Decadal scale oscillations and trend in the Indian monsoon rainfall     

Lakshmi Krishnamurthy  V. Krishnamurthy 《Climate Dynamics》2014,43(1-2):319-331

The emerging need for extended climate prediction requires a consideration of the relative roles of climate change and low-frequency natural variability on decadal scale. Addressing this issue, this study has shown that the variability of the Indian monsoon rainfall (IMR) consists of three decadal scale oscillations and a nonlinear trend during 1901–2004. The space–time structures of the decadal oscillations are described. The IMR decadal oscillations are shown to be associated with Atlantic Multidecadal Oscillation (AMO), Atlantic tripole oscillation and Pacific Decadal Oscillation (PDO). The sea surface temperatures (SSTs) of the North Pacific and North Atlantic Oceans are also resolved as nonlinear decadal oscillations. The SST AMO mode has high positive correlation with IMR while the SST tripole mode and SST PDO have negative correlation. The trend in IMR increases during the first half of the period and decreases during the second half. The IMR trend is modified when combined with the three decadal oscillations.  相似文献   

AGCM simulations of intraseasonal variability associated with the Asian summer monsoon   总被引：6，自引：0，他引：6  

D. E. Waliser  K. Jin  I.-S. Kang  W. F. Stern  S. D. Schubert  M. L. C. Wu  K.-M. Lau  M.-I. Lee  V. Krishnamurthy  A. Kitoh  G. A. Meehl  V. Y. Galin  V. Satyan  S. K. Mandke  G. Wu  Y. Liu  C.-K. Park 《Climate Dynamics》2003,21(5-6):423-446

The intraseasonal variability associated with the Asian summer monsoon as simulated by a number of atmospheric general circulation models (AGCMs) are analyzed and assessed against observations. The model data comes from the Monsoon GCM Intercomparison project initiated by the CLIVAR/Asian–Australian Monsoon Panel. Ten GCM groups, i.e., the Center for Ocean–Land–Atmosphere Studies (COLA), Institute of Numerical Mathematics (DNM), Goddard Space Flight Center (GSFC), Geophysical Fluid Dynamics Laboratory (GFDL), Institute of Atmospheric Physics (IAP), Indian Institute of Tropical Meteorology (IITM), Meteorological Research Institute (MRI), National Center for Atmospheric Research (NCAR), Seoul National University (SNU), and the State University of New York (SUNY), participated in the intraseasonal component of the project. Each performed a set of 10 ensemble simulations for 1 September 1996–31 August 1998 using the same observed weekly SST values but with different initial conditions. The focus is on the spatial and seasonal variations associated with intraseasonal variability (ISV) of rainfall, the structure of each model's principal mode of spatial-temporal variation of rainfall [i.e. their depiction of the Intraseasonal Oscillation (ISO)], the teleconnection patterns associated with each model's ISO, and the implications of the models' ISV on seasonal monsoon predictability. The results show that several of the models exhibit ISV levels at or above that found in observations with spatial patterns of ISV that resemble the observed pattern. This includes a number of rather detailed features, including the relative distribution of variability between ocean and land regions. In terms of the area-averaged variance, it is found that the fidelity of a model to represent NH summer versus winter ISV appears to be strongly linked. In addition, most models' ISO patterns do exhibit some form of northeastward propagation. However, the model ISO patterns are typically less coherent, lack sufficient eastward propagation, and have smaller zonal and meridional spatial scales than the observed patterns, and are often limited to one side or the other of the maritime continent. The most pervasive and problematic feature of the models' depiction of ISV and/or their ISO patterns is the overall lack of variability in the equatorial Indian Ocean. In some cases, this characteristic appears to result from some models forming double convergence zones about the equator rather than one region of strong convergence on the equator. This shortcoming results in a poor representation of the local rainfall pattern and also significantly influences the models' representations of the global-scale teleconnection patterns associated with the ISO. Finally, analysis of the model ensemble shows a positive relationship between the strength of a model's ISV of rainfall and its intra-ensemble variability of seasonal monsoon rainfall. The implications of this latter relation are discussed in the context of seasonal monsoon predictability.  相似文献   

