An assessment of future extreme precipitation in western Norway using a linear model

A Linear Model (Smith and Barstad, 2004) was used to dynamically downscale Orographic Precipitation over western Norway from twelve General Circulation Model simulations. The GCM simulations come from the A1B emissions scenario in IPCC's 2007 AR4 report. An assessment of the changes to future Orographic Precipitation (time periods: 2046–2065 and 2081–2100) versus the historical control period (1971–2000) was performed. Results showed increases in the number of Orographic Precipitation days and in Orographic Precipitation intensity. Extreme precipitation events, as defined by events that exceede the 99.5%-ile threshold for intensity for the considered period, were found to be up to 20% more intense in future time periods when compared to 1971–2000 values. Using station-based observations from the control period, the results from downscaling could be used to generate simulated precipitation histograms at selected stations. <br><br> The Linear Model approach also allowed for simulated changes in precipitation to be disaggregated according to their causal source: (a) the role of topography and (b) changes to the amount of moisture delivery to the site. The latter could be additionaly separated into moisture content changes due to the following: (i) temperature, (ii) wind speed, and (iii) stability. An analysis of these results suggested a strong role of moist stability and warming in the increasing intensity of extreme Orographic Precipitation events in the area

Stord Orographic Precipitation Experiment (STOPEX): an overview of phase I

STOPEX (Stord Orographic Precipitation Experiment) is a research project of the Geophysical Institute, University of Bergen, Norway, dedicated to the investigation of orographic effects on fine scale precipitation patterns by a combination of numerical modelling and tailored measurement campaigns. Between 24 September and 16 November 2005 the first field campaign STOPEX I has been performed at and around the island of Stord at the west coast of Norway, about 50 km south of Bergen. 12 rain gauges and 3 autonomous weather stations have been installed to measure the variability of precipitation and the corresponding meteorological conditions. This paper gives an overview of the projects motivation, a description of the campaign and a presentation of the precipitation measurements performed. In addition, the extreme precipitation event around 14 November with precipitation amounts up to 240 mm in less than 24 h, is described and briefly discussed. In this context preliminary results of corresponding MM5 simulations are presented, that indicate the problems as well as potential improvement strategies with respect to modelling of fine scale orographic precipitation

A Downscaling Approach Toward High-resolution Surface Mass Balance Over Antarctica

The Antarctic ice sheet surface mass balance shows high spatial variability over the coastal area. As state-of-the-art climate models usually require coarse resolutions to keep computational costs to a moderate level, they miss some local features that can be captured by field measurements. The downscaling approach adopted here consists of using a cascade of atmospheric models from large scale to meso-gamma scale. A regional climate model (Modegravele Atmospheacuterique Reacutegional) forced by meteorological reanalyses provides a diagnostic physically-based rain- and snowfall downscaling model with meteorological fields at the regional scale. Although the parameterizations invoked by the downscaling model are fairly simple, the knowledge of small-scale topography significantly improves the representation of spatial variability of precipitation and therefore that of the surface mass balance. Model evaluation is carried out with the help of shallow firn cores and snow height measurements provided by automatic weather stations. Although downscaling of blowing snow still needs to be implemented in the model, the net accumulation gradient across Law Dome summit is shown to be induced mostly by orographic effects on precipitation