Jb. Halverson et al., An ensemble of convective systems on 11 February 1993 during TOGA COARE: Morphology, rainfall characteristics, and anvil cloud interactions, M WEATH REV, 127(6), 1999, pp. 1208-1228
An active day during the Coupled Ocean-Atmosphere Response Experiment (COAR
E) Intensive Observation Period (IOP) is examined in which nine convective
systems evolved and moved eastward across the region of shipboard radar cov
erage in the Intensive Flux Array (IFA) within westerly wind burst conditio
ns. The detailed genesis, morphology, and interactions between these cloud
systems are documented from a radar and satellite perspective. One of these
systems was a large and complex elliptical cluster, among the largest obse
rved during the Tropical Ocean Global Atmosphere COARE. Multiple, parallel
deep convective lines spaced 20-30 km apart and embedded within this system
were initially oriented from north-northwest to south-southeast, oblique t
o the storm motion. Furthermore, the lines underwent counterclockwise reali
gnment as the system moved eastward. The influence of strong lower-troposph
eric directional and speed shear on these convective system properties is e
xamined in the context of a dynamic, large-scale near-equatorial trough/tra
nsequatorial flow regime. A daily analysis of flow conditions during the 11
9-day IOP revealed that this type of synoptic regime was present in the IFA
at least 40% of the time.
Radar-derived rainfall statistics are examined throughout the life cycles o
f each individual convective system. Spatial mapping of accumulated rainfal
l reveals long, linear swaths produced by the most intense cells embedded w
ithin convective lines. The evolution of rainfall properties includes an in
crease in the stratiform rainfall fraction and areal coverage in later gene
rations of systems, with a peak in total rainfall production after local mi
dnight. These trends can be explained by anvil cloud interactions originati
ng within the sequence of closely spaced disturbances, including the effect
s of both enhanced midtropospheric moisture and also strong reversing (east
erly) shear. The issue of boundary layer recovery between the frequent, int
ense convective systems on this day is also examined.