The environmental conditions associated with squall lines (SL) that were observed during the period of 13 April-13 May 1987 (GTE/ABLE-2B) originating at the northern coast of South America and propagating over the Amazon Basin are documented. The St, observed on 5-7 May are examined in more detail. The SL days had in common a stronger and deeper low-level jet when compared with the days without SL. Two possible explanations are found for the intensification of the low-level jet: propagating easterly waves in the tropical Atlantic, which eventually reach Manaus, and localized heat sources in the western Amazon. Both were observed on 5-6 May. It is suggested that numerical simulations should be performed to unravel the relative importance of each large-scale mechanism.
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Cohen et al. (1995) studied this question.