Observation based analysis of the growth of MJO time scale from its nonlinear scale interactions with the synoptic scales     

D. R. Chakraborty 《Meteorology and Atmospheric Physics》2005,89(1-4):87-103

Summary The present paper addressed the issue of growth of planetary boundary-layer fluxes on the time scale of MJO based on ECMWF reanalysis daily data of 180 days covering April–September, 2001. Diagnostic analysis of this data set utilises computations of moisture and sensible heat fluxes in the frequency domain which involve nonlinear interactions phenomena of MJO time scale with the synoptic scales. Basically the whole computations performed are based on surface similarity theory and Richardson number dependent K-theory in the surface and planetary boundary layer (PBL), respectively, both invoke triple product nonlinearilies. Present observational study shows that among the totality of the triads participating in phase-locking phenomena, a prominent band of those reside in the MJO time scales (30 to 60 days) and the synoptic time scales (3 to 7 days). The study suggests that the low frequency variability on MJO time scale in moisture and sensible heat flux arises from its nonlinear interactions with synoptic time scales. The results show that the phases of the three interacting oscillations associated with specific humidity/SST, Richardson number dependent instability factor and wind shear are positive and reasonably close to each other. The amplitudes of the synoptic scale oscillations are not insignificant compared to that of MJO. These dynamical aspects regarding the phases and amplitudes of the three participating oscillations favour the nonlinear interactions of MJO to the synoptic scales and thus lead to rapid exchange of energy transfer to the former.Visiting scientist from Indian Institute of Tropical Meteorology, Pune-411008, India.  相似文献   

Numerical Simulation of Andhra Severe Cyclone (2003): Model Sensitivity to the Boundary Layer and Convection Parameterization   总被引：1，自引：0，他引：1  

C. V. Srinivas  R. Venkatesan  D. V. Bhaskar Rao  D. Hari Prasad 《Pure and Applied Geophysics》2007,164(8-9):1465-1487

The Andhra severe cyclonic storm (2003) is simulated to study its evolution, structure, intensity and movement using the Penn State/NCAR non-hydrostatic mesoscale atmospheric model MM5. The model is used with three interactive nested domains at 81, 27 and 9 km resolutions covering the Bay of Bengal and adjoining Indian Peninsula. The performance of the Planetary Boundary Layer (PBL) and convective parameterization on the simulated features of the cyclone is studied by conducting sensitivity experiments. Results indicate that while the boundary layer processes play a significant role in determining both the intensity and movement, the convective processes especially control the movement of the model storm. The Mellor-Yamada scheme is found to yield the most intensive cyclone. While the combination of Mellor-Yamada (MY) PBL and Kain-Fritsch 2 (KF2) convection schemes gives the most intensive storm, the MRF PBL with KF2 convection scheme produces the best simulation in terms of intensity and track. Results of the simulation with the combination of MRF scheme for PBL and KF2 for convection show the evolution and major features of a mature tropical storm. The model has very nearly simulated the intensity of the storm though slightly overpredicted. Simulated core vertical temperature structure, winds at different heights, vertical winds in and around the core, vorticity and divergence fields at the lower and upper levels—all support the characteristics of a mature storm. The model storm has moved towards the west of the observed track during the development phase although the location of the storm in the initial and final phases agreed with the observations. The simulated rainfall distribution associated with the storm agreed reasonably with observations.  相似文献   

Land use indicators of a watershed in arid region, western Rajasthan using Remote Sensing and GIS     

Debashis Chakraborty  Dibyendu Dutta  H Chandrasekharan 《Journal of the Indian Society of Remote Sensing》2001,29(3):115-128

The vegetation dynamics and land use/land cover types of Birantiya Kalan watershed located in the arid tracts of western Rajasthan have been characterized and evaluated using Remote Sensing and Geographical Information System (GIS). The watershed under study falls in the transitional plain of Luni Basin and is characterized by Aravali ranges in the eastern half and vast alluvial plains in the west. The land use/land cover types, as identified are cropland, fallow, forest, land with scrub, land without scrub, sandy area and the water body. Land with scrub occupied maximum area (39% area of the watershed) in 1996 in place of crop land which was dominant (43% of total area) in the year 1988. During eight years period, seasonal fallow land increased significantly and the areal extent of water body decreased to almost half. Vegetation vigour types have been classified into very poor, poor. moderate, good and very good categories. Moderate vigour type reduced from 62 to 27% and poor type increased from 34 to 68% during the period 1988 to 1996. Other vegetation vigour types have not shown any significant changes. To quantify the changes over the years in both vegetation and land use/land cover, weightages have been given to each type and composite values of both vegetation vigour and land use types for 1996 and 1988 have been calculated. It has been observed that the ratio for vegetation vigour has been found to be 0.85 showing that the overall vegetation have not improved after the treatment. The ratio for land use is found to be 1.01, which indicates negligible change in land use.  相似文献   

