Material Transport in the Ocean Mixed Layer: Recent Developments Enabled by Large Eddy Simulations

Material transport in the ocean mixed layer (OML) is an important component of natural processes such as gas and nutrient exchanges. It is also important in the context of pollution (oil droplets, microplastics, etc.). Observational studies of small-scale three-dimensional turbulence in the OML are difficult, especially if one aims at a systematic coverage of relevant parameters and their effects, under controlled conditions. Numerical studies are also challenging due to the large-scale separation between the physical processes dominating transport in the horizontal and vertical directions. Despite this difficulty, the application of large eddy simulation (LES) to study OML turbulence and, more specifically, its effects on material transport has resulted in major advances in the field in recent years. In this paper we review the use of LES to study material transport within the OML and then summarize and synthesize the advances it has enabled in the past decade or so. In the first part we describe the LES technique and the most common approaches when applying it in OML material transport investigations. In the second part we review recent results on material transport obtained using LES and comment on implications

Revisiting the formulations for the longitudinal velocity variance in the unstable atmospheric surface layer.” Quarterly

Because of its non-conformity to Monin-Obukhov Similarity Theory (MOST), the effects of thermal stratification on scaling laws describing the streamwise turbulent intensity σ u normalized by the turbulent friction velocity (u * ) continue to draw research attention. A spectral budget method has been developed to assess the variability of σ u /u * under unstable atmospheric stratification. At least three different length-scales -the distance from the ground (z), the height of the atmospheric boundary laye

The influence of local meteorological conditions on the circadian rhythm of corn (Zea mays L.) pollen emission

Field experiments were performed to study the diurnal cycle of corn pollen emission and its relation to local meteorological conditions, including temperature, relative humidity, solar radiation, mean wind speed, and turbulence quantities. Pollen concentrations were measured from canopy height to twice this level using four Rotorod samplers located on a pole in the middle of the corn field. The measured pollen concentration at canopy height was used as a surrogate for the pollen source strength while the concentrations above canopy represented the pollen transported upwards from canopy height. At twice the canopy height, the pollen concentration decreased considerably to about 30% of the canopy height values. During the mornings, pollen was emitted in large quantities while during the afternoons, airborne pollen concentrations decreased and no significant atmospheric pollen was measured from about 2 h prior to sunset until sunrise the next morning. The actual time that airborne pollen was first recorded differed from day-to-day and depended on the time required for the anthers to dry and open, as well as there being sufficiently strong winds to entrain the pollen away from the plants. On four consecutive mornings diurnal atmospheric pollen concentration distributions were bi-modal in time. The first pollen concentration peak happened shortly before the direct irradiance peak on the anthers suggesting that direct solar irradiation might be important for drying the anthers. The subsequent dip in pollen concentration seemed to be linked to a lull in mean and turbulent wind conditions. Analysis of the vertical velocity fluctuations, sw, showed that the fraction of pollen transported upwards from canopy height increased with increasing sw. In addition, Quadrant– Hole analysis applied to the turbulence data sets of 2 days suggested that low values of ejection duration fractions were associated with low values of pollen concentration, while high values were associated with high concentration values. The diurnal pattern of ejection duration fractions was similar to the pattern of the fraction of pollen that reached twice the canopy height, indicatin