23rd september 2010 2010 eumetsat meteorological satellite conference córdoba, spain

The High Resolution Winds product (HRW), at the Satellite Application Facility on support

to Nowcasting and Very Short Range Forecasting (NWCSAF)

23rd September 20102010 EUMETSAT Meteorological Satellite Conference

Córdoba, SpainJavier García Pereda ([email protected])

NWCSAF Project TeamAgencia Estatal de Meteorología, Madrid, Spain

2010 EUMETSAT Meteorological Satellite Conference - Córdoba, Spain, September 2010

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I. NWCSAF High Resolution Winds product.- Tracer calculation. - Quality control.- Height assignment. - Orographic flag.- Tracking.

II. NWCSAF/HRW version v3.0. - Validation.

- Examples of use: 22-23 Dec. 2009 Rapid Cyclogenesis in Portugal.

27-28 Feb. 2010 Rapid Cyclogenesis ‘Xynthia’.

III. Future developments in NWCSAF/HRW product.

IV. Conclusions.

Index


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• As you already know, the Satellite Application Facility on support to Nowcasting and Very short range forecasting (NWCSAF) was established between Eumetsat & Aemet (Spanish National Weather Service):

- To enhance Nowcasting tasks through the development and support on the use of a software package calculating in near real time Meteorological products from MSG and Polar satellite data.

NWCSAF High Resolution Winds product


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• High Resolution Winds (HRW) is among its products.

• Objective: to provide high density sets of satellite winds (AMVs),

for near real time meteorological

applications, from MSG/HRVIS &

MSG/IR108 image data.



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• HRW product can be useful for:

- Nowcasting tasks: * Flux displacement * Watch and warning

of strong winds * Convergence

(specially around cloud systems)

* Small scale circulation * Wind singularities.

- Assimilation in:* Analysis/Forecasting

applications (incl. NWP models).



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Input data:• Full Resolution SEVIRI/HRVIS & IR10.8 data.• NWP data for the working region (not mandatory but fairly recommended): - Temperature, Wind, Geopotential, Surface temperature forecast.• NWCSAF/Cloud Type output file for the working slot (not mandatory).

Output data:• Two BUFR bulletins, with AMVs related to up to two different scales of tracers

- “Basic scale”: Tracer size: 24 pixels.- “Detailed scale”: Tracer size: 12 pixels. • Detailed winds can be calculated in areas where:- No basic tracers are found.- Basic tracers are large, with the possibility of a more meticulous search.

Current version of NWCSAF/HRW product:• HRW v3.0, available since spring 2010.



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Main steps of HRW algorithm:

• Preprocessing: Initialization of SEVIRI & NWP data through NWCLIB library included in NWCSAF software.

• Tracer calculation with two different methods:- Gradient - Tracer characteristics.

• Height assignment: one of two different height levels is defined for each tracer,depending on the NWCSAF/Cloud type output value related to the tracer:

- Cloud top - Cloud base.

• Tracer tracking / Wind calculation: Selection of up to three correlation centres with Euclidean differences or Cross correlation methods.

• Quality control with Eumetsat Quality Indicator method (also used at MPEF).

• Orographic flag test: tracers affected by land influence are rejected.



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Methods for the tracer calculation:• Gradient / Sharp edge: searching of well defined cloud edges, considering

a minimum brightness value and a minimum brightness difference. Very efficient, fast, well proven.

• Tracer characteristics: filling holes in coverage.

Longer, but still reasonable computing time.

Each “starting location” is checked for:• A threshold separating “bright” vs. “dark” pixels.

(the cloudiness in front and the background).• A distribution of bright pixels showing a “well defined shape”.

(trying to avoid “too linear” cloudy elements).• A small scattering of IR-channel temperatures in the bright pixels.

(to avoid multilevel cloudiness).

NWCSAF/HRW algorithm: Tracer calculation


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Example of a good and a bad tracer for “Tracer Characteristics method”, due to:

– A clear / unclear separation of bright pixels.

– A nonlinear / linear bright pixel shape.

NWCSAF/HRW algorithm: Tracer calculation

Example of Tracer Determination: - “Gradient method” tracers in Green. - “Tracer characteristics method” tracers in Red. (With both methods, tracers are found throughout all the image).


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• Height assigment based on two different height levels calculated with IR10.8 brightness temperature: - Cloud top: Temp. of coldest non isolated class of smoothed temp. histogram. - Cloud base: calculated with Tbase = Tmean + K· σtemp (Schmetz et al. 1996).

NWCSAF/HRW algorithm: Height assignment

For each case, the height level usedis based on the NWCSAF/Cloud typerelated to the tracer: - Cloud top for “High semitransparent thick and meanly thick clouds”. - Cloud base for all other valid clouds.

