Variability of surface roughness and turbulence intensities at a coastal site in India   总被引：4，自引：0，他引：4  

Radhika Ramachandran  J. Winston Jeeva Prakash  K. Sen Gupta  K. Narayanan Nair  P. K. Kunhikrishnan 《Boundary-Layer Meteorology》1994,70(4):385-400

Surface-layer features with different prevailing wind directions for two distinct seasons (Southwest Monsoon and Northeast Monsoon) on the west coast of India are studied using data obtained from tower-based sensors at a site located about 500 m from the coast. Only daytime runs have been used for the present analysis. The surface boundary-layer fluxes have been estimated using the eddy correlation method. The surface roughnessz ₀ obtained using the stability-corrected wind profiles (Paulson, 1970) has been found to be low for the Southwest monsson season. For the other season,z ₀ is relatively high. The drag coefficientC _D varies with height in the NE monsoon season but not in the season with lowz ₀. This aspect is reflected in the wind profiles for the two seasons and is discussed in detail. The scaling behaviour of friction velocityu _* and the turbulence intensity of longitudinal, lateral and vertical winds _u, _v and _w, respectively) are further examined to study their dependence on fetch. Our study shows that for the non-dimensional case, _u/u_* and _v/u_* do not show any surface roughness dependence in either season. On the other hand, for _w/u_* for the season with lowz ₀, the values are seen to agree well with that of Panofskyet al. (1977) for homogeneous terrain whereas for the other season with highz ₀, the results seem to conform more to the values observed by Smedman and Högström (1983) for coastal terrain. The results are discussed in the light of observations by other investigators.  相似文献   

Atmospheric Surface-Layer Processes During the Total Solar Eclipse Of 11 August 1999     

Prakash M. Ramchandran  Radhika Ramchandran  K. Sen Gupta  S. M. Patil  P. N. Jadhav 《Boundary-Layer Meteorology》2002,104(3):445-461

The central path of the total solar eclipse (TSE) of 11 August 1999 mostly passedthrough a region of active monsoon in India, with the eclipse ending around localsunset. Measurements in the surface layer (SL) were carried out close to the eclipseaxis at Akola (20°42' N, 77°2' E) in central India. The globalradiation flux reaching the surface vanishes around totality at 1803:24 (LT), followedby a small recovery before again dipping to zero at sunset. The temperatures in the SL, and subsoil at 50-mm depth, show a local minimum with a lag of about 10 min after the second contact, whereas the lag appears to vanish when the temperature series is detrended. The SL exhibits near-neutral, though generally stable, conditions from about 1500 hr itself due to heavy cloud cover followed by the eclipse-induced cooling of the surface. The wind component across the eclipse axis vanishes at totality, the wind vector aligning with the azimuth of the traversing moon shadow. The deceleration of the mean flow can be due to the combined effect of the colder surface and downward heat flux, where the locally altered horizontal temperature gradients may cause, as in this instance, the cessation of the cross flow.The oscillations in temperature and wind that show significant peaks, around 90–100 min as well as the semi-period of the eclipse near 60 min, persist for several hours past the eclipse event. A fresh analysis of the published data on the TSE of 7 March 1970 shows spectral peaks in the temperature nearly coincident with those already reported from the surface pressure records. The oscillations in the SL fields during the two TSE events are very similar implying that the source mechanism is also likely to be the same in both the cases.  相似文献   

Short-Period Features of the Interplanetary Plasma and Their Evolution     

S.R. Prabhakaran Nayar  V. Sanalkumaran Nair  V.N. Radhika  K. Revathy 《Solar physics》2001,201(2):405-417

The solar wind plasma exhibits many features of the solar surface passed on to the interplanetary medium as temporal variations due to the solar rotation. The yearly average values of solar wind velocity, and geomagnetic index A _p during 1965–1999 were found to exhibit long period evolution. They were found to peak around the declining phase of each solar cycle. While the solar wind velocity peaks around the second half of the declining phase, the IMF field strength increases around the first half of the declining phase of each solar cycle. The power spectrum of these parameters shows peaks around 37-day, 30-day, 27-day, 13.5-day, 9-day, and 7-day periods. The temporal evolution of the power spectrum of the solar wind plasma parameters and the geomagnetic activity index A _p are also studied in detail and presented with the help of contour graphs. These studies indicate that the strength of the quasi-periodicities in the interplanetary medium evolves with time.  相似文献   

Generation of Vegetation Fraction and Surface Albedo Products Over India from Ocean Colour Monitor (OCM) Data Onboard Oceansat-2     

A. Senthil Kumar  T. Radhika  P.K. Saritha  V. Keerthi  R. N. Anjani  M. Suresh Kumar  K. S. Sekhar  P. Satyanarayana  M. S. Naga Sudha  M. V. R. Sesha Sai  V. K. Dadhwal 《Journal of the Indian Society of Remote Sensing》2014,42(4):701-709

