排序方式： 共有36条查询结果，搜索用时 28 毫秒
21.
S. G. Gopalakrishnan Frank Freedman Maithili Sharan T. V. B. P. S. Rama Krishna 《Pure and Applied Geophysics》2005,162(10):1795-1809
With the exception of intermittency and waves, a brief review of the observed and modeled mean structure of the nocturnal boundary layer (NBL) is presented. The effect of gentle slopes on strong and weak wind NBL was investigated here using a one-dimensional model, with a simple correction term to account for the slope effects, identical to the one used by Brost and Wyngaard (1978). The study indicates that the wind profiles, temperature profiles and surface layer turbulence characteristics are extremely sensitive to the imposed geostrophic wind when small slopes are present especially for light winds. This is due to the complex interaction between the buoyancy driven slope flow and the imposed geostrophic wind that in turn influence the shear generation of turbulence. Finally, the current issues in the modeling of weak wind boundary layer are discussed. 相似文献
22.
The application of the weighted and unweighted least-squares method to the analysis of the individual concentrations of short-lived radon daughters in the open atmosphere, where, unlike in the mines the levels are low, is discussed. The method can be optimized to give minimum counting errors by proper choice of collection times and counting periods. By analysing a large number of samples it is shown that the least squares method gives better accuracy than the simultaneous equations method generally in use. The calculation can be simplified by using the unweighted least-squares analysis without significant loss in accuracy. The levels of RaA, RaB and RaC in surface air at Bombay during the period January-June 1975, calculated using the least-square method, are presented. The activity ratios of RaC/RaB are shown to have an average value around 0.6–0.9 even at 18 m height. The RaB/RaA activity ratios however show a much larger scatter than the RaC/RaB values. The possible reasons for these differences are discussed. The application of the least-squares method to the analysis of Th-B and Th-C is also described. 相似文献
23.
P. Murugavel V. Gopalakrishnan Vimlesh Pant A. K. Kamra 《Journal of Earth System Science》2008,117(1):273-280
Airborne measurements of the number concentration and size distribution of aerosols from 13 to 700 nm diameter have been made at four vertical levels across a coastline at Bhubaneswar (20°25′N, 85°83′E) during the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) programme conducted in March–April 2006. The measurements made during the constant-level flights at 0.5, 1, 2 and 3 km altitude levels extend ～100 km over land and ～150km over ocean. Aerosol number concentrations vary from 2200 to 4500 cm?3 at 0.5 km level but are almost constant at ～ 6000 cm?3 and ～ 800 cm?3 at 2 and 3 km levels, respectively. At 1km level, aerosol number concentration shows a peak of 18,070 cm?3 around the coastline. Most of the aerosol size distribution curves at 0.5 km and 1 km levels are monomodal with a maxima at 110nm diameter which shifts to 70 nm diameter at 2 and 3 km levels. However, at the peak at 1 km level, number concentration has a bimodal distribution with an additional maximum appearing in nucleation mode. It is proposed that this maxima in nucleation mode at 1 km level may be due to the formation and transport of new particles from coastal regions. 相似文献
24.
A. A. Sin’kevich B. Boe Yu. P. Mikhailovskii Yu. A. Dovgalyuk N. E. Veremei V. Gopalakrishnan P. Murugavel S. D. Pawar 《Russian Meteorology and Hydrology》2018,43(4):209-217
The results are presented of complex investigation of clouds in India which were seeded with a glaciogenic reagent from the aircraft. The seeding effect was assessed by the comparison of radar characteristics of the seeded clouds with the characteristics of clouds within the radar field of view. The maximum reflectivity increase in the seeded clouds in comparison with clouds in the natural cycle, an increase in the precipitation flux and specific mass of precipitated hail are observed. The merging of seeded clouds was observed during the study. It is shown that this process affects cloud characteristics resulting in the significant (by several times) increase in the precipitation flux. The measurements of electric discharges registered by the lightning detection network demonstrated that there were no lightning strikes in the seeded clouds, although the calculations indicated an increase in the electric activity of the clouds. 相似文献
25.
A. A. Sin’kevich Yu. A. Dovgalyuk N. E. Veremei A. B. Kurov Yu. P. Mikhailovskii E. V. Bogdanov M. L. Toropova A. A. Ignat’ev A. Kh. Adzhiev A. M. Malkarova A. M. Abshaev V. Gopalakrishnan P. Murugavel S. D. Pawarr 《Russian Meteorology and Hydrology》2017,42(8):494-502
The three-dimensional nonstationary model of a convective cloud is used for investigating a thunderstorm with hail which developed over Pyatigorsk on May 29, 2012 and produced a severe hailstorm. The values of cloud characteristics (liquid water content, ice content, vertical velocity, etc.) are obtained. The importance ofconsidering wind shear is noted. The simulation results are used to analyze the transformation of precipitation field and the electric charge structure of the analyzed cloud during its development. 相似文献
26.
