Relationships between Extratropical Precipitation Systems and UTLS Temperatures and Tropopause Height from GPM and GPS-RO

This study characterizes the relationship between extratropical precipitation systems to changes in upper troposphere and lower stratosphere (UTLS) temperature and tropopause height within different environments. Precipitation features (PFs) observed by the Global Precipitation Measurement (GPM) satellite are collocated with GPS radio occultation (RO) temperature profiles from 2014 to 2017 and classified as non-deep stratospheric intrusion (non-DSI; related to convective instability) or deep stratospheric intrusion (DSI; related to strong dynamic effects on the tropopause). Non-DSI PFs introduce warming (up to 1 K) in the upper troposphere, transitioning to strong cooling (up to −3.5 K) around the lapse rate tropopause (LRT), and back to warming (up to 2.5 K, particularly over the ocean) in the lower stratosphere. UTLS temperature anomalies for DSI events are driven predominantly by large scale dynamics, with major cooling (up to −6 K) observed from the mid-troposphere to the LRT, which transitions to strong warming (up to 4 K) in the lower stratosphere. Small and deep non-DSI PFs typically result in a lower LRT (up to 0.4 km), whereas large but weaker PFs lead to a higher LRT with similar magnitudes. DSI events are associated with larger LRT height decreases, with anomalies of almost −2 km near the deepest PFs. These results suggest intricate relationships between precipitation systems and the UTLS temperature structure. Importantly, non-DSI PF temperature anomalies show patterns similar to tropical convection, which provides unification of previous tropical research with extratropical barotropic convective impacts to UTLS temperatures.

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.

Extending water vapor trend observations over Boulder into the tropopause region: Trend uncertainties and resulting radiative forcing

Thirty years of balloon-borne measurements over Boulder (40°N, 105°W) are used to investigate the water vapor trend in the tropopause region. This analysis extends previously published trends, usually focusing on altitudes greater than 16 km, to lower altitudes. Two new concepts are applied: (1) Trends are presented in a thermal tropopause (TP) relative coordinate system from -2 km below to 10 km above the TP, and (2) sonde profiles are selected according to TP height. Tropical (TP _z > 14 km), extratropical (TP _z < 12 km), and transitional air mass types (12 km < TP _z < 14 km) reveal three different water vapor reservoirs. The analysis based on these concepts reduces the dynamically induced water vapor variability at the TP and principally favors refined water vapor trend studies in the upper troposphere and lower stratosphere. Nonetheless, this study shows how uncertain trends are at altitudes -2 to +4 km around the TP. This uncertainty in turn has an influence on the uncertainty and interpretation of water vapor radiative effects at the TP, which are locally estimated for the 30 year period to be of uncertain sign. The much discussed decrease in water vapor at the beginning of 2001 is not detectable between -2 and 2 km around the TP. On lower stratospheric isentropes, the water vapor change at the beginning of 2001 is more intense for extratropical than for tropical air mass types. This suggests a possible link with changing dynamics above the jet stream such as changes in the shallow branch of the Brewer-Dobson circulation.