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131.
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
132.
Gas exchange experiments were conducted in the tropical Atlantic Ocean during a ship expedition with FS Meteor using a small rubber raft. The temporal change of the mixing ratios of CO, H2, CH4 and N2O in the headspace of a floating glass box and the concentrations of these gases in the water phase were measured to determine their transfer velocities across the ocean-atmosphere interface. The ocean acted as a sink for these gases when the water was undersaturated with respect to the mixing ratio in the headspace. The transfer velocities were different for the individual gases and showed still large differences even when normalized for diffusivity. Applying the laminar film model, film thicknesses of 20 to 70 m were calculated for the observed flux rates of the different gas species. When the water was supersaturated with respect to atmospheric CO, H2, CH4 and N2O, the transfer velocities of the emission process were smaller than those determined for the deposition process. In case of H2 and CH4, emission was even not calculable although, based on the observed gradient, the laminar film model predicted significant fluxes at the air-sea interface. The results are interpreted by destruction processes active within the surface microlayer. 相似文献
133.
Transient and stationary spectra of kinetic energy (KE), available potential energy (APE) and enstrophy (EN), and their spectral fluxes as a function of the two-dimensional wavenumbern were computed for July 1979. Triangular truncation at zonal wavenumber 42 was used for computation. The slopes of various
spectra in the wavenumber range 14≤n≤25 were obtained by fitting a straight line in log-log scale by the least square method. The transientKE, APE andEN spectra in the lower (upper) troposphere had slopes −2·21 (−2·30), −2·65 (−2·64) and −0·36 (−0·46), respectively. The effect
of stationary and divergent motion on the slope values was investigated. The possible correlation between the slope and percentage
of transient component in the combined energy and enstrophy was examined to identify the transient motion of the atmosphere
with the two-dimensional homogeneous isotropic turbulence. The vertically averaged slope of kinetic energy and enstrophy in
the lower (upper) troposphere was close to the value at 700 (200) hPa level.
The spectral fluxes of kinetic energy and enstrophy in the wavenumber range 14≤n≤25 satisfied, to a very rough approximation, the criteria of inertial subrange. The stationary fluxes were small. The estimated
stationary-transient component of flux was larger, comparable and less than the corresponding transient flux of APE, KE and
EN.
Representative levels for computation of energy and enstrophy spectra and their fluxes in the lower and upper troposphere
were identified. 相似文献
134.
135.
136.
分析了1983年江淮流域入梅前、梅雨期以及出梅后垂直积分的水汽输送和水汽通量散度分布,计算了南海和中国东部地区的水汽收支。结果指出:江淮流域入梅前,华南地区降水的水汽主要来自印度西南季风和东南季风气流;梅雨期降水的水汽主要来自印度西南季风气流;出梅后华北雨季则主要受中低纬水汽输送气流汇合的影响。分析表明,江淮流域梅雨期是印度西南季风气流加强并东进北上,西太平洋高压东撤所造成的;而梅雨结束则是由于西南季风气流减弱西退和西太平洋高压西进北上所造成的;此外,还讨论了水汽输送、水汽通量辐合与云量及我国东部降水的关系。 相似文献
137.
本文根据核爆炸岩石熔融玻璃的地球化学研究结果,与超速陨石撞击坑的熔岩进行比较,获得在远离热力学平衡条件下,各种玻璃和熔岩在化学成分上分布十分均匀的重要结论。岩石玻璃和熔岩是由基岩各组成岩石按一定比例混合熔融形成的。它们的主量元素和痕量元素丰度受基岩元素背景值制约。文中根据熔体和靶岩的化学成分,计算了熔岩各组成岩石的百分比。玻璃陨石是地壳岩石受撞击熔融形成的。同一撒布区的玻璃陨石化学成分相近,说明起源于同一源坑;而玻璃陨石化学成分的不同,则说明母岩组成分量的差异。因此,文中通过模拟计算,得出各玻璃陨石的组成源岩。澳大利亚撒布区的玻璃陨石,Al2O3,K2O 和Na2O 与 SiO2及 K2O/Na2O 比值不完全相同,说明澳大利亚撒布区存在着几个不同的源岩和源坑,至少有印支、爪哇、菲律宾和澳大利亚四个相应撞击坑。 相似文献
138.
The surface parameters are being evaluated using a methodology which considers the vertical temperature structure of MONTBLEX
’90. For this 30 metre micrometeorological tower data are utilised. In this process, a concept of isolated layers has been
introduced. The parameters have been evaluated following two successive iterative processes to give a consistent value both
in the flux-profile relation and the related similarity relation.
The heat flux obtained using the present methodology, is then utilised to examine its interplay with the synoptic as well
as mesoscale features. The existence of such an interplay is observed. 相似文献
139.
N. P. Sukumaran 《Journal of Earth System Science》1994,103(4):489-497
Examined in this paper is the tentative history of the depositional flux of230Thxs (the unsupported fraction of230Th scavenged from the overlying water column), for the Late Quaternary period from a sediment core of the Central Indian Basin
(CIB). The measured depositional flux of230Thxs is found substantially higher than that of the possible theoretical flux from the overlying water column. Historical records,
reconstructed from the230Thxs chronology suggests that the depositional flux has varied considerably with time, reflecting an enhanced scavenging during
the Holocene and the preceding interglacial periods whereas, comparatively lower flux than the predicted one occurred during
the Last Glacial Maximum (LGM) period. The average ratio of the measured depositional flux to that of the predicted flux from
the overlying water column, indicates that the core site acts as a sink for230Thxs and based on the existence of bottom current activity; the230Thxs could be the result of focusing of younger sediments. The depositional index (Di) has also been calculated to quantify the
extent of lateral supply throughout the core with time. The estimated (Di) suggests that bottom focusing and feeble deposition
and/or winnowing processes had occurred and that the former was most prevalent during the Holocene and the preceding interglacials,
whereas the latter was observed at the LGM period. 相似文献
140.