Observed responses of tides and gravity waves in the MLT region to the Madden-Julian Oscillation

This work analyzed the intraseasonal variability of non-migrating tides DE3 and gravity wave momentum fluxes (GWMF) in the mesosphere and lower thermosphere (MLT) region and discussed the possible connection with the tropospheric MJO. Based on the joint observations of the TIMED-TIDI satellite and the 120°E meridian meteor radar chain, we revealed a significant broad-band intra-seasonal signal in the DE3 amplitude around the equator with a clear seasonal dependence. The intraseasonal variability of DE3 in zonal winds (DE3-U) has a strong amplitude in boreal winter, up to 1-2 times the seasonal average, while the variability is usually within 20% during other seasons. The response of MLT DE3 tides to the MJO in different seasons was further discussed together with the MJO activity index. The results suggested that the DE3-U in boreal winter generally has a larger amplitude during MJO phases 4–6 (~10%–40%), while the amplitude is smaller for other MJO phases (~−10%–−40%). As for the GWMF estimation, the 12-year continuous observation of the Mohe meteor radar (53.5°N, 122.3°E) was analyzed. The results showed that intraseasonal GWMF variability is also prominent during boreal winter. Composite analysis for DJF season according to MJO phases revealed that the zonal GMWFs notably increased in MJO P4 by ~2–4 m²/s², and a Monte Carlo test was designed to examine the statistical significance. The response in zonal winds differs from the GMWF response by two MJO phases (i.e., 1/2π). Additionally, time-lagged composites revealed the strengthened westward GWMF occurred ~25–35 days after MJO P4, coincident with the MJO impact on the polar vortex as previous works revealed. Overall, this work emphasized that the tropical sources (MJO) impress the intraseasonal signal from the troposphere to the MLT region, either tropics or extratropics.