Impact of Argo data assimilation in an Ocean General Circulation Model

Neeraj Agarwal , Rashmi Sharma, Sujit Basu, Abhijit Sarkar and Vijay K Agarwal

Meteorology and Oceanography Group
Space Applications Center, I.S.R.O.
Ahmedabad-380015

In this study global temperature and salinity profiles available from Argo have been assimilated into an Ocean General Circulation Model (OGCM). Argo is a global programme under which it is planned to deploy around 3,000 floats all over the globe that can provide temperature and salinity profiles at a spatial and temporal resolution of 3°X3° and 10 days respectively. OGCM used for the study is based on Modular Ocean Model –version3 (MOM-3) of Geophysical Fluid Dynamics Laborartory (GFDL), NOAA. The model is global in zonal direction and extends upto ±80° in latitude with a variable horizontal resolution from 0.5° to 2°. There are 38 vertical levels with 16 levels in top 110 meters. In the control run the model was forced with daily Quickscat derived scatterometer winds for the period Jan 2004- July 2005 and air temperature, specifc humidity, net short-wave and net long wave radiation from NCEP reanalysis. In another run called the “assimilation run” we assimilated global monthly averaged Argo temperature and salinity profiles for the period Jan 2004 – Dec 2004 in the OGCM. Since there are gaps in the Argo data therefore we used Levitus data as the background field and blended the Argo data wherever available. The resultant field was then assimilated into the OGCM using nudging technique. Temperature and salinity from both (control and assimilation) the runs were compared with independent observations from TRITON buoys. Detailed analysis of the impact will be presented in the workshop