[A-CG42] Science in the Arctic Region

[ACG42-P06] An Assessment of Lower Tropospheric Moisture Advection Towards the Arctic Amplification Pattern Using a Large-scale Ensemble Model Dataset

*Masatake Hori¹, Masakazu Yoshimori¹, Jinro Ukita¹ (1.University of Tokyo, Atmosphere and Ocean Research Institute)

Keywords:Polar Amplification, Moisture advection

The Arctic warms faster than the global average in a phenomenon known as Arctic amplification (AA). AA predominantly influences the lower troposphere where moisture is concentrated. Here, we investigate the role of moisture advection in the lower troposphere under the progression of global warming. We use the ‘database for policy decision making for future climate change’ (d4PDF), an AGCM large-scale ensemble model dataset which consists of a 60-year historical and non-warming simulation with 100 members each. The dataset also includes a 60-year simulation of the climate 4K and 2K warmer than the pre-industrial climate with 90 and 54 members each. Using the non-warming simulation (HPB-NAT) as a reference, we examine the difference in moisture advection under changing basic states of the historical simulation (HPB) and future simulations (HFB-2K / 4K). In this study, the total difference in horizontal advection is separated to account for the change in climatological wind and moisture gradient from their deviations and is further decomposed to quantify the effect of dynamical change and thermodynamical changes. During summer, horizontal advection is negative over the mid-latitudes and positive in the Arctic, indicating that evaporation is enhanced over the continental land surface and moisture is advected towards the relatively dry Arctic region predominantly by the effect of transient eddies. During winter, horizontal advection is negative over the North Atlantic due to the effect of moisture supplied from the sea surface via evaporation. This effect is enhanced under the progression of global warming due to diminishing sea ice and increased evaporation, thereby turning the effect of horizontal advection in the lower troposphere into drying the atmosphere. Conversely, horizontal and vertical advection in the middle and upper troposphere increases with warming, indicating that within the column-integrated moisture of the atmosphere, the contribution of local effects via evaporation becomes more dominant under the progression of global warming.