ARL Weekly News – June 11, 2021

Recent Events

Boundary Layer Workshop

Temple Lee, Michael Buban, LaToya Myles, Bruce Baker, and Rick Saylor participated in the Second Boundary Layer Workshop, hosted by Tilden Meyers and David Turner on 1-2 June. The workshop sought to prioritize scientific questions associated with the atmospheric boundary layer and to develop a cross-lab research plan to address these questions. The workshop is the second Boundary Layer workshop; hosted to help coordinate the efforts on the characterizing and measuring the boundary layer.

Temple Lee gave a presentation with Bruce Baker, Ed Dumas, Michael Buban, and Travis Schuyler as coauthors, entitled “Routine Boundary Layer Sampling using UxS to Improve Weather Forecasts” to NEOTAC (New Observations and Concept of Operations for Tropical Cyclones) on 3 June. In the talk, Temple summarized scientific results from recent field campaigns during which ATDD has deployed uncrewed aircraft systems. He also highlighted ongoing work in which ATDD is using UxS flights to support weather forecasting operations at the local Weather Forecast Office (WFO) in Morristown, Tennessee, and he discussed plans to scale UxS operations to other WFOs in the eastern US.

HYSPLIT Capabilities Briefing to NWS Western Region WFO’s

On Wednesday June 9th, Alice Crawford, Sonny Zinn and Mark Cohen from ARL’s HYSPLIT team met with over 60 analysts from NWS Weather Forecasting Offices (WFOs) in the NWS Western Region to present information on HYSPLIT capabilities for emergency response available on the web operations center, WOC as well as to answer questions and elicit feedback. The meeting was organized with the help of Roham Abtahi, the NWS liaison for HYSPLIT to the WFO’s and Sarah Rogowski, an emergency response specialist at the NWS Western Region Headquarters, regional operations center.

Many attendees conduct regular exercises with HYSPLIT WOC capabilities at their WFO’s and have utilized HYSPLIT in response to real events. They were able to share some of their expertise and perspectives. Topics discussed included what numerical weather prediction models are available to drive HYSPLIT, options for creating the source term for HYSPLIT, the similarities and differences between HYSPLIT and other models used for emergency response including ALOHA and HPAC, HYSPLIT/ ALOHA integration, use of pollutant-specific parameters in simulations, volcanic ashfall forecasting by the WFO’s, PM2.5 modeling for in-situ oil burns, and planned future capabilities. Attendees expressed enthusiasm for development of probabilistic products for chemical releases, smoke, airborne volcanic ash, and ashfall. ARL scientists have been developing HYSPLIT ensemble output utilizing NOAA’s numerical weather prediction model ensembles such as the global ensemble forecasts system (GEFS) and high resolution ensemble forecast (HREF). The ensemble output can provide information such as ensemble frequency of exceedance of an AEGL (acute exposure guideline level) or concentration given a probability threshold.

JCSDA Technical Review

Youhua Tang attended the 18th JCSDA (Joint Center for Satellite Data Assimilation) Technical Review Meeting and Science Workshop, June 7 – 11, 2021, and presented his work titled “Develop and Evaluate Assimilating AIRNow Observation with JEDI for RRFS-CMAQ” on June 9. It shows that assimilating the in-situ measurement is a reliable method to correct the bias of the aerosol initial conditions of NOAA inline air quality model, RRFS-CMAQ (Rapid Refresh Forecast System with CMAQ chemical mechanism).  Unlike the satellite aerosol optical depth data assimilation, this method can be used at night or under the cloud, and is available hourly. This work was funded by the NOAA JTTI FY20 to improve the aerosol prediction in the NOAA unified forecast system.

Eastern Snow Conference

John Kochendorfer attended the Eastern Snow Conference and acted as a judge of student presentations. This meeting is unique in that the limited spots available for oral presentations are typically awarded to students. This is done to help promote their work, and give them more experience providing such presentations.

NOAA Deltas Award Scholarship

ARL’s Michelle Howard and her NOAA based Delta Sigma Theta Sorority, Inc. sisters (NOAA Deltas) will present an HBCU scholarship award this weekend. This event will be included in the Montgomery County (MD) Parade of Scholarships. Visit to see the options for viewing the scholarship parade.

