scholarly journals Spatial rainfall patterns associated with Indian northeast monsoon derived from high resolution rainfall estimates of Chennai DWR

MAUSAM ◽  
2021 ◽  
Vol 67 (4) ◽  
pp. 767-788
Author(s):  
B. AMUDHA ◽  
Y. E. A. RAJ ◽  
R. ASOKAN ◽  
S. B. THAMPI
Keyword(s):  
High Resolution ◽  
Grid Point ◽  
Historical Analysis ◽  
Rain Gauge ◽  
Spatial Distributions ◽  
Northeast Monsoon ◽  
Absolute Deviation ◽  
Peninsular India ◽  
Data Set ◽  
Point Data

The Indian northeast monsoon (NEM) season benefits the southeastern parts of peninsular India during the period October-November-December (OND).  In this study, which is a first of this type for the Indian  region, certain new and salient features of the NEM rainfall (RF) have been derived utilising the very high resolution (333 m × 333 m) radar estimated rainfall (RERF) data generated by the Doppler Weather Radar (DWR) at Chennai for the 12 year period (2002-13), over a circular area of 100 km radius spreading over both land and ocean. More than 2.8 lakhs of grid point data per day have been processed. Rain gauge measured rainfall (RGRF) data of 34 inland stations has also been used. Monthwise spatial distributions of RERF for October, November and December and for the entire season OND have been generated. It is shown through rigorous analysis that RERF is heavier closer to the coast and for a given longitude over land, southern latitudes receive 10-15% more RF than the northern latitudes. Decrease of RF eastwards into Bay of Bengal (BoB) is gradual whereas westwards over inland it is sharp and almost linear.  By and large, the climatological features of NEM derived from historical analysis of RGRF data are well-captured by the analysis based on RERF data. A few new features of monthly and seasonal RF have also been identified. For the 34 stations, 12 year data set for OND, the mean RERF and RGRF values are 629.8 mm and 627.4 mm respectively yielding a difference of just 2.4 mm but with a substantial mean absolute deviation of 69.2 mm. RERF during pre-NEM days of Oct contributed to 10% of the seasonal OND total. RERF in the area of study, during days of cyclonic disturbances (CD days) is nearly twice over outer oceanic areas of BoB than over land.  It has been shown that during the onset to withdrawal period of NEM, RERF is heavier over areas close to the coast (75 cm) than oceanic areas (68 cm) within the 100 km radius of the DWR. High RF zones approximately extending 25-30 km westwards into land and around 30-40 km eastwards over the ocean have been delineated. Spatial distributions of RERF during the various phases of NEM, viz., dry, weak, normal, active and vigorous as identified from the RGRF data have been generated, critically analysed and results drawn.  In the case of vigorous, active and vigorous (AV) NEM days excluding CD days, a relatively high daily RERF patch of 5-6 cm located approximately 5-10 km west of the coast inland and in the SW sector of Chennai DWR has been identified. During post-NEM withdrawal days of December, oceanic areas of eastern sector are shown to receive highest RF compared to land areas, a feature consistent with the withdrawal pattern of NEM. The instrumental limitations and artifacts of radars contributing to errors in RERF have been discussed.

scholarly journals Assessment of small-scale variability of rainfall and multisatellite precipitation estimates using a meso-rain gauge network measurements from southern peninsular India

2015 ◽  
Vol 12 (10) ◽  
pp. 10389-10429
Author(s):  
K. Sunilkumar ◽  
T. Narayana Rao ◽  
S. Satheeshkumar
Keyword(s):  
High Resolution ◽  
Spatial Variability ◽  
Diurnal Cycle ◽  
Rain Gauge ◽  
Spatiotemporal Variability ◽  
Small Scale ◽  
Northeast Monsoon ◽  
Peninsular India ◽  
Precipitation Estimates ◽  
Rain Gauge Network

