Waves and Turbulence in the Vicinity of a Chinook Arch Cloud

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  • 1 Environmental Sciences Centre (Kananaskis), The University of Calgary, Calgary, Alberia T2N IN4
  • | 2 Flight Research Laboratory, National Aeronautical Establishment, National Research Council of Canada, Ottawa, K1A OR6
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Abstract

Instrumented aircraft flights were made near a chinook arch cloud in the lee of the Rocky Mountains in Alberta, Canada. The aircraft data combined with satellite imagery have shown that the arch cloud, based near 5500 m MSL, extended about 50 km in the alongwind direction and more than 900 km in the crosswind direction and was embedded in the crest of a gravity wave 95 km in length. The wave displacement amplitude in the temperature field was about 800 m with estimated vertical motions of 1.6 m s−1. The wave persisted more than 10 h, moving eastward at a, mean speed of about 6 m s−1, somewhat slower than the wind speed at the same height. Light turbulence was found in the wave crests and troughs. The possibility that the wave was partially trapped is discussed with respect to the simultaneous observation of more than one long lee wave cycle in some of the temperature data.

Abstract

Instrumented aircraft flights were made near a chinook arch cloud in the lee of the Rocky Mountains in Alberta, Canada. The aircraft data combined with satellite imagery have shown that the arch cloud, based near 5500 m MSL, extended about 50 km in the alongwind direction and more than 900 km in the crosswind direction and was embedded in the crest of a gravity wave 95 km in length. The wave displacement amplitude in the temperature field was about 800 m with estimated vertical motions of 1.6 m s−1. The wave persisted more than 10 h, moving eastward at a, mean speed of about 6 m s−1, somewhat slower than the wind speed at the same height. Light turbulence was found in the wave crests and troughs. The possibility that the wave was partially trapped is discussed with respect to the simultaneous observation of more than one long lee wave cycle in some of the temperature data.

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