Abstract
A series of idealized experiments with the NOAA Experimental Hurricane Weather Research and Forecasting Model (HWRFX) are performed to examine the sensitivity of idealized tropical cyclone ...(TC) intensification to various parameterization schemes of the boundary layer (BL), subgrid convection, cloud microphysics, and radiation. Results from all the experiments are compared in terms of the maximum surface 10-m wind (VMAX) and minimum sea level pressure (PMIN)—operational metrics of TC intensity—as well as the azimuthally averaged temporal and spatial structure of the tangential wind and its material acceleration.
The conventional metrics of TC intensity (VMAX and PMIN) are found to be insufficient to reveal the sensitivity of the simulated TC to variations in model physics. Comparisons of the sensitivity runs indicate that (i) different boundary layer physics parameterization schemes for vertical subgrid turbulence mixing lead to differences not only in the intensity evolution in terms of VMAX and PMIN, but also in the structural characteristics of the simulated tropical cyclone; (ii) the surface drag coefficient is a key parameter that controls the VMAX–PMIN relationship near the surface; and (iii) different microphysics and subgrid convection parameterization schemes, because of their different realizations of diabatic heating distribution, lead to significant variations in the vortex structure.
The quantitative aspects of these results indicate that the current uncertainties in the BL mixing, surface drag, and microphysics parameterization schemes have comparable impacts on the intensity and structure of simulated TCs. The results also indicate that there is a need to include structural parameters in the HWRFX evaluation.
The feedback effects of sea-spray on the heat and momentum fluxes under equilibrium conditions associated with winds of tropical cyclones are investigated using a one-dimensional coupled sea-spray ...and atmospheric surface-layer (ASL) model. This model is capable of simulating the microphysical aspects of the evaporation of saline water droplets of various sizes and their dynamic and thermal interaction with the turbulence mixing that is simulated by the Mellor–Yamada 1.5-order closure scheme. Sea-spray droplet generation is described by a state-of-the-art parametrization that predicts the size spectrum of sea-spray droplets for a given surface forcing. The results from a series of simulations indicate the way in which evaporating droplets of various sizes modify the turbulence mixing near the surface, which in turn affects further droplet evaporation. All these results are direct consequences of the effects of sea-spray on the balance of turbulent kinetic energy in the spray-filled surface layer. In particular, the overall impact of sea-spray droplets on the mean wind depends on the wind speed at the level of sea-spray generation. When the wind speed is below 40 m s
−1
, the droplets are small in size and tend to evaporate substantially and thus cool the spray-filled layer, while for wind speeds above 50 m s
−1
, the size of the droplets is so large that they do not have enough time to evaporate much before falling back into the sea. The sensible heat carried by the droplets is released to the ambient air, increasing the buoyancy of the surface layer and enhancing the turbulent mixing. The suspension of sea-spray droplets reduces the buoyancy and makes the surface layer more stable, decreasing the friction velocity and the downward turbulent mixing of momentum. The results from the numerical experiments also suggest that, in order not to violate the constant flux assumption critical to the Monin–Obukhov similarity theory, a displacement equal to the mean wave height should be included in the logarithmic profiles of the wind and thermal fields.
Abstract
Three bulk microphysics schemes with different complexities in the Weather Research and Forecasting Model are compared in terms of the individual microphysical process terms of the ...hydrometeor mass and number mixing ratio tendency equations in an idealized 2D squall-line case. Through evaluation of these process terms and of hydrometeor size distributions, it is shown that the differences in the simulated population characteristics of snow, graupel, and rainwater are the prominent factors contributing to the differences in the development of the simulated squall lines using these schemes. In this particular case, the gust front propagation speed produced by the Thompson scheme is faster than in the other two schemes during the first 2 h of the simulation because it has a larger dominant graupel size. After 2 h into the simulation, the initially less intense squall lines in the runs using the WSM6 and Morrison schemes start to catch up in intensity and development to the run using the Thompson scheme. Because the dominant size of graupel particles in the runs using the WSM6 and Morrison schemes is smaller, these particles take more time to fall below the freezing level and enhance the rainwater production and its evaporative cooling. In the run using the Thompson scheme, the graupel production slows down at later times while the snow particle growth increases, leading to more snow falling below the freezing level to melt and surpass graupel particle melting in the production of rainwater.
