Observations and Modeling of Atmospheric Profiles in the Arctic Seasonal Ice Zone

Monday, 15 December 2014
Zheng Liu, Axel J B Schweiger and Ronald W Lindsay, University of Washington, Polar Science Center, Applied Physics Laboratory, Seattle, WA, United States
We use the Polar Weather Research and Forecasting (WRF) model to simulate atmospheric conditions during the Seasonal Ice Zone Reconnaissance Survey (SIZRS) in the summer of 2013 over the Beaufort Sea. With the SIZRS dropsonde data, we evaluate the performance of WRF simulations and two forcing data sets: the ERA-Interim reanalysis and the Global Forecast System (GFS) analysis.
General features of observed mean profiles, such as low-level temperature inversion, low-level jet (LLJ) and specific humidity inversion are reproduced by Polar WRF, ERA-Interim, and GFS. A near-surface warm bias and a low-level moist bias are found in ERA-Interim. WRF significantly improves the mean LLJ, with a lower and stronger jet and a larger turning angle than the forcing. The improvement in the mean LLJ is likely related to the lower values of the boundary layer diffusion in WRF than in ERA-Interim and GFS. The relative humidity profiles have large differences between the observations, the ERA-Interim, and the GFS. The WRF simulated relative humidity closely resembles the forcings, suggesting the need to obtain more and better-calibrated humidity data in this region.
An inappropriate thresholding mechanism for sea ice concentrations in the ECMWF model is identified. During summer, sea ice concentrations over large areas are set to zero when the satellite-retrieved sea surface temperature is higher than 274.26 K. This thresholding affects both the ERA-Interim and the ECMWF operational model. The impact of this issue on the atmospheric boundary layer in the marginal ice zone is still unknown.