Summary
The environmental conditions in advance of three West African disturbance lines and three Eastern Atlantic squall lines are examined as is the modification of the environment during the passage of such storms over a site. A comparison with other tropical squall lines observed over Venezuela is made. A model of the relative airflow within a West African disturbance line is presented and some aspects of storm movement are considered. The hydraulic jump analogy and a density current model are applied to the convective systems and the results obtained are compared with observations. The hydraulic jump analogy gives reasonable predictions for the storms' speeds and the density current model results show that for the West African disturbance lines, as well as the Venezuelan storms, a close relationship exists between the storm speed and the speed of the density current. As this relationship is not observed in the Eastern Atlantic squall lines, it appears that the density current model is not applicable to convective systems occurring over the ocean.
Zusammenfassung
Es werden die Verhältnisse im Bereich von drei sich annähernden westafrikanischen Störungslinien und von drei ostatlantischen Böenlinien wie auch die Modifikation der Umgebung beim Durchzug solcher Störungen untersucht. Ein Vergleich mit anderen über Venezuela beobachteten tropischen Böenlinien wird gemacht. Ein Modell der relativen Luftströmung in einer westafrikanischen Störungslinie wird dargelegt und einige Aspekte der Bewegung der Störung werden in Betracht gezogen. Die hydraulische Jump-Analogie und ein Dichtestrom-Modell werden auf konvektive Systeme angewendet und die Ergebnisse werden mit Beobachtungen verglichen. Die hydraulische Jump-Analogie gibt vernünftige Vorhersagen für die Störungsgeschwindigkeiten, und das Dichtestrom-Modell zeigt das Ergebnis, daß sowohl bei westafrikanischen Störungslinien wie auch bei den Störungen in Venezuela eine enge Beziehung zwischen der Störungsgeschwindigkeit und der Geschwindigkeit des Dichtestromes besteht. Da diese Beziehung nicht bei ostatlantischen Böenlinien beobachtet wird, scheint es, daß das Dichtestrom-Modell auf konvektive Systeme über dem Ozean nicht anwendbar ist.
Similar content being viewed by others
References
ASECNA, B. E.: Operation Pre-GATE ASECNA, 1–10 Août 1973. Research Report, ASECNA, Dakar, Senegal (1974).
ASECNA, B. E.: Operation Pre-GATE ASECNA, 1–10 Août 1973, Compléments d'Analyse. Research Report, ASECNA, Dakar, Senegal (1975).
Aspliden, C. I., Tourre, Y., Sabine, J. B.: Some Climatological Aspects of West African Disturbance Lines During GATE. Mon. Weath. Rev.104, 1029–1035 (1976).
Benjamin, T. B.: Gravity Currents and Related Phenomena. J. Fluid Mech.31, Part 2, 209–248 (1968).
Burpee, R. W.: The Origin and Structure of Easterly Waves in the Lower Troposphere of North Africa. J. Atmos. Sci.29, 77–90 (1972).
Burpee, R. W.: Some Features of Synoptic-Scale Waves Based on a Compositing Analysis of GATE Data. Mon. Weath. Rev.103, 921–925 (1975).
Burpee, R. W.: The Influence of Easterly Waves on the Patterns of Precipitation in Tropical Northern Africa. In: Lectures on Forecasting of Tropical Weather, Including Tropical Cyclones, with Particular Relevance to Africa, WMO No. 492, WMO, Geneva, pp. 41–71 (1977).
Charba, J.: Application of Gravity Current Model to Analysis of Squall-Line Gust Front. Mon. Weath. Rev.102, 140–156 (1974).
Dhonneur, G.: Essai de synthèse sur les lignes de grains en Afrique Occidentale et Centrale. Publication No. 20, ASECNA, Dakar (1971).
Dhonneur, G.: Nouvelle approche des réalités météorologiques de l'Afrique Occidentale et Centrale. Doctoral Thesis, Université de Dakar, Dakar (1974).
Eldridge, R. H.: A Synoptic Study of West African Disturbance Lines. Quart. J. R. Met. Soc.83, 303–314 (1957).
