The Role of Latent Heating Anomalies in Exciting the Summertime Eurasian Circulation Trend Pattern and High Surface Temperature

Abstract

Dynamical mechanisms for the summer Eurasian circulation trend pattern are investigated by analyzing reanalysis data and conducting numerical model simulations. The daily circulations that resemble the Eurasian circulation trend pattern are identified and categorized into two groups based on surface warming signal over central and eastern Europe. In the group with large warm anomaly, the upper-level circulation takes on a wave packet form over Eurasia, and there are enhanced latent heating anomalies centered over the North Sea and suppressed latent heating anomalies over the Caspian Sea. The numerical model calculations indicate that these latent heating anomalies can excite an upper-level circulation response that resembles the Eurasian circulation trend pattern. Additional analysis indicates that trends of these two latent heating centers contribute to the long-term circulation trend. In the weak warm anomaly group, the circulation pattern takes on a circumglobal teleconnection (CGT) pattern, and there is no heating signal that reinforces the circulation. These results indicate that not all CGT-like patterns excite temperature anomalies that are persistent and in phase with the trend pattern, and that quasi-stationary forcings, such as the latent heating anomalies, play an important role in driving the boreal summer circulation anomaly that accompanies the strong and persistent surface temperature signal.