Observations of a Strong Intraseasonal Oscillation in the MLT Region During the 2015/2016 Winter Over Mohe, China

Using meteor radar measurements at Mohe (MH, 53.5 degrees N, 122.3 degrees E) and the reanalysis data from 2011 to 2020, the characteristics of intraseasonal oscillations (ISOs) in the mesosphere and lower thermosphere (MLT) region over MH are investigated for the first time. The radar observation shows a prominent ISO with periods of 40-60 days in the zonal wind during the 2015/2016 winter. The observed ISO is the strongest in the oscillation period of 30-60 days during nearly a decade of observation. The ISO amplitude reaches a maximum of 16 m/s at 90 km. The vertical structure indicates that intraseasonal variabilities in the lower mesosphere contribute to the ISO in the MLT region. By bandpassing the zonal wind obtained from the reanalysis data along 122.5 degrees E at 52 km in the Northern Hemisphere with cutoff periods of 40 and 60 days, we show that ISOs in the tropical and mid-latitude mesosphere are related to each other. Our results also indicate that the tropical mesospheric ISO and the tropospheric Madden-Julian Oscillations (MJO) are highly correlated. Our analysis suggests that the MJO in the equatorial troposphere may contribute to the enhancement of the ISO in the MLT region over MH. Additionally, a very strong El Nino during the 2015/2016 winter was accompanied by the positive Indian Ocean Dipole, which confines the active MJO in phases 2-4 for a long time. This may be the reason that in the oscillation period of 30-60 days, the ISO observed at MH is the strongest during almost a decade of observation.