title: Submesoscale transition from geostrophic flows to internal waves in the northwestern Pacific upper ocean.
abstract: With radar interferometry, the next-generation Surface Water and Ocean Topography satellite mission will improve the measured sea surface height resolution down to 15 km, allowing us to investigate for the first time the global upper ocean variability at the submesoscale range. Here, by analysing shipboard Acoustic Doppler Current Profiler measurements along 137°E in the northwest Pacific of 2004-2016, we show that the observed upper ocean velocities are comprised of balanced geostrophic flows and unbalanced internal waves. The transition length scale, Lt, separating these two motions, is found to depend strongly on the energy level of local mesoscale eddy variability. In the eddy-abundant western boundary current region of Kuroshio, Ltcan be shorter than 15 km, whereas Ltexceeds 200 km along the path of relatively stable North Equatorial Current. Judicious separation between the geostrophic and internal wave signals represents both a challenge and an opportunity for the Surface Water and Ocean Topography mission.
authors.affiliation: Department of Oceanography, University of Hawaii at Manoa, 1000 Pope Road, Honolulu, Hawaii 96822, USA.
authors.forename: Bo
authors.initials: B
authors.lastname: Qiu
authors.affiliation: Global Environment and Marine Department, Japan Meteorological Agency, 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan.
authors.forename: Toshiya
authors.initials: T
authors.lastname: Nakano
authors.affiliation: Department of Oceanography, University of Hawaii at Manoa, 1000 Pope Road, Honolulu, Hawaii 96822, USA.
authors.forename: Shuiming
authors.initials: S
authors.lastname: Chen
authors.affiliation: Laboratoire d'Océanographie Physique et Spatiale, Ifremer/CNRS/UBO/IRD, Plouzane 29280, France.
authors.forename: Patrice
authors.initials: P
authors.lastname: Klein