Lee-wave clouds and denitrification of the polar stratosphere
Abstract
We present a hypothesis that the known formation of nitric acid hydrates in lee-wave ice clouds produces a "standing crop" of nitric acid trihydrate (NAT) particles, and that growth and sedimentation of these particles efficiently denitrifies the polar stratosphere. Simulations using a simple two-dimensional model illustrate that the large NAT number concentrations produced in lee waves (>0.1 cm^(−3)) lead to low gas-phase HNO_3 concentration in the cloud layer, limiting subsequent particle growth. Provided the NAT existence temperature is not exceeded, these particles slowly sediment out of the cloud layer, at which point further growth is initiated. As a result of the long residence time and vertical wind shear, NAT particles produced in geographically selective regions over a short duration can cause extensive denitrification throughout the lower stratosphere. Our model illustrates that a single hypothetical lee-wave nucleation event [10 hours, 1000 km width (along a longitude) × 100 m altitude] is sufficient to produce significant denitrification (∼25%) vortex-wide.
Additional Information
© 2002 American Geophysical Union. Received 7 August 2001; revised 30 October 2001; accepted 12 December 2001; published 10 May 2002. The authors thank Leslie Lait, Paul Newman, and Mark Schoeberl for access to trajectory calculations via the NASA Goddard Automailer. We are grateful to Stefan Fueglistaler, Beiping Luo, David Fahey and Ross Salawitch for helpful comments that improved this manuscript. Finally, we thank Thomas Peter and an anonymous reviewer for their insightful comments.Attached Files
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