Relative roles of land- and ocean-atmosphere interactions in Asian-Pacific thermal contrast variability at the precessional band

Abstract

In a 250-kyr transient simulation of the Community Earth System Model (CESM), we identified a precessional forced seesaw of the summer middle-upper tropospheric eddy temperature between Asia and the North Pacific as the paleo-APO (Asian-Pacific oscillation). The paleo-APO variability is out of phase with the precession parameter. Corresponding to a positive paleo-APO phase, both the subtropical anticyclonic circulation over the North Pacific and the East Asian summer monsoon (EASM) strengthen. Summer anomalous sea surface temperature shows a western cold-eastern warm pattern over the extratropical North Pacific and a zonal positive-negative-positive pattern over the tropical Pacific. The variations in the simulated paleo-APO and East Asian southerly wind at the precessional band agree well with the geological proxies at the Dongge, Sanbao, Linzhu, and Hulu caves in China, which also implies that these proxies may well reflect the variability in the southerly wind over East Asia. Sensitivity experiments further reveal that the reduced precession parameter may enhance the positive paleo-APO phase and the associated EASM because of the response of the land-atmosphere interactions to the precessional insolation changes. The effect of the ocean-atmosphere interactions on the paleo-APO is secondary.

Orbital-scale Asian summer monsoon variations: Paradox and exploration

“…In regard to sea-land spatial patterns of the ASM precipitation, the ocean and continent responses to NHSI are fundamentally different in their precession phases. The simulation results of different models are basically identical: On the whole, when NHSI is high (P min ), precipitation increases over continents and decreases over oceans, and vice versa (e.g., Battisti et al, 2014;Wang et al, 2016;Wu et al, 2016;Bosmans et al, 2018;Tabor et al, 2018;Lee et al, 2019;Huang et al, 2020) (Figures 1 and 2). For example, Bosmans et al (2018) simulated the precipitation differences of high NHSI minus low NHSI (or P min minus P max ) in the ASM region (Figures 1 and 2).…”

“…Therefore, from the perspective of sea-land spatial pattern, the summer monsoon precipitation responses to the NHSI precession change, as a whole, are fundamentally different between the ocean and continent in the vast ASM domain. That is, to a first order, when NHSI is high, precipitation increases over the continent and decreases over the ocean (e.g., Battisti et al, 2014;Wang et al, 2016;Wu et al, 2016;Bosmans et al, 2018;Tabor et al, 2018). The essence of the seemingly fundamental difference suggests that the sea-land monsoon records characterized just different aspects of the Asian monsoon system, which can explain why they are apparently different.…”