DOAS observations of formaldehyde and its impact on the HO<Subscript>x</Subscript> balance in the tropical Atlantic marine boundary layer     

Anoop S. Mahajan  Lisa K. Whalley  Elena Kozlova  Hilke Oetjen  Luis Mendez  Kate L. Furneaux  Andrew Goddard  Dwayne E. Heard  John M. C. Plane  Alfonso Saiz-Lopez 《Journal of Atmospheric Chemistry》2010,66(3):167-178

Measurements of formaldehyde (HCHO) were made at the Cape Verde Atmospheric Observatory between November 2006 and June 2007 using the Long-Path Differential Optical Absorption Spectroscopy (LP-DOAS) technique. Observations show that typical HCHO mixing ratios ranged between 350 and 550 pptv (with typical 2-σ uncertainties of ~110 pptv), with several events of high HCHO, the maximum being 1,885?±?149 pptv. The observations indicate a lack of strong seasonal or diurnal variations, within the uncertainty of the measurements. A box model is employed to test whether the observations can be explained using known hydrocarbon photochemistry; the model replicates well the typical diurnal profile and monthly mean values. The model results indicate that on average 20% of HO₂ production and 10% of OH destruction can be attributed to the mean HCHO levels, suggesting that even at these low average mixing ratios HCHO plays an important role in determining the HO_x (HO₂+OH) balance of the remote marine boundary layer.  相似文献   

Magnetic mineralogical variability along Deccan trap basalt borehole (KBH07), Koyna deep continental drilling program,western Maharashtra,India     

S. J. Sangode  M. Venkateshwarulu  Rasika Mahajan  Vinay Randive 《Journal of the Geological Society of India》2017,90(6):769-775

A 1248 m long core (KBH 07, 17°18′07″ N; 73°47′28.2″E, 960m above msl) drilled up to basement in the Deccan traps from Koyna region was sampled at ～10m interval for magnetic mineralogical studies.Analysis of routine rock magnetic parameters (mass specific magnetic susceptibility: χ_lf, frequency dependence of susceptibility: χ_fd, susceptibility of anhysteretic remanance: χ_ARM, saturation isothermal remanance: SIRM, remanance coercivty: B_(0)CR, Soft_IRM, Hard_IRM, S-Ratio, SIRM/χ_lf, χ_ARM/χ_lf) and density (σ, gm/cc) depicted significant higher order temporal variation. The χ_lf varies between 13 and 309 x 10-8m3/kg and is independent of density variation. The χ_ARM, B_(0)CR and S-Ratios indicate majority of SD-PSD ferrimagnets with episodes of MD ferrimagnetic concentration and few hard coercivity components. The giant plagioclase lath bearing (GPB) horizons show highest variability of ferrimagnetic concentration marked by anomalous peaks. Overall the variability of rock magnetic parameters independent of lava flow units suggest that the changeover in magnetic mineral concentration, composition and domain size occur at major episodes in magma composition (e.g., primary source, crustal contamination and fractional crystallization). The studied parameters are therefore examined to mark intervals of (i) magma compositional changes, (ii) zones of oxidative conditions and (iii) rapid/slow cooling intervals demanding detailed petrologic studies. We identified one I order trend, four II order cycles and eight III order cycles for the purpose of correlation. Notable peak in χ_lf at 650–700m, the changeover in rock magnetic parameters at ～930 m and ～280 m can facilitate marker intervals while several higher order variations can be adopted for high resolution correlation to other boreholes in the region. The complex variation in rock magnetic parameters independent of flow units reflect temporal magnitudes of compositional variability, cooling and emplacement history that needs detailed petro-mineralogical attempts; and the present data is useful for high order inter-core correlations under the deep drilling program.  相似文献   

Statistical significance of trends in monthly heavy precipitation over the US     

Salil Mahajan  Gerald R. North  R. Saravanan  Marc G. Genton 《Climate Dynamics》2012,38(7-8):1375-1387

