AEWs is mostly transient and short lived, CCKWs do modify the AEW propagation speed and westward-filtered relative vorticity, indicating that they may have some longer-term influences on the AEW life cycle. Overall, this analysis provides a more comprehensive view of the AEW–CCKW relationship than has previously been established, and supports assertions by previous studies that CCKW-associated convection, specific humidity, and vorticity may modify the favorability of AEWs to TC genesis over the Atlantic.

© 2022 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Quinton A. Lawton, quinton.lawton@rsmas.miami.edu

Abstract

While considerable attention has been given to how convectively coupled Kelvin waves (CCKWs) influence the genesis of tropical cyclones (TCs) in the Atlantic Ocean, less attention has been given to their direct influence on African easterly waves (AEWs). This study builds a climatology of AEW and CCKW passages from 1981 to 2019 using an AEW-following framework. Vertical and horizontal composites of these passages are developed and divided into categories based on AEW position and CCKW strength. Many of the relationships that have previously been found for TC genesis also hold true for non-developing AEWs. This includes an increase in convective coverage surrounding the AEW center in phase with the convectively enhanced (“active”) CCKW crest, as well as a buildup of relative vorticity from the lower to upper troposphere following this active crest. Additionally, a new finding is that CCKWs induce specific humidity anomalies around AEWs that are qualitatively similar to those of relative vorticity. These modifications to specific humidity are more pronounced when AEWs are at lower latitudes and interacting with stronger CCKWs. While the influence of CCKWs on AEWs is mostly transient and short lived, CCKWs do modify the AEW propagation speed and westward-filtered relative vorticity, indicating that they may have some longer-term influences on the AEW life cycle. Overall, this analysis provides a more comprehensive view of the AEW–CCKW relationship than has previously been established, and supports assertions by previous studies that CCKW-associated convection, specific humidity, and vorticity may modify the favorability of AEWs to TC genesis over the Atlantic.

© 2022 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Quinton A. Lawton, quinton.lawton@rsmas.miami.edu
Save