Flares From the Giant ar 9433 on 24 April 2001     

Joshi  Anita  Chandra  Ramesh  Uddin  Wahab 《Solar physics》2003,217(1):173-186

We present H CCD observations of three small-to-medium-size two-ribbon flares observed in the giant AR 9433 on 24 April 2001. Flare observations at other associated wavelengths (e.g., soft X-rays (SXR), hard X-rays (HXR), microwaves (MW)) obtained from archives are also presented and compared. We have tested the Neupert effect for the most energetic third flare. The flare observations are in agreement with the thick-target model. In the case of this flare the HXR emitting electrons appears to be the heating source of SXR and H emissions. The flares are also studied in EUV and UV emissions using TRACE data. We discuss the complexity of the magnetic field using SOHO/MDI magnetograms. The flares are observed to occur in both (f/p) polarity regions in highly sheared magnetic field with emerging flux regions and MMFs.  相似文献   

Surge dynamics of disaster displaced populations in temporary urban shelters: future challenges and management issues     

Md Shahab Uddin  Mokbul Morshed Ahmad  Pennung Warnitchai 《Natural Hazards》2018,91(1):201-220

A tropical cyclone (TC) precipitation prediction scheme has been developed based on the physical quantities of the NCEP/NCAR reanalysis data as potential predictors and using fuzzy neural network (FNN) model. TC precipitation samples from 172 tropical cyclones (TCs) affecting Guangxi, China, spanning 1980–2015 are used for model development. The FNN model input is constructed from potential predictors by employing both a stepwise regression method (SRM) and a locally linear embedding (LLE) algorithm. The LLE algorithm is capable of finding meaningful low-dimensional architectures hidden in their nonlinear high-dimensional data space and separating the underlying factors. In this scheme, the newly developed model, which is termed the FNN–LLE model, is used for daily TC precipitation prediction from 20:00 (Beijing Time, or BT) of the previous day to 20:00 BT of the current day at 89 stations covering Guangxi, China. Using identical modeling samples and independent samples, predictions of the FNN–LLE model are compared with the widely used SRM and interpolation method using the fine-mesh data of the European Centre for Medium-Range Weather Forecasts (ECMWF) in terms of the performance of TC rainfall prediction at 89 stations in Guangxi. The root-mean-square error (RMSE), bias, and equitable threat score (ETS) results were employed to assess the predicted outcomes. Results show that the FNN–LLE model is superior to the interpolation method by ECMWF and SRM for TC precipitation prediction with RMSE values of 21.94, 24.07, and 25.22 in FNN–LLE model, interpolation method by ECMWF and SRM, respectively. Moreover, FNN–LLE model having average bias and ETS values close to 1.0 gave better predictions than did the interpolation method by ECMWF and SRM.  相似文献   

Effects of stand characteristics on tree species richness in and around a conservation area of northeast Bangladesh     

Muha Abdullah Al Pavel  Sharif A. Mukul  Mohammad Belal Uddin  Kazuhiro Harada  Mohammed A. S. Arfin Khan 《山地科学学报》2016,13(6):1085-1095

We investigated the effect of tree cover, forest patch and disturbances on tree species richness in a highly diverse conservation area of northeast Bangladesh. A systematic sampling protocol was adopted and 80 sub-plots from twenty five 1 ha plots were used for the vegetation survey. Linear regression analysis was performed to understand the effect of patch area, disturbances and tree cover on tree species richness. Ordination using Redundancy analysis (RDA) and Non-metric Multi Dimensional Scaling (NMDS) were also performed to explore the tree species compositional similarities along the stand characteristics gradient and locations of the sample plots. Our study revealed that, forest patch size has greater influence on species richness. Areas with medium level of disturbances have shown greater species richness. In constrained ordination the selected explanatory variables regulated the richness of common species. Our findings can be useful for better forest management and restoration of landscapes of conservation needs using ecologically important species.  相似文献   

Multiwavelength Study of the M8.9/3B Solar Flare from AR NOAA 10960     

Pankaj Kumar  A. K. Srivastava  B. Filippov  Wahab Uddin 《Solar physics》2010,266(1):39-58

We present a multiwavelength analysis of a long-duration, white-light solar flare (M8.9/3B) event that occurred on 04 June 2007 from AR NOAA 10960. The flare was observed by several spaceborne instruments, namely SOHO/MDI, Hinode/SOT, TRACE, and STEREO/SECCHI. The flare was initiated near a small, positive-polarity, satellite sunspot at the center of the active region, surrounded by opposite-polarity field regions. MDI images of the active region show a considerable amount of changes in the small positive-polarity sunspot of δ configuration during the flare event. SOT/G-band (4305 Å) images of the sunspot also suggest the rapid evolution of this positive-polarity sunspot with highly twisted penumbral filaments before the flare event, which were oriented in a counterclockwise direction. It shows the change in orientation, and also the remarkable disappearance of twisted penumbral filaments (≈35?–?40%) and enhancement in umbral area (≈45?–?50%) during the decay phase of the flare. TRACE and SECCHI observations reveal the successive activation of two helically-twisted structures associated with this sunspot, and the corresponding brightening in the chromosphere as observed by the time-sequence of SOT/Ca?ii H line (3968 Å) images. The secondary, helically-twisted structure is found to be associated with the M8.9 flare event. The brightening starts six?–?seven minutes prior to the flare maximum with the appearance of a secondary, helically-twisted structure. The flare intensity maximizes as the secondary, helically-twisted structure moves away from the active region. This twisted flux tube, associated with the flare triggering, did not launch a CME. The location of the flare activity is found to coincide with the activation site of the helically-twisted structures. We conclude that the activation of successive helical twists (especially the second one) in the magnetic-flux tubes/ropes plays a crucial role in the energy build-up process and the triggering of the M-class solar flare without a coronal mass ejection (CME).  相似文献   

