Limited Influence of Localized Tropical Sea-Surface Temperatures on Moisture Transport into the Arctic

Arctic moisture transport is dominated by planetary-scale waves in reanalysis. Planetary waves are influenced by localized Sea-Surface Temperature (SST) features such as the tropical warm pool. Here, an aquaplanet model is used to clarify the link between tropical SST anomalies and Arctic moisture transport. In a zonally uniform setup with no climatological east-west gradients, Arctic moisture transport is dominated by transient planetary waves, as in reanalysis. Warming tropical SSTs by heating the ocean strengthens Arctic moisture transport, mediated mostly by changes in water vapor rather than eddies. This strengthening occurs whether the tropical warming is zonally uniform or localized. Cooling tropical SSTs weakens Arctic moisture transport; however, unlike warming, the pattern matters, with localized cooling producing stronger transport changes owing to nonlinear feedbacks in the surface energy budget. Thus, the simulations show that localized tropical SST anomalies influence Arctic moisture transport differently than uniform anomalies, but only in cooling scenarios. Plain Language Summary Northward transport of water vapor strongly influences Arctic climate. Most of the transport is accomplished by atmospheric waves with large east-west scale extending around the earth. These waves can be generated by warm ocean waters in the western tropical Pacific. Here, a simplified climate model with an ocean-covered surface is used to clarify the processes linking the tropical ocean and Arctic moisture transport. Arctic transport in the model is accomplished by waves that are similar to observations, suggesting it is a useful tool. Warming the tropical ocean strengthens Arctic transport similarly whether the warming pattern is concentrated in a specific location or spread out equally at all longitudes. The strengthening results mostly from an increase in water vapor arising from an increase in the holding capacity of the atmosphere at warmer temperatures. Cooling the tropical ocean weakens Arctic transport but, unlike warming, cooling concentrated in a specific location weakens the transport more than if it is spread out equally at all longitudes. The different responses arise because ocean temperatures adjust differently to warming vs. cooling. Thus, localized cooling of tropical ocean temperatures appears to be a special case in terms of its influence on moisture transport into the Arctic.