Gan, B., L. Wu, F. Jia, S. Li, W. Cai, H. Nakamura, M. A. Alexander and A. J. Miller, 2017:

On the response of the Aleutian Low to greenhouse warming


Journal of Climate, in press

Abstract. Past and future changes in the Aleutian Low are investigated by using observation-based sea level pressure (SLP) datasets and CMIP5 multi-models. It is found that the Aleutian Low intensity, measured by the North Pacific Index (NPI), has significantly strengthened during the 20th century, with the observed centennial-trend double the modeled counterpart for the multi-model average of historical simulations, suggesting compound signals of anthropogenic warming and natural variability. As climate warms under the strongest future warming scenario, the climatological-mean Aleutian Low will continue to intensify and expand northward, as manifested in the significant decrease (-1.3 hPa) of multi-model-averaged NPI which is 1.6 times its unforced internal variability and the central area of low-pressure (SLP < 999.0 hPa) expanded about 7 times that in the 20th century. A suite of idealized experiments further demonstrate that the deepening of the Aleutian Low can be driven by an El-Nino-like warming of the tropical Pacific sea surface temperature (SST), with a reduction in the climatological-mean zonal SST gradient, which overshadows the dampening effect of a weakened wintertime land-ocean thermal contrast on the Aleutian Low change in a warmer climate. While the projected deepening of Aleutian Low on multi-model average is robust, individual model portrayals vary primarily in magnitude. Inter-model difference in surface warming amplitude over the Asian continent, which is found to explain about 31% of variance of the NPI changes across models, has a greater contribution than that in the spatial pattern of tropical Pacific SST warming (which explains about 23%) to model uncertainty in the projection of Aleutian Low intensity.

Preprint (pdf)