Size dependence of the mesospheric dust temperature and its influence on the noctilucent clouds and polar mesosphere summer echo phenomena

The temperature of dust in the Earth's mesosphere, which is determined by collisions with the neutral gas, absorption of radiation from the Sun, the Earth and its own thermal radiation, in general increases with dust size [Grams and Fiocco, 1977]. This may lead to situations where there is a maximum size of the dust r_C above which the dust temperature is too high for condensation of water vapor to occur. Dust of this size can still accrete other elements. If they accrete a sufficient amount of elements, with low ionization potential as a surface "contamination," their photoelectric properties may change. We suggest that this can lead to their charges changing from the "normal" low negative value of pure ice particles to the positive charges which rocket in situ observations have shown to exist. In such cases we will have a situation with small, newly created and negatively charged dust particles coexisting with larger and positively charged dust charges. Agglomeration of dust particles will then be an effective process. We also demonstrate that the changes in the polar surface temperature of the Earth during the polar mesosphere summer echo (PMSE) season can influence the mesospheric dust temperature and by this have a potential effect on the shape of the occurrence rate curve of the PMSE.