The use of Local Area Coverage (LAC) data from Ocean Color Monitor (OCM) sensor of Oceansat-2 with its high radiometric resolution (12 bits/pixel) and 2-day repeat cycle for rapid monitoring of vegetation growth and estimating surface albedo for the Indian region is demonstrated in this study. For the vegetation monitoring, normalized difference vegetation index (NDVI) and vegetation fraction (VF) products were estimated by maximum value composite approach fortnightly and were resampled to 1 km. The surface albedo products were realized by converting narrow-band eight-band spectral reflectance OCM data to a) visible (300–700 nm) and b) broad band (300–3,000 nm) data. For validation, the derived products were compared with respective MODIS global products and found to be in good agreement.  相似文献   

Direct and Indirect Validation of Potential Fishing Zone Advisory off the Coast of Uttara Kannada,Karnataka     

Sanjeev P. Deshpande  K. V. Radhakrishnan  U. Gopalakrishna Bhat 《Journal of the Indian Society of Remote Sensing》2011,39(4):547-554

The technique of predicting Potential Fishing Zone using satellite derived sea surface temperature and chlorophyll is becoming an important aspect for the fishermen. In the present study an attempt has been made to compare fish density/catch per unit effort in the areas predicted by Satellite imagery and available to fishermen via electronic display boards at the fish landing centers of Uttara Kannada district, Karnataka with those of non predicted areas. Direct and Indirect validation was done. Direct method means comparing the catch using fishing vessels simultaneously in the notified region with that of catch from non notified region. And in indirect method by comparing catch data from landing centers on notified days with that of non notified days. Direct validation off Karwar showed that catch was significantly higher in notified (PFZ) area with high densities as compared to non notified (non PFZ) regions. When comparisons of landing center data of Karwar, Tadadi and Bhatkal are done it is evident that in all the centers during the period under study, higher catches were observed on notified days than non notified days except in Bhatkal centre in 2009–10. There by validating the accuracy of PFZ predictions and economic gains to fishermen.  相似文献   

Controlling NOx Emission of Crude Rice Bran Oil Blend for Sustainable Environment     

Subramani Saravanan  Govindan Nagarajan  Radhakrishnan Ramanujam  Santhanam Sampath 《洁净——土壤、空气、水》2011,39(6):515-521

The main objective of this work is to investigate the factors influencing the NOx control of a stationary diesel engine fuelled with crude rice bran oil blend with lesser effect on smoke density and brake thermal efficiency (BTE). Fuel injection timing, percentage of EGR, and fuel injection pressure are chosen as the factors for the objective and NOx emission, smoke density, and BTE are considered as the response variables. To critically analyze the effects of the chosen factors on the objective three levels were chosen in each factor and the experiments were designed by following the design of experiments method. Taguchi's L₉ orthogonal array was used to conduct the tests with different combination of factor levels. Through analysis of variance (ANOVA) method, the most influencing factors and also the significance of each factor affecting each response variable were found out. Response graph was drawn for each response variable to determine the optimum combination of factor levels in achieving the objective and the obtained combination was confirmed experimentally.  相似文献   

Low-frequency internal waves and their influence on transmission loss variability     

P. V. Hareesh Kumar  A. Raghunadha Rao  K. Anilkumar  M. Padmanabham  K. G. Radhakrishnan 《Natural Hazards》2011,57(3):643-656

Analysis of the time series data collected from a stationary location in the continental shelf of the southeastern Arabian Sea during different month indicated prominent internal wave (IW) activity. Time evolution of temperature, resolved using Morlet wavelet technique, revealed that maximum energy was concentrated in the diurnal band at the density interface, whereas within the interior of thermocline, the dominant energy concentration shifted to semi-diurnal band. Both these harmonics have maximum amplitude (>15 m) during the pre-monsoon and monsoon season when the water column was highly stratified (>0.05 kg/m⁴), but they were not discernable in the temperature record when the stratification was weak (i.e., especially during winter). An acoustic propagation model based on ray theory, Bellhop (http:/oalib.hlsresearch.com/modes/acoustictoolbox/at.zip) was utilized to compute the transmission loss (TL) associated with the passage of low-frequency IWs. The TL was computed using the model considering (1) range-dependent and range-independent environmental scenario and (2) for different source and receiver depth configurations. Intermittent fading of acoustic signals was observed in the presence of IW. It was also observed that fading of signals very much depends on the source–receiver configuration.  相似文献   

Influence of two different dietary zinc sources in freshwater prawn Macrobrachium rosenbergii post larvae     

Thirunavukkarasu  Muralisankar  Periyakali  Saravana Bhavan  Subramanian  Radhakrishnan  Perumal  Santhanam 《中国海洋湖沼学报》2019,37(1):290-299

Journal of Oceanology and Limnology - A feeding experiment was conducted to evaluate the effects of bulk zinc (B-Zn) and zinc nanoparticles (Zn-NPs) on survival, growth, compositions of amino acid...  相似文献   

John Bolton — astronomer extraordinary     

V. Radhakrishnan 《Journal of Astrophysics and Astronomy》1993,14(3-4):115-120

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The pulsar velocities and their binary origins (invited review)     

V. Radhakrishnan  C. S. Shukre 《Astrophysics and Space Science》1986,118(1-2):329-336

The observed proper-motions are shown to indicate that most pulsars come from binary systems. Due to a remarkable relationship between the speed of a pulsar and that of its progenitor in orbit, it is concluded that these binaries went through a common-envelope phase. This provides independent support to similar conclusions drawn from stellar evolution considerations.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.  相似文献