Identification

Title

Mechanisms influencing cirrus banding and aviation turbulence near a convectively enhanced upper-level jet stream

Abstract

Mechanisms supporting a cold-season aviation turbulence outbreak over the northwest Atlantic Ocean and adjacent coastal regions of North America are investigated using high-resolution numerical simulations. Two distinct episodes of moderate-or-greater turbulence in the upper troposphere are observed, and the simulations suggest the turbulence is linked to eastward-translating mesoscale perturbations of negative potential vorticity (PV) emanating from upstream organized deep convection along the anticyclonic shear side of an upper-level jet. Within the exit region of the jet where the turbulence episodes occur, thermodynamic and kinematic fields in the vicinity of the PV perturbations exhibit structural characteristics of mesoscale inertia–gravity waves. These wavelike perturbations are shown to facilitate turbulence by influencing the vertical shear and static stability, which promotes mesoscale regions of banded cirrus clouds, near or within which the observed turbulence occurs. The simulations also suggest that the turbulence arises from fundamentally different mechanisms in the two episodes. In the first and most severe turbulence episode, mesoscale wave-related vertical shear enhancements lead to Kelvin–Helmholtz instability (KHI) near aircraft cruising altitudes (~8.9-11.2 km MSL). Simulated KHI is most prevalent near relatively isolated areas of shallow, moist convection, where smaller-scale internal gravity waves originating in the middle troposphere in response to the shallow convection may play a role in excitation of the KHI located above. The second turbulence episode is consistent with simulated thermal-shear instability related to wave-induced mesoscale reductions in upper-tropospheric static stability. However, unlike for the earlier episode of enhanced turbulence, cloud-radiative feedbacks are necessary for the instability and mesoscale regions of banded cirrus to develop.

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http://n2t.net/ark:/85065/d7j104tv

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eng

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geoscientificInformation

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publication

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2016-01-01T00:00:00Z

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2016-08-01T00:00:00Z

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Copyright 2016 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be "fair use" under Section 107 or that satisfies the conditions specified in Section 108 of the U.S. Copyright Law (17 USC, as revised by P.L. 94-553) does not require the Society's permission. Republication, systematic reproduction, posting in electronic form on servers, or other uses of this material, except as exempted by the above statements, requires written permission or license from the AMS. Additional details are provided in the AMS Copyright Policies, available from the AMS at 617-227-2425 or amspubs@ametsoc.org. Permission to place a copy of this work on this server has been provided by the AMS. The AMS does not guarantee that the copy provided here is an accurate copy of the published work.

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OpenSky Support

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UCAR/NCAR - Library

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PO Box 3000

Boulder

80307-3000

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opensky@ucar.edu

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http://opensky.ucar.edu/

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