Global water balance and atmospheric water vapour transport at last glacial maximum: climate simulations with the Canadian Climate Centre for Modelling and Analysis atmospheric general circulation model

A series of new simulations of the climate state at last glacial maximum ha s been performed using the Canadian second-generation atmospheric general c irculation model and are described herein. The primary goal has been to ass ess the dynamic changes in the global water balance and water vapour transp ort that were characteristic of the climate state during this epoch of Eart h's history. We pay special attention to comparisons of the atmospheric mod el simulations of last glacial maximum climate with those produced with a m uch simpler coupled energy balance-ice-sheet model, which has been designed to simulate the late Pleistocene cycle of glacial-interglacial ice volume variations. Our analyses, using the atmospheric model, demonstrate that the vigour of the hydrological cycle was markedly decreased under last glacial maximum conditions, as would be expected on the simplest thermodynamic gro unds. The primary components of the hydrological cycle in the atmospheric m odel, namely precipitation and evaporation, constitute essential mechanisms that control ice-sheet mass balance. We also investigate changes in the No rthern Hemisphere stationary wave patterns, as well as changes in the total and eddy moisture transport by the global circulation at last glacial maxi mum to illustrate the role played by the dynamics of the atmosphere in the maintenance of the Northern Hemisphere ice sheets. In particular, we find t hat the enhancement of the stationary wave pattern along with the convergen ce in atmospheric water vapour transport produces increased cooling and sno w accumulation at last glacial maximum over the southeastern lobes of the L aurentide Ice Sheet. This suggests an explanation for the previously unexpl ained extension of these lobes deep into the New England states.