A Method for Calculating Reliable Supersaturation Reveals Low Values in Tropical Rainy-Season Clouds

Abstract High supersaturation on the order of 10% in unpolluted moist convection is a prerequisite for substantial warm-phase aerosol invigoration. However, such high supersaturation has not yet been confidently observed. To accurately detect high supersaturation, the analysis method must avoid generating spuriously high values, and one such method is presented here. Applied to aircraft data from GoAmazon’s relatively unpolluted rainy season, the method finds only low supersaturation: the observed values have a median of 0.5% and are all less than about 1%. Combining both rainy-season and dry-season measurements, the convective supersaturation during GoAmazon is found to scale as the boundary-layer aerosol concentration to the −2/3 power, as previously predicted. For moist convection of any type, a 10% supersaturation would require a very high vertical velocity, a very low sum of droplet diameters per volume, or some high/low combination of both.