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Analyses & Numerical Prediction Analysis and Prediction Operations Bulletin No. 44
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Since the 1st July 1995, the National Meteorological Operations Centre (NMOC) in Melbourne has been a Regional Specialised Meteorological Centre (RSMC) for Environmental Emergency Response (EER), with responsibility for the Regional Association V area. As part of its responsibility, RSMC Melbourne is required to provide advice, in the form of a basic set of products, on the transport of pollutants resulting from nuclear disasters, volcanic eruptions, forest fires and, perhaps, other causes. The system is maintained in a state of readiness so that the ad-hoc requests for products can be satisfied quickly.
The EER system, in RSMC Melbourne, is based around the HYSPLIT Atmospheric Transport Model (ATM) developed, over a number of years, by Roland Draxler at NOAA's Air Resources Laboratory and further developed, for Bureau use, by Dr Dale Hess and Les Logan in BMRC (Draxler 1992, 1994, 1997; Draxler and Hess 1997, 1998). The ATM is driven by meteorological input resulting from the operational NWP systems.
Up until recently, the operational EER system was based on HYSPLIT Version 3.0 and received input from only GASP. Over the last few months, this older system has been upgraded to HYSPLIT Version 4.0, adding a number of improvements and new features such as multiple sources, and the use of other NWP systems for generating meteorological input.In addition, an interactive web facility has been introduced for internal Bureau use.
A simplified schematic diagram of the operational EER system is shown in Figure 1. The EER system interfaces with all of the current operational NWP systems in NMOC, viz. GASP, LAPS, SE and SW MESO_LAPS and TLAPS. The necessary pre-processing, providing the interface, is performed after each run of these NWP systems - thus minimising the time required to produce up-to-date meteorological input for the ATM part of the system. A critical facet of the system is the manual interaction whereby the operational person on duty has to define the running mode of the HYSPLIT4 ATM - ie the nature of the episode, the type of guidance required and the location, and characteristics, of the source(s) or observations. Products can be disseminated by fax or through the web. The operational system is run using NMOC's "SMS" scheduler, with the task-edit facilty providing the mechanism for manual interaction. Currently, most of the processing associated with the operational EER system is performed on the NEC SX-4 supercomputer.
The HYSPLIT4 (ie Hybrid Single-Particle Lagrangian Integrated Trajectories, version 4) system, developed by Roland Draxler at NOAA, models the atmospheric transport and dispersion of pollutant plumes originating from a variety of sources (eg nuclear, volcanic, fire and, eventually, chemical). The "hybrid" part of the acronym refers to the use of both movable 'Lagrangian' (for the advection and diffusion calculations) and fixed 'Eulerian' (for the concentration calculations) modelling frames of reference within the system.
The current operational configuration of the system makes use of another "hybrid" feature of HYSPLIT4, which was not available in version 3, viz. a mixed algorithm which considers puff dispersion in the horizontal and particle dispersion in the vertical. On the release of a single puff of pollutant from a source, the puff will be advected by the mean wind and will expand as a result of diffusion processes in the turbulent atmosphere. In the system, the puff is allowed to grow laterally to a certain size, after which it splits into several new puffs, each with their respective fraction of the pollutant mass. These new puffs will, in turn, be subject to advection and diffusion. The splitting of puffs could also occur vertically. However, in the operational configuration, particle - rather than puff - dispersion has been chosen for the vertical calculations. (In cases of strong atmospheric mixing, puff splitting in the vertical can result in too many puffs being generated.)
The HYSPLIT4 system also includes a number of other processes for removing, adding to, or changing the composition of the pollutant plume (summarised schematically in Figure 2). Dry deposition is the transport of pollutant gaseous or particulate species onto surfaces (in the absence of precipitation). In the system, a dry deposition velocity can be defined explicitly or can be calculated using details about the nature of the surface. For particles, gravitational settling, requiring estimates of particle shape, size and density, is another option. In wet deposition, the pollutant is scavenged by the atmospheric hydrometeors and is thus delivered to the earth's surface. The HYSPLIT4 system allows for both within-cloud ("washout") and below-cloud ("rainout") scavenging. If the winds are sufficiently strong, and the pollutant is not bound to the surface, then resuspension can also occur. In the case of nuclear incidents, radioactive decay is incorporated. Chemical transformations will eventually be included in the system.
The HYSPLIT4 system can be run in a purely trajectory, or advective, mode (see Figure 1) producing either forward or backward trajectory plots at specified levels. Alternatively, it can be run in a dispersion mode producing exposure (or concentration) and surface deposition charts integrated over various time periods and layers. (It is noted that it is not possible to run the dispersion calculation backwards, since dispersion is an irreversible process.) The nature of a source can be defined according to its strength, height and size, and the duration of emission.
After completion of the 00 or 12 UTC runs of the operational NWP systems (LAPS, SE and SW MESO_LAPS, TLAPS and GASP) each day, jobs are automatically initiated using NMOC's SMS scheduling system to extract the necessary fields (viz. surface pressure, surface height, precipitation and the multi-level: temperature, specific humidity and wind components). These fields are then interpolated horizontally (to an internal grid) and temporally, before being packed into a form suitable for direct input into HYSPLIT4.
