Ice nucleating particles in the Canadian High Arctic during the fall with implications for climate feedback mechanisms in the region

Although most of the dust present in the atmosphere originates from low-latitude arid deserts, it has been increasingly recognised that there are significant sources of High-Latitude Dust (HLD) in locations such as Iceland, Greenland, North American Arctic or North Eurasia [1]. The emission, transport and deposition of HLD can interact with the atmosphere, cryosphere and the marine ecosystem in several ways. Particularly, HLD has the potential to act as significant source of atmospheric Ice-Nucleating Particles (INP), competing with other sources such as dust and other INP types from lower-latitude arid sources [2, 3]. INPs are the fraction of aerosol particles that can trigger ice-formation in supercooled water droplets, that otherwise would remain unfrozen until temperatures of about -36 oC.Ice formation initiated by the presence of INPs dramatically affects the amount of solar radiation reflected by clouds containing both liquid water and ice, known as mixed-phase clouds. However, ice-related processes in mixed-phase clouds such as the INP concentration are commonly oversimplified in most climate models, which leads to large discrepancies in the amount of water and ice that the models simulate at mid- to high-latitudes [4]. These present-day divergences in simulated mixed-phase clouds lead to a large uncertainty in the cloud climate feedback. This feedback is associated to the fact that mid- to high-latitude mixed-phase clouds dampen a part of the of the global temperature rise associated with greenhouse gases [5] [6].Here we will explain the importance of understanding the chemical and ice-nucleating properties of HLD, as well as how it is emitted, transported and deposited for the cloud climate feedback. We will present new results from aircraft studies of the ice nucleating ability of HLD as well as modelling work which shows that this dust can be transported to altitudes and regions where it has the potential to influence mixed-phase clouds and climate.

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Physical properties of High Arctic tropospheric particles during winter

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-7781-2009 ◽

2009 ◽

Vol 9 (2) ◽

pp. 7781-7823 ◽

Cited By ~ 2

Author(s):

L. Bourdages ◽

T. J. Duck ◽

G. Lesins ◽

J. R. Drummond ◽

E. W. Eloranta

Keyword(s):

Boundary Layer ◽

Inversion Layer ◽

Lower Troposphere ◽

High Arctic ◽

Mixed Phase ◽

Ice Crystals ◽

Blowing Snow ◽

Ice Clouds ◽

Arctic Conditions ◽

Mixed Phase Clouds

Abstract. A climatology of particle properties in the wintertime High Arctic troposphere is constructed using measurements from a lidar and cloud radar located at Eureka, Nunavut Territory (80° N, 86° W). Four different particle groupings are considered: aerosols, mixed-phase clouds, ice clouds and boundary-layer ice crystals. Two-dimensional histograms of occurrence probabilities against depolarization and radar/lidar colour ratio, as well as their vertical distributions, are presented. The largest ice crystals originate from mixed-phase clouds, whereas the smallest are topographic blowing snow residuals in the boundary layer. Ice cloud crystals have depolarization and size decreasing with height. The depolarization trend is associated with the large ice crystal sub-population. Small crystals depolarize more than large ones in ice clouds at a given altitude, and show constant modal depolarization with height. Ice clouds in the mid-troposphere are sometimes observed to precipitate to the ground. Water clouds are constrained to the lower troposphere and are associated with the surface inversion layer depth. Aerosols are most abundant near the ground and are frequently mixed with the other particle types. The data are used to construct a classification chart for particle scattering in wintertime Arctic conditions.

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Three-channel single-wavelength lidar depolarization calibration

Atmospheric Measurement Techniques ◽

10.5194/amt-11-861-2018 ◽

2018 ◽

Vol 11 (2) ◽

pp. 861-879 ◽

Cited By ~ 2

Author(s):

Emily M. McCullough ◽

Robert J. Sica ◽

James R. Drummond ◽

Graeme J. Nott ◽

Christopher Perro ◽

...