Fernandez, W.: Environmental Conditions and Structure of Some Types of Convective Mesosystems Observed over Venezuela. Arch. Met. Geoph. Biokl., Ser. A29, 249–267 (1980).
Fernandez, W., Thorpe, A. J.: An Evaluation of Theories of Storm Motion Using Observations of Tropical Convective Systems. Mon. Weath. Rev.107, 1306–1319 (1979).
Fortune, M. A.: Properties of African Squall Lines Inferred from Time-Lapse Satellite Imaginary. Mon. Weath. Rev.108, 153–168 (1980).
Freeman, J. C., Jr.: An Analogy between Equatorial Easterlies and Supersonic Gas Flow. J. Met.5, 138–146 (1948).
Hamilton, R. A., Archbold, J. W.: Meteorology of Nigeria and Adjacent Territory. Quart. J. R. Met. Soc.71, 231–264 (1945).
Houze, R. A.: Squall Lines Observed in the Vicinity of the Researcher During Phase III of GATE. Preprints 16th Radar Meteorology Conf., Houston. Amer. Met. Soc. 206–209 (1975).
Houze, R. A.: Structure and Dynamics of a Tropical Squall Line System. Mon. Weath. Rev.105, 1540–1567 (1977).
Keulegan, G.: The Motion of Saline Fronts in Still Water. Nat. Bur. of Standards Rep., U.S. Dept. of Commerce, Wash., D.C., 29 pp. (1958).
LeRoux, M.: Processus de formation et d'évolution des lignes de grains de l'Afrique Tropicale Septentrionale. Recherches de Climatologie Tropical No. 1, Dept. Géographie, Université de Dakar, Dakar (1976).
Mansfield, D. A.: Squall Lines Observed in GATE. Quart. J. R. Met. Soc.103, 569–574 (1977).
Middleton, G. V.: Experiments on Density and Turbidity Currents. Canadian J. Earth Sci.3, 523–546 (1966).
Miller, M. J., Betts, A. K.: Travelling Convective Storms over Venezuela. Mon. Weath. Rev.105, 833–848 (1977).
Moncrieff, M. W., Miller, M. J.: The Dynamics and Simulation of Tropical Cumulonimbus and Squall Lines. Quart. J. R. Met. Soc.102, 373–394 (1976).
Obasi, G. O. P.: The Environmental Structure of the Atmosphere Near West African Disturbance Lines. International Tropical Meteorology Meeting, Nairobi. Amer. Met. Soc., Boston, Part II, 62–66 (1974).
Payne, S. W., McGarry, M. M.: The Relationship of Satellite Inferred Convective Activity to Easterly Waves over West Africa and the Adjacent Ocean During Phase III of GATE. Mon. Weath. Rev.105, 413–420 (1977).
Riehl, H., Rossignol, D., Lückefedt, W.: On the Structure and Maintenance of West African Squall Lines. Institut für Meteorologie, Freie Universität Berlin, 29 pp. (1974).
Simpson, J. E.: A Comparison Between Laboratory and Atmospheric Density Currents. Quart. J. R. Met. Soc.95, 758–765 (1969).
Simpson, J. E.: Effects of the Lower Boundary on the Head of a Gravity Current. J. Fluid Mech.53, Part 4, 759–768 (1972).
Tepper, M.: A Proposed Mechanism of Squall-Lines: The Pressure Jump Line. J. Met.7, 21–29 (1950).
Tschirhart, G.: Les conditions aérologiques à l'avant des lignes de grains en Afrique Equatoriale. Météorologie Nationale, France, Service Météorologique de l'A. E. F., Monogr. No. 11, 28 pp. (1958).
Zipser, E. J.: Mesoscale and Cloud-Scale Downdrafts as Distinct Components of Squall-Line Structure. Mon. Weath. Rev.105, 1568–1589 (1977).
Author information
Authors and Affiliations
Additional information
With 5 Figures
Rights and permissions
About this article
Cite this article
Fernandez, W. Environmental conditions and structure of the West African and Eastern Tropical Atlantic squall lines. Arch. Met. Geoph. Biocl. A. 31, 71–89 (1982). https://doi.org/10.1007/BF02257743
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF02257743