Rm. Banta et al., IMPLICATIONS OF SMALL-SCALE FLOW FEATURES TO MODELING DISPERSION OVERCOMPLEX TERRAIN, Journal of applied meteorology, 35(3), 1996, pp. 330-342
Small-scale, topographically forced wind systems often have a strong i
nfluence on flow over complex terrain. A problem is that these systems
are very difficult to measure, because of their limited spatial and t
emporal extent. They can be important however, in the atmospheric tran
sport of hazardous materials. For example, a nocturnal exit jet-a narr
ow stream of cold air-which flowed from Eldorado Canyon at the interfa
ce between the Rocky Mountains and the Colorado plains near the Rocky
Flats Plant (RFP), swept over RFP for about 3 h in the middle of the n
ight of 4-5 February 1991. It extended in depth from a few tens of met
ers to approximately 800 m above the ground. Because the jet was so na
rrow (2 km wide), it was poorly sampled by the meteorological surface
mesonet, but it did prove to have an effect on the dispersion of trace
r material released from RFP, producing a secondary peak in measured c
oncentration to the southeast of RFP. The existence and behavior of th
e jet was documented by Environmental Technology Laboratory's Doppler
lidar system, a scanning, active remote-sensing system that provides f
ine resolution wind measurements. The lidar was deployed as a part of
a wintertime study of flow and dispersion in the RFP vicinity during F
ebruary 1993. The MATHEW-ADPIC atmospheric dispersion model was run us
ing the case study data from this night. It consists of three major mo
dules: an interpolation scheme; MATHEW, a diagnostic wind-flow algorit
hm that calculates a mass-consistent interpolated flow; and ADPIC, a d
iffusion algorithm. The model did an adequate job of representing the
main lobe of the tracer transport, but the secondary lobe resulting fr
om the Eldorado Canyon exit jet was absent from the model result. Beca
use the jet was not adequately represented in the input data, it did n
ot appear in the modeled wind field. Thus, the effects of the jet on t
he transport of tracer material were not properly simulated by the dia
gnostic model.