Depolarization calibration and measurements using the CANDAC Rayleigh–Mie–Raman lidar at Eureka, Canada

McCullough, Emily; Sica, R. J.; Drummond, J. R.; Nott, G. J.; Perro, C. W.; Thackray, Colin P.; Hopper, J. T.; Doyle, Jonathan; Duck, Thomas J.; Walker, Kaley A.

doi:10.5194/amt-10-4253-2017

Cited by 13 publications

(34 citation statements)

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“…The maximum signal in the parallel channel would usually be twice as large as the maximum signal in the perpendicular channel, even without the partially polarizing effects of the CRL's receiver optics. The CRL's optics exacerbate this effect to a factor of approximately 21 times (McCullough et al, 2017). This signal mismatch on the PMT, as well as very low signal rates in the perpendicular measurements, is detrimental to traditional calculations of d. Traditional depolarization parameter calculations are simple to calibrate but require long integration times and/or integration over large range scales (relative to the time and altitude scale of variation within the clouds) to produce acceptable uncertainties in the calculated values.…”

Section: Introductionmentioning

confidence: 99%

“…Figure 1 is a schematic of the lidar receiver in this configuration. McCullough et al (2017) discuss the calibration and first results of this addition, using the depolarization parameter, d, found using traditional methods. The depolarization parameter is the fraction of backscattered light which has become unpolarized through scattering interactions with the atmosphere (Gimmestad, 2008).…”

Section: Introductionmentioning

confidence: 99%

“…The pellicle beam splitter reflects 50 % of this residual 532 nm light toward the Polarotor and into the depolarization channels' detector (parallel and perpendicular polarization-sensitive channels, measured using the same PMT on alternate laser shots). The depolarization hardware, which was added in 2010, consists of the pellicle beam splitter, the Polarotor, and the interference filter, focusing lens, and PMT to the right of the Polarotor in this figure (McCullough et al, 2017). No other receiver optics were modified in order to reduce the impact of this depolarization upgrade on the pre-existing lidar channels.…”

Section: Introductionmentioning

confidence: 99%

“…The depolarization parameter is the fraction of backscattered light which has become unpolarized through scattering interactions with the atmosphere (Gimmestad, 2008). Calculation methods in McCullough et al (2017) were based on parallel-polarized (with respect to the outgoing laser plane of polarization as the beam exits the roof) and perpendicular-polarized measurement profiles which, at CRL, are made using a single PMT and a rotating prism which allows through light of each polarization plane on alternate laser shots. Diagram of CRL's receiver system.…”

Section: Introductionmentioning

confidence: 99%

“…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 polarizationdependent 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.…”

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confidence: 99%

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Three-channel single-wavelength lidar depolarization calibration

et al. 2018

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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 polarizationdependent 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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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Three-channel single-wavelength lidar depolarization calibration

et al. 2018

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Unprecedented Spring 2020 Ozone Depletion in the Context of 20 Years of Measurements at Eureka, Canada

et al. 2021

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In the winter and spring of 2019/2020, the unusually cold, strong, and stable polar vortex created favorable conditions for ozone depletion in the Arctic. Chemical ozone loss started earlier than in any previous year in the satellite era and continued until late March, resulting in the unprecedented reduction of the ozone column. The vortex was located above the Polar Environment Atmospheric Research Laboratory in Eureka, Canada (80°N, 86°W) from late February to the end of April, presenting an excellent opportunity to examine ozone loss from a single ground station. Measurements from a suite of instruments show that total column ozone was at an all-time low in the 20-year data set, 22-102 DU below previous records set in 2011. Ozone minima (<200 DU), enhanced OClO and BrO slant columns, and unusually low-HCl, ClONO 2 , and HNO 3 columns were observed in March. Polar stratospheric clouds were present as late as 20 March, and ozonesondes show unprecedented depletion in the March and April profiles (to <0.2 ppmv). While both chemical and dynamical factors lead to reduced ozone when the vortex is cold, the contribution of chemical depletion (based on the variable correlation of ozone and temperature) was exceptional in spring 2020 when compared to typical Arctic winters. Mean chemical ozone loss over Eureka was estimated to be 111-126 DU (27%-31%) using April measurements and passive ozone from the SLIMCAT chemical transport model. While absolute ozone loss was generally smaller in 2020 than in 2011, percentage ozone loss was greater in 2020.Plain Language Summary While an ozone hole forms over Antarctica every year, the Arctic typically does not experience such dramatic ozone loss. The chlorine and bromine (halogen) reactions that destroy ozone require very low temperatures that are rarely observed in the Arctic stratosphere. The winter and spring of 2019/2020, however, was unusually cold in the Arctic, and consequently, a large amount of ozone was destroyed by halogen chemistry. To understand the behavior of ozone in spring 2020, we use measurements from the Polar Environment Atmospheric Research Laboratory in Eureka, Canada. Eureka (at 80°N) is one of the northernmost research stations in the world, and thus an ideal location to observe ozone loss. Spring 2020 ozone minima were lower than any in the 20-year data set, and ozone destruction was ongoing until the end of March, which is rare in the Arctic. While ozone concentrations are largely determined by circulation patterns in the Arctic stratosphere, chemistry in spring 2020 was a much larger factor than usual. Halogen chemistry destroyed 27%-31% of the total ozone, compared to about 10% in a typical winter. The only year on record with comparable ozone loss is 2011, and a larger percentage of the ozone column was lost in 2020. BOGNAR ET AL.

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Description and Comparison of Aerosol Properties Over Cluj-Napoca - Romania and Koforidua – Ghana, Using Aeronet Network Data

Amouzouvi¹,

Dzagli²,

Ştefănie³

et al. 2019

Studia UBB Ambientum

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This article presents a description and a comparative study of the optical and microphysical properties of aerosols measured above Cluj-Napoca city in Romania and above Koforidua city in Ghana. Atmospheric aerosols have a major impact on climate and our health. We analyzed the Aerosol Optical Thickness at 440 nm (AOT), the Ångström parameter (α 440 – 870 nm), the fine and coarse volume concentrations and the single scattering albedo, in order to describe the aerosol properties at these 2 stations. We used daily averages which are calculated for every day when the available number of measurements is higher than 3. At CLUJ_UBB station, the Aerosol Optical Thickness at 440 nm wavelength has values between 0.031 and 0.699, with an average of 0.229 ± 0.11. At Koforidua_ANUC station, the AOT440 has values between 0.106 and 2.580, with an average of 0.742 ± 0.50, much higher than the values measured at CLUJ_UBB. The aerosol at the two locations has different properties, at Cluj-Napoca the urban industrial type is predominant while at Koforidua the predominant type is mineral dust.

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Depolarization calibration and measurements using the CANDAC Rayleigh–Mie–Raman lidar at Eureka, Canada

Cited by 13 publications

References 54 publications

Three-channel single-wavelength lidar depolarization calibration

Three-channel single-wavelength lidar depolarization calibration

Unprecedented Spring 2020 Ozone Depletion in the Context of 20 Years of Measurements at Eureka, Canada

Description and Comparison of Aerosol Properties Over Cluj-Napoca - Romania and Koforidua – Ghana, Using Aeronet Network Data

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