El Niño/Southern Oscillation (ENSO) Related Variations in Particulate Export Fluxes in the Western and Central Equatorial Pacific     

Hodaka Kawahata  Lallan Prasad Gupta 《Journal of Oceanography》2003,59(5):663-670

Time-series data from sediment trap moorings intermittently deployed during 1991–1999 show that the fluxes of biogenic material (carbonate, opal and organic matter, including amino acids) and other related parameters are temporally and spatially distinct across the Western Pacific Warm Pool (WPWP). These variations resulted from the El Niño and La Niña conditions, which alternately prevailed over the equatorial Pacific Ocean during the mooring deployments. The westernmost WPWP (a hemipelagic region) recorded relatively high average total mass and amino acid fluxes during the El Niño event. This was in sharp contrast to the eastern part of the WPWP (oligotrophic and weak upwelling regions) which recorded higher flux values during the La Niña event. Settling particulate organic matter was rich in labile components (amino acids) during La Niña throughout the study area. Relative molar ratios of aspartic acid to β-alanine together with relative molar content of non-protein amino acids β-alanine and γ-aminobutyric acid) suggested that organic matter degradation was more intense during La Niña relative to that during El Niño in the WPWP. This study clearly shows that during an El Niño event the well documented decrease in export flux in the easternmost equatorial Pacific is accompanied by a significant increase in export flux in the westernmost equatorial Pacific Ocean.  相似文献   

Cosmic ray synthesis of organic molecules in Titan's atmosphere     

Louis A. Capone  John Dubach  Robert C. Whitten  Sheo S. Prasad  Krishnamurthy Santhanam 《Icarus》1980,44(1):72-84

We have studied the possible synthesis of organic molecules by the absorption of galactic cosmic rays in an N₂CH₄H₂ Titan model atmosphere. The cosmic-ray-induced ionization results in peak electron densities of 2 × 10³ cm^?3, with NH₄⁺, C₃H₉⁺, and C₄H₉⁺ being among the important positive ions. Details of the ion and neutral chemistry relevant to the production of organic molecules are discussed. The potential importance of $\text{N}\text{(}{}^2\text{D)}$ reactions with CH₄ and H₂ is also demonstrated. Although the integrated production rate of organic matter due to the absorption of the cosmic ray cascade is much less than that by solar ultraviolet radiation, the production of nitrogen-bearing organic molecules by cosmic rays may be greater.  相似文献   

Active, weak and break spells in the Indian summer monsoon     

V. S. Prasad  T. Hayashi 《Meteorology and Atmospheric Physics》2007,95(1-2):53-61

Summary Active weak and break phases of the Indian summer monsoon for the period 1958–2002 are studied using ERA-40 data. The criteria for identifying the break are proposed and tested using the 850 hPa level horizontal wind shear. Independent datasets such as All-India Rainfall, NOAA Outgoing Long-wave Radiation and CMAP rainfall datasets are used for the verification of the proposed criteria. On leave from the National Center for Medium Range Weather Forecasting, A-50 Institutional Area, Phase-II, Sector 62, Noida, U.P., India.  相似文献   

Surface and upper air meteorological features during onset phase of 2003 monsoon     

O. P. Singh  H. R. Hatwar  Onkari Prasad 《Journal of Earth System Science》2007,116(4):305-310

The second campaign of the Arabian Sea Monsoon Experiment (ARMEX-II) was conducted in two phases viz., March–April and May–June 2003. In the present work, the buoy and ocean research vessel data collected during the second phase of ARMEX-II have been analysed to bring out the characteristic features of monsoon onset. The results have shown that the thermodynamical features such as build up of lower tropospheric instability and increased height of zero degree isotherm occurred about a week before the monsoon onset over Kerala and adjoining southeast Arabian Sea. There was a sharp fall in the temperature difference between 850 and 500 hPa, and the height of zero degree isotherm about 2–3 days before the monsoon onset. The flux of sensible heat was positive (sea to air) over south Arabian Sea during the onset phase. Over the Bay of Bengal higher negative (air to sea) values of sensible flux prevailed before the monsoon onset which became less negative with the advance of monsoon over that region. The pre-onset period was characterized by large sea surface temperature (SST) gradient over the Arabian Sea with rapid decrease towards north of the warm pool region. The buoy observations have shown that SST remained close to 30.5°C in the warm pool region during the pre-onset period in 2003 but only 2–3 degrees away (north of this region) SSTs were as low as 28.5–29°C. An interesting aspect of sea level pressure (SLP) variability over the Indian seas during the onset phase of summer monsoon 2003 was undoubtedly, the highest SLP in the warm pool region inspite of very high SSTs.  相似文献   