Irrigation command area inventory and assessment of water requirement using IRS-1B satellite data     

V Hari Prasad  A K Chakraborti  T R Nayak 《Journal of the Indian Society of Remote Sensing》1996,24(2):85-96

Monitoring the crop acreage and irrigation water requirements vis-a-vis irrigation water supplies is important to obtain a realistic view of the “irrigation potential” and “potential utilised”. Satellite data provides information on crop area and thereby net irrigation water requirements of crops. A pilot study was taken up in Mahendragarh distributary canal in Haryana State to estimate net irrigation water requirement of crops under 17 minors for kharif and rabi seasons of 1992–93 period using IRS-1B satellite geocoded FCC images. These water requirements, when analysed with canal and tubewell water supplies for crops, show largescale deficiencies in the irrigation command area.  相似文献   

On the vibrations of a composite orthotropic cylinder placed in a magnetic field     

Hari Sankar Chakraborty 《Pure and Applied Geophysics》1969,76(1):71-78

Summary The problems of radial vibration of a composite orthotropic cylinder subjected to a uniform axial magnetic field forms the chief interest of the paper.  相似文献   

Crustal structure of the Indian subcontinent     

Hari Narain 《Tectonophysics》1973,20(1-4):249-260

Studies carried out by various investigators up to 1971 to delineate the Indian crustal structure using body wave travel times, surface wave dispersion and gravity methods are summarised and reviewed. The average crustal thickness is found to be 35–40 km in the Indian peninsular shield, 30–35 km in the Indo Gangetic plains and 60–80 km in the Himalayas and the Tibetan plateau region. The limitations of the various methods used and the errors in the estimation of crustal thickness by them are discussed. As no deep refraction work for crustal studies has been carried out so far in India, this topic is not covered in this study.  相似文献   

Improved seasonal climate forecasts for the Caribbean region using the Florida State University Synthetic Superensemble     

R. S. Ross  A. Chakraborty  A. Chen  L. Stefanova  S. Sirdas  T. N. Krishnamurti 《Meteorology and Atmospheric Physics》2007,98(3-4):137-174

Summary Climate variations in the Caribbean, largely manifest in rainfall activity, have important consequences for the large-scale water budget, natural vegetation, and land use in the region. The wet and dry seasons will be defined, and the important roles played by the El Ni?o-Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO) in modulating the rainfall during these seasons will be discussed. The seasonal climate forecasts in this paper are made by 13 state of the art coupled atmosphere-ocean general circulation models (CGCMs) and by the Florida State University Synthetic Superensemble (FSUSSE), whose forecasts are obtained by a weighted combination of the individual CGCM forecasts based on a training period. The success of the models in simulating the observed 1989–2001 climatology of the various forecast parameters will be examined and linked to the models’ success in predicting the seasonal climate for individual years. Seasonal forecasts will be examined for precipitation, sea-surface temperature (SST), 2-meter air temperature, and 850 hPa u- and v-wind components during the period 1989–2001. Evaluation metrics include root mean square (RMS) error and Brier skill score. It will be shown that the FSUSSE is superior to the individual CGCMs and their ensemble mean both in simulating the 1989–2001 climatology for the various parameters and in predicting the seasonal climate of the various parameters for individual years. The seasonal climate forecasts of the FSUSSE and of the ensemble mean of the 13 state of the art CGCMs will be evaluated for years (during the period 1989–2001) that have particular ENSO and NAO signals that are known to influence Caribbean weather, particularly the rainfall. It will be shown that the FSUSSE provides superior forecasts of rainfall, SST, 2-meter air temperature, and 850 hPa u- and v-wind components during dry summers that are modulated by negative SOI and/or positive NAO indices. Such summers have become a feature of a twenty-year pattern of drought in the Caribbean region. The results presented in this paper will show that the FSUSSE is a valuable tool for forecasting rainfall and other atmospheric and oceanic variables during such periods of drought.  相似文献   

Micrometeorological Observations of a Microburst in Southern Finland     

Leena Järvi  Ari-Juhani Punkka  David M. Schultz  Tuukka Petäjä  Harri Hohti  Janne Rinne  Toivo Pohja  Markku Kulmala  Pertti Hari  Timo Vesala 《Boundary-Layer Meteorology》2007,125(2):343-359

