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Turbulence data measured with fast response instruments at two sites with distinct conditions were available. The ability of a mesoscale model in the simulation of turbulent fluxes and boundary layer height was assessed in case studies covering periods in the Southern Hemisphere summer and winter. The energy apportionment at both locations was properly reproduced. In summer, at the site with native forest, the sensible heat flux was well estimated and the latent heat flux was underestimated. At the other site (commercial plantation) the sensible heat flux was properly represented and the latent heat flux was slightly overestimated. In winter, the best results were obtained at the implanted forest site. The performance of the model at the native forest site was very satisfactory when homogeneous initial soil moisture was considered. A model intercomparison between the boundary layer height obtained with an analytical model and the mesoscale model showed the influence of data and methodologies used in the two approaches. [ABSTRACT FROM AUTHOR]

Turbulence data measured with fast response instruments at two sites with distinct conditions were available. The ability of a mesoscale model in the simulation of turbulent fluxes and boundary layer height was assessed in case studies covering periods in the Southern Hemisphere summer and winter. The energy apportionment at both locations was properly reproduced. In summer, at the site with native forest, the sensible heat flux was well estimated and the latent heat flux was underestimated. At the other site (commercial plantation) the sensible heat flux was properly represented and the latent heat flux was slightly overestimated. In winter, the best results were obtained at the implanted forest site. The performance of the model at the native forest site was very satisfactory when homogeneous initial soil moisture was considered. A model intercomparison between the boundary layer height obtained with an analytical model and the mesoscale model showed the influence of data and methodologies used in the two approaches. [ABSTRACT FROM AUTHOR]

Through comparing the mean wind profiles observed overland during the passages of four typhoons, and the gradient wind speeds calculated based on the sea level pressure data provided by a numerical model, the present paper discusses, (a) whether the gradient balance is a valid assumption to estimate the wind speed in the height range of 1250 m ~ 1750 m, which is defined as the upper-level mean wind speed, in a tropical cyclone over land, and (b) if the super-gradient feature is systematically observed below the height of 1500 m in the tropical cyclone wind field over land. It has been found that, (i) the gradient balance is a valid assumption to estimate the mean upper-level wind speed in tropical cyclones in the radial range from the radius to the maximum wind (RMW) to three times the RMW, (ii) the super-gradient flow dominates the wind field in the tropical cyclone boundary layer inside the RMW and is frequently observed in the radial range from the RMW to twice the RMW, (iii) the gradient wind speed calculated based on the post-landfall sea level pressure data underestimates the overall wind strength at an island site inside the RMW, and (iv) the unsynchronized decay of the pressure and wind fields in the tropical cyclone might be the reason for the underestimation. [ABSTRACT FROM AUTHOR]

The present study highlights the importance of examining the contribution of Saharan dust (SD) sources not only in terms of overall mass contribution but also in terms of composition, size distribution and inhaled dose. The effect of SD intrusions on PM and the respective major and trace metals mass concentrations and size distributions was investigated in a suburban site in Athens, Greece. SD events were associated, on average, with lower boundary layer heights (BLH) compared to the non-Sahara (nSD) dust days. During SD events, PM 1-10 concentrations showed an increasing trend with increasing atmospheric BLH, in contrary to the fine PM (PM 1). Generally, increased PM 1 and CO (i.e. anthropogenic origin) levels were observed for BLH lower than around 500 m. The average contribution of SD to PM 10 and PM 2.5 mass concentration was roughly equal to 30.9% and 19.4%, respectively. The mass size distributions of PM and specific major and trace elements (Na, Al, Si, S, Cl, K, Ca, Fe, and Zn) displayed a somewhat different behavior with respect to the mass origin (Algeria-Tunisia vs Libya-Egypt), affecting in turn the regional deposition of inhaled aerosol in the human respiratory tract (HRT). The average PM deposited mass in the upper and lower HRT was 80.1% (Head) and 26.9% (Lung; Tracheobronchial and Pulmonary region) higher for SD days than for nSD days. Higher doses were estimated in the upper and lower HRT for the majority of the elements, when SD intrusions occurred, supporting the increasingly growing interest in exploring the health effects of SD. Only the mass deposition for S, and Na in the lower HRT and Zn in the upper HRT was higher in the case of nSD. [Display omitted] • Mass/Elemental size distributions displayed different structure with air mass origin. • The size limit separating the fine and coarse mode was at 1 μm. • Increase of 80.1% (Head) and 26.9% (Lung) in PM deposition mass during SD events. • The majority of the SD events were associated with an apparent shallow boundary layer. • Health impacts from allergens, pollen and heavy metals need to be assessed further. [ABSTRACT FROM AUTHOR]