Picrite basalts and related lavas from the Deccan Traps of Western India     

P. Krishnamurthy  K. G. Cox 《Contributions to Mineralogy and Petrology》1977,62(1):53-75

Detailed chemical and mineralogical data are given for three sequences of basalts and picrite basalts from bore-holes in Western India. The picrite basalts show bulk compositional variation generated by the fractionation of olivine and chromite. Evolved picrite basalt magma appears to have given rise to basalt by the fractionation of olivine+clinopyroxene, despite the presence of abundant plagioclase phenocrysts. It is suggested that a slow settling rate for plagioclase relative to clinopyroxene and olivine is sufficient to account for this feature. The high degree of equilibrium crystallisation which many of the lavas have apparently undergone is interpreted in terms of the mechanism of compensated crystal settling (Cox and Bell, 1972). Experimentally determined atmospheric pressure phase relations are used to model dyke-like magma chambers in some detail. Finally volumetric and age relationships are used to argue that the picrite basalts, despite their porphyritic nature, crystallised from ultramafic liquids containing in some cases at least 16% MgO.  相似文献   

Vertical structure and characteristics of 23–60 day (zonal) oscillations over the tropical latitudes during the winter months of 1986 — Results of equatorial wave campaign—II     

R. Raghavarao  R. Suhasini  R. Sridharan  B. V. Krishnamurthy  O. P. Nagpal 《Journal of Earth System Science》1990,99(3):413-423

The equatorial wave campaign-II which formed a part of the Indian Middle Atmosphere Programme (IMAP), was conducted from SHAR (13.7°N, 80.2°E) from 15 January to 28 February 1986. Winds were measured from ground to 60 km by means of high altitude balloon and a meteorological rocket (RH-200), once everyday, for 45 days. The frequencies of the oscillations in the deviations of the east-west component of the winds from its mean at each height with one kilometer interval were obtained by the maximum entropy (ME) method and phases/amplitudes of these frequencies were determined by the least squares technique on the wind variation time series. The ME method has the inherent advantage of providing periodicities up to 1.5 times the data length. The height structure of the long period waves of > 23 day periodicities that have larger amplitudes nearly by a factor of 2 as compared to the medium (9 to 22 day) or shorter period (4 to 8 day) ones, reveal two height regions of enhanced amplitudes, one in the troposphere and another in the upper stratosphere/lower mesosphere, that too, mostly in the regions of positive (westerly increasing or easterly decreasing with height) wind shears. The waves are seen to be inhibited in the negative wind shear regions. From the abrupt changes in the altitude variation of phase, the possible source region has been identified. The vertical wavelengths have been estimated to be 34 km and 19 km in the troposphere and lower stratosphere respectively and 8 km in the upper stratosphere and lower mesosphere. Around 56 km the wave amplitude is reduced to 1/4 of its value below, while the vertical shear strength in the mean wind doubled up. The tropospheric waves are suggested to be Rossby waves of extratropical origin penetrating to tropical latitudes. The stratospheric/mesospheric waves however appear to emanate from a source around the stratopause.  相似文献   

Mapping of environs of Dharavi slums of Greater Bombay for site suitability using enhanced Landsat thematic mapper (TM) imagery     

V. Raghavswamy  N. C. Gautam  J. Krishnamurthy 《Journal of the Indian Society of Remote Sensing》1989,17(1):49-54

Slums are universal and a ubiquitous part of the urban landscape. Dharavi, the biggest slum in the whole of Greater Bombay, encompasses 4.0 sq.km. of reclaimed land with 3.50 lakh inhabitants and 75,000 hutments. Majority of the slums of Indian cities, being structurally small with high density of dwellings and uniform building material, seldom give subtle ’spectral signature’ on the satellite imagery. Here, an attempt has been made to map by visual techniques the land use of Dharavi and environs of 20 sq.km area, using optically enhanced Landsat (TM) FCC of January, 1986, on 1:25,000 sale, The study has clearly brought out the land use details, the areas undergoing reclamation, and those susceptible to hazards like floods and marine erosion. A few alternate sites, based on geomorphic attributes are suggested for resettlement of Dharavislum and their areas are also quantified. The results of the present work is a part of the project study completed for a larger area covering 150sq. kms.  相似文献   

A potassium-rich Alkalic Suite from the Deccan Traps,Rajpipla, India   总被引：4，自引：0，他引：4  