On the afternoon of 3 July 2004 in Hyytiälä (Juupajoki, Finland), convective cells produced a strong downburst causing forest damage. The SMEAR II field station, situated near the damage site, enabled a unique micrometeorological analysis of a microburst with differences above and inside the canopy. At the time of the event, a squall line associated with a cold front was crossing Hyytiälä with a reflectivity maximum in the middle of the squall line. A bow echo, rear-inflow notch, and probable mesovortex were observed in radar data. The bow echo moved west-north-west, and its apex travelled just north of Hyytiälä. The turbulence data were analysed at two locations above the forest canopy and at one location at sub-canopy. At 1412 EET (Eastern European Time, UTC+2), the horizontal and vertical wind speed increased and the wind veered, reflecting the arrival of a gust front. At the same time, the carbon dioxide concentration increased due to turbulent mixing, the temperature decreased due to cold air flow from aloft and aerosol particle concentration decreased due to rain scavenging. An increase in the number concentration of ultra-fine particles (< 10 nm) was detected, supporting the new particle formation either from cloud outflow or due to rain. Five minutes after the gust front (1417 EET), strong horizontal and downward vertical wind speed gusts occurred with maxima of 22 and 15 m s^?1, respectively, reflecting the microburst. The turbulence spectra before, during and after the event were consistent with traditional turbulence spectral theory.  相似文献   

Mildly alkaline basalts from Pavagadh Hill, India: Deccan flood basalts with an asthenospheric origin     

J. D. Greenough  K. R. Hari  A. C. Chatterjee  M. Santosh 《Mineralogy and Petrology》1998,62(3-4):223-245

Summary Of twelve flows at Pavagadh Hill, the two three-phenocryst-basalt flows with Mg#0.70 and Ni/MgO33 are the most primitive and perhaps as primitive as any basalts in the Deccan province. Scatter on variation diagrams and the occurrence of primitive flows at two different levels in the volcanic sequence implies that most rocks are probably not, strictly speaking, comagmatic. Nevertheless, mass balance calculations indicate a generalized differentiation scheme from primitive basalt to hawaiite that involved removal of olivine, augite, plagioclase and Fe-Ti oxides in the proportions 40:33:22:5 with 50% of the magma remaining. Crustal assimilation had a minimal effect on evolution of the basalts but rhyolites at the top of the volcanic sequence may have been produced by crustal melting following prolonged heat release from alkali basalt pooled along fault zones in the continental crust. Major element based calculations indicate that the most primitive basalts were generated by 7 to 10% melting of mantle peridotite. These low percentages of melting, typical of alkali basalts, are consistent with the steep slopes on chondrite-normalized REE diagrams. Low heavy REE concentrations point to residual garnet in the source region. Incompatible element concentrations (e.g. Rb, Ba, Zr, La) in Pavagadh basalts exceed those in Deccan tholeiitic basalts but are substantially lower than those reported for some other Deccan alkali basalts. Obviously Pavagadh basalts do not reflect the lowest percentages of melting and greatest amount of source region metasomatic enrichment attained in the Deccan province. Deccan tholeiitic and alkali basalts are largely characterized by low La/Nb ratios and high La/Ba ratios similar to those in oceanic island basalts. This indicates minimal involvement of the subcontinental lithospheric mantle in their petrogenesis. Comparison with continental mafic magma provinces where a subcontinental lithospheric mantle imprint is common indicates long periods of extension and/or melting of mantle lithosphere still hot from pre-extension subduction are more likely to produce magmas bearing the lithospheric imprint.

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Alkalische Basalte von Pavagadh Hill, Indien: Deccan-Flutbasalte von Astenosphärischer Herkunft

