Measuring and forecasting atmospheric icing on structures

Alain HeimoMeteotest, Switzerland

MC Chairman/COST727

COST 727 Action

COST: European Cooperation in Science and Technology

COST is one of the longest-running instruments supporting co-operation among scientists and researchers across Europe.

Atmospheric icing causes severe financial losses and reduces security and human safety :

- Power line transmission …

Atmospheric icing: Why is it a problem?

Spain 2002 Germany 2005

Norway 1961

Atmospheric icing causes severe financial losses and reduces security and human safety :

- Power transmission- Icing of structures (e.g.:TV- and telecommunication towers, ski-lifts) ...

Atmospheric icing: Why is it a problem?

On TV-towers the ice load maybe several tensof tons.

Design of loads, safety, operational stops..

Atmospheric icing causes severe financial losses and reduces security and human safety :

- Power transmission- Icing of structures (e.g.:TV- and telecommunication towers, ski-lifts)- Telephone lines, Forest economy...

Atmospheric icing: Why is it a problem?

Ice load + high winds !

Atmospheric icing causes severe financial losses and reduces security and human safety :

- Power transmission- Icing of structures (e.g.:TV- and telecommunication towers, ski-lifts)- Power lines, Telephone lines, Forest economy- Wind turbines...

Atmospheric icing: Why is it a problem?

- Uncertainities in prediction of production- Additional loads /design- Safety: falling ice, operational safety- Reduction in power production due to:

- reduced lift- shut-down - mechanical failures- iced wind sensors

Atmospheric icing causes severe financial losses and reduces security and human safety :

- Power transmission- Icing of structures (e.g.:TV- and telecommunication towers, ski-lifts)- Power lines, Telephone lines, Forest economy- Wind Power production- Aviation ...

Atmospheric icing: Why is it a problem?

source: http://meted.ucar.edu

Icing at airports and in the air

No icing

Icing

WMO/CIMO Wind Instrument IntercomparisonMont Aigoual, France, 1992-1993 Organized by France, Switzerland & WMO Participating countries: 11Instruments tested: 26

Atmospheric icing: former activities

Jungfraujoch, Switzerland

Conclusions from the final report:

-… The formation of ice makes almost all the calculated parameters incoherent.- … We have not been able to characterize the icing phenomena from ice detectors.- … It appears difficult to be both “accurate” and rugged for severe icing.

EUMETNET SWS-II (2000-2003)

Goal:Acquisition of meteorological data under icing conditions in Finland (Luosto), France (Mt. Aigoual) and Switzerland (Säntis)

Measurement period: 1.10.2001 to 30.4.2002

Atmospheric icing: former activities

Conclusions and recommendations:

- …. Already during the installation and test period proceeding the experiment, it was quickly recognized that the lack of adequate instruments for the characterization of ice accretion would represent a serious drawback for the whole experiment.

- … it is important that more care is given within the meteorological community to produce accurate measurements under harsh conditions and to promote measurements of icing.

Luosto, finland

• to develop the understanding of icing (especially in-cloud icing) and freezing rain in the atmospheric boundary layer (ABL)

• to produce information on distribution of icing over Europe

• to improve the potential to observe icing monitor icing forecast icing

COST 727 Main Objectives (MoU 2004):

Participating countries

Parties: list of countries and date of acceptance

Country Date Country Date Country Date Country Date

Austria 29/01/2004 Bulgaria 10/03/2004 Czech

Republic

20/04/200

4

Finland 29/01/2004

Germany 29/01/2004 Hungary 29/01/2004 Norway 29/01/200

4

Slovakia 05/04/2005

Spain 15/06/2004 Sweden 22/06/2004 Switzerland 15/06/200

4

United

Kingdom

15/06/2004

Total: 12

Non-COST Participant: Japan (Kanagawa Institute of Technology)

Objectives:

To develop scientific understanding of icing processes together with modeling and forecasting of icing.

Measurements:

To compile existing sources of icing data in Europe To harmonize ongoing measurement programs in Europe To fulfill the WMO/CIMO request to provide guidance for performing measurements under harsh icing conditions. To promote the development of robust, rugged icing detectors to be deployed at automatic meteorological stations as well as at other sites where icing effects may be critical. Simple sensors delivering a yes/no information are needed as well as more sophisticated instruments yielding values of ice thickness/weight, types of ice.

Modelling:

To develop numerical meteorological models for icing studies with improved icing parameterizations and verification of icing models with ground-truth data. To perform climatological icing studies and mapping of icing severity

Achieved during the last 2 years:

-Based on preliminary measurements, selection of 2 «  reference » sensors for the detection of ice accretion (Goodrich 0847LH1) and for the measurement of ice loads (Combitech Mk I)

Measurements of icing

Principle: ultrasonic resonance

+ promising results from earlier studies

- difficult to get it from manufacturer (military regulations)- only little measurement data available

Principle: weighting of ice

+ designed according to ISO 12494 definition+ operational from the beginning+ promising results

- design improvements needed (e.g.

oscillations)

Measurements of icing

Achieved during the last 2 years:

- Based on preliminary measurements, selection of 2 «  reference » sensors for the detection of ice accretion (Goodrich 0847LH1) and for the measurement of ice loads (Combitech Mk I)- Calibration of the « reference » instruments in a dedicated icing wind tunnel facility (Kanagawa Institute, Tokyo, Japan)

in Cryospheric Environment Simulator at Shinjo Branch of National Research Institute for Earth Science and Disaster Prevention

in Kanagawa Institute of Technology

< 20m/s (with a larger test section)

< 100m/s (in a smaller test section)

> -25 deg. Cel.

