Thunderstorms can drastically disturb daily weather conditions, causing sudden changes in temperature, wind, and humidity. These disturbances begin with falling rain. As raindrops fall below the base of the cloud, some of the rain evaporates. This cools the surrounding air, thereby making it denser than the surrounding air. This denser air sinks toward the ground, forming a downdraft, which, upon reaching the surface, spreads outward in all directions. As a result, thunderstorms can abruptly replace warm, calm surface conditions with cool, gusty winds produced within the cloud. This process is highly turbulent and promotes strong exchanges of energy, aerosols, and important gases (such as carbon dioxide) between the atmosphere and the surface.
Maurício I. Oliveira and his colleagues have recently conducted a new study that explores the effects thunderstorms have on the evolution of meteorological conditions at the ATTO site based on the extensive micrometeorological dataset of the ATTO project.
The scientists analyzed high-frequency measurements of a large dataset of storms that impacted ATTO between August 2021 and December 2023. They constructed the dataset by applying a storm-detection algorithm specifically adapted to leverage the ATTO micrometeorological dataset. Such a large dataset of 410 storm cases was important for the scientists to determine the statistics of storm occurrence at ATTO as well as the average characteristics of the turbulence disturbances they cause. This would not be possible from isolated case studies.
The team found remarkable results based on this new storm dataset. Some key findings include:
- Storms impact the ATTO site at a high frequency; on average, a storm impacts the site every other day. They are most common from April through September and are least common from December through March.
- Most events occur from midafternoon through early evening.
- The dense Amazon forest is efficient at dampening the effects of storms. In other words, the airflow below the forest canopy is only disturbed by the strongest storms. Above the forest canopy, the unimpeded thunderstorm airflow behaves in agreement with classic conceptual models of storm flows.
- The storm-induced turbulent disturbances display well-defined evolution patterns, as indicated by a comprehensive (composite) analysis of all cases. This suggests that the enhanced forest-atmosphere exchanges induced by storms can be effectively modeled to provide more complete depictions of surface-atmosphere interactions needed for weather and climate predictions.
The comprehensive analysis for a large sample of storms, such as the one provided in this study, is fundamental to understanding the effects of thunderstorms in the Amazon. Although several aspects of the interaction between storms and the Amazon forest were unraveled in this study, several others remain to be investigated. For instance, the team is currently studying the meteorological conditions that produced the storms documented in the dataset, the formation mechanisms of turbulence produced by storms, their impacts on greenhouse gas exchanges between the forest and the atmosphere, among other topics. In addition, the team is expanding the storm dataset.
Oliveira et al. published the study “Convective cold pools and attendant turbulence at the Amazon Tall Tower Observatory (ATTO)” in the journal Atmospheric Research.
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