Effects of buoyancy on Langmuir circulation

Based on the Navier-Stokes equation, an equation describing the Langmuir circulation is derived by a perturbation method when the influences of Coriolis force and buoyancy force are both considered. The approach used in the analysis is similar to the works carried out by Craik and Leibovich [J. Fluid Mech. 73 (1976) 401], Leibovich [J. Fluid Mech. 79 (1977) 715] and Huang [J. Fluid Mech. 91 (1979) 191]. Potential applications of the equation proposed are discussed in the area of Antarctic circumpolar current.

风和竞争对毛乌素沙地４种植物的影响

自然生境中，风是一种重要的生态/环境因子，已经引起生态学家的广泛兴趣。然而，目前对风和竞争如何共同影响植物行为的理解还很少。本文基于野外控制实验，研究赖草（Leymus secalinus）、黍（Panicum miliaceum）、油蒿（Artemisia ordosica）和雾冰藜（Bassia dasyphylla）四种沙生植物生长和形态特征对风和竞争的综合反应，以及降雨量变化是否修饰风和竞争的生态学效应。 风和竞争显著影响赖草和黍的生长和形态特征。赖草和黍的总生物量和分蘖数受密度效应影响较大，没有竞争的植株生物量和分蘖数都显著高于有竞争的植株。赖草和黍的根冠比和株高则受风因素的显著影响：风速越大，植株越趋向于降低株高并将更多的生物量分配到地下部分。除赖草株高显著外，竞争和风对两种植物生长和形态特征的交互作用不明显。 在风、竞争和水分实验中，风、竞争及其交互作用对油蒿和雾冰藜形态特征均有显著影响。油蒿株高在中风环境中最大，而雾冰藜株高在大风环境中最小;油蒿基径在弱风环境中最小，而雾冰藜则相反。种内竞争情况下的油蒿株高和基径显著高于种间竞争，而雾冰藜则相反。种内竞争情况下的油蒿株高和基径随风速的增大而减小;种间竞争情况下的油蒿株高和基径在弱风环境中最小，中等风区最大。油蒿和雾冰藜的分枝数都受竞争的显著影响，种间竞争情况下的油蒿分枝数显著高于种内竞争，而雾冰藜则相反。风显著影响油蒿的茎重比和雾冰藜的冠重比。油蒿的茎重比随风速的降低而降低。弱风环境中，雾冰藜的冠重比显著高于强风环境下的。风和竞争的交互作用显著影响油蒿生物量。种内竞争情况下，油蒿生物量在大风环境中最大，中风环境中最小;种间竞争情况下，油蒿生物量在中风环境中最大，弱风环境最小。水分显著影响油蒿的茎重比，以及雾冰藜的根冠比和基径，而对这两个种的其他生长和形态特征无显著影响。低水分情况下，油蒿的茎重比显著较高，雾冰藜的基径显著较低，并且分配更多生物量到地上部分。 这些结果初步表明，单优群落中的优势种或呈聚集分布的种群中，植株的生长符合“密度效应”原则，即密度越大，单株植物的生物量越小;并且在大风环境中，趋向于分配更多生物量到地下部分。种内竞争情况下油蒿幼苗的竞争能力强于种间竞争，这可能是自然群落中的油蒿不是聚集分布的一个原因。

Effect of wind speed on loss of water from Nostoc flagelliforme colonies

The effects of wind speed on loss of water from N. flagelliforme colonies were investigated indoors in an attempt to assess its ecological significance in field. Wind enhanced the process of waterless; the half-time of desiccation at wind speeds of 2.0 and 3.4 m s(-1) was, respectively, shortened to one-third and one-fifth at 20 degrees C and, to one-sixth and one-eighth at 27 degrees C that of still air. Photosynthetic efficiency was not affected before the wet alga lost about 50% water.

The effects of random surface waves on the steady Ekman current solutions

The response of near-surface current profiles to wind and random surface waves are studied based on the approach of Jenkins [1989. The use of a wave prediction model for driving a near surface current model. Dtsch. Hydrogr. Z. 42,134-149] and Tang et al. [2007. Observation and modeling of surface currents on the Grand Banks: a study of the wave effects on surface currents. J. Geophys. Res. 112, C10025, doi:10.1029/2006JC004028]. Analytic steady solutions are presented for wave-modified Ekman equations resulting from Stokes drift, wind input and wave dissipation for a depth-independent constant eddy viscosity coefficient and one that varies linearly with depth. The parameters involved in the solutions can be determined by the two-dimensional wavenumber spectrum of ocean waves, wind speed, the Coriolis parameter and the densities of air and water, and the solutions reduce to those of Lewis and Belcher [2004. Time-dependent, coupled, Ekman boundary layer solutions incorporating Stokes drift. Dyn. Atmos. Oceans. 37, 313-351] when only the effects of Stokes drift are included. As illustrative examples, for a fully developed wind-generated sea with different wind speeds, wave-modified current profiles are calculated and compared with the classical Ekman theory and Lewis and Belcher's [2004. Time-dependent, coupled, Ekman boundary layer solutions incorporating Stokes drift. Dyn. Atmos. Oceans 37, 313-351] modification by using the Donelan and Pierson [1987. Radar scattering and equilibrium ranges in wind-generated waves with application to scatterometry. J. Geophys. Res. 92, 4971-5029] wavenumber spectrum, the WAM wave model formulation for wind input energy to waves, and wave energy dissipation converted to currents. Illustrative examples for a fully developed sea and the comparisons between observations and the theoretical predictions demonstrate that the effects of the random surface waves on the classical Ekman current are important, as they change qualitatively the nature of the Ekman layer. But the effects of the wind input and wave dissipation on surface current are small, relative to the impact of the Stokes drift. (C) 2008 Elsevier Ltd. All rights reserved.

THE EFFECTS OF MONSOONS AND CONNECTIVITY OF SOUTH CHINA SEA ON THE SEASONAL VARIATIONS OF WATER EXCHANGE IN THE LUZON STRAIT

Seasonal variations of water exchange in the Luzon Strait are studied numerically using the improved Princeton Ocean Model (POM) with a consideration of the effects of connectivity of South China Sea (SCS) and monsoons. The numerical simulations are carried out with the strategy of variable grids, coarse grids for the Pacific basin and fine grids for the SCS. It. is shown that the Mindoro Strait plays an important role in adjusting the water balance between the Pacific and the SCS. The SCS monsoon in summer seasons hinders the entrance of the Pacific water into the SCS through the Luzon Strait while the SCS monsoon in winter seasons promotes the entrance of Pacific water into the SCS through the Luzon Strait. However, the SCS monsoon does not affect the annual mean Luzon Strait transport, as is mainly determined by the Pacific basin wind.

Effects of winds, tides and storm surges on ocean surface waves in the Sea of Japan

Ocean surface waves are strongly forced by high wind conditions associated with winter storms in the Sea of Japan. They are also modulated by tides and storm surges. The effects of the variability in surface wind forcing, tides and storm surges on the waves are investigated using a wave model, a high-resolution atmospheric mesoscale model and a hydrodynamic ocean circulation model. Five month-long wave model simulations are inducted to examine the sensitivity of ocean waves to various wind forcing fields, tides and storm surges during January 1997. Compared with observed mean wave parameters, results indicate that the high frequency variability in the surface wind filed has very great effect on wave simulation. Tides and storm surges have a significant impact on the waves in nearshores of the Tsushima-kaihyo, but not for other regions in the Sea of Japan. High spatial and temporal resolution and good quality surface wind products will be crucial for the prediction of surface waves in the JES and other marginal seas, especially near the coastal regions.