SAL - Structure, Ampliutde, Location Institute for Atmospheric Physics – University of Mainz Name of method: SAL - Structure, Ampliutde, Location Investigators: Marcus Paulat, Heini Wernli – Institute for Atmospheric Physics, University of Mainz Christoph Frei – Bundesamt für Meteorologie und Klimatologie, MeteoSwiss Zürich Martin Hagen - Institut für Physik der Atmosphäre, DLR Oberpfaffenhofen Literature / References: none - presentations at workshops in Boulder (2006) and ECMWF (2007) - manuscript in preparation (Wernli et al., MWR) 16. February 2007

What kind of data? only gridded data fields: so far only precipitation, in principle also applicable to other fields with well-structures signatures (e.g. wind gusts) presently used FC data: ECMWF and COSMO-LM precipitation forecasts (accumulated over 1 or 24 h) over Germany on rotated lon/lat grid with 7 km horizontal resolution presently used OBS data: gridded rain gauge data set on same grid as models, based upon ~4000 stations with 24 h values; 1-h disaggregated fields through combination of rain gauge and radar data Marcus Paulat Christoph Frei Martin Hagen Heini Wernli

Basic strategy (I): General concept consider precipitation in pre-specified area (e.g. river catchment) SAL consists of three independent components components address quality of structure (S), amplitude (A) and location (L) of QPF in that area according to SAL a forecast is perfect if S = A = L = 0 S requires the definition of precipitation objects, using a threshold value but: no attribution between precipitation objects in forecast and observations! Marcus Paulat Christoph Frei Martin Hagen Heini Wernli

Basic strategy (II): Definition of the components A = (D(Rmod) - D(Robs)) / 0.5*(D(Rmod) + D(Robs)) D(…) denotes the area-mean value (e.g. catchment) normalized amplitude error in considered area A  [-2, …, 0, …, +2] L = |r(Rmod) - r(Robs)| / distmax r(…) denotes the centre of gravity of the precipitation field in the area normalized location error in considered area L  [0, …, 1] A = amplitude error L = location error S = structure error S = (V(Rmod*) - V(Robs*)) / 0.5*(V(Rmod*) + V(Robs*)) V(…) denotes the weighted volume average of all scaled precipitation objects in considered area normalized structure error in considered area S  [-2, …, 0, …, +2] Marcus Paulat Christoph Frei Martin Hagen Heini Wernli

circular precipitation object Basic strategy (III): The S component scaling for every object: R* = R / Rmax; R*  [Rthresh/Rmax, …, 1] R R* Rmax 1 S gives information about the size and shape of the objects in a way that is essentially independent of their amplitudes Rthresh Rthresh/Rmax x x V(R) V(R*) circular precipitation object Marcus Paulat Christoph Frei Martin Hagen Heini Wernli

Basic strategy (IV): Example 1 Rmax 1 OBS x V(R*) x R R* 1 MOD Rmax x V(R*) x A < 0 S = 0 Marcus Paulat Christoph Frei Martin Hagen Heini Wernli

Basic strategy (V): Example 2 Rmax 1 OBS x V(R*) x R R* 1 MOD Rmax x V(R*) x A = 0 S > 0 Marcus Paulat Christoph Frei Martin Hagen Heini Wernli

summer seasons 2001-2004 for catchment Rhine S A L - statistics: 24h accumulated A-component 1 -1 -2 2 S-component summer seasons 2001-2004 for catchment Rhine aLMo ECMWF Marcus Paulat Christoph Frei Martin Hagen Heini Wernli

Kind of verification information / Verification questions 3 independent components to quantify quality of structure, amplitude and location of QPF information is valid for a pre-specified area (e.g. river catchment, state, field campaign area, …) questions: - is the domain averaged precipitation amount correctly forecast? -> A - is the centre of the precipitation distribution in the domain correctly forecast? -> L - does the forecast capture the typical structure of the precipitation field (e.g. large broad vs. small peaked objects)? -> S Marcus Paulat Christoph Frei Martin Hagen Heini Wernli

Strength relatively intuitive physically meaningful information about amplitude, location and structure of QPF relatively intuitive SAL approach is close to “subjective human judgement” (claim) no attribution between objects is required (difficult for small objects) computationally simple Marcus Paulat Christoph Frei Martin Hagen Heini Wernli

Weaknesses and limitations non-perfect QPFs can yield S = A = L = 0 (slight modification of L component is underway) no consideration of orientation of objects currently very simple definition of objects (threshold value) S value is sensitive to choice of threshold used for object definition (tests are underway to quantify sensitivity) so far only preliminary results for Germany have been computed Marcus Paulat Christoph Frei Martin Hagen Heini Wernli