Investigation of dust related phenomena in the Earth's upper atmosphere.

The Earths middle, or upper atmosphere contain some intriguing phenomena, such as the noctilucent clouds (NLC) and the abnormally strong radar reflecting layers (PMSE) at 80-90 km height, the highest clouds in the atmosphere. These clouds increase in st rength and extent and it is speculated if this is linked to climatic changes. Similar radar layers (PMWE) occurring in the winter at heights 55-75 km have recently been observed. The upper atmosphere is difficult to investigate since direct in situ meas urements can only be done by rockets. Most observations are done as remote sensing with radars, lidars and satellites. We have made significant discoveries with our new types of rocket instrumentation and miniaturized rocket payloads. We have also foun d a new radar technique, the overshoot method, which is able to give more information on the physical state in the NLC/PMSE cloud layers than what can be extracted by conventional methods. The investigations on the phenomena of the upper atmosphere will be continued and expanded in the present project. The radar investigations with the new overshoot technique will be done in new international campaigns and we will expand the investigations in radar frequency down to 50 MHz with a new radar financed by U iTø and NFR. We have developed, and will continue to develop new rocket instrumentation. We will in particular pursue the findings from our dust probe, where it is likely that one until now unwanted secondary charging effect, from impacting dust particl es, can be used to find the sizes of dust particles. Our experimental activities will continue to be supported by theoretical modeling of the conditions in the dust layers. We will also pursue the confirmation of our recent prediction that non-visual background dust in the upper atmosphere may be identified from radar observations of meteor trails.