Northern Hemisphere summer temperature and specific humidity anomalies from two reanalyses

Abstract

This study investigates the magnitude and spatial extent of extreme summer temperature and specific humidity events in the extratropical northern hemisphere (NHEXT) using the NCEP Reanalysis (1979-2012) and the 20 th century reanalysis (1871-2010). Specifically, we look at the percentage of area exceeding standard deviation thresholds in layer-averaged (500 mb-1000 mb) temperature and surface-level specific humidity to classify extremes. We find that: (1) areas of the NHEXT, including the southwestern tip of Greenland, experienced a summer heat wave during 2012 that was almost as extreme in spatial extent and magnitude as the Russian heat wave of 2010, (2) there is an increasing trend in summer heat waves and positive specific humidity anomalies and a decreasing trend in summer cold waves and negative specific humidity anomalies, and (3) while similar patterns in the global trend (1979-2012) in variability exist for both temperature and specific humidity, areas of increased variability are not necessarily the areas that have experienced extreme heat waves. Key Points A summer 2012 heat wave near Greenland rivaled the extremity of Russia 2010 The magnitude and spatial extent of extreme heat waves has increased since 1979 Heat waves are not occurring in areas of increased variability since 1979 ©2013. American Geophysical Union. All Rights Reserved.