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The tropical tropopause layer (TTL) acts as a transition layer between the\udtroposphere and the stratosphere over several kilometers, where air has both\udtropospheric and stratospheric properties. Within this region, a fine-scale\udfeature is located: the tropopause inversion layer (TIL), which consists of a\udsharp temperature inversion at the tropopause and the corresponding high\udstatic stability values right above, which theoretically affect the\uddispersion relations of atmospheric waves like Rossby or inertia–gravity\udwaves and hamper stratosphere–troposphere exchange (STE). Therefore, the TIL\udreceives increasing attention from the scientific community, mainly in the\udextratropics so far. Our goal is to give a detailed picture of the\udproperties, variability and forcings of the tropical TIL, with special\udemphasis on small-scale equatorial waves and the quasi-biennial oscillation\ud(QBO).  We use high-resolution temperature profiles from the COSMIC satellite\udmission, i.e., ∼ 2000 measurements per day globally, between 2007 and\ud2013, to derive TIL properties and to study the fine-scale structures of\udstatic stability in the tropics. The situation at near tropopause level is\uddescribed by the 100 hPa horizontal wind divergence fields, and the vertical\udstructure of the QBO is provided by the equatorial winds at all levels, both\udfrom the ERA-Interim reanalysis.  We describe a new feature of the equatorial static stability profile: a\udsecondary stability maximum below the zero wind line within the easterly QBO\udwind regime at about 20–25 km altitude, which is forced by the descending\udwesterly QBO phase and gives a double-TIL-like structure. In the lowermost\udstratosphere, the TIL is stronger with westerly winds. We provide the first\udevidence of a relationship between the tropical TIL strength and\udnear-tropopause divergence, with stronger (weaker) TIL with near-tropopause\uddivergent (convergent) flow, a relationship analogous to that of TIL strength\udwith relative vorticity in the extratropics.  To elucidate possible enhancing mechanisms of the tropical TIL, we quantify\udthe signature of the different equatorial waves on the vertical structure of\udstatic stability in the tropics. All waves show, on average, maximum cold\udanomalies at the thermal tropopause, warm anomalies above and a net TIL\udenhancement close to the tropopause. The main drivers are Kelvin,\udinertia–gravity and Rossby waves. We suggest that a similar wave modulation\udwill exist at mid- and polar latitudes from the extratropical wave modes

The tropical tropopause inversion layer: variability and modulation by equatorial waves