M. K. Yau

Simulation of blowing snow in the Canadian Arctic using a double-moment model

We describe in this paper the development of a double-moment modelof blowing snow and its application to the Canadian Arctic. Wefirst outline the formulation of the numerical model, whichsolves a prognostic equation for both the blowing snow mixingratio and total particle numbers, both moments of particles thatare gamma-distributed. Under idealized simulations, the modelyields realistic evolutions of the blowing snow particledistributions, transport and sublimation rates as well as the thermodynamic fields at low computational costs. A parametrizationof the blowing snow sublimation rate is subsequently derived. The model and parametrization are then applied to a Canadian Arctictundra site prone to frequent blowing snow events. Over a period of210 days during the winter of 1996/1997, the near-surfacerelative humidity consistently approaches saturationwith respect to ice. These conditions limit snowpack erosion byblowing snow sublimation to ≈3 mm snow water equivalent (swe)with surface sublimation removing an additional 7 mm swe.We find that our results are highly sensitiveto the proper assimilation of the humidity measurements and the evolving thermodynamic fields in the atmospheric boundary layer during blowingsnow. These factors may explain the lower values of blowing snow sublimationreported in this paper than previously published for the region.

A BULK BLOWING SNOW MODEL

We present in this paper a simple and computationally efficient numerical model that depicts a column of sublimating, blowing snow. This bulk model predicts the mixing ratio of suspended snow by solving an equation that considers the diffusion, settling and sublimation of blowing snow in a time-dependent mode. The bulk model results compare very well with those of a previous spectral version of the model, while increasing its computational efficiency by a factor of about one hundred. This will allow the use of the model to estimate the effects of blowing snow upon the atmospheric boundary layer and to the mass balance of such regions as the Mackenzie River Basin of Canada.

A climatology of adverse winter-type weather events

Using the European Centre for Medium-Range Weather Forecasts Re-Analysis gridded data, a global climatology of blowing snow, blizzard, and high-windchill events is conducted for the period 1979–1993. The results show that these phenomena occur primarily over flat, open surfaces with long seasonal or perennial snow covers such as the Greenland and Antarctic ice fields as well as the Arctic tundra. On a regional scale, emphasis is given to the Mackenzie River Basin (MRB) of Canada, where fewer events take place within the boreal forest as opposed to the Arctic tundra. Interannual and monthly variabilities in the number of events are also evident and are due primarily to 10-m wind speed anomalies at high latitudes for blowing snow and blizzard events, while high-windchill events are more sensitive to air temperatures near the surface. We also find that high-windchill episodes are the more frequent events, since they occur at 9.3% of all possible grid points and times on a yearly basis, while blowing snow at 6.5% and blizzards at 1.4% are less common events. Compositing of principal meteorological fields show that anticyclones and lee cyclones are prominent features associated with blowing snow events in some sections of the MRB.

Simulation of an Arctic Ground Blizzard Using a Coupled Blowing Snow–Atmosphere Model

A ground blizzard occurred from 16 to 18 November 1996 in the northern sectors of the Mackenzie River basin of Canada and the adjacent Beaufort Sea. This hazardous event, accompanied by a low-level jet with wind speeds approaching 20 m s21 and extensive blowing snow near the surface (but clear sky aloft), is forced by a strong sea level pressure gradient that forms between a rapidly intensifying anticyclone over the Nunavut and Northwest Territories of Canada and an intense depression over the frozen Arctic Ocean. The event is first simulated at a horizontal grid size of 18 km using the uncoupled Canadian Mesoscale Compressible Community (MC2) model. This experiment is shown to capture the rapid anticyclogenesis event within 2 hPa of its central sea level pressure and the blizzard conditions near the Canadian Arctic coastline and the Beaufort Sea. Meteorological conditions observed at Trail Valley Creek (TVC), a small Arctic tundra watershed in which ground blizzard conditions were experienced during the event, are also accurately reproduced by the uncoupled simulation with the notable exception of the blowing snow process. Thus, the mesoscale model is then coupled to the ‘‘PIEKTUK’’ blowing snow model, and a second simulation is conducted. This additional experiment reveals the presence of extensive blowing snow associated with a strong low-level jet over TVC and the adjacent frozen Beaufort Sea. Over the 2-day event, blowing snow sublimation and transport combined to erode 1.6 mm snow water equivalent from the surface mass balance of TVC. The concurrent moistening and cooling of near-surface air due to blowing snow sublimation emerge during the blizzard but to a lesser extent than in an idealized modeling framework, as a consequence of entrainment and advective processes. Therefore, blowing snow sublimation rates are evaluated to be 1.8 times larger than in the stand-alone application of the PIEKTUK model to the same data.

Recent Studies on the Climatology and Modeling of Blowing Snow in the Mackenzie River Basin

This chapter presents a multi-scale analysis of the contribution of blowing snow to the hydrometeorology of the Mackenzie River Basin (MRB). A climatology of adverse wintertime weather events demonstrates that blowing snow events are rare within the forested sections of the MRB but become more frequent in the northern parts of the Basin covered by tundra, which experience the largest impacts of blowing snow transport and sublimation due to large-scale processes. A parameterization for blowing snow sublimation based on the PIEKTUK-D model and the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (ERA-15) data is used to determine that the combined processes of surface and blowing snow sublimation deplete 29 mm yr-1 snow water equivalent, or about 7% of the watershed’s annual precipitation. This study provides only a first-order estimate of the contribution of surface sublimation and blowing snow to the MRB surface mass balance because of limitations with the dataset and some uncertainties in the blowing snow process.