Mesoscale NWP developments

Jeanette Onvlee

WGNE meeting 2014, Melbourne

11 March, 2014

Data assimilation• Use of fine scale observations• Towards more flow-dependent algorithms

The forecast model• Grey zone issues• Towards sub-km scales• Surface characterization• Stable boundary layer

Probabilistic forecasting

Typhoon forecasting

Outline

WGNE 2014, 20140311

Towards optimal use of hi-res observations

Obs of interest: radar, GPS, high-resolution sounders, aircraft obs, surface (satellite) data, boundary layer remote sensing. Search for useful new observations from non-meteorological networks

Impact assessment: OSE’s, increasingly also by routine monitoring of tools familiar to global modelling community: DFS, FSO, …

Emphasis shifting towards: how to get highest/longest impact, with e.g.:• QC and bias correction• Cloud assimilation• Rapid update/rapid refresh modes and spinup studies• Scales to apply; blending with large scales from the nesting model?• Impact of model bias• Introduction of more advanced (flow-dependent) DA methods

WGNE 2014, 20140311

Mesoscale data assimilation algorithms

Towards more sophisticated mesoscale data assimilation algorithms:

- 4D-VAR (incl methods how to make faster/more scalable; e.g. Gaussian quadrature)

- Many flavours of ensemble data assimilation, for use in both DA and LAM EPS: combinations of EnKF/(L)ETKF with 3-/4D ensVar

- New methods to address non-additive (displacement) errors from gaming industry: field alignment / image warping techniques

WGNE 2014, 20140311

HAC meeting 5, 20130506

Grey zone experiment:Cold air outbreak, 31st January 2010

WGNE 2014, 20140311

WGNE 2014, 20140311

Cold air outbreak; WGNE grey-zone test; 2-km schemes’ with convection

MODIS

observation

AROME

ALARO

NCEP

NCAR

Unified Model

(tamed conv.)

WGNE 2014, 20140311

Cold air outbreak; WGNE grey-zone test; 2-km schemes’ without convection

MODIS

observation

AROME (no sh. cv.)

ALARO

NCEP

NCAR

Unified Model

WGNE 2014, 20140311

Drivers towards hectometric resolution models: 1. complex terrain

FROST-14: (sub-)km scale models for Sochi area

非住家の屋根が東北東に約 50m飛散

住家倒壊

常総市つくば市

被害分布の長さ：約 17

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被害分布の幅：約 500ｍ

北条

平沢

吉沼

山木

テクノパーク大穂

新石下大沢新田

住家の屋根はぎとられる

12:35

12:37

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12:53

http://mainichi.jp

Rainfall region that caused Tornado

http://www.jma.go.jp/jma/press/1205/11c/120511tsukuba_tornado.pdf

Tornadoes Occurred on 6Tornadoes Occurred on 6thth May 2012 May 2012Drivers towards hectometric scale models: 2. small-scale severe weather phenomena

・ Positions and durations differed among the ensemble members.

Tornados occurred in three areas, which were ｔｈｅ same as the observations though they were shifted northward by 10 km.

Positions of vortices more than 0.1(1/s)

10 members (83%)duration: 6-36min

Observed positions

Courtesy: K. Saito

Driver towards hectometric solutions nr 3: Needs from aviation - AROME-airport

system

AROME hourly assimilation at 2.5km using AROME-France forecast as first guess (on red domain) : two additional wind profilers

AROME forecast at 500m performed on green domain to produce boundary conditions to a Wake-Vortex prediction model

Areas covered by the models, AROME-airport 2.5km domain (red) AROME-airport 500m domain (green)

Zoom of an AROME-airport 500m forecast, vectors show wind direction and force, shaded areas is orography.

RMSE of wind force for:AROME-France (green) AROME-airport 2.5 km (red) AROME-airport 500m (blue) X-axis is the forecast range in hours.

Model setup – UM vn8.2 PS32

UKV – 1.5km grid length, 70 levels,

2D subgrid turbulence scheme,

BL mixing in vertical.

500m model – 500x400 km

200m model – 300x200 km

100m model – 150x100 km

High res models: 140 vertical levels, 3D subgrid turbulence scheme,RHcrit is 0.97 (0.91) in 1st few layers decreasing smoothly to 0.9 (0.8) at ~3.5km.Also: research on scale-sensitive shallow convection formulation

Set of nested models.

High resolution simulations for the COPE experiment, summer 2013

Courtesy: M. Bush

3rd August – convergence line

• 03rd August case had a nice line of showers down the centre of the peninsula which the 500m model captured quite nicely.

