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171.
The physical nature of motions with scales intermediate between approximately isotropic turbulence and quasi-linear internal gravity waves is not understood at the present time. Such motions play an important role in the energetics of small scales processes, both in the ocean and in the atmosphere, and in vertical transport of heat and constituents. This scale range is currently interpreted either as a saturated gravity waves field or as a buoyancy range of turbulence.We first discuss some distinctive predictions of the classical (Lumley, Phillips) buoyancy range theory, recently improved (Weinstock, Dalaudier and Sidi) to describe potential energy associated with temperature fluctuations. This theory predicts the existence of a spectral gap in the temperature spectra and of an upward mass flux (downward buoyancy and heat fluxes), strongly increasing towards large scales. These predictions are contrasted with an alternate theory, assuming energetically insignificant buoyancy flux, proposed by Holloway.Then we present experimental evidences of such characteristic features obtained in the lower stratosphere with an instrumented balloon. Spectra of temperature, vertical velocity, and cospectra of both, obtained in homogeneous, weakly turbulent regions, are compared with theoretical predictions. These results are strongly consistent with the improved classical buoyancy range theory and support the existence of a significant downward heat flux in the buoyancy range.The theoretical implications of the understanding of this scale range are discussed. Many experimental evidences consistently show the need for an anisotropic theory of the buoyancy range of turbulence. 相似文献
172.
广东地区河流阶地和冲积扇沉积物中砂岩砾石风化晕随时间增厚。风化晕生长速度呈指数衰减,并拟合于下列公式:T 1485D4.13这里T=时间,以年表示,D=沉积物表部约50块砾石风化晕厚度的加权平均值,以毫米表示。利用风化晕厚度确定出广东地区河流第一和第二级阶地分别为1000—13300年和8600—26500年,肇庆盆地北部山前地带第Ⅰ和第Ⅱ级冲积扇分别为51500年和24400年。同时,在构造地貌变形分析的基础上,估算出本区三条主要北东向断裂带在晚更新世—中全新世的垂直断层作用速度为0.6—1.6毫米/年,中全新世甚或晚更新世晚期以来的活动速度极小 相似文献
173.
Emissions of N2O, CH4, and CO2 from soils at two sites in the tropical savanna of central Venezuela were determined during the dry season in February 1987. Measured arithmetic mean fluxes of N2O, CH4, and CO2 from undisturbed soil plots to the atmosphere were 2.5×109, 4.3×1010, and 3.0×1013 molecules cm-2 s-1, respectively. These fluxes were not significantly affected by burning the grass layer. Emissions of N2O increased fourfold after simulated rainfall, suggesting that production of N2O in savanna soils during the rainy season may be an important source for atmospheric N2O. The CH4 flux measurements indicate that these savanna soils were not a sink, but a small source, for atmospheric methane. Fluxes of CO2 from savanna soils increased ninefold two hours after simulated rainfall, and remained three times higher than normal after 16 hours. More research is needed to clarify the significance of savannas in the global cycles of N2O, CH4, CO2, and other trace gases, especially during the rainy season. 相似文献
174.
Two sets of radiosounding measurements, taken at different hours from some stations in the Po Valley area, were examined in order to obtain the values of precipitable waterw and determine the shapes of the vertical distribution curves of absolute humidity. From these curves, we calculated the bestfit values of scale heightsH
1 andH
2 in the 0÷5 km and 5÷10 km altitude intervals, respectively. The analysis of the radiosounding data clearly shows that parametersw andH
1 are closely related to the evolutionary features of the meteorological conditions on synoptic scale and are influenced, to a lesser extent, by the diurnal variations in the atmospheric ground layer. Seasonal average curves of temperature and absolute humidity, as functions of altitude, were also defined from the radiosounding measurements taken at various hours of the day. Moreover, interpolation methods in time (applied to a 12-hour range) and in space (range of about 300 km) were proposed for determining parametersw andH
1 from the radiosounding measurements taken at different hours from the same station or from different stations at the same hour. Reliability tests, made by comparing the same station or from different stations at the same hour. Reliability tests, made by comparing the values given by the interpolation methods with those directly obtained from the radiosounding measurements, show that these evaluations ofw andH
1 are affected by standard errors of estimate, which are comparable to the errors usually made in analyzing the radiosounding data. 相似文献
175.
176.
NumericalModellingoftheEffectsofOzoneontheSummerAtmosphericCirculationWangQianqian(王谦谦);WangYinhui(汪迎辉);SongYu(宋煜)(Naminginst... 相似文献
177.
Carlsberg Ridge, northern Indian Ocean: gravity and isostasy 总被引:1,自引:0,他引:1
178.
179.
180.
Amino acid nitrogen in atmospheric aerosols: Occurrence,sources and photochemical modification 总被引:2,自引:0,他引:2
The presence of amino acids in atmospheric precipitation and aerosols has been noted for many years, yet relatively little is known about these or other nitrogen containing organic compounds in the atmosphere. Marine and continental rainwater analyses indicate that atmospheric aerosols, and subsequently atmospheric precipitation, may contain substantial levels of free and combined amino acids. The most likely source of amino N in the remote marine atmosphere appears to be the injection of proteinaceous material through the action of bursting bubbles at the sea-air interface or the long range transport from terrestrial sources. The capacity of these substrates to undergo photooxidation and photodegradation in the atmosphere to simpler species, such as ammonium ions, carboxylic acids, and for the S containing amino acids, oxidized forms of sulfur, has received little attention from atmospheric chemists. The photochemistry of covalently bound amino groups, particularly as found in peptides and amino acids, is discussed here with the purpose of summarizing what is known of their occurrence and their possible importance to atmospheric chemistry. 相似文献