Signature of a Sudden Stratospheric Warming in the near-ground 7Be flux.

Abstract:

We present here a study of the impact of one Sudden Stratospheric Warming (SSW) upon the atmospheric vertical dynamics based on ⁷Be measurements in near ground air, using both numerical and conceptual. In late September 2002, an unprecedented SSW event occurred in the southern hemisphere (SH), causing changes in the tropospheric circulation, ozone depletion and weakening of the polar jet in the mesosphere. There is an observational evidence suggesting that anomalies in the stratosphere play an important role in driving tropospheric weather producing tropospheric changes that can persists for up to 60 days in NH and up to about 90 days in the SH, as observed after the 2002 SSW (Thompson et al., 2005). Radioactive environmental techniques for tracing large-scale air-mass transport have been applied in studies of atmospheric dynamics for decades and they are becoming more and more precise due to the improvement of the instrumental sensitivity and associated modeling. Temporal variations of the cosmogenic ⁷Be concentration in the near-surface atmosphere can provide information on the air mass dynamics, precipitation patterns, stratosphere-troposphere coupling and cosmic ray variations. The present study is based on an analysis of ⁷Be concentration measured in near-ground air in the city of Angra dos Reis, Rio de Janeiro state, Brazil between 1987 and 2009. Using a simplified tropospheric ⁷Be model deposition based on a two-layer transport model, Pacini (2011) reported that the occurrence of strong downward air flux leave an imprint of the 3D motion of air masses to the near-ground air ⁷Be data in the studied region. In this work, we have further developed the two-layer model by adding one more layer: the lower stratosphere (LS). In normal conditions, the contribution of the LS ⁷Be to the near-ground isotopic variability would be very small. On the other hand, stratospheric source can be crucial for the SSW event, indicating that a strong stratospheric air intrusion happened after the SSW and induced a downward flux of stratospheric aerosols from the LS to the ground level lasting several months after the SSW peak, showing that its tropospheric consequences can be much larger than it is usually considered.