An experimental investigation of the airflow structure in the near surface region over the wind-sheared air-water interface is reported. The two-dimensional velocity fields in a plane perpendicular to the water surface were measured using particle image velocimetry (PIV) technique over a wind speed range from 1.5 to 4.4 m s −1 . The results show a reduction in the mean velocity magnitudes and the tangential stresses when gravity waves appear on the surface. An enhanced vorticity layer was observed immediately above the water surface that extended to a height of approximately 2 cm. The vorticity was enhanced by an order of magnitude, and the energy dissipation rate was enhanced by a factor of 7 in this layer at all wind speeds. The vertical profiles of Reynolds stress, energy production, and dissipation indicate the contribution of surface waves in the enhanced transfer of momentum and energy between the two fluids. The results in this study show that the flow dynamics in a layer immediately adjacent to the water surface whose thickness is of the order of the significant wave height is significantly different from that at greater heights. Thus, it is concluded that the quantitative investigation of the flow in the immediate vicinity of the interface is vital for an improved understanding of the heat, mass, and momentum exchange between air and water. The present study demonstrates that PIV is an effective technique to accurately measure the velocity fields in this region.

Results from an experimental study, investigating the similarities and dissimilarities of the airflow structure over water and solid surfaces for smooth and wavy conditions, are reported. The experiments were conducted at the same location, under identical flow conditions. The two-dimensional velocity fields were measured using particle image velocimetry technique over a wind speed range from 1.5 to 4.4 m s−1. The mean velocity profiles for all surface configurations showed the logarithmic behavior. The profiles of different turbulent properties followed similar trend over water and solid surfaces, however, their magnitudes varied over different surface types. The results show that the level of enhancement of normalized Reynolds stress, rates of energy production, and dissipation from the free-stream region toward the surface is higher over the water surface especially in the presence of waves as compared to that over the solid surface. It is also observed that the normalized magnitudes of turbulent properties are largest above the water surface and smallest above the wavy solid wall. It is concluded that, at a given free stream condition, the flow behavior over the solid surface is not necessarily similar to that over the water surface.

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Multivariate analysis was conducted to explore the moist temperate forests of the Shangla district, Khyber Pakhtunkhwa. The prime objective was to quantitatively describe and differentiate the vegetation groups and the factors that determine the boundaries and composition of plant communities in the Shangla district. This was achieved by sampling all common species in a complex vegetation mosaic coinciding with local gradients in topography and soil distribution. Ward’s clustering dendrogram demonstrated four significant vegetation clusters with respect to environmental effects. These four major groups of the tree vegetation were superimposed on the ordination plane: 1. Pinus wallichiana, the dominant group associated with Abies pindrow; 2. Abies pindrow and the Picea smithiana group; 3. Dominant Cedrus deodara associated with the Pinus wallichiana, Abies pindrow, Picea smithiana, and Quercus baloot group; 4. Pinus roxberghii pure group. The key controlling factors for each group were the environmental characteristics (i.e., edaphic factors, topographic factors, soil physical properties, and soil nutrients). The results revealed elevation (p <0.001) to be the prominent factor in the composition of plant communities. Furthermore, pH, soil moisture, maximum water holding capacity, and soil physical properties (sand, silt, and clay) also showed a significant (p < 0.05) relationship with vegetation. The other environmental factor did not show a significant relationship with vegetation. Ward’s cluster dendrogram of understory species also demonstrated four groups. Group 1 comprises two subgroups, a and b, with the highest number of species, i.e., Digeteria sanguinalis, Fragaria nubicola, Verbascum Thapsus, Pinus wallichiana seedlings, and Polygonatum multiflorium, respectively. The second large group contains twenty-five species out of eight stands, and the dominant species was Tagetis minuta. Eighteen species out of six stands were found in group 3, which was considered the smallest group. Group 4 consisted of seven stands containing twenty-four species of ground flora, with Anaphalis scopulosa followed by Adiantum venustum as the dominant species. The environmental characteristics of the understory vegetation showed a resemblance with the tree communities. With the exception of elevation, the other factors did not show a significant correlation.

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