The High Arctic experiences prolonged periods of total darkness in the winter and continuous daylight in the summer, influencing its atmosphere and composition in ways that are still not fully understood. Conducting atmospheric measurements in this remote region is challenging, particularly during polar night when solar-viewing instruments are not operational. An Extended-range Atmospheric Emitted Radiance Interferometer (E-AERI) was installed at the Polar Environment Atmospheric Research Laboratory (PEARL) at Eureka, Canada (80°N, 86°W) in October 2008. The E-AERI is a moderate resolution (1cm−1) Fourier transform infrared spectrometer that measures the absolute downwelling infrared spectral radiance from the atmosphere between 400 and 3000 cm−1 (3.3-25 µm). These measurements, which are independent of sunlight, are being used to establish a year-round record of trace gas columns and cloud properties in the High Arctic.
E-AERI spectra have been used to retrieve total column concentrations of O3, CO, CH4, and N2O year-round through the implementation of the updated SFIT4 retrieval algorithm, which is based on the optimal estimation method. Arctic cloud microphysical properties (cloud optical depth, thermodynamic phase, and effective radius) can be retrieved from E-AERI spectra using the Cloud Atmospheric Radiation Retrieval Algorithm (CLARRA), which also uses an iterative optimal estimation technique, in which forward-model calculations are performed using the Line-by-Line Radiative Transfer Model (LBLRTM) and the Discrete Ordinate Radiative Transfer Model (DISORT). This presentation will provide an overview of the trace gas measurements and preliminary results for the retrieval of cloud microphysical properties.