ON THE ROLE OF DUST IN THE SUMMER MESOPAUSE

We propose that dust formed at the cool summer mesopause may have optical properties very different from that measured for bulk material of ice. The smallness of the dust and possible surface impurities may lead to high photoelectric yields and low workfunctions. For such reasons the dust in the summer mesopause may, at least occasionally, be charged to substantial positive surface potentials while pure ice, with its high photoelectric workfunction, would be charged to low and negative potentials by collisions with plasma particles. The presence of 'dressed' dust particles, with surface potentials of some volts, can lead to enhanced radar backscatter. We also suggest that the apparent reductions in electron density ('bite-out'), which have been observed in the radar backscatter region, can be caused by the inability of an electrostatic probe to deflect the massive dust particles. The dust density which is required by our model to explain radar backscatter and electron bite-outs is of the order of 10 cm-3 for dust of radius above 5 × 10-6 cm. © 1990.