Condign volumes 1 to 3

Read from the scan by GLM-OCR; expect the odd misread word.

# UNCLASSIFIED

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either direction) and often have a hollow centre. Water spouts occur similarly at sea. Tornadoes are predominantly cyclonic in rotation. All three phenomena move at prevailing wind-speed.

## CONDENSATION & DISSIPATION TRAILS

10. 'Contrails' and 'Distrails' are well known visual effects in the sky. Drawn into aerodynamic vortices (i.e. wing-tip vortices), these can fragment to provide unusual visual phenomena. Distrails are formed when an aircraft flies in relatively dry air just above a thin layer of cloud such that the down-wash penetrates the layer. This can produce a series of 'holes'. Pendulous blobs (with the probable appearance of spheres) can occur.

## GLORY & CORONAS

11. Coronas are colourful concentric rings centred on bright light sources. They are caused by water droplets or ice crystals of relatively uniform size. However, observers in both Texas and Finland have reported coronas caused by pollen particles. Coronas can be distinguished from halos in that they commonly have a radius angle of 22 degrees, although the extremes reported for halos have boundaries of 4 to 46 degrees. The key filter to use in UAP identification is that coronas are always centred on a bright object. Figure 7(a) shows the shadow of a crucial peak thrown onto mist. The observer (on the peak) is surrounded by a multicoloured 'Glory' of corona rings. In fact until the advent of aircraft only mountaineers could observe the effect. This is due to the refraction and diffraction of light by the mist droplets. This effect can also be seen from aircraft when their shadow falls on droplet clouds. On the ground it is especially noticeable in

hilly country, when air close to the ground cools and flows into valleys overnight. Some of the ice particles in cirrus wave clouds at temperatures of -40 to -50 degrees C, apparently form faceted uni-axial polyhedral crystals, while others resemble spheres. It is well known that 'Glory' results from the interference of light rays back-scattered from internally reflected and circumferential ray paths (the latter is unique to spheres).

12. As seen at Figure 7(b), the incident ray couples to a sphere as a surface wave, is critically refracted into the sphere, reflects, and is critically refracted back to the surface, spends a short period as a surface wave and is directed back towards the original source. A curved wavefront is formed by exciting the rays to the right and left of the glory ray. Rotating this curved wavefront (Figure 7(c)), through an angle $ (\Pi) $ , as directed by spherical geometry, reveals that a wavefront shape associated with the Glory is a toroid. Propagation of this wavefront to a far field gives rise to a strong axial focusing, because the infinite number of rays from the ring around the flat part of the wavefront all go in the same direction. As soon as the observer moves off the exact back-scattered axis, only two rays contribute to the scattering and it is the interference between the left and right rays of the toroidal wavefront that produces the 'Glory'.

## HALOS & ARCS

13. A halo is observed when looking at the sun through high altitude cirro-stratus (which is several thousand feet deep and composed of non-spherical ice crystals which have also recently been suspected of producing 'Glories'. It is a cloud type which readily forms aircraft condensation trails). The halo angular radius (i.e. half