Variability of Low-Level Coastal Jet and Marine Stratocumulus Clouds in the Southeast Pacific

Two-way coupled COAMPS®/NCOM system with the NCODA ocean data assimilation is used to study the air-ocean interaction and cloud variability over the Southeast Pacific. There is large variability of low-level coastal jet along the Chilean coast, which impacts the boundary layers for both the atmosphere and the ocean. The strong jet carries cold and dry air over the warm ocean surface, receives large heat fluxes from the ocean, and induces strong vertical mixing in both boundary layers. More clouds but with decoupled boundary layer structure are characterized offshore during the strong jet period. Along the Chilean coast, the strong jet induces oceanic upwelling and results cooler sea surface temperature (SST), which leads to much weaker turbulent kinetic energy and less clouds. Variance analysis for offshore area indicates that the negative correlations are over 81% between the wind speed and SST and over 63% between the liquid water path and SST. Since the oceanic responses to the coastal jet with time lag, the correlation increases with one-day lag, resulted a complex concomitant cyclic change between the strong coastal jet, SST and clouds. Forcing mechanisms for the cloud variability related to the oceanic upwelling are discussed. The results are compared with available observation from the VAMOS Ocean Cloud Atmosphere Land Study (VOCALS).

COAMPS – Coupled Ocean Atmospheric Mesoscale Prediction System COAMPS® is a registered trademark of the Naval Research Laboratory NCOM – Navy Coastal Ocean Model NCODA – Navy Coupled Ocean Data Assimilation