A better understanding of how storms form and grow over complex terrain
Fast, Jerome D — Pacific Northwest National Laboratory
Area of research:
Around the world, major mountain ranges significantly influence the birth and growth of large, intense thunderstorms. These storms generate substantial rainfall and severe weather. Prior efforts to link storm development and the nearby atmospheric environment used only a handful of events or simulations. A new study used radar observations collected in central Argentina during the 2018-2019 Cloud, Aerosol and Complex Terrain Interactions (CACTI) field campaign to track nearly 7,000 storms over a six and a half month period. Researchers matched the storm tracks to nearby weather balloon and geostationary satellite measurements. The results demonstrate that nearby temperature, humidity, wind conditions, and interactions between neighboring storms exert important control on the growth of thunderstorms.
Understanding the processes linking the initiation and growth of storms with local environmental conditions remains inadequate, making these processes poorly represented in weather and climate models. Researchers developed a new methodology to track convective storms from three-dimensional scanning radar observations and match them with near-storm environmental conditions. The developed database contains nearly 7,000 tracked convective storms, including corresponding storm properties such as duration, width, depth, intensity, and environments derived from radar and satellite data. Researchers can now comprehensively explore the processes that lead to storm evolution and apply this knowledge to models to assess and reduce prediction biases.
Researchers characterized the full range of deep convective storm life cycles—from initiation to demise—and identified how their morphologies and precipitation characteristics relate to the ambient environmental conditions observed near the Sierras de Córdoba (SDC) range in central Argentina during the CACTI field campaign. The analyses show that the SDC range strongly influences storm initiation and growth. Convective cells preferentially initiate just east of the SDC ridge during the afternoon and frequently intensify and grow larger throughout the evening as they travel east towards the plains. Wider and more intense storm cells occur in the more unstable and humid low-level environments. The relative humidity and vertical wind shear at middle levels of the atmosphere also affect the size and depth of the cells. Rapid growth in storm width exhibits dependence on large vertical wind shear and low-level moisture. Evolution of the vertical structure of cells, such as maximum radar reflectivity, cell width, and raindrop sizes, are strongly influenced by environmental instability, low-level moisture, and the presence of other cells nearby.