Abstract. This paper describes the establishment of a dense rain gauge network and small-scale variability in rain storms (both in space and time) over a complex hilly terrain in southeast peninsular India. Three years of high-resolution gauge measurements are used to evaluate 3 hourly rainfall and sub-daily variations of four widely used multisatellite precipitation estimates (MPEs). The network consists of 36 rain gauges arranged in a near-square grid area of 50 km × 50 km with an intergauge distance of ~ 10 km. Morphological features of rainfall in two principal monsoon seasons (southwest monsoon: SWM and northeast monsoon: NEM) show marked seasonal differences. The NEM rainfall exhibits significant spatial variability and most of the rainfall is associated with large-scale systems (in wet spells), whereas the contribution from small-scale systems is considerable in SWM. Rain storms with longer duration and copious rainfall are seen mostly in the western quadrants in SWM and northern quadrants in NEM, indicating complex spatial variability within the study region. The diurnal cycle also exhibits marked spatiotemporal variability with strong diurnal cycle at all the stations (except for 1) during the SWM and insignificant diurnal cycle at many stations during the NEM. On average, the diurnal amplitudes are a factor 2 larger in SWM than in NEM. The 24 h harmonic explains about 70 % of total variance in SWM and only ~ 30 % in NEM. The late night-mid night peak (20:00–02:00 LT) observed during the SWM is attributed to the propagating systems from the west coast during active monsoon spells. Correlograms with different temporal integrations of rainfall data (1, 3, 12, 24 h) show an increase in the spatial correlation with temporal integration, but the correlation remains nearly the same after 12 h of integration in both the monsoons. The 1 h resolution data shows the steepest reduction in correlation with intergauge distance and the correlation becomes insignificant after ~30 km in both monsoons. Evaluation of high-resolution rainfall estimates from various MPEs against the gauge rainfall indicates that all MPEs underestimate the weak and heavy rain. The MPEs exhibit good detection skills of rain at both 3 and 24 h resolutions, however, considerable improvement is observed at 24 h resolution. Among different MPEs, Climate Prediction Centre morphing technique (CMORPH) performs better at 3 hourly resolution in both monsoons. The performance of TRMM multisatellite precipitation analysis (TMPA) is much better at daily resolution than at 3 hourly, as evidenced by better statistical metrics than the other MPEs. All MPEs captured the basic shape of diurnal cycle and the amplitude quite well, but failed to reproduce the weak/insignificant diurnal cycle in NEM.

scholarly journals Onset of northeast monsoon over South Peninsular India

MAUSAM ◽  
2021 ◽  
Vol 71 (3) ◽  
pp. 503-512
Author(s):  
SATYANARAYANA G C ◽  
NAIDU C V ◽  
RAO D V BHASKAR ◽  
UMAKANTH N ◽  
NAVEENA N
Keyword(s):  
Bay Of Bengal ◽  
Arabian Sea ◽  
Grid Point ◽  
India Meteorological Department ◽  
Onset Date ◽  
Data Sets ◽  
Northeast Monsoon ◽  
Peninsular India ◽  
Northern Latitudes ◽  
High Pressure Zone

The onset dates of the northeast monsoon over South Peninsular India are determined using the wind data at 850 hPa and 200 hPa, OLR, mean sea level pressure data for the domain 40° E to 120° E, 0° to 40° N.  These three data sets are sourced from NCEP/NCAR reanalysis daily data sets. Further the daily grid point (0.25° Lat. × 0.25° Long.) rainfall data over India from Indian Meteorological Department is considered for delineation of rainfall pattern. The total length of the data of the above mentioned parameters is 21 years (1994 to 2014).                  Pentad distributions of the above parameters for the domain  considered  are prepared for examining the circulation patterns and rainfall activity. The pentads taken for the study are from 55th (28th September - 2nd October) pentad to 65th (17-21 November) pentad. In the determination of the northeast monsoon over South Peninsular India, the following points are considered: (i) The persistence of the northeasterlies at 850 hPa level, (ii) Occurrence of the rainfall over the South Peninsular India, (iii) Presence of east-west oriented trough [Intertropical Convergence Zone (ITCZ)] in the lower latitudes from Ethiopia region to Malaysia region passing through South Arabian Sea, southern region of South Peninsular India and South Bay of Bengal,  (iv) The presence of low pressure over the southwest Bay of Bengal at the surface, (v) Persistence of a high pressure zone in northern latitudes of India (extending from the Saudi Arabia/Jordan region to the Head Bay of Bengal running through North Arabian Sea, Gujarat and Orissa), (vi) Presence of subtropical ridge at 200 hPa level around 17.5° N, (vii) Presence of north-south ridge over theeastern parts of China and (viii) Presence of relatively low OLR values over South Peninsular India when compared to the northern latitudes.                 If any pentad satisfies the above points, the middle date of the pentad is considered as the date of onset of northeast monsoon over South Peninsular India.  If any pentad satisfies all the points except point number 2, importance is given to the persistence of northeasterlies and the middle date of the pentad will be declared as the onset date.  By following the criteria, the dates of onset of northeast monsoon are determined for the latest 21 years.  These dates are compared with those of the India Meteorological Department.

