Links Between Vertical Distribution of Moisture and Convective Frequency and Intensity in the Amazon Rain Forest

While prior work has demonstrated that a strong positive relationship exists between total Precipitable or Column Water Vapor (CWV) and precipitation in the tropics, how the regional vertical distribution of moisture may affect tropical rainfall and convective triggering remains unclear. In this study, we apply eof analysis to 14 years of morning soundings of specific humidity from Manaus, Brazil, in the central Amazon, to isolate four characteristic moisture vertical structures which we relate to the statistics of diurnal timescale precipitation. Two of the modes, characterized by either the highest and lowest CWV and with wetter and drier departures from the mean moisture profile throughout the vertical, support the CWV-precipitation scaling. The two remaining modes, of statistically similarly distributed intermediate CVW values, manifest vertical structures with either relatively reduced or enhanced moisture in the planetary boundary layer and the opposite moisture behavior in the free troposphere. Of the two intermediate CVW modes, the top heavy (TH) moisture profile is associated with higher rain rates than the bottom-heavy (BH) profile; in fact, TH (BH) days show comparable daily rain rates to the high (low) CWV mode. Thermodynamically, TH days exhibit the lowest convective available potential energy (CAPE) values of the four modes, with the opposite observed for the BH mode. Convective inhibition (CIN), by contrast, is highest (lowest) for the TH (BH) modes. Considering the preceding day's conditions for TH profiles shows a warmer surface as compared to the event day and suggests that moisture is convectively lifted upwards from the boundary layer over the diurnal time scale possibly due to reduced CIN on the previous day. The day prior to BH days is relatively cooler at the surface. Hence, TH days possibly demonstrate the impact of convection on CAPE which is consumed as convection initiates over a daily time scale as CIN is gradually overcome in a moist environment. This is contrasted with previous results from dry regions where CIN is generally low due to continuous surface heating and convection is triggered on short time scales upon the availability of enough moisture. Hence, our results suggest that convection in the Amazon could be limited by energy especially during the summer and transition seasons.