Trajectory analysis using a weather prediction model is performed for five cases to interpret the formation of enhanced bands of vertically integrated water vapor (IWV) in the central and eastern ...Pacific that are frequently seen in satellite images from the Special Sensor Microwave Imager. The connection of these enhanced bands with poleward water vapor transport from the Tropics is also examined. It is shown that the leading end of the enhanced IWV bands (defined as the most eastward and poleward end) is the manifestation of moisture convergence in the warm conveyor belt associated with extratropical cyclones, while the bands away from the leading end result mainly from moisture convergence along the trailing cold fronts. There is evidence that some enhanced IWV bands may be associated with a direct poleward transport of tropical moisture along the IWV bands from the Tropics all the way to the extratropics. The trajectory analysis, together with the seasonal mean sea level pressure analysis, indicates that a favorable condition for the occurrence of a direct, along-IWV band transport of tropical (defined as south of 23.5'N) moisture to the U.S. West Coast in the eastern Pacific is a weakened subtropical ridge in the central Pacific with an enhanced southwesterly low-level flow. The authors hypothesize that the direct poleward transport of tropical moisture within an enhanced IWV band in the eastern Pacific is most possible in the neutral El Nino-Southern Oscillation (ENSO) phase and is least possible in the El Nino phase.
Abstract
This paper focuses on parameterizing the effect of sea spray at hurricane-strength winds on the momentum and heat fluxes in weather prediction models using the Monin–Obukhov similarity ...theory (a common framework for the parameterizations of air–sea fluxes). In this scheme, the mass-density effect of sea spray is considered as an additional modification to the stratification of the near-surface profiles of wind, temperature, and moisture in the marine surface boundary layer (MSBL). The overall impact of sea-spray droplets on the mean profiles of wind, temperature, and moisture depends on the wind speed at the level of sea-spray generation. As the wind speed increases, the mean droplet size and the mass flux of sea-spray increase, rendering an increase of stability in the MSBL and the leveling-off of the surface drag. Sea spray also tends to increase the total air–sea sensible and latent heat fluxes at high winds. Results from sensitivity testing of the scheme in a numerical weather prediction model for an idealized case of hurricane intensification are presented along with a dynamical interpretation of the impact of the parameterized sea-spray physics on the structure of the hurricane boundary layer.
Exposure assessment is crucial for risk assessment for nanomaterials. We propose a framework to aid exposure assessment in consumer products. We determined the location of the nanomaterials and the ...chemical identify of the 580 products listed in the inventory maintained by the Woodrow Wilson International Center for Scholars, of which 37% used nanoparticles suspended in liquids, whereas <1% contained “free airborne nanoparticles”. C₆₀ is currently only used as suspended nanoparticles in liquids and nanosilver is used more as surface bound nanoparticles than as particles suspended in liquids. Based on the location of the nanostructure we were able to further group the products into categories of: (1) expected, (2) possible, and (3) no expected exposure. Most products fall into the category of expected exposure, but we were not able to complete a quantitative exposure assessment mainly due to the lack of information on the concentration of the nanomaterial in the products--a problem that regulators and industry will have to address if we are to have realistic exposure assessment in the future. To illustrate the workability of our procedure, we applied it to four product scenarios using the best estimates available and/or worst-case assumptions. Using the best estimates available and/or worst-case assumptions we estimated the consumer exposure to be 26, 15, and 44 μg kg⁻¹ bw year⁻¹ for a facial lotion, a fluid product, and a spray product containing nanoparticles, respectively. The application of sun lotion containing 2% nanoparticles result in an exposure of 56.7 mg kg⁻¹ bw d⁻¹ for a 2-year-old child, if the amounts applied correspond to the European Commission recommendations on use of sunscreen.
