1. Manual PV modifications; a measure of forecaster's expertise Karine Maynard, Philippe Arbogast CNRM/GAME, Météo-France/CNRS, Toulouse, France. Email: philippe.arbogast@meteo.fr IV. Results V. Conclusion I. Introduction Senior forecaster expertise at Météo-France: Verifies NWP outputs at the very short range against observations in real time Recognizes coherent dynamical features using conceptual models Assessment of upper-level dynamics expressed in terms of PV/dynamical tropopause within NWP using satellite images (WV channels, Ozone) And since 2005 : PV modifications (dynamical tropopause –1.5 PVU height field- drawing) of global analyses (or +3h,+6h forecasts) in real time. Purpose: Do several forecasters come to the same conclusion in terms of initial conditions errors depiction and modifications? II. Case study: windstorm KLAUS (24 December 2009) 200hPa wind and MSLP; 22 January 2009 1200UTC 200hPa wind and MSLP; 23 January 2009 1200UTC 24 January 2009 0600UTC 24 January 2009 0900UTC 24 January 2009 Wind gust maximum III. Initial condition modifications Comparison between 6 h range forecast and observations valid at 1200 UTC 23 January 2009. Upper left panel: Meteosat total-column ozone (high ozone contents go from blue to black) with 1.5 PVU geopotential forecast (solid contour below 10000 m). Upper right panel: same model field superimposed to Meteosat 6.2 m image. Bottom left panel: surface observation with model MSLP (every 5 hPa). Bottom right panel: Initial tropopause height field (below 6000 m, blue solid lines) and modified one ( brown contours). Vertical cross sections along the axis displayed in the right panel before modification (upper panel) and after tropopause and MSLP modification and inversion (bottom panel) at 1200 UTC 23 January 2009. In the area of the upper-level precursor a lowering of the tropopause level leads to an increase of the upper-level vorticity maximum (blue contours). Consistently, the system increases the low-stratosphere PV. PV inversion, in turn, build wind and temperature fields everywhere. The specification of a lower boundary condition, here the MSLP field, is allowed in such a 2nd order partial derivative equation. It is worth noticing that the increase of low- stratosphere PV leads to a redistribution of isentropic surfaces (black contours) and an increase of the relative vorticity maximums. The wind component orthogonal to the section is then significantly increased (bold black contours). The low-level cyclone amplitude is increased by the deepening of the MSLP field. In the new initial state (bottom panel) the low-level and upper-level vorticity maximums are now of comparable amplitudes. t 12 UTC 23 Jan 2009 12UTC 24 Jan 2009 06 UTC 23 Jan 2009 Operational run Modified runs Operational run observations better than R6 AND R12 oper Worst than R6 AND R12 oper RMS Error for MSLP RMS Error for 10m wind magnitude Oper 1200UTC MSLP RMSE Oper 1200UTC wind RMSE Oper R12 RMSE 3 first EOFs of the 14x14 covariance matrix of the perturbations set (resp 50%, 9%,5% of the total variance) 25 experiments/attempts of model state improvement have been achieved by 4 different senior forecasters and 3 scientists. A subset of 14 randomly chosen runs has been built (2 runs for each forecaster/scientist) Intrinsic uncertainty in human PV modifications Fairly good reliability of corrections provided by different experts (common features represent 50% of the total variance) Evidence of model improvement Common expertise better than than individual one (The projection onto the first EOF is correlated to the forecast improvement) Skill of the modified forecasts against available operational runs