The equations governing atmospheric flow imply transfers of energy and potential enstrophy between scales. Accurate simulation of turbulent flow requires that numerical models, which have finite resolution and truncation errors, adequately capture these interscale transfers, particularly between resolved and unresolved scales. It is therefore important to understand how accurately these transfers are modelled in the presence of scale‐selective dissipation or other forms of subgrid model. Here, the energy and enstrophy cascades in numerical models of two‐dimensional turbulence are investigated using the barotropic vorticity equation. Energy and enstrophy transfers in spectral space due to truncated scales are calculated for a high‐resolution reference solution and for several explicit and implicit subgrid models at coarser resolution. The reference solution shows that enstrophy and energy are removed from scales very close to the truncation scale and energy is transferred (backscattered) into the large scales. Some subgrid models are able to capture the removal of enstrophy from small scales, though none are scale‐selective enough; however, none are able to capture accurately the energy backscatter. We propose a scheme that perturbs the vorticity field at each time step by the addition of a particular vorticity pattern derived by filtering the predicted vorticity field. Although originally conceived as a parametrization of energy backscatter, this scheme is best interpreted as an energy ‘fixer’ that attempts to repair the damage to the energy spectrum caused by numerical truncation error and an imperfect subgrid model. The proposed scheme improves the energy and enstrophy behaviour of the solution and, in most cases, slightly reduces the root mean square vorticity errors.
Objective To compare population-based metrics for assessing progress toward the U.S. National HIV/AIDS Strategy (NHAS) goals. Design Analysis of surveillance data from persons living with HIV/AIDS (PLWHA) in King County (KC), WA, 2005–2009. Methods We examined indicators of the timing of HIV diagnosis [intertest interval, CD4 count at diagnosis, and AIDS ≤1 year of diagnosis (late diagnosis)]; linkage to initial care [CD4 or viral load (VL) report ≤3 months after diagnosis] and sustained care [a laboratory report 3–9 months after linkage]; engagement in continuous care in 2009 [≥2 laboratory reports ≥3 months apart]; and virologic suppression. Results Thirty-two percent of persons had late HIV diagnoses, 31% of whom reported testing HIV negative in the 2 years preceding their HIV diagnosis. Linkage to sustained care, but not linkage to initial care, was significantly associated with subsequent virologic suppression. Among 6070 PLWHA in KC, 65% of those with ≥1 VL reported in 2009 and 53% of all PLWHA had virologic suppression. Although only 66% of all PLWHA were engaged in continuous care, 81% were defined as engaged using the denominator proposed in the NHAS (≥1 laboratory result reported in 2009 excluding persons establishing care in the second half of the year). Conclusions Proposed metrics for monitoring the HIV care continuum may not accurately measure late diagnoses or linkage to sustained care and are sensitive to assumptions about the size of the population of PLWHA. Monitoring progress toward achievement of NHAS goals will require improvements in HIV surveillance data and refinement of care metrics.
Abstract. Atmospheric dynamical cores are a fundamental component of global atmospheric modeling systems and are responsible for capturing the dynamical behavior of the Earth's atmosphere via numerical integration of the NavierStokes equations. These systems have existed in one form or another for over half of a century, with the earliest discretizations having now evolved into a complex ecosystem of algorithms and computational strategies. In essence, no two dynamical cores are alike, and their individual successes suggest that no perfect model exists. To better understand modern dynamical cores, this paper aims to provide a comprehensive review of 11 non-hydrostatic dynamical cores, drawn from modeling centers and groups that participated in the 2016 Dynamical Core Model Intercomparison Project (DCMIP) workshop and summer school. This review includes a choice of model grid, variable placement, vertical coordinate, prognostic equations, temporal discretization, and the diffusion, stabilization, filters, and fixers employed by each system.
In some areas, classifying HIV cases among foreign-born blacks as occurring in African Americans dramatically alters the epidemiological picture of HIV. Country of birth should be consistently included in local and national analyses of HIV surveillance data.
Background Prevention and clinical efforts are increasingly focused on improving the HIV care cascade, the sequential steps from diagnosis to engagement in care and viral suppression. Monitoring of this cascade is largely dependent on HIV laboratory surveillance data. However, little is known about the completeness of these data or the true care status of individuals for whom no data are reported. Methods We investigated people presumed to be living with HIV/AIDS in King County, WA, who had no laboratory results reported to HIV surveillance for at least 1 year between 2006 and 2010. We determined whether each person had relocated, died, or remained in the county. Results Of 7379 HIV-infected people presumed living in King County, 2545 (35%) had 1 or more 12-month gap in laboratory reporting. Among these individuals, 47% had relocated, 7% died, and 38% remained in King County; we were unable to determine the status of 8%. Of individuals remaining in the area, 91% had evidence of returning to or being in HIV care. Case investigations reduced the proportion of individuals thought to be out of care in 2011 from 27% to 16%. Conclusions Investigations of individuals without laboratory results reported to HIV surveillance identified large numbers of people who are no longer living in the area. Our findings suggest that current estimates of the HIV care cascade may be too pessimistic and that individual case investigations are required to accurately define the size and composition of the population of people living with HIV in local areas.
Rarely, results of EIA tests for antibodies to HIV-1 may be persistently negative in some HIV-1 subtype B-infected persons with AIDS. Physicians treating patients with illnesses or CD4 cell counts suggestive of HIV infection, but for whom results of HIV EIA are negative, should consider p24 antigen, nucleic acid amplification, or viral culture testing to document the presence of HIV.
Recently, a standard test case suite for 2-D linear transport on the sphere was proposed to assess important aspects of accuracy in geophysical fluid dynamics with a "minimal" set of idealized model configurations/runs/diagnostics. Here we present results from 19 stateof-the-art transport scheme formulations based on finitedifference/finite-volume methods as well as emerging (in the context of atmospheric/oceanographic sciences) Galerkin methods. Discretization grids range from traditional regular latitude-longitude grids to more isotropic domain discretizations such as icosahedral and cubed-sphere tessellations of the sphere. The schemes are evaluated using a wide range of diagnostics in idealized flow environments. Accuracy is assessed in single-and two-tracer configurations using conventional error norms as well as novel diagnostics designed for climate and climate-chemistry applications. In addition, algorithmic considerations that may be important for computational efficiency are reported on. The latter is inevitably computing platform dependent.The ensemble of results from a wide variety of schemes presented here helps shed light on the ability of the test case suite diagnostics and flow settings to discriminate between algorithms and provide insights into accuracy in the context of global atmospheric/ocean modeling. A library of benchmark results is provided to facilitate scheme intercomparison and model development. Simple software and data sets are made available to facilitate the process of model evaluation and scheme intercomparison.
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