Multi-scale Predictability Aspects of a Severe European Winter Storm

Transcription

1 1 Multi-scale Predictability Aspects of a Severe European Winter Storm NASA MODIS James D. Doyle, C. Amerault, P. A. Reinecke, C. Reynolds Naval Research Laboratory, Monterey, CA

2 Mesoscale Predictability Lorenz (1969) argued that because of rapid upscale propagation of initial condition uncertainties, the predictability of mesoscale motions should be very limited (~10 km scale limited to ~1 h). More optimistic views based on high-resolution NWP models suggest that skillful mesoscale predictions can be expected using reasonably accurate synoptic-scale initial conditions. How do these viewpoints apply to a high-impact weather event? 2

3 Extratropical Cyclone Xynthia Largest impact on Europe in a decade with insured losses of $2-4B 63 fatalities; storm surge in France (> 7.5 m); Damaging winds (150 mph) Synoptic-scale was well predicted (ECMWF, GFS); mesoscale not as well What are the key mesoscale initial state sensitivity characteristics? La Faute, SW France Xynthia Crossed Western Europe between 27 Feb. and 1 Mar L'Aguillon sur Mer, France La Rochelle, SW France dailymail.co.uk La Rochelle, SW France dailymail.co.uk1 + A Guarda, NW Spain dailymail.co.uk Nuissier et al dailymail.co.uk dailymail.co.uk 3

4 Composite Total Precipitable Water 00 UTC 26 Feb 00 UTC 29 Feb (CIMSS) Xynthia developed within a plume of high precipitable water. Hypothesis: This moist plume (or atmospheric river) is a key ingredient for the intensification of Xynthia. UW CIMSS 4

5 Adjoint Model Adjoint allows for the mathematically rigorous calculation of forecast sensitivity of a response function to changes in initial state t i t f Nonlinear Forward Model Basic State Adjoint Optimal Perturbations Adjoint Model Tangent Linear Model Nonlinear Forward Model Test TL Approx. Using Optimal Perturbations ~1 m s -1, ~1 K COAMPS Moist Adjoint Model Setup Dynamics: nonhydrostatic, nested Physics: PBL, surface flux, microphysics, Kuo Response Function, J: kinetic energy (1 km deep) Resolution: Dx=45 km, 15 km (36h) 15 km COAMPS is a registered trademark of NRL 45 km 5

6 Synoptic-Scale 10-m Winds and Sea Level Pressure 500-mb Geopotential Heights and Winds 00Z 12Z Feb (36 (0 h) m Winds and Sea Level Pressure 00Z 28 Feb (36 h) Z/28 00Z/28 00Z/27 12Z/ (996) Simulated (Analysis) 960 (966) 964 (971) 984 (986) Phasing of waves in N. and S. branches, raises predictability questions. Nonlinear model accurately predicts the track and central pressure. Synoptic-scale models (NCEP GFS, GEFS, ECMWF) predicted a major cyclone 72 h in advance (R. Grumm), but mesoscale details were lacking. 6

7 Low-level Winds 10-m Winds and Sea Level Pressure 2200 UTC 27 February 2010 ASCAT Winds 925-mb 10-m Winds q and at Sea 34 Level h (15-km Pressure Nest) m/s Larrry O Neill (Oregon State Univ) 0 Strong low-level jet is present along the bent-back front. The 15-km mesh 10-m winds are in close agreement with ASCAT. 7

8 Accuracy of Adjoint Model Evolved Optimal u at 850-hPa (36 h) Tangent Linear Model Nonlinear Model km 45 km -20 Tangent Linear Model 56 0 Nonlinear Model Good agreement between perturbations evolved in the moist tangent linear and nonlinear models for Dx= 45 and 15 km. 15 km km -56 8

9 Nested Adjoint Sensitivity PV and Moisture Sensitivity 1200 UTC 26 February 2010 (Analysis) hPa PV 700-hPa and Sensitivity PV to PV hPa q v 700-hPa and Sensitivity q v to q v Low-level PV filament coincident with a moist low-level jet. Adjoint sensitivities (PV, u, T, q v ) are maximized along southern shortwave. Moisture sensitivity is 5x greater than wind sensitivity (and 2x larger than T). Moisture and PV analysis uncertainties project on to sensitive regions.

