Conditions leading to the onset of the Indian monsoon: A satellite perspective   总被引：1，自引：0，他引：1  

B. Simon  S. H. Rahman  P. C. Joshi 《Meteorology and Atmospheric Physics》2006,93(3-4):201-210

Summary The summer monsoon onset-2004 over the Kerala Coast (Southern tip of the Indian Peninsula) was monitored in real-time using the Tropical Rainfall Measuring Mission (TRMM)/TMI derived total precipitable water vapor, wind speed and sea surface temperature (SST), National Centre for Environmental Prediction (NCEP) and QuikScat wind data. The 2004 onset was of a gradual type, with an early start (24 May), followed by slow growth to full strength (10 June). Hence, the unambiguous forecasting of such onsets becomes very difficult. The water vapor build up over the western Arabian Sea is one of the necessary conditions that gives us a lead time of two and half weeks for the onset of monsoon. The strength of the Hadley cell (monitored using NCEP meridional wind), which is associated with a large convective heat source is also used as a predictive parameter with a lead-time of two weeks. The other dynamical conditions considered are the early May propagation of the Madden Julian Oscillation (MJO) followed by a second MJO, which began in the Western Indian Ocean (WIO) and the kinetic energy over the South East Arabian Sea, with an early start around 24 May (50 m²/s²) and strengthening around 10 June (80 m²/s²). The setting of large-scale monsoon current using various satellite derived parameters and the distinct features for the year 2004 have been delineated.  相似文献   

Flood assessment and early warning of the reoccurrence of river blockage at the Baige landslide     

GAO Yunjian  ZHAO Siyuan  DENG Jianhui  YU Zhiqiu  RAHMAN Mahfuzur 《地理学报(英文版)》2021,31(11):1694-1712

On 10th Oct.and 3rd Nov.2018,two successive landslides occurred in the Jinsha River catchment at Baige Village,Tibet Autonomous Region,China.The landslides blocked the major river and formed the barrier lake,which finally caused the huge flood disaster loss.The hillslope at Baige landslide site has been still deforming after the 2018 slidings,which is likely to fail and block the Jinsha River again in the future.Therefore the investigation of 2018 flood disaster at the Baige landslide is of a great significance to provide a classic case for flood assessment and early warning for the future disaster.The detailed survey revealed that the outstanding inundations induced bank collapse disasters upstream the Baige landslide dams,and the field investigations and hydrological simulation suggested that the downstream of the Baige landslide were seriously flooded due to the two periods of the outburst floods.On these bases,the early warning process of potential outburst floods at the Baige landslide was advised,which contains four stages:Outburst Flood Simulating Stage,Outburst Flood Fore-casting Stage,Emergency Plan and Emergency Evacuation Stage.The study offers a con-ceptual model for the mitigation of landslides and flood disasters in the high-relief mountain-ous region in Tibet.  相似文献   

Cretaceous Environments of Afghanistan:A Synthesis Based on Selected Sections     

Abdul Rahman Ashraf  Ashok Sahni 《世界地质(英文版)》2003,6(1)

The Cretaceous of Afghanistan is marked by great facies diversity. The evolution of Cretaceous basins is part of a complex accretionary history involving three distinct tectonic units namely the Asian (Russian) Block separated from the Indian plate by a rather well defined transcurrent fault (Chaman-Nuski). The southwestern component is representedby the Iran-Afghanistan plate. The Lower Cretaceous of the Asian Block is represented by the Red-Grit Series which isconformable to the underlying Upper Jurassic sequences. The transition is marked by evaporitic facies dominated by salt,gypsum and marl deposits. In south Afghanistan volcanic rocks occur at Farah, with the emplacement of plutonics inwest-central Afghanistan. The Upper Cretaceous of north Afghanistan is marked by richly fossiliferous, lime stone-dominated sequences. The Upper Cretaceous of southern Afghanistan is marked by strong ophiolitic magrmatism.  相似文献   

Evolution of geophysical parameters over the Indian Ocean region during contrasting monsoon years of 2002 and 2003 using TRMM/TMI data     

