Wednesday, 11 July 2018
Regency A/B/C (Hyatt Regency Vancouver)
Observations of cloud properties and radiative and turbulent fluxes over the Arctic ocean are sparse due to difficulties with operating and maintaining instruments, particularly during the winter. Using observational data from the SHEBA campaign in the late 1990s, past studies have shown that clouds are particularly difficult to simulate over Arctic ocean. The Norwegian Young Sea Ice (N-ICE2015) field campaign was recently performed from January through July 2015 during which a research vessel (R/V Lance) was frozen into thin, young sea ice in the Arctic ocean north of Svalbard. N-ICE2015 deployed a comprehensive suite of instruments to measure atmospheric and cloud properties including surface meteorology, twice-daily radiosonde profiles, radiative fluxes, turbulent fluxes and cloud macrophysical properties. We use these observations to evaluate the performance of the polar version of the Weather Research and Forecasting model (Polar WRF) over sea ice in three seasons. During winter, a succession of synoptic storms was observed during which the surface temperature ranged between -40 to 0 C. In some cases, the surface temperature changed dramatically within several hours. These storms also modified the near-surface temperature and humidity structure, as well as the radiative fluxes, sensible heat flux, and cloud impacts at the surface. Before N-ICE2015, storms of this magnitude had not been thoroughly characterized in the Arctic. The observed conditions during the spring and summer were more typical of the Arctic. Preliminary comparisons during one of the winter storms shows that the surface pressure is well simulated by Polar WRF. Even though the magnitudes of the surface temperature and infrared upwelling and downwelling fluxes are fairly well represented, the timing of the changes are delayed by approximately 12-18 hours. Despite the shift in time, this indicates that Polar WRF appears to simulate the Arctic clear and opaquely cloudy states well during N-ICE2015. We will provide additional testing of Polar WRF over the entire N-ICE2015 campaign using different cloud and boundary-layer parameterization schemes with particular emphasis on their effect on the surface energy balance over young, thin sea ice.
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