Informal Seminar: Diurnal cycle of sea surface temperature in frontal regions and reflections on an Observing Air-Sea Interactions Strategy (OASIS)

by Dr Meghan Cronin (NOAA)


There is growing recognition that coupling of the ocean and atmosphere depends upon proper representation of the ocean’s skin temperature, which differs from the bulk sea surface temperature (SST) or deeper foundation SST due to the cool skin effect and the presence of a diurnal warm layer.  In this seminar, I will present monthly climatologies of bulk 1-m SST diurnal cycle computed at NOAA tropical Pacific mooring sites, and explain the large spatial and seasonal variability, as well as the daily-averaged rectified effects, in terms of daily-averaged wind stress and buoyancy forcing using a modified Fairall et al. (1996) 1-dimensional mixed layer model. Satellite and ERA5 fields are then used to evaluate the patterns of rectified diurnal warming in comparison to the cool skin effect, atmospheric and oceanic Monin-Obukhov Depth scales, and the differences between the daily-averaged skin versus foundation temperatures.  As hypothesized by Chelton et al. (2001), the equatorial cold tongue’s SST front is associated with a front in the “Stability Depth Scale”. In the stabilized equatorial cold tongue, the SST diurnal cycle is large and cool skin effect is minimized; while on the  the warm side of the front, both the atmospheric and oceanic boundary layers are destabilized, resulting in a reduced SST diurnal cycle amplitude and increased cool skin effect. As a consequence, the equatorial cold tongue’s SST front results in a front in the diurnal SST cycle amplitude and the cool skin effect.

In the latter part of the seminar, I will also provide reflections on the new UN Ocean Decade Programme, Observing Air-Sea Interactions Strategy (OASIS), which I co-chair.