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Abstract Over the course of his career, Fuqing Zhang drew vital new insights into the dynamics of meteorologically significant mesoscale gravity waves (MGWs), including their generation by unbalanced jet streaks, their interaction with fronts and organized precipitation, and their importance in midlatitude weather and predictability. Zhang was the first to deeply examine “spontaneous balance adjustment”—the process by which MGWs are continuously emitted as baroclinic growth drives the upper-level flow out of balance. Through his pioneering numerical model investigation of the large-amplitude MGW event of 4 January 1994, he additionally demonstrated the critical role of MGW–moist convection interaction in wave amplification. Zhang’s curiosity-turned-passion in atmospheric science covered a vast range of topics and led to the birth of new branches of research in mesoscale meteorology and numerical weather prediction. Yet, it was his earliest studies into midlatitude MGWs and their significant impacts on hazardous weather that first inspired him. Such MGWs serve as the focus of this review, wherein we seek to pay tribute to his groundbreaking contributions, review our current understanding, and highlight critical open science issues. Chief among such issues is the nature of MGW amplification through feedback with moist convection, which continues to elude a complete understanding. The pressing nature of this subject is underscored by the continued failure of operational numerical forecast models to adequately predict most large-amplitude MGW events. Further research into such issues therefore presents a valuable opportunity to improve the understanding and forecasting of this high-impact weather phenomenon, and in turn, to preserve the spirit of Zhang’s dedication to this subject. 

The tropical Andes of southern Peru and northern Bolivia have several major mountain summits suitable for ice core paleoclimatic investigations. However, incomplete understanding of the controls on the isotopic ( δD, δ¹⁸O) composition of precipitation and a paucity of field observations in this region continue to limit ice-core-based paleoclimate reconstructions. This study examines four years of daily observations of δD and δ¹⁸O in precipitation from a citizen scientist network on the northeastern margin of the Altiplano, to identify controls on the subseasonal spatiotemporal variability in δ¹⁸O during the wet season (November–April). These data provide new insights into modern δ¹⁸O variability at high spatial and temporal scales. We identify a regionally coherent subseasonal signal in precipitation δ¹⁸O featuring alternating periods of high and low δ¹⁸O of 9–27-day duration. This signal reflects variability in precipitation delivery driven by synoptic conditions and closely relates to variations in the strength of the South American low-level jet and moisture availability over the study area. The annual layer of snowpack on the Quelccaya Ice Cap observed in the subsequent dry season retains this subseasonal signal, allowing the development of a snow-pit age model based on precipitation δ¹⁸O measurements, and demonstrating how synoptic variability is transmitted from the atmosphere to mountaintop snowpacks along the Altiplano’s eastern margin. This result improves our understanding of the hydrometeorological processes governing δ¹⁸O and δD in tropical Andean precipitation and has implications for improving paleoclimate reconstructions from tropical Andean ice cores and other paleoclimate records.