Latitudinal variability and intensity of the South Pacific subtropics over the past 1200 years

Abstract:

Indo-Pacific extratropical Southern Hemisphere (SH) sea-level pressure anomaly (SLPa) fields are presented for the past millennium (after Goodwin et al., 2013). The multivariate array of proxy data from South Africa, Australia/New Zealand, Patagonian South America and Antarctica were simultaneously evaluated against global climate model output in order to identify climate state analogues that are most consistent with the majority of proxy data. We present the mean SLP, SLP anomaly and surface windfield patterns derived from these analogues to illustrate the vacillation of the tropics and the evolution of low frequency changes in the extratropics.

A poleward shift in the subtropical ridge (STR) was a strong feature of the Southern Hemisphere from 900 to 1300 CE during the Medieval Climate Anomaly (MCA) and again from 1650-1750 CE during the Little Ice Age (LIA). The Hadley Cell expansion in the Australian and Southwest Pacific, region together with the poleward shift of the zonal westerlies is contemporaneous with previously reported Hadley Cell expansion in the North Pacific and Atlantic regions, and suggests that bipolar climate symmetry was a feature of the MCA.

We also present the impacts of South Pacific windfield and ocean wave field changes associated with the tropical expansion, on extreme storm frequency, Eastern Australian coastline reorganization and on human migration. The intensification and poleward expansion of the Pacific subtropical anticyclone culminating in AD 1140 to 1260, opened an anomalous climate window for off-wind sailing routes for Polynesians colonise the far corners of the Polynesian Triangle, New Zealand, Easter Island and Hawaii (Goodwin et al., 2014).

Goodwin, I. D., et al., (2013). A reconstruction of extratropical Indo-Pacific sea-level pressure patterns during the Medieval Climate Anomaly. Climate Dynamics, DOI 10.1007/s00382-013-1899-1.

Goodwin, I.D., et al. (2014). Climate windows for Polynesian Voyaging to New Zealand and Easter Island. PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1408918111