Dynamical role of the Rocky Mountain controlled by East Asian topographies in modulating the tropospheric westerly jet in northern winter

Abstract

Large-scale mountains like Asian topographies and the Rocky Mountains have important influences on subtropical jet streams (STJs) over downstream regions in winter. The dynamical role of the Rocky Mountains in modulating STJs with and without the existence of East Asian (EA) topographies in northern winter is investigated via numerical experiments. In agreement with previous studies, the Rocky Mountains (topographic forcing), with the existence of EA topographies, can only strengthen the STJ from the east coast of North America to the western Atlantic region. The independent role of the Rocky Mountains, however, strengthens the STJ over not only the east coast of North America but also over Pacific regions. It is found that the existence of EA topographies can dramatically strengthen the EA trough, as well as a downstream ridge which, in the upstream of the Rocky Mountains, acts to partly cancel out the strengthening of the anticyclone to the north of the Rocky Mountains and the northward warm air transport in the high latitudes of Pacific regions due to the Rocky Mountains’ forcing alone. Such circulation changes effectively weaken the Rocky Mountains–forced strengthening of the meridional temperature gradient in the midlatitude North Pacific, and thus the STJ there. Therefore, EA topographies are of great importance in modulating the role of the Rocky Mountains as a dynamical forcing of STJ variability.

Keywords

• Rocky Mountains
• East Asian topographies
• topographic forcing
• subtropical jet stream