Turbulent mixing and its impact on lower tropospheric moisture over tropical ocean

Abstract

The variability of lower tropospheric humidity is a crucial feature of the tropical climate. Among the processes that impact moisture budget, the vertical transport by turbulent mixing is generally overlooked. Using observations from Cooperative Indian Ocean experiment on intraseasonal variability/Dynamics of the Madden-Julian Oscillation (MJO), CINDY/DYNAMO, campaign, this is a first attempt to quantify it over the tropical ocean. Turbulent patches of ∼100 m depth are observed in relation with large vertical gradients of specific humidity. Intense mixing is diagnosed within these intermittent patches. Three approaches are used to diagnose the overall effect of this intermittent turbulence. Large uncertainties on the corresponding eddy diffusivity coefficient arise from parameters hard to experimentally constrain. However, dry conditions are associated with steep moisture vertical gradients above the boundary layers. Owing to the uncertainties on the eddy diffusivity, these gradients can correspond to negligible or to significant moisture tendencies (∼0.5-1 g kg-1 d-1) during the recovery following a dry intrusion or the preconditioning stage of an MJO.