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Four distinct meteorological regimes in the Amazon basin have been examined to distinguish the contributions from boundary layer aerosol and convective available potential energy (CAPE) to continental cloud structure and electrification. The lack of distinction in the electrical parameters (peak flash rate, lightning yield per unit rainfall) between aerosol‐rich October and aerosol‐poor November in the premonsoon regime casts doubt on a primary role for the aerosol in enhancing cloud electrification. Evidence for a substantial role for the aerosol in suppressing warm rain coalescence is identified in the most highly polluted period in early October. The electrical activity in this stage is qualitatively peculiar. During the easterly and westerly wind regimes of the wet season, the lightning yield per unit of rainfall is positively correlated with the aerosol concentration, but the electrical parameters are also correlated with CAPE, with a similar degree of scatter. Here cause and effect are difficult to establish with available observations. This ambiguity extends to the “green ocean” westerly regime, a distinctly maritime regime over a major continent with minimum aerosol concentration, minimum CAPE, and little if any lightning.

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The occurrence frequency and rainfall production of mesoscale convective systems (MCSs) relative to smaller groups of convective clouds over the tropical oceans is not well known. Eighty days of shipboard radar data collected during the recent Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) were used to provide a detailed view of convection in the western Pacific warm pool, a region of global climatological significance. The aim of this study was to document the frequency of occurrence, rainfall production, and depth of convection observed during TOGA COARE within a simple and meaningful framework of convective horizontal organization. Organization was characterized in terms of the horizontal scale and morphology of convective systems. Precipitation events were defined based on whether they attained the length scale of an MCS, and on whether convection was organized into lines.About four-fifths of rainfall during COARE was associated with MCS-scale squall lines. These occurred in a variety of wind regimes but tended to be most common prior to low-level westerly wind maxima. Systems of isolated cells produced 12% of all COARE rainfall and were observed during periods of both very weak and very strong low-level winds. These two modes occurred about equally as often, and together they accounted for about 90% of observed convection. Cloud height populations associated with MCS organization were distinct from sub-MCS-scale cloud systems, with more rainfall from shallower clouds for sub-MCS convection. The distribution of total rainfall by cloud height for COARE was interpreted as a superposition of rainfall-cloud height distributions from each mode of organization. These results raise the possibility that isolated cell periods may represent a distinct, nonnegligible heat source in the large-scale heat budget when compared to the dominant MCS-scale systems.

Vertical structures of 2-day waves and the Madden-Julian oscillation (MJO) are projected onto vertical normal modes for a quiescent tropical troposphere. Three modes capture the gross tropospheric structure of 2-day waves, while only two modes are needed to represent most of the baroclinic structure of the MJO. Deep circulations that project onto the first baroclinic mode are associated with deep cumulonimbus and stratiform rainfall. Shallow circulations that project onto higher wavenumber modes are associated with precipitating shallow cumulus and congestus and stratiform rainfall. For both disturbances the horizontal divergence contributed by shallow modes is an important factor in the column-integrated moist enthalpy budget. These modes converge moist static energy for a time prior to when deep circulations export moist static energy. These results highlight the importance of properly representing the effects of shallow cumulus, congestus, and stratiform precipitation in theories of convectively coupled waves and in atmospheric models.