Boreal lakes moderate seasonal and diurnal temperature variation and perturb atmospheric circulation: analyses in the Community Earth System Model 1 (CESM1)

摘要

We used a lake thermal physics model recently coupled into the Community Earth System Model 1 (CESM1)to study the effects of lake distribution in present and future climate. Under present climate, correcting thelarge underestimation of lake area in CESM1 (denoted CCSM4 in the configuration used here) caused 1℃spring decreases and fall increases in surface air temperature throughout large areas of Canada and the US.Simulated summer surface diurnal air temperature range decreased by up to 4℃, reducing CCSM4 biases.These changes were much larger than those resulting from prescribed lake disappearance in some present-daypermafrost regions under doubled-CO_2 conditions. Correcting the underestimation of lake area in presentclimate caused widespread high-latitude summer cooling at 850 hPa. Significant remote changes includeddecreases in the strength of fall Southern Ocean westerlies. We found significantly different winter responseswhen separately analysing 45-yr subperiods, indicating that relatively long simulations are required to discernthe impacts of surface changes on remote conditions. We also investigated the surface forcing of lakes usingidealised aqua-planet experiments which showed that surface changes of 2℃ in the Northern Hemisphereextra-tropics could cause substantial changes in precipitation and winds in the tropics and SouthernHemisphere. Shifts in the Inter-Tropical Convergence Zone were opposite in sign to those predicted by someprevious studies. Zonal mean circulation changes were consistent in character but much larger than thoseoccurring in the lake distribution experiments, due to the larger magnitude and more uniform surface forcingin the idealised aqua-planet experiments.