A preliminary microscopic examination of ice crystals collected from seeding experiments (Schaefer, Finnegan), during the Seventh Yellowstone Field Research Expedition, has indicated that several types of joined ice crystals appear on sampling plates. The number of joined ice crystals comparative to the individual ice crystals on the same plate seems dependent on location, environment, temperature gradient and electric field at the sampling area.

Photomicrographic analysis reveals that the character of joined ice crystals could be classified into three types (Figure).

(1) "I" Formation - Two or more ice crystals joined in a straight line, such as I-1and I-2. It appears mostly near great temperature gradient areas, such as those surrounding hot geysers and pools, where existing electric fields have previously been recorded by scientists. It may be assumed that a charge separation has taken place within a crystal with its polarity corresponding to the existing electric field. Attracting force between opposite charges contribute to the formation of the ice crystal chain in a straight line I

(2) "T" Formation - Two individual ice crystals joined perpendicular to each other by an exact 90 degree, such as T-1 and T-2. This phenomenon appears in most environments, provided that the ice crystals are growing in an adequately moisturized surrounding.

It is known that latent heat will be released during the condensation process of an ice crystal. In this case, of plate or spherical crystals, the temperature difference exists between the surface and its interior, and charge separation will be taking place within the ice crystal, which can be explained by thermoelectric effect. The sign of the charge is corresponding to the temperature with net negative charge concentration in a warmer region (surface).

In the case of column or needle crystals, the rate of moisture deposition is greater on the ends of an ice crystal than on the center region. Then, the net negative charge will be concentrated at both ends - warmer region of the ice crystal. Again, in both cases, the attracting force between opposite charges contribute to the "T" formation of joined ice crystals.

(3) Irregular Formation - It can be explained that individual single ice crystals fall on top of each other during sampling periods on a collective plate.

This phenomenon of joined ice crystals has been previously observed in seeding experiments in a laboratory cloud chamber with controlled conditions (Smith-Johannsen, Cheng). The above possible interpretation may provide some answers to this unusual natural phenomenon.

YELLOWSTONE FIELD RESEARCH

EXPEDITION--VII-1967