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

Zachary M Subin,Lisa N Murphy,Fuyu Li,Céline Bonfils,William J Riley

doi:10.3402/tellusa.v64i0.15639

Abstract

ABSTRACTWe 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 the large underestimation of lake area in CESM1 (denoted CCSM4 in the configuration used here) caused 1 °C 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 °C, reducing CCSM4 biases. These changes were much larger than those resulting from prescribed lake disappearance in some present-day permafrost regions under doubled-CO2 conditions. Correcting the underestimation of lake area in present climate caused widespread high-latitude summer cooling at 850 hPa. Significant remote changes included decreases in the strength of fall Southern Ocean westerlies. We found significantly different winter responses when separately analysing 45-yr subperiods, indicating that relatively long simulations are required to discern the impacts of surface changes on remote conditions. We also investigated the surface forcing of lakes using idealised aqua-planet experiments which showed that surface changes of 2 °C in the Northern Hemisphere extra-tropics could cause substantial changes in precipitation and winds in the tropics and Southern Hemisphere. Shifts in the Inter-Tropical Convergence Zone were opposite in sign to those predicted by some previous studies. Zonal mean circulation changes were consistent in character but much larger than those occurring in the lake distribution experiments, due to the larger magnitude and more uniform surface forcing in the idealised aqua-planet experiments.

Highlights

Because several studies have investigated the regional effects of changing lake distribution in climate models, but few studies have investigated the remote responses to any type of terrestrial-surface change, we focused on local and remote atmospheric responses, even though local responses may be stronger or more robust
We investigated whether either the mean states or variances of the North Atlantic Oscillation (NAO), Northern Annular Mode (NAM) or El Nino-Southern Oscillation (ENSO) were altered in the coupled experiments
While most Climate Model Intercomparison Project 3 (CMIP3) climate models underestimated diurnal surface air temperature range (DTR) throughout land areas (Randall et al, 2007), we found that CCSM4 overestimated summer DTR in boreal regions (Fig. 6c), including regions where lake area is underestimated (Fig. 1b, c)

Summary

Introduction

Lakes have different surface properties than surrounding land, altering surface fluxes enough to cause significant changes in regional temperature (Krinner, 2003; Dutra et al, 2010; Samuelsson et al, 2010). Temperate and high-latitude lakes tend to be cooler than surrounding land in the spring and summer due to increased seasonal thermal inertia and shifts from sensible to latent heat fluxes (Lofgren, 1997; Krinner, 2003; Rouse et al, 2008; Dutra et al, 2010).

Methods

Results

Discussion

Conclusion