Spectacular tropical storms are a common threat for communities around the globe, but the physical mechanisms that drive storm conditions are under investigation. Here Tao and Zhang conduct experiments to better understand the relationship between storm development and vertical wind shear, the difference in wind speed and direction over different altitudes in the atmosphere. Wind shear can influence the shape and behavior of tropical storms, and parsing this connection has far-reaching benefits: Predicting vertical wind shear near a tropical cyclone contributes to more accurate forecasts of storm intensity—a valuable tool for both economic and humanitarian reasons.
The researchers used the Weather Research and Forecasting model to look at the impact of variations in vertical wind shear and moisture perturbation. They created a control thermodynamic environment, with a constant sea surface temperature of 27°C and an initial storm vortex with maximum surface wind speed of 15 meters per second at a radius of 135 kilometers. They used this foundation to explore changes in storm behavior under different environmental shear or minute initial moisture perturbations.
The team found that in scenarios with a mean environmental shear of 6 meters per second, random shear perturbations with relatively high variability had a bigger influence on storm development and intensification than random moist convection. Under most conditions, the random nature of convection had some influence on the onset of “rapid intensification” by affecting storm structure and changing the strength of storm circulation; a slower circulation is less resistant to environmental shear, and the storm can unravel.
Overall, the researchers found that although predictability of sheared storms can be intrinsically limited given even minute initial uncertainties, inaccurate wind shear predictions translated to big errors in tropical cyclone prediction. Identifying the role of these variables contributes to a better scientific understanding of the complex behavior of Earth’s atmosphere. Further research may help translate this knowledge into improved forecasting capabilities and better serve the communities affected by tropical cyclones. (Journal of Advances in Modeling Earth Systems (JAMES), doi:10.1002/2015MS000474, 2015)
—Lily Strelich, Freelance Writer
Citation: Strelich, L. (2016), Wind shear measures help predict tropical cyclones, Eos, 97, doi:10.1029/2016EO044845. Published on 3 February 2016.