Geoscience Reference
In-Depth Information
ICE-NUCLEATING AND OPTICAL PROPERTIES
OF ICE CLOUD SEEDED BY DIMETHYL
SULFOXIDE (DMSO)
L. N. BISWAS
∗
,A.HAZRA
†
,P.MAITI
∗
, V. MANDAL
∗
,
U. K. DE
∗,§
and K. GOSWAMI
‡
∗
Atmospheric Science Research, Environmental Science Programme,
Jadavpur University, Kolkata 700032, India
†
Department of Atmospheric Science, National Taiwan University,
Taipei, Taiwan 106, ROC
‡
Department of Physics, Jadavpur University, Kolkata 700032, India
§
deutpal2003@yahoo.com
The widespread presence of DMS (Dimethyl sulfide) in sea water and its
atmosphere is now established. DMS may be oxidized into DMSO (Dimethyl
Sulfoxide), and its presence in the atmosphere is also established.
DMSO was seeded inside a cold room to examine its ice-nucleating
characteristics and to study the optical properties of the iced cloud. It was
found to be a good ice-nucleating agent. The maximum nucleation occurred
at
−
21.0
◦
C, which is the eutectic temperature of DMSO and water bivariate
system. The variation of modal value of the dimension of crystal with seeding
temperature had consistent pattern with the count of crystal nucleation. When
DMSO-coated Ammonium Sulfate dust was seeded, two peaks in nucleation
count appeared. While the highest peak was at
−
21.0
◦
C, like the previous
experiment, the second highest peak occurred at
−
18.2
◦
C, which is the eutectic
temperature of Ammonium sulfate and water combine. However, the crystal
count increases manifold. In this case also, the modal value of crystal size had
a consistent pattern with the variation of crystal count.
To study the optical properties, a laser beam of wavelength 633 nm is
sent through the iced cloud. In general, the forward-scattering intensity is
greater than the backward-scattering intensity by an order of 1 or 2. But,
from
−
18
◦
Cto
−
13
◦
C, the backward-scattering dominates over the forward-
scattering. This feature is attributed to halo effect, as the cubic and hexagonal
shaped ice crystals dominate then. Apart from that, the variation of scattering
coecient, extinction coecient, and optical thickness of the ice cloud, with
seeding temperature is also presented.
§
Corresponding author.
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