A simulation of Argo float distribution in the Southern Ocean

Spatial distribution of the Argo floats in the Southern Ocean was simulated based on an output of a high resolution ocean general circulation model. Giving initial uniform distribution of the floats, numerical simulations were performed for the parking depths of 2000 m and 1000 m, respectively, with and without sea ice. When the sea ice was ignored, the floats were distributed almost uniformly even four years later but generally showed northward shift. Under sea ice condition, most of the floats were lost south of 62°S one year after the float deployment while most of the floats survived north of 53°S if the sea ice concentration was considered as the survival rate of the float in the corresponding region. The simulation was made for two different parking depths; one was 2000 m and the other 1000 m. The parking depth of 2000 m is the standard sampling depth for the international Argo project and many of the Argo floats drift at the same level of the sampling depth. Recently several float operators have employed so called the "park and profile" maneuver of the Argo float. That is, the parking depth is shallower than the sampling depth and the float dives down to the sampling depth just before making observation. In order to simu- late the drift of the "park and profile" type floats, we performed a simulation for the parking depth of 1000 m. Product of a high-resolution ocean general circulation model (OGCM) run by JAMSTEC was used for the simulation. The horizontal velocity output was stored every five days during the last year of the seasonal vari- ability experiment of the model run. This output was used as the seasonal velocity data for the float drift sim- ulation. The velocity data at Level 1 (top layer at 5-m depth) and at Level 43 (2045 m), which were closest to the sea surface and the parking depth of 2000 m, respec- tively, were used. The velocity data at Level 32 (1007 m) was also used for the simulation for the park- ing depth of 1000 m. The time step of the simulation corresponded to two hours.