The PMC Turbo Experiment: Design, Development, and Results

• Main Author: Kjellstrand, Carl Bjorn
• Format: Thesis
• Language: unknown
• Published: Columbia University 2021
• Subjects: Atmosphere; Physics; Gravity waves > Measurement; Mesosphere; Thermosphere; Canada; Northwest Passage; Esrange; Northwest passage
• Online Access: https://dx.doi.org/10.7916/d8-az4s-b142; https://academiccommons.columbia.edu/doi/10.7916/d8-az4s-b142

In the middle and upper atmosphere, dynamics of scales from tens of meters to thousands of kilometers primary arise due to the influence of gravity waves propagating from lower altitudes. In order to understand the structure and variability of these regions of our planet's atmosphere, we must understand the propagation, influences, and dissipation of gravity waves. However, gravity waves and their influences are difficult to measure. Their largest and most observable effects occur in the remote mesosphere and lower thermosphere and the relevant spatial scales extend across many orders of magnitude. The EBEX group discovered a novel method to observe polar mesospheric clouds, which are a sensitive tracer of gravity waves and their associated dynamics. This discovery motivated the Polar Mesospheric Cloud Turbulence (PMC Turbo) experiment. Polar mesospheric clouds form an extremely thin but bright layer at roughly 80 kilometer altitude in which we can observe brightness fluctuations created by gravity wave dynamics and the resulting instabilities. PMC Turbo included seven pressure vessels, each of which contained an optical camera, hard drives, and computers that controlled the image capture, flight control, and communication with ground stations. The cameras captured spatial scales from gravity waves with wavelengths of roughly 10-100 kilometers, instability dynamics at scales from about 1-10 kilometers, and the fine structure at the inner scale of turbulence down to 20 meters. PMC Turbo flew at 38 kilometer altitude and remained afloat for nearly six days. During this time, it travelled from Esrange Space Center in Sweden to the Northwest Passage in Canada. Complementary data from other instruments provides additional atmospheric context to the PMC Turbo measurements. During flight, the PMC Turbo cameras captured images of polar mesospheric clouds tracing Kelvin-Helmholtz instabilities with a high signal-to-noise ratio. Kelvin-Helmholtz instabilities play major roles in energy dissipation and structure of geophysical fluids, and they have a close relationship with gravity waves. The PMC Turbo images include complicated interactions and secondary instabilities leading to turbulence. These dynamics provide insight into the atmospheric conditions and rate of energy dissipation in the mesosphere and lower thermosphere.