development of 1- 4km resolution data...

© Crown copyright 2005

DEVELOPMENT OF 1- 4KM RESOLUTION DATA ASSIMILATION

FOR NOWCASTING AT THE MET OFFICESue Ballard, November 2005

Z. Li, M. Dixon, S.Swarbrick, O.Stiller and H. Lean

Met Office, JCMM, Reading University + others


Background

Aim: to replace nowcasting system Hazardous weather , especially flood risk

Boscastle, North Cornwall16th August 2004 Estimated Cost £500million

Data Assimilation vital for these short period forecasts

4km UK 2005 short period 24-36 hours1.5km UK 2006 short period 24-36 hours1-1.5km ~ 2008-2010 0 to 6 hours hourly


Comparison of 00 UTC 12km and spun-up 4 and 1 km forecasts of 12-18UTC rainfall accumulations for 16th August 2004

4km

12kmPeak Accumulations >60mmon 4 km gridPositional error and false alarm

20 km radius from Boscastle

1km

radar


High Resolution Trial Model

1 km76 levelsResolved convection

4 km38 levelsMass-limited convection


Current HRTM Assimilation Options

12 km 3D-Var Data Assimilation With or without moisture and Latent Heat Nudging (LHN) using AC scheme

(referred to as MOPS data – moisture observationprocessing system)

i.e. spin up 4km, 1km from 12km T+1 each cycle.

4km 3D-VAR with continuous cycles with or without MOPS

1km with nudged reconfigured 4km increments using IAUWith or without LHN and moisture nudging using AC scheme

IAU – increments output from 3D-Var and fixed over time windowAC scheme – increments depend on latest model fields so vary with timestep through weighting factor and model evolution/impact of data


Moisture Observation Preprocessing

Surface reports

Satellite data Radar data

Precipitation5km smoothed to 15km HourlyTesting 15min

Nudge model state

3D Cloud fraction

3D Relative humidity

Resolution: 15km, 3 hours

(Testing 1 hour)


3D-Var system including MOPS RH and LH nudging via AC scheme

T-3 T-1 T+0 T+1

AC scheme/UM3D cloud fractionSurface rainrate

IAU3 hour f/c: background Hourly ModelOb

Nudging RH & Latent heat

T+2T-2 T+3Next analysisPrevious analysis

Conventionalobservations

3D-Var (FGAT)

Obs window


Period over which observations and analysis increments are nudged into Unified Model

6hr accumulations from13Z to 19Z 16/8/04 from 12UTC analysis

Rain rates at 14.30 UTC from 12UTC analysis

Spun-up from 12km T+1With 4km 3D-Var +MOPS radar


Domain average rain rates

7 Cases x 4 cycles summer 2004Prognostic rain (1 and 4km)Reduced wt MOPS (12,4,1km)Water loading

7 Cases x 4 cycles summer 2004Prognostic rain (1 and 4km)Increased wt MOPS (12,4,1km)

Black – radar Blue 12 km Green – 4km Orange -1km Dashed – spinup


T+2 Forecast precipitation rate for 20UTC 27April 2004

WaterLoading+ReducedMOPS wts

12km 4km 1km radar


T+4 Forecast precipitation rate for 22UTC 27April 2004

12km 4km 1km radar

WaterLoading+ReducedMOPS wts


Statistics for 4 cycles of assimilation and forecast data time9,12,15,18UTC 27 April 2004

Skill score for radar area for accumulation greater than 2mm against sampling radius

Orange 4kmblue12km

Orange 4kmWater loadingReduced wt MOPSblue 12km


Impact of hourly cloud data T+2

Radar

3-hourlydata

Hourlydata

No MOPS


Scores for 1 hour accums 50km radius 1mm threshold

Blue 12kmGreen 4kmRed 1km

Solid AssimDotted spinup


Scores for 6 hour accums 1% threshold

Blue 12kmGreen 4kmRed 1km

Solid AssimDotted spinup


theta inc

12km analysis

“new” 4km analysis

/12km back

“new” 4km analysis

/4km back & half length

standard 4km analysis doesn’t see obs outside domain

Zero at boundary

4km short wave analysis 12km long waves

Problem of small domain Scale selective analysis

1hr accumulations from 23Z to 24Z 27/04/04 from 18UTC analysis

12km radar

With 4kmScale Selectiveat 180km 3D-Var

With 4km 3D-Var

Observed radial wind compared with radial wind diagnosed from 1km model

Domain radius 90km, centred on Chilbolton


Impact of S-band radar radial wind datav-component of velocity at 410m

12km analysis 4kmstandard

Scale selectiveRadar dataIn 12km and 4km

ScaleSelectiveRadar in 4km only


Conclusions

Need 1-4km to capture small scale severe eventsNeed DA to overcome spin-up of explicit convection

However long range forecasts can be better than short range

MOPS RH & LHN improves locationsAmounts sensitive to model formulation, weights, frequency of dataNeeds further development but ideally want to use assimilation of cloud and precipitation in 3D-Var and 4D-Var

Need to combine synoptic scale and convective analysisNeed improved background error covariancesNeed to move towards full analysis for 1km model


Plans - ongoing

4kmMOPS - Hourly cloud, 15min precipitation, filtering, weightsBackground errors – lagged/unlagged, lengthscalesOperational doppler radar winds – superobbing, errors, monitoring

Salford Univ and COST 731

Observations – Satellite Applications + Radar Group + ObsRadar reflectivity – observation operators, compare model and obs

Reading UnivGeostationary imagery – low level moisture, cloud topRadar refractivity – low level moisture (Reading Univ)Wind profiler humidity, ground based radiometer, cloud radar

Development of 3D-Var and 4D-Var for direct assimilation of cloud and precipitation

3D-Var MOPS cloud cover, precipitation rate – currently not resourcedCloudy radiance, PF physics, infrastructure


Plans - Future

Aim: 1hrly forecasts 0-6hours 1-1.5km NOWCASTSalso 36 hour UK forecasts ?

Need to move towards full analysis for 1km modelIdeally want 4D-Var and Ensembles

- Start with 3D-Var +MOPSneed to build on experience with 4km and NAEUse reduced vertical resolution (and horizontal?) for analysis?High resolution dataBalance and background errorsVariable resolution modelSurface analysis – SST and soil mositure


Other Collaborations

DARC (Reading University)PhD – combining small scale and large scale in LAM analysisPost-doc/lecturer – surface friction in control variablePost-doc/lecturer – non-linear evolution of Gaussian pdfsPost-doc – balance at convective scale Post-doc – wavelet transforms

EPSRC project – Peter Clark, Surrey, Aston


Current/planned data sources include:

Surface observations : now SYNOPs hourly, 69 stations every 10mins, full network every 10 mins by 2006-2009

AMDAR : now every 3 hours take off and landing can request hourly at extra cost

Geostationary imagery: every 15mins

Radar VAD profile: every hour user requirement, every 15mins potentially

Radar radial doppler winds: every 15mins, 5 elevations range 125km now 2 radars

Rainfall rate analysis : now every 15minutes 12 radars potentially every 5 mins

Radar reflectivity : 12 radars every 5 mins , 5 elevations range 255km

Cloud cover analysis: every hour (potentially every 15mins)

Wind profiler: 5 sites every 30mins (poss 15mins)

GPS: every 15mins 70-150 sites in GB end 2006

Integrated system – wind profiler, microwave radiometer (1+2), cloud radar, ceilometer, GPS


Radar Network Coverage – 2006

1km resolution

2km

5km


Coverage in SE England


Questions & Answers

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