Editorial Type:
Article
Article Type:
Research Article

Interactions of Diabatic Heating in Convective Superbursts with Energy Conversion Processes in the Genesis of Cape Verde Hurricanes from African Easterly Waves

Robert S. Ross Earth, Ocean, and Atmospheric Science, The Florida State University, Tallahassee, Florida

Search for other papers by Robert S. Ross in
Current site
Google Scholar
PubMed Close
,
T. N. Krishnamurti Earth, Ocean, and Atmospheric Science, The Florida State University, Tallahassee, Florida

Search for other papers by T. N. Krishnamurti in
Current site
Google Scholar
PubMed Close
, and
S. Pattnaik Earth, Ocean, and Atmospheric Science, The Florida State University, Tallahassee, Florida

Search for other papers by S. Pattnaik in
Current site
Google Scholar
PubMed Close
Print Publication:
01 Mar 2012
DOI:
https://doi.org/10.1175/2011MWR3621.1
Page(s):
748–773
Restricted access

Abstract

This paper defines a mechanism for the genesis of tropical cyclones from African easterly waves (AEWs) over the eastern Atlantic, the so-called Cape Verde storms. Convective “superbursts” produce strong diabatic heating, which then strengthens the African easterly jet (AEJ), leading to enhanced barotropic energy conversions, which occur at the critical developmental stages of the system.

Diabatic heating is calculated using the Ertel isentropic potential vorticity (IPV) equation, while energy conversions are determined using energy equations first derived by Lorenz. The genesis mechanism is developed from studying Hurricane Bill (2009), as well as Tropical Storm Debby, Hurricane Helene, and a nondeveloping AEW, all from the 2006 NASA African Monsoon Multidisciplinary Analysis (NAMMA) field experiment, using the NCEP Final (FNL) analyses and the Advanced Research Weather Research and Forecasting model (WRF-ARW) simulations.

A striking and singular maximum in the diabatic heating due to the convective superburst is shown to precede by 24–36 h a pronounced maximum in positive barotropic energy conversion, which is demonstrated to occur simultaneously with the strengthening of the AEJ. The maximum in barotropic energy conversion is documented to occur in the developmental stages of the system, typically in the depression or early storm stages.

A physical mechanism is developed to explain how a mesoscale convective superburst can lead subsequently to an enhanced synoptic-scale AEJ over the eastern Atlantic, an enhanced jet that is critical to the genesis mechanism.

The findings agree with cited idealized studies by other investigators who found that moist AEWs grow 3 times stronger than dry waves as a result of faster AEJ development and larger barotropic energy conversions.

Additional affiliation: Indian Institute of Tropical Meteorology, Pune, India.

Corresponding author address: Robert S. Ross, Earth, Ocean, and Atmospheric Science, The Florida State University, Tallahassee, FL 32306-4520. E-mail: rross@fsu.edu

Abstract

This paper defines a mechanism for the genesis of tropical cyclones from African easterly waves (AEWs) over the eastern Atlantic, the so-called Cape Verde storms. Convective “superbursts” produce strong diabatic heating, which then strengthens the African easterly jet (AEJ), leading to enhanced barotropic energy conversions, which occur at the critical developmental stages of the system.

Diabatic heating is calculated using the Ertel isentropic potential vorticity (IPV) equation, while energy conversions are determined using energy equations first derived by Lorenz. The genesis mechanism is developed from studying Hurricane Bill (2009), as well as Tropical Storm Debby, Hurricane Helene, and a nondeveloping AEW, all from the 2006 NASA African Monsoon Multidisciplinary Analysis (NAMMA) field experiment, using the NCEP Final (FNL) analyses and the Advanced Research Weather Research and Forecasting model (WRF-ARW) simulations.

A striking and singular maximum in the diabatic heating due to the convective superburst is shown to precede by 24–36 h a pronounced maximum in positive barotropic energy conversion, which is demonstrated to occur simultaneously with the strengthening of the AEJ. The maximum in barotropic energy conversion is documented to occur in the developmental stages of the system, typically in the depression or early storm stages.

A physical mechanism is developed to explain how a mesoscale convective superburst can lead subsequently to an enhanced synoptic-scale AEJ over the eastern Atlantic, an enhanced jet that is critical to the genesis mechanism.

The findings agree with cited idealized studies by other investigators who found that moist AEWs grow 3 times stronger than dry waves as a result of faster AEJ development and larger barotropic energy conversions.

Additional affiliation: Indian Institute of Tropical Meteorology, Pune, India.

Corresponding author address: Robert S. Ross, Earth, Ocean, and Atmospheric Science, The Florida State University, Tallahassee, FL 32306-4520. E-mail: rross@fsu.edu
Save
Cover Monthly Weather Review
Monthly Weather Review

  • Avila, L. A., R. J. Pasch, and J. Jiing, 2000: Atlantic tropical systems of 1996 and 1997: Years of contrast. Mon. Wea. Rev., 128, 3695–3706.

    • Search Google Scholar
    • Export Citation

  • Chen, T. S., 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

  • Cornforth, R. J., B. J. Hoskins, and C. D. Thorncroft, 2009: The impact of moist processes on the African easterly jet-African easterly wave system. Quart. J. Roy. Meteor. Soc., 135, 894–913.

