M2 Internal Tide off Oregon: Inferences from Data Assimilation

Thursday, May 2, 2002 - 11:00am - 11:20am
Keller 3-180
Alexandre Kurapov (Oregon State University)
(Joint work with G. D. Egbert, J. S. Allen, R. N. Miller).

A linearized baroclinic, spectral in time inverse model has been applied to study the M2 internal tide in an area off the mid-Oregon coast where measurements of surface data are available from two coast-based high frequency (HF) radars. Assumed simplified dynamics makes implementation of a rigorous generalized inverse method (GIM) possible. Representer functions obtained as a part of the GIM solution show that for superinertial flows information from the surface velocity measurements propagates to depth along wave characteristics. Most baroclinic signal contained in the data comes from outside the computational domain, so data assimilation (DA) is used to restore baroclinic currents at the open boundary (OB). Experiments with synthetic data demonstrate that the choice of the error covariance for the OB condition affects model performance. A covariance consistent with assumed dynamics is obtained by nesting, using representers computed in a larger domain. Harmonic analysis of currents from HF radars and an ADCP mooring off Oregon for May-July 1998 reveals substantial intermittence of the internal tide, both in amplitude and phase. Assimilation of the surface current measurements captures the temporal variability and improves ADCP/solution rms difference.