热带大气季节内振荡与对西北太平洋台风生成数的影响研究

MODULATION OF TYPHOON GENESIS OVER THE WESTERN NORTH PACIFIC BY INTRASEASONAL OSCILLATION

用典型年合成方法分析研究了1979—2006年西北太平洋多台风年和少台风年热带大气ISO的影响。结果表明,热带大气ISO对西北太平洋台风的生成具有明显的调节作用。多台风年,菲律宾以西地区大气季节内振荡较弱,东传不明显;菲律宾以东地区积云对流较强,热带大气30～60 d低频振荡也偏强,与台风生成相关的传播特征为源自赤道140～160°E附近季节内振荡的西北方向传播。这种异常的30～60 d低频振荡对周围大气环流有正反馈的作用,从而导致积云对流的进一步加强,这种强的积云对流会引起赤道西风异常,产生异常Walker环流,在菲律宾附近形成风场的低层辐合、高层辐散,增强那里的上升气流,有利于台风生成。少台风年,菲律宾以西地区低频活动较强,东传明显,菲律宾以东的低频活动较弱。这种西强东弱的低频活动形式,使得大气低层在菲律宾以西地区为低频东风异常,菲律宾以东地区为低频西风异常,导致在菲律宾以东的西北太平洋大气产生低层低频风辐散、高层辐合的形势,增强下沉运动,不利于台风的生成。

The intraseasonal oscillation（ISO） is studied for the years of less or more typhoon genesis from 1979 to 2006.It is indicated that the ISO strongly affects the typhoon genesis.In the years of more typhoon genesis,the ISO was weak in the area to the west of the Philippines;at the same time,the ISO was strong in the area to the east of it,with significant northwestward propagation.In this situation,the Walker cell seemed to shift gradually westward from the tropical western Pacific to the tropical eastern Indian Ocean,and then convergent winds appeared in the lower atmosphere while divergent winds in the upper atmosphere,suggesting the presence of enhanced ascending flow in favor of typhoon genesis.Moreover,in the years of less typhoon genesis,the ISO gradually became stronger with a significant eastward propagation from the eastern Indian Ocean to the area around 120 °E.During these years,the Walker circulation gradually moved eastward,and then the divergent winds in the upper and lower atmosphere were not favorable for the typhoon genesis in the Western North Pacific.