Environmental conditions and structure of some types of convective mesosystems observed over Venezuela

Abstract

SummaryA classification of storms in squall lines, thunderstorm clusters, and isolated thunderstorms was made using radar data collected during the second phase of the Venezuelan International Meteorological and Hydrological Experiments (VIMHEX-1972). The nearenvironmental conditions in advance of these types of storms are examined. The modification of the environment, as deduced from the dry static energy, moist static energy, latent heat content and relative winds is also studied, and a conceptual model for the storms is presented. Finally, some aspects of storm movement are described. Zusammenfassung Umgebungsverh/iltnisse und Struktur einiger iiber Venezuela beobachteter Typen yon konvektiven MesosystemenMit Verwendung yon in der zweiten Phase der Venezueler internationalen meteorologischen und hydrologischen Experimente (VIMHEX-1972) gesammelten Radar-Daten wurde eine Klassifikation yon Unwettem in Btenlinien, in Gewittergruppen und in isolierten Gewittern vorgenommen. Die Verh~ltnisse in der nahen Umgebung w~hrend des Vorrtickens dieser Typen yon Unwetter werden untersucht. Die Modifikation der Umgebung wird, abgeleitet aus der trocken-statischen Energie, aus der feucht-statischen Energie, aus dem latenten W~irmegehalt und aus den relafiven Winden, ebenfalls studiert und ein fiir die Unwetter entwickeltes Modell wird vorgelegt. SchlieNich werden einige Aspekte der Bewegung der Unwettergebflde beschrieben.

Use of a Rain Gauge Network to Infer the Influence of Environmental Factors on the Propagation of Quasi-Linear Convective Systems in West Africa

“…This suggests that the method is not particularly sensitive to the true factors that influence squall-line propagation in West Africa. Fernandez (1982) reported that a "hydraulic jump analogy" based on the work of Hamilton and Archbold (1945), Freeman (1948), and Tepper (1950 provided good estimates of the propagation speed of three West African squall lines observed during August 1973. Within this framework, a mechanism that produced sudden vertical accelerations below an inversion creates a disturbance in the height of the inversion that propagates as a gravity wave.…”

“…Within this framework, a mechanism that produced sudden vertical accelerations below an inversion creates a disturbance in the height of the inversion that propagates as a gravity wave. The associated pressure jump travels at a rate C given by Fernandez (1982) as …”

“…For the three aforementioned squall lines, Fernandez (1982) used this method to forecast a mean speed of 11.5 m s…”

“…Bolton (1984) claimed that West African squall lines move slightly faster than the midtropospheric jet stream, Fernandez (1980) showed that squall lines in Venezuela move at approximately the speed of the midlevel environmental wind, and Mansfield (1977) demonstrated that squall lines over water during GATE moved faster than the winds at any tropospheric level. The values of LS were significantly correlated (r ϭ ϩ0.363) with the observed wind speeds at 650 hPa (i.e., approximately 3.5 km), with LS averaging about 3 m s Ϫ1 faster than the winds at this level.…”

“…Thus, the forecast value of this method is limited. The successful use of the method by Fernandez (1982) seems to be related to the small range of values of H observed in the three storms from 1973.…”