The record of Himalayan erosion preserved in the sedimentary rocks of the Hatia Trough of the Bengal Basin and the Chittagong Hill Tracts,Bangladesh     

Y. Najman  R. Allen  E. A. F. Willett  A. Carter  D. Barfod  E. Garzanti  J. Wijbrans  M. J. Bickle  G. Vezzoli  S. Ando  G. Oliver  M. J. Uddin 《Basin Research》2012,24(5):499-519

The Cenozoic sedimentary succession of Bangladesh provides an archive of Himalayan erosion. However, its potential as an archive is currently hampered by a poor lithostratigaphic framework with limited age control. We focus on the Hatia Trough of the Bengal Basin and the adjacent fold belt of the Chittagong Hill Tracts which forms the outermost part of the west‐propagating Indo‐Burmese wedge. We present a basin‐wide seismic stratigraphic framework for the Neogene rocks, calibrated by biostratigraphy, which divides the succession into three seismically distinct and regionally correlatable Megasequences (MS). MS1 extends to NN15‐NN16 (ca. 2.5–3.9 Ma), MS2 to NN19‐NN20 (ca. 0.4–1.9 Ma) and MS3 to present day. Our seismic mapping, thermochronological analyses of detrital mineral grains, isotopic analyses of bulk rock, heavy mineral and petrographic data, show that the Neogene rocks of the Hatia Trough and Chittagong Hill Tracts are predominantly Himalayan‐derived, with a subordinate arc‐derived input possibly from the Paleogene IndoBurman Ranges as well as the Trans‐Himalaya. Our seismic data allow us to concur with previous work that suggests folding of the outer part of the west‐propagating wedge only commenced recently, within the last few million years. We suggest that it could have been the westward encroachment and final abutment of the Chittagong Hill Tracts fold belt onto the already‐uplifted Shillong Plateau that caused diversion of the palaeo‐Brahmaputra to the west of the plateau as the north‐east drainage route closed.  相似文献   

Variation in comet P/Halley     

P. S. Goraya  H. K. Duggal  R. K. Srivastava  Wahab Uddin 《Earth, Moon, and Planets》1989,44(2):197-198

Photoelectric photometry (UBV) of Comet P/Halley performed on April 29, 1986 has been presented. The observations show short-term variability in light. The amplitude of variability in U filter is much more than in B and V filters.  相似文献   

Multiwavelength Study on Solar and Interplanetary Origins of the Strongest Geomagnetic Storm of Solar Cycle 23     

Pankaj Kumar  P. K. Manoharan  Wahab Uddin 《Solar physics》2011,271(1-2):149-167

We study the solar sources of an intense geomagnetic storm of solar cycle 23 that occurred on 20 November 2003, based on ground- and space-based multiwavelength observations. The coronal mass ejections (CMEs) responsible for the above geomagnetic storm originated from the super-active region NOAA 10501. We investigate the H?? observations of the flare events made with a 15 cm solar tower telescope at ARIES, Nainital, India. The propagation characteristics of the CMEs have been derived from the three-dimensional images of the solar wind (i.e., density and speed) obtained from the interplanetary scintillation data, supplemented with other ground- and space-based measurements. The TRACE, SXI and H?? observations revealed two successive ejections (of speeds ???350 and ???100 km?s^?1), originating from the same filament channel, which were associated with two high speed CMEs (???1223 and ???1660 km?s^?1, respectively). These two ejections generated propagating fast shock waves (i.e., fast-drifting type II radio bursts) in the corona. The interaction of these CMEs along the Sun?CEarth line has led to the severity of the storm. According to our investigation, the interplanetary medium consisted of two merging magnetic clouds (MCs) that preserved their identity during their propagation. These magnetic clouds made the interplanetary magnetic field (IMF) southward for a long time, which reconnected with the geomagnetic field, resulting the super-storm (Dst _peak=?472 nT) on the Earth.  相似文献   

Photometric study of BZ Eridani     

R. K. Srivastava  Wahab Uddin 《Astrophysics and Space Science》1986,126(1):105-118

The 1980–1981U, B, andV observations of the eclipsing binary BZ Eridani have been presented. A new period of BZ Eri comes out to be 0^d.6641703. The colour curves of the system show appreciable variations, and are indicative of intrinsic variability. The secondary minimum falls nearly at phase 0.5. Some interesting features are given. The features of BZ Eri are changing. Some light variations are visible around the phase of the secondary minimum. The discussion reveals that BZ Eri is a complicated system.  相似文献   

A Hydrological Approach to Control Acid Mine Pollution for Lake Hope     

Moid Uddin Ahmad 《Ground water》1970,8(6):19-24

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Establishing a baseline to evaluate future impacts to groundwater resources in North Kuwait     

Amitabha Mukhopadhyay  Adnan Akber  Tariq Rashed  Vincent Kotwicki  Saif Uddin  Abdullah Bushehri 《Environmental Earth Sciences》2016,75(4):324

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