1. Model calculationsMeasurements An extreme precipitation event during STOPEX I J.Reuder and I. Barstad Geophysical Institute, University of Bergen, Norway Contact:Geophysical Institute, University of Bergen Allegaten 70, N-5007 Bergen, Norway joachim.reuder@gfi.uib.no idar.barstad@gfi.uib.no Introduction STOPEX (Stord Precipitation Experiment) is a project at the Geophysical Institute in Bergen dedicated to the investigation of orographic effects on fine scale precipitation by numerical modeling and measure- ments. During the field campaign STOPEX I from September 26 to November 16, 2005, 12 rain gauges (P1-P12) and 3 autonomous weather stations (W1- W3) have been installed on and around the island of STORD, approximately 50 km south of Bergen, Norway (see maps below). The island extends about 10 km east-west and 25 km north-south and reaches a maximum altitude of 700 m. The approach of nearly undisturbed marine air by flow from southwest to northwest makes this site a suitable test-bed for orographic precipitation and related micro-physics. Summary Precipitation measurements show a high horizontal variability due to orographic effects (50 to 243 mm within an accumulation period of 15 to 20 hours) State-of-the-art model simulations using MM5 can, even with a horizontal resolution of 1 km, only reproduce about 50 % of the observed maximum precipitation values The linear model is able to reproduce the observed maximum precipitation only in case of very short hydrometeor conversion times Detailed analysis is topic of an ongoing master thesis Instrumentation: Precipitation measurements have been performed by HOBO RG2 data logging rain gauges with a resolution of 0.2 mm. The instruments have been validated by a 3 month intercomparison with the official measurements of the Norwegian Meteorological Service met.no. A good agreement in daily precipitation sum was found with a slight underestimation (up to 5 %) of the HOBO instruments for daily precipitation sums above 15 mm. References: Barstad, I., and R. B. Smith, Evaluation of an orographic precipitation model, Journal of Hydrometeorology, 6, 85-99, 2005. Dudhia and the MM5 tutorial class staff, PSU/NCAR Mesoscale Modeling System Tutorial Class Notes and User’s Guide, 2005. (http://www.mmm.ucar.edu/mm5/documents/tutorial-v3-notes.html) Smith, R. B., and I. Barstad, A linear theory of orographic precipitation, Journal of Atmospheric Sciences, 61, 1377-1391, 2004. Acknowledgements: We are grateful to our colleagues A. Sandvik for the realization of MM5 simulations and T. de Lange for the technical support during preparation, execution and evaluation of the field campaign. Linear model: The following equations are solved in Fourier space and Fast-Fourier- Tranformed (FFT) back to real space: where q c (x, y) and q s (x, y) are vertically integrated cloud water density and hydrometeor density, respectively. τ c and τ f are the time constants for conversion from cloud water to hydrometeors (i.e., rain or snow) and fallout of hydrometeor. S(x,y) is the source term for cloud water due to forced lifting, see Smith and Barstad (2004) for more details. Case study November 14: The synoptic situation was characterized by the passage of a low pressure system associated with moderate to strong (40-50 kts) winds from south-west to west in the lower troposphere. The extreme precipitation event during November 13 and 14, 2005 has been hind- casted by two different numerical simula- tions. Both, the Penn State/UCAR model MM5 and a linear model have been used to deter- mine the precipitation distribution during the event with high spatial resolution. MM5: MM5 has been setup with 4 nestings (27 km – 9 km- 3 km – 1 km), the boundary conditions have been taken from ECMWF analysis. For cloud and precipitation microphysics the explicit moisture scheme 5 (Reisner mixed phase scheme) has been used (Dudhia et al., 2005). max. 110 mm (observed maximum 243 mm; see Figs. 2 and 4) max. 70 mm max. 210 mm  c = 500 s  c = 200 s Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 7 Fig. 6 terrain U = 25 m s -1 V = 6 m s -1