VOLCANIC ASH FORECASTING AT THE CANADIAN METEOROLOGICAL CENTRERené Servranckx, Réal D'Amours, Michel Jean, Joseph-Pierre Toviessi
and Serge Trudel
AbstractVolcanic ash clouds pose a real threat to aircraft safety. More than 80 jet airplanes have encountered volcanic ash clouds in the past 15 years often resulting in damage to the aircraft and its engines. Once released, the ash plume can drift over great distances and cause disruptions to air traffic, even thousands of kilometres from its source. This was the case in September 1992 following the eruption of Mount Spurr in Alaska. Given the immediate threat posed by volcanic ash, predicting its movement and dispersion in the atmosphere is an important challenge that must be answered in real time. To this task, the Canadian Meteorological Centre (CMC) of the Atmospheric Environment Program (AEP) of Environment Canada uses a sophisticated computer system and a numerical transport and dispersion model, the CANadian Emergency Response Model (CANERM), which runs on a NEC SX3R supercomputer. This paper presents a general description of the CANERM model and some aspects of the CMC operational response to volcanic eruptions. A few examples of recent applications of CANERM are also presented. 1. IntroductionThe numerical simulation of atmospheric dispersion is used increasingly to assess the state of the environment. Well known examples are: the use of numerical dispersion models with complex chemistry schemes for studies of atmospheric oxidants and acid rain phenomenon (for example Chang et al., 1987), the simulation of accidental releases of toxic and radioactive materials (Pudykiewicz, 1988 and 1989) and the use of transport and dispersion model to forecast volcanic ash plume behaviour (Heffter and Stunder, 1993). The development of the CANadian Emergency Response Model (CANERM) was initiated by the Atmospheric Environment Service (AES) in response to the Chernobyl nuclear accident. The first Canadian simulation of the Chernobyl dispersion was performed in real time with a simple 2-D hemispheric model quickly adapted for the situation (Pudykiewicz, 1988). Following the emergency simulation, extensive development work with a three-dimensional (3D) tracer model was conducted and new simulations were made using objectively analyzed meteorological fields over a period of one month (Pudykiewicz, 1989). In 1993, the Canadian Meteorological Centre (CMC) was designated by the World Meteorological Organization (WMO) as a Regional Specialized Meteorological Centre (RSMC) for the provision of atmospheric transport modelling advice during nuclear emergencies along with Washington (NOAA- ARL), Bracknell (United Kingdom Meteorological Office), Toulouse (Météo- France) and Melbourne (Australia). More recently, the International Civil Aviation Organization (ICAO) has approached the Canadian Meteorological Centre to become a Volcanic Ash Advisory Centre (VAAC) with an area of responsibility covering Canada, its adjacent waters and the northwest Atlantic. CANERM has been adapted to predict the transport and the dispersion of volcanic ash. The current version constitutes the core of a sophisticated computer system designed to produce quick and real-time dispersion simulations in a forecast or diagnostic mode. 2. The CANadian Emergency Response Model (CANERM)CANERM is a fully 3-dimensional Eulerian model for medium and long range transport of pollutants in the atmosphere. A detailed description of the model can be found in Pudykiewicz (1988, 1989). Advection is calculated using the semi-Lagrangian method. Diffusion is modeled according to the gradient (K) theory; diffusivities in the horizontal and in the vertical are dependent on the state of the boundary layer at low levels, and constant in the free atmosphere. The model simulates wet and dry scavenging and provides estimates of wet and dry deposition. CANERM uses the concept of virtual source (Pudykiewicz, 1988) to model unresolved subgrid scale effects of emission and dispersion processes near the point of release. The virtual source is expressed as a 3D Gaussian function. CANERM operates on a polar stereographic grid and can be run for any volcano on the globe. The horizontal resolution is 150 km in the hemispheric configuration, 50 km in the continental configuration and 25 km in the limited area configuration. The operational version of the model has 11 vertical levels in the "sigma" (s) terrain following coordinates (Phillips, 1957). An experimental version with 25 vertical levels is also available. CANERM is fully integrated into the operational setup of the CMC. The operational procedures reside on a front- end workstation and are accessible to the duty meteorologist through an Xwindow menu. It can be executed at any time and the results are usually available between 30 and 60 minutes from the time of notification. CANERM uses meteorological fields provided by the global data assimilation system in a diagnostic mode, or by the regional or global forecast model, in a forecast mode. In the diagnostic mode, the last seven days of analyzed meteorological fields are always on-line. In the forecast mode, data are available to 72 hours twice a day and to 240 hours once a day. Based on the data collected from satellite imagery and other sources following the 1992 Mount Spurr eruptions, development work was done on CANERM using a hindcast mode along with archived data. The model was tuned, visual ash cloud criteria were defined and default scenario conditions were established. (NOTE: for a sample of the data available for the Spurr eruptions, please consult the web pages of the Alaska Volcano Observatory (AVO) at http//www.avo.alaska.edu/ and the Michigan Technological University University (MTU) at http://www.geo.mtu.edu/volcanoes/ ). 3. Volcanic ash forecasts at CMCThe threat of volcanic hazards to aviation safety first received public attention when several commercial jet aircrafts were damaged in the early 1980s after flying through volcanic ash clouds that had travelled several hundred miles from their source (FAA, Aviation Safety Journal). Because of this threat to aviation, CANERM is now used routinely to produce volcanic ash transport and dispersion forecasts. These forecasts are of great use to aviation meteorologists who issue volcanic ash SIGMETs, airline flight dispatchers, etc. The volcanic ash forecast charts are available for transmission on METSIS and ANIKOM and are produced whenever an eruption threatens the Canadian airspace. Work is currently underway to provide access to the outputs on the Internet. The model is also executed upon request from the National Meteorological Service of another country. 3.1 Volcanic ash forecasts
The charts depict the presence of volcanic ash in three altitude ranges: surface to FL200, FL200 to FL350 and FL350 to FL600. The charts consist of two vertical columns of 3 panels, depicting forecast position of the volcanic ash in a 6 and 12h prognosis on the first chart and an 18 and 24h prognosis on the second Additional charts, valid at forecast times up to 72 hours are also available The average ash concentrations in the layer is labelled as "LGT" (10 to 100 micrograms/m3), "MDT" (100 to 1000 micrograms/m3) and "HVY" (greater than 1000 micrograms/m3). It should be noted that, based on the best available information, even "LGT" areas constitute a potential danger to aircraft in flight and should be avoided by pilots. The criterion used to define the outermost contour ("LGT") is similar to the one used for the VAFTAD (NOAA-ARL) model single contour depiction of the "visual" ash cloud (Heffter and Stunder, 1993). The following information is printed at the bottom of each chart: name of the volcano after the WMO symbol for a volcanic eruption site to indicate the location of the volcano on the chart , time and date of the eruption, latitude and longitude. The "CYCLE" information is for internal use at CMC only. In addition, the following message is always included: "SEE CURRENT SIGMET FOR WARNING AREA - VOIR SIGMET COURANT POUR ZONE D'AVERTISSEMENT". This is to draw attention to the fact that the maps are to be used as guidance only and that the SIGMETs are the authoritative warning messages. This message is also found on the VAFTAD outputs.