Zusammenfassung Im Gebiet von Pavagadh Hill, Indien, treten 12 Spät-Deccan und rhyolithische alkalibasaltische Ergüsse und Intrusiva auf. Variationsdiagramme zeigen, daß die Abfolge nicht komagmatisch ist. Zusammen mit Berechnungen der Massenbilanz unterstützen sie vielmehr ein Zwei-Stadienmodell für die Entstehung von Hawaiiten aus sehr primitiven (i.e. Mg#=Mg/(Mg+.(0.9*Fe_totat)) at.%0.70) Basalten. Olivin und Augit dominierten die frühe Fraktionierung während Augit vorherrschte als der Magmaanteil von 65% auf 50% sank. Die Entfernung von Plagioklas spielte bei der Differentiation nur eine geringe Rolle. Niedrige Th/Nb (0,2), Rb/Sr(<0,12) und K/NbVerhältnisse geben keine Hinweise auf signifikante Assimilation von Krustenmaterial. Die Seltene-Erd-Verteilungsmuster (SEE), niedrige Gehalte an schweren SEE sowie die Hauptelementspektren der Alkalibasalte weisen auf eine granatführende Ursprungsregion und auf einen Aufschmelzungsgrad von nur 7% bis 10% hin. Es gibt jedoch auch stärker alkalische (höhere Rb, Zr etc.) Deccanbasalte (i.e. Rajpipla). Die Assoziation von Deccanalkalibasalten, Rhyolithen und Störungszonen zeigt, daß letztere die Extraktion von Magma aus dem Mantel erleichterten und dazu führten, daß Magma aus Magmenkammern Krustenschmelzen (Rhyolithe) produzierte. Deccanbasalte tendieren zu hohen La/Ba und niedrigen La/Nb-Verhältnissen; dies weist auf eine asthenosphärische Herkunft hin, selbst wenn die Gesteine verhältnismäßig spät gebildet wurden (i.e. Pavagadh). Längere Perioden von Krustenextension oder von Subduktion, die der Extension vorhergeht, führt offensichtlich zur Entstehung von Magmen mit einer lithosphärischen Komponente.

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Cation diffusion in aluminosilicate garnets: experimental determination in pyrope-almandine diffusion couples     

Jibamitra Ganguly  Weiji Cheng  Sumit Chakraborty 《Contributions to Mineralogy and Petrology》1998,131(2-3):171-180

Diffusion couples made from homogeneous gem quality natural pyrope and almandine garnets were annealed within graphite capsules under anhydrous conditions at 22–40 kbar, 1057–1400 °C in a piston-cylinder apparatus. The concentration profiles that developed in each couple were modeled to retrieve the self diffusion coefficients [D(I)] of the divalent cations Fe, Mg, Mn and Ca. Because of their usually low concentrations and lack of sufficient compositional change across the interface of the diffusion couples, only a few reliable data can be obtained for D(Ca) and D(Mn) from these experiments. However, nine sets of D(Fe) and D(Mg) data were retrieved in the above P-T range, and cast in the form of Arrhenian relation, D=D ₀exp{−[Q(1 bar)+PΔV ⁺]/RT}. The values of the activation energy (Q) and activation volume (ΔV ⁺) depend on whether f _O2 is constrained by graphite in the system C-O or held constant. For the first case, we have for Fe:Q(1 bar)=65,532±10,111 cal/mol, D ₀=3.50 (±2.30)×10⁻⁵ cm²/s, ΔV ⁺=5.6(±2.9) cm³/mol, and for Mg:Q(1 bar)=60,760±8,257 cal/mol, D ₀=4.66 (±2.48)×10⁻⁵ cm²/s, ΔV ⁺=5.3(±3.0) cm³/mol. Here the ΔV ⁺ values have been taken from Chakraborty and Ganguly (1992). For the condition of constant f _O2, the Q values are ∼9 kcal lower and ΔV ⁺ values are ∼4.9 cm³/mol larger than the above values. Lower temperature extrapolation of the Arrhenian relation for D(Mg) is in good agreement with the Mg tracer diffusion data (D ^* _Mg) of Chakraborty and Rubie (1996) and Cygan and Lasaga (1985) at 1 bar, 750–900 °C, when all data are normalized to the same pressure and to f _O2 defined by graphite in the system C-O. The D ^* _Mg data of Schwandt et al. (1995), on the other hand, are lower by more than an order of magnitude than the low temperature extrapolation of the present data, when all data are normalized to the same pressure and to f _O2 defined by the graphite buffer. Comparison of the D(Fe), D(Mg) and D(Mn) data in the pyrope-almandine diffusion couple with those in the spessartine-almandine diffusion couple of Chakraborty and Ganguly (1992) shows that the self diffusion of Fe and Mn are significantly enhanced with the increase in Mn/Mg ratio; the enhancement effect on D(Mg) is, however, relatively small. Proper application of the self diffusion data to calculate interdiffusion coefficient or D matrix elements for the purpose of modeling of diffusion processes in natural garnets must take into account these compositional effects on D(I) along with the effects of thermodynamic nonideality, f _O2, and pressure. Received: 8 May 1997 / Accepted: 2 October 1997  相似文献