Precipitation, Cloud Cover, and Mixing Layer Observations at the Iqaluit Supersite

Reliable measurements of light precipitation, cloud cover, and mixing layer height (MLH) are required to quantify the Arctic water cycle and improve parameterization schemes in numerical weather prediction models. Satellite and ground-based observations of light precipitation are frequently underestimated at high latitudes, where 80% of precipitation is light (< 1 mmh-1). Cloud cover and MLH parameterization schemes are also poorly constrained in the Arctic due to a lack of observations. Environment and Climate Change Canada (ECCC) has recently commissioned a supersite in Iqaluit, NU (64oN, 69oW) to provide automated and continuous observations of altitude-resolved winds, clouds and aerosols, visibility, sensible heat flux, turbulence, and precipitation. New high-resolution cloud and MLH products from a Vaisala CL31 ceilometer are being used to investigate model performance and parameterization schemes. Initial MLH comparisons with the new High Resolution Deterministic Prediction System Arctic domain indicate good agreement, with greater MLH variability observed by the ceilometer. The suite of instruments at Iqaluit can measure the thickness, height, and composition of very light precipitation, as demonstrated during an intensive observation period (January 18 to 22, 2016). Vertical advection of blowing snow up to 450 m a.g.l. was observed by a Doppler Lidar during periods of increased surface winds (> 10 m/s), followed by an ice crystal layer that was observed up to 500 m a.g.l. These events were undetected by traditional precipitation gauges, causing the under-reporting of light precipitation. Given the prevalence of blowing snow and ice crystal events in the Arctic and their large radiative surface forcing of up to 36 W/m2, this can have important consequences when quantifying the Arctic water cycle and radiative balance.