• The higher resolution models have lots of little showers • Cells appear to get smaller as grid length is reduced

Similar features are more generally observed also in other models. Also: more problems with numerical stability, need for significantly higher vertical resolution at these scales

Courtesy: M. Bush

Higher resolution, scientific open questions

• “Some open questions for hectometric resolutions– Do we need 3D features ? (physics, turbulence) : Probably not at 500m,

our models have other uncertainties that must overwrite the refinement gain of 3D parameterizations.

– Which shallow convection scheme do we need ?– Coupling frequency, coupling zone size.– Physiographic fields resolution.– Volume of the data to treat.

• For finer resolutions (LES mode)– Issues like 3D parameterizations that might have been avoided for 500m

resolutions should become problematic.– Which turbulence parameters, turbulence mixing length.”

Need for experimentation to clarify how best to handle shallow convection/turbulence grey zonesin parametrizations! Pier Siebesma: Extend existing grey zone project to higher resolutions?

Courtesy: L. Auger

WGNE 2014, 20140311

Are we trying to run before we can walk?

• We are rushing towards hectometric scale resolutions, while we have only just gotten over the grey zone for deep convection

• At present resolutions the convection-permitting models still suffer from several (severe) systematic errors, which will not magically disappear on finer scales; deal with them first?!?

• We also have only started to e.g. get aerosols in and disentangle the complex interplay between radiation, clouds, microphysics and aerosols; do this first?!?

• But under pressure of the driving forces, we enhance complexity by adding two new grey zone problems of shallow convection representation and (3D?) turbulence

• Surely we cannot ignore the issue of very limited predictability at these small scales? Accompany this VHR experimentation with VHR ensemble information, if so, how?

WGNE 2014, 20140311

Need for 3D-radiation? Tilted column modelling

Courtesy: K. Nielsen

WGNE 2014, 20140311

Physiography datasets

Sand Clay

• Detailed and high-quality datasets essential for surface characterization in VHR modelling. However, for many well-known (global) datasets

• quality is generally NOT uniform over the dataset’s geographical area

• some gross errors exist which can have significant local meteorological impact (and you do not want to attribute this erroneously to forecast model error!)

=> Look at them critically for your own domain!

Stable boundary layer:

Preparations for GABLS-4 experiment

Testing new parametrizations

1D test with EFB closure: Comparison for GABLS1 (e.g. Holtslag et al, 2003):

• # of convection-permitting LAM EPS growing

• Increasing link with ensemble DA

• Experimentation with different physics and surface perturbation types

– Stochastic physics / SPPT

– Multi-physics schemes

– Multi-model schemes

– Different surface quantities

• Added value wrt deterministic model

• Still quite underdispersive: are we capturing the mechanisms of uncertainty correctly?

• Calibration important but often not in place

• Much effort sofare spent in “getting EPS up and running”, is it time to start paying more attention to intrinsic (limitations of) predictability??

Probabilistic forecasting on convection-permitting scales

WGNE 2014, 20140311

TIGGE-LAM: GEOWOW archive at ECMWF

WGNE 2014, 20140311

Data provider progress status information

http://tigge.ecmwf.int/tigge/d/inspect/tigge/tigge/monitoring/lam/prod

Courtesy: T. Pacagnella

Yu H., S.T. Chan, B. Brown, and Coauthors, 2012, TCRR

Products from limited area models (LAMs) are widely used by operational forecast agencies in the western North Pacific region, but their application is generally limited to the host agency. For track forecasts, TLFDP verification has shown that it is difficult for LAM’s to add value to the global models. But for intensity / precipitation / wind they might.

WMO-Typhoon Landfall FDP (TLFDP)

Specific objectives of TM-MWFR proposal:

1. set up guidelines and establish a data center for international exchange of TC forecast products from NWP models and EPSs, both global and limited-area (preferably including convection-permitting);

2. evaluate the participating models' performance on the prediction of TC intensity and precipitation up to 48 hours;

3. understand the physical mechanisms for the performance of different LAM models/EPSs;

4. understand the performance and impact of different data assimilation systems;

5. understand the impact of different observing systems on TC forecast quality (e.g. TC bogus, targetted observations);

6. propose skillful multi-model consensus forecast scheme for TC intensity and precipitation up to 48 hours, both deterministic and probabilistic, which should be region-dependent;

7. find out the minimum forecast range that the model output becomes useful;

8. enhance the application of advanced LAMs and LAM-EPSs in operational forecast agencies globally.

WGNE 2014, 20140311