Role of sublimation and riming on the precipitation distribution in the Kananaskis Valley, Alberta, Canada

Abstract

Abstract. The phase of precipitation and its distribution at the surface can affect water resources and the regional water cycle of a region. A field project was held in March–April 2015 on the eastern slope of the Canadian Rockies to document precipitation characteristics and associated atmospheric conditions. During the project, 60 % of the particles documented were rimed, in relatively warm and dry conditions. Rain-snow transitions also occurred aloft and at the surface in sub-saturated conditions. Solid precipitation falling through a saturated atmospheric layer with temperatures > 0 °C will start melting. In contrast, if the melting layer is sub-saturated, the solid precipitation undergoes sublimation, which increases the depth of the rain-snow transition. In this context, this study investigates the role of sublimation and riming on precipitation intensity and type reaching the surface in the Kananaskis Valley, Alberta, where the field campaign took place during March–April 2015. To address this, a set of numerical simulations of an event of mixed precipitation observed at the surface was conducted. This event on 31 March 2015, was documented with a set of devices at the main observation site (Kananaskis Emergency Services, KES) including a precipitation gauge, disdrometer, and micro rain radar. Sensitivity experiments were performed to assess the impacts of temperature changes from sublimation and the role of the production of snow pellets (riming) aloft on the surface precipitation evolution. A warmer environment associated with no temperature changes from sublimation leads to a peak in the intensity of snow pellets at the surface. When the formation of snow pellets is not considered, the maximum snowfall rate occurred at later times. Results suggest that unrimed snow reaching the surface is formed on the western flank and is advected eastward. In contrast, snow pellets would form aloft in the Kananaskis Valley. The cooling from sublimation and melting by rime particles increases the vertical shear near KES. Overall, this study illustrated that the presence of snow pellets influenced the surface evolution of precipitation type in the valley due to the horizontal transport of precipitation particles.