A Wind Tunnel Study of the Seasonal Shelter Efficiency of Deciduous Windbreaks

HighlightsSeasonal leaf shedding is a key factor affecting the airflow field and shelter efficiency of deciduous windbreaks.The wind deceleration region around modeled Elaeagnus angustifolia L. (Russian olive) windbreaks was larger in winter than in summer, but the intensity of the wind speed reduction was relatively low.The shelter efficiency of E. angustifolia windbreaks in winter was not less than 80% of that in summer.Abstract. The shelter efficiency of windbreaks constructed with deciduous plants changes with their phenological stage. We used Elaeagnus angustifolia L. (Russian olive) as an example and investigated the airflow field and shelter efficiency of deciduous windbreaks with summer facies (with leaves) and winter facies (without leaves) by means of scaled wind tunnel simulation experiments. Our study revealed that different canopy seasonal porosities exert different wind speed reductions inside the windbreaks, which also determine the upwind and downwind wind speed variation. The variation in wind speed was greater in summer than in winter. For the windbreak with summer facies, a large wind acceleration region above and before the windbreak and a strong wind deceleration region inside and after the windbreak were observed. The wind deceleration region around the windbreak with winter facies was larger than that in summer, but the intensity of the wind speed reduction was relatively low. The results of our study further show that although E. angustifolia windbreaks are highly porous in winter, the shelter efficiency was not less than 80% of that in summer. Like any wind tunnel study on windbreaks, producing an artificial plant model that is highly similar to the real field plant is difficult. Nevertheless, our results clearly revealed the wind reduction patterns of deciduous windbreaks due to seasonal porosity caused by leaf shedding, which may provide valuable data for assessing the shelter efficiency of deciduous windbreaks. Keywords: Airflow field, Elaeagnus angustifolia, Seasonal porosity, Wind reduction.

The Iron Curtain of WC9 Stars

High resolution (Δλ ≈ 0.1å) IUE spectra have been obtained of the two WC9 stars HD 164270 and HD 136488, covering the wavelength range λλ1150–2050. The former star shows P Cygni profiles indicating a stellar wind terminal velocity of v∞ ≈ −1400 km s−1, and the latter v∞ ≈ −1800 km s−1. A common feature in the spectra of both stars is narrow displaced absorptions due to Fe III (UV34) transitions arising from a metastable lower level. These features are displaced at subterminal velocities (−830 km s−1 for HD 164270 and −1030 km s−1 for Hd 136488) and are believed to be formed in the deceleration region of their stellar winds. The properties of these inferred Fe III circumstellar shells derived from these data are discussed.