In addition, trajectory maps are also routinely produced for any location on the planet in hindcast, forecast or mixed modes. 3.2 Scenario used to run CANERMWhen an eruption occurs, there is little if any information on how much ash is released or the duration of the eruption. Any real time information on the eruption is usually in the form of qualitative statements such as "It is a major eruption". This is clearly a problem when having to choose initial conditions describing the eruption in order to run the model. Nonetheless, based on the cases to which CMC has responded, the volcanic ash forecasts are of great use to the aviation community and the meteorologists when used in conjunction with satellite imagery and trajectory forecasts. The inputs required from the duty meteorologist before CANERM can be run are the latitude and longitude of the volcano, time and date of the eruption, duration of the eruption, time function to be used for the release (constant, exponential or gaussian), the amount of ash released in the atmosphere and the plume height. Since the source strength is usually unknown, predefined default characteristics can be used. They are:
The model can be run again as new weather data or source strength information become available. 3.3 Recent examples of the operational response to volcanic eruptionsCANERM was used successfully to forecast the track of volcanic ash clouds in recent years. A few examples follow. Spurr, Alaska (61°18'N, 152°15'E) : Following 39 years of inactivity, Mount Spurr erupted on 27 June, 18 August and 17 September 1992. Extensive data were collected and analysed (USGS, 1995). Each eruption produced large clouds of volcanic ash that affected air traffic operations over a wide area of the United States and Canada. The September eruption was particularly interesting with respect to air traffic disruptions. The circulation in the upper atmosphere was such that the ash cloud remained well defined and visible for a period of at least 72 hours. Because of the strong winds, the ash had traveled thousands of kilometres by that time resulting in air traffic problems in many areas, particularly near the Great Lakes. CANERM and the trajectory model were run in real time to provide guidance to the forecast centres. In Canada, SIGMETS were issued from British Columbia and the Yukon to Newfoundland over a three day period.
Figures 3 to 9 present some of the satellite imagery of the ash plume and the CANERM outputs for the September and August 1992 eruptions.
Rabaul, Papua New Guinea (4°27'S, 152°20'E) : Simultaneous outbursts on opposite sides of the Rabaul caldera occurred around 20 UTC on 18 September 1994 as the intra-caldera cones Tavurvur and Vulcan began erupting. The ash column elevation was estimated at 70,000 feet above sea level.
Figure 10 shows the satellite imagery taken by NOAA-12. Figure 11 shows the CANERM forecast valid at about the same time. CANERM has captured the essential features of the volcanic ash plume: a westward displacement of the plume to the north of the volcano and a south to southeast displacement south of it. Klyuchevskoi, Kamchatka (56°03'N, 160°39'E) : A major eruption around 18 UTC on 30 September 1994. The ash column elevation was estimated at 50,000-65,000 feet above sea level. Because of the upper air flow, it was feared that the Canadian airspace might be affected by the volcanic ash 30 to 36 hours following the start of the eruption. CANERM was executed with a series of scenarios and the forecast charts were transmitted to the Weather Centres in Edmonton, Vancouver and Whitehorse. SIGMETs were issued beginning early on 2 October (Beal, 1994).
Figure 12 shows a composite map of the estimated ash silicate mass (kg/km2) for that eruption. It was produced by the Department of Geological Engineering and Sciences at Michigan Technological University. The corresponding CANERM 24 hour forecast is presented in figure 13. 4. Conclusion
Real time products and services related to volcanic ash are available in a fully operational weather analysis and forecasting system at the Canadian Meteorological Centre. This system is based on state of the art numerical weather prediction models, on a continuous assimilation of current meteorological data covering the world and on a global telecommunications capability. A team of professional meteorologists and computer scientists is on duty 24 hours everyday of the year to insure a continuous operation and maintenance of the system. In addition, a team of specialists in atmospheric transport and dispersion is always on-call. The operational applications of CANERM have shown that the model produces useful guidance and that it is an important tool for meteorologists and various agencies responding to volcanic eruptions. NOTES: Others documents can be accessed at the Operations Branch of the Canadian Meteorological Centre WWW page. For any additional information, please contact René Servranckx. References
Created :
2002-08-26
Modified :
2002-12-18
Reviewed :
2002-12-18
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