The HYSPLIT model - Tracing its evolution and path to success

The HYSPLIT atmospheric transport and dispersion model (ATDM) is a complete system for computing air parcel trajectories as well as modeling complex transport and dispersion, chemical transformation, and deposition. HYSPLIT is used world-wide by researchers, emergency responders, government agencies, and industries seeking to comprehend the fate and origins of substances released into the atmosphere. Applications range from forecasting locust migration to planning prescribed burns to identifying and quantifying sources of pollution and hazardous materials. This presentation offers an overview of HYSPLIT's development from 1980 to the present, with a focus on pivotal elements contributing to its success.In the late 1960s and early 1970s, scientists at NOAA’s Air Resources Laboratory (ARL) developed the Mesoscale Diffusion (MESODIFF) model to address health and safety concerns at the Idaho National Reactor Testing Station. This groundwork led to the development of HYSPLIT version 1 in the early 1980s which calculated pollutant puffs' trajectories using rawinsonde data. The name originally stood for Hybrid Single-Particle Lagrangian Integrated Trajectory model. However, the model outgrew this description and as of HYSPLIT version 5, the name is no longer used as an acronym. As HYSPLIT evolved technically, its array of applications expanded. In addition to nuclear release applications, operational use of HYSPLIT at NOAA grew to include forecasting for volcanic ash, smoke from fires, planning for prescribed burns, dust, and release of hazardous chemicals from incidents such as train derailments and refinery fires. ARL scientists also applied HYSPLIT to important problems such as estimating the transport and deposition of polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofurans (PCDD/F) to the Great Lakes, estimating the fate and transport of PCDD/F emitted from the in situ burning of sea surface oil following the Deepwater Horizon spill, and understanding if ash from an eruption of Mount St. Helens could pose a risk to nuclear waste treatment facilities at Hanford, WA. To support the variety of applications, HYSPLIT developed a flexible framework capable of modeling simple to very complex emission scenarios and ingesting different and multiple meteorological datasets as input. This flexibility then encouraged more growth as a wide range of users outside of NOAA discovered that HYSPLIT could be applied to their area of interest. Active engagement and collaboration between ARL scientists and the atmospheric science community and emergency response communities to make HYSPLIT available and accessible to a diverse audience from experts to novices in atmospheric science and modeling has been an important contributor to HYSPLIT’s success. A web-based interface, the Real-time Environmental Applications and Display sYstem (READY) was initially developed in 1997 and it was probably the first trajectory and dispersion model available publicly through the web. READY was created to allow other federal agencies to run HYSPLIT remotely and display graphical results, however, it quickly became popular with researchers and the public. In addition to the online interface, the code is downloadable for popular operating systems like Windows, macOS, and Linux, and is complemented by training materials, training sessions, and partnerships with various entities. The HYSPLIT modeling system continues to evolve to meet the needs and challenges of the current era as the current HYSPLIT group at NOAA ARL carries on incorporating the latest advancements in atmospheric science and computing technology, expanding into new application areas, and leveraging new and existing partnerships.