Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
This thesis dwells on the physical properties of the unique highest clouds, called Noctilucent Clouds (NLCs) or Polar Mesospheric Clouds (PMCs) in the earth’s atmosphere at around the summer and winter mesopause of 80-90 km, a height characterised by extremely low parameters. These are restrictedly observable in both the hemispheres, mid-May to mid-August in the Northern Hemisphere and mid-November to mid-February in the Southern Hemisphere, and at latitudes 50-65° North or South from earth. Noctilucent clouds have attracted the attention of scientists as well as during the last couple of decades especially due to their some inconclusive physical features and processes such as reliable knowledge typical shape and size distribution, most important initial condensation nuclei responsible for their formation, occurrence frequency etc.
Researchers have reached to a consensus regarding NLC such as vertically buoyant gravity waves play a great role for making mesopause region to be their occurrence stage. The size range of the particles has been determined from visual observation; in-situ rocket using photometers, satellite remote sensing satellite sensor SCIAMACHY and ALOMAR Rayleigh/Mie/Raman (RMR) LIDAR, and majority of the researches have shown that the effective particle size generally remains smaller than 75nm.
The NLC particle size determination model employed in this project assumes Mie scatterers using mono-modal log-normal distribution. Color ratios of the volume backscattering coefficients were measured using 355 nm, 532 nm, and 1065 nm that can help determine the physical properties and understand their microphysical landscape. Our theoretical results are in agreement with the experimental results from ALOMAR Rayleigh/Mie/Raman Lidar by Cossart von. et.al. (1999) rendering a strong proxy for physical properties assessment. Physical characteristics of the NLCs would be further established by advancing knowledge in the size distribution and occurrence of these clouds with altitude.