Estimation of Optimal Gravity Wave Parameters for Climate Models using

PULIDO M

Honolulu Hawaii, USA

Conferencia; American Geophysical Union. Chapman Conference; 2011

American Geophysical Union

There is a current need to constrain the parameters of gravity wave drag schemes of climate models using observational information instead of tuning them arbitrarily. An inverse technique is presented  to estimate parameters from gravity wave schemes. We define a cost function that measures the differences between the zonal and meridional components of the 'observed' gravity wave drag field and the gravity wave drag calculated with a scheme.The proposed inverse technique is composed by a genetic algorithm and a variational assimilation technique based on conjugate gradients. The first is used to estimate a close enough first guess and then conjugate gradients is applied.  It is concluded that the parameter estimation using this hybrid technique is robust over a broad range of prescribed 'true' parameters. Estimations using 'observed' gravity wave drag from Pulido and Thuburn (2008) are performed, the gravity wave drag given by the parameterization for an optimal set of global parameters does not reproduce the observed features. On the other hand, if the parameters are allowed to vary with the latitude, a good fit of the observed gravity wave drag is obtained, except at the tropical lower stratosphere. In this region some relaxations of the parameterization are proposed in order to have a better agreement with the forcing needed to drive the QBO. Simulations with the dynamical stratosphere model using the optimal parameters are performed an important reduction of the model error is obtained.