Dust storm forecasting at the uk met office
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Dust storm forecasting at the UK Met Office. Castellanetta Marina, Italy, June 2014. Malcolm E. Brooks 1 *, Kerry Day 1 , Bruce Ingleby 2 , Yaswant Pradhan 1 , David Walters 1 , 1 Met Office, Exeter, UK 2 ECMWF, Reading, UK. Global Model Forecasts. N512 (~25km) resolution, 70 levels

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Dust storm forecasting at the UK Met Office

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Dust storm forecasting at the UK Met Office

Castellanetta Marina, Italy, June 2014

Malcolm E. Brooks1*, Kerry Day1, Bruce Ingleby2, Yaswant Pradhan1, David Walters1,

1 Met Office, Exeter, UK

2 ECMWF, Reading, UK


Global Model Forecasts

  • N512 (~25km) resolution, 70 levels

  • 4D VAR ensemble-hybrid data assimilation of wind, temperature, humidity etc.

  • 4D Var assimilation of MODIS dust obs. over Land

  • Soil Moisture assimilation uses ASCAT/Synop obs

  • Dust advected with 2 bins

  • Forecasts daily at 00Z and 12Z, runs for 144 hours

  • N768 (~17km) resolution upgrade due July 2014

  • N1024 (~10km) due in 2016(ish!)


Downscaling the Global capability to high resolution

  • Global resolution converging on SAM

  • Implies SAM retirement

  • Does a higher resolution model work for dust?

Global (25km)

SAM (12km)

Afghan (4km)


Downscaling the Global capability to high resolution

  • Global model drives an Afghan 4km ‘dynamical downscaler’

  • Initialised from global, for every forecast,

    with global data at boundaries

  • No independent assimilation of obs


Downscaling the Global capability to high resolution

  • Meant to ‘add detail’ to global forecasts. Does it?

  • It appears to do that – needs more detailed verification.


Downscaling the Global capability to high resolution

Consistent performance across global, SAM and 4km resolutions.


Using dust observations to initialise forecasts

  • 12km LAMs will be retired in late 2014.

  • Focus on improving the global model,

    • either in the forecast model or assimilation of dust observations


Assimilation of Dust Observations

Merged MODIS “DEEP BLUE” and standard AOD product:

  • Near global coverage over a day (before filtering).

  • Uses obs only over land.

    • Standard MODIS filtered by type.

    • All DEEPBLUE obs included.

  • Results from ocean assimilation to come later.


Assimilation of Dust Observations:mean behaviour

  • Test results of re-running global forecasting system for December 2011, into January 2012.

  • Assimilating MODIS obs mostly adds dust

    • Esp. over Asia

    • Dust redistributed in Sahara

  • Improves skill vs AERONET.

  • Went operational in April 2013.


Upcoming developments - global resolution and dynamics

  • Global model upgrade due in July 2014 includes:

    • New dynamical core:

      • Improved solver, slight change of grid.

      • Less diffusive, more energetic, as forecast evolves.

      • More expensive, but more scalable on many cores.

    • Resolution upgrade from N512 (~25km) to N768 (~17km).

    • Physics upgrades to improve ‘weather’: surface T, cloud etc.

    • The most significant NWP upgrade at the Met Office in at least a decade.

    • No direct impact on dust forecast,

      • but does the dust forecast maintain skill?

    • Part of the ‘Global Atmosphere’ (GA) model development process.

      • Current model is GA3.1, upgrading to GA6.1.


Upcoming developments - global resolution and dynamics

GA6.1 model

Current (GA3.1) model

  • Comparison of dust AOD from current operational and resolution/dynamics/physics upgrade (untuned).

  • No major differences stand out.

  • Time mean AODs also similar.


Current (GA3.1) model

GA6.1 model

  • Long range forecast drift away from the DA analysis (forecast bias):

    • Slightly reduced in the GA6.1 model.

    • Forecast model is slightly more consistent with the DA, and hence obs.


Upcoming developments - global resolution and dynamics

Skill scores vs AERONET:

  • Equitable Threat Score

    • 0 – no skill

    • 1 – perfect model.

  • L1.5 data, 1hr window

  • Forecast shows skill, and GA6.1 neutral to slightly positive.

  • Poor skill at low AOD events – non dust aerosol?

  • Moderate dust events improved in GA6.1

  • ETS always poor for rare events.


Upcoming developments - Dust interacting with radiation

  • Proposed model upgrade for late 2014

    • Interactive dust used in radiation (instead of climatology).

    • No change at analysis time.

    • Bias at T+120 broadly similar, with a dipole pattern over N. Africa.

    • With a slight reduction in biases over N. Africa bias pattern.

    • Small (positive) impact on dust and general forecast evolution.

      • A reasonable dust climatology does most of the work.

      • Our dust has reflective optical properties (SSA = ~0.95 to ~0.97).


Upcoming developments - Include MODIS obs. over ocean

  • Proposed model upgrade for late 2014

    • Bellouin, N., Boucher, O., Haywood, J., and Reddy, M. S. (2005) Global estimate of aerosol direct radiative forcing from satellite measurements Nature, 2005, 438, 1138-1141.

