Extratropical processes and forecast errors

Transcription

1 Extratropical processes and forecast errors Heini Wernli With contributions from: Andreas Dörnbrack, Sarah Jones, George Craig Maxi Böttcher, Hanna Joos, Andreas Schäfler, Matthias Zimmer, Florian Meier, Andreas Béguin, Olivia Martius, Sandro Buss THORPEX PDP Working Group and WGNE Workshop Diagnosis of Model Errors, 7 July 2010

2 Processes and forecast errors Rossby wave breaking (frequency, geographical distribution) Intense winds (upper tropospheric jet, orographic jets) Extratropical cyclones: track, intensity Warm conveyor belts (the diabatic element of cyclones, including complex cloud microphysics) and associated downstream development Diabatic Rossby waves (a special category of cyclones) Mesoscale precipitation forecasts

3 Rossby wave breakings in the ECHAM5 climate model On 310 K in winter Climate simulations with different horizontal resolution T42 T106 Béguin et al (in prep.)

4 Rossby wave breakings in the ECHAM5 climate model On 310 K in winter Climate simulations with different horizontal resolution T42 T106 hemispheric Underestimation weak overestimation in N Pacific ERA40

5 Forecast errors (4): Accuracy of winds Example: Aircraft observations within upper-level jet stream PV distribution on 310 K surface Error > 15 m/s Aircraft measurements ECMWF analysis Wind speed NCEP analysis from Sandro Buss

6 Forecast errors (4): Accuracy of winds Example: Wind lidar observations of Greenland tip jet Horizontal wind speed Difference LIDAR - ECMWF analysis N S MODIS (Aqua) 14:55 UTC 24 November 2003 Substantial analysis errors associated with intense wind features from Andreas Dörnbrack

7 Forecast quality of extratropical cyclone tracks % percentage of analysis tracks matched by forecast track forecast lead time (hrs) ECMWF from Florian Meier GME

8 intensity hpa underestimated overestimated Mean difference of minimum SLP (ana - fc) forecast lead time (hrs) ECMWF from Florian Meier

9 Warm conveyor belts 0.5 pvu - PV anomaly intense latent heating (>20K), i.e., strong cross-isentropic flow L 1.5 pvu + PV anomaly characteristic modification of potential vorticity (PV): in low troposphere: increase ~0.5 ~1.5 pvu due to dh/dz > 0 in upper troposphere: decrease ~1.5 ~0.5 pvu due to dh/dz < pvu

10 Warm conveyor belts and downstream development Loop: WCB outflow triggers/enhances upper-level waves strat. air TP tropospheric air colors: PV on 315 K X: WCB outflow K

11 Warm conveyor belts and downstream development Loop: WCB outflow triggers/enhances upper-level waves 0 h +6 h +12 h +18 h

12 Warm conveyor belts & downstream impacts ana +3.5 ana WCB PV on 320 K

13 Warm conveyor belts & downstream impacts ana +3.5 ana WCB fc +3.5 fc +5 - WCB too weak

14 Cloud physics and PV evolution in WCBs Questions: PV IWC What microphysical processes determine the PV evolution along WCBs? - condensation - freezing - evaporation / sublimation What determines final PV value of WCB outflow? LWC from Hanna Joos

15 Cloud physics and PV evolution in WCBs from Hanna Joos

16 Lidar observations of WCBs water vapor mixing ratio Example from COPS July main WCB crossings with the lidar section boundary layer measurements of rising air parcels ( m) WCB crossings in the upper troposphere (7-8 km): 2 days after the ascent from Andreas Schäfler

17 Lidar observations of WCBs Questions: - How accurate are analyses / forecasts in WCB inflow & outflow regions? - How relevant are errors for prediction of downstream flow evolution? significant analysis error in WCB inflow region from Andreas Schäfler

18 Diabatic Rossby waves 18 Dec UTC GOES IR satellite image ECMWF analysis: PV mean hPa (colors) SLP contours Böttcher and Wernli (MWR, submitted)

19 DRW case study Dec Dec UTC GOES IR satellite image ECMWF analysis: PV mean hPa (colors) SLP contours Böttcher and Wernli (MWR, submitted)

20 DRW case study Dec Dec UTC GOES IR satellite image deepening of 34hPa/24h! ECMWF analysis: PV mean hPa (colors) SLP contours Böttcher and Wernli (MWR, submitted)

21 DRW case study: significant medium-range fc errors fc17_00 18_18 fc17_12 fc18_00 fc18_12

22 DRW case study: significant medium-range fc errors 20_00

23 DRW case study: significant medium-range fc errors 20_12

24 DRW case study: significant medium-range fc errors 21_ hpa 979 hpa 998 hpa 965 hpa

25 Quality of COSMO-7 precipitation forecasts: equilibrium vs. non-equilibrium convection Convective time scale: τ c ~ CAPE / d(cape)/dt ~CAPE/R Quality measure: SAL (Wernli et al. 2008, MWR): good forecasts characterized by light dot in center of diagram τ c < 12 hrs (equilibrium convection) τ c > 12 hrs (non-eq. conv.) Zimmer, Craig et al (in prep.)

26 Synthesis Significant short to medium-range forecast errors still exist typically associated with the evolution of baroclinic wave systems Occasionally large differences between analyses and in-situ measurements (wind, humidity) Key research area: interaction between (parameterization of) microphysics and dynamics, for instance in WCBs: microphysical processes latent heating diabatic PV modification large-scale flow evolution Novel insight from investigating model errors from a feature-based or weather system-specific perspective

27 Suggestions for the way forward Combined theoretical / diagnostic / modeling & experimental research initiatives on national and international level, e.g., - research based upon existing datasets (T-PARC, YOTC, ) - T-NAWDEX initiative ( ) with field experiment(s) in 2012/2013(?) and strong diagnostic / modeling components in the pre- and post-field phase We should make clever use of unprecedented high-resolution and high-quality model and observational datasets!

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