- 1Istituto Nazionale di Geofisica e Vulcanologia, Rome 00143, Italy (giovanni.muscari@ingv.it)
- 2Ca' Foscari University of Venice Department of Environmental Sciences, Informatics and Statistics, Ca’ Foscari University of Venice, Venezia-Mestre 30172, Italy
- 3Laboratory for Models and Measurements for Air Quality, and Climate Observations SSPT-CLIMAR-AOC ENEA, 00123 Rome, Italy
- 4Department of Physics, Sapienza University of Rome, 00184 Rome, Italy
- 5Department of Information Engineering, Electronics and Telecommunications, Sapienza University of Rome, 00184 Rome, Italy
- 6Laboratory for Atmospheric and Space Physics, University of Colorado, 80303 Boulder CO, USA
- 7Laboratory for Models and Measurements for Air Quality, and Climate Observations SSPT-CLIMAR-AOC ENEA, 00044 Frascati, Italy
In the Arctic, cloud optical thickness (COT) estimations are scarce due to limited site accessibility, short sunlit seasons, and high surface albedo, which enhances the multiple scattering. This work presents a comparison of estimates of COT obtained by means of different types of measurements collected on the north-western coast of Greenland, an area presenting alternatively high and low surface albedo, depending on the season. Our approach exploits ground-based zenith spectral radiance (ZSR) measurements in the 320-950 nm wavelength range as well as downward shortwave irradiance (DSI, 310-2800 nm) and Liquid Water Path (LWP) measurements. All measurements are carried out at the Thule High Arctic Atmospheric Observatory (THAAO, 76.5° N, 68.8° W, 225 m asl, https://www.thuleatmos-it.it/), where LWP measurements have been performed from 2016 to 2024, while DSI and ZSR measurements started in 2009 and 2021, respectively, and are still ongoing. The analysis also includes COT values from MODIS aboard Terra/Aqua.
COT values are calculated for two case studies of low and high surface albedo values, focusing on total cloud cover conditions and liquid clouds. The COT values retrieved from the ZSRs are obtained by using various combinations of transmissivities at different wavelengths. Numerical simulations allowed us to provide uncertainties for the ZSR COT estimates. We found that the use of broadband albedo values in the retrievals instead of spectrally-resolved ones is the largest source of uncertainties. The COT values obtained with the different methods during the two case studies range between 1 and 45.
Results show that the ZSR-based retrievals lack sensitivity for clouds with COT between 6 and 14. Numerical simulations can explain this shortcoming and they will also be presented. For COT larger than 14, the ZSR-based estimates agree very well with the other methods employed. We will discuss in detail how the different estimates compare to one another and show that, given the observatory measurements capabilities, estimates of COT could be performed continuously and with good accuracy in high surface albedo conditions by means of ZSR and DSI measurements.
How to cite: Muscari, G., Calì Quaglia, F., Tosco, M., Meloni, D., Di Bernardino, A., Di Iorio, T., Focardi, A., Pace, G., Schmidt, S. K., and di Sarra, A.: Cloud optical thickness measurements in high albedo conditions at the Thule High Arctic Atmospheric Observatory (THAAO), Greenland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18587, https://doi.org/10.5194/egusphere-egu25-18587, 2025.
