Effect of orographic gravity wave drag on Northern Hemisphere climate in transient simulations of the last deglaciation

Abstract Long transient simulations of the last deglaciation are increasingly being performed to identify drivers multiple rapid Earth system changes that occurred in this period. Such frequently prescribe temporal variations ice sheet properties, which can play an important role controlling atmospheric and surface climate. To preserve a model’s standard performance simulating climate, it is common apply time dependent orographic variations, including parameterised sub-grid scale variances, as anomalies from pre-industrial state. This study investigates causes two abrupt climate change events Northern Hemisphere extratropics occurring between 16 14 thousand years ago Hadley Centre coupled general circulation model (HadCM3). One event characterized by regional comprising centennial cooling ~ 10 °C across Fennoscandia followed warming less than 50 well synchronous shifts Annular Mode. The second has comparable but temporally reversed characteristics. Sensitivity experiments reveal exclusively caused artificially large values gravity wave drag, resulting combined use anomaly method along with unique inclusion orography linearly interpolates timesteps reconstruction. Palaeoclimate modelling groups should therefore carefully check effects their terms palaeoclimate prescribed topographic evolution.