NWCSAF/Cloud type also used to discard: - Wrong cloud types: “Cloud free/contaminated by ice terrain”. - Cloud types with bad statistics: “Fractional & high semitransparent thin clouds”. 0% 50% 100% 150%

ALL

Undefined/Multiple cloud types

Fractional clouds

Very low stratus/cumulus

Low stratus/cumulus

Medium stratus/cumulus

High opaque stratus/cumulus

Very high opaque stratus/cumulus

High semitransparent above low /medium clouds

High semitransparent thick clouds

High semitransparent meanly thick clouds

High semitransparent thin clouds

Relative value of the different NRMSVDs, respect to that of the height level with the best fit

CLOUD BASE MEAN INTERPOLATION LEVEL CLOUD TOP


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• Given a set of tracers at “t-Δt slot”,“Tracking candidates” of the same size are defined at “t slot”,with one of two well known methods: - Euclidean differences (default).

- Cross correlation.

• The best three matching “Tracking candidates” are kept,to perform a final selection step at Quality Control.

• NWP wind guess used as default to reduce tracking area/running time.

NWCSAF/HRW algorithm: Tracking


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• Quality Indicator method, developed at Eumetsat for the AMV calculation at MPEF (K.Holmlund 1998), is adapted for HRW product.

• Several tests on consistency (partial QIs) are if possible computed:• Temporal test (vector/direction/speed consistency with AMVs in previous slot).• Spatial test (vector consistency between neighbour AMVs).• Forecast test (vector consistency with NWP forecast winds).

For Detailed winds also:• Two scale test (vector consistency with simultaneous Basic winds).

• Partial QIs defined by statistical fitting functions given by the method.

The overall QI is the average sum of partial QI,with a double contribution of the spatial test.

NWCSAF/HRW algorithm: Quality Control


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• For each tracer and its up to three correlation centres,the centre with best quality tests is selected for the final AMV selection.

• For a balance between reduction of errors and reduction of AMV population with a bigger QI, a QI threshold = 83 is defined as default.

NWCSAF/HRW algorithm: Quality Control


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• An “Orographic flag” is also calculated to reject tracers affected by land influence.

• The Algorithm calculates for 1x1 Degree Lat/Lon “Orographic Geographical Boxes”:- Min./Max. Representative Heights (3% & 97% Height Histogram Centiles).- Barometric conversion of Heights to Max./Min. Representative Pressures.

NWCSAF/HRW algorithm: Orographic flag


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• Defined the “Orographic Geographical Boxes”, an Orographic Flag valueis assigned to each tracer:

Or.flag = 1 Tracer below the Mean Pressure level of the corresponding geographical box

Or.flag = 2 Tracer below the highest level with orogr. influence [defined as Min.Represent.Pressure - 25 hPa]

Else, if stability is found at the tracer location, previous positions of the tracer are calculated with the corresponding AMV:

Or.flag = 3 Tracer below highest level with orographic influence, at any of the previous positions up to two hours (An obstacle has been found). Or.flag = 4 No obstacle has been found, but stability is still present at the previous positions (The obstacle might be farther).

Else, Or.flag = 5 (All other conditions: no orographic influence is found).



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- Orographic flags = 1,2 logically restricted to tracers near the ground.

- The general flux is better represented in mountain areas without Orographic flags = 1,2: - Visible f.ex. in this case around the Atlas range in Algeria.


- The Normalized RMSVD is at least a 50% worse when Orographic Flag = 1,2.- The Orographic Flag is good to filter out around a 3% of low level winds with worse quality, whose displacement is less correlated with atmospheric flows.


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• The latest HRW v3.0 (included in NWCSAF v2010) is a very important step forward in the product:

• AMVs are calculated for the first time from both MSG/HRVIS & MSG/IR108 channels > Possibility of monitoring winds/flows without night intermittencies

(as required by the users in previous meetings/surveys).

• HRW v3.0 has been optimized > Calculation of AMVs in ~2 min. under linux environment.

• HRW v3.0 has also been adapted to work in “Rapid scan mode”.

NWCSAF/HRW Version v3.0


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Example of evolution between HRW v2.2 & v3.0 (Nominal mode, European & Mediterranean area)

1. There is a visible increase in the number of available AMVs (~2.5 times respect to HRW v2.2).

2. HRVIS & IR108 AMVs complement each other, giving information about different cloud patterns.



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Example of HRW v3.0 outputs in “Nominal mode” and “Rapid scan mode”

Main characteristics of HRW in “Rapid scan mode”: - A 10 minute time difference between the initial tracer image and the later tracking image. - The possibility to rerun HRW algorithm with every new MSG slot every five minutes. - The amount of winds in “Rapid scan” is multiplied by ~3 with a similar quality.



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A validation of HRW product isavailable at the NWCSAF Helpdeskwww.nwcsaf.org.

In general: - HRW reached its “Target accuracy” and has been operative for several years, with similar quality for HRVIS & IR108 winds.

- Statistics errors are a bit larger than for the AMVs by other centres (like MPEF), but: - data density is much higher - data are available in near real time - the differences keep on decreasing

with each new version.

NWCSAF/HRW Version v3.0: Validation

With these results, HRW product can be very useful in operative forecasting, as we are going to see in the next two examples.


