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. This paper reports on a project to compare the representation of the semiannual oscillation (SAO)in the equatorial stratosphere and lower mesosphere within six major global atmospheric reanalysisdatasets and with recent satellite Sounding of the Atmosphere Using Broadband Emission Radiometry (SABER) and Microwave Limb Sounder (MLS) observations. All reanalyses have a goodrepresentation of the quasi-biennial oscillation (QBO) in the equatorial lower and middlestratosphere and each displays a clear SAO centered near the stratopause. However, the differencesamong reanalyses are much more substantial in the SAO region than in the QBO-dominated region. Thedegree of disagreement among the reanalyses is characterized by the standard deviation (SD) of themonthly mean zonal wind and temperature; this depends on latitude, longitude, height, andtime. The zonal wind SD displays a prominent equatorial maximum that increases with height, whilethe temperature SD reaches a minimum near the Equator and is largest in the polar regions. Along the Equator,the zonal wind SD is smallest around the longitude of Singapore, where consistently high-qualitynear-equatorial radiosonde observations are available. Interestingly, the near-Singapore minimumin SD is evident to at least ∼3 hPa, i.e., considerably higher than the usual∼10 hPa ceiling for in situ radiosonde observations. Our measurement of theagreement among the reanalyses shows systematic improvement over the period considered(1980–2016), up to near the stratopause. Characteristics of the SAO at 1 hPa, such as itsdetailed time variation and the displacement off the Equator of the zonal wind SAO amplitudemaximum, differ significantly among the reanalyses. Disagreement among the reanalyses becomesstill greater above 1 hPa. One of the reanalyses in our study also has a version producedwithout assimilating satellite observations, and a comparison of the SAO in these two versionsdemonstrates the very great importance of satellite-derived temperatures in the realistic analysisof the tropical upper stratospheric circulation.

Representation of the equatorial stratopause semiannual oscillation in global atmospheric reanalyses