Solar Eclipse Impact on Gravity Wave Generation and Propagation in the Lower Stratosphere during the December 2020 Total Solar Eclipse – Lessons Learnt for Designing the 2023 and 2024 Campaigns

Atmospheric gravity waves (AGWs) are important because of their overarching climate impacts that are difficult to model. Other than the ubiquitous AGW sources (e.g., topography, jet imbalance, deep convection) that exert a net climate effect from the lower atmosphere to the upper atmosphere, an expansion of observational techniques in recent decades facilitate further study of sporadic AGW sources, which greatly advances our understanding of AGW generation mechanisms from a deep perturbation of the atmosphere (e.g., volcano eruption, satellite launch). A total solar eclipse (TSE) produces a large temporary radiative cooling perturbation in the atmosphere which disturbs the atmosphere and can lead to the generation of AGWs. Previous studies regarding eclipse-driven AGWs focused on planetary boundary layers or the ionosphere, while eclipse-driven AGW’s generation mechanisms and propagation characteristics are still largely unknown.

A radiosonde campaign was carried out during the 14 December 2020, TSE event over two stations in southern Chile. 50 balloons were launched at each station in an hourly cadence, resulting in 52 hours of coverage. Although an atmospheric river event coinciding with the TSE overpass caused launching difficulties and data gaps, we were still able to extract AGW characteristics from ~ 2/3 of the measurements using two independent AGW extraction methods, both of which suggested significant changes when the eclipse passed by.

We further employ an AGW ray-tracing model (GROGRAT) to successfully delineate different AGW sources as jet imbalance, TSE, and topography before, during and after the TSE, respectively. While the jet and topography sources are apparently in the troposphere, the altitude of the eclipse-driven AGW source is likely above the lower stratosphere regime. However, hourly launch in only two nearby stations is still sub-optimal to differentiate weak eclipse-AGWs from other AGWs and high-frequency perturbations.

With the novel findings from this study, we have better planned for the 2023 and 2024 national eclipse ballooning campaigns (NEBP). A “super-site” with several radiosonde sites nearby will launch balloons in a “relay” style to enable (1) a time series that resolves high-frequency AGWs much better; (2) a more robust way to identify the eclipse-AGW signal from the strong background AGWs. The NEBP campaign will cover the entire eclipse overpass in the continental U.S., which will provide an unprecedented opportunity to comprehensively study the eclipse-AGW generation mechanism for the first time.