Abstract
AbstractWe present a study on the long‐term variation of lunar semidiurnal (LSD) tides in the mesosphere and lower thermosphere (MLT). The study is based on a meteor radar chain along ∼120°E meridian, which consists of five stations located at Mohe (MH, 53.5°N, 122.3°E), Beijing (BJ, 40.3°N, 116.2°E), Wuhan (WH, 30.5°N, 114.6°E), Sanya (SY, 18.3°N, 109.6°E), and Ledong (LD, 18.4°N, 109.0°E), respectively. Using the Lomb‐Scargle spectral analysis and least squares fitting method, strong quarter‐annual oscillations in the LSD are found at the three midlatitude stations and their magnitudes are comparable. The LSD magnitudes exhibit clear seasonal and latitudinal differences. The monthly mean magnitudes of LSD reach the maximum in January at all five stations but in other seasons they behave differently at different stations. Besides, the effects of polar vortex weakening (PVW) and quasi‐biennial oscillation (QBO) phases on the LSD are discussed. Based on the 12 PVW events, our study observes that the enhancement of the LSD is not always related to the commencements of PVW events. The enhancements of the LSD during the easterly QBO phase are generally stronger than those enhancements during the westerly QBO phase in the MLT region. The easterly QBO phase could modulate the mesospheric zonal mean zonal winds at low latitudes during the PVWs, which is in favor of amplifying the LSD. Our results suggest that the QBO phase is an important factor in enhancing the LSD in the MLT region during PVW events.
Published Version
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