Studies of Noctilucent Clouds With an Inter-Continental Network of Automatic Digital Cameras

Noctilucent clouds (NLC) are the highest clouds in the Earth's atmosphere, occurring around the mesopause at 80-85 km altitudes. They can be seen during summer nights (May-September in the northern hemisphere). These clouds are composed of small ice particles scattering sunlight, making NLC readily visible against the dark twilight sky. NLC are excellent indicators of the physical state of the mesosphere and may be readily studied with ground- based instruments. The presence (or absence) of NLC is determined by the complex combination of a number of characteristics of the mesosphere: temperature, abundance of water vapor, meteor dust particles and hydrated ions. NLC are not uniformly distributed in the mesosphere around the globe, but some processes control their spatial and temporal variability. A ground-based network of digital cameras is an excellent tool to monitor NLC formation and dynamics around the globe as well as to study the wind regime and wave activity in the mesosphere. Since 2004, automatic digital cameras have been operating during summer time (May 25 - August 15) to register NLC. In 2007 the five cameras were in Athabasca (Canada), Port Glasgow (Scotland), Aarhus (Denmark), Moscow (Russia), and Novosibirsk (Russia). These points have near the same latitudes (between 55N and 57N) and are separated by a long distance in longitude. This provides comparable NLC observations in the same latitude circle and allows studying NLC homogeneity on continental scales as well as gravity and planetary wave activity. The combination of NLC observations made from ground and space will provide us valuable information on the NLC geographical distribution and atmospheric processes taking place in the mesosphere during the NLC season.