Seasonality of the QBO Impact on Equatorial Clouds

Abstract

Abstract The Quasi‐Biennial Oscillation (QBO) dominates the interannual variability in the tropical lower stratosphere and is characterized by the descent of alternating easterly and westerly zonal winds. The QBO impact on tropical clouds and convection has received great attention in recent years due to its implications for weather and climate. In this study, a 15‐year record of high vertical resolution cloud observations from CALIPSO and a 50 hPa zonal wind QBO index from ERA5 are used to document the QBO impact on equatorial (10°S–10°N) clouds. Observations from radio occultations, the CERES instrument, and the ERA5 reanalysis are also used to document the QBO impact on temperature, cloud radiative effect (CRE), and zonal wind, respectively. It is shown that the QBO impact on zonal mean equatorial cloud fraction has a strong seasonality. The strongest cloud fraction response to the QBO occurs in boreal spring and early summer, which extends from above the mean tropopause to ∼12.5 km and results in a significant longwave CRE anomaly of 1 W/m 2 . The seasonality of the QBO impact on cloud fraction is synchronized with the QBO impacts on temperature and zonal wind in the tropical upper troposphere. Plain Language Summary Approximately every 2 years, eastward or westward winds in the stratosphere above the equator reverse their direction. This pattern of alternating wind direction is called the Quasi‐Biennial Oscillation (QBO). In this study, we use fine vertical resolution satellite data to examine the QBO impact on clouds, which can be signals of storminess and can impact weather and climate. We find that the QBO impact on equatorial clouds spans a deep vertical extent of the upper troposphere and shows a strong seasonality. These cloud responses imply a significant change in the Earth's radiation budget. We also find that the seasonal variations in QBO‐cloud connections are concurrent with seasonal variation in QBO‐related wind and temperature signals. These changes are most significant during northern hemisphere spring and early summer. Key Points The Quasi‐Biennial Oscillation (QBO) significantly impacts high equatorial clouds during boreal spring and early summer QBO‐related cloud changes result in a statistically significant change in the longwave cloud radiative effect by ∼1 Wm −2 The seasonality of the QBO impact on clouds is synchronized with upper tropospheric intrusions of QBO related temperature and zonal wind