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Page 1 Developments in regional DA Oct 2007 © Crown copyright 2007 Mark Naylor, Bruce Macpherson, Richard Renshaw, Gareth Dow Data Assimilation and Ensembles, Met R & D Developments in regional data assimilation at the Met Office EWGLAM / SRNWP 2007 new NAE UK4
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Page 2 Developments in regional DA Oct 2007 © Crown copyright 2007 NAE Data Assimilation changes 2007 GPS IWV introduced (1 per 6 hr) aerosol background error reduced AIRS over land introduced (above 400hPa) More frequent ATOVS data ( + thinning 40 80km) More frequent GPS IWV data (1 per hr) PF-Model Convection cease soil temperature increments under snow introduce IASI introduce ASCAT Mar 07 Aug 07 Nov 07
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Page 3 Developments in regional DA Oct 2007 © Crown copyright 2007 Impact of LS subsidence (similar to first ECMWF scheme) positive impact on moisture field Cape closure perturbations (main term) positive impact on virtually all fields PF convection parametrisation in 4DVAR (Olaf Stiller) Two contributions: Unsteady/noisy UM convection scheme motivated statistical approach with time smoothing of input fields from nonlinear model
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Page 4 Developments in regional DA Oct 2007 © Crown copyright 2007 PF convection – linearisation test (Olaf Stiller) after 6 hours
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Page 5 Developments in regional DA Oct 2007 © Crown copyright 2007 PF convection - trial results Summer 2006 NAE trial Generally beneficial in most variables +1% on UK Index (skill score for T2m, v10m, rain, cloud, visibility) rms PMSL rms T2m
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Page 6 Developments in regional DA Oct 2007 © Crown copyright 2007 soil temperature increments ΔT (soil level 1) = ΔT (atmosphere level 1) in NAE helps retain benefit of screen temperature assimilation (no screen level assimilation or ΔT (soil) in global model) CNTL no ΔT(soil) mean T2m rms T2m
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Page 7 Developments in regional DA Oct 2007 © Crown copyright 2007 soil temperature increments …..under snow ΔT (soil level 1) = ΔT (atmosphere level 1) not sensible when snow insulates the soil Feb 07 night-time T2m errors in Finland ~10-15K soil temp difference (NAE-GLOBAL) snow cover 20K !
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Page 8 Developments in regional DA Oct 2007 © Crown copyright 2007 Ground GPS IWV (operational since March 07) Operational coverage
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Page 9 Developments in regional DA Oct 2007 © Crown copyright 2007 Ground GPS IWV ● Pre-operational trials gave slight benefit in screen temperature, rain, cloud and visibility. (~0.5% on UK Index) ● Obs frequency increased to hourly (Aug 07) with neutral impact / slight benefit ● Further trials to optimise assimilation underway- adjusting obs errors and forward model
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Page 10 Developments in regional DA Oct 2007 © Crown copyright 2007 IASI trial 1-month trial – May 2007 Global trials gave benefit in PMSL & upper-level winds NAE trial showed small benefit in UK pmsl mean rms CNTL IASI
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Page 11 Developments in regional DA Oct 2007 © Crown copyright 2007 ASCAT ASCAT data – implementation due Nov 07 in NAE 10-day NAE trial May 2007(impact neutral), following longer global trials ASCAT observations for QY18, with ERS2 and Seawinds
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Page 12 Developments in regional DA Oct 2007 © Crown copyright 2007 Weather radar – VAD winds Currently assimilated 61 rejected 26
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Page 13 Developments in regional DA Oct 2007 © Crown copyright 2007 VAD wind impact experiment 3-week 24km NAE 4DVAR test, autumn 2006 CNTL noVAD mean pmsl rms pmsl
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Page 14 Developments in regional DA Oct 2007 © Crown copyright 2007 VAD wind impact experiment - 2 Pmsl benefit statistically significant when error bars computed for mean difference in CNTL / noVAD errors
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Page 15 Developments in regional DA Oct 2007 © Crown copyright 2007 Part 2
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Page 16 Developments in regional DA Oct 2007 © Crown copyright 2007 4km UK model assimilation 3DVAR nudging scheme for cloud & rainfall assimilation eight 3-hourly cycles per day forecasts to t+36 from 03, 09, 15, 21 UTC lateral boundaries from hh-3 run of 12km NAE
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Page 17 Developments in regional DA Oct 2007 © Crown copyright 2007 UK model – increased vertical resolution 38 70 levels same top at ~40km 7 16 levels in bottom 1km lowest theta level at 5m lowest wind level at 2.5m due for implementation Nov 2007
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Page 18 Developments in regional DA Oct 2007 © Crown copyright 2007 UK model – 70 level forecast error covariances variant of lagged NMC method 74 forecast pairs t+12 – t+24 horizontal scales psi130km chi180km Ap130km mu 90km log m 90km
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Page 19 Developments in regional DA Oct 2007 © Crown copyright 2007 UK model – 70 level case study trial – pmsl (17 cases) mean rms L38 L70
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Page 20 Developments in regional DA Oct 2007 © Crown copyright 2007 UK model – 70 level case study trial – T2m mean rms L38 L70
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Page 21 Developments in regional DA Oct 2007 © Crown copyright 2007 UK model – 70 level case study trial – RH2m mean rms L38 L70
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Page 22 Developments in regional DA Oct 2007 © Crown copyright 2007 UK model – 70 level case study trial – v10m rms vector mean speed L38 L70
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Page 23 Developments in regional DA Oct 2007 © Crown copyright 2007 UK model – 70 level case study trial – cloud cover rmsmean L38 L70
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Page 24 Developments in regional DA Oct 2007 © Crown copyright 2007 UK model – 70 level case study trial – 6-hourly rainfall 0.2mm /6 hr 1mm /6 hr 4mm /6 hr solid L38 dashed L70
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Page 25 Developments in regional DA Oct 2007 © Crown copyright 2007 Future work Upgrade NAE (and global) to 70 levels (Feb 08). Initial 1-month trial in NAE completed Physics package still under development MOPS cloud data in 4DVAR to replace nudging PF model boundary layer scheme (autumn 08) ensemble-based covariances ? replace NAE continuous assimilation with single cycle spin-up from previous global ‘update’ analysis 2009: new computer retain 12km NAE when global 25km nest 1.5km UK model with variable resolution perimeter into 12km NAE
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Page 26 Developments in regional DA Oct 2007 © Crown copyright 2007 OPERA composite NAE impact experiment is planned with OPERA composite (Spring 08) promote benefits to NWP of radar data exchange within Europe clarify requirements from NWP for operational radar data hub prepare for eventual operational assimilation
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Page 27 Developments in regional DA Oct 2007 © Crown copyright 2007 Questions?
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Page 28 Developments in regional DA Oct 2007 © Crown copyright 2007 Visibility/Aerosol tuning 3-week package trial consisting of:- Reduced visibility background error Climatological aerosol in radiation (not prognostic aerosol) Maximum aerosol concentration reduced (200µg/kg) Relaxation to climatological aerosol increased (20days) Significant benefit seen in Screen temperature
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