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Orographic influences during winter precipitation events on the Avalon Peninsula, Newfoundland

Published online by Cambridge University Press:  17 May 2001

C E Banfield
Affiliation:
Department of Geography, Memorial University of Newfoundland, St. John's, Newfoundland A1B 3X9, Canada
D R Hudak
Affiliation:
Atmospheric Environment Service, 14780 Jane Street, King City, Ontario L7B 1A3, Canada
A D Thomson
Affiliation:
Department of Physics, University of Toronto, Toronto, Ontario M5S 1A7, Canada present affiliation: Defence Research Establishment Ottawa, 3701 Carling Avenue Ottawa, Ontario, Canada, K1A 0Z4
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Abstract

Precipitation enhancement over a low coastal hill in winter is demonstrated for particular associations of synoptically determined onshore airflow and local geography encountered over south-eastern Newfoundland. Four such cases, involving a mixture of pre-warm-frontal precipitation types at surface temperatures just below freezing, are analysed using comparative surface gauge records from sites at the coast and hill summit and detailed volume scan data from a Doppler radar. Whilst precipitation at the hill summit and upwind coast was of similar overall duration in each case, the surface rates on the hilltop exceeded those at the coast by 1.0-4.0 mm h-1 during different stages of the events. Analysis of the Doppler reflectivity patterns reveals that intensities are especially enhanced near the windward hill crest, supporting the observed association of greatest enhancement with a strong local upslope wind component exceeding 20 m s-1. In the majority of these cases the enhancement is maintained primarily by the ‘seeder-feeder’ mechanism, which appears to be accelerated during precipitation transitions and with the surface warm front 120-150 km distant; however, a preliminary phase of enhancement due to topographically induced uplift of stable pre-frontal air is also recognised in one case.

Type
Research Article
Copyright
© Royal Meteorological Society

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