Observations of Submesoscale Surface Currents and Winds with a Doppler Scatterometer

Ocean surface currents and winds are intrinsically coupled essential climate variables (EVCs) that play a key role in air-sea interactions. Although their interaction is important at all scales, at ocean submesoscales (1 km to 30 km) ocean vertical velocities and the interaction between surface winds and ocean fronts play a critical role. High-resolution ocean modeling and limited ship observations have resulted in an improved understanding of the physics of these scales. However, direct synoptic observations of simultaneous winds and currents at these scales are not readily available from spaceborne sensors. Under NASA's IIP and AITT programs, a new instrument, called DopplerScatt, has been developed that is able to fill in this measurement gap. DopplerScatt measures vector winds using traditional pencil-beam scatterometer principles at Ka-band frequency. By adding Doppler capabilities to the pencil beam concept, it can provide simultaneous ocean surface current measurements. Flying in its current platform, DopplerScatt images instantaneously a 25 km swath, so that over the course of a typical 5 hour flight, one can estimate synoptic winds and currents at 200 m resolution over areas on the order of 200 km x 100 km. DopplerScatt has participated in multiple campaigns during the last two years, collecting synoptic measurements in the California Current, in the Mississippi River Plume region, and over a large mesoscale eddy in the Gulf of Mexico. DopplerScatt data products include not only surface vector fields, but also ocean divergence and relative vorticity, as well as wind stress curl and divergence. Using these data, we characterize the statistics of their submesoscale variability and co-variability, including joint probability density functions, structure functions, and power spectra for spatial scales ranging from 1 km to 100 km, a critical region where it is expected that the transition between forward and inverse energy cascades should be observable.