< 20m/s (1m by 1m test section)

> -25 deg. Cel.

Sprayers not installed all the time

Icing wind tunnel test

Measurements of icing

Achieved during the last 2 years:

-Based on preliminary measurements, selection of 2 «  reference » sensors for the detection of ice accretion (Goodrich 0847LH1) and for the measurement of ice loads (Combitech Mk I)- Calibration of the « reference » instruments in a dedicated icing wind tunnel facility (Kanagawa Institute, Tokyo, Japan)- Installation and operation of 6 test stations in Europe equipped with the Combitech Mk I (2007:2008) and the Goodrich 0847LH1 (2008): Luosto (Finland), Sveg (Sweden), Zinnwald (Germany), Deadwater Fell (United Kingdom), Studnice (Czech Republic) and Guetsch (Switzerland)

European test stations

Czech Republic (Studnice)

Switzerland (Guetsch test station)

Germany (Zinnwald)

Åre, Sweden

Luosto fell,Finland

Deadwater Fell, UK

Achieved during the last 2 years:

-Based on preliminary measurements, selection of 2 «  reference » sensors for the detection of ice accretion (Goodrich 0847LH1) and for the measurement of ice loads (Combitech Mk I)- Calibration of the « reference » instruments in a dedicated icing wind tunnel facility (Kanagawa Institute, Tokyo, Japan)- Installation and operation of 6 test stations in Europe equipped with the Combitech Mk I (2007:2008) and the Goodrich 0847LH1 (2008): Luosto (Finland), Sveg (Sweden), Zinnwald (Germany), Deadwater Fell (United Kingdom), Studnice (Czech Republic) and Guetsch (Switzerland)- Setup of the first European Icing Dataset containing all meteorological parameters necessary for icing modeling and simulation -> winter 2007-2008: selection of 3 major icing events for each station

Measurements of icing

• The theoretical basic knowledge is presently available, based on the ISO 12494 standards (Makkonen formula) and new cloud microphysics schemes built in the WRF model code

• Verification data are now available and standardized for sites located all around Europe. Unfortunately more data (winters) are needed.

• Preliminary results show that the current version of the WRF model is able to perform very accurate simulations of icing events at all test stations in Europe (especially for the collapse of a measurement tower in Switzerland)

• Measured site information about the Liquid Water content and Droplet Size Distribution are still missing

• Tentative simulation runs of wet snow accretion and freezing rain events have been started

Modelling icing of structures

• WRF is a modern mesoscale, non-hydrostatic numerical weather prediction model developed mainly by NCAR, NOAA and NCEP (USA) designed for mesoscale and high resolution forecasts.

• WRF has the advantage of a very sophisticated calculation of clouds and precipitation.

• Applications from Large Eddy Simulations: Δx = 100mto regional climate simulations: Δx = 100km.

• WRF is meant to gradually replace its predecessor, MM5.

Numerical modeling of ice accretion

Following the ISO12494 standard (Atmospheric icing of structures), the in-cloud ice accretion on a cylinder can be expressed by the formula:

Numerical modeling of ice accretion

VAwdt

Dm 321 where 1 = Collision efficiency2 = Sticking efficiency3 = Accretion efficiencyw = Mass concentration of cloud water (LWC)A = Cross sectional areaV = Wind speed

Specific input data from measurements or from 3D weather models are needed to compute α1 and α 3:

•Temperature, Wind speed, humidity <- standard measurements• LWC <- Simulated by WRF• Median Volume Droplet size <- unknown at present (fixed value assumed).

Test simulations have been carried out with the weather model WRF extended with the above algorithm.

Case #1: Luosto (Finland) December 2007

WRF simulation

96h WRF simulation 800m grid size

120h WRF simulation 800 m grid size

Case #2: Schwyberg (Switzerland) November 2007

WRF simulation

Tower collapse at Schwyberg, Switzerland

Data acquisition failure

Ice load and strong winds -> tower collapse

Case #3: Mapping (tentative)28.12.2007 – 7.01.2008

WRF simulation

• Measurementso Continuous operation of the 6 test stations equipped with the 2

“reference” instrumentso Upgrade of the present instruments together with the manufacturero Extend dataset with the winter 2008-2009 measurements

• Modelingo Upgrade WRF model with updated microphysics (PhD)o Perform simulations based on the EIDo Perform sensitivity studies with LWC and MVD

Activities until end of Action

For further details, please visit poster P2(40)

Announcement:

The Final Workshop of COST-727 Action

13th International Workshop on Atmospheric Icing on Structures IWAIS

will be held jointly in Andermatt (Switzerland) , 8-11.9.2009

Please register at: www.IWAIS2009.ch

Thank you for your attention !