Direct Sea Surface Height Data Assimilation

New methods are developed for assimilating satellite sea surface height anomaly (SSHA) and velocity observations into a numerical ocean model of the Gulf of Mexico. Vertical correlations, derived from historical ocean profiles of temperature (T) and salinity (S), are used to relate T and S to geopotential (G) by integrating the specific volume anomaly vertical structure. The resulting vertical correlations (of T & T, T & S, T & G, S & S, etc.) are then used to assimilate SSHA and velocity observations by creating increments of subsurface T, S, and velocity. Velocity is related to G using the geostrophic relation. Since satellite derived SSHA observations are the most important data stream used to improve numerical ocean forecasts, this presentation will focus on SSHA data assimilation. The Naval Research Laboratory traditionally employs a method where SSHA data is used to create ocean synthetic subsurface profiles of T and S, which are then assimilated as observations in an ocean forecasting system. The latest version has a one-dimensional variational scheme based on historically observed ocean vertical correlations for T and S globally at ½ degree resolution. The new method uses these correlations directly within the 3DVAR Navy Coupled Ocean Data Assimilation system, without making synthetics. The results from both assimilation methods will be compared and discussed. The velocities from these assimilation methods are validated relative to the 295 drifters deployed in July 2012 in the north-eastern Gulf of Mexico as part of the Gulf of Mexico Grand Lagrangian Deployment (GLAD). This system will also utilized velocity data from the upcoming drifter deployment of the LAgrangian Submesoscale ExpeRiment (LASER).