• Avila, L. A., , Pasch R. J. , , and Jiing J. , 2000: Atlantic tropical systems of 1996 and 1997: Years of contrast. Mon. Wea. Rev., 128 , 36953706.

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

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Dunion, J. P., , and Velden C. S. , 2004: The impact of the Saharan air layer on Atlantic tropical cyclone activity. Bull. Amer. Meteor. Soc., 85 , 353365.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hendricks, E. A., , and Montgomery M. T. , 2004: The role of “vortical” hot towers in the formation of Tropical Cyclone Diana (1984). J. Atmos. Sci., 61 , 12091232.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hopsch, S. B., , Thorncroft C. D. , , Hodges K. , , and Aiyyer A. , 2007: West African storm tracks and their relationship to Atlantic tropical cyclones. J. Climate, 20 , 24682483.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hopsch, S. B., , Thorncroft C. D. , , and Tyle K. R. , 2010: Analysis of African easterly wave structures and their role in influencing tropical cyclogenesis. Mon. Wea. Rev., in press.

    • Search Google Scholar
    • Export Citation
  • Karyampudi, V. M., , and Carlson T. N. , 1988: Analysis and numerical simulations of the Saharan air layer and its effect on easterly wave disturbances. J. Atmos. Sci., 45 , 31023136.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Karyampudi, V. M., , and Pierce H. F. , 2002: Synoptic-scale influence of the Saharan air layer on tropical cyclogenesis over the eastern Atlantic. Mon. Wea. Rev., 130 , 31003128.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Karyampudi, V. M., and Coauthors, 1999: Validation of the Saharan dust plume conceptual model using lidar, Meteosat, and ECMWF data. Bull. Amer. Meteor. Soc., 80 , 10451074.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Krishnamurti, T. N., , Bhaskar J. , , Bedi H. S. , , and Mohanty U. C. , 2000: Diabatic effects on potential vorticity over the global tropics. J. Meteor. Soc. Japan, 78 , 527542.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Montgomery, M. T., , Nichols M. E. , , Cram T. A. , , and Saunders A. B. , 2006: A vortical hot tower route to tropical cyclogenesis. J. Atmos. Sci., 63 , 355386.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Norquist, D. C., , Recker E. E. , , and Reed R. J. , 1977: The energetics of African wave disturbances as observed during phase III of GATE. Mon. Wea. Rev., 105 , 334342.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ross, R. S., , and Krishnamurti T. N. , 2007: Low-level African easterly wave activity and its relation to Atlantic tropical cyclogenesis in 2001. Mon. Wea. Rev., 135 , 39503964.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Thorncroft, C. D., , and Hodges K. , 2001: African easterly wave variability and its relationship to Atlantic tropical cyclone activity. J. Climate, 14 , 11661179.

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

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Zhang, H., , McFarquhar G. M. , , Cotton W. R. , , and Deng Y. , 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
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 10 10 2
PDF Downloads 3 3 1

Energy Transformation and Diabatic Processes in Developing and Nondeveloping African Easterly Waves Observed during the NAMMA Project of 2006

View More View Less
  • 1 Department of Meteorology, The Florida State University, Tallahassee, Florida
  • | 2 Indian Institute of Tropical Meteorology, Pune, India
  • | 3 Department of Meteorology, The Florida State University, Tallahassee, Florida
© Get Permissions
Restricted access

Abstract

This paper provides an understanding of essential differences between developing and nondeveloping African easterly waves, which was a major goal of NAMMA, NASA’s field program in the eastern Atlantic, which functioned as an extension of the African Monsoon Multidisciplinary Analysis (AMMA) program during 2006.

Three NAMMA waves are studied in detail using FNL analysis: NAMMA wave 2, which developed into Tropical Storm Debby; NAMMA wave 7, which developed into Hurricane Helene; and NAMMA wave 4, which did not develop within the NAMMA domain. Diagnostic calculations are performed on the analyzed fields using energy transformation equations and the isentropic potential vorticity equation.

The results show that the two developing waves possess clear and robust positive barotropic energy conversion in conjunction with positive diabatic heating that includes a singular burst of heating at a particular time in the wave’s history. This positive barotropic energy conversion is facilitated in waves that have a northeast–southwest tilt to the trough axis and a wind maximum to the west of this axis. The nondeveloping wave is found to have the same singular burst of diabatic heating at one point in its history, but development of the wave does not occur due to negative barotropic energy conversion. Such conversion is facilitated by a northwest–southeast tilt to the trough axis and a wind maximum to the east of this axis.

The conclusions about wave development and nondevelopment formulated in this research are viewed as important and significant, but they require additional testing with detailed observational- and numerical-based studies.

Corresponding author address: Robert S. Ross, Dept. of Meteorology, The Florida State University, Tallahassee, FL 32306-4520. Email: rross@fsu.edu

This article included in the West African Weather Prediction and Predictability special collection.

Abstract

This paper provides an understanding of essential differences between developing and nondeveloping African easterly waves, which was a major goal of NAMMA, NASA’s field program in the eastern Atlantic, which functioned as an extension of the African Monsoon Multidisciplinary Analysis (AMMA) program during 2006.

Three NAMMA waves are studied in detail using FNL analysis: NAMMA wave 2, which developed into Tropical Storm Debby; NAMMA wave 7, which developed into Hurricane Helene; and NAMMA wave 4, which did not develop within the NAMMA domain. Diagnostic calculations are performed on the analyzed fields using energy transformation equations and the isentropic potential vorticity equation.

The results show that the two developing waves possess clear and robust positive barotropic energy conversion in conjunction with positive diabatic heating that includes a singular burst of heating at a particular time in the wave’s history. This positive barotropic energy conversion is facilitated in waves that have a northeast–southwest tilt to the trough axis and a wind maximum to the west of this axis. The nondeveloping wave is found to have the same singular burst of diabatic heating at one point in its history, but development of the wave does not occur due to negative barotropic energy conversion. Such conversion is facilitated by a northwest–southeast tilt to the trough axis and a wind maximum to the east of this axis.

The conclusions about wave development and nondevelopment formulated in this research are viewed as important and significant, but they require additional testing with detailed observational- and numerical-based studies.

Corresponding author address: Robert S. Ross, Dept. of Meteorology, The Florida State University, Tallahassee, FL 32306-4520. Email: rross@fsu.edu

This article included in the West African Weather Prediction and Predictability special collection.

Save