Unexpectedly high concentrations of ultrafine particles were observed over a wide range of latitudes in the upper troposphere and lower stratosphere. Particle number concentrations and size distributions simulated by a numerical model of ion-induced nucleation, constrained by measured thermodynamic data and observed atmospheric key species, were consistent with the observations. These findings indicate that, at typical upper troposphere and lower stratosphere conditions, particles are formed by this nucleation process and grow to measurable sizes with sufficient sun exposure and low preexisting aerosol surface area. Ion-induced nucleation is thus a globally important source of aerosol particles, potentially affecting cloud formation and radiative transfer.

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The quasi‐biennial oscillation (QBO) is a tropical lower stratospheric, downward propagating zonal wind variation, with an average period of ~28 months. The QBO has been constantly documented since 1953. Here we describe the evolution of the QBO during the Northern Hemisphere winter of 2015–2016 using radiosonde observations and meteorological reanalyses. Normally, the QBO would show a steady downward propagation of the westerly phase. In 2015–2016, there was an anomalous upward displacement of this westerly phase from ~30 hPa to 15 hPa. These westerlies impinge on or “cutoff” the normal downward propagation of the easterly phase. In addition, easterly winds develop at 40 hPa. Comparisons to tropical wind statistics for the 1953 to present record demonstrate that this 2015–2016 QBO disruption is unprecedented.