Ice crystal characterization in cirrus clouds: a sun-tracking camera system and automated detection algorithm for halo displays
Halo displays in the sky contain valuable information about ice crystal shape and orientation: e.g., the 22° halo is produced by randomly oriented hexagonal prisms while parhelia (sundogs) indicate oriented plates. HaloCam, a novel sun-tracking camera system for the automated observation of hal...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-07-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/10/2499/2017/amt-10-2499-2017.pdf |
| _version_ | 1818479715960225792 |
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| author | L. Forster M. Seefeldner M. Wiegner B. Mayer B. Mayer |
| author_facet | L. Forster M. Seefeldner M. Wiegner B. Mayer B. Mayer |
| author_sort | L. Forster |
| collection | DOAJ |
| description | Halo displays in the sky contain valuable information about ice
crystal shape and orientation: e.g., the 22° halo is produced
by randomly oriented hexagonal prisms while parhelia (sundogs)
indicate oriented plates. HaloCam, a novel sun-tracking camera system
for the automated observation of halo displays is presented. An
initial visual evaluation of the frequency of halo displays for the
ACCEPT (Analysis of the Composition of Clouds with Extended
Polarization Techniques) field campaign from October to mid-November
2014 showed that sundogs were observed more often than
22° halos. Thus, the majority of halo displays was produced
by oriented ice crystals. During the campaign about 27 % of
the cirrus clouds produced 22° halos, sundogs or upper tangent
arcs. To evaluate the HaloCam observations collected from regular
measurements in Munich between January 2014 and June 2016, an
automated detection algorithm for 22° halos was developed,
which can be extended to other halo types as well. This algorithm
detected 22° halos about 2 % of the time for this
dataset. The frequency of cirrus clouds during this time period was
estimated by co-located ceilometer measurements using temperature
thresholds of the cloud base. About 25 % of the detected
cirrus clouds occurred together with a 22° halo, which implies
that these clouds contained a certain fraction of smooth, hexagonal
ice crystals. HaloCam observations complemented by radiative transfer
simulations and measurements of aerosol and cirrus cloud optical
thickness (AOT and COT)
provide a possibility to retrieve more detailed information about ice
crystal roughness. This paper demonstrates the feasibility of
a completely automated method to collect and evaluate a long-term
database of halo observations and shows the potential to characterize
ice crystal properties. |
| first_indexed | 2024-12-10T11:14:25Z |
| format | Article |
| id | doaj.art-53222f8b4edb4c24a17e4a926cba3bb3 |
| institution | Directory Open Access Journal |
| issn | 1867-1381 1867-8548 |
| language | English |
| last_indexed | 2024-12-10T11:14:25Z |
| publishDate | 2017-07-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Measurement Techniques |
| spelling | doaj.art-53222f8b4edb4c24a17e4a926cba3bb32022-12-22T01:51:16ZengCopernicus PublicationsAtmospheric Measurement Techniques1867-13811867-85482017-07-01102499251610.5194/amt-10-2499-2017Ice crystal characterization in cirrus clouds: a sun-tracking camera system and automated detection algorithm for halo displaysL. Forster0M. Seefeldner1M. Wiegner2B. Mayer3B. Mayer4Chair of Experimental Meteorology, Ludwig-Maximilians-Universität, Munich, GermanyChair of Experimental Meteorology, Ludwig-Maximilians-Universität, Munich, GermanyChair of Experimental Meteorology, Ludwig-Maximilians-Universität, Munich, GermanyChair of Experimental Meteorology, Ludwig-Maximilians-Universität, Munich, GermanyInstitut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt, Oberpfaffenhofen, GermanyHalo displays in the sky contain valuable information about ice crystal shape and orientation: e.g., the 22° halo is produced by randomly oriented hexagonal prisms while parhelia (sundogs) indicate oriented plates. HaloCam, a novel sun-tracking camera system for the automated observation of halo displays is presented. An initial visual evaluation of the frequency of halo displays for the ACCEPT (Analysis of the Composition of Clouds with Extended Polarization Techniques) field campaign from October to mid-November 2014 showed that sundogs were observed more often than 22° halos. Thus, the majority of halo displays was produced by oriented ice crystals. During the campaign about 27 % of the cirrus clouds produced 22° halos, sundogs or upper tangent arcs. To evaluate the HaloCam observations collected from regular measurements in Munich between January 2014 and June 2016, an automated detection algorithm for 22° halos was developed, which can be extended to other halo types as well. This algorithm detected 22° halos about 2 % of the time for this dataset. The frequency of cirrus clouds during this time period was estimated by co-located ceilometer measurements using temperature thresholds of the cloud base. About 25 % of the detected cirrus clouds occurred together with a 22° halo, which implies that these clouds contained a certain fraction of smooth, hexagonal ice crystals. HaloCam observations complemented by radiative transfer simulations and measurements of aerosol and cirrus cloud optical thickness (AOT and COT) provide a possibility to retrieve more detailed information about ice crystal roughness. This paper demonstrates the feasibility of a completely automated method to collect and evaluate a long-term database of halo observations and shows the potential to characterize ice crystal properties.https://www.atmos-meas-tech.net/10/2499/2017/amt-10-2499-2017.pdf |
| spellingShingle | L. Forster M. Seefeldner M. Wiegner B. Mayer B. Mayer Ice crystal characterization in cirrus clouds: a sun-tracking camera system and automated detection algorithm for halo displays Atmospheric Measurement Techniques |
| title | Ice crystal characterization in cirrus clouds: a sun-tracking camera system and automated detection algorithm for halo displays |
| title_full | Ice crystal characterization in cirrus clouds: a sun-tracking camera system and automated detection algorithm for halo displays |
| title_fullStr | Ice crystal characterization in cirrus clouds: a sun-tracking camera system and automated detection algorithm for halo displays |
| title_full_unstemmed | Ice crystal characterization in cirrus clouds: a sun-tracking camera system and automated detection algorithm for halo displays |
| title_short | Ice crystal characterization in cirrus clouds: a sun-tracking camera system and automated detection algorithm for halo displays |
| title_sort | ice crystal characterization in cirrus clouds a sun tracking camera system and automated detection algorithm for halo displays |
| url | https://www.atmos-meas-tech.net/10/2499/2017/amt-10-2499-2017.pdf |
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