Validation of PERSIANN Precipitation Product Using TAWN Rain Gauge Network Over Different Agro-climatic Zones in Tamil Nadu

2021 ◽  
Vol 108 (september) ◽  
pp. 1-6
Author(s):  
Venkadesh Samykannu ◽  
◽  
Pazhanivelan S ◽  
Keyword(s):  
High Altitude ◽  
Tamil Nadu ◽  
Rain Gauge ◽  
Northeast Monsoon ◽  
Data Set ◽  
Climatic Zones ◽  
Rain Gauges ◽  
Precipitation Estimation ◽  
Cauvery Delta ◽  
Rain Gauge Network

Currently, several satellite-precipitation products were developed using multiple algorithms to estimate rainfall. This study carried out using Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN) product over seven agro-climatic zones of Tamil Nadu during the northeast monsoon (NEM) season of October to December for 2015-2017 (three years) against 118 rain-gauges data of Tamil Nadu Agricultural Weather Network (TAWN). The performance compares aggregated seasonal scale of rainfall using continuous (CC, RMSE, and NRMSE) statistical approaches. It was observed that PERSIANN is accurate in the high-altitude hilly zone and the Cauvery delta zone. For 2015, 2016, and 2017, the correlation values were 0.77, 0.52, and 0.71, respectively. The highest RMSE value was measured for northeast zone (NEZ) during 2015 (222.17 mm), and the lowest was determined for 22.63 in the High-altitude hilly zone (HAHZ) during 2016 and NRMSE had less errors during all three seasons. The study concluded that the PERSIANN data set could be useful substitute for rain-gauge precipitation data.

scholarly journals Characteristics of movement of low level clouds associated with onset / wet spells of northeast monsoon of Indian sub-continent as derived from high resolution INSAT OLR data

MAUSAM ◽  
2021 ◽  
Vol 67 (2) ◽  
pp. 357-376
Author(s):  
B. AMUDHA ◽  
Y. E. A. RAJ ◽  
R. ASOKAN
Keyword(s):  
High Resolution ◽  
Tamil Nadu ◽  
North Indian Ocean ◽  
Wave Radiation ◽  
Sri Lankan ◽  
Northeast Monsoon ◽  
Peninsular India ◽  
Superposed Epoch Analysis ◽  
The North ◽  
Epoch Analysis

Characteristics of the northeast monsoon (NEM) have been studied utilising the outgoing long wave radiation (OLR) data derived over the north Indian Ocean and south peninsular India (SPI) from the series of Indian geostationary satellites. The contrasting feature of movement of the equatorial cloud zone from southeast to northwest direction during the onset phase of NEM has been reiterated using 1° × 1° gridded high resolution OLR data for the period 2000-2012.  Presence of OLR values less than 180 Wm-2 over a large part of coastal Tamil Nadu on the date of onset and the simultaneous commencement of rainfall with clouding approaching SPI from southeast is clear from the study of superposed epoch analysis of the data. Triad means of OLR also substantiate this inference. During active spells of NEM which succeed prolonged dry spells, replication of the south to north movement of clouding by the OLR contours and the plausible reasons for such a movement have been brought out. The active monsoon situation existing over Sri Lankan region during the withdrawal phase of NEM over SPI is demonstrated with the depiction of the movement of OLR contours less than 230 Wm-2 over the region.  

scholarly journals A statistical analysis of the differences between rainfall estimated by Chennai DWR and conventional rainfall data on monthly and seasonal scales during the Indian northeast monsoon season

MAUSAM ◽  
2021 ◽  
Vol 68 (2) ◽  
pp. 261-278
Author(s):  
B. AMUDHA ◽  
Y. E. A. RAJ ◽  
S. B. THAMPI
Keyword(s):  
Statistical Analysis ◽  
Monsoon Season ◽  
India Meteorological Department ◽  
Rain Gauge ◽  
Northeast Monsoon ◽  
Statistical Parameters ◽  
Absolute Deviation ◽  
Correction Technique ◽  
Grid Points ◽  
Yearly Means

