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During the Conjugate Point Experiment (COPEX) campaign performed at Boa Vista (2.80°N;60.70°W, dip angle 21.7°N) from October to December 2002, 15 medium-scale gravity waves in the OHNIR airglow images were observed. Using a Keogram image analysis, we estimate their parameters. Most of the waves propagate to Northwest, indicating that their main sources are Southeast of Boa Vista. Quasi-simultaneous plasma bubble activities in the OI 630 nm images were observed in seven cases. The distances between the bubble depletions have a linear relationship with the wavelengths of the gravity waves observed in the mesosphere, which suggests a direct contribution of the mesospheric medium-scale gravity waves in seeding the equatorial plasma bubbles.  相似文献   

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Vertical stability of a water column can be computed from the formula: N2=g2[dρdP?1c2] where ρ is density, P is pressure, g is gravity, and c is sound speed.Because Ekman's density equation is not consistent with Wilson's sound speed equation, large errors are introduced by combining these two equations to calculate the vertical stability. However, this difficulty can be overcome with the Wang and Millero density equation derived consistently from Wilson's sound speed equation. In addition to its simplicity, the computation of vertical stability from the above formula using Wilson's sound speed equation and Wand and Millero's density equation can be shown to generally give the most accurate results.  相似文献   

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It is important to examine the ratio of measured to total sediment discharge to determine the error in measured sediment transport rates from depth-integrated samplers. The ratio of measured to total sediment discharge as well as the ratio of suspended to total sediment discharge are examined based on the Modified Einstein Procedure. Both ratios reduce to a function of the ratio of shear velocity, u*, to the fall velocity, ω, of suspended material, u*/ω, and the ratio, h/ds, of flow depth, h, to the median grain size of bed material, d50. In rivers transporting fine material (such as silt or clay), the ratio of suspended to total load is a function of the ratio, h/d50. In this study, it is found that the ratio of measured to total load becomes a simple function of flow depth. For fine sediment transport, with a Rouse number (Ro) <0.3, at least 80% of sediment load is in suspension when h/d50>15, and at least 90% of sediment load is measured from depth integrating samples when h>1m. Detailed measurements from 35 river stations in South Korea demonstrate that sand sizes and finer fractions predominantly are transported in suspension. Also, at least 90% of sand and finer fractions are transported in suspension in gravel and sand bed rivers when the discharge is larger than the mean annual discharge.  相似文献   

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