Synchronous polar winter starphotometry and lidar measurements at a High Arctic station

[摘要] We present recent progress on nighttime retrievals of aerosol and cloudoptical properties over the PEARL (Polar Environmental Atmospheric ResearchLaboratory) station at Eureka (Nunavut, Canada) in the High Arctic(80° N, 86° W). In the spring of 2011 and 2012, astar photometer was employed to acquire aerosol optical depth (AOD) data, whilevertical aerosol and cloud backscatter profiles were measured using theCANDAC Raman Lidar (CRL). We used a simple backscatter coefficient threshold(β_thr) to distinguish aerosols from clouds and, assuming thataerosols were largely fine mode (FM)/sub-micron, to distinguish FM aerosolsfrom coarse mode (CM)/super-micron cloud or crystal particles. Usingprescribed lidar ratios, we computed FM and CM AODs that were compared withanalogous AODs estimated from spectral star photometry. We found(β_thr dependent) coherences between the lidar andstar photometer for both FM events and CM cloud and crystal events withaveraged, FM absolute differences being <∼0.03 when associatedR² values were between 0.2 and 0.8. A β_thr sensitivitystudy demonstrated that zero crossing absolute differences and R² peakswere in comparable regions of the β_thr range (or physicalreasons were given for their disparity). The utility of spectral vs.temporal cloud screening of star photometer AODs was also illustrated. Ingeneral our results are critical to building confidence in the physicalfidelity of derived, weak amplitude, star photometry AODs and, in turn,towards the development of AOD climatologies and validation databases forpolar winter models and satellite sensors.

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