Response of the North Atlantic storm track to climate change shaped by ocean–atmosphere coupling

A poleward shift of the mid-latitude storm tracks in response to anthropogenic greenhouse-gas forcing has been diagnosed in climate model simulations1, 2. Explanations of this effect have focused on atmospheric dynamics3, 4, 5, 6, 7. However, in contrast to storm tracks in other regions, the North Atlantic storm track responds by strengthening and extending farther east, in particular on its southern flank8. These adjustments are associated with an intensification and extension of the eddy-driven jet towards western Europe9 and are expected to have considerable societal impacts related to a rise in storminess in Europe10, 11, 12. Here, we apply a regression analysis to an ensemble of coupled climate model simulations to show that the coupling between ocean and atmosphere shapes the distinct storm-track response to greenhouse-gas forcing in the North Atlantic region. In the ensemble of simulations we analyse, at least half of the differences between the storm-track responses of different models are associated with uncertainties in ocean circulation changes. We compare the fully coupled simulations with both the associated slab model simulations and an ocean-forced experiment with one climate model to establish causality. We conclude that uncertainties in the response of the North Atlantic storm track to anthropogenic emissions could be reduced through tighter constraints on the future ocean circulation

Water vapor effect on low frequency variability and storm-tracks

International audienceStorm tracks are an important component of the climate system, particularly for winter at mid-latitudes when they determine the daily weather and supply most of the precipitation. Recently, the way synoptic waves break along the storm-tracks (cyclonically or anticyclonically) in the eastern part of the oceanic basins was shown to influence the latitudinal displacement of the jet and the low frequency variability like the North Atlantic Oscillation (NAO). The characteristics of the coupling between low frequency variability and the dynamics of weather systems still need to be better assessed. We use a quasi-geostrophic model on the sphere to study the interaction between low frequency variability and synoptic systems for the northern mid-latitude climate. A dry and a moist version of the model are used to study the effect of humidity on synoptic activity and especially the type of wave breaking, cyclonic or anticyclonic. Different forcing climatologies are used to assess the sensitivity of the storm track and the influence of water vapor

Water vapor effect on low frequency variability and storm-tracks

International audienceStorm tracks are an important component of the climate system, particularly for winter at mid-latitudes when they determine the daily weather and supply most of the precipitation. Recently, the way synoptic waves break along the storm-tracks (cyclonically or anticyclonically) in the eastern part of the oceanic basins was shown to influence the latitudinal displacement of the jet and the low frequency variability like the North Atlantic Oscillation (NAO). The characteristics of the coupling between low frequency variability and the dynamics of weather systems still need to be better assessed. We use a quasi-geostrophic model on the sphere to study the interaction between low frequency variability and synoptic systems for the northern mid-latitude climate. A dry and a moist version of the model are used to study the effect of humidity on synoptic activity and especially the type of wave breaking, cyclonic or anticyclonic. Different forcing climatologies are used to assess the sensitivity of the storm track and the influence of water vapor

Water vapor effect on low frequency variability and storm-tracks

International audienceStorm tracks are an important component of the climate system, particularly for winter at mid-latitudes when they determine the daily weather and supply most of the precipitation. Recently, the way synoptic waves break along the storm-tracks (cyclonically or anticyclonically) in the eastern part of the oceanic basins was shown to influence the latitudinal displacement of the jet and the low frequency variability like the North Atlantic Oscillation (NAO). The characteristics of the coupling between low frequency variability and the dynamics of weather systems still need to be better assessed. We use a quasi-geostrophic model on the sphere to study the interaction between low frequency variability and synoptic systems for the northern mid-latitude climate. A dry and a moist version of the model are used to study the effect of humidity on synoptic activity and especially the type of wave breaking, cyclonic or anticyclonic. Different forcing climatologies are used to assess the sensitivity of the storm track and the influence of water vapor

Impact of greenhouse gas concentration changes on the surface energetics in the IPSL-CM4 model: regional warming patterns, land/sea warming ratio, glacial/interglacial differences

