Atmosphere Ocean Science Colloquium
Arctic-Antarctic Parity in High-latitude Climate Sensitivity: the Aerial Hydrologic Cycle, Ocean Dynamics, and Meridional Energy Transports
Speaker: Hansi Alice Singh, Pacific Northwest National Laboratory
Location: Warren Weaver Hall 1302
Date: Wednesday, December 6, 2017, 3:30 p.m.
The Arctic and the Antarctic differ substantially in their mean state climates and responses to anthropogenic forcing in the modern era. Nevertheless, robust inter-hemispheric similarities in the high-latitude climate response to CO2-forcing are evident over longer time scales, which we consider here. Similarities between the Arctic and Antarctic response to quasi-equilibrium CO2-doubling manifest clearly in the Lagrangian aerial hydrologic cycle, where the remote (i.e. non-local) moisture contribution to polar precipitation increases significantly in both hemispheres. This response closely follows the global hydrologic cycle response to CO2-doubling, where an increase in the moisture transport length scale widens the distance between moisture sources and sinks. In winter, on the other hand, a greater fraction of polar precipitation comes from local moisture sources due to enhanced turbulent (sensible and latent) heat fluxes over areas of sea ice retreat. This hemispheric parity in the winter Lagrangian hydrologic cycle response to CO2-doubling is due to hemispheric parity in the dynamic ocean response: enhanced turbulent surface fluxes are due to a poleward shift in the ocean heat flux convergence (OHFC), which pushes the winter sea ice edge poleward and increases local (polar) evaporation. The poleward shift in the OHFC enhances polar warming while damping extrapolar warming; as a result, polar climate sensitivity increases. Radiative feedback analysis shows that changes in the OHFC warm polar surface temperatures while cooling the atmosphere aloft, which augments the positive lapse rate feedback in the high latitudes in both hemispheres. These findings imply a fundamental asymmetry between the efficacy of oceanic and atmospheric energy transports in driving polar warming, which suggests that the partitioning of meridional energy transport changes between atmosphere and ocean impacts polar amplification.