Preprints
https://doi.org/10.5194/amt-2023-121
https://doi.org/10.5194/amt-2023-121
16 Jun 2023
 | 16 Jun 2023
Status: a revised version of this preprint was accepted for the journal AMT and is expected to appear here in due course.

Observations of Dust Particle Orientation with the SolPol direct sun polarimeter

Vasiliki Daskalopoulou, Panagiotis Ioannis Raptis, Alexandra Tsekeri, Vassilis Amiridis, Stelios Kazadzis, Zbigniew Ulanowski, Vassilis Charmandaris, Konstantinos Tassis, and William Martin

Abstract. Dust particles in lofted atmospheric layers may present a preferential orientation, which could be detected from the resulting dichroic extinction of the transmitted sunlight. The first indications were provided relatively recently on atmospheric dust layers using passive polarimetry, when astronomical starlight observations of known polarization were found to exhibit an excess in linear polarization, during desert dust events that reached the observational site. We revisit the previous observational methodology by targeting dichroic extinction of transmitted sunlight through extensive atmospheric dust layers utilizing a direct-Sun polarimeter, which is capable to continuously monitor the polarization of elevated aerosol layers. In this study, we present the unique observations from the Solar Polarimeter (SolPol) for different periods within two years, when the instrument was installed in the remote monitoring station of PANGEA - the PanHellenic Geophysical Observatory of Antikythera in Greece. SolPol records polarization, providing all four Stokes parameters, at a default wavelength band centred at 550 nm with a detection limit of 10-7.

We, overall, report on detected increasing trends of linear polarization, reaching up to 700 parts per million, when the instrument is targeting away from its zenith and direct sunlight propagates through dust concentrations over the observatory. This distinct behaviour is absent on measurements we acquire on days with lack of dust particle concentrations, and in general of low aerosol content. Moreover, we investigate the dependence of the degree of linear polarization to the layers’ optical depth under various dust loads and solar zenith angles, and attempt to interpret these observations as an indication of dust particles being preferentially aligned in the Earth’s atmosphere.

Vasiliki Daskalopoulou et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2023-121', Anonymous Referee #1, 05 Jul 2023
  • RC2: 'Comment on amt-2023-121', Anonymous Referee #2, 18 Jul 2023

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2023-121', Anonymous Referee #1, 05 Jul 2023
  • RC2: 'Comment on amt-2023-121', Anonymous Referee #2, 18 Jul 2023

Vasiliki Daskalopoulou et al.

Data sets

D-TECT: SolPol measurements Vasiliki Daskalopoulou, Panagiotis I. Raptis, Alexandra Tsekeri, Vassilis Amiridis, Stelios Kazadzis, Zbigniew Ulanowski, Vassilis Charmandaris, Konstantinos Tassis, and William Martin https://doi.org/10.5281/zenodo.7233498

Model code and software

SolPol data algorithm Vasiliki Daskalopoulou https://github.com/NOA-ReACT/SolPol

Vasiliki Daskalopoulou et al.

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Executive editor
From the handling editor : I think this paper is of particular interest to the geoscience community (following peer review) though likely too arcane for broader public/media. There's been a lot of discussion of the potential for preferentially oriented dust particles and this has impacts for remote sensing and modeling. So this seems to be an important step towards real characterisation of them. I agree with the authors' provided comment here so reproduce it below: Atmospheric dust particles with irregular shapes may present a preferential orientation in the Earth's atmosphere. This alignment can be detected from the resulting dichroic extinction of the transmitted sunlight through the elevated dust layers. Since mineral dust is one of the most abundant atmospheric aerosols and plays a significant role to the radiative forcing of the global climate, the somewhat elusive observation of particle orientation will be a game changer to existing remote sensing measurement techniques and the implementation of particle dynamics in desert dust transport models. With our research, we utilize a specifically designed direct sun Solar Polarimeter (SolPol), installed and operated on a remote observatory in Greece, and report on unique observations of enhanced linear polarization during dust events. We aim to interpret our measurements as the first observations of atmospheric dust particle orientation by measuring direct sunlight.
Short summary
Atmospheric dust particles may present a preferential alignment due to their shape on long range transport. Since dust is abundant and plays a key role to global climate, the elusive observation of orientation will be a game changer to existing measurement techniques and the representation of particles in climate models. We utilize a specifically designed instrument, SolPol, and target the Sun from the ground for large polarization values under dusty conditions, a clear sign of orientation.