Linear polarization signatures of atmospheric dust with the SolPol direct-sun polarimeter
<p>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...
| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-10-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/16/4529/2023/amt-16-4529-2023.pdf |
| Summary: | <p>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 2 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<span class="inline-formula"><sup>−7</sup></span>.</p>
<p>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 on 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.</p> |
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| ISSN: | 1867-1381 1867-8548 |