on CLOUD PHYSICS
JULY 31-AUGUST 4,
of natural ice pellets collected in a thunderstorm reveal
that electrically charged and particle embedded micro-droplets
are being ejected by bursting of air bubbles released from
the melting ice pellets. The observation of the physical appearance
of more than 500 natural ice pellets (Figs. 1, 2) show that
a large number of ice pellets have a spicule on their surface, in some cases multiple spicules. Ice pellets with a crack
on the surface or semi-spherical pellets also can be found
in the sample. There is a strong indication that extremely
high pressure exists inside the ice shell of a water drop
during the rapid freezing process. Unfrozen water in the form
of microdroplets is suggested to be forced out from such spicules,
or cracks, of the freezing water drops (Cheng, 1970).
- Ice pellet with one
- Ice pellet with multiple
- Semi-spherical pellets
or pellets with cracks......10%
- Spherical pellets..................................................15%
- LEFT: FROZEN RAIN
DROPS (ICE PELLETS) from
- NATURE THUNDERSTORM
- RIGHT: FROZEN WATER
DROPS from LAB. EXP.
Two types of air bubbles are
observed in the collected ice pellets:
(1) Spherical or cylindrical air bubbles which are
formed by the release of dissolved air in the water drop at
the ice-water interface, due to different solubility of air
in water and ice, during the freezing process as observed
by Cheng (1973a).
(2) Numerous micros-size air bubbles are also observed
in some cases in the form of milk- like opaque areas in the
ice pellets (Fig. 3).
is suggested that these are formed by the rapid release of
interior pressure by excreted unfrozen water from the ice
shell of a freezing water drop.
An ice pellet placed in a
warmer environment with a temperature above its melting point
will first become covered with a melted film of liquid water.
As the outer layer of ice melts, entrapped air bubbles
can be observed moving toward the surface of the melting ice
pellet. They remain at the ice surface for a few seconds,
but eventually separate from the ice surface as melting continues.
The air bubbles then travel radically with extremely high
velocity in the liquid water surrounding the melting ice pellet
(Fig. 4). On close microscopically examination, numerous micro-droplets
being ejected from the melting ice pellet by bursting of the
released air bubbles at the water-air interface. These
ejected micro-droplets are formed from the shattered
bubble film and by breakdown of a jet from the collapsed bubble
cavity. (Blanchard, 1963). Three groups of micro-droplets
with different masses being ejected from the water surface by the bursting of a stream of
air bubbles produced by
a hypodermic needle are shown in
particulates, embedded in ice pellets, tend to become attached
to the surface of released air bubbles (Fig. 6) in the melting
process and are then subsequently ejected into the surrounding
environment with the micro-droplets by bursting these air
bubbles (Fig. 7).
Ejected micro-droplets are
collected on glass slides
coated with gelatin and attached to a pair of electrodes.A
high voltage (1000 V DC) is applied to the electrodes in order
to deflect charged droplets to the respective electrodes.
A grounded conducting plate is placed between the melting ice pellet
and the electrodes
and a small opening in the center of the conducting
plate works as a pathway for the ejected droplets to reach the collecting slides. In this way, possible induction
by an electric field to the melting ice pellet and
the ejecting droplets can be eliminated. Study of
property of ejected droplets, simply by counting the number
of collected droplets from both electrodes,
indicates that 70%75% of
the ejected droplets carry a negative electric
charge. The electrical conductivity of water from the
melted ice pellet is l2Ox10-6 ohm/cm.
of melting artificial
ice spheres, made from water with
various electrical conductivity by dissolving salt into it,
reveal interesting results as shown in Fig. 9, and
that electrical properties of ejected micro-droplets
are closely associated with the salt concentration in water from melting ice pellets.
Electrical Conductivity X10-6(ohm/cm)
% of Negatively
|Natural Ice Pellet
Artificial Ice Spheres:
- 1. DistilledWater
- 2. With Less
- 3. With
- 4. Sea Water
and electrification of hydrometeors during phase transition
play an important role in generation and separation of electricity
in the atmosphere. It is widely accepted that the charge generation
and separation processes in a thundercloud are closely associated
with the development of precipitation and the main charge
centers that appear above the freezing level. It is reported,
from observations made inside thunderclouds that lightning
flashes coincide with the appearance of solid precipitation
in the form of ice pellets or soft hail. Ejection of electrically
charged microdroplete by freezing a super-cooled water drop
(Cheng, 1970) and sublimational breakup of electrically charged
secondary ice fragments from a growing ice particle (Schaefer
& Cheng,1971, Cheng, 1973b) were previously reported.
Electrification of melting ice particles has been studied
by Magono and Kikuchi, 1963; Dinger, 1965; and Drake, 1968.
The observation of the ejection of electrically charged micro-droplets
by bursting of air bubbles released from the melting ice pellet
represents a third stage of microscopical process of fragmentation
and electrification of hydrometeors, below freezing level,
in the atmosphere.
D.C. (1963). The
electrification of the, atmosphere by particles from
bubbles in the sea.
- Prog.Oceanog., 1, 71-202.
R .J. (1970). Water
drop freezing: ejection of micro-droplets.
- Science, 170, 3965, 13931396.
R.J. (l973a). Photomicroscopical
investigation of fragmentation of hydrometeors in the
- The Microscope, 21, 3, 149160.
R.J. (1973b). The
mechanism of multiplication process of glaciations in
of 8th Intl. Conf. on Nucleation, Leningrad, U.S.S.R.,
J.E. (1965). Electrification
associated with the melting of snow and ice.
- J. Atmos. Sçi., 22,
J.E. (1968). Electrification
accompanying the melting of ice particles.
- Q. J. Roy. Met.
Soc 94, 176191.
- Msgono, C. and Kikuchi, K. (1963). On the positive electrification of snow crystals in
the process of their melting.
- J. Met. Soc. Japan, 41, 270277.
BUBBLE FORMATION on ICE SURFACE:
of air bubbles, which were observed at the INTERFACE
of ICE and WATER on the
surface of the FREEZING DROP(1mm). The air bubbles were
formed as a result of the decrease of solubility of
air in water when the temperature of the drop increased
upon freezing.---due to releast lathen heat.
has LESS SOLUBILITY in ICE than WATER
by POLARIZED MICROSCOPE, REVIEWED MANY AIR BUBBLES ( BACK
POCKETS) AGAINST COLORED ICE.
BUBBLES WERE FORMED DURING FREEZING of WATER ON ICE SURFACE.
RINGS OF BUBBLES ZONES INSIDE THE HAILSTONE INDICATED
THIS HAIL HAD TRAVELLED ( UP & DOWN) MANY TIMES INSIDE
BUBBLES being RELEASED from A MELTING ICE PELLET
than 300 air bubbles (average diameter of 50 um) are being
released and accelerated
radially from a half melted ice pellet--
(1 mm). which
is following by ejection of micro-droplets by busting
of these air bubbles from a melting ice pellet.
outside temperture of the melting ice pellet and water
is warmer than the frozen
pellet, due to latent heat released during PHASE CHANGE
of ice to water,
note those air bubbles keep distance with each other because
they each carried same sign of electric charge(-).