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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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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

  • Radar data for model validation


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)

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

Period 2 - neutral signal


Radar Data Impacts - subjective

OPER

t+15

NO radar

assimilation

t+15


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 data

3-hourly

hourly


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)


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)

  • 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

  • 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

MORECS

Nimrod SSDM

Radar

artefacts

Relax to

climatology


Radar wind assimilation

VAD profile availability

(CWINDE project)

  • operational since 2001

  • monthly monitoring

  • quarterly quality reports


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

  • 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

Frequency bias


LAM verification v UK radar

Work in progress for:

  • UK Mesoscale

  • DWD LM

  • Hirlam reference

  • …any more?


  • 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 withhigher resolution in time

  • Mesoscale Model trial verification

Frequency bias for

hourly totals > 0.17mm

(v Nimrod radar)


  • 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

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

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

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.

Rainfall rate difference (advection-no advection)

Rainfall rate (mm/hr)

Orography (m)

10hr model forecast.


VerificationDartmoor River Catchment Rainfall 3 Hour Accumulations

Exe

Teign

Dart

Tamar

Avon & Erme

No Rain Advection

With Rain Advection

Radar

2km Model Forecasts


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

No Rain Advection

With Rain Advection


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?


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