A Global Monthly Sea Surface Temperature Climatology

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  • 1 National Center for Atmospheric Research, Boulder, Colorado
  • | 2 Climate Analysis Center, Washington, D.C.
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Abstract

A new global 2°×2° monthly sea surface temperature (SST) climatology, primarily derived from a 1950–1979-based SST climatology from the Climate Analysis Center (CAC), is presented and described. The CAC climatology has been modified by using data from the Comprehensive Ocean-Atmosphere Data Set to improve the SST estimates in the regions of the Kuroshio and the Gulf Stream. This results in considerably larger and more realistic SST gradients in these regions. This modified climatology is smoothed in time using a truncated Fourier series to eliminate mean annual cycle fluctuations of three months or less, and finally, some spatial smoothing is applied over the high-latitude southern oceans.

This new SST climatology, which we call the Shea-Trenberth-Reynolds (STR) climatology, is compared with the Alexander and Mobley (AM) SST climatology often used as a lower boundary condition by general circulation models. Significant differences are noted. Generally, the STR climatology is warmer in the Northern Hemisphere and in the subtropics of the Southern Hemisphere during the northern winter. It is often colder south of 45°S in all months. The largest differences are more than 5°C in the Kuroshio and Gulf Stream regions, and in the mid- to high-latitude southern oceans, the SSTs are often more than 2°C lower. In addition, the STR climatology is temporally and spatially less noisy than the AM SST climatology.

Global SST anomalies spanning the period 1982 to 1990 are discussed. The largest anomalies are associated with the El Niño (1982–83 and 1986–87) and La Niña (1988) events in the tropical Pacific. However, because of differences in procedures in producing the 1982–1990 SSTs compared with the CAC climatology, the anomalies in certain regions are really compensating for deficiencies in the climatology and should not be interpreted as true climate anomalies.

Abstract

A new global 2°×2° monthly sea surface temperature (SST) climatology, primarily derived from a 1950–1979-based SST climatology from the Climate Analysis Center (CAC), is presented and described. The CAC climatology has been modified by using data from the Comprehensive Ocean-Atmosphere Data Set to improve the SST estimates in the regions of the Kuroshio and the Gulf Stream. This results in considerably larger and more realistic SST gradients in these regions. This modified climatology is smoothed in time using a truncated Fourier series to eliminate mean annual cycle fluctuations of three months or less, and finally, some spatial smoothing is applied over the high-latitude southern oceans.

This new SST climatology, which we call the Shea-Trenberth-Reynolds (STR) climatology, is compared with the Alexander and Mobley (AM) SST climatology often used as a lower boundary condition by general circulation models. Significant differences are noted. Generally, the STR climatology is warmer in the Northern Hemisphere and in the subtropics of the Southern Hemisphere during the northern winter. It is often colder south of 45°S in all months. The largest differences are more than 5°C in the Kuroshio and Gulf Stream regions, and in the mid- to high-latitude southern oceans, the SSTs are often more than 2°C lower. In addition, the STR climatology is temporally and spatially less noisy than the AM SST climatology.

Global SST anomalies spanning the period 1982 to 1990 are discussed. The largest anomalies are associated with the El Niño (1982–83 and 1986–87) and La Niña (1988) events in the tropical Pacific. However, because of differences in procedures in producing the 1982–1990 SSTs compared with the CAC climatology, the anomalies in certain regions are really compensating for deficiencies in the climatology and should not be interpreted as true climate anomalies.

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