page 1 developments in regional da oct 2007 © crown copyright 2007 mark naylor, bruce macpherson,...

Developments in regional DA Oct 2007 © Crown copyright 2007

Mark Naylor, Bruce Macpherson, Richard Renshaw, Gareth DowData Assimilation and Ensembles , Met R & D

Developments in regional data assimilation

at the Met OfficeEWGLAM / SRNWP 2007

new NAEUK4


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


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 approachwith time smoothing of input fields from nonlinear model


PF convection – linearisation test (Olaf Stiller)

after 6 hours


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


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


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 !


Ground GPS IWV (operational since March 07)

Operational coverage


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


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


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


Weather radar – VAD winds

Currently assimilated 61 rejected 26


VAD wind impact experiment

3-week 24km NAE 4DVAR test, autumn 2006

CNTL

noVAD

mean

pmsl

rms

pmsl


VAD wind impact experiment - 2

Pmsl benefit statistically significant when error bars computed for mean difference in CNTL / noVAD errors


Part 2


4km UK model assimilation

3DVARnudging scheme for cloud & rainfall assimilationeight 3-hourly cycles per day forecasts to t+36 from 03, 09, 15, 21 UTC lateral boundaries from hh-3 run of 12km NAE


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


UK model – 70 level forecast error covariances

variant of laggedNMC method

74 forecast pairs t+12 – t+24

horizontal scales psi 130km chi 180km Ap 130km mu 90km log m 90km


UK model – 70 level case study trial – pmsl (17 cases)

mean rms

L38

L70


UK model – 70 level case study trial – T2m

mean rms

L38

L70


UK model – 70 level case study trial – RH2m

mean rms

L38

L70


UK model – 70 level case study trial – v10m

rms

vector

mean

speed

L38

L70


UK model – 70 level case study trial – cloud cover

rmsmean

L38

L70


UK model – 70 level case study trial – 6-hourly rainfall

0.2mm /6 hr

1mm /6 hr

4mm /6 hr

solid L38

dashed L70


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


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


Questions?


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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