P. Krishnamurthy  K. G. Cox 《Contributions to Mineralogy and Petrology》1980,73(2):179-189

The Rajpipla Alkalic Suite is the most potassium-enriched group of basaltic rocks so far described from the Deccan Traps. In the same area however early tholeiitic flows and late tholeiitic dykes show the potassium-poor nature characteristic of most Deccan Trap magmas. The rocks of the alkalic suite are highly porphyritic and their major element variation can be interpreted in terms of crystal fractionation dominated by clinopyroxene. Plagioclase, which is an important phenocryst phase, has fractionated only in relatively small amounts as a result of a lack of density contrast between it and the liquids. A dyke-like form for the magma chambers in which fractionation has taken place is postulated to account for the abundance of highly porphyritic types. The Rajpipla area is also notable as being one of the few Deccan localities where rhyolites are found.Abbreviations AB ankaramitic basalt - PB porphyritic basalt - PTB porphyritic trachybasalt - FPM feldsparphyric mugearite - M mugearite - TR trachyte - P. RHY potassic rhyolite - Th. B. tholeiitic basalt - Th. D. tholeiitic dolerite - Af alkali feldspar  相似文献   

Analysis of Coastal Fog from a Ship During the C-FOG Campaign     

Wang  S.  Fernando  H. J. S.  Dorman  C.  Creegan  E.  Krishnamurthy  R.  Wainwright  C.  Wagh  S.  Yamaguchi  R. 《Boundary-Layer Meteorology》2021,181(2-3):365-393

This work presents ship-based measurements of fog off St John’s, Newfoundland, on 13 September 2018 during the Coastal Fog field campaign. The measurements included cloud-particle spectra, cloud-base height and aerosol backscatter, radiation, turbulence, visibility, and sea-surface temperature. Radiosonde soundings were made at intervals of less than 2 h. Fog occurred in two episodes during the passage of an eastward-moving synoptic low-pressure system. The boundary-layer structure during the first fog episode consisted of three layers, separated by two saturated temperature inversions, and capped by a subsidence inversion. The lowest layer was fog, and the upper layers were cloud. The second fog episode consisted of one well-mixed fog layer capped by a subsidence inversion. Low wind speeds and stable stratification maintained low surface-layer turbulence during fog. Droplet size distributions had typical bimodal distributions. The visibility correlated with the droplet number concentration and liquid water content. The air temperature was higher than the sea-surface temperature for the first 30 min of the first fog episode but was lower than the sea for the remainder of all fog. The sensible heat flux was upward, from sea to air, for the first 62% of the first fog episode and then reversed to downward, from air to sea, for the remainder of the first fog episode and the second fog episode. The counter-gradient heat fluxes observed (i.e., opposite to what is expected from the instantaneous air–sea temperature difference) appear to be related to turbulence, entrainment, and stratification in the fog layer that overwhelmed the influence of the air–sea temperature difference. While the synoptic-scale dynamics preconditioned the area for fog formation, the final step of fog appearance in this case was nuanced by stratification–turbulence interactions, local advective processes, and microphysical environment.

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Study of Stratus-Lowering Marine-Fog Events Observed During C-FOG     

Wagh  Sandeep  Krishnamurthy  Raghavendra  Wainwright  Charlotte  Wang  Sen  Dorman  Clive E.  Fernando  Harindra J. S.  Gultepe  Ismail 《Boundary-Layer Meteorology》2021,181(2-3):317-344

Boundary-Layer Meteorology - Two stratus-lowering marine fog events observed on 28 September and 4 October 2018 during the Coastal Fog (C-Fog) field campaign that took place offshore of eastern...  相似文献   

Correction to: Atmospheric Turbulence Measurements at a Coastal Zone with and without Fog     

Grachev  Andrey A.  Krishnamurthy  Raghavendra  Fernando  Harindra J. S.  Fairall  Christopher W.  Bardoel  Stef L.  Wang  Sen 《Boundary-Layer Meteorology》2021,181(2-3):423-424

Boundary-Layer Meteorology -  相似文献   

Coastal-Fog Microphysics Using In-Situ Observations and GOES-R Retrievals     

Gultepe  I.  Pardyjak  E.  Hoch  S. W.  Fernando  H. J. S.  Dorman  C.  Flagg  D. D.  Krishnamurthy  R.  Wang  Q.  Gaberšek  S.  Creegan  E.  Scantland  N.  Desjardins  S.  Heidinger  A.  Pavolonis  M.  Heymsfield  A. J. 《Boundary-Layer Meteorology》2021,181(2-3):203-226

Boundary-Layer Meteorology - The objective of this work is to evaluate GOES-R (Geostationary Operational Environmental Satellites-R series) data-based fog conditions which occurred during the C-FOG...  相似文献