Apparent vertical propagation of the NAM index due to an embedded wave structure

作者：Kodera Kunihiko^*; Coughlin Katie

来源：Journal of the Meteorological Society of Japan, 2007, 85(6): 927-931.

DOI：10.2151/jmsj.85.927

The leading empirical orthogonal EOF) of the geopotential height is called the Northern Annular Mode (NAM). Stratosphere-troposphere connections seen in the multilevel NAM signal are often considered as due to a propagation of the annular structure. However, the tropospheric leading EOF contains not just an annular structure, but also a wave structure. This indicates that the NAM index is sensitive to changes in wave activity.
A previous study showed that an apparent downward propagation of the NAM index can appear as a result of a reflection of wave 1 due to a stratospheric sudden warming. If this result is correct, we may also expect to find a reverse case. Here we show a case when an amplification of a tropospheric wave I leads to a stratospheric warming, an apparent upward propagation of the "Annular" mode signal, i.e., change in the amplitude of the NAM index appears due to a projection on the wave component of the tropospheric NAM.

• 出版日期2007-12
• 单位中国气象科学研究院