Recent Publications

Regional Variability in Tundra and Boreal Carbon Dioxide Assessed.

“Statistical upscaling of ecosystem CO2 fluxes across the terrestrial tundra and boreal domain: Regional patterns and uncertainties,” by Anna-Maria Virkkala and co-authors, including John Kochendorfer from ARL, was published online in Global Change Biology. The paper, which is available here:, describes CO2 flux estimates derived using different techniques to upscale available flux measurements over a vast region of the far north.

Abstract:  The regional variability in tundra and boreal carbon dioxide (CO2) fluxes can be high, complicating efforts to quantify sink-source patterns across the entire region. Statistical models are increasingly used to predict (i.e., upscale) CO2 fluxes across large spatial domains, but the reliability of different modeling techniques, each with different specifications and assumptions, has not been assessed in detail. Here, we compile eddy covariance and chamber measurements of annual and growing season CO2 fluxes of gross primary productivity (GPP), ecosystem respiration (ER), and net ecosystem exchange (NEE) during 1990–2015 from 148 terrestrial high-latitude (i.e., tundra and boreal) sites to analyze the spatial patterns and drivers of CO2 fluxes and test the accuracy and uncertainty of different statistical models. CO2 fluxes were upscaled at relatively high spatial resolution (1 km2) across the high-latitude region using five commonly used statistical models and their ensemble, that is, the median of all five models, using climatic, vegetation, and soil predictors. We found the performance of machine learning and ensemble predictions to outperform traditional regression methods. We also found the predictive performance of NEE-focused models to be low, relative to models predicting GPP and ER. Our data compilation and ensemble predictions showed that CO2 sink strength was larger in the boreal biome (observed and predicted average annual NEE −46 and −29 g C m−2 yr−1, respectively) compared to tundra (average annual NEE +10 and −2 g C m−2 yr−1). This pattern was associated with large spatial variability, reflecting local heterogeneity in soil organic carbon stocks, climate, and vegetation productivity. The terrestrial ecosystem CO2 budget, estimated using the annual NEE ensemble prediction, suggests the high-latitude region was on average an annual CO2 sink during 1990–2015, although uncertainty remains high.

Incorporating STILT features into HYSPLIT

Incorporating features from the Stochastic Time-Inverted Lagrangian Transport (STILT) model into the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model: A unified dispersion model for time-forward and time-reversed applications was authored by ARL’s Chris Loughner, B. Fasoli, A.F. Stein, and J.C. Lin (2021) and published in the, Journal of Applied Meteorology and Climatology, 60, 799-810, doi:10.1175/JAMC-D-20-0158.1.

Abstract:  The Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT) is a state-of-the-science atmospheric dispersion model that is developed and maintained at the National Oceanic Atmospheric Administration’s Air Resources Laboratory. In the early 2000s, HYSPLIT served as the starting point for development of the Stochastic Time-Inverted Lagrangian Transport (STILT) model that emphasizes backward-in-time dispersion simulations to determine source regions of receptors. STILT continued its separate development and gained a wide user base. Since STILT was built on a now outdated version of HYSPLIT and lacks long-term institutional support to maintain the model, incorporating STILT features into HYSPLIT allows these features to stay up to date. This paper describes the STILT features incorporated into HYSPLIT, which include a new vertical interpolation algorithm for WRF-derived meteorological input files, a detailed algorithm for estimating boundary layer height, a new turbulence parameterization, a vertical Lagrangian time scale that varies in time and space, a complex dispersion algorithm, and two new convection schemes. An evaluation of these new features was performed using tracer release data from the Cross Appalachian Tracer Experiment and the Across North America Tracer Experiment. Results show that the dispersion module from STILT, which takes up to double the amount of time to run, is less dispersive in the vertical direction and is in better agreement with observations when compared with the existing HYSPLIT option. The other new modeling features from STILT were not consistently statistically different than existing HYSPLIT options. Forward-time simulations from the new model were also compared with backward-in-time equivalents and were found to be statistically comparable to one another.