277 / 2024-09-13 11:37:20

Impacts of PV- Circulation Crossing the Boundaries of Northern Troposphere on Climate Variability and Extreme Weather

PV substance (PVS), PV circulation (PVC), crossing boundary PVC, East Asian summer monsoon, winter cold-air outbreak and snow storm

The source of potential vorticity (PV) substance (PVS) of the atmosphere is at the earth’s surface, whereas the PVS variation within a limited region depends on the sum of the effective PV flux crossing the boundary surface surrounding the region. Because the PV circulation (PVC) is the time- integral of effective PV flux, the monthly mean gross PVS in the troposphere of Northern Hemisphere (NH) is determined by the sum of PVC penetrating the enveloped three boundaries: the PVC cross- the equatorial vertical section (CEPVC), the tropopause (CUPVC), and the earth’s surface (CBPVC). Because the CBPVC is associated with surface potential temperature and circulation, for an equilibrium gross PVS in the hemisphere, the change in CEPVC or/and CUPVC can induce the climate change near the surface and extreme weathers through the adjustment of the atmospheric internal PVC changes.

Data diagnoses demonstrate that the wind- shear related PVC penetrates the tropopause downward over the NH high latitudes, travels southward in general to the Southern Hemisphere (SH), penetrates the tropopause upward over the SH high latitudes, and travels northward back to the northern stratosphere. In spring, the CEPVC associated with tropical El Nino- like SST anomaly can induce cold anomaly over the Eurasia in mid-high latitudes. In July, the interannual change in CBPVC on the Tibetan Plateau can lead to precipitation anomaly in the downstream area along the Meiyu front; whereas the combination effects of the CEPVC and CUPVC can result in a meridional seesaw of precipitation over the East Asian summer monsoon area. Case study indicates that in winter, the abnormal convergence of the CUPVC along the upper tropospheric front where the meridional gradient of PVS is maximized can trigger extreme cold-air outbreak and heavy snow storm.