Statistical Methods for Spatial Data Analysis     

V. K. Prasad 《The Photogrammetric Record》2006,21(116):414-415

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Crop yield estimation model for Iowa using remote sensing and surface parameters     

Anup K. Prasad  Lim Chai  Ramesh P. Singh  Menas Kafatos 《International Journal of Applied Earth Observation and Geoinformation》2006

Numerous efforts have been made to develop various indices using remote sensing data such as normalized difference vegetation index (NDVI), vegetation condition index (VCI) and temperature condition index (TCI) for mapping and monitoring of drought and assessment of vegetation health and productivity. NDVI, soil moisture, surface temperature and rainfall are valuable sources of information for the estimation and prediction of crop conditions. In the present paper, we have considered NDVI, soil moisture, surface temperature and rainfall data of Iowa state, US, for 19 years for crop yield assessment and prediction using piecewise linear regression method with breakpoint. Crop production environment consists of inherent sources of heterogeneity and their non-linear behavior. A non-linear Quasi-Newton multi-variate optimization method is utilized, which reasonably minimizes inconsistency and errors in yield prediction.  相似文献   

Impact of a consistent height reassignment method for INSAT derived cloud motion vectors     

V. S. Prasad  K. J. Ramesh  A. K. Bohra  Sant Prasad 《Meteorology and Atmospheric Physics》2003,83(3-4):163-172

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Geomorphic characterization and diversity of the fluvial systems of the Gangetic Plains   总被引：2，自引：0，他引：2  

R. Sinha  Vikrant Jain  G. Prasad Babu  S. Ghosh 《Geomorphology》2005,70(3-4):207

The extensive Gangetic alluvial plains are drained by rivers which differ strongly in terms of hydrological and sediment transport characteristics. These differences are manifested in the geomorphic diversity of the plains. The Western Gangetic Plains (WGP) are marked by a degradational topography with incised channels and extensive badland development in some parts, while the Eastern Gangetic Plains (EGP) are characterized by shallow, aggrading channels with frequent avulsions and extensive flooding. We interpret such geomorphic diversity in terms of differences in stream power and sediment supply from the catchment areas. The rivers draining the western plains are marked by higher stream power and lower sediment yield that result in degradation. In comparison, the rivers draining the eastern Gangetic Plains have lower stream power and higher sediment yield that result in aggradation. The variation of stream power, a function of channel slope and high sediment yield, is attributed to differences in rainfall and rate of uplift in the hinterland. It is suggested that such differences have resulted in a marked geomorphic diversity across the plains. It is also suggested that such diversity has existed for a fairly long time because of climatic and tectonic variance.  相似文献   

Variability of aerosol optical depth over indian subcontinent using modis data     

Anup K. Prasad  Ramesh P. Singh  Ashbindu Singh 《Journal of the Indian Society of Remote Sensing》2004,32(4):313-316

High AOD is observed over the Ganga basin throughout the year unlike southern India, is alarming as this basin is one of the most productive basins of Indian subcontinent having population of more than 460 million. AOD is found to be increasing rapidly since 2000 in summer season that may cause adverse effect to the agricultural crops and also to the human health. Increased aerosol loading may likely affect the rainfall which is responsible for the observed drought conditions over the Indian subcontinent. Detailed analysis of AOD, crop yields and rainfall data are required to understand the impact of increasing aerosol loading over the Indian subcontinent.  相似文献   

Sea State Hindcast with ECMWF Data Using a Spectral Wave Model for Typical Monsoon Months     

B. Prasad Kumar  Ruchi Kalra  S. K. Dube  P. C. Sinha  A. D. Rao 《Natural Hazards》2004,31(2):537-548

A third generation wave prediction model (WAM) suitably modified for the Indianseas was used to simulate the sea state during typical monsoon months of July 1987,88 and 89. During July 1987, small-scale disturbances over the Arabian Sea and theBay of Bengal as reported from earlier works were noticed in the wave hindcast. Thegridded monthly averaged wave heights for the above periods were compared with theGEOSAT altimeter data. A comparison between model computed wave parameters andavailable ship observations was also carried out for July 1987, 88 and 89.The modelwas run with ECMWF analyzed wind field for a period of one month. The comparisonshowed that the wave heights from the model matches with those from GEOSATAltimeter and ships of opportunity.  相似文献