Exploring the discrepancy between the seasonality of atmospheric convection and precipitation in the Colombian Amazon region

Atmospheric convection is the main mechanism responsible for precipitation in tropical and equatorial regions, whose rainfall regimes are high. Thus, the number of convective events and precipitation are expected to have similar seasonalities. However, the number of convective events in the northwestern Amazon region has a bimodal seasonal distribution, whereas precipitation has a clear unimodal regime. This discrepancy may be related to seasonal variability in convective dynamics in this region; for example, aerosol concentrations, moisture sources and/or surface fluxes may vary significantly at the seasonal scale, which may in turn impact fundamental properties of the convective systems. In order to investigate this, we identify deep convective events between 2011 and 2021 with an automated algorithm that uses infrared geostationary satellite data, and obtain  daily precipitation from available in-situ measurements. Other precipitation products with better coverage, such as IMERG, are not suitable due to their poor representation in this region on short timescales (daily or sub daily). The largest discrepancy between the seasonality of the number of convective events and monthly precipitation takes place during May-August, when the number of convective events decreases, but precipitation reaches its peak monthly values. We find that during those months, mean precipitation per convective event is highest, as well as the average horizontal extent of the events. This suggests that the nature of convective events varies significantly throughout the year, which may give rise to this discrepancy in seasonality. Possible causes for this may be related to: a) aerosol concentrations, which have a strong seasonality related to biomass burning and could potentially impact microphysical processes, b) varying sources of moisture due to the seasonal migration of the ITCZ, and c) seasonal changes in surface fluxes. Here we present a detailed analysis of the seasonality of various properties of the convective events in this region and explore these hypotheses in order to better understand the dynamics of convection in the Amazon region of Northwestern South America. This investigation highlights the complexity in the dynamics of deep convection at low latitudes beyond a simple correspondence with rainfall.   Keywords: tropical convection, Colombia, Amazon, precipitation, rainfall regime