The product of the von Hippel-Lindau gene, pVHL, targets the α subunits of the heterodimeric transcription factor hypoxia-inducible factor (HIF) for polyubiquitination in the presence of oxygen. The ...binding of pVHL to HIF is governed by the enzymatic hydroxylation of conserved prolyl residues within peptidic motifs present in the HIFα family members. By using a biochemical purification strategy, we have identified a human homolog of Caenorhabditis elegans Egl9 as a HIF prolyl hydroxylase. In addition, we studied the activity of a structurally diverse collection of low molecular weight inhibitors of procollagen prolyl 4-hydroxylase as potential inhibitors of the HIF hydroxylase. A model compound of this series stabilized HIF in a variety of cells, leading to the increased production of its downstream target, vascular endothelial growth factor.
A case study is carried out for the 29 July–3 August 2000 episode of the Central California Ozone Study (CCOS), a typical summertime high-ozone event in the Central Valley of California. The focus of ...the study is on the low-level winds that control the transport and dispersion of pollutants in the Central Valley. An analysis of surface and wind profiler observations from the CCOS field experiment indicates a number of important low-level flows in the Central Valley: 1) the incoming low-level marine airflow through the Carquinez Strait into the Sacramento River delta, 2) the diurnal cycle of upslope–downslope flows, 3) the up- and down-valley flow in the Sacramento Valley, 4) the nocturnal low-level jet in the San Joaquin Valley, and 5) the orographically induced mesoscale eddies (the Fresno and Schultz eddies). A numerical simulation using the advanced research version of the Weather Research and Forecasting Model (WRF) reproduces the overall pattern of the observed low-level flows. The physical reasons behind the quantitative differences between the observed and simulated low-level winds are also analyzed and discussed, although not enough observations are available to diagnose thoroughly the model-error sources. In particular, hodograph analysis is applied to provide physical insight into the impact of the large-scale, upper-level winds on the locally forced low-level winds. It is found that the diurnal rotation of the observed and simulated hodographs of the local winds varies spatially in the Central Valley, resulting from the combining effect of topographically induced local forcing and the interaction between the upper-level winds and the aforementioned low-level flows. The trajectory analysis not only further confirms that WRF reproduces the observed low-level transport processes reasonably well but also shows that the simulated upper-level winds have noticeable errors. The results from this study strongly suggest that the errors in the WRF-simulated low-level winds are related not only to the errors in the model’s surface conditions and atmospheric boundary layer physics but also to the errors in the upper-level forcing mostly prescribed in the model’s lateral boundary conditions.
Aim: To describe the diagnostic and therapeutic management of cytomegalovirus (CMV) anterior uveitis unassociated with retinal necrosis in immunocompetent patients. Methods: Patients referred between ...2001 and 2003 for management of unilateral, chronic, recurrent uveitis associated with secondary glaucoma underwent extensive investigation including laboratory tests for herpes virus infections. Specific antiviral treatment was initiated in all cases and the level of ocular inflammation was evaluated during the follow up. Results: Five patients, three men and two women, were included. Median age was 50 years old (range 30–80 years). Anterior unilateral uveitis without iris atrophy was observed in all cases. Uveitis was chronic in three cases and recurrent in two cases. Glaucoma was observed in all patients with a median intraocular pressure of 30 mm Hg (range 22–43 mm Hg). Five patients responded initially to specific anti-CMV therapy. Even though glaucoma surgery was necessary in two cases, both ocular inflammation and glaucoma were controlled in all cases. Relapses occurred in three cases after cessation of therapy, requiring prolonged maintenance therapy with valganciclovir. Conclusions: CMV infection and specific antiviral therapy should be considered in all cases of relapsing or chronic iridocyclitis and secondary glaucoma. Maintenance regimens of valganciclovir may be necessary to prevent further relapses.
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