The IAOOS Seaglider Project A few notes for the OPNet meeting, May 27-28, 2009 prepared by F. Høydalsvik, met.no Project participants: F. Høydalsvik, C. Mauritzen, C. Lee, J. Gobat, and K.A. Orvik
Ocean Weather Station Mike (OWSM)(10 km range circle) Red line: Seaglider SG-017 OWSM Section (Summer/Autumn 2008). Yellow line: Seaglider SG-160. The Svinøy Section. Ongoing, deployed January 24, 2009.
SG-160 Depth-averaged currents Feb 10 – Mar 7, 2009
Along-track hydrography 35 Salinity Temperature Note the very small stratification during winter Pot. density
Seaglider operations • Seaglider SG-017: Zonal transects at 66 °N between the shelf break and 1°W, passing through the OWSM area. July-November 2008 • SG-160: Currently operating at the Svinøy Section (deployed January 24, 2009) • The western branch of the NAC is the part most difficult to monitor by using traditional methods (Orvik et al, 2001). • The glider is more comfortable in the deep sea, spends less energy. • We focus on the part of the NAC west of the slope (900 m or deeper). • The slope current or eastern branch of the NAC is being monitored using current meters.
Seaglider operations • Successful operation in rough weather in the open sea, yielding data traditionally not captured • High data density. Hydrography, [O2], fluorescence, red & blue backscatter. • Typical dive: 4-6 km horizontal distance, down to 1000 m. Vertical profiles obtained by interpolation. • Long distances can be covered. Near-synoptic transects impossible. • High-frequency variations are “smoothed out”. With very large variations (e.g., 14 Sv in the eastern branch on a 25 h time scale, Orvik et al, 2001) • A ship transect with VM-ADCP does not necessarily give a better representation of the current than a glider transect of roughly three weeks duration.
SST from satellite data(Jan-Mar 2009, provided by S. Eastwood) & SG-160 tracks. Black, thick line is 4.8°C. The traditional Svinøy Section stops at 64°40’N, 0°E.
(A) (B) (C) (D) Absolute geostrophic velocities/volume transport. (A) From direct integration of thermal wind eqs. (B) Smoothed using a 12-dive running mean. (C) Transport per length unit. Dashed line: Transport from the smoothed field. (D) Max. diving depth / bathymetry
Conclusions so far: • The NAC has dominating current cores, with large velocities, but the transport outside the cores is significant. • We find recirculation cells, a continuously meandering front, and eddies, but no sign of a large-scale, permanent recirculation between the western and eastern branch. This is consistent with drifter data (e.g. Jakobsen et al, 2003; Inga Coszalka, pers. comm.) • The transports we find are somewhat larger than those found assuming negligible barotropic / deep water velocities in the area.