The Impact of Pacific and Atlantic Land-Sea Thermal Contrast on the Mid-Latitude Atmosphere

It is widely recognised that with climate change land is warming at a faster rate than the oceans, and that the trend will persist in time. In the Northern Hemisphere extratropics the strong winter thermal contrast between cold continents and relatively warmer oceans is thus expected to decrease, but the magnitude of the change will be basin dependent, for example as a result of the slow warming of the North Atlantic. While global mid-latitude land-sea thermal contrast influences the mean state of the atmosphere by setting the shape of planetary waves and the position and intensity of the mid-latitude jets, the dynamical importance of the thermal contrast of the individual basins is less clear. Here we run idealised simulations in which we prescribe the surface temperature on the continents and on the oceans, and we study the response to reduced Pacific or Atlantic land-sea thermal contrast. Thanks to the individual-basin approach we show that the first (Asia - Pacific contrast) is particularly relevant in setting the shape and amplitude of planetary waves and that its impact reflects strongly on the strength and position of the Pacific and Atlantic jet, while the second (North-America - Atlantic contrast) has a weaker imprint on the tropospheric state.