Seasonal variation of shallow-to-deep convection transition and its link to the environmental conditions over the Central Amazon

This study aims to characterize the seasonal variation of the shallow-to-deep convection transition and understand how environmental conditions impact the behavior of this transition using data collected from the Observations and Modeling of the Green Ocean Amazon (GOAmazon) field campaign in the Central Amazon (Manaus). The diurnal cycle of the rain/cloud fraction shows that the wet season has more extensive shallow convection before the transition to deep convection with larger fractional coverage and rainfall; deep convection in the transition season is more intense and has higher vertical extension and a stronger updraft. Surface meteorology, atmospheric moisture, instability, and wind shear are contrasted for the shallow/congestus convection (SC) cases and the locally formed shallow-to-deep convection transition (LD) cases. The comparisons suggest that occurrence of the LD is generally promoted under the conditions of high atmospheric moisture and instability but has a weaker dependence on wind shear. The relative importance of these environmental controls also varies in different seasons: The dry and transition seasons require a deeper moist layer from the boundary layer to midtroposphere than the wet season; convective available potential energy (CAPE) is higher during the transition season, but it is a less important factor for shallow-to-deep convection transition than in other seasons; LD only has significantly larger wind shears than SC during the dry season.