Subseasonal and Interannual Temperature Variability in Relation to Extreme Temperature Occurrence over East Asia

Abstract

his study investigates interannual variability in the frequency of occurrence of daily surface air temperature (SAT) extremes over East Asia in summer and winter between 1979 and 2009. In particular, this study examines the dominant seasonal SAT patterns, as obtained through empirical orthogonal function (EOF) analysis, and the associated variability in SAT extreme occurrence. Overall, the authors find that changes in extreme temperature occurrence associated with these dominant patterns are impacted by both shifts and narrowing/broadening of the subseasonal SAT probability distribution functions (PDFs). In summer, the leading pattern features large SAT anomalies in midlatitude East Asia centered over Mongolia. Over this center of action, positive SAT anomalies are accompanied by decreased precipitation and soil moisture, which increases the ratio of sensible to latent heat flux. Consequently, subseasonal SAT variance increases, resulting in an enhanced occurrence of positive SAT extremes relative to a simple SAT PDF shift. In winter, the leading pattern, which is highly correlated with the Arctic Oscillation, features large loadings in high-latitude Siberia that decay southward. In contrast with summer, large-scale dynamics play a larger role in the leading pattern: positive SAT anomalies are accompanied by a weakened and northward-shifted storm track, reduced subseasonal SAT variance, and a more pronounced decrease of cold extreme occurrence relative to a simple PDF shift. Finally, a brief look at the secular trends suggests that both shifts and narrowing/broadening of the PDF may also impact long-term trends in SAT extreme occurrence over some regions of East Asia.