Infrared Emission Measurements of Radiation and Trace Gas Variability in the High Arctic

The objective of this Ph.D. is to investigate the atmospheric radiative budget and composition in the high Arctic using a new (prototype) interferometer. The Canadian Network for the Detection of Atmospheric Change has equipped the Polar Atmospheric Environment Research Laboratory (PEARL) at Eureka, Nunavut (80ยบN, 86ยบW) with an Extended-range Atmospheric Emitted Radiance Interferometer (E-AERI), which was installed in October 2008 at the PEARL Ridge Lab (610 m a.s.l.). The E-AERI measures the infrared (IR) thermal emission of the atmosphere in the 400-3000 cm-1 (3.3-25 μm) spectral region. An older AERI, the Polar AERI (P-AERI), was stationed in Eureka from 2006-2009 and was located at sea level. The impact of clouds and ice crystals on the radiative budget were investigated from two altitudes using these two AERIs. The increased radiance due to the presence of clouds was found to be larger at Eureka than at the Southern Great Plains (SGP), indicating that cloud cover plays an important role in the Arctic's radiative budget. This thesis presents the first measurements of the two surface cooling-to-space windows (at 10 and 20 μm) in the high (> 75o N) Arctic. Distributions of brightness temperatures were filtered based on cloud cover and do not vary in the summer, indicating that the 20 μm window is closed when water vapour is a maximum. Trends in downwelling radiance were found in several spectral microregions corresponding to these cooling-to-space windows and meteorological conditions (temperature, water vapour, cloud cover). Trends at 10 μm during the winter were positive, in the opposite direction, and significantly larger (factor > 3) than any of the seasonal trends detected at the SGP, indicating that changes in the downwelling radiance are accelerated in the high Arctic compared to lower latitudes. Spectra recorded by the E-AERI were also used to retrieve total column concentrations of O3, CO, CH4, and N2O year-round to fill a gap in the PEARL data series, providing the first continuous ground-based trace gas measurements throughout polar night at Eureka. This work involved the implementation of the SFIT2 retrieval algorithm modified for emission spectra. E-AERI trace gas retrievals were characterized and comparisons to other spectrometers at Eureka are within uncertainties (1-9% differences). An investigation of the diurnal and seasonal cycle of CO was performed to highlight the usefulness of continuous, year-round measurements at Eureka.Ph.D