Details of the source are entered manually using the edit facility of the SMS scheduling system. The basic details required for successful running include the latitude/longitude and the height (above sea level) of the source. Other details required depend on the nature of the source and may include,for example, the starting heights of trajectories, height of ash cloud, actual time of release and release amount per hour (if known). Currently, the system caters for for point or uniform line sources. However, it could be extended to area and volume sources. Unless otherwise specified, a nuclear dispersion run will assume a release of Cs-137, and a volcanic ash dispersion run will assume the presence of 7 types of particles with a size spectrum from 0.3 to 30 m and densities of 2.5 g/cc (corresponding to a mixture of pumice, shards and basalt).
At the present time, the following running configurations are readily available under the standard setup of the operational EER system:
Forecast Forward and Forecast Backward Trajectories to:
+144 hrs for GASP
+48 hrs for LAPS and TLAPS
+36 hrs for SE and SW MESO_LAPS
Analysed Backward Trajectories from:
-144 hrs for GASP
-96 hrs for LAPS and TLAPS
Forecast Nuclear Dispersion to:
+72 hrs for GASP
+48 hrs for LAPS and TLAPS
+36 hrs for SE and SW MESO_LAPS
Forecast Volcanic Ash Dispersion to:
+48 hrs GASP and TLAPS
Forecast Smoke Dispersion to:
+72 hrs for GASP
+48 hrs for LAPS and TLAPS
+36 hrs for SE and SW MESO_LAPS
The basic products are in chart form and are produced using NCAR graphics. Sample output from the system is shown in Figures 3-9. Figure 3 shows typical forecast forward trajectories from a single source, using the SW MESO_LAPS meteorological input data. The lateral, or horizontal, depiction of trajectory paths are annotated by the times (in UTC) at 6-hourly intervals. The vertical motion is displayed below the main charts with tick marks indicating the 6-hourly intervals. Figure 4 shows 6-day backward trajectories ending at Cape Grim, derived using analysis data from GASP. Examples of nuclear dispersion output showing forecast exposure and ground level deposition are shown in Figures 5 and 6, respectively. A panel chart (see Figure 7), from a volcanic ash run, depicts the extent of the ash cloud for different layers (associated with flight-levels). Figures 8 and 9 show output from multi-source runs associated with the fires in South-East Asia in the latter part of 1997. Many other transport and dispersion products can be generated, if required. (It is noted that, through the EER suite of scheduler, satellite images and meteorological charts can be generated for a given location of interest, anywhere over the globe.)
Internal Bureau requests for products can be made at any time through the Shift Supervisor of NMOC (PH: 613 9669 4035) or, alternatively, sent via email to: rto@bom.gov.au. However, requests for volcanic ash guidance should be addressed to the Volcanic Ash Advisory Centre (VAAC), in Darwin. As mentioned above, certain details of the source (including its latitude and longitude) need to be specified. After successful running of the task in NMOC, the resulting charts will be faxed to the requesting person. (In the case of external requests from delegated authorities within RA V, requests and dissemination will be via fax.)
Figure 3. Forecast Forward Trajectories from Perth, using SW MESO_LAPS data.
Figure 4. 6-day Backward Trajectories ending at Cape Grim, using GASP analysis data.
Figure 5. Example of Exposure Chart from Nuclear Dispersion run, using LAPS data.
Figure 6. Forecast Ground-level Deposition from Nuclear Dispersion run, using LAPS data.
Figure 7. Panel Display, from Volcanic Ash Dispersion run showing extent of Ash Cloud.
Figure 8. Forecast Forward Trajectories from 5 sources, during SE Asian fire episode 1997.
Figure 9. Forecast Concentrations from 5 sources, during SE Asian fire episode 1997.
A number of ongoing products are generated each day. These include:
(i) forecast backward and analysed backward trajectories, using LAPS data, for Cape Grim (see DIFACS slots 280 and 281);
(ii) forecast forward trajectories and dispersion charts from a number of sources over Victoria, using SE MESO_LAPS data.
(iii) forecast trajectory and dispersion charts relating to the monthly EER tests with RSMC Montreal and RSMC Washington and available, via a registered user, through the external web.
and
(iv) a number of hardcopy products, in NMOC, monitoring air movements over Australia and South East Asia.
It is planned to make a number of improvements to the operational system. These include a direct postscript to faxstream link for the chart output, a backup system on the NMOC's HP servers and a more integrated approach to the use of the meteorological input data (where the system will decide which is the best meteorological data to use at a given location). Also, the meteorological input could be expanded to include surface fluxes and other quantities and to make better use of the higher frequency NWP output available. As mentioned previously, an extension of the system to include a full range of chemical transformations is also needed. In the future, an effort will also be made to quantify the concentration of particles of different sizes. The monitoring of hot-spots (especially with respect to fires and volcanoes) using satellite remote sensing needs to be incorporated into the overall system.
Draxler, R.R. 1992. Hybrid Single-Particle Lagrangian Integrated Trajectories (HY-SPLIT): Version 3.0 -- User's Guide and Model Description. NOAA Tech. Mem. ERL ARL-195.
Draxler, R.R. 1994. HY-SPLIT Deposition Module. NOAA Tech. Mem. ERL ARL.
Draxler, R.R. 1997. HYSPLIT_4.0 -- User's Guide. NOAA Tech. Mem. ERL ARL (Draft Version).
Draxler, R.R. and Hess, G.D. 1997. Description of the HYSPLIT_4 Modelling System. NOAA Tech. Mem. ERL ARL-224.
Draxler, R.R. and Hess, G.D. 1998. Overview of the HYSPLIT_4 Modelling System for Trajectories, Dispersion and Deposition. Australian Meteorological Magazine, in press.
Pasquill, F. and Smith, F.B. 1983. Atmospheric Diffusion. 3rd Edition. Halstead Press.
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