Wind-Driven Thermocline Variability in the Pacific: A Model–Data Comparison

Jo Ann Lysne National Center for Atmospheric Research, Boulder, Colorado

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Clara Deser National Center for Atmospheric Research, Boulder, Colorado

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Abstract

The spatial and temporal patterns of interannual temperature variability within the main thermocline (200–400-m depth) of the Pacific (30°S–60°N) during 1968–97 are documented in two observational datasets and an ocean general circulation model forced with observed winds and air temperatures. Analysis of the processes responsible for the subsurface temperature variance is used to verify the performance of the model and as a basis for assessing the realism of the two observational archives. The subsurface temperature variance is largest in the western portion of the basin, with maxima along the Kuroshio Current Extension and along the equatorward flanks of the subtropical gyres in both hemispheres. In the latter regions, approximately half of the temperature variability may be attributed to local wind-induced Ekman pumping fluctuations one season earlier. A contribution from westward-propagating Rossby waves is also evident in the band 10°–20°N. In contrast, subsurface temperature fluctuations along the Kuroshio Current Extension exhibit little relation to local Ekman pumping variations. Rather, they are linked to basin-scale wind stress curl changes ∼4 yr earlier. Similarities and differences between the two observational subsurface temperature archives are discussed.

Corresponding author address: Dr. Clara Deser, Climate and Global Dynamics Division, NCAR, P. O. Box 3000, Boulder, CO 80307. Email: cdeser@ucar.edu

Abstract

The spatial and temporal patterns of interannual temperature variability within the main thermocline (200–400-m depth) of the Pacific (30°S–60°N) during 1968–97 are documented in two observational datasets and an ocean general circulation model forced with observed winds and air temperatures. Analysis of the processes responsible for the subsurface temperature variance is used to verify the performance of the model and as a basis for assessing the realism of the two observational archives. The subsurface temperature variance is largest in the western portion of the basin, with maxima along the Kuroshio Current Extension and along the equatorward flanks of the subtropical gyres in both hemispheres. In the latter regions, approximately half of the temperature variability may be attributed to local wind-induced Ekman pumping fluctuations one season earlier. A contribution from westward-propagating Rossby waves is also evident in the band 10°–20°N. In contrast, subsurface temperature fluctuations along the Kuroshio Current Extension exhibit little relation to local Ekman pumping variations. Rather, they are linked to basin-scale wind stress curl changes ∼4 yr earlier. Similarities and differences between the two observational subsurface temperature archives are discussed.

Corresponding author address: Dr. Clara Deser, Climate and Global Dynamics Division, NCAR, P. O. Box 3000, Boulder, CO 80307. Email: cdeser@ucar.edu

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