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and $ \varpi_{p} $ is the plasma frequency which is related to $ N_{c} $ by:

$$
\omega_ {p} = 5. 6 4 \times 1 0 ^ {3} \sqrt {N _ {c}}
$$

7. Thus radar energy entering a medium of lower refractive index is a similar situation to total internal reflection in optics.

8. Calculations show that to reflect 10 GHz microwaves a plasma should be at least 1-2 cm in thickness and less than -20dB through-transmission. It is possible for very high RF energies to be reflected (although the case here is much attenuated by the arrival of a radar pulse having suffered propagation attenuation $ \alpha 1 / R^{2} $ (which will be repeated on the reverse journey for a monostatic radar inspection).

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10. It should also be noted that the greatest visual luminosity occurs when the frequency of the oscillation of ions and electrons is equal to the applied frequency:

$$
4 \pi_ {c} ^ {2} / \mathrm {m} \omega_ {0} ^ {2} = 1
$$

## BALL LIGHTNING AS A RADAR REFLECTOR

11. As stated at Working Paper No. 2, ball and bead lightning (which do not always

appear as spheres), may have diameters as small as a few cm and as large as 12-15 metres. For the ball lightning sphere to 'float', its gaseous density is known （1.29 x $ 1 0^{-3} $ gm $ \mathrm{cm}^{-3} $ ）, but its plasma density is not known, unless this can be deduced via its colour/temperature characteristic.

12. Radar Echoing Areas The radar echoing area of ball lightning would be expected to be of the order calculated from its physical size. A transition between a strongly reflecting target and an almost completely absorbing target occurs. The possible RCS values for plasma spheres are different from that of metallic spheres (who's RCS is a function of sphere radius and radar wavelength), with the radar echoing area of plasma spheres dependent also on ionisation level. An 'overdense' plasma sphere (or other shape) may be treated as a perfect reflector. However other plasmas depend, for their RCS, upon interference effects between the backscattered wave and tightly bound surface waves. This gives the plasma the properties of a dielectric, even when it is overdense. For example, a collisionless homogeneous plasma sphere with low electron density may have a RCS value of -60dB, peaking between 1 to $ 8 \mathrm{m}^{2} $ as the density increases, but falling to $ 1 \mathrm{m}^{2} $ as the density increases yet further. These values are for D/E(L) Band assessments.

## DUSTY PLASMAS AS RADAR REFLECTORS

13. It is argued that dust' particles possibly of ice, form noctilucent clouds. (These are of the type, see Working Paper No. 13, which are sometimes reported as UAPs) A more recent understanding of dusty plasmas is at Working Paper No 19 "Charged Dust Aerosols'). It can be postulated that the plasmas containing these particles comprises two ionic components (one single charged atomic or molecular ion and a positive, or negative, multiple charged dust particle). Due to the tendency of the plasma to charge neutrally, a kind of charged cloud forms