Barbara J. B. Stunder

NOAA’s HYSPLIT Atmospheric Transport and Dispersion Modeling System

AbstractThe Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT), developed by NOAA’s Air Resources Laboratory, is one of the most widely used models for atmospheric trajectory and dispersion calculations. We present the model’s historical evolution over the last 30 years from simple hand-drawn back trajectories to very sophisticated computations of transport, mixing, chemical transformation, and deposition of pollutants and hazardous materials. We highlight recent applications of the HYSPLIT modeling system, including the simulation of atmospheric tracer release experiments, radionuclides, smoke originated from wild fires, volcanic ash, mercury, and wind-blown dust.

Real-time Environmental Applications and Display sYstem: READY

Abstract Air quality forecasters, emergency responders, aviation interests, government agencies, and the atmospheric research community are among those who require access to tools to analyze and predict the transport and dispersion of pollutants in the atmosphere. Because of this need, the unique web-based Real-time Environmental Applications and Display sYstem (READY) has been under continuous development since 1997 to provide access to a suite of tools for producing air parcel trajectory and dispersion model results and displaying meteorological data. READY provides a “quasi-operational” portal to run the HYSPLIT atmospheric transport and dispersion model and interpret its results. Typical user applications include modeling the release of hazardous pollutants and volcanic ash, forest fire and prescribed burn smoke forecasting, poor air quality events, and various climatological studies. In addition, READY provides the user with quick access to meteorological data interpolated to the location of interest, helping in the interpretation of the HYSPLIT model results.

An Assessment of the Quality of Forecast Trajectories

Abstract Forecast and “analysis” (reference) trajectories were computed from six sites over North America at three altitudes (500, 1000, and 1500 m above ground) twice a day for a one-year period using Nested Grid Model wind fields. The reference meteorology was a series of short-term forecasts. Absolute error (distance between reference and forecast trajectory), relative error (absolute error divided by forecast trajectory travel distance), and the angle between the reference and forecast trajectory were also computed. The mean relative error for all the forecast trajectories for a travel time of 36 h is about 35%; the 90th percentile of the relative error is about 65%. The forecast is slightly biased to the left of the reference early in the forecast period. Absolute error and travel distance both are larger in winter than summer, so that the relative error is generally constant throughout the year. Differences in mean error among the three starting altitudes, among the six origin sites, and between the...

Airborne Volcanic Ash Forecast Area Reliability

Abstract In support of aircraft flight safety operations, daily comparisons between modeled, hypothetical, volcanic ash plumes calculated with meteorological forecasts and analyses were made over a 1.5-yr period. The Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model simulated the ash transport and dispersion. Ash forecasts and analyses from seven volcanoes were studied. The volcanoes were chosen because of recent eruptions or because their airborne ash could impinge on well-traveled commercial aircraft flight paths. For each forecast–analysis pair, a statistic representing the degree of overlap, the threat score (TS), was calculated. A forecast was classified as acceptable if the TS was greater than 0.25. Each forecast was also categorized by two parameters: the forecast area quadrant with respect to the volcano and a factor related to the complexity of the meteorology. The forecast complexity factor was based on the degree of spread using NCEP ensemble output or using a HYSPLIT offs...

Source location of air pollution and cardiac autonomic function: Trajectory cluster analysis for exposure assessment

Although many studies report that exposure to air pollution harms health, few have examined associations between pollution sources and health outcomes. We hypothesized that pollution originating in different locations has different associations with heart rate variability (HRV) among 497 men from the Normative Aging Study in Boston, Massachusetts. We identified the paths that air masses traveled (‘back-trajectories’) before arriving in Boston on the days the men were examined. Next, we classified these trajectories into six clusters. We examined whether the association of measured air pollutants with HRV (standard deviation of normal-to-normal intervals, high-frequency power (HF) and low-frequency power (LF), and LF/HF ratio) differed by cluster. We also examined whether the clusters alone (not considering air pollution measurements) showed different associations with HRV. The effects of black carbon (BC) on all HRV measures were strongest on days with southwest trajectories. Subjects who were examined on days where air parcels came from west had the strongest associations with ozone. All particle pollutants (particulate matter <2.5 μm in aerodynamic diameter (PM2.5), BC, and sulfates) were associated with increased LF/HF ratio on days with relatively short trajectories, which are related to local, slow-moving air masses. We also observed significant increases in LF/HF in days where air came from the northwest and west, compared to north trajectory days. Health effects associated with exposure to air pollution can be evaluated using pollutant concentrations as well as aspects of the pollution mixture captured by identifying locations where air masses originate. Independent effects of both these indicators of pollution exposure were seen on cardiac autonomic function.

