Use of radar data in modelling at the met office uk
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EWGLAM / COST-717 Joint Session. Use of radar data in modelling at the Met Office (UK). Bruce Macpherson Mesoscale Assimilation, NWP Met Office. Outline. Radar data for assimilation into: atmospheric models land surface models Radar data for NWP model verification

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Use of radar data in modelling at the Met Office (UK)

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Use of radar data in modelling at the met office uk

EWGLAM / COST-717 Joint Session

Use of radar data in modelling at the Met Office (UK)

Bruce Macpherson

Mesoscale Assimilation, NWP

Met Office


Outline

Outline

  • Radar data for assimilation into:

    • atmospheric models

    • land surface models

  • Radar data for NWP model verification

  • Radar data for model validation


Rainfall assimilation at the met office

Rainfall Assimilation at the Met Office

  • 1996 - Operational assimilation of 3-hourly rain rates from UK weather radar network into Mesoscale Model

  • 1997 - NWP forecast impact studies on radar data

  • 1997 - test assimilations of lightning data as proxy rainfall

  • 1998 - Assimilation of hourly radar data

  • 2000 - Radar Quality Estimate used in assimilation

  • 2001/2 - French & German radars added to UK composite

  • 2003 - Retuning for ‘New Dynamics’ model version


Radar data impacts objective scores v radar analyses

Radar Data Impacts - objective scores (v radar analyses)

Period 1 - significant benefit up to t+6/12

Period 2 - neutral signal


Radar data impacts subjective

Radar Data Impacts - subjective

OPER

t+15

NO radar

assimilation

t+15


Radar data impacts hourly v 3 hourly data

Radar Data Impacts: hourly v 3-hourly data

3-hourly

radar data

Hourly

radar data

T+3

T+3


Radar data impacts hourly v 3 hourly data1

Radar Data Impacts: hourly v 3-hourly data

3-hourly

hourly


Use of radar data in modelling at the met office uk

Relativeimportance of radar assimilation for short-period rain forecasts

No of Cases

showing

benefit

Light rain

aircraft

Radar &

satellite

sonde

surface

Heavy rain


Radar coverage and quality estimate nimrod system

Radar Coverage and Quality Estimate(Nimrod system)


Mesoscale model rainfall assimilation

Mesoscale Model Rainfall Assimilation

  • Data: hourly surface rain rates, pure radar -no gauge/satellite

  • QC & processing (with help from NWP):

    • clutter & anaprop removal-- bright band correction

    • range correction-- orographic enhancement

    • weekly radar calibration v gauge

Monthly

Totals

 Raw radar

Corrected

radar 


Mesoscale model rainfall assimilation ii

Mesoscale Model Rainfall Assimilation (II)

  • Averaging: 5km raw data ==> 15km (model ~12km)

  • Assimilation: latent heat nudging (LHN)

    • target rainfall analysis Ran = (Rmod + W Robs) / (1+W)

    • Robsinterpolated from hourly values to model timestep

    • assimilation increments ( T) filtered on scale 2x


Land surface assimilation

Land Surface Assimilation

  • For agricultural and hydrological products, soil moisture input to mesoscale model

  • Current system: “MORECS”

    • rainfall data ~150 daily gauges over UK

    • weekly analysis on 40km grid

    • interpolated variable is % of average annual rainfall

  • New system: “Soil State Diagnosis Model (SSDM)”

    • rainfall data: Nimrod radar analysis

    • hourly analysis on 5km grid (same as SSDM)


Uk mes soil moisture

UK Mes soil moisture

MORECS

Nimrod SSDM

Radar

artefacts

Relax to

climatology


Radar wind assimilation

Radar wind assimilation

VAD profile availability

(CWINDE project)

  • operational since 2001

  • monthly monitoring

  • quarterly quality reports


Radar data to verify nwp rainfall forecasts

Radar data to verify NWP rainfall forecasts

  • on monthly timescale, gauges and ‘corrected’ radar tell roughly same overall story

v radar

Model skill

v gauge

Month ==>


Global model precipitation verification over u k

Global Model precipitation verification over U.K

  • Models

  • 6 models, mostly 09/2000-10/2002

  • 12Z runs up to 72h

  • 24h accumulation

  • up-/down-scaled to 96*96 km2 by box averaging

  • Observations

  • corrected radar data

  • upscaled to 96*96 km2 by box averaging


Global model precipitation verification over u k 0 24h forecasts

Global Model precipitation verification over U.K., 0-24h forecasts

Frequency bias


Lam verification v uk radar

LAM verification v UK radar

Work in progress for:

  • UK Mesoscale

  • DWD LM

  • Hirlam reference

  • …any more?


Use of radar data in modelling at the met office uk

  • For short NWP trials and batches of case studies, radar provides

    • better spatial sampling than gauges

    • clearer link with forecaster’s subjective assessment

v radar


Radar may allow study of model behaviour with higher resolution in time

…..radar may allow study of model behaviour withhigher resolution in time

  • Mesoscale Model trial verification

Frequency bias for

hourly totals > 0.17mm

(v Nimrod radar)


Use of radar data in modelling at the met office uk

  • and maps of verification v radar can begin to show land/sea differences

Rain/no-rain (>0.4 mm/6hrs)Frequency biast+12-18 hr forecastsautumn 2000

v radar


Observations of evaporation

Observations of Evaporation

94GHz Radar-Derived Ice Water Content (below 0ºC)

Radar data provided by Robin Hogan (Reading Univ.) and RCRU (RAL)

02 Apr 2000

11 Dec 1999


Model obs comparison

Model/Obs Comparison

Average ice evaporative depth scale from the Chilbolton 94 GHz cloud radar and the operational UM for 20 separate days in Oct, Nov, Dec 1999.


Fastex iop 16 validation

FASTEX IOP 16: Validation

Comparison of the reference and modified model ice evaporative depth scales with 94GHz radar observation statistics

Average depth scale

Reference:1260 m

Modified: 780 m

Obs: 640 m (=160m)

Modified model = higher vertical resolution, double ice evaporation rate and two thirds of ice fall speed


Impact of including rain advection on rainfall distribution

Impact of including rain advection on rainfall distribution.

Rainfall rate difference (advection-no advection)

Rainfall rate (mm/hr)

Orography (m)

10hr model forecast.


Verification dartmoor river catchment rainfall 3 hour accumulations

VerificationDartmoor River Catchment Rainfall 3 Hour Accumulations

Exe

Teign

Dart

Tamar

Avon & Erme

No Rain Advection

With Rain Advection

Radar

2km Model Forecasts


Use of radar data in modelling at the met office uk

VerificationCorrelation between model surface rainfall and NIMROD radar-derived surface rainfall for Dartmoor

No Rain Advection

With Rain Advection


Future plans

Future Plans

  • Limited area 4D-Var operational 2005

    • with radar derived surface rainfall data in 2006

  • Experimental 4D-Var assimilation of radar radial winds

    • project with Salford University

  • Partial Dopplerisation of UK radar network

    • 7 radars by 2006

  • Convective scale model by 2008

    • develop radar verification techniques

    • establish viable radar assimilation method


Questions

Questions?


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