Preprints
https://doi.org/10.5194/gmd-2020-374
https://doi.org/10.5194/gmd-2020-374

Submitted as: model evaluation paper 30 Nov 2020

Submitted as: model evaluation paper | 30 Nov 2020

Review status: a revised version of this preprint was accepted for the journal GMD and is expected to appear here in due course.

A Mechanistic Analysis of Tropical Pacific Dynamic Sea Level in GFDL-OM4 under OMIP-I and OMIP-II Forcings

Chia-Wei Hsu1, Jianjun Yin1, Stephen M. Griffies2,3, and Raphael Dussin2 Chia-Wei Hsu et al.
  • 1University of Arizona, Department of Geoscience, 1040 E 4th St, Tucson, AZ 85721, USA
  • 2NOAA Geophysical Fluid Dynamics Laboratory, Princeton USA
  • 3Princeton University Atmospheric and Oceanic Sciences Program, Princeton USA

Abstract. The sea level over the tropical Pacific is a key indicator reflecting vertically integrated heat distribution over the ocean. Here we use the Geophysical Fluid Dynamics Laboratory OM4 (GFDL-OM4) global ocean-sea ice model forced by both the CORE and JRA55-do atmospheric states (OMIP-I and OMIP-II) to evaluate the model performance and biases compared against available observations. We find persisting mean state dynamic sea level (DSL) bias along 9° N even with updated wind forcing in JRA55-do relative to CORE. The mean state bias is related to biases in wind stress forcing and geostrophic currents in the 4° N to 9° N latitudinal band. The simulation forced by JRA55-do significantly reduces the bias in DSL trend over the northern tropical Pacific relative to CORE. In the CORE forcing, the anomalous westerly wind trend in the eastern tropical Pacific causes an underestimated DSL trend across the entire Pacific basin along 10° N. The simulation forced by JRA55-do significantly reduces the bias in DSL trend over the northern tropical Pacific relative to CORE. We also identify a bias in the easterly wind trend along 20° N in both JRA55-do and CORE, thus motivating future improvement. In JRA55-do, an accurate Rossby wave initiated in the eastern tropical Pacific at seasonal time scale corrects a biased seasonal variability of the northern equatorial counter-current in the CORE simulation. Both CORE and JRA55-do generate realistic DSL variation during El Nino. We find an asymmetry in the DSL pattern on two sides of the equator is strongly related to wind stress curl that follows the sea level pressure evolution during El Niño.

Chia-Wei Hsu et al.

 
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Chia-Wei Hsu et al.

Chia-Wei Hsu et al.

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Short summary
The new surface forcing from JRA55-do (OMIP II) significantly improved the underestimated sea level trend across the entire Pacific ocean along 10° N in the simulation forced by CORE (OMIP I). We summarize and list out the reasons for the existing sea level biases across all studied time scales as a reference for improving the sea level simulation in the future. This study about the evaluation and improvement of ocean climate models should be of broad interest to a large modeling community.