Mesoscale Gravity Waves and Midlatitude Weather: A Tribute to Fuqing Zhang

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 our 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.

Gravity wave drag parameterizations for Earth's atmosphere

“…The residual of the nonlinear balance equation is found to be a useful quantity in diagnosing regions of flow imbalance and predicting regions of wave generation (Zhang et al 2000, 2001, Zhang 2004. Readers are also referred to the review by Ruppert et al (2021) on this topic. 2) Adjustment emission (see 3.2-3.4 of Plougonven and Zhang 2014): in this mechanism well-balanced flow more continuously radiates GWs during the course of its nearbalanced evolution.…”

“…𝜌̅ 𝑢 G) decreases with height, the importance of GWs in the general circulation tends to increase with height. In the lower-to mid-troposphere, GWs have less influence on large-scale momentum but are still important in initiating convection and convective organization (Bretherton and Smolarkiewicz 1989, Pandya and Durran 1996, Shige and Satomura 2000, Lac et al 2002, Fovell et al 2006, Lane and Zhang 2011, Ruppert et al 2021). In the upper troposphere and lower stratosphere, GWD does become important in the zonal mean climate (Palmer et al 1986, Bacmeister 1993, Butchart et al 1998).…”

Observational Characterization of Atmospheric Disturbances Generating Meteotsunamis in the Balearic Islands

“…In the Mediterranean Sea, meteotsunamis have mostly been related to gravity waves (Vilibić et al, 2020). For these waves to propagate over large distances, certain conditions are needed to prevent their dissipation (Ruppert et al, 2022). Monserrat et al (1991) and Monserrat and Thorpe (1992) discovered that during the occurrence of meteotsunamis at Ciutadella the conditions in the lower troposphere were at least partially favorable to the generation of a wave duct.…”

“…In the Mediterranean Sea, meteotsunamis have mostly been related to gravity waves (Vilibić et al., 2020). For these waves to propagate over large distances, certain conditions are needed to prevent their dissipation (Ruppert et al., 2022). Monserrat et al.…”

Climate projections of meteotsunami hazards

“…The most common weather conditions driving meteotsunami events are associated with mesoscale processes such as atmospheric mesoscale gravity waves (MGWs), convective storms, frontal passages/ squall lines and tropical cyclones. Atmospheric MGWs may be generated by unbalanced jet streaks through the so-called spontaneous balance adjustment (Ruppert et al, 2022) and may be preserved over long distances via wave ducting in the lower troposphere (Lindzen and Tung, 1976;Monserrat and Thorpe, 1996). Consequently, MGWs can generate meteotsunamis due to rapid surface pressure oscillations up to >5 hPa in less than an hour (e.g., Sheremet et al, 2016).…”