Aircraft measurements of spectral solar up- and downward irradiances in the Arctic during the ACLOUD campaign 2017

Jäkel, Evelyn; Schäfer, Michael; Ehrlich, André; Becker, Sebastian; Klingebiel, Marcus

doi:10.1594/pangaea.899177

Cited by 2 publications

(2 citation statements)

References 1 publication

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“…However, airborne operation of the CMP22 in Arctic conditions may increase these uncertainties depending on solar zenith angle and environmental conditions, as described by Ehrlich et al (2023) on a high altitude aircraft and Su et al (2008) in a laboratory study and on active stabilization performance (Wendisch et al, 2001). The data are corrected for the aircraft specific operation as summarized in Ehrlich et al (2019) Spectral solar irradiances are measured on Polar 5 with the Spectral Modular Airborne Radiation measurement sysTem (SMART; Jäkel et al, 2019a;Wendisch et al, 2001) covering the spectral range between 345 nm and 2150 nm with a spectral resolution of 3-15 nm (Ehrlich et al, 2019). Additional remote sensing observations aboard Polar 5 include the Airborne Mobile Aerosol Lidar (AMALi) system (Stachlewska et al, 2010) and the Microwave Radar/radiometer for Arctic Clouds (MiRAC; Kliesch and Mech, 2019;Mech et al, 2019).…”

Section: Airborne Observationsmentioning

confidence: 99%

Evaluation of downward and upward solar irradiances simulated by the Integrated Forecasting System of ECMWF using airborne observations above Arctic low-level clouds

Müller,

Ehrlich,

Jäkel

et al. 2023

Preprint

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Abstract. The simulations of upward and downward irradiances by the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts are compared to broadband solar irradiance measurements from the Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD) campaign. For this purpose, offline radiative transfer simulations with the ecRad radiation scheme using the operational IFS output were performed. The simulations of the downward solar irradiance agree within the measurement uncertainty. However, the IFS underestimates the reflected solar irradiances above sea ice significantly by −35 Wm−2. Above open ocean, the agreement is closer with an overestimation of 29 Wm−2. A sensitivity study using measured surface and cloud properties is performed with ecRad to quantify the contributions of the surface albedo, cloud fraction, ice and liquid water path and cloud droplet number concentration to the observed bias. It shows that the IFS sea ice albedo climatology underestimates the observed sea ice albedo, causing more than 50 % of the bias. Considering the higher variability of in situ observations in the parameterization of the cloud droplet number concentration leads to a smaller bias of −27 Wm−2 above sea ice and a larger bias of 48 Wm−2 above open ocean by increasing the range from 36–69 cm−3 to 36–200 cm−3. Above sea ice, realistic surface albedos, cloud droplet number concentrations and liquid water paths contribute most to a bias improvement. Above open ocean, realistic cloud fractions and liquid water paths are most important to reduce the model-observation differences.

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Section: Airborne Observationsmentioning

confidence: 99%

Evaluation of downward and upward solar irradiances simulated by the Integrated Forecasting System of ECMWF using airborne observations above Arctic low-level clouds

Müller,

Ehrlich,

Jäkel

et al. 2023

Preprint

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“…Combining the downward irradiance F i measured by SMART (Jäkel et al, 2019a) and the angularly resolved radiances I r from the fish-eye camera (Jäkel and Ehrlich, 2019) allows the calculation of the HDRF at flight altitude (Eq. 4), whereby the spectrally resolved irradiances were converted into the spectral range of each camera channel using the individual relative spectral response function from the spectral calibration.…”

Section: Calculation Of and Uncertainty In The Hdrfmentioning

confidence: 99%

Airborne measurements of directional reflectivity over the Arctic marginal sea ice zone

et al. 2022

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Abstract. The directional reflection of solar radiation by the Arctic Ocean is mainly shaped by two dominating surface types: sea ice (often snow-covered) and open ocean (ice-free). In the transitional zone between them, the marginal sea ice zone (MIZ), the surface reflection properties are determined by a mixture of the reflectance of both surface types. Retrieval methods applied over the MIZ need to take into account the mixed directional reflectivity; otherwise uncertainties in the retrieved atmospheric parameters over the MIZ may occur. To quantify these uncertainties, respective measurements of reflection properties of the MIZ are needed. Therefore, in this case study, an averaged hemispherical–directional reflectance factor (HDRF) of the inhomogeneous surface (mixture of sea ice and open ocean) in the MIZ is derived using airborne measurements collected with a digital fish-eye camera during a 20 min low-level flight leg in cloud-free conditions. For this purpose, a sea ice mask was developed to separate the reflectivity measurements from sea ice and open ocean and to derive separate HDRFs of the individual surface types. The respective results were compared with simulations and independent measurements available from the literature. It is shown that the open-ocean HDRF in the MIZ differs from homogeneous ocean surfaces due to wave attenuation. Using individual HDRFs of both surface types and the sea ice fraction, the mixed HDRF describing the directional reflectivity of the inhomogeneous surface of the MIZ was retrieved by a linear weighting procedure. Accounting for the wave attenuation, good agreement between the average measured HDRF and the constructed HDRF of the MIZ was found for the presented case study.

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Aircraft measurements of spectral solar up- and downward irradiances in the Arctic during the ACLOUD campaign 2017

Cited by 2 publications

References 1 publication

Evaluation of downward and upward solar irradiances simulated by the Integrated Forecasting System of ECMWF using airborne observations above Arctic low-level clouds

Evaluation of downward and upward solar irradiances simulated by the Integrated Forecasting System of ECMWF using airborne observations above Arctic low-level clouds

Airborne measurements of directional reflectivity over the Arctic marginal sea ice zone

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