Large and local-scale features associated with heat waves in the United States in reanalysis products and the NARCCAP model ensemble

This study investigates the role of large-scale and local-scale processes associated with heat waves using two reanalysis products, and evaluates the performance of the regional climate model ensemble used in the North America Regional Climate Change Program (NARCCAP) in reproducing these processes. The Continental US is divided into eight different climate divisions to investigate different mechanisms associated with heat waves. At the large scale, heat waves are associated with terrestrial warm air advection to the Northeast, Midwest and Northern Great Plains, and with oceanic warm air advection for the Southeast and Southern Great Plains. Over the western US, reduced maritime cool air advection results in local warming. At the local scale, antecedent precipitation deficits lead to the continuous drying of soil, more net radiative energy is partitioned into sensible heat flux and acts to warm surface air temperature, especially over the Great Plains. NARCCAP-simulated large-scale meteorological patterns and temporal evolution of antecedent local scale terrestrial conditions are shown to be very similar to those of the reanalysis products. Even though extreme temperature is overestimated by the NARCCAP ensemble over the US, different heat wave metrics are realistically represented both in terms of the inter-annual variability and spatial representation. However, NARCCAP overestimates the magnitude of heatwaves over the Northeast, Midwest and Northern Great Plains, partially due to anomalous heat advection through large-scale forcing.