Regional eddy-permitting state estimation of the circulation in the Northern Philippine Sea

Transcription

1 Regional eddy-permitting state estimation of the circulation in the Northern Philippine Sea Bruce D. Cornuelle, Ganesh Gopalakrishnan, Peter F. Worcester, Matthew A. Dzieciuch, and Matthew Mazloff Scripps Institution of Oceanography University of California at San Diego, La Jolla, California USA SUPPORTED BY ONR GODAE DA/MEAP Workshop UCSC 7/12/16

2 Main Points: Eddy-permitting 4DVAR succeeded with two month integrations in the very energetic Philippine Sea This was accomplished by filtering the adjoint using increased viscosity and is part of a multiscale approach. The estimate was cross-validated by independent observations and forecasts including acoustics The 4DVAR has been generalized to include line integrals along ray paths, including PIES.

3 Motivation The Philippine Sea has strong westward-propagating eddies with surface currents >= 1 m/s Their meridional heat flux has been estimated at.09pw, about 15% of the total, but variable. The eddies merge with the Kuroshio affecting the western boundary current The state estimation was in support of an acoustic transmission experiment, which included a test of assimilation of acoustic observations.

4 AVISO mapped SSH anomaly (m) weekly 1/1/ /31/2011

5 Roemmich & Gilson, JPO, 2001

6 Baroclinic structure associated with surface signature Composite eddy collected from superposing many observations Tilted eddy results in Northward eddy heat transport Composite Eddy from N. Pacific XBT transect

7 NPAL Philippine Sea Experiment T1 T6: WRC transceivers 660 km diameter DVLA Moored oceanographic sensors CTD Acoustic Seagliders

8 Outline: Introduction to the modeling and state estimation Non-acoustic evaluation of the state estimates Acoustic evaluation of the state estimates Analysis of the tracked ray travel times State estimation using travel times

9 MITgcm configuration 1/6 degree regional: 115E-170E, 15S-30N 50 levels with 2.5m spacing in the upper ocean Surface forcing is derived from NCEP/NCAR Reanalysis (1 degree, daily averaged) Initial and boundary conditions from global HYCOM-NCODA (excellent!) Integrated , compared to AVISO SSH (no Ice or BGC, but Mazloff does Ocean-Ice-BGC assimilation in the Southern Ocean at 1/6 degree)

10 SSH 25 Nov 2005 (m) Example: snapshot Of tropical Pacific Western Boundary

11 4D-Var State Estimation Fit model to observations using 4D-Var (adjoint) (ECCO package for MITgcm) Adjust initial conditions, boundary conditions, and forcing (within error bars) Estimate is a free forward run of the model that should match the observations (within error bars) Is a dynamically-consistent reanalysis for research use, including sensitivities

12 Adjoint linearity tests. Cost function is average SSH in a region (green)

13 -1 day -8 days 100 m2/s2-15 days -22 days

14 -1 day -8 days 5000 m2/s2-15 days -22 days

15 Filtered adjoint is less sensitive to model state (less nonlinear) Spatial RMS difference between adjoints from different iterations At different viscosities

16 Observations Along-track altimeter sea surface height Temperature and salinity profiles from Argo Geoid constraints from GRACE ( HMEAN ) SST from TMI and AMSR-E (microwave) CTDs, XBTs, and other profiles Using 2 month windows, observations only in subregion. How long is best? (Model error) Analysis and forecasts start April Comparison to obs: Hindcast, Forecast

17 Bathymetry (m) (+ Argo locs) Argo: 5/1/10-6/30/10

18 Non-Acoustic State estimate results Reduces misfit variance 30% from HYCOM Fits SSH best, also Argo T and S Controlled by initial T, S primarily

19 RMS difference with AVISO (m) Hindcast Persistence Reference AVISO climatology HYCOM Analysis State estimate

20 State estimate evaluation Smoother than HYCOM starting point, but may not fit as well at any one time. Test against future data (forecast, cross-validation) shows improvement due to the optimization. Also compare to T, S, acoustics

21 RMS difference with AVISO (m) Forecast Persistence AVISO climatology State estimate Reference HYCOM Analysis

22 Comparison against independent T observations on the DVLA Black = Before, Red = After, Gold = assumed obs. error

23 Main Points: Eddy-permitting 4DVAR succeeded with two month integrations in the very energetic Philippine Sea This was accomplished by filtering the adjoint using increased viscosity and is part of a multiscale approach. The estimate was cross-validated by independent observations and forecasts including acoustics Same eddy tilt and heat flux as Roemmich and Gilson; also calculated salt flux

24 Extra Slides