Trends in monthly heavy precipitation, defined by a return period of one year, are assessed for statistical significance in observations and Global Climate Model (GCM) simulations over the contiguous United States using Monte Carlo non-parametric and parametric bootstrapping techniques. The results from the two Monte Carlo approaches are found to be similar to each other, and also to the traditional non-parametric Kendall’s τ test, implying the robustness of the approach. Two different observational data-sets are employed to test for trends in monthly heavy precipitation and are found to exhibit consistent results. Both data-sets demonstrate upward trends, one of which is found to be statistically significant at the 95% confidence level. Upward trends similar to observations are observed in some climate model simulations of the twentieth century, but their statistical significance is marginal. For projections of the twenty-first century, a statistically significant upwards trend is observed in most of the climate models analyzed. The change in the simulated precipitation variance appears to be more important in the twenty-first century projections than changes in the mean precipitation. Stochastic fluctuations of the climate-system are found to be dominate monthly heavy precipitation as some GCM simulations show a downwards trend even in the twenty-first century projections when the greenhouse gas forcings are strong.  相似文献   

NEHRP soil classification and estimation of 1-D site effect of Dehradun fan deposits using shear wave velocity     

A.K. Mahajan   《Engineering Geology》2009,104(3-4):232-240

Shear wave velocity of the near surface soil at nearly 50 sites in the sub Himalayan mountain exit covering Doon fan deposits, was determined using Multi-channel Analysis of Surface Waves (MASW), a seismic reflection technique. Based on the average shear wave velocity of the upper 30 m soil column, sites in the Dehradun fan are predominantly classified as class ‘D’ (180–360 m/s). Similarly, sites located on the northwestern, eastern and southeastern sides of the fan deposit have shear wave velocities (in the upper 30 m soil) greater than 360 m/s, thereby classifying them as class ‘C’ (360–760 m/s) in accordance with NEHRP provisions. Some of the sites towards the southwestern side of the fan deposits had average shear wave velocities less than 180 m/s and could be classified as soil class ‘E’. One dimensional site effects, including amplification and dynamic period were calculated for the majority of the sites. However, some of the representative suite of sites across the north–south profile of Dehradun fan has been discussed here. Although the attenuation is greater on the southwestern side of the Dehradun fan deposits (i.e. thicker, low velocity sediments) and the sites had been classified as class ‘D’ and ‘E’ but the site amplification tends to be greater in the northern and northwestern part of the city due to large impedance contrast with in the near surface soils.  相似文献   

GIS application to determine the effect of topography on landuse in Ashwani Khad watershed     

Sudhir Mahajan  Pankaj Panwar  Deepak Kaundal 《Journal of the Indian Society of Remote Sensing》2001,29(4):243-248

The landuse status of Ashwani Khad watershed has been obtained using 1RS-ID satellite data for 1999 and further topographic analysis has been carried out using GIS software-ARC/ INFO and ARCVIEW. It has been found that of the total geographical area (85.30 sq. km) of the Ashwani Khad watershed which lies between 30°50′ to 31°N latitude and 77°05′ to 77° 15′E longitude in Himachal Pradesh, 54.53 % constituted wasteland, 33.55% agriculture and least 11.92 % forest. The altitude, aspect and slope have exhibited marked effect on land utilization. Agriculture and wasteland have been found maximum in mid altitude (1300-1500 m) and moderate slopes (13.2-26.4 degree), whereas, agriculture and forest have been maximum in flat and north aspect.  相似文献   

Proper depiction of monsoon depression through IRS-P4 MSMR     

P. N. Mahajan  R. M. Khaladkar  S. G. Narkhedkar  Sathy Nair  P. C. Joshi  P. K. Pal 《Journal of Earth System Science》2004,113(2):223-233

In this paper, daily variations of satellite-derived geophysical parameters such as integrated water vapour (IWV), cloud liquid water content (CLW), sea surface temperature (SST) and sea surface wind speed (SSW) have been studied for a case of monsoon depression that formed over the Bay of Bengal during 19th-24th August 2000. For this purpose, IRS P4 MSMR satellite data have been utilized over the domain equator — 25‡N and 40‡-100‡E. An integrated approach of satellite data obtained from IRS-P4, METEOSAT-5 and INSAT was made for getting a signal for the development of monsoon depression over the Indian region. Variations in deep convective activity obtained through visible, infrared and OLR data at 06 UTC was thoroughly analyzed for the complete life cycle of monsoon depression. Geophysical parameters obtained through IRS-P4 satellite data were compared with vorticity, convergence and divergence at 850 and 200 hPa levels generated through cloud motion vectors (CMVs) and water vapour wind vectors (WVWVs) obtained from METEOSAT-5 satellite. This comparison was made for finding proper consistency of geophysical parameters with dynamical aspects of major convective activity of the depression. From the results of this study it is revealed that there was strengthening of sea surface winds to the south of low-pressure area prior to the formation of depression. This indicated the possibility of increase in cyclonic vorticity in the lower troposphere. Hence, wind field at 850 hPa with satellite input of CMVs in objective analysis of wind field using optimum interpolation (OI) scheme was computed. Maximum cyclonic vorticity field at 850 hPa was obtained in the region of depression just one day before its formation. Similarly, with the same procedure maximum anticyclonic vorticity was observed at 200 hPa with WVWVs input. Consistent convergence and divergence at 850 and 200 hPa was noticed with respect to these vorticities. In association with these developments, we could get lowest values of OLR (120 W/m² ) associated with major convective activity that was consistent with the maximum values of integrated water vapour (6-8gm/cm²) and cloud liquid water content (50-60 mg/cm² ) persisting particularly in the southwest sector of the monsoon depression.  相似文献   

