David P. Bacon

Evaluation of the Operational Multiscale Environment Model with Grid Adaptivity against the European Tracer Experiment

Abstract The Operational Multiscale Environment Model with Grid Adaptivity (OMEGA) is a multiscale nonhydrostatic atmospheric simulation system based on an adaptive unstructured grid. The basic philosophy behind the OMEGA development has been the creation of an operational tool for real-time aerosol and gas hazard prediction. The model development has been guided by two basic design considerations in order to meet the operational requirements: 1) the application of an unstructured dynamically adaptive mesh numerical technique to atmospheric simulation, and 2) the use of embedded atmospheric dispersion algorithms. An important step in proving the utility and accuracy of OMEGA is the full-scale testing of the model using simulations of real-world atmospheric events and qualitative as well as quantitative comparisons of the model results with observations. The main objective of this paper is to provide a comprehensive evaluation of OMEGA against a major dispersion experiment in operational mode. Therefore, O...

Multiple estimates of transmissibility for the 2009 influenza pandemic based on influenza-like-illness data from small US military populations.

Rapidly characterizing the amplitude and variability in transmissibility of novel human influenza strains as they emerge is a key public health priority. However, comparison of early estimates of the basic reproduction number during the 2009 pandemic were challenging because of inconsistent data sources and methods. Here, we define and analyze influenza-like-illness (ILI) case data from 2009–2010 for the 50 largest spatially distinct US military installations (military population defined by zip code, MPZ). We used publicly available data from non-military sources to show that patterns of ILI incidence in many of these MPZs closely followed the pattern of their enclosing civilian population. After characterizing the broad patterns of incidence (e.g. single-peak, double-peak), we defined a parsimonious SIR-like model with two possible values for intrinsic transmissibility across three epochs. We fitted the parameters of this model to data from all 50 MPZs, finding them to be reasonably well clustered with a median (mean) value of 1.39 (1.57) and standard deviation of 0.41. An increasing temporal trend in transmissibility (, p-value: 0.013) during the period of our study was robust to the removal of high transmissibility outliers and to the removal of the smaller 20 MPZs. Our results demonstrate the utility of rapidly available – and consistent – data from multiple populations.

Simulation of Flows with Large Gradients using Adaptive Mesh Refinement

The Euler equations are solved for non-hydrostatic atmospheric flow problems in two dimensions using the Conservation Laws Package (CLAWPACK) with adaptive mesh refinement (AMR). The CLAWPACK software uses high-resolution wave propagation methods (LeVeque 2002) for solving hyperbolic conservation laws. In the current study, the Riemann problem is solved using flux-based wave decomposition (Bale et al. 2002; LeVeque 2002; Ahmad and Lindeman 2007). The computational efficiency achieved by using adaptive mesh refinement is demonstrated. The methodology shows promise for simulating multi-scale, time-critical and computationally intensive flow problems and flows which are dominated by large gradients of velocities and other thermodynamic quantities. A decrease in computational resources while maintaining the accuracy of the solution has obvious benefits in responding to emergency-response scenarios, such as dispersion of hazardous materials in the atmosphere.

Simulation of the Santa Ana Winds (Vientos de Satán)

*† ‡ § The Operational Multiscale Environment model with Grid Adaptivity (OMEGA) is used to simulate an episode of the Santa Ana winds over Southern California. The OMEGA model is based on an unstructured adaptive grid. The use of an unstructured gird allows the model to resolve complex terrain features with a good degree of accuracy and is ideally suited to simulate atmospheric flows which develop due to topographic forcing. This paper describes in detail simulations using the OMEGA model for an episode of the Santa Ana winds during October 2007. The wind and turbulence fields obtained from OMEGA were used to drive the Atmospheric Dispersion Model (ADM). The results of the ADM simulation of the Santa Ana fires are also reported.

Acoustic Ray-Tracing on Unstructured Adaptive Grids

*† ‡ § ** †† A computationally efficient acoustic ray-tracing code based on unstructured adaptive grids is described in detail. The use of unstructured grids allows wave propagation simulations on complex computational domains. Detailed surface layer physics is included to take into account the atmospheric variability under different stability conditions and landuse inhomogeneities. The ray-tracing model has been coupled with meso- and microscale atmospheric flow models. The method shows promise in simulating long-range acoustic wave propagation in the atmosphere over complex terrain.