The first Doppler Weather Radar (DWR) of India Meteorological Department has been functional at Chennai since the year 2002 providing various meteorological and hydrological products. Validation and statistical analysis  of  the DWR estimated rainfall (RERF, x) data with rain gauge measured rainfall (RGRF, y) of 34 land based stations located in the semi-circular land area within 100 km radius of  Chennai DWR (CDLR100) has been performed for  the northeast monsoon (NEM) season of October-November-December (OND)  for the  12 year period 2002-13. The monthly and seasonal data have been derived using more than 1.42 lakh discrete daily RERF values available at a high resolution of 333 m × 333 m.          The major objective of the study is to compute the various statistical parameters of x and y including the bias between them on monthly and seasonal scales and to draw certain inferences. The analysis was done using three different types of averaging.  The yearly means  of  x and  y for OND over CDLR100 manifested both positive and negative epochs with the mean absolute deviation (MAD) computed as 11 cm (17% of mean). The short term normals over CDLR100 are derived as 274.9, 262.6, 96.5 and 629.8 mm for x and 243.8, 254.6, 128.0 and 627.4 mm for y for October, November, December and OND yielding bias values of -31.2, -8.0, 31.5 and -2.4 mm respectively.  The MAD for OND rainfall computed by pooling in all the 12 ´ 34 values is quite substantial at around 19 cm (30% of mean). The RF bias for each month / NEM season is shown to be independent of the geographical locations of the stations using correlation analysis.  Based on the raw values of  x and a proportional correction technique, estimated values of at the 1.42 lakh grid points  of  CDLR100  were derived yielding spatial means  of  273.3, 262.2, 92.5 and 628.4 mm for  x  and 243.4, 254.3, 122.9 and  622.1 mm  for   for the three months and OND respectively. The importance of size  of  the bias in the correct interpretation  of  x  has been discussed.  A few suggestions  based  on certain  statistical considerations have been putforth for decreasing the bias.  

Algorithms for automated montage synthesis of images from laser-scanning confocal microscopes

1995 ◽  
Vol 53 ◽  
pp. 650-651
Author(s):  
D. E. Becker
Keyword(s):  
Image Analysis ◽  
High Resolution ◽  
Laser Scanning ◽  
Cell Counting ◽  
Wide Area ◽  
Data Set ◽  
Computational Synthesis ◽  
Automated Cell Counting ◽  
Partial View ◽  
The Individual

An efficient, robust, and widely-applicable technique is presented for computational synthesis of high-resolution, wide-area images of a specimen from a series of overlapping partial views. This technique can also be used to combine the results of various forms of image analysis, such as segmentation, automated cell counting, deblurring, and neuron tracing, to generate representations that are equivalent to processing the large wide-area image, rather than the individual partial views. This can be a first step towards quantitation of the higher-level tissue architecture. The computational approach overcomes mechanical limitations, such as hysterisis and backlash, of microscope stages. It also automates a procedure that is currently done manually. One application is the high-resolution visualization and/or quantitation of large batches of specimens that are much wider than the field of view of the microscope.The automated montage synthesis begins by computing a concise set of landmark points for each partial view. The type of landmarks used can vary greatly depending on the images of interest. In many cases, image analysis performed on each data set can provide useful landmarks. Even when no such “natural” landmarks are available, image processing can often provide useful landmarks.

Recording Epigraphic Sources as Part of Artworks

2020 ◽  
pp. 128-144
Author(s):  
Gabriele Pieke
Keyword(s):  
Original Artwork ◽  
Art History ◽  
Historical Analysis ◽  
Relevant Information ◽  
Ancient Egypt ◽  
Historical Study ◽  
Data Set ◽  
Line Drawings ◽  
Color Data ◽  
Written Word

Art history has its own demands for recording visual representations. Objectivity and authenticity are the twin pillars of recording artistic data. As such, techniques relevant to epigraphic study, such as making line drawings, may not always be the best approach to an art historical study, which addresses, for example, questions about natural context and materiality of the artwork, the semantic, syntactic, and chronological relation between image and text, work procedures, work zones, and workshop traditions, and interactions with formal structures and beholders. Issues critical to collecting data for an art historical analysis include recording all relevant information without overcrowding the data set, creating neutral (i.e., not subjective) photographic images, collecting accurate color data, and, most critically, firsthand empirical study of the original artwork. A call for greater communication in Egyptology between epigraphy/palaeography and art history is reinforced by drawing attention to images as tools of communication and the close connection between the written word and figural art in ancient Egypt.

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