Abstract
The Sea surface KInematics Multiscale monitoring (SKIM) satellite mission is designed to explore ocean surface current and waves. This includes tropical currents, notably the poorly known patterns of divergence and their impact on the ocean heat budget, and monitoring of the emerging Arctic up to 82.5 • N. SKIM will also make unprecedented direct measurements of strong currents, from boundary currents to the Antarctic circumpolar current, and their interaction with ocean waves with expected impacts on air-sea fluxes and extreme waves. For the first time, SKIM will directly measure the ocean surface current vector from space. The main instrument on SKIM is a Ka-band conically scanning, multi-beam Doppler radar altimeter/wave scatterometer that includes a state-of-the-art nadir beam comparable to the Poseidon-4 instrument on Sentinel 6. The well proven Doppler pulse-pair technique will give a surface drift velocity representative of the top meter of the ocean, after subtracting a large wave-induced contribution. Horizontal velocity components will be obtained with an accuracy better than 7 cm/s for horizontal wavelengths larger than 80 km and time resolutions larger than 15 days, with a mean revisit time of 4 days for of 99% of the global oceans. This will provide unique and innovative measurements that will further our understanding of the transports in the upper ocean layer, permanently distributing heat, carbon, plankton, and plastics. SKIM will also benefit from co-located measurements of water vapor, rain rate, sea ice concentration, and wind vectors provided by the European operational satellite
Highlights
United States John Wilkin, Rutgers University, The State University of New Jersey, United States Matthew Mazloff, University of California, San Diego, United States
surface KInematics Multiscale monitoring (SKIM) will benefit from co-located measurements of water vapor, rain rate, sea ice concentration, and wind vectors provided by the European operational satellite
SKIM builds on the proven altimetry technique for sea surface height and derived geostrophic near-surface current estimates, adding a global monitoring of all ageostrophic flow components
Summary
Satellite altimetry, combined with gravimetry and in situ drifter climatology, has provided a wealth of observations on surface currents during the past 25 years. Retrieving geostrophic currents from altimetry in icecovered regions is possible (Armitage et al, 2017, 2018), albeit at too low resolution compared to the dominant energycontaining structures, with horizontal scales characterized by the Rossby deformation radius, typically smaller than 10 km in these regions Both small-scale eddies and wind-driven currents must be resolved in the ice-covered regions to better quantify and understand the cross-shelf fluxes of heat and freshwater (e.g., Spall et al, 2018; Stewart et al, 2018), the location and evolution of the polar and subpolar gyres (Armitage et al, 2017, 2018; Dotto et al, 2018), as well as the regions of deep water convection (e.g., Lique and Thomas, 2018). SKIM will be the first mission to provide much needed data on surface currents, ice drift and wave spectra (e.g., Stopa et al, 2018), at higher spatio-temporal resolution than is available today These observations are needed to improve the parameterizations of turbulent fluxes, sea ice rheology, wave-ice interactions, and ocean circulation in climate models and weather forecasting systems. With SKIM, kinematic variables (surface current, ice drift, waves) can be resolved at smaller scales than those at which dynamic variables (sea level, wind stress) are available today, and complementary to planned higher resolution missions such as SWOT for sea level (Morrow et al, 2019), and CIMR for surface temperature and salinity (Kilic et al, 2018)
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