Review and intercomparison of operational methods for the determination of the mixing height

Various features of different stability regimes of the stable boundary layer are discussed. Traditional layering is examined in terms of the roughness sublayer, surface layer, local similarity, z-less stratification and the region near the boundary-layer top. In the very stable case, the strongest turbulence may be detached from the surface and generated by shear associated with a low level jet, gravity waves or meandering motions. In this case, similarity theory and the traditional concept of a boundary-layer break down. The elevated turbulence may intermittently recouple to the surface. Inability to adequately measure turbulent fluxes in very stable conditions limits our knowledge of this regime.

Stratified atmospheric boundary layers

Air quality is concerned with pollutants in both the gas phase and solid or liquid phases. The latter are referred to as aerosols, which are multifaceted agents affecting air quality, weather and climate through many mechanisms. Unlike gas pollutants, aerosols interact strongly with meteorological variables with the strongest interactions taking place in the planetary boundary layer (PBL). The PBL hosting the bulk of aerosols in the lower atmosphere is affected by aerosol radiative effects. Both aerosol scattering and absorption reduce the amount of solar radiation reaching the ground and thus reduce the sensible heat fluxes that drive the diurnal evolution of the PBL. Moreover, aerosols can increase atmospheric stability by inducing a temperature inversion as a result of both scattering and absorption of solar radiation, which suppresses dispersion of pollutants and leads to further increases in aerosol concentration in the lower PBL. Such positive feedback is especially strong during severe pollution events. Knowledge of the PBL is thus crucial for understanding the interactions between air pollution and meteorology. A key question is how the diurnal evolution of the PBL interacts with aerosols, especially in vertical directions, and affects air quality. We review the major advances in aerosol measurements, PBL processes and their interactions with each other through complex feedback mechanisms, and highlight the priorities for future studies.

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Aerosol and boundary-layer interactions and impact on air quality

Western boundary currents (WBC) influence the global ocean circulation and climate, whereas it locally reaches out differently the continental margins relief. This study analyses the response of WBC over their interactions with the corn of South America Margin. Particularly, the North and East sectors of Rio Grande do Norte (RN) on northeastern Brazil are investigated based upon bathymetry, in situ currents measurements, and simulations of oceanic currents using the CROCO model. The RN margin provides a critical pathway to the WBC along the East and North sectors, which are narrow and retracted shelves (up to 40 km offshore) with steep upper continental slopes (1:11). These sectors are separated by the shallower topography of the Touros High which extends 80 km offshore. The results reveal that the interactions of the Northern Brazilian Undercurrent (NBUC) with the RN northern margin physiography produces a recirculating current region forced by current shear. Eddies and meanders are explicit in February and August, with meander predominance in the latter month because of the increasing of wind intensity eastward. The accelerated core position of NBUC (> 1.0 m.s1) corresponds to the upper slope region of Touros High on both months, and confirms the constrain effect of the margin on the NBUC. The change of margin direction from the N-S to E-W leads to the decreasing of current velocity (~0.1m.s1) near the northern continental slope. This contrast produces an abrupt variation in the shear velocities forming vortices and meanders. Thus, the physiography of the Touros High, the margin directions, and the intensity of the winds control these features development on a regional scale. These oceanic events near the shelf slope affect the sedimentary and ecological system on Brazilian Equatorial continental shelves.

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Dissertação de Mestrado

. The important roles of the planetary boundary layer (PBL) in climate, weather and air quality have long been recognized, but little is known about the PBL climatology in China. Using the fine-resolution sounding observations made across China and reanalysis data, we conducted a comprehensive investigation of the PBL in China from January 2011 to July 2015. The boundary layer height (BLH) is found to be generally higher in spring and summer than that in fall and winter. The comparison of seasonally averaged BLHs derived from observations and reanalysis, on average, shows good agreement, despite the pronounced inconsistence in some regions. The BLH, derived from soundings conducted three or four times daily in summer, tends to peak in the early afternoon, and the diurnal amplitude of BLH is higher in the northern and western subregions of China than other subregions. The meteorological influence on the annual cycle of BLH is investigated as well, showing that BLH at most sounding sites is negatively associated with the surface pressure and lower tropospheric stability, but positively associated with the near-surface wind speed and temperature. In addition, cloud tends to suppress the development of PBL, particularly in the early afternoon. This indicates that meteorology plays a significant role in the PBL processes. Overall, the key findings obtained from this study lay a solid foundation for us to gain a deep insight into the fundamentals of PBL in China, which helps to understand the roles that the PBL plays in the air pollution, weather and climate of China.

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F. Beyrich

Papers

Mixing height estimation from sodar data — A critical discussion☆