A numerical simulation model is developed to investigate wave profiles and velocities in harbor channels. The Galerkin Technique is coupled with the finite element method in the flow model. An important feature is the addition of terms in the momentum equation to account for the vertical accelerations. The model can be used by ocean engineers to analyze the effects of varying channel geometry on wave oscillations and velocities in a channel connecting a harbor to the ocean. 相似文献
27.
Wave interaction with twin plate wave barrier 总被引：3，自引：0，他引：3
The wave transmission and reflection characteristics and wave induced pressures on single surface plate and twin plate barriers were investigated experimentally for a wide range of wave heights and periods in regular and random waves. Seven different spacing between the plates were tested. It is found in general, hydrodynamically the twin plate is better than the single surface plate to reduce the wave transmission and increase the wave reflection. It is found that the transmission coefficient of twin plate reduced from 0.8 to 0.3 when the relative plate width is increased from 0.18 to 0.84. Transmission coefficient of twin plate barrier shows oscillating behavior, when relative plate width is increased due to blocking and pumping effect. The reflection coefficient increased from 0.25 to 0.65, when the relative width of the plate is increased from 0.18 to 0.84. The increase in spacing between the plates was also found to increase the reflection coefficient. The transmission coefficient, Kt for 98% probability of non-exceedence was found to be minimum and is about 0.60 when the relative spacing between the plate is about 0.12, compared to Kt=0.76 for single surface plate. The reflection coefficient for 98% probability of non-exceedence was found to exceed 0.66 for single surface plate, whereas it is 0.73 for twin plate with relative spacing of about 0.40. From the investigation with wide range of input parameters, it is found that the twin plate barrier needs to be designed for highest 98% pressure ratio of 2.0, which is equal to the static pressure induced by the design incident wave height. 相似文献
28.
Yuki Chan Amy Li Singaram Gopalakrishnan Paul K.S. Shin Rudolf S.S. Wu Stephen B. Pointing Jill M.Y. Chiu 《Marine pollution bulletin》2014
Hypoxia alters the oxidation–reduction balance and the biogeochemical processes in sediments, but little is known about its impacts on the microbial community that is responsible for such processes. In this study, we investigated the effects of hypoxia and the ubiquitously dispersed flame-retardant BDE47 on the bacterial communities in marine surface sediments during a 28-days microcosm experiment. Both hypoxia and BDE47 alone significantly altered the bacterial community and reduced the species and genetic diversity. UniFrac analysis revealed that BDE47 selected certain bacterial species and resulted in major community shifts, whereas hypoxia changed the relative abundances of taxa, suggesting slower but nonetheless significant community shifts. These two stressors targeted mostly different taxa, but they both favored Bacteroidetes and suppressed Gammaproteobacteria. Importantly, the impacts of BDE47 on bacterial communities were different under hypoxic and normoxic conditions, highlighting the need to consider risk assessments for BDE47 in a broader context of interaction with hypoxia. 相似文献
29.
Sankar R Rajkumar M SUN Jun Gopalakrishnan A Vasanthan T M Ananthan G Trilles J P 《海洋学报(英文版)》2011,30(1):113-117
Three species,Bathynomus decemspinosus,B.doederleini and B.kensleyi (Crustacea,Isopoda,Cirolanidae),are reported for the first time from the Parangipettai coastal waters,Southeast coast of India.Several Trilasmis (Temnaspis) tridens (Cirripedia Thoracica,Lepadomorpha) were attached to the pleopods of some individuals.So,five bathynomid species are currently reported from India. 相似文献
30.
Yu. P. Mikhailovskii A. A. Sin’kevich S. D. Pawar V. Gopalakrishnan Yu. A. Dovgalyuk N. E. Veremei E. V. Bogdanov A. B. Kurov A. Kh. Adzhiev A. M. Malkarova A. M. Abshaev 《Russian Meteorology and Hydrology》2017,42(6):377-387
The results of observation of the development of a high-depth thunder-hail storm is presented. The measurements were carried out with the MRL-5 weather radar and LS8000 lightning detection system. The electrical parameters of the investigated cloud obtained with LS8000 as well as their relations to radar-derived cloud characteristics and to the indirect criteria of electrical conditions computed on their basis are analyzed. The possibility to forecast thunderstorm based on different thermodynamic criteria is investigated. The high correlation was revealed between the total lightning current in the LF range and the lightning flash rate in the LF and VHF ranges. The total charge transferred by negative lightnings from this cloud to the ground is equal to 387 C; the average value of charge per one lightning is 0.44 C. Regression equations linking the radar criteria of lightnings and the lightning flash rate are presented. 相似文献