Subsurface Ocean Temperature Responses to the Anthropogenic Aerosol Forcing in the North Pacific

Separating the climate response to external forcing from internal climate variability is a key challenge. While most previous studies have focused on surface responses, here we examine zonal-mean patterns of North Pacific subsurface temperature responses. In particular, the changes since 1950 driven by anthropogenic aerosol emissions are found by using a pattern recognition method. Based on the single-forcing large-ensemble simulations from two models, we show that aerosol forcing caused a nonmonotonic temporal response and a characteristic zonal-mean pattern within North Pacific, which is distinct from the pattern associated with internal variability. The aerosol-forced pattern with the nonmonotonic temporal feature shows a substantial temperature change in subpolar regions and a reversed change on the southern flank of the subtropical gyre. A similar characteristic pattern and nonmonotonic time evolution are extracted from the subsurface observations, which likely reflect the subsurface responses to the aerosol forcing, although differences exist with the simulated responses.