Verification of the NOAA Smoke Forecasting System: Model Sensitivity to the Injection Height

Abstract A detailed evaluation of NOAA’s Smoke Forecasting System (SFS) is a fundamental part of its development and further refinement. In this work, particulate matter with a diameter less than or equal to 2.5-μm (PM2.5) concentration levels, simulated by the SFS, have been evaluated against satellite and surface measurements. Four multiday forest fire case studies, one covering the continental United States, two in California, and one near the Georgia–Florida border, have been analyzed. The column-integrated PM2.5 concentrations for these cases compared to the satellite measurements showed a similar or better statistical performance than the mean performance of the SFS for the period covering 1 September 2006–1 November 2007. However, near the surface, the model shows a tendency to overpredict the measured PM2.5 concentrations in the western United States and underpredict concentrations for the Georgia–Florida case. Furthermore, a sensitivity analysis of the model response to changes in the smoke relea...

A pervasive role for biomass burning in tropical high ozone/low water structures

Air parcels with mixing ratios of high O3 and low H2O (HOLW) are common features in the tropical western Pacific (TWP) mid-troposphere (300–700 hPa). Here, using data collected during aircraft sampling of the TWP in winter 2014, we find strong, positive correlations of O3 with multiple biomass burning tracers in these HOLW structures. Ozone levels in these structures are about a factor of three larger than background. Models, satellite data and aircraft observations are used to show fires in tropical Africa and Southeast Asia are the dominant source of high O3 and that low H2O results from large-scale descent within the tropical troposphere. Previous explanations that attribute HOLW structures to transport from the stratosphere or mid-latitude troposphere are inconsistent with our observations. This study suggest a larger role for biomass burning in the radiative forcing of climate in the remote TWP than is commonly appreciated.

An evaluation of air pollutant exposures due to the 1991 Kuwait oil fires using a Lagrangian model

Abstract A Lagrangian model was adapted to simulate the transport, dispersion, and deposition of pollutants from the Kuwait oil fires. Modifications to the model permitted radiative effects of the smoke plume to modify the pollutants vertical mixing. Calculated SO 2 (sulfur dioxide) air concentrations were compared with the observations from several intensive aircraft measurement compaigns as well as longer-term ground-based measurements. Model sensitivity tests and comparison to the aircraft measurements confirmed (1) the magnitude of the tabulated emission rates for SO 2 and carbon soot; (2) the most appropriate value for the smokes specific extinction coefficient was about 4 m 2 g −1 ; (3) that the model was sensitive to the vertical mixing in the first 100 km downwind from the fires; (4) that the SO 2 conversion rate was about 6% h −1 ; and (5) although there were large variations in the height of the initial smoke plume and ground-level concentrations were most sensitive to that height, an average value of 1500 m a.g.l. (above ground level) provided reasonable model predictions. Six ground-level sampling locations, all along the Arabian Gulf Coast, were used for model evaluation. Although the measurements and model calculations were in qualitative agreement, the highest space- and time-paired correlation coefficient was only 0.40. The monitoring stations were located in industrial areas, requiring the subtraction of a background concentration of anywhere from 5 to 34 μg m −3 , which at some stations was larger than the contribution from the oil fires smoke. The coastal location and lack of correlation between some of the sites suggested that mesoscale flow features not properly represented in the coarse meteorological data used in the computations may have influenced the smoke transport.

Modeling the CAPTEX Vertical Tracer Concentration Profiles

Abstract Perfluorocarbon tracer concentration profiles measured by aircraft 600–900 km downwind of the release locations during CAPTEX are discussed and compared with some model results. In general, the concentrations decreased with height in the upper half of the boundary layer where the aircraft measurements were made. The results of a model sensitivity study suggested that the shape of the profile was primarily due to winds increasing with height and relative position of the sampling with respect to the upwind and downwind edge of the plume. Further modeling studies showed that relatively simple vertical mixing parameterizations could account for the complex vertical plume structure when the model had sufficient vertical resolution. In general, the model performed better with slower winds and corresponding longer transport times.

Long-Range Forecast Trajectories of Volcanic Ash from Redoubt Volcano Eruptions

The Redoubt Volcano in Alaska began a series of eruptions on 14 December 1989. Volcanic ash was often reported to reach heights where, as it moved with the upper-level flow, it could affect aircraft operations thousands of km from the eruption. In an agreement between the National Oceanic and Atmospheric Administration (NOAA) and the Federal Aviation Administration, the NOAA Air Resources Laboratory (ARL) was assigned responsibility for providing long-range forecast trajectories of volcanic ash during a volcanic hazards alert. An ARL immediate-response program was implemented for the Redoubt Volcano eruptions. The response products, in the form of tables, maps, and written messages are discussed. An evaluation of the forecast trajectories is included. The evaluation is based on after-the-fact trajectories from analyzed wind fields and on actual ash cloud sightings. For 90% of the cases verified at 300 mb, the average forecast error was less than 25% of the downwind distance from the eruption (this often i...