The seasonal frequency of noctilucent clouds has been discussed on the basis of visual data from the Northern Hemisphere. It is shown that there is a strong dependence on the atmospheric constitution at the mesospheric level and the seasonal transition in the mesopause. Before spring transition and after autumn transition of the mesosphere at the 80 km level no NLC are observed on the Northern Hemisphere. Conversely we can conclude the same distribution for the Southern Hemisphere and the strong relation between transition periods and occurrence of NLC.
Extracts from Otto Jesse's papers relating to twilight studies, noctilucent clouds and atmospheric movements are presented here to illustrate his contribution to the subject during the years 1884-1901. The most important result of his activity was the establishment of the Berlin “Atmospheric Programme” which included regular monitoring of noctilucent clouds by visual and photographic means. Furthermore, Jesse studied problems of dynamic processes in noctilucent clouds and in the corresponding upper atmospheric layers.
Based on visual noctilucent cloud data, the effect of the autumn transition of winds in the mesosphere is investigated. Following the autumnal transition of the mesospheric winds no noctilucent clouds were observed. The higher temperature of the winter mesosphere can be physically explain the fact that no noctilucent clouds occur during winter of the Northern Hemisphere. Accordingly, noctilucent clouds only occur on the typical summer mesosphere related to the low temperature there and due to the stable condition of the then mesospheric region.
A new interpretation of celestial phenomena became apparent after the appearance of the great aurora of March 1716. The philosopher Wolff presented a general lecture to the public in which he explained the aurora as a normal celestial phenomenon.
The development of the great aurora of January 18, 1770 has been discussed in a fundamental paper by Silberschlag (1770) and other authors. The aurora was observed in middle and low latitudes and in Northern latitude. In Central Europe it displayed all typical auroral forms, including the Corona.