Characteristics of tornado-scale vortices in an intensifying tropical cyclone
Observations have revealed the presence of tornado-scale vortices(TSVs)within the boundary layer of tropical cyclones(TCs),which significantly impact near-surface gustiness.Based on Weather Research and Forecasting Model-Advanced Research WRF(WRF-ARW),a high-resolution numerical experiment in simulating Hurricane Earl(2010)is conducted to analyze the activity characteristics of TSVs in boundary-layer.During the strengthening process of Earl,the number of TSVs increases with the intensification of Earl,especially during its peak.On one hand,the strengthening of the tropical cyclone(TC)provides a stronger background field,making it easier for TSVs to form.On the other hand,the stronger background field leads to an extended lifespan for TSVs,resulting in a higher number of concurrent TSVs at any given moment.The area that TSV generating gradually shifts from the left side of the vertical wind shear to the up-shear left as Earl develops,near the secondary circulation updraft and the maximum vertical vorticity,where often meets the necessary conditions of unstable vertical and horizontal wind shear.The results of TSV vorticity budget analysis further indicate that the stretching term associated with horizontal wind shear and the tilting term associated with vertical wind shear are important factors in the generation and development of TSVs,which implies that the generation and development of TSV may be related to vertical shear instability and horizontal shear instability.
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