Keyword(s):

Traditional Method ◽

High Arctic ◽

High Signal ◽

Canadian High Arctic ◽

Polar Night ◽

Elastic Channel ◽

A New Technique ◽

Mixed Phase Clouds ◽

Parameter Values ◽

Polarization Independent

Abstract. Linear depolarization measurement capabilities were added to the CANDAC Rayleigh–Mie–Raman lidar (CRL) at Eureka, Nunavut, in the Canadian High Arctic in 2010. This upgrade enables measurements of the phases (liquid versus ice) of cold and mixed-phase clouds throughout the year, including during polar night. Depolarization measurements were calibrated according to existing methods using parallel- and perpendicular-polarized profiles as discussed in ). We present a new technique that uses the polarization-independent Rayleigh elastic channel in combination with one of the new polarization-dependent channels, and we show that for a lidar with low signal in one of the polarization-dependent channels this method is superior to the traditional method. The optimal procedure for CRL is to determine the depolarization parameter using the traditional method at low resolution (from parallel and perpendicular signals) and then to use this value to calibrate the high-resolution new measurements (from parallel and polarization-independent Rayleigh elastic signals). Due to its use of two high-signal-rate channels, the new method has lower statistical uncertainty and thus gives depolarization parameter values at higher spatial–temporal resolution by up to a factor of 20 for CRL. This method is easily adaptable to other lidar systems which are considering adding depolarization capability to existing hardware.

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Physical properties of High Arctic tropospheric particles during winter

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-6881-2009 ◽

2009 ◽

Vol 9 (18) ◽

pp. 6881-6897 ◽

Cited By ~ 25

Author(s):

L. Bourdages ◽

T. J. Duck ◽

G. Lesins ◽

J. R. Drummond ◽

E. W. Eloranta

Keyword(s):

Boundary Layer ◽

Lower Troposphere ◽

High Arctic ◽

Mixed Phase ◽

Blowing Snow ◽

Particle Scattering ◽

Ice Crystal ◽

Ice Clouds ◽

Ice Cloud ◽

Mixed Phase Clouds

Abstract. A climatology of particle scattering properties in the wintertime High Arctic troposphere, including vertical distributions and effective radii, is presented. The measurements were obtained using a lidar and cloud radar located at Eureka, Nunavut Territory (80° N, 86° W). Four different particle groupings are considered: boundary-layer ice crystals, ice clouds, mixed-phase clouds, and aerosols. Two-dimensional histograms of occurrence probabilities against depolarization, radar/lidar colour ratio and height are given. Colour ratios are related to particle minimum dimensions (i.e., widths rather than lengths) using a Mie scattering model. Ice cloud crystals have effective radii spanning 25–220 µm, with larger particles observed at lower altitudes. Topographic blowing snow residuals in the boundary layer have the smallest crystals at 15–70 µm. Mixed-phase clouds have water droplets and ice crystal precipitation in the 5–40 µm and 40–220 µm ranges, respectively. Ice cloud crystals have depolarization decreasing with height. The depolarization trend is associated with the large ice crystal sub-population. Small crystals depolarize more than large ones in ice clouds at a given altitude, and show constant modal depolarization with height. Ice clouds in the mid-troposphere are sometimes observed to precipitate to the ground. Water clouds are constrained to the lower troposphere (0.5–3.5 km altitude). Aerosols are most abundant near the ground and are frequently mixed with the other particle types. The data are used to construct a classification chart for particle scattering in wintertime Arctic conditions.

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Three-channel single-wavelength lidar depolarization calibration

10.5194/amt-2017-328 ◽

2017 ◽

Cited By ~ 1

Author(s):

Emily M. McCullough ◽

Robert J. Sica ◽

James R. Drummond ◽

Graeme Nott ◽

Christopher Perro ◽

...

Keyword(s):

Traditional Method ◽

High Arctic ◽

High Signal ◽

Canadian High Arctic ◽

Polar Night ◽

Elastic Channel ◽

A New Technique ◽

Mixed Phase Clouds ◽

Parameter Values ◽

Polarization Independent

Abstract. Linear depolarization measurement capabilities were added to the CANDAC Rayleigh-Mie-Raman lidar (CRL) at Eureka, Nunavut, in the Canadian High Arctic in 2010. This upgrade enables measurements of the phases (liquid versus ice) of cold and mixed-phase clouds throughout the year, including during polar night. Depolarization measurements were calibrated according to existing methods using parallel- and perpendicular-polarized profiles as discussed in McCullough et al. (2017). We present a new technique that uses the polarization-independent Rayleigh elastic channel in combination with one of the new polarization-dependent channels, and show that for a lidar with low signal in one of the polarization-dependent channels, this method is superior to the traditional method. The optimal procedure for CRL is to determine the depolarization parameter using the traditional method at low resolution (from parallel and perpendicular signals), and then to use this value to calibrate the high-resolution new measurements (from parallel and polarization-independent Rayleigh elastic signals). Due to its use of two high-signal-rate channels, the new method has lower statistical uncertainty, and thus gives depolarization parameter values at higher spatial-temporal resolution by up to a factor of 20 for CRL. This method is easily adaptable to other lidar systems which are considering adding depolarization capability to existing hardware.

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