Large surface radiative forcing from topographic blowing snow residuals measured in the High Arctic at Eureka

G Lesins,V P Walden,L Bourdages,E W Eloranta,T J Duck,J R Drummond

doi:10.5194/acp-9-1847-2009

G Lesins, V P Walden + Show 4 more

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https://doi.org/10.5194/acp-9-1847-2009

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Abstract

Abstract. Ice crystals, also known as diamond dust, are suspended in the boundary layer air under clear sky conditions during most of the Arctic winter in Northern Canada. Occasionally ice crystal events can produce significantly thick layers with optical depths in excess of 2.0 even in the absence of liquid water clouds. Four case studies of high optical depth ice crystal events at Eureka in the Nunavut Territory of Canada during the winter of 2006/07 are presented. They show that the measured ice crystal surface infrared downward radiative forcing ranged from 8 to 36 W m−2 in the wavelength band from 5.6 to 20 μm for 532 nm optical depths ranging from 0.2 to 1.7. MODIS infrared and visible images and the operational radiosonde wind profile were used to show that these high optical depth events were caused by surface snow being blown off 600 to 800 m high mountain ridges about 20 to 30 km North-West of Eureka and advected by the winds towards Eureka as they settled towards the ground within the highly stable boundary layer. This work presents the first study that demonstrates the important role that surrounding topography plays in determining the occurrence of high optical depth ice crystal events from residual blowing snow that becomes a source of boundary layer ice crystals distinct from the classical diamond dust phenomenon.

Highlights

Ice crystals are a commonly observed atmospheric phenomenon occurring during the winter months at high latitudes in the presence of a strong surface-based temperature inversion
This work presents the first study that demonstrates the important role that surrounding topography plays in determining the occurrence of high optical depth ice crystal events from residual blowing snow that becomes a source of boundary layer ice crystals distinct from the classical diamond dust phenomenon
The main purpose of this paper is to investigate whether ice crystal events at Eureka, Canada have high enough optical depths to be radiatively important and to better understand their origins

Summary

Introduction

Ice crystals are a commonly observed atmospheric phenomenon occurring during the winter months at high latitudes in the presence of a strong surface-based temperature inversion. The Meteorological Service of Canada (MANOBS, 2006) classifies ice crystals (IC) as a type of frozen precipitation defined as “a fall of non-branched ice crystals, in the form of needles, columns or plates, often so tiny that they seem to be suspended in the air. These crystals may fall from cloud or from a cloudless sky. Eureka is located on Slidre Fiord on Ellesmere. Island at 79.99 N and 85.93 W in the Canadian High Arctic It is the second farthest northern weather station in Canada, after Alert which is located at the northern end of Ellesmere. Eureka lies at the mouth of a broad valley rising gently to the North

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