The mesospheric part of this project aims to provide better understanding of the characteristics of clouds at the polar summer mesospause. Existing and new observations made by atmospheric radars in Kiruna, and at sites in Queen Maud Land , Antarctica (Wasa/Aboa, Troll, Maitri), are / will be used. The aim is to compare observations in rather different conditions (different hemispheres, different geomagnetic and meteorological environments) with theories relating radar echoes from the clouds (Polar Mesosphere Summer Echoes, PMSE) to the cloud properties. Comparison of radar echoes with direct measurements of cloud ice particle properties by satellite will also be used. Mesospheric clouds are expected to increase in response to increasing amounts of CO2 and CH4 in the atmosphere. So far, any increase is too small to be reliably separated from natural variations. The project will develop and test new independent calibration methods to allow the recent decade´s observations of radar echoes from the clouds to be accurately compared to observations made in past and future decades.
Responsible scientist: Prof. Sheila Kirkwood
The objectives of the project are studies of mesospheric dynamics, turbulence, solar and geomagnetic influence on PMSE/PMWE, long-term trends in occurrence, strength and aspect sensitivity of PMSE, mechanisms of echo generation. Uses primarily measurements by the ESRAD MST radar located near Kiruna (ESRAD), MARA MST radar located in Antarctica as well as EISCAT VHF and UHF radars (EISCAT). ESRAD PMSE data are available since 1997. Active probing PMSE/PMWE using ionospheric modification experiments with the EISCAT Heating facility (EISCAT_HEATING).
Responsible scientist: Dr. Evgenia Belova
Noctilucent clouds are a wonderful natural laboratory for the investigation of wave activity around the summer mesopause. The extremely low temperatures at the polar summer mesopause are far from the radiative balance. If radiative processes control the thermal structure of the mesosphere, one would expect warm summers and cold winters (the polar mesosphere is illuminated by the Sun 24 hours a day in summer and vice versa in winter). However observations made in the 1950’s have showed exactly the opposite result: low summer temperatures and warm winter ones. This is a result of dynamical processes caused by a vertical air motion conjugated with a complex wave activity in the middle atmosphere. The key role in these processes is supposed to belong to gravity wave propagations and their breaking. There is also a strong influence of planetary waves on global scales as well as of turbulent eddies of a few meters. This dynamical forcing drives the polar summer mesopause around 60 degrees away from radiative equilibrium temperatures.
Noctilucent clouds provide us important information on characteristics of atmospheric gravity waves of small (wavelength of 5–10 km), medium (10–100 km) and large scales (100–1000 km) which produce large temperature variations up to 5–10 K. Also, multipoint observations of NLCs around the globe allows for investigating huge atmospheric planetary waves having wavelengths from several thousand up to 20000 km in the sub-polar and polar regions and typical periods of 2-, 5- and 16-days, which are one of the major players in the middle atmosphere producing strong disturbances of the basic state of the atmosphere, with temperature disturbances of 1–8 K.
Responsible scientist: Dr. Peter Dalin