1 00/XXXX © Crown copyright Use of radar data in modelling at the Met Office (UK) Bruce Macpherson Mesoscale Assimilation, NWP Met Office EWGLAM / COST-717 Joint Session

2 00/XXXX © Crown copyright Outline Radar data for assimilation into: –atmospheric models –land surface models Radar data for NWP model verification Radar data for model validation

3 00/XXXX © Crown copyright Rainfall Assimilation at the Met Office Operational assimilation of 3-hourly rain rates from UK weather radar network into Mesoscale Model NWP forecast impact studies on radar data test assimilations of lightning data as proxy rainfall Assimilation of hourly radar data Radar Quality Estimate used in assimilation 2001/2 - French & German radars added to UK composite Retuning for ‘New Dynamics’ model version

4 00/XXXX © Crown copyright Radar Data Impacts - objective scores (v radar analyses) Period 1 - significant benefit up to t+6/12 Period 2 - neutral signal

5 00/XXXX © Crown copyright Radar Data Impacts - subjective OPER t+15 NO radar assimilation t+15

6 00/XXXX © Crown copyright Radar Data Impacts: hourly v 3-hourly data 3-hourly radar data Hourly radar data T+3

7 00/XXXX © Crown copyright Radar Data Impacts: hourly v 3-hourly data 3-hourly hourly

8 00/XXXX © Crown copyright Relative importance of radar assimilation for short-period rain forecasts Radar & satellite aircraft surface No of Cases showing benefit sonde Light rain Heavy rain

9 00/XXXX © Crown copyright Radar Coverage and Quality Estimate (Nimrod system)

10 00/XXXX © Crown copyright 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 

11 00/XXXX © Crown copyright Mesoscale Model Rainfall Assimilation (II) Averaging: 5km raw data ==> 15km (model ~12km) Assimilation: latent heat nudging (LHN) –target rainfall analysis R an = (R mod + W R obs ) / (1+W) –R obs interpolated from hourly values to model timestep –assimilation increments (  T) filtered on scale 2  x

12 00/XXXX © Crown copyright 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)

13 00/XXXX © Crown copyright UK Mes soil moisture Relax to climatology Radar artefacts MORECS Nimrod SSDM

14 00/XXXX © Crown copyright Radar wind assimilation VAD profile availability (CWINDE project) operational since 2001 monthly monitoring quarterly quality reports

15 00/XXXX © Crown copyright Radar data to verify NWP rainfall forecasts on monthly timescale, gauges and ‘corrected’ radar tell roughly same overall story Model skill Month ==> v gauge v radar

16 00/XXXX © Crown copyright Global Model precipitation verification over U.K Models 6 models, mostly 09/ / Z runs up to 72h 24h accumulation up-/down-scaled to 96*96 km 2 by box averaging Observations corrected radar data upscaled to 96*96 km 2 by box averaging

17 00/XXXX © Crown copyright Global Model precipitation verification over U.K., 0-24h forecasts Frequency bias

18 00/XXXX © Crown copyright LAM verification v UK radar UK Mesoscale DWD LM Hirlam reference …any more? Work in progress for:

19 00/XXXX © Crown copyright 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

20 00/XXXX © Crown copyright …..radar may allow study of model behaviour with higher resolution in time Mesoscale Model trial verification Frequency bias for hourly totals > 0.17mm (v Nimrod radar)

21 00/XXXX © Crown copyright and maps of verification v radar can begin to show land/sea differences v radar Rain/no-rain (>0.4 mm/6hrs) Frequency bias t hr forecasts autumn 2000

22 00/XXXX © Crown copyright Observations of Evaporation 02 Apr Dec GHz Radar-Derived Ice Water Content (below 0ºC) Radar data provided by Robin Hogan (Reading Univ.) and RCRU (RAL)

23 00/XXXX © Crown copyright 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.

24 00/XXXX © Crown copyright 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

25 00/XXXX © Crown copyright Impact of including rain advection on rainfall distribution. Rainfall rate (mm/hr)Orography (m) Rainfall rate difference (advection-no advection) 10hr model forecast.

26 00/XXXX © Crown copyright Verification Dartmoor River Catchment Rainfall 3 Hour Accumulations Avon & Erme Dart Teign Tamar Exe With Rain AdvectionNo Rain Advection Radar 2km Model Forecasts

27 00/XXXX © Crown copyright Verification Correlation between model surface rainfall and NIMROD radar-derived surface rainfall for Dartmoor With Rain AdvectionNo Rain Advection

28 00/XXXX © Crown copyright 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

29 00/XXXX © Crown copyright Questions?