Global Warming Pattern Formation: Sea Surface Temperature and Rainfall*

Abstract

Spatial variations in sea surface temperature (SST) and rainfall changes over the tropics are investigated based on ensemble simulations for the first half of the twenty-first century under the greenhouse gas (GHG) emission scenario A1B with coupled ocean-atmosphere general circulation models of the Geophysical Fluid Dynamics Laboratory (GFDL) and National Center for Atmospheric Research (NCAR). Despite a GHG increase that is nearly uniform in space, pronounced patterns emerge in both SST and precipitation. Regional differences in SST warming can be as large as the tropical-mean warming. Specifically, the tropical Pacific warming features a conspicuous maximum along the equator and a minimum in the southeast subtropics. The former is associated with westerly wind anomalies whereas the latter is linked to intensified southeast trade winds, suggestive of wind-evaporation-SST feedback. There is a tendency for a greater warming in the northern subtropics than in the southern subtropics in accordance with asymmetries in trade wind changes. Over the equatorial Indian Ocean, surface wind anomalies are easterly, the thermocline shoals, and the warming is reduced in the east, indicative of Bjerknes feedback. In the midlatitudes, ocean circulation changes generate narrow banded structures in SST warming. The warming is negatively correlated with wind speed change over the tropics and positively correlated with ocean heat transport change in the northern extratropics. A diagnostic method based on the ocean mixed layer heat budget is developed to investigate mechanisms for SST pattern formation.Tropical precipitation changes are positively correlated with spatial deviations of SST warming from the tropical mean. In particular, the equatorial maximum in SST warming over the Pacific anchors a band of pronounced rainfall increase. The gross moist instability follows closely relative SST change as equatorial wave adjustments flatten upper-tropospheric warming. The comparison with atmospheric simulations in response to a spatially uniform SST warming illustrates the importance of SST patterns for rainfall change, an effect overlooked in current discussion of precipitation response to global warming. Implications for the global and regional response of tropical cyclones are discussed.

Global Precipitation: Means, Variations and Trends During the Satellite Era (1979–2014)

“…Patterns of precipitation anomalies have been the subject of numerous studies (e.g., Dai and Wigley 2000;Held and Soden 2006;Xie et al 2010;Gu and Adler 2013). However, with global estimates from GPCP we can summarize the mean impact of ENSO during the satellite era across the globe.…”

Oceanic sources of continental precipitation and the correlation with sea surface temperature

“…It could, for example, also indicate that both local SST and land precipitation are increased by global warming, without the necessity of additional moisture transport from the oceanic region. Neither can we simply assume these correlations to remain static in time in view of the fact that these increased SSTs are predicted to increase heterogeneously over the globe [Xie et al, 2010], which may lead to changes in atmospheric circulation.…”

Classification of CMIP5 Future Climate Responses by the Tropical Sea Surface Temperature Changes

“…The spatial distribution of tropical precipitation changes will depend on the current precipitation climatology and also on future SST warming pattern (Christensen et al 2013). The first effect is to increase precipitation near the currently rainy regions ("wet-getwetter" effect; Held and Soden 2006;Chou et al 2009), and the second effect is to increase precipitation where warming of SST exceeds the tropical mean and vice versa ("warmer-get-wetter" mechanism; Xie et al 2010;Chadwick et al 2013;Ma and Xie 2013).…”