A 22-Year Evaluation of Convection Reaching the Stratosphere Over the United States

Stratosphere-reaching moist convection can significantly alter the dynamics, chemistry, and climate of the Earth system. This study seeks to add to the emerging understanding of the frequency, depth, and stratospheric impact of such events using 22 years (1996-2017) of ground-based radar observations in the contiguous United States. While most prior studies identify such storms using the temperature lapse-rate tropopause (LRT) as a troposphere-stratosphere boundary, this study is the first to identify convection that reaches into stratospheric air below the LRT (tropopause depressions, excluding folds) as well. It is found that tropopause depression (TD) overshooting and LRT overshooting occur at similar frequency over the United States, with TD overshooting being more episodic in nature than LRT overshooting. TD overshooting is also found more often throughout the cooler months of the year, while LRT overshooting dominates all overshooting in the summer months. Stratospheric residence of overshoot material, as estimated using trajectory calculations driven by large-scale winds, suggests that the vast majority of TD overshoot material does not remain in the stratosphere within 5 days downstream and rarely impacts altitudes more than 1 km above the LRT. Conversely, the majority of LRT overshoot material remains in the stratosphere downstream and routinely impacts altitudes >1 and >2 km above the tropopause. Key Points Stratosphere-reaching convection over the United States is roughly twice as frequent as previously recognized Convection that overshoots tropopause depressions (stratospheric air below the lapse-rate tropopause) is common but has a limited impact Tropopause depression overshooting is more episodic than lapse-rate tropopause overshooting

Automated summary

Stratosphere-reaching moist convection plays a significant role in Earth's dynamics, chemistry, and climate. This study, using 22 years of radar observations in the United States, reveals that tropopause depression overshooting is more episodic and common in cooler months, while lapse-rate tropopause overshooting dominates in the summer. The majority of tropopause depression material does not remain in the stratosphere, whereas most of the lapse-rate tropopause overshoot material does.