Search Results

You are looking at 1 - 5 of 5 items for

  • Author or Editor: Glenn D. Rolph x
  • Refine by Access: All Content x
Clear All Modify Search
Glenn D. Rolph
and
Roland R. Draxler

Abstract

Initialization and forecast fields from the National Weather Service's (NWS) Nested Grid Model (NOM) were archived on the 90 km calculational grid at 2-hour intervals out to 12 hours twice per day, for the 3-month period of January–March 1987. The resulting time series of meteorological data were used to determine the sensitivity of calculated trajectories to changes in temporal and spatial density of meteorological data during a wide range of synoptic conditions. Trajectories were started from 63 evenly spaced locations, twice per day, for a duration of 4 days each over the 74-day period. The 9324 separate trajectories were computed using the meteorological data at 90, 180, and 360 km grid spacing and at 2-, 4-, 6-, and 12-hour time intervals. Calculated trajectories were compared with the base “truth” case of 2-hour data on the 90 km grid.

Trajectories were most sensitive to changes in temporal resolution when the grid resolution was 90 and 180 km. Trajectories computed on the coarser 360 km grid had substantially larger deviations from the base case and were no longer sensitive to changes in temporal resolution. Relative horizontal transport deviations ranged from 5–25% of the travel distance at 96 hours depending upon the spatial and temporal resolution. Results suggest that it rawinsonde observations are the primary source of meteorological data (400 km spacing every 12 hours), then the greatest improvement in trajectory accuracy can be achieved by enhancing the temporal frequency of observations to 6-hour intervals. Results were not different when trajectories were categorized by cyclonic or anticyclonic conditions. However, horizontal deviations during cyclonic conditions were as much as 30% larger than those during anticyclonic conditions. This was attributed primarily to stronger wind speeds in cyclonic systems.

Full access
Jeffery T. McQueen
,
Roland R. Draxler
, and
Glenn D. Rolph

Abstract

One of the activities of the National Oceanic and Atmospheric Administration's Air Resources Laboratory is to predict the consequences of atmospheric releases of radioactivity and other potentially harmful materials. This paper describes the application of the Regional Atmospheric Modeling System (RAMS) to support air quality forecasting. The utility of using RAMS for real time prediction of local-scale flows and for detailed postevent analysis is examined for a Nuclear Regulatory Commission exercise at the Susquehanna nuclear power plant in Pennsylvania. During the exercise (10 December 1992) a strong East Coast low pressure system created complex interactions between the regional-scale and local topographical features of the Susquehanna River valley.

Results from a series of sensitivity experiments indicated significant topographical forcing and vertical de-coupling although the synoptic forcing was quite strong in this relatively wide and shallow valley. The best agreement between the RAMS predictions and observations was obtained with horizontal and vertical resolutions of 2.5 km and at 12 m above ground level for the first vertical wind level, respectively. Therefore, it would have been very difficult to configure RAMS to predict the local circulations in real time, given the very high resolution requirements. The vertical resolution needed to properly resolve terrain forcings in the Susquehanna Valley was similar to vertical resolution used by other researchers over steeper and narrower valleys. However, the horizontal resolution requirements were not as critical: about 10 times coarser than in more complex terrain. The degree of topographical smoothing was also found to have a significant effect upon the predictions. Experiments performed by assimilating all available surface-level winds in the model domain with various degrees of nudging slightly improved the simulation of the low-level winds. Subsequent analyses indicated that pressure-driven channeling and downward momentum mixing were the primary physical mechanisms for this case.

Full access
Jerome L. Heffter
,
Barbara J. B. Stunder
, and
Glenn D. Rolph

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 included distances beyond 5000 km). At 500 mb, the forecast error was less than 50%. Errors were inversely proportional to wind speeds.

Full access
Ariel F. Stein
,
Glenn D. Rolph
,
Roland R. Draxler
,
Barbara Stunder
, and
Mark Ruminski

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 release height shows that the simulated surface and column-integrated PM2.5 concentrations are very sensitive to variations in this parameter. Indeed, the model capability to represent the measured values is highly dependent on the accuracy of the determination of the actual injection height and in particular to whether the smoke injection actually occurred below or above the planetary boundary layer.

Full access
Glenn D. Rolph
,
Roland R. Draxler
,
Ariel F. Stein
,
Albion Taylor
,
Mark G. Ruminski
,
Shobha Kondragunta
,
Jian Zeng
,
Ho-Chun Huang
,
Geoffrey Manikin
,
Jeffery T. McQueen
, and
Paula M. Davidson

Abstract

An overview of the National Oceanic and Atmospheric Administration’s (NOAA) current operational Smoke Forecasting System (SFS) is presented. This system is intended as guidance to air quality forecasters and the public for fine particulate matter (≤2.5 μm) emitted from large wildfires and agricultural burning, which can elevate particulate concentrations to unhealthful levels. The SFS uses National Environmental Satellite, Data, and Information Service (NESDIS) Hazard Mapping System (HMS), which is based on satellite imagery, to establish the locations and extents of the fires. The particulate matter emission rate is computed using the emission processing portion of the U.S. Forest Service’s BlueSky Framework, which includes a fuel-type database, as well as consumption and emissions models. The Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model is used to calculate the transport, dispersion, and deposition of the emitted particulate matter. The model evaluation is carried out by comparing predicted smoke levels with actual smoke detected from satellites by the HMS and the Geostationary Operational Environmental Satellite (GOES) Aerosol/Smoke Product. This overlap is expressed as the figure of merit in space (FMS), the intersection over the union of the observed and calculated smoke plumes. Results are presented for the 2007 fire season (September 2006–November 2007). While the highest FMS scores for individual events approach 60%, average values for the 1 and 5 μg m−3 contours for the analysis period were 8.3% and 11.6%, respectively. FMS scores for the forecast period were lower by about 25% due, in part, to the inability to forecast new fires. The HMS plumes tend to be smaller than the corresponding predictions during the winter months, suggesting that excessive emissions predicted for the smaller fires resulted in an overprediction in the smoke area.

Full access