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

摘要

TLarge-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.摘要本文通过数值模拟，研究了有无东亚地形存在时，落基山地形作用对冬季北半球副热带西风急流的影响，分析了东亚大地形对落基山地形的调制作用。结果表明，东亚地形的存在能够完全抑制落基山地形对太平洋副热带急流的加强作用，使得落基山地形作用仅能加强其下游的大西洋副热带急流。主要原因是东亚大地形可抑制落基山地形北侧反气旋环流的发展，进而抑制中纬度太平洋地区经向温度梯度的加强。该结果有助于我们进一步理解北半球大地形强迫作用，及其相互调制作用对对流层天气和环流结构的影响。