Example: SG17 net transports

 

Seaglider 17

In collaboration with the Integrative Observational Platforms Group at Applied Physics Laboratory, University of Washington, Seaglider 017 was successfully deployed on July 3, 2008 at 66 degrees North 6 degrees East, and operated until November 12. It measured salinity, temperature, density, oxygen, as well as variables characterizing optical water properties at Ocean Weather Station Mike (OWSM) and its vicinity.

The glider went in transects from the continental shelf break outside of Helgeland to a point west of OWSM to cover both branches of the Norwegian Atlantic Current.

The Norwegian Coast Guard is gratefully acknowledged for their assistance in deploying the Seaglider. In February 2008, They also assisted in recovering the Seaglider after a deployment that was unsuccessful due to an error in the computer setup. Storage facility for the Seaglider between the February and July cruises wasprovided by the Norwegian Coastal Administration (in Ålesund). They also provided storage for Seaglider boxes and equipment.

Results

During the time Seaglider 17 was operational in the OWSM Section, it collected data material that served as a basis to develop a and assess a method to estimate volume and heat fluxes in the Norwegian Atlantic Current (NAC). This method, which is based on the thermal wind equations, is yields results that are consistent with earlier estimates from traditional instruments and methods. The validity of this method is still being evalueated, but is indeed promising.

We find among others that:

  • NAC exhibits a chaotic character with eddies, meanders and recirculation.

  • Recirculation is found just west of the eastern branch (as found by Orvik et al, 2001)

  • The western branch and the frontal structure is meandering and unsteady: Atlantic water is found as far as the westernmost point of measurment (1ºW), together with significant deep currents

  • From the summer Seaglider sections between approximately 6ºE and 1ºW (at 66ºN), we estimate volume transports between 7.7 Sv and 9.9 Sv, and heat transports from 218 TW to 266 TW.

  • Due to strong currents at the shelf break, transport estimates in the eastern branch are insecure.

  • The barotropic part of vn is generally more important than its baroclinic part, except in some areas (e.g. in the core of the western branch). In the total volume transport of the NAC, the barotropic part dominates.

  • The total transport obtained from the velocity at maximum diving depth, vn(Hm), is somewhat smaller than - but comparable to - the total transport using vn. 

 

 

Along-track potential density

Cross-track geostrophic
transport
and velocity
 

 Thermal wind velcoty profile

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