In the current issue of the Journal of the Atmospheric Sciences, 溏心vlog免费B站 physical oceanographer Dr. Isaac Ginis describes how he and a team of scientists are refining the model by incorporating the factors that favor the formation of large eddies near the sea surface and their effect on wind speed and air humidity. Other members of the team include Alexander P. Khain and Elena Morozovsky of the Institute of Earth Sciences, Hebrew University of Jerusalem, Israel.
The authors speculate that large eddies, or circular currents of air, are a pervasive feature in tropical cyclones and suggests that they can contribute significantly to the transfer of energy, heat, and moisture from the ocean to the atmosphere.
鈥淟ack of adequate consideration of the large eddy effects near the surface of the ocean may be one of the reasons for the limited tropical cyclone intensity forecast skill by hurricane prediction models,鈥� said Ginis. 鈥淭he recently implemented to operational Geophysical Fluid Dynamics Laboratory (GFDL)/ 溏心vlog免费B站 (溏心vlog免费B站) coupled hurricane-ocean model helped to improve the intensity predictions measured by the central pressure. However, it has not always translated into improvements in predicting maximum wind speed. This is mainly due to underestimations of the surface winds in strong tropical cyclones.鈥�
In strong wind conditions the GFDL/溏心vlog免费B站 model tends to underpredict surface wind speeds for a given central pressure. It is most likely the result of inadequate representation of the physical processes connected with the storm, in particular the contribution of large eddies in the modeling of the area near the sea surface and how the atmosphere and ocean interact.
The main objective in the study was to investigate the mechanisms leading to the formation of large eddies under tropical cyclone conditions and assess their effects on the factors that determine a storm鈥檚 intensity using a high-resolution, atmospheric computer model.
Ginis, Khain, and Morozovsky presented a new method to describe large eddies in both general circulation and regional weather prediction models, including hurricane models. Their approach is called 鈥渟uperparameterization,鈥� which consists of an eddy-resolving, two-dimensional system embedded into a weather prediction model, allowing explicit simulations of large eddies.
Based on the results of their numerical simulations, the scientists found that when the wind speed is high enough, a strong vertical wind shear that develops near the sea surface triggers conditions that allow for genesis of large eddies. They concluded that a strong background wind, typical for hurricanes, and evaporation from the ocean are the necessary conditions for the formation of large eddies in the lower part of the atmosphere.
The experiments demonstrated that as soon as large eddies arise, they affect the transport of heat, moisture, and momentum, modifying the structure of the atmosphere and the way it interacts with the ocean. The most significant manifestation of these effects is a significant increase of the near-surface wind speed, and evaporation from the sea surface, which can double in strong winds.
鈥淭hese results demonstrate the important role that large eddies play in high wind speed conditions,鈥� said Ginis. 鈥淚nclusion of these effects in the tropical cyclone models may potentially lead to substantial improvements in the prediction of storm intensity.鈥�
Ginis鈥檚 work on this project was partially supported by the National Science Foundation. Khain and Morozovsky were supported by the Lady Davis Foundation and the U.S.-Israel Binational Science Foundation.