March 20, 2025

HYSPLIT simulation of ash from a hypothetical eruption of Mount Spur. Credit: Alice Crawford (NOAA)

The Air Resources Laboratory’s (ARL) HYSPLIT model is one of the most extensively used atmospheric transport and dispersion models in the atmospheric sciences community. It has been used in a variety of simulations including applications tracking and forecasting the release of radioactive material, wildfire smoke, dust, allergens and volcanic ash. HYSPLIT has been in use for more than 25 years; undergoing many updates throughout this time. The most recent update, HYSPLIT v9, has now been approved for implementation into the National Weather Service’s National Center for Environmental Protections (NCEP) operations. The HYSPLIT v9 codel provides significant enhancements, including updates to the code, the addition of a transfer coefficient matrix (TCM) capability (which represents the amount of materials moving from one area into another) for volcanic ash and radiological releases, and stronger integration with global weather prediction models.

Developed after the Fukushima-Daiichi Nuclear Power Station radiological release in March 2011, TCM is a now ready to be used in operations. This approach enables rapid updates, can represent uncertainty in emissions and to estimate emissions using available observations. The radiological release upgrade supports modeling and meets requests from the International Atomic Energy Agency (IAEA). The volcanic ash upgrade will help fulfill new International Civil Aviation Organization requirements for Volcanic Ash Advisory Centers (VAACs), improving their workflow and providing uncertainty information in aviation hazard forecasts. Enhanced coupling with other models strengthens HYSPLIT’s ability to support responses to global events and assess their impact on the United States.

The Environmental Modeling Center approved the implementation on February 24, followed by approval from NCEP on February 26. As of now, implementation is scheduled for early June. Partially funded by the Joint Technology Transfer Initiative, implementation was a collaborative effort between EMC and ARL.