Development of Pre-Tropical Cyclone Disturbances over Western North Pacific:A Case Study

• 作 者: 段晶晶 吴立广
• 机 构: 南京信息工程大学,南京210044
• 出 处: 第30届中国气象学会年会
• 发表日期: 2013年6期
• 关键词: Pre-TC Disturbance MRG wave barotropic conversion

　　This study addresses the development of the pre-tropical cyclone (pre-TC) disturbances that occur in the western North Pacific (WNP) for the period 11 August to 10 September in 2004.Typhoon Megi,Chaba,Aere and Songda generate in the MT eastward extension period during the 31 days of before half time,while Sarika generates during subsequent suppressed phase.TC genesis is all accompanied by pre-TC disturbance.Megi,Aere,Songda and Sarika generate in the cyclonic region of the wave train.When the pre-TC disturbance is detected in the easternmost location of the MT,cyclonic circulation can couple with the MRG wave anticlockwise circulation.Meanwhile,the MRG wave anticlockwise circulation associated with pre-TC disturbance for Megi and Aere develop a clearly southwest-northeast tilt.The pre-TC disturbance for Songda and Sarika also first appears around the far eastern end of the MT,but the MRG wave northeast-southwest titled anticlockwise circulation is not obvious.The synoptic-scale disturbance for typhoon Chaba forms in a region where circulation of the MRG wave is clockwise and convection is inactive.From the energy budget we can see that when the pre-TC disturbance at the far eastern end of the MT,energy accumulation is a promising contributor for the initial pre-TC disturbance growth.As the disturbances move northwestward entering the monsoon shear region,the term due mainly to the southwest-northeast tilt of the disturbances and the background zonal wind shear increases obviously.The barotropic conversion mechanism may be the main reason for the synoptic-scale disturbances developing into typhoons.It is worth noting that in the initial stage,the synoptic-scale disturbance for Sarika also obtains energy from the background circulation.Afterwards,the term related to the eddy circulation nonlinear effect play an important role for the development of this disturbance.