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A rapid cyclogenesis from the Atlantic and entering Portugal during the night 22-23 December 2009 (with deepening stronger than 20 hPa/24 h),

caused important damages (people wounded, damages in houses and infrastructures) along a narrow strip moving northeast from the Tagus mouth into the inner country (south of the centre of the low, with 969.4 hPa at Cabo Carvoeiro).

22-23 Dec. 2009 Rapid Cyclogenesis in Portugal


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HRW product is able to identify a narrow area of Hurricane force low level winds coming from the ocean related to the area where the main damages occurred (15 min. mean winds between 125-150 km/h in the layer 850-1000 hPa)


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Only two Surface wind observations were available inthe affected area, with Wind gusts ~140 km/h:

- Cabo Carvoeiro - Dois Portos

A later Analysis of Surface winds consideringextrapolation of Doppler Radar Windsby the Portuguese Instituto de Meteorologia showsAreas with 10 m. Maximum winds >150 km/h and >200 km/h in the affected regions around 23 Dec 2009, 04:30Z.


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The areas in Portugal and all the Spanish Mediterranean, where HRW product defines its 850-1000 hPa Hurricane force winds were not identified by the ECMWF model forecast used for HRW calculation. HRW can be helpful for Watch & Warning tasks, beyond the possibilities of the NWP model used for the HRW calculation


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27-28 Feb. 2010 Rapid Cyclogenesis ‘Xynthia’

During 27-28 February 2010, Rapid Cyclogenesis ‘Xynthia’(Deepening ~ 20 hPa/24 h, Min. Surf. Pressure ~ 968 hPa) crosses NW Iberian Peninsula & Bay of Biscay into France.

Although not as strong as other Cyclogenesis before(Lothar in 1999; Klaus in 2009), it was very damaging:> 65 deaths in several European countries (Specially in France, through floodings caused by the spring tide and a 1.5 m storm surge).> Property losses higher than 1000 million euros.> Around one million homes without electricity in Western and Central France.


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HRW product defines very clearly the areas with strongest winds:- Wind strength over France more important than over the Iberian Peninsula.- Anyhow, Hurricane force winds less widespread than in the Dec.2009 Portugal Cyclogenesis. - Sustained Storm force winds in France moving northeast from Coastal areas

(Departments of Loire Atlantique, Vendée, Charente Maritime, Gironde) into the inner country.


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Comparing HRW output in France (Storm force low level winds) with Surface Wind observations, the path followed by the strongest winds is clearly identified.



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Comparing against ECMWF Model wind fields, HRW v3.0 confirms the Model forecast respect to the trajectory of Xynthia and the areas suffering the strongest winds,

but in general winds are weaker than expected.


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The temporal evolution of HRW winds permits also to identify where the hardest winds are striking at every moment.

The capabilities of HRW product for operative forecasting are shown with its dense wind fields: - Spatial and temporal identification of winds - Verification of the NWP model wind forecast


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> Extension of HRW product to calculate AMVs with other MSG channels.

- WV6.2 & WV7.3 Water Vapour channels.

> Changes in HRW algorithm through external collaborations. - Collaboration with Régis Borde

(from EUMETSAT Meteorology Dept.) to test and implement:

CCC method for Height assignment (defining height only through the pixels contributing most to the image correlation).

Future developments in HRW product

Developments during the Continuous Development and Operations Phase (until 2012):


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Future developments in HRW product

Other developments being now defined for CDOP-2 Phase (2012 - 2017):

> Application of HRW product to calculate displacements/trajectories.

> New WFA (Wind Field Analysis) product:- Calculation of wind field grids through the interpolation of HRW winds into NWP model data.- Several applications possible: Convergence & vorticity fields,

humidity convergence & vertical mass transport.

> New EXIM (Extrapolated Imagery) product: - Extrapolation into the future of satellite images/NWCSAF products considering the displacement of image elements with HRW data.

> Development of new WPR (Vertical Winds profiles) product: - Calculation of AMVs from MTG/IRS height defined humidity fields,

with vertical wind profiles and wind shear as derived products.


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• NWCSAF/High Resolution Winds product has proved to be useful in operational forecasting, specially with the new version of the algorithm HRW v3.0. => It permits the monitoring in near real time of winds and flows.

=> It includes a “Rapid Scan mode configuration”, with a quicker and more dense update of the wind data.

• An important increase in the use of HRW product is expected with version v3.0.

• The users collaboration (including you!) is specially required to evaluate the impact of HRW data assimilation in NWP Regional/Mesoscale models.

(We have still no experience with this application of HRW data!).

=> This work could be even economically awarded through a NWCSAF Visiting Scientist Activity, with the elaboration of a Report on the impact of HRW data assimilation in NWP models.

Do not hesitate to contact me about this or any other matter

through email [email protected] at any moment during this “Eumetsat Conference”.

Conclusions

mailto:[email protected]

23rd september 2010 2010 eumetsat meteorological satellite conference córdoba, spain

Documents

high resolution winds

polar satellite data

satellite application

detailed winds

warning of strong winds

output data

resolution sevirihrvis

input data