S. H. Rahman  B. Simon  P. C. Joshi 《Theoretical and Applied Climatology》2007,89(3-4):211-227

Summary The evolution of geophysical parameters over Indian Ocean during two contrasting monsoon years 2002 (drought) and 2003 (normal) were studied using TRMM/TMI satellite data. Analysis indicates that there was a lack of total water vapour (TWV) build up over Western Indian Ocean (WIO) during May 2002 (drought) when compared to 2003 (normal). Negative (positive) TWV anomalies were found over the WIO in May 2002 (2003). In 2002, negative SST anomaly of ∼1.5 °C is found over entire WIO when compared to 2003. Anomalously high sea surface wind speed (SWS) anomaly over the South West Indian Ocean (SWIO) and WIO would have resulted in cooling of the sea surface in May 2002 in comparison to 2003. In 2003 the wind speed anomaly over entire WIO and Arabian Sea (AS) was negative, whereas sea surface temperature (SST) anomaly was positive over the same region, which would have resulted in higher moisture availability over these regions. A negative (positive) TWV anomaly over Eastern Arabian Sea (EAS) and positive (negative) anomaly over WIO forms a dipole structure. In the month of June no major difference is seen in all these parameters over the Indian Ocean. In July 2002 the entire WIO and AS was drier by 10–15 mm as compared to 2003. The pentad (5 day) average TWV values shows high (>55 mm) TWV convergence over EAS and Bay of Bengal (BoB) during active periods of 2003, which gives high rainfall over these regions. However, during 2002 although TWV over BoB was >55 mm but it was ∼45–55 mm over EAS during entire July and hence less rainfall. The evaporation has been calculated from the bulk aerodynamic formula using TRMM/TMI geophysical products. It has been seen that the major portion of evaporative moisture flux is coming from southern Indian Ocean (SIO) between 15 and 25° S. Evaporation in June was more over AS and SIO in 2003 when compared to 2002 which may lead to reduce moisture supply in July 2002 and hence less rainfall compared to July 2003.  相似文献   

CENOZOIC ALLUVIUM IN SINGAPORE: ITS PALEOENVIRONMENT RECONSTRUCTED FROM A SECTION     

Avijit Gupta  M.A.  PH.D.    Ausafur Rahman  MSc.  Ph.D.  P.P. Wong  M.A.  Ph.D. 《Singapore journal of tropical geography》1980,1(2):40-46

  相似文献   

Palaeomagnetic Secular Variation for Recent Normal and Reversed Epochs, from the Newer Volcanics of Victoria, Australia     

Aziz-ur Rahman 《Geophysical Journal International》1971,24(3):255-269

  相似文献   

Gamma Ray and Hadron generated Čerenkov Photon Spectra at Various Observation Altitudes     

M. A. Rahman  P. N. Bhat  B. S. Acharya  V. R. Chitnis  P. Majumdar  P. R. Vishwanath 《Experimental Astronomy》2001,11(2):113-131

We study the propagation of erenkov photons generated by Very HighEnergy -rays and hadrons in the atmosphere. The photon productionheight distributions are estimated from semi-empirical methods andcompared with those derived by standard simulation techniques. Incidentspectra at various observation altitudes are then derived after applyingwavelength dependent corrections due to photon attenuation in theatmosphere during the propagation of photons from the height of productionto the height of observation. These are generated both for -ray and hadron primaries of various energies. The derivedproduction height distributions agree very well with those generated bythe simulation package `CORSIKA' at all energies and for both -ray and proton primaries. The incident photon spectra are found to beboth altitude and primary energy dependent. The peak ofthe incident spectrum shifts towards the shorter wavelength withincreasing altitude of observation for a given primary. Also the peak ofthe photon spectrum shifts towards the shorter wavelength withincreasing energy of the primary at a given altitude. The fraction of the UVcomponent in the incident erenkov spectrum is estimated both for-ray and hadronic primaries at various observation altitudes andenergies. Hadron generated erenkov spectra are marginally richer in UVlight and the difference increases slightly at higher altitudes. The fraction of the UV to the visible light in the erenkov spectrum could be a usefulparameter to separate -rays from cosmic ray background only if onecan measure this fraction very accurately.  相似文献   

Changes in the frequency of tropical cyclones over the North Indian Ocean   总被引：3，自引：0，他引：3  