International audienceThe direct effect of greenhouse gas (GHG) changes is a warming of the atmosphere due to greater long-wave (LW) radiation absorption. Nevertheless, many other processes and feedbacks also take place which modify the whole climatic system and especially the surface energy budget, which determine the precise value of the surface temperature change. In this study, we decompose the surface energy fluxes to determine and quantify the role of many different processes in explaining the surface temperature response to an increase in GHG forcing in a coupled Ocean-Atmosphere General Circulation Model (AOGCM), IPSL-CM4. In particular, we show that the direct feedback effect consisting of greater backward LW radiation due to greater LW emission is particularly strong as is the effect of an increase in water vapor in the atmosphere due to greater temperatures. Nevertheless, many other terms are also important. We use this decomposition to understand the role of the different processes in the polar amplification, the warming contrast between the oceans and the continents and the differences in the surface warming under interglacial (preindustrial) and glacial (Last Glacial Maximum) conditions. This decomposition could be usefull to compare the sensitivity of different AOGCMs to a GHG forcing

Impact of greenhouse gas concentration changes on the surface energetics in the IPSL-CM4 model: regional warming patterns, land/sea warming ratio, glacial/interglacial differences

International audienceThe direct effect of greenhouse gas (GHG) changes is a warming of the atmosphere due to greater long-wave (LW) radiation absorption. Nevertheless, many other processes and feedbacks also take place which modify the whole climatic system and especially the surface energy budget, which determine the precise value of the surface temperature change. In this study, we decompose the surface energy fluxes to determine and quantify the role of many different processes in explaining the surface temperature response to an increase in GHG forcing in a coupled Ocean-Atmosphere General Circulation Model (AOGCM), IPSL-CM4. In particular, we show that the direct feedback effect consisting of greater backward LW radiation due to greater LW emission is particularly strong as is the effect of an increase in water vapor in the atmosphere due to greater temperatures. Nevertheless, many other terms are also important. We use this decomposition to understand the role of the different processes in the polar amplification, the warming contrast between the oceans and the continents and the differences in the surface warming under interglacial (preindustrial) and glacial (Last Glacial Maximum) conditions. This decomposition could be usefull to compare the sensitivity of different AOGCMs to a GHG forcing

Impact of greenhouse gas concentration changes on the surface energetics in the IPSL-CM4 model: regional warming patterns, land/sea warming ratio, glacial/interglacial differences

International audienceThe direct effect of greenhouse gas (GHG) changes is a warming of the atmosphere due to greater long-wave (LW) radiation absorption. Nevertheless, many other processes and feedbacks also take place which modify the whole climatic system and especially the surface energy budget, which determine the precise value of the surface temperature change. In this study, we decompose the surface energy fluxes to determine and quantify the role of many different processes in explaining the surface temperature response to an increase in GHG forcing in a coupled Ocean-Atmosphere General Circulation Model (AOGCM), IPSL-CM4. In particular, we show that the direct feedback effect consisting of greater backward LW radiation due to greater LW emission is particularly strong as is the effect of an increase in water vapor in the atmosphere due to greater temperatures. Nevertheless, many other terms are also important. We use this decomposition to understand the role of the different processes in the polar amplification, the warming contrast between the oceans and the continents and the differences in the surface warming under interglacial (preindustrial) and glacial (Last Glacial Maximum) conditions. This decomposition could be usefull to compare the sensitivity of different AOGCMs to a GHG forcing

Impact of greenhouse gas concentration changes on the surface energetics in the IPSL-CM4 model: regional warming patterns, land/sea warming ratio, glacial/interglacial differences

International audienceThe direct effect of greenhouse gas (GHG) changes is a warming of the atmosphere due to greater long-wave (LW) radiation absorption. Nevertheless, many other processes and feedbacks also take place which modify the whole climatic system and especially the surface energy budget, which determine the precise value of the surface temperature change. In this study, we decompose the surface energy fluxes to determine and quantify the role of many different processes in explaining the surface temperature response to an increase in GHG forcing in a coupled Ocean-Atmosphere General Circulation Model (AOGCM), IPSL-CM4. In particular, we show that the direct feedback effect consisting of greater backward LW radiation due to greater LW emission is particularly strong as is the effect of an increase in water vapor in the atmosphere due to greater temperatures. Nevertheless, many other terms are also important. We use this decomposition to understand the role of the different processes in the polar amplification, the warming contrast between the oceans and the continents and the differences in the surface warming under interglacial (preindustrial) and glacial (Last Glacial Maximum) conditions. This decomposition could be usefull to compare the sensitivity of different AOGCMs to a GHG forcing