High-wavenumber variability in the California Current: Evaluating sub-100-km scales with high-resolution altimetry, ADCP, and model output
Event: 2019 Ocean Surface Topography Science Team Meeting
Session: Science III: Mesoscale and sub-mesoscale oceanography
Presentation type: Type Oral
The TOPEX/Poseidon and Jason series of altimeters have provided pioneering observations of mesoscale sea surface height variability, resolving oceanic features at scales larger than about 50 to 70 km. More recently, altimeters have offered potential to resolve scales smaller than 50 km via new processing strategies and new types of altimeters, such as Ka-band altimeters and instruments taking advantage of Synthetic Aperture Radar (SAR) mode, Delayed Doppler technology. Looking ahead, the Surface Water Ocean Topography (SWOT) altimeter is anticipated to resolve scales of 10 to 15 km. A challenge, however, in evaluating the performance of these new altimeters arises from the difficulty of obtaining in situ measurements that resolve the small oceanic scales that they are designed to detect. In this study we use high-resolution observations from altimetry and shipboard acoustic Doppler current profiler (ADCP) data, together with high-resolution model output, to explore the characteristics of upper ocean variability at scales smaller than 100 km, typical of the oceanic submesoscale. We focus on the California Current, targeted as a key region for SWOT cal/val. We use regional and global model configurations to explore the mechanisms driving high-frequency and high-wavenumber variability. One hypothesis is that remote tidal forcing from outside the region is responsible for generating high-frequency and high-wavenumber energy, resulting in a spatial distribution of internal wave variance that is diminished in the lee of topographic barriers and enhanced where waves break. We assess model performance relative to current meter observations in the time domain and relative to ADCP data and high-resolution nadir altimetry (from Jason-1/2, AltiKa, and Sentinel-3) in the spatial domain.