Atmospheric Pressure for Filtered free surface! =

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Introduction

Starting from NEMO_3.3 release the OPA component of the system includes also the possibility to force the model using the Atmospheric pressure filed provided externally. The code has been developed by MERCATOR and tested using the time-splitting option. The main goal of this work is to test the usage of Atmospheric pressure Forcing using the filtered free surface formulation. Originally it has been planned also to study the influence of different lateral open boundary condition parameterizations, however due to the decision to froze the OBC and BDY modules developments until a merge of the two modules will be completed the sensitivity study of the LOBC has been postponed.

Experiment set-up

Basic NEMO model configuration is described in Oddo et al. 2009. Model domain covers the whole Mediterranean Sea plus a “large” Atlantic box, where the model is nested with the Global ¼ Degree MERCATOR operational model. External Lateral Open Boundary Condition data are monthly climatology obtained from 10 year global experiment. The main difference with standard NEMO code concerns the volume conservation. In Standard OPA code, in case of filtered free surface option, the volume conservation is imposed. In the present version of the model the Mass/Volume? transport across the model domain lateral open boundaries is driven by a generalized Flather’s algoritm (Oddo et al. 2008) see eq. 3 in Odo et al 2010. Four different experiment have been performed in order to understand the differences in using the Atmospherci pressure forcing in case of time-splitting and filtered free surface formulation.

EXP1 reproduces the Oddo et al 2010, experiment with NEMO_3.3.1, so it has the filtered free surface formulation and no atmospheric pressure (AP)

EXP2 is the same of EXP1 plus the introduction of the AP.

EXP3 is the same model step-up of EXP1 but with time-splitting option.

EXP4 is EXP3 plus the introduction of the AP forcing.

Results and Discussion

Conclusions

Bibliography

16. Oddo and N. Pinardi. Lateral open boundary conditions for nested limited area models: A scale selective approach. Ocean Modelling Volume 20, Issue 2, 2008, Pages 134-156

16. Oddo, M. Adani, N. Pinardi, C. Fratianni, M. Tonani, and D. Pettenuzzo. A nested Atlantic-Mediterranean Sea general circulation model for operational forecasting. Ocean Sci., 5, 461-473, 2009