 |
| Titel |
Some effects of ice crystals on the FSSP measurements in mixed phase clouds |
| VerfasserIn |
G. Febvre, J.-F. Gayet, V. Shcherbakov, C. Gourbeyre, O. Jourdan |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 12, no. 19 ; Nr. 12, no. 19 (2012-10-01), S.8963-8977 |
| Datensatznummer |
250011488
|
| Publikation (Nr.) |
 copernicus.org/acp-12-8963-2012.pdf |
|
|
|
|
|
| Zusammenfassung |
| In this paper, we show that in mixed phase clouds, the
presence of ice crystals may induce wrong FSSP 100 measurements
interpretation especially in terms of particle size and subsequent bulk
parameters. The presence of ice crystals is generally revealed by a bimodal
feature of the particle size distribution (PSD). The combined measurements
of the FSSP-100 and the Polar Nephelometer give a coherent description of
the effect of the ice crystals on the FSSP-100 response. The FSSP-100
particle size distributions are characterized by a bimodal shape with a
second mode peaked between 25 and 35 μm related to ice crystals. This
feature is observed with the FSSP-100 at airspeed up to 200 m s−1 and
with the FSSP-300 series. In order to assess the size calibration for clouds
of ice crystals the response of the FSSP-100 probe has been numerically
simulated using a light scattering model of randomly oriented hexagonal ice
particles and assuming both smooth and rough crystal surfaces. The results
suggest that the second mode, measured between 25 μm and 35 μm,
does not necessarily represent true size responses but
corresponds to bigger aspherical ice particles. According to simulation
results, the sizing understatement would be neglected in the rough case but
would be significant with the smooth case. Qualitatively, the Polar
Nephelometer phase function suggests that the rough case is the more
suitable to describe real crystals. Quantitatively, however, it is difficult
to conclude. A review is made to explore different hypotheses explaining the
occurrence of the second mode. However, previous cloud in situ measurements suggest
that the FSSP-100 secondary mode, peaked in the range 25–35 μm, is
likely to be due to the shattering of large ice crystals on the probe inlet.
This finding is supported by the rather good relationship between the
concentration of particles larger than 20 μm (hypothesized to be ice
shattered-fragments measured by the FSSP) and the concentration of (natural)
ice particles (CPI data). In mixed cloud, a simple estimation of the number
of ice crystals impacting the FSSP inlet shows that the ice crystal
shattering effect is the main factor in observed ice production. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|