The springtime western Pacific pattern: its formation and maintenance mechanisms and climate impacts

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  • 1 Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing, China
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Abstract

Based on daily data from the Japanese 55-year Reanalysis (JRA-55) covering the springs from 1958 to 2018, this study examines the formation mechanisms and climate impacts of springtime western Pacific (WP) pattern as subseasonal climate variability over North Pacific. Results suggest that the springtime WP pattern arises from a weak dipole-like disturbance over North Pacific and disturbances over East Asia. The energetic analysis suggests that the baroclinic energy conversion acts as an important energy source to balance the available potential energy loss caused by transient eddies and diabatic heating and acts as a kinetic energy (KE) source for the WP pattern. For the feedback forcing by total transient eddies, it acts as a major KE source for the WP pattern before day 0 and acts as a strong KE sink after day 0. It turns out that the barotropic energy conversion makes only weak KE contribution to the WP pattern.

Once the WP pattern forms, East Asia and North America experience strong surface air temperature anomalies of opposite signs, while strong sea surface temperature anomalies are found to occur over mid-latitude and tropical North Pacific at the same time. Concurrently, the Pacific jet and the storm track shift north-southward around their climatological position. In addition, a dipole-like shallow convective anomaly appears over mid-latitude North Pacific, and a band of anomalous deep convection tends to occur in the tropics as the energy of the WP pattern propagates into the region.

Corresponding author address: Benkui Tan, Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Yiheyuan Road 5, Beijing 100871, China. E-mail: bktan@pku.edu.cn

Abstract

Based on daily data from the Japanese 55-year Reanalysis (JRA-55) covering the springs from 1958 to 2018, this study examines the formation mechanisms and climate impacts of springtime western Pacific (WP) pattern as subseasonal climate variability over North Pacific. Results suggest that the springtime WP pattern arises from a weak dipole-like disturbance over North Pacific and disturbances over East Asia. The energetic analysis suggests that the baroclinic energy conversion acts as an important energy source to balance the available potential energy loss caused by transient eddies and diabatic heating and acts as a kinetic energy (KE) source for the WP pattern. For the feedback forcing by total transient eddies, it acts as a major KE source for the WP pattern before day 0 and acts as a strong KE sink after day 0. It turns out that the barotropic energy conversion makes only weak KE contribution to the WP pattern.

Once the WP pattern forms, East Asia and North America experience strong surface air temperature anomalies of opposite signs, while strong sea surface temperature anomalies are found to occur over mid-latitude and tropical North Pacific at the same time. Concurrently, the Pacific jet and the storm track shift north-southward around their climatological position. In addition, a dipole-like shallow convective anomaly appears over mid-latitude North Pacific, and a band of anomalous deep convection tends to occur in the tropics as the energy of the WP pattern propagates into the region.

Corresponding author address: Benkui Tan, Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Yiheyuan Road 5, Beijing 100871, China. E-mail: bktan@pku.edu.cn
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