Land use changes in ashwani khad watershed using GIS techniques     

Sudhir Mahajan  Pankaj Panwar 《Journal of the Indian Society of Remote Sensing》2005,33(2):227-232

  相似文献   

SATELLITE-OBSERVED RADIATIVE ENERGY BUDGET DURING ONSET PHASE OF SUMMER MONSOON     

P.N. Mahajan  G.R. Chinthalu  S. Rajamani 《热带气象学报(英文版)》1997,3(2):215-224

In this paper satellite-derived radiative energy budget such as shortwave radiative heating,longwaveradiative heating and net radiation balance have been studied for the onset phase of summer monsoon1979. Since cloud play an important role in determining diabatic heating field as well as being a reflectionof status of the monsoon itself, the day to day evolution of clouds from TIROS-N satellite has beenmade. Satellite-derived radiative heating rates from surface to 100 hPa were computed for each 100 hPathickness layer. These heating rates were then compared with the observed latitudinal distribution of total radintive heating rates over the domain of the study. From the results of our study it was found thatthe characteristic features such as net radiative heating rates of the order of 0.2℃/day at upper tropospheric level(100-200 hPa)and cooling throughout the lower tropospheric layers with relatively lesscooling between 500-700 hPa layer observed.in a case of satellitexierived radiative energy budget agreewell with the characteristic features of observational radiative energy budget over the domain of thestudy. Therefore, it is suggested that radiative energy budget derived from satellite observati0ns be usedwith great potential and confidence for the evolution of complete life cycle of monsoon over the Indianregion for different years.  相似文献   

Viscous effects on penetrating shafts in clays     

Sandeep P. Mahajan  Muniram Budhu 《Acta Geotechnica》2006,1(3):157-165

The penetration of rigid objects such as piles and penetrometers into soils creates a zone of soil disturbance around them. The extent of this disturbed zone influences the resistance of the moving rigid body. This paper presents a theoretical framework to analyze the resistance in the disturbed zone created by a shaft penetrating a clay soil. The soil is modeled as a viscous material after it reaches failure [critical state (CS)]. The results of this analysis show that the viscous drag stress component on the shaft surface is influenced by the size of disturbed zone that has reached CS around the shaft, the shear viscosity of the soil and the velocity profile (or strain rate) in the CS zone around the shaft. The size of CS zone, the velocity profile and the viscosity of soil are interdependent. Large variation in viscous drag occurs when the size of the CS soil zone is less than four times the shaft’s radius. Limiting drag occurs when the size of the CS soil zone exceeds six times the shaft’s radius. The theoretical velocity distribution of the movement of soil in the CS zone shows that the soil is dragged along with shaft in the near field (close to the shaft surface) and moves upwards in the far field.  相似文献   

Ultraviolet Photoprocessing of Interstellar Dust Mantles as a Source of Polycyclic Aromatic Hydrocarbons and Other Conjugated Molecules     

Greenberg JM  Gillette JS  Muñoz Caro GM  Mahajan TB  Zare RN  Li A  Schutte WA  de Groot M  Mendoza-Gómez C 《The Astrophysical journal》2000,531(1):L71-L73

By co-depositing a gas mixture of simple carbon- and nitrogen-containing molecules with water on a 10 K surface and exposing it to ultraviolet radiation, we were able to form a residue. This residue was then placed aboard the EURECA satellite behind a magnesium fluoride window and exposed to solar radiation for 4 months before it was returned and analyzed. The resulting residue is believed to simulate the photoprocessing of organic dust mantles in the interstellar medium. Mass spectrometry indicated that the photoprocessing created a rich mixture of polycyclic aromatic hydrocarbons (PAHs) and other conjugated organic molecules, which may explain how PAHs are replenished in space.  相似文献