HR: 15:10h
AN: G23A-07 INVITED     [Abstracts]
TI: Subarctic Bottom Pressure Oscillation observed by GRACE, linked to ENSO
AU: * Zlotnicki, V
EM: vz@pacific.jpl.nasa.gov
AF: Jet Propulsion Lab. California Inst. Technology, MS 300-323. 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: Song, Y
EM: song@pacific.jpl.nasa.gov
AF: Jet Propulsion Lab. California Inst. Technology, MS 300-323. 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: Wahr, J
EM: wahr@lemond.colorado.edu
AF: U. Colorado, Campus Box 390, Boulder, CO 80309-0390 United States
AB: The Gravity Recovery and Climate Experiment (GRACE) satellites have observed strong signals during 2003-04 in the meridional differences in ocean bottom pressure (OBP) in the high-latitude N. Pacific (50N minus 25N) and in the Indian Ocean sector of the Antarctic Circumpolar Current (55S minus 25 S). `Strong' means peak-to-peak amplitudes in the annual variability of 6 mbars, when averaged zonally over about 4,000 km. Reasonableness of the signal is determined by comparison with outputs from a non-Boussinesq model that does not assimilate data, as well as with a version of the ECCO model with altimetric data assimilation. Focussing on the N. Pacific signal, there is a strong hint of interannual trend in both data and model. The non-Boussinesq model is then used to analyze a 50 year long time series of model output. We find that the N. Pacific signal leads the Ni¤o3.4 index by more than 12 months with a correlation of 0.52 in the 99% significant interval. The model also shows a moderate east-west OBP oscillation in the tropical Pacific. Unlike the subarctic Pacific oscillation, the bottom pressure difference between the eastern (Ni¤o3.4 region) and the western tropical Pacific (warm-pool region) is in phase with the Ni¤o3.4 index with a correlation 0.82 and has a characteristics of eastward mass-shift during El Ni¤o events, indicating their direct effect on deep oceans, however, the GRACE satellites cannot `see' this much smaller E-W signal. Lower latitude applications of GRACE data, with signals of ~1-2 mbar, need to wait for expected improvements in GRACE fields after one or more reprocessing cycles. The E-W difference also amplifies the zonal errors in GRACE data, while the N-S differences then to cancel them.
DE: 4532 General circulation
DE: 4594 Instruments and techniques
DE: 1223 Ocean/Earth/atmosphere interactions (3339)
DE: 1299 General or miscellaneous
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting