Geoscience Reference
In-Depth Information
recognized as ice or cloud condensation nuclei (IN or CCN).
15
−
18
In the
present work, DMSO is identified as a good IN.
The behavior of DMSO as IN has been studied inside a laboratory
scale cold room over the negative side of 0
◦
C starting from
22
◦
Conthe
lower end. The ice nucleation ability is found to be maximum at
−
21.0
◦
C,
which is also the eutectic temperature of DMSO and water bivariate system.
In fact, this observation is consistent with what has been noted in the case
of many other seeding agents.
18
−
21
Above that temperature, the nucleation
ability gradually falls off and almost vanishes near 0
◦
C. The mode of the
dimension of falling crystals at different seeding temperatures was noted,
and the modal value has consistent temperature-variational pattern with
the crystal count. No nucleation ability is noted above 0
◦
C, unlike the
agents like ammonium sulfate,
18
benzoin dust,
22
urea,
20
or the bacteria
Pseudomonas aeruginosa
.
23
In reality some of the DMSO particulates are supposed to be carried
to the middle and upper atmosphere by convection, and these have the
ability to form heterogeneously nucleated ice cloud. The concerned clouds
can scatter and absorb solar radiation as well as the radiation emitted from
the earth, and have the ability to modify the solar radiation budget of
the earth. In order to estimate the extent of modification to the radiation
budget due to DMSO, study of bulk-scattering properties and absorption
characteristics of ice crystals formed at different temperatures and over the
entire spectrum of solar radiation is necessary. This particular exercise is
partially taken up in the present study.
DMSO exists dominantly near the sea surface, and it can exist as liquid
drop particularly over the tropical sea region. The liquid drops of DMSO
may coat many solid aerosols. As a large fraction of the aerosols are in the
form of sulfates,
24
the effect of coating of a dominant sulfate i.e. Ammonium
Sulfate, by DMSO has also been studied.
To study the optical properties of ice cloud nucleated by DMSO, a
5 mW plane-polarized He-Ne laser beam (wavelength 633 nm) was passed
through it. The observational procedures were almost identical to a similar
work done for sodium chloride dust and aqueous solution.
21
The time for
crystal growth and fall out can be estimated from the rise and fall of
scattering intensity at different angles with time. The variation of scattering
intensity at different angles with change of seeding temperature is noted.
The scattering coecient, extinction coecient, and optical depth are also
evaluated.
−
