Bologna Limited Area Model Research Articles

Sensitivity of Precipitation Forecast Skill Scores to Bilinear Interpolation and a Simple Nearest-Neighbor Average Method on High-Resolution Verification Grids

Abstract Grid transformations are common postprocessing procedures used in numerical weather prediction to transfer a forecast field from one grid to another. This paper investigates the statistical effects of two different interpolation techniques on widely used precipitation skill scores like the equitable threat score and the Hanssen–Kuipers score. The QUADRICS Bologna Limited Area Model (QBOLAM), which is a parallel version of the Bologna Limited Area Model (BOLAM) described by Buzzi et al., is used, and it is verified on grids of about 10 km (grid-box size). The precipitation analysis is obtained by means of a Barnes objective analysis scheme. The rain gauge data are from the Piedmont and Liguria regions, in northwestern Italy. The data cover 243 days, from 1 October 2000 to 31 May 2001. The interpolation methods considered are bilinear interpolation and a simple nearest-neighbor averaging method, also known as remapping or budget interpolation, which maintains total precipitation to a desired degree...

An Integrated Forecast System over the Mediterranean Basin: Extreme Surge Prediction in the Northern Adriatic Sea

Abstract A previsional system for the forecast of the state of the Mediterranean Sea and of surges in the northern Adriatic Sea has been designed and tested. The system consists of a limited area model (the Bologna Limited Area Model, BOLAM), which computes high-resolution pressure and surface wind fields, to serve as the input of a wave model (WAM) and of a shallow water model (two-dimensional Princeton Ocean Model, POM-2D). Results of two case studies are presented, chosen to test the ability of the system to predict extreme surge events originating from cyclonic circulation over the Mediterranean basin. The two case studies cover the periods 4–9 October 1998 and 11–22 November 1996. Comparison with observed buoy data shows that the results of the WAM simulations forced by the wind fields obtained from the high-resolution BOLAM model are significantly better than those obtained using a lower-resolution forcing from the ECMWF analyses. Two domains corresponding to the entire Mediterranean basin and to th...

An economical second-order advection scheme for numerical weather prediction

A very simple second-order Eulerian scheme for the advection equation, based on a forward (backward) time integration on even (odd) grid points, is studied. the proposed scheme is similar, but not equivalent, to the so-called ‘hopscotch method’, developed in the 1960s and early 1970s for the advection-diffusion equation, and is stable up to Courant number 2.0. It is shown that, in the case of the advection equation, the proposed scheme has the same advantages yielded by the forward-backward scheme in the case of the shallow-water equations; in particular, it is equivalent to the application of centred time and space differencing on the Eliassen grid. the new scheme, unlike the classical leapfrog scheme, can be coupled to the forward-backward integration of the gravity-wave problem in primitive-equation models. With the aid of the proposed scheme, an explicit version of the atmospheric, Bologna Limited-Area Model (developed in recent years at the FISBAT Institute of the National Council of Research of Italy) is devised, and a comparison with the semi-implicit version of the same model is performed. the explicit version runs with a double time step, achieving the same accuracy with significantly less computer time and storage. It is suggested that the new time scheme is particularly suitable for numerical weather prediction on massively parallel computing machines based on SIMD (Single Instruction Multiple Data) and distributed memory architecture, which strongly penalize non-local algorithms.