Intraseasonal variation of the black carbon aerosol concentration and its impact on atmospheric circulation over the southeastern Tibetan Plateau

Abstract

The black carbon (BC) concentration over the southeastern Tibetan Plateau is modulated by atmospheric intraseasonal variations and in turn affects atmospheric circulation through both direct radiative atmospheric warming and surface cooling. Based on an intraseasonal dry‐wet phase transition over the southeastern Tibetan Plateau, we investigated the short‐term radiative‐dynamic coupling of the atmosphere with changes in the concentration of BC using both observations and numerical sensitivity experiments. The observed local concentrations of BC increased by >50% as a result of the enhanced convergence and upward migration associated with the development of an intraseasonal anomalous lower‐level cyclone. Calculations using an offline radiation transfer model showed that this increase in BC concentration led to ~4 W/m2 of atmospheric radiative warming and ~2 W/m2 of surface radiative cooling. Consequently, an anomalous lower‐level cyclone with an average wind speed of 0.5 m/s (~10% of the natural change from a dry to a wet phase) developed in a linear baroclinic model and an aerosol‐aware WRF model, which was mainly a result of the atmospheric warming while the surface cooling played only a minor role. Although the change in precipitation was small, cloud fraction was significantly increased due to the enhanced upward motion in the atmosphere. This warrants further studies of cloud adjustments to the BC concentration on both cloud fraction and microphysics aspects. The present study illustrates that consideration of aerosol‐circulation coupling is imperative to advance the subseasonal prediction of atmospheric circulation.

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