The impact of different glacial boundary conditions on atmospheric dynamics and precipitation in the North Atlantic region

D Hofer,A Dehnert,C C Raible,J Kuhlemann

doi:10.5194/cp-8-935-2012

Abstract

Abstract. Using a highly resolved atmospheric general circulation model, the impact of different glacial boundary conditions on precipitation and atmospheric dynamics in the North Atlantic region is investigated. Six 30-yr time slice experiments of the Last Glacial Maximum at 21 thousand years before the present (ka BP) and of a less pronounced glacial state – the Middle Weichselian (65 ka BP) – are compared to analyse the sensitivity to changes in the ice sheet distribution, in the radiative forcing and in the prescribed time-varying sea surface temperature and sea ice, which are taken from a lower-resolved, but fully coupled atmosphere-ocean general circulation model. The strongest differences are found for simulations with different heights of the Laurentide ice sheet. A high surface elevation of the Laurentide ice sheet leads to a southward displacement of the jet stream and the storm track in the North Atlantic region. These changes in the atmospheric dynamics generate a band of increased precipitation in the mid-latitudes across the Atlantic to southern Europe in winter, while the precipitation pattern in summer is only marginally affected. The impact of the radiative forcing differences between the two glacial periods and of the prescribed time-varying sea surface temperatures and sea ice are of second order importance compared to the one of the Laurentide ice sheet. They affect the atmospheric dynamics and precipitation in a similar but less pronounced manner compared with the topographic changes.

Highlights

The climate in glacial periods is of great interest, as it represents a state that is fundamentally different compared to today
We focus on the surface air temperature (SAT) and precipitation in the two present-day simulations which are compared to the monthly mean output of the years 1971–2000 of the ERA-40 reanalysis data (Uppala et al, 2005) interpolated to the 0.9 × 1.25◦ resolution of the CCSM4 output
Using the ocean surface conditions of simulations with a fully coupled atmosphere-ocean general circulation model (CCSM3) as input to a higher resolved atmospheric general circulation model (CCSM4), we investigated the impact of different glacial boundary conditions on the temperature, precipitation and atmospheric dynamics in the North Atlantic region

Summary

Introduction

The climate in glacial periods is of great interest, as it represents a state that is fundamentally different compared to today. The climate in earlier periods of the last glaciation is less understood as proxy data availability is further reduced. Sea level reconstructions indicate changes in the order of several tens of metres during the last glaciation For the LGM, the extent and height of the ice sheets are relatively well known (Peltier, 2004), but uncertainties strongly increase when going further back in time. For the earlier part of the last glacial period the knowledge of the climate, and of the lower boundary conditions is limited due to the lack of proxy data. One way to overcome these limitations is the use of climate models which enables us to test different boundary conditions and to investigate their impact on the climate

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Results

Conclusion