The eastern Tropical Pacific hydroclimate over the last 120kyr: a perspective from HadCM3.

Abstract:

The focus of the majority of studies looking into the evolving tropical pacific climate on glacial/interglacial timescales has been the role of the changing orbital forcing. While this is of course the fundamental forcing that drives changes in the climate on these time scales, without a fully interactive Earth System Model the effects that the evolving ice sheets/sea level and green house gases have on the climate will be missed. In the absence of such models these other forcings must be imposed. While the impact on the temperature in both the high latitudes, and to some extent in the tropics, of all of the forcings is reasonably clear, their impact on the hydroclimate is less obvious. In this study we shall investigate what role all of the different forcings that vary over a glacial/interglacial cycle play on the hydroclimate in the eastern Tropical Pacific.

We use as the basis of our study a set of three climate model experiments using the model HadCM3. Each of these simulates the last 120 thousand years as a series of time slices in one of three configurations: varying the orbital forcing; varying the orbital and greenhouse gas forcing; varying the orbital, greenhouse and ice sheet/sea level forcing. With these experiments we can deconvolve the role that each forcing plays. We will show that, in addition to the orbital forcing, both the greenhouse gas forcing and the ice sheet configuration have a large impact on the eastern Tropical Pacific's hydroclimate. Using a set of more idealised model simulations we shall elucidate the mechanisms by which each of these different forcing mechanism causes the simulated changes.