Date of Award

5-17-2024

Document Type

Thesis

Abstract

This thesis presents new observations of noctilucent clouds (NLCs), and their environment made with collocated Rayleigh and resonance lidars at Poker Flat Research Range (PFRR), Chatanika, Alaska (65°N, 147° W). In 2019, the Rayleigh Density Temperature Lidar (RDTL) at PFRR was extended to a three-channel system and employed for NLC measurements. RDTL yields measurements with signals a factor of 3-4 times higher than previous studies allowing measurements at higher resolution and to higher altitudes. This study is based on 14 observations in late July and early August between August 8, 2019, and August 11, 2022. NLCs were detected in 10 of the 14 observations, or 70% of the time. The lidar density profiles derived above and below the clouds are used to interpolate the density profiles through the clouds and provide a more accurate estimate of the cloud properties. The clouds are characterized in terms of brightness, duration, and altitude. The NLC peaks are found to be between 80.5 and 84.8 km with backscatter ratios between 7 and 216, and backscatter coefficients between 1.2x10⁻¹⁰ m⁻¹sr⁻¹ and 5.7x10⁻⁹ m⁻¹sr⁻¹. The cloud characteristics are compared with previous lidar observations at PFRR, and their occurrence is compared with observations from the CIPS instrument on the AIM satellite. The continuous lidar density profiles are used to determine the temperatures through the cloud layers, with an initial measurement of temperature above the NLCs at 90 km. Using the collocated Sodium Resonance Wind Temperature Lidar (SRWTL) at PFRR, cloud temperatures are found to be between 141 K and 161 K at 82 km. The temperatures are analyzed in terms of signal quality and other model and satellite sources of temperature. The temperature measurements are discussed in terms of the 'Thermostat Mechanism' where NLCs actively regulate their thermal environment to produce an 'equithermal submesopause'.

Handle

http://hdl.handle.net/11122/15147

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