Geoscience Reference
In-Depth Information
time variation of direct intensity, one can conclude that within 2 min after
seeding all the crystals precipitate out. Crystal formation becomes complete
within the first 30 s, thereafter the crystals remain floating for nearly 50 s,
and falling down of crystals becomes complete in the next 40 s.
5. Conclusion
The widespread presence of DMS in atmosphere and ocean is now estab-
lished. DMS has strong possibility of being oxidized in the atmosphere, and
then DMSO may be a product. Reports are also available for the production
of DMSO due to biosynthesis of DMS by phytoplanktons. Some DMSO may
be lifted to middle and upper atmosphere by convection, and then it has
a strong possibility of acting as IN. It is known that nearly 30% of the
earth is always covered by cirrus cloud,
35
−
38
which is mainly formed by
ice crystals, and DMSO is supposed to have some contribution to it. So,
DMSO is expected to play a role in the modification of the solar energy
budget of the earth.
It is noted that DMSO has good ice-nucleating ability over a long range
of temperature on the negative side of 0
◦
C. A sharp peak in that ability is
attained at the eutectic temperature of DMSO and water combine. DMSO
can exist in liquid state over the tropical ocean surface and it has then
the chance of coating various particulate aerosols. It may be noted that
DMSO-coated Ammonium Sulfate particles have much greater nucleation
ability. The study of nucleation characteristics of other DMSO-coated solid
aerosols is also needed to assess the extent of its influence in the solar energy
modification on earth.
Forward-scattering of the heterogeneous ice cloud formed by DMSO is
significant. Though the back-scattering is in general less than the forward-
scattering by an order of 1 or 2, it attains a value more than the forward-
scattering from
−
18
◦
Cto
−
13
◦
C, when cubic and hexagonal crystals
dominate. It seems, the halo effect then dominates. In the laboratory, when
convection is absent, all crystals due to DMSO fall down within 2 min of
seeding.
Acknowledgment
The authors' thanks are due to Indian Meteorological Department,
Government of India for the sanction of the research project. The present
work is a part of the project.
