Article ID: 2025-017
The Japanese Reanalysis for Three Quarters of a Century (JRA-3Q) with top at 0.01 hPa (high-top) is investigated focusing on the semiannual oscillation (SAO) in the tropical middle atmosphere, together with the other high-top reanalyses, ERA5 and MERRA-2, and the MLS and SABER satellite data. By removing the annual component and using the SAO component alone in the SABER data spanning the recent two decades, the seasonal cycle of the mesospheric SAO (MSAO) at 0.01 hPa is found to have significantly larger first cycle than the second cycle in a year with the largest easterly wind in boreal spring. The seasonal cycle of the stratospheric SAO (SSAO) at 1 hPa shows commonly in both satellite data that the easterly wind amplitude in boreal winter is double as large as that in boreal summer, while the westerly wind amplitudes in boreal spring and autumn are nearly the same. The two satellite data exhibit that the MSAO amplitude has significant and negative trend, about −5 and −7 m s−1 decade−1 at 0.01 hPa in MLS and SABER, respectively. JRA-3Q reproduces well the seasonal cycle of the SAO, i.e., the calendar-locked downward propagation of the SAO from 0.01 hPa to 10 hPa with clear separation between the MSAO and SSAO, despite the MSAO being substantially underestimated compared to the satellite observations. The SSAO amplitude at 1 hPa is significantly increasing in JRA-3Q over about three decades from 1970s to 2000s, and it exhibits slight decreasing trend over the recent two decades from 2000s. Before 1970s the SSAO wavelet spectra are less concentrated around 6 months and the wavelet spectra around the annual component are significantly larger than those after 1970s in JRA-3Q and ERA5. None of the reanalyses show any hint of the MSAO significant and negative trend at 0.01 hPa.
