Abstract
The eastward- and westward-traveling 10-day waves with zonal wavenumbers up to 6 from surface to the middle mesosphere during the recent 12 years from 2007 to 2018 are deduced from MERRA-2 data. On the basis of climatology study, the westward-propagating wave with zonal wave number 1 (W1) and eastward-propagating waves with zonal wave numbers 1 (E1) and 2 (E2) are identified as the dominant traveling ones. They are all active at mid- and high-latitudes above the troposphere and display notable month-to-month variations. The W1 and E2 waves are strong in the NH from December to March and in the SH from June to October, respectively, while the E1 wave is active in the SH from August to October and also in the NH from December to February. Further case study on E1 and E2 waves shows that their latitude–altitude structures are dependent on the transmission condition of the background atmosphere. The presence of these two waves in the stratosphere and mesosphere might have originated from the downward-propagating wave excited in the mesosphere by the mean flow instability, the upward-propagating wave from the troposphere, and/or in situ excited wave in the stratosphere. The two eastward waves can exert strong zonal forcing on the mean flow in the stratosphere and mesosphere in specific periods. Compared with E2 wave, the dramatic forcing from the E1 waves is located in the poleward regions.
Highlights
We report global characteristics of 10-day waves with various zonal wavenumbers presented in the MERRA-2 data during the recent 12 years from 2007 to 2018
In order to check the reliability of the 10-day wave results deduced from MERRA-2 data, we present the latitude versus altitude structures of the 10-day wave amplitude in temperature at latitudes between 50° S and 50° N in Fig. 1, and provide detailed comparisons with the results from Forbes and Zhang (2015)
Summary and discussion A least-squares harmonic fitting procedure is applied to extract the 10-day waves with zonal wavenumbers varying from -6 to 6 in the recent 12 years from 2007 to 2018
Summary
Planetary waves (PWs) are oscillations of very predominantly tropospheric origin with typical periods of about 2–30 days in the troposphere and lower stratosphere (TLS), the mesosphere and lower thermosphere (MLT), as well as the ionosphere (Vincent 1990; Forbes et al 1995; Hirooka 2000; Riggin et al 2006; McDonald et al 2011; Yue et al 2012; Moudden and Forbes 2014; Forbes and Zhang 2015; Pancheva et al 2016). The large amplitude occurrence rates of the 13 waves for the zonal wind, meridional wind, and temperature are presented in the top row of Fig. 2.
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