LIDEX: Eddy Statistics from Objective Analysis of Altimetry Long ZhouAdvisor: Dave Hebert2nd Student Seminar, 03/20/2006

Outline Reasons for Objective Analysis Mapping domain DatasetExamples of mapped sea level anomalies (SLA) Comparing between outputs from 4 and 2 satellites Evolving eddy field during 2 months Comparison with the hydrographic survey Eddy statistics during 02/25/2003 to 05/08/2005 rms SLA and EKE Averaged velocity Eddy propagation Summary and future work

Reasons for this work b. Correlation scales should vary in different regions, while AVISO merged maps use identical along-track correlation for the same latitude.

c. This mapping technique is expected to show a more realistic picture of ocean mesoscale activity.

OA outputAVISO merged mapsSpatial resolution9 km1/3 degreeTemporal resolutionDailyEvery 7 days

Figure 1: Spatial coverage [4.75N 12.86N 24.25W 32.45W] Lagrangian Isopycnal Dispersion Experiment (LIDEX)

DatasetJETG along-track SLA for 02/25/2003 to 05/08/2005

JE along-track SLA for 03/13/2003 to 12/02/2003CTD data from LIDEX cruise, 03/25/2003 to 04/16/2003

Next page: sample satellite ground tracks for bNote: GFO=Geosat Follow-on

Jason1EnvisatTopex2GFO

Examples of mapped SLA

01-March-2005 to 01-May-2005

Red line and circles show the cruise zigzag track and CTD stations.Two black squares represent casts taken on 4/5/03 and 4/15/03. It took 22 days (3/25/03-4/16/03) to cover the stations from west to east.Comparison with the hydrographic survey

Root-mean-square SLA fieldEddy Statistics during 02/25/2003 to 05/08/2005 Time averaged eddy kinetic energy

-24 to 17-4.6 to 6.3

Distance-time plot of SLA along a latitudinal section. Numbers of days are relative to 1/1/2003.The slope of the black line signifies a westward eddy propagation speed of 8.1 cm/s.

Summary SLA maps with high spatial and temporal resolutions (9km&1day) can be produced with the mapping error variance below 60% of the measurement error variance from the along-track altimeter data. Root-mean-square SLA and eddy kinetic energy (EKE) show high levels of eddy energy within 2 degrees south of the southern LIDEX deployment site. Time-averaged geostrophic velocity and SLA field describe the existence of strong flow between 5N and 6N west of 29W and between 9N and 11N east of 26W. Averaged u along each latitude ranges from -24 to 17 cm/s and averaged v along longitude, from -4.6 to 6.3 cm/s. The longitude-time SLA distributions at 11.88N are dominated by westward propagation at a speed of 8.1 cm/s probably due to wind-forced Rossby wave motions.

Expand spatial coverage.Effective diffusion from numerical experiments based on advective-diffusion equation with idealized passive tracer in generated geostrophic flow field.Random walk. Compare results with floats statistics.Future Work

Acknowledgement GSO:Dave HebertTom RossbyEverybody in Watkins WHOI:Valery Kosnyrev Dennis McGillicuddy

Real-time Altimeter Data Research Group at Colorado Center for AstrodynamicsCLS Space Oceanography Division

Establishment of the Correlation Model