O. P. Singh  T. M. Ali Khan  Md. S. Rahman 《Meteorology and Atmospheric Physics》2000,75(1-2):11-20

Summary  Changes in the frequency of tropical cyclones developing over the Arabian Sea and the Bay of Bengal have been studied utilizing 122 year (1877–1998) data of tropical cyclone frequency. There have been significant increasing trends in the cyclone frequency over the Bay of Bengal during November and May which are main cyclone months. During transitional monsoon months; June and September however, the frequency has decreased. The results have been presented for five months, i.e., May-November which are relevant as far as tropical cyclone frequency over the Arabian Sea and the Bay of Bengal are concerned. The tropical cyclone frequency in the Arabian Sea has not shown any significant trend, probably due to small normal frequency. The frequency time series has been subjected to the spectral analysis to obtain the significant periods. The cyclone frequency over the Bay of Bengal during May has shown a 29 year cycle. A significant 44 year cycle has been found during November. Over the Arabian Sea significant cycles of 13 and 10 years have been observed during May-June and November, respectively. The tropical cyclone frequency in the North Indian Ocean has a prominent El Ni?o-Southern Oscillation (ENSO) scale cycle (2–5 years) during all above five months. The annual cyclone frequency exhibits 29 year and ENSO scale (2–4 years) oscillations. There is a reduction in tropical cyclone activity over the Bay of Bengal in severe cyclone months May and November during warm phases of ENSO. Examination of the frequencies of severe cyclones with maximum sustained winds ≥ 48 knots has revealed that these cyclones have become more frequent in the North Indian Ocean during intense cyclone period of the year. The rate of intensification of tropical disturbances to severe cyclone stage has registered an upward trend. Received June 7, 1999/Revised March 20, 2000  相似文献   

Estimation of catchment yield and associated uncertainties due to climate change in a mountainous catchment in Australia          下载免费PDF全文

Md Mahmudul Haque  Ataur Rahman  Dharma Hagare  Golam Kibria  Fazlul Karim 《水文研究》2015,29(19):4339-4349

This paper examines the impacts of climate change on future water yield with associated uncertainties in a mountainous catchment in Australia using a multi‐model approach based on four global climate models (GCMs), 200 realisations (50 realisations from each GCM) of downscaled rainfalls, 2 hydrological models and 6 sets of model parameters. The ensemble projections by the GCMs showed that the mean annual rainfall is likely to reduce in the future decades by 2–5% in comparison with the current climate (1987–2012). The results of ensemble runoff projections indicated that the mean annual runoff would reduce in future decades by 35%. However, considerable uncertainty in the runoff estimates was found as the ensemble results project changes of the 5^th (dry scenario) and 95^th (wet scenario) percentiles by ?73% to +27%, ?73% to +12%, ?77% to +21% and ?80% to +24% in the decades of 2021–2030, 2031–2040, 2061–2070 and 2071–2080, respectively. Results of uncertainty estimation demonstrated that the choice of GCMs dominates overall uncertainty. Realisation uncertainty (arising from repetitive simulations for a given time step during downscaling of the GCM data to catchment scale) of the downscaled rainfall data was also found to be remarkably high. Uncertainty linked to the choice of hydrological models was found to be quite small in comparison with the GCM and realisation uncertainty. The hydrological model parameter uncertainty was found to be lowest among the sources of uncertainties considered in this study. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Parameter uncertainty of the AWBM model when applied to an ungauged catchment          下载免费PDF全文

Md Mahmudul Haque  Ataur Rahman  Dharma Hagare  Golam Kibria 《水文研究》2015,29(6):1493-1504

In this study, a quantitative assessment of uncertainty was made in connection with the calibration of Australian Water Balance Model (AWBM) for both gauged and ungauged catchment cases. For the gauged catchment, five different rainfall data sets, 23 different calibration data lengths and eight different optimization techniques were adopted. For the ungauged catchment case, the optimum parameter sets obtained from the nearest gauged catchment were transposed to the ungauged catchments, and two regional prediction equations were used to estimate runoff. Uncertainties were ascertained by comparing the observed and modelled runoffs by the AWBM on the basis of different combinations of methods, model parameters and input data. The main finding from this study was that the uncertainties in the AWBM modelling outputs could vary from ?1.3% to 70% owing to different input rainfall data, ?5.7% to 11% owing to different calibration data lengths and ?6% to 0.2% owing to different optimization techniques adopted in the calibration of the AWBM. The performance of the AWBM model was found to be dominated mainly by the selection of appropriate rainfall data followed by the selection of an appropriate calibration data length and optimization algorithm. Use of relatively short data length (e.g. 3 to 6 years) in the calibration was found to generate relatively poor results. Effects of different optimization techniques on the calibration were found to be minimal. The uncertainties reported here in relation to the calibration and runoff estimation by the AWBM model are relevant to the selected study catchments, which are likely to differ for other catchments. The methodology presented in this paper can be applied to other catchments in Australia and other countries using AWBM and similar rainfall–runoff models. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献