    • Jones, T. A., and Christopher, S. A. (2011) A reanalysis of MODIS fine mode fraction over ocean using OMI and daily GOCART simulations, Atmos. Chem. Phys., 11, 5805-5817, doi:10.5194/acp-11-5805-2011

  • Includes MODIS observations over ocean, in specified regions:

  • Non dust aerosol filtered using additional MODIS retrievals, using criteria:

    • Fine Mode Fraction ≤ 0.4

    • Angstrom Exponent ≤ 0.5

    • Effective Radius > 1.0 μm

    • Mass Concentration ≥ 1.2×10−4 kg m-2

    • AOD > 0.1 (still under review)


Upcoming developments - Include MODIS obs. over ocean

  • Proposed model upgrade for late 2014

    • An example set of MODIS obs, after filtering, for a typical DA cycle.


Upcoming developments - Include MODIS obs. over ocean

GA6.1 model

+ MODIS ocean

  • Comparison of dust AOD the upcoming GA6.1 model, and including MODIS over ocean (plus interactive dust).

  • Dust is being added

    in Saharan/other outflow.


GA6.1 model

+ MODIS ocean

  • By improving the analysis, the forecast drift from analysis changes:

    • Highlights future model developments to improve (long range transport):

    • Change fallspeeds? size distribution? Retune emissions? Soil properties in W. Africa?


Upcoming developments - Include MODIS obs. over ocean

MODIS Ocean ETS:

  • Improves all AODs at T+0

  • Skill score increase persists to T+24

  • and to T+120,

  • throughout the forecast


Upcoming developments - Dust included in global ensemble

T+0, main run

T+120, main run

  • The GA6.1 operational suite is now running, in parallel, for final testing of performance, timeliness and robustness.

  • Dust included in the global ensemble when this parallel suite was set up.

  • Global 12 member ensemble, twice daily.

  • N400 (~30km) resolution, forecasts to T+144.


T+0

T+120

Main run

  • Individual N400 ensemble members, broadly comparable to the N768 main run.

Ensemble


Main run

  • Ensemble mean also broadly comparable to N768 main run.

  • Ensemble Std. Dev. is interesting.

  • This is very much initial work – where do we go from here?

  • N400 dust configuration may need tuning.

  • Ensemble DA now an option for dust.

Ens. mean


Summary:

  • Dust forecasting at the Met Office started with Local Area Models for defence applications.

  • We have since moved to a global model,

    • which successfully drives dust in high resolution dynamical downscalers.

  • Global Model forecasts benefit from MODIS dust observations over land (merging standard and DEEPBLUE).

  • Met Office to upgrade global resolution, dynamical core and model physics. Dust forecast performance is neutral to slightly improved.

  • Using forecast dust interactively in model radiation gives a very small benefit (relative to a dust climatology).

  • Assimilating filtered MODIS AOD over ocean gives a larger improvement in dust forecast skill.

  • Dust now included in our Global Ensemble forecasts, but we are not sure what to do with it yet.


Questions?

  • Dust AOD for 21Z, Thursday 6th June 2014, from 12Z Friday 30th May.


Questions?

  • Dust AOD for 12Z, Thursday 6th June 2014, from 12Z Friday 30th May (GA6.1, parallel suite)


Questions?

  • Ensemble mean dust AOD for 12Z, Thursday 6th June 2014, from 12Z Friday 30th May


Questions and answers


Dust Model Details

  • NWP only: Verical flux partitioned to bins with prescribed emission size distribution


Assimilation of Dust Observations

Met Office/Imperial College London AOD retrieval using SEVIRI (MSG):

  • Uses differences in IR channels

  • and a radiative transfer model, with 16 days of NWP model data to find a dust-free comparison.

  • Produces hourly observations.


Assimilation of Dust Observations: Assessment

  • Comparing against AERONET observations.

  • An ETS of 1 is a perfect forecast

  • 0 has no skill – this is a hard score as the obs a daylight only, so have a shorter time window than precip verification.

  • Dust assimilation gives a large increase in skill

  • Including SEVIRI is not quite right yet.


Upcoming developments - Dust interacting with radiation

  • Proposed model upgrade for late 2014

    • Interactive dust used in radiation (instead of climatology).

    • NWP index: an internal metric of large scale global forecast performance

    • Interactive dust has a small positive impact.


Dust emission control from soil properties

  • Libyan coast dust: regular occurrence in the model, during the 2011 Air campaign

  • Intense scrutiny of forecasts and SEVIRI pink imagery during this period.

  • Benghazi was a source, but the coastal dust did not happen!


Total Vertical flux:

Gillette (1979)

Dust emission control from soil properties

  • Current combination of constraints and data do not give ‘optimal’ results…

  • Need to look to other soil datasets


Dust emission control from soil properties

Reprocess current HWSD data?

Even old datasets like Zobler 1degree look useful…

Recent datasets like GMINER30 have a lot more detail. Are they useful?

Geomorphology from Digital Elevation Models.


Dust emission control from soil properties

  • A preferential source map:

  • Ginoux (widely used)

  • Marticorena ’97:

  • or Bullard ’11:

  • Both global coverage and high resolution is required.


Dry river beds, lakebeds, Wadis

e.g. Sistan Basin – often dry

  • Our emission scheme lacks alluvial sediement…


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