Preliminary DIMM and MASS Nighttime Seeing Measurements at PEARL in the Canadian High Arctic

Results of deploying a differential image motion monitor (DIMM) and a DIMM combined with a multiaperture scintillation sensor (MASS/DIMM) are reported for campaigns in 2011 and 2012 on the roof of the Polar Environment Atmospheric Research Laboratory (PEARL). This facility is on a 610 m high ridge at latitude 80°N, near the Eureka weather station on Ellesmere Island, Canada. The median seeing at 8 m elevation is 0″.85 or better based on DIMM data alone, but is dependent on wind direction and likely includes a component due to the PEARL building itself. Results with MASS/DIMM yield a median seeing less than 0″.76. A semiempirical model of seeing versus ground wind speed is introduced which allows agreement between these datasets, and with previous boundary-layer profiling by lunar scintillometry from the same location. This further suggests that best 20th percentile seeing reaches 0″.53, of which typically 0″.30 is due to the free atmosphere. Some discussion for guiding future seeing instrumentation and characterization at this site is provided.