Meteorologisk Institutt met.no OPNet, Geilo May 27, 2009LPR 1 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

Meteorologisk Institutt met.no OPNet, Geilo May 27, 2009LPR 2 Red line: Seaglider SG-017 OWSM Section (Summer/Autumn 2008). Yellow line: Seaglider SG-160. The Svinøy Section. Ongoing, deployed January 24, Ocean Weather Station Mike (OWSM) (10 km range circle)

Meteorologisk Institutt met.no OPNet, Geilo May 27, 2009LPR 3 SG-160 Depth- averaged currents Feb 10 – Mar 7, 2009

Meteorologisk Institutt met.no OPNet, Geilo May 27, 2009LPR 4 35 Along-track hydrography Salinity Temperature Pot. density Note the very small stratification during winter

Meteorologisk Institutt met.no OPNet, Geilo May 27, 2009LPR 5 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

Meteorologisk Institutt met.no OPNet, Geilo May 27, 2009LPR 6 Successful operation in rough weather in the open sea, yielding data traditionally not captured High data density. Hydrography, [O 2 ], 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. Seaglider operations

Meteorologisk Institutt met.no OPNet, Geilo May 27, 2009LPR 7 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.

Meteorologisk Institutt met.no OPNet, Geilo May 27, 2009LPR 8 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 (A) (B) (C) (D)

Meteorologisk Institutt met.no OPNet, Geilo May 27, 2009LPR 9 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.

Meteorologisk Institutt met.no OPNet, Geilo May 27, 2009LPR 10 Thank you