2:55 PM - 3:10 PM
[AAS06-17] A Statistical Analysis of Downward Propagation of Planetary Wave Packets in the Stratosphere Using Large Ensemble Data
Keywords:planetary wave packet, downward propagation, wave activity flux
Our former analyses (Matsuyama and Hirooka, JpGU Meeting 2019) investigated downward propagation of planetary wave packets from the stratosphere to the troposphere during winter in the Northern Hemisphere and its influence on the tropospheric circulation by the use of JRA-55 reanalysis data over the past 60 years. In the study, we partitioned the longitudinal circle into eight sectors of 45 degrees longitude and set a criterion value for each sector to the vertical component of Plumb’s (1985) wave activity flux (WAFz) at 30 hPa, to show the geographical frequency distribution of the extracted downward propagation events and features of the composited geopotential height distribution during the event occurrence. However, the numbers of the events were not enough for statistical analysis in some longitudinal sectors, for example, in the Western Hemisphere. Hence, we make a statistical analysis of the downward propagation using the large ensemble data, d4PDF (Mizuta et al., 2017). We introduce following two methods to extract strong downward propagation events. The first method is the same as in our former analysis. In this case, similar results are obtained to those based on JRA-55. Moreover, enough numbers of the events are extracted for statistical discussions, because of the large member number in d4PDF, i.e., 100 members. In the second method, a criterion is set for each grid point (2.5°×2.5°); resultantly, more detailed geographical frequency distribution of the events is successfully obtained. Although the overall feature of the geographical distributions of the events obtained by the two methods is similar each other, significant differences are found in the composited geopotential distribution during the event occurrence.