Improved representation of vertical (T,S) profiles using real-time assimilation in Arctic waters

Realistic description of vertical sound speed profiles are essential for underwater acoustic modelling. Sound speed profiles are usually derived from vertical profiles of salinity and temperature and oceanographic variable areas are often a challenge to acoustic modelling. Temperature and salinity profiles can be obtained from numerical ocean models, which has the advantage that they have high spatiotemporal resolution and cover large geographical areas. Ocean models are continuously improving, but still have challenges when it comes to placement and extension of oceanographic features such as fronts and eddies. One solution to reduce the error in ocean models is assimilation of measured vertical temperature and salinity profiles. Here we present a results from two measurement campaigns north of Svalbard in the fall of 2019 and 2020. Vertical temperature and salinity profiles were collected and used for assimilation in an operational ocean model covering the Norwegian Arctic. About 15% of the measurements were kept outside the assimilation as reference data to compare the model result with measurements. To study the effect of assimilation, a control run without assimilation was also conducted and in 2020 even a model run with assimilation of other available data was done. The study showed that assimilation improved the ocean model results. Especially the assimilated model better reproduced warm and saline water masses. The root-mean-square errors in both salinity and temperature were also reduced.