The large-scale summertime wave pattern over the western North Pacific, with a northwest-southeast orientation, is known as a synoptic wave train (SWT). Understanding potential changes in the SWT due to climate change is important, as the SWT can trigger tropical cyclones in the western North Pacific. Dr. Xinyi Zhou and Dr. Tim Li, supported by CPO’s Climate Variability & Predictability (CVP) program, used NCEP-NCAR reanalysis data to study trends in summertime synoptic-scale, or large-scale, wave train (SWT) activity over the western North Pacific since 1950. They found a rising increase in SWT intensity with no changes in structure and propagation characteristics. Changes to dynamic factors, such as vertical motion, alone could not explain the trend, but thermodynamic factors such as sea surface temperature, moisture, and atmospheric instability clearly showed accompanying increasing trends. Zhou and Li propose a synoptic activity index that combines the two factors in order to describe the observed long-term trend of the SWT intensity. Their study is published in the Journal of Metrological Research.