9:30 AM - 9:45 AM
[ACG32-03] Changes in the North Pacific Stationary-Transient Wave Interference and Downstream Regional Impacts on Subseasonal-to-Seasonal Timescale
Keywords:Atmospheric teleconnection, Stationary wave, Surface climate extremes, Tropical convection, Regional climate variability
Wave interference between transient eddies and climatological stationary eddies is a key physical process that modulates atmospheric heat and moisture transport by changing the extratropical large-scale circulation. The amplitude of wave interference becomes the largest during boreal winter when extratropical stationary waves and the associated zonally asymmetric forcing are strongest. Recent studies showed that the global wave interference in the wintertime can be driven by anomalous tropical and extratropical diabatic heating, which results in Arctic warming through enhanced poleward moisture and heat transport. In this study, we focus on the wave interference over the North Pacific Ocean where interference occurs most vigorously and is characterized by a quadrupole pattern of upper-level circulation anomalies. Through the analysis of observational data and simulations from the Seamless System for Prediction and Earth System Research (SPEAR), a coupled global climate model developed at the Geophysical Fluid Dynamics Laboratory, we address how such regional wave interference impacts climate extremes over North America in the current climate and how these downstream impacts will change in future projections.
In the observational analysis, it is found that transient eddies preceding the North Pacific wave interference are developed by the tropical Pacific warm-pool convection and a Eurasian wave train. During constructive interference days, circulation anomalies are centered over the Gulf of Alaska and eastern North America, which promotes the advection of warm, moist air into the Arctic Ocean and cold, dry air into central North America. As a result, the west coast of the United States undergoes a significant decrease of precipitation, while cold temperature anomalies are developed and sustained over central and eastern North America. The opposite features are found during destructive interference days. By employing percentile thresholds to define precipitation and temperature extremes, we further showed that the probabilities of those regional climate extremes are also significantly regulated by the occurrence of the North Pacific wave interference.
Results from the SPEAR model output showed that both the structure of climatological stationary eddies and the observed features of the North Pacific wave interference are well reproduced in model historical simulations. From future projection, climatological stationary waves over the eastern North Pacific become weaker than those in historical simulations, in accordance with an eastward shift of the localized tropical convection that affects the North Pacific wave interference. Due to this structural change of climatological stationary waves in the late 21st century, North American climate extremes driven by the North Pacific wave interference occurs less frequently and shifts eastward. The eastward displacement of downstream impact is similarly found on the seasonal timescale. Our results indicate that the prediction of changes in structure of climatological stationary eddies and the regional wave interference is pivotal for understanding the future regional climate variability.
In the observational analysis, it is found that transient eddies preceding the North Pacific wave interference are developed by the tropical Pacific warm-pool convection and a Eurasian wave train. During constructive interference days, circulation anomalies are centered over the Gulf of Alaska and eastern North America, which promotes the advection of warm, moist air into the Arctic Ocean and cold, dry air into central North America. As a result, the west coast of the United States undergoes a significant decrease of precipitation, while cold temperature anomalies are developed and sustained over central and eastern North America. The opposite features are found during destructive interference days. By employing percentile thresholds to define precipitation and temperature extremes, we further showed that the probabilities of those regional climate extremes are also significantly regulated by the occurrence of the North Pacific wave interference.
Results from the SPEAR model output showed that both the structure of climatological stationary eddies and the observed features of the North Pacific wave interference are well reproduced in model historical simulations. From future projection, climatological stationary waves over the eastern North Pacific become weaker than those in historical simulations, in accordance with an eastward shift of the localized tropical convection that affects the North Pacific wave interference. Due to this structural change of climatological stationary waves in the late 21st century, North American climate extremes driven by the North Pacific wave interference occurs less frequently and shifts eastward. The eastward displacement of downstream impact is similarly found on the seasonal timescale. Our results indicate that the prediction of changes in structure of climatological stationary eddies and the regional wave interference is pivotal for understanding the future regional climate variability.