Influence and Mechanism of Indian Ocean Basin Model on the Asymmetry of Pacific Subtropical High in the Northern and Southern Hemispheres

Abstract

Subtropical anticyclone has an important influence in weather and climate in China， which is affected by the tropical sea surface temperature （SST） anomaly in the Indian Ocean for its formation.However， there is limited studies for the corresponding influence mechanism.In order to probe impact as well as the mechanism of the SST anomaly over the Indian Ocean on the subtropical high， the El Nino-Southern Oscillation （ENSO） signal is filtered out.By using the reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research （NCEP/NACR） from 1980 to 2020， this study tries to explore the influence and mechanism of the Indian Ocean basin model （IOBM） on subtropical high in the Pacific Ocean through dynamical diagnose in perspective of energy， and verifies the results by numerical model simulation by the Geophysical Fluid Dynamics Laboratory Atmospheric Model （GFDL AM2.1）.The results show that eastern-spreading of the Kelvin wave is motivated by the SST anomaly in the Indian Ocean in summer.Meanwhile， low-level anticyclone anomaly appears in the northwest Pacific Ocean， resulting in the subtropical anticyclone is stronger than the climatological mean.Thus， the precipitation is less in regions from the South China Sea to Eastern Philippines.In winter， during the positive phase of the IOBM， the east wind anomalies are stimulated in Australia， resulting in large-area negative anomalies of precipitation occurred over the western Pacific.Non-uniform distribution of precipitation is caused by the asymmetry in circulation of subtropical high over the Pacific Ocean in the northern and southern hemispheres.Result by the dynamical diagnose reveals that when the phase of IOBM is positive， the wind field convergence zone is superposed by the disturbance energy growth area， whereas in winter such two regions do not cooperate with each other.As a result， the subtropical high is abnormally strong in the northwestern Pacific in summer and with indistinct abnormally in Australia in winter.The numerical simulation verifies that the asymmetry of anticyclonic circulation and precipitation anomalies are closely related to the symmetrical SST anomaly in Indian Ocean along the equator， both in its position and intensity.The result of model simulation demonstrates the reliability of the conclusions of synthesis analysis and energy diagnosis.Thus， the IOBM plays a significant role on the symmetrical structure of the Western Pacific subtropical high in northern and southern hemispheres， as well as in the precipitation in East Asia and Australia regions， which provides a theoretical basis for formation mechanism of the asymmetry of the Pacific subtropical high in the southern and northern hemisphere during the warming of the entire Indian Ocean basin.

Keywords

• indian ocean basin model
• northwest pacific subtropical high
• kelvin wave
• precipitation anomaly in china