Geoscience Reference
In-Depth Information
and halo.
30
−
32
It is reported that hexagonal crystals can produce halo when
back-scattering intensity significantly increases. This happens mainly due
to successive reflection and refraction in a hexagonal crystal.
33
Since at
the seeding temperature of
13
◦
C, the crystals are dominantly hexagonal
in shape and also there are some cubic and prism-shaped crystals, the
dominant back-scattering intensity at
−
13
◦
C seems to be due to halo effect.
In fact, strong back-scattering effect is generally observed in cirrus cloud
top region.
31
The optical parameters like scattering coecient, extinction coecient,
and optical thickness are three important optical parameters, characteri-
zing a crystal cloud. The variation of scattering coecient with seeding
temperature is presented in Fig. 6, for different angles of scattering. The
scattering coecient is found to attain the peak value at
−
21
◦
C for all
−
13
◦
C. The back-
scattering coecient at 144
◦
is found to be greater than the forward-
scattering coecient at 36
◦
at that temperature. Around
angles of scattering. It shows a second peak close to
−
16
◦
C,
the back-scattering coecient at 144
◦
is found to have the maximum value,
as cubic crystals are dominant. However, the absolute value is quite less
there. A representative diagram for the variation of extinction coecient
18
◦
Cto
−
−
Fig. 6.
Variation of scattering coecient with seeding temperature.