10 Nested Adjoint Sensitivity PV and Moisture Sensitivity 10 q, U (normal), and Sensitivity to PV PVU 60 q, q, and Sensitivity to q Restructuring of PV (connection of anomalies) leads to intensification. Sloping PV and q v sensitivity are maximized along mid-level front. Unshielding of PV and rapid growth of tilted perturbations (Orr mechanism).

11 Nested Adjoint Sensitivity 700-hPa Height and Sensitivity to u 15 km 45 km Adjoint sensitivity evolution reveals multi-scale nature of the gradient and rapid propagation (remote maxima >2500 km / 36h). 11

12 Nested Adjoint Sensitivity 700-hPa Height and u optimal perturbation Power Spectrum 15 km (0-36h) 27 h 36 h 15 km 18 h 15 km 9 h 45 km Optimal perturbation evolution shows rapid perturbation growth (30x growth in 36 h) and upscale cascade. Rapid perturbation growth near moisture and PV analysis uncertainties. 12

13 Evolved Optimal Perturbations Sea-Level Pressure and 10-m Winds (00Z 28 Feb, 36 h) 13 Control (NLM) Optimal Adjoint (+ pert) Moist Optimal Perturbation Adjoint (- pert) Only mb / 31 m s mb / 34 m s mb / m s -1 0 The structure and intensity of the cyclone, low-level jet, and front change markedly with the evolved perturbations (negative and positive). Moisture perturbations in the NLM grow much faster than temperature and wind perturbations.

14 Summary and Future Plans 14 Initial moisture is a key factor for low-level jet and Xynthia s intensity: -Moisture sensitivity is 5 times greater than U and 2 times more than T. Sensitivity characteristics: - Sloped sensitivity structures along the front. - Rapid growth (via PV unshielding) and propagation (2500 km/36 h). Mesoscale predictability of Xynthia is limited by very rapid growth: -Moist processes in the presence of PV introduce inherent uncertainty. -Motivates the use of ensembles for high-impact weather events. Future plans: -Comparison with other severe European winter storms (Lothar, Klaus). - Klaus results show very different characteristics (zonal flow). -Improvement to the adjoint moist physics (linear physics).

15 ECMWF Ensemble Forecast 72-h Forecast Valid 00Z 28 February Large colored dots show the maximum 1 km winds (kts) with a 300 mile radius of the dot. The isobars are from the higher resolution deterministic model run. (T. Hewson ECMWF; R. Grumm NWS) 15

16 Moisture Analysis Uncertainty Comparison with NOGAPS and COAMPS Analyses mb 850-mb q v COAMPS q v Sensitivity Analysis 850-mb q v Analysis Difference COAMPS-NOGAPS Significant regions of uncertainty in the moisture analysis are coincident or near regions of greatest moisture uncertainty (similar issues with the PV analysis)

17 Analysis Uncertainty Comparison with NOGAPS and COAMPS Analyses 850-mb 850-mb q COAMPS q Sensitivity Analysis 850-mb 850-mb PV COAMPS PV Sensitivity Analysis 850-mb q COAMPS-NOGAPS 850-mb PV COAMPS-NOGAPS Local analysis differences of q and PV in sensitive regions. 17

18 Evolved Optimal Perturbations 10-m SLP and Wind Speed for NLM (12Z 28 Feb, 48 h) 18 NLM Control NLM Perturbed (12h Beyond Adjoint time) Adjoint Perturbations Have Lasting Impact on the Cyclone and Evolution (3.5 hpa deeper, displacement of low, and different jet structure).

19 Nested Adjoint Sensitivity PV and Moisture Sensitivity 1200 UTC 26 February 2010 (Analysis) hPa PV 700-hPa and Sensitivity PV to PV hPa q v 700-hPa and Sensitivity q v to q v Low-level PV filament coincident with a moist low-level jet. Adjoint sensitivities (PV, u, T, q v ) are maximized along southern shortwave. Moisture sensitivity is 5x greater than wind sensitivity (and 2x larger than T).