平流层爆发性增温期间行星波的活动

利用逐日的NCEP再分析资料分析了1978～2004年期间发生的18次强爆发性增温时平流层中下层行星波1波和2波的异常以及极涡崩溃的形式.分析表明, 爆发性增温前期1波都异常增幅, 波振幅达到峰值之后的一段时间内发生爆发性增温, 然而在增温过程中行星波2波的变化却有明显不同, 可分为三种情况: (1) 在增温前期, 行星波2波很弱; 在增温期间, 行星波2波异常发展, 伴随着极涡崩溃的形式是由偏心型向偶极型过渡. (2) 在增温前期, 行星波2波较强; 在增温期间, 行星波2波明显减弱, 极涡的变化形式是远离极地, 在极地外围活动, 但不发生分裂.(3) 在增温前期, 行星波2波不太强; 在增温期间, 行星波2波有所发展, 但始终强不过1波, 极涡的变化是先偏离极地, 然后发生不对称的变形.作者还计算和分析了EP通量及其散度, 利用波流相互作用理论对这三种行星波的异常变化及其与爆发性增温的关系进行解释.

Planetary Wave Activity During Stratospheric Sudden Warming

In order to investigate the characteristics of planetary wave activity during stratospheric sudden warming(SSW),the abnormality of planetary waves of wave number 1 and wave number 2 in the mid-lower stratosphere in 18 major SSW events during 1979-2004 is analyzed using the daily averaged NCEP data,and the distortion and the breakdown of polar vortex of the 18 major SSW events have also been studied.Then the EP flux and its divergence are calculated and analyzed to explain the activities of planetary wave and their relation with SSW.The results show that the planetary wave of wave number 1 unusually grows in the pre-SSW period,and SSW takes place after the peak amplitude of wave number 1,which agrees with Labitzke's conclusions(1978,1981),however,the variations of the planetary-wave amplitude in various SSW events are much different,which show in the following three types.For type 1,the planetary wave of wave number 2 in the pre-SSW period is very weak,it unusually grows too stronger in the mid-SSW period,while planetary wave of wave number 1 becomes weak,which also accord with Labitzke's conclusions.In this type the polar vortex breaks down and splits into two cyclonic centers;for type 2,the planetary wave of wave number 2 in the pre-SSW period is correspondingly stronger,nevertheless,in the mid-SSW period both planetary waves of wave number 1 and wave number 2 are distinctly weak,at the same time the polar vortex moves outside of the polar region,but does not breakdown;for type 3,planetary wave of wave number 2 in the pre-SSW period is not very strong,while it develops slightly in the mid-SSW period,however,it cannot surpass planetary wave of wave number 1 in any case,simultaneously,the polar vortex firstly moves out from the polar region and then asymmetric split in form occurs.The calculated EP flux and the EP flux divergence show that the distribution of the EP flux for the various type of SSW are much different,therefore the vertical transport of the planetary wave for the various type of SSW are not the same. While in all events the EP flux convergence for the wave number 1 and wave number 2 in the pre-SSW and mid-SSW appears in the stratosphere from middle and high latitude to the polar region,which causes zonal mean westerly wind weakened, even become easterly wind.According to the theory of thermal wind,this means that temperature gradient from middle and high latitude to the polar region reverses its direction,that is to say the temperature suddenly turns high nearby the polar region.