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Predictability of Tropical Freshwater Lenses due to Convective and Stratiform Rain During SPURS-2
[24-May-17] Thompson, E., Drushka, K., Asher, W., Schanze, J., Jessup, A., and Clark, D.
Presented at the Global Ocean Salinity and the Water Cycle Workshop
This study seeks to understand the impact of convective and stratiform rainfall on salinity stratification observed during the 2016 SPURS-2 experiment. Previous observational studies have demonstrated a wind-speed-dependent correlation between in-situ salinity stratification and maximum rain rate. However, questions remain about the temporal lag between the maximum rain rate and evolution of the freshwater lens, and how rain intensity impacts the lifetime of a freshwater lens. Radar and disdrometer measurements have shown that a majority of local rain accumulation variability can be explained by differences in rain intensity, spatial heterogeneity, and drop size distributions between stratiform and convective precipitation features. The frequency and predictability of stratiform and convective precipitation has been addressed in numerous previous studies. However, observations are still needed to understand whether convective or stratiform rain elements are more efficient in creating and maintaining freshwater lenses, and what that may imply about tropical freshwater lens frequency, duration, and predictability. To address these questions about freshwater lenses, we have analyzed oceanic and atmospheric data from the 2016 SPURS-2 field campaign in the tropical eastern Pacific. Specifically, we consider wind speed (ship-based and reanalysis), raindrop size distribution (ship-based disdrometer), rain rate/accumulation/spatial extent (satellite, ship-based gauge, and ship-based marine navigation radar), and in-situ ship-based salinity profiles in the upper 5 m. Using ship-based data, we estimate both the overall probability that a freshwater lens will form, and also its lifetime, following a convective or stratiform rain event. After comparing ship-, reanalysis-, and satellite-based wind and rain estimates, freshwater lens probabilities are recalculated using these routinely available global datasets.

This presentation included several animations which are provided here in MP4 format: Slide 10 | Slide 15

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