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A Numerical Study of Cirrus Bands and Low-Static-Stability Layers Associated with Tropical Cyclone Outflow

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Title: A Numerical Study of Cirrus Bands and Low-Static-Stability Layers Associated with Tropical Cyclone Outflow
Authors: Kawashima, Masayuki Browse this author →KAKEN DB
Keywords: Instability
Mesoscale processes
Tropical cyclones
Cirrus clouds
Mesoscale models
Issue Date: 1-Nov-2021
Publisher: American Meteorological Society
Journal Title: Journal of the Atmospheric Sciences
Volume: 78
Issue: 11
Start Page: 3691
End Page: 3716
Publisher DOI: 10.1175/JAS-D-21-0047.1
Abstract: Prominent cirrus cloud banding occurred episodically within a northern cirrus canopy of Typhoon Talim (2017) during its recurvature. The generation mechanisms of the cirrus bands and low-static-stability layers that support the bands are investigated using a numerical simulation with the Advanced Research version of the Weather Research and Forecasting Model. Inspection of model output reveals that thin layers of near-neutral to weakly unstable static stability are persistently present in the upper and lower parts of the upper-level outflow, and shallow convection aligned along the vertical shear vector is prevalent in these layers. The cirrus banding occurs as the lowered outflow from the weakening storm ascends slantwise over a midlatitude baroclinic zone, and updrafts of the preexisting shallow convection in the upper part of the outflow layer become saturated. It is shown that the strong outflow resulting from violation of gradient-wind balance in the core region, by itself, creates the low-static-stability layers. Analyses of potential temperature and static stability budgets show that the low-static-stability layers are created mainly by the differential radial advection of radial thermal gradients on the vertical edges of the outflow. The radial thermal gradients occur in response to the outward air parcel acceleration in the core region and deceleration in the outer region, which, by inducing compensating vertical mass transport into and out of the outflow, act to tilt the isentropes within the shear layers. The effects of environmental flow and cloud-radiative forcing on the cirrus banding are also addressed.
Type: article
Appears in Collections:低温科学研究所 (Institute of Low Temperature Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

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