Exploring covariabilities of the high-summer subtropical upper-level pressure systems in the Northern Hemisphere

The Northern Hemisphere subtropical upper -tropospheric pressure systems, i.e., South Asian high (SAH), midPacific Trough (MPT), and mid -Atlantic Trough (MAT), play key roles in regulating the Eurasian-Pacific-North American climate, but their covariabilities and drivers remain unclear. Here, we reveal two seesaw -like teleconnections between MPT and western SAH (WSAH) and between MPT and MAT during the boreal high summer, respectively, and explore their associations with the tropical Pacific and Atlantic sea surface temperature (SST) anomalies. The MPT-WSAH teleconnection, featured by coherent variations between WSAH and MPT, is coupled with enhanced western Pacific subtropical high and Asian mid -latitude low in the low-level troposphere. In contrast, the MPT-MAT teleconnection features an out -of -phase relationship between MPT and MAT, which is associated with westward expanded western Pacific subtropical high but weakened North Atlantic subtropical high. Both two teleconnections are closely linked to Pacific SST anomalies. However, the former is mainly driven by the hybrid La Nina in the tropical Pacific, where cold SST anomalies spreading eastward since preceding winter. Whereas the latter corresponds to the central Pacific La Nina since late -spring mainly driven by preceding successive SST warming in the tropical North Atlantic. Above conclusions are further confirmed by the simulated results from the numerical experiments, which are performed using the US National Center for Atmospheric Research global Community Atmosphere Model version 4.