Simulated Synoptic Variability and Storm Tracks Over North America at the Last Glacial Maximu

Transient eddy activity over North America during a simulated Last Glacial Maximum (LGM) is modeled by measuring synoptic variability, Eady growth rate, and comparing daily time series distribution plots of 2-m reference temperatures. The role of transient eddies in the climate, south of the Laurentide Ice Sheet (LIS), is not well understood. Quantifying changes to transient eddy activity will assist future climate modelers who wish to simulate the climate of an ice sheet terminating in a continental interior at the mid-latitudes. A band pass temporal filter is used to isolate synoptic scale variability in a simulated LGM climate using the Geophysical Fluid Dynamics Laboratory (GFDL) coupled atmospheric-ocean general circulation model CM2.1 for both January and July. LGM climate is simulated using orbital parameters, greenhouse gas concentrations, and sea level values set to 21,000 years before present and the ICE-5G ice sheet reconstruction used as climate forcings. A control run used pre-industrial (PI) values for comparison. Maximum Eady growth rate is used to quantify baroclinic wave growth of transient eddies. Transient eddy activity is suppressed over LIS in January. Increased activity is concentrated along the coastline of the Gulf of Mexico and the east coast of North America. In July, this increased transient eddy activity is found over the unglaciated landmass south of the ice sheet where it is less prevalent in the control run. Frequency distributions of daily 2-m reference temperatures depict warming events south of the ice that are likely associated with transient eddies in both January and July. In July, there is a notable increase of these events compared to PI.