    • 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, 3077–3107.

    • Search Google Scholar
    • Export Citation

  • Dunion, J. P., and C. S. Velden, 2004: The impact of the Saharan air layer on Atlantic tropical cyclone activity. Bull. Amer. Meteor. Soc., 85, 353–365.

    • 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, 5587–5646.

    • Search Google Scholar
    • Export Citation

  • Hendricks, E. A., and M. T. Montgomery, 2004: The role of “vortical” hot towers in the formation of Tropical Cyclone Diana (1984). J. Atmos. Sci., 61, 1209–1232.

    • Search Google Scholar
    • Export Citation

  • Hong, S.-Y., H.-M. H. Juang, and Q. Zhao, 1998: Implementation of prognostic cloud scheme for a regional spectral model. Mon. Wea. Rev., 126, 2621–2639.

    • Search Google Scholar
    • Export Citation

  • Hong, S.-Y., J. Dudhia, and S.-H. Chen, 2004: A revised approach to ice microphysical processes for the bulk parameterization of clouds and precipitation. Mon. Wea. Rev., 132, 103–120.

    • Search Google Scholar
    • Export Citation

  • Hopsch, S. B., C. D. Thorncroft, K. Hodges, and A. Aiyyer, 2007: West African storm tracks and their relationship to Atlantic tropical cyclones. J. Climate, 20, 2468–2483.

    • Search Google Scholar
    • Export Citation

  • 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, 1399–1419.

    • Search Google Scholar
    • Export Citation

  • Janjic, Z. I., 1994: The step-mountain Eta coordinate model: Further developments of the convection, viscous sublayer, and turbulence closure schemes. Mon. Wea. Rev., 122, 927–945.

    • Search Google Scholar
    • Export Citation

  • Janjic, Z. I., 1996: The surface layer in the NCEP Eta Model. Preprints, 11th Conf. on Numerical Weather Prediction, Norfolk, VA, Amer. Meteor. Soc., 354–355.

    • Search Google Scholar
    • Export Citation

  • Janjic, Z. I., 2000: Comments on “Development and evaluation of a convection scheme for use in climate models.” J. Atmos. Sci., 57, 3686.

    • Search Google Scholar
    • Export Citation

  • Janjic, Z. I., 2002: Nonsingular implementation of the Mellor–Yamada level 2.5 scheme in the NCEP meso model. NCEP Office Note 437, 61 pp.

    • Search Google Scholar
    • Export Citation

  • Karyampudi, V. M., and H. F. Pierce, 2002: Synoptic-scale influence of the Saharan air layer on tropical cyclogenesis over the eastern Atlantic. Mon. Wea. Rev., 130, 3100–3128.

    • Search Google Scholar
    • Export Citation

  • Krishnamurti, T. N., J. Bhaskar, H. S. Bedi, and U. C. Mohanty, 2000: Diabatic effects on potential vorticity over the global tropics. J. Meteor. Soc. Japan, 78, 527–542.

    • Search Google Scholar
    • Export Citation

  • Mlawer, E. J., S. J. Taubman, P. D. Brown, M. J. Iacono, and S. A. Clough, 1997: Radiative transfer for inhomogeneous atmosphere: RRTM, a validated correlated-k model for the longwave. J. Geophys. Res., 102 (D14), 16 663–16 682.

    • Search Google Scholar
    • Export Citation

  • Monin, A. S., and A. M. Obukhov, 1954: Basic laws of turbulent mixing in the surface layer of the atmosphere (in Russian). Contrib. Geophys. Inst. Acad. Sci. USSR, 151, 163–187.

    • Search Google Scholar
    • Export Citation

  • Montgomery, M. T., M. E. Nichols, T. A. Cram, and A. B. Saunders, 2006: A vortical hot tower route to tropical cyclogenesis. J. Atmos. Sci., 63, 355–386.

    • Search Google Scholar
    • Export Citation

  • Norquist, D. C., E. E. Recker, and R. J. Reed, 1977: The energetics of African wave disturbances as observed during phase III of GATE. Mon. Wea. Rev., 105, 334–342.

    • 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

  • Ross, R. S., T. N. Krishnamurti, S. Pattnaik, and A. Simon, 2009: Energy transformation and diabatic processes in developing and non-developing African easterly waves observed during the NAMMA project of 2006. Wea. Forecasting, 24, 1524–1548.

    • 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

  • Zhang, H., G. M. McFarquhar, S. M. Saleeby, and W. R. Cotton, 2007: Impacts of Saharan dust as CCN on the evolution of an idealized tropical cyclone. Geophys. Res. Lett., 34, L14812, doi:10.1029/2007GL029876.

    • Search Google Scholar
    • Export Citation

  • Zhang, H., G. M. McFarquhar, W. R. Cotton, and Y. Deng, 2009: Direct and indirect impacts of Saharan dust acting as cloud condensation nuclei on tropical cyclone eyewall development. Geophys. Res. Lett., 36, L06802, doi:10.1029/2009GL037276.

    • 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 584 418 53
PDF Downloads 116 26 5