scholarly journals Possible mechanisms related to internal dynamics for anomalously high rainfall during August 2020 of Indian Summer Monsoon

Author(s):  
Malay Ganai ◽  
Sahadat Sarkar ◽  
Radhika Kanase ◽  
R. Phani Murali Krishna ◽  
P Mukhopadhyay

Abstract In the present study, an investigation is made to understand the physical mechanism behind the anomalous high rainfall during August 2020 over the Indian subcontinent using both observation and GFS T1534 weather forecast model. According to India Meteorological Department (IMD), the country receives 27% excess rainfall in the month of August 2020. The excess rainfall is mainly contributed by the 5 well marked low pressure systems which formed over Bay of Bengal and moved west-northwestwards across central India up to Western Madhya Pradesh and Rajasthan. The analysis reveals that the observed anomalous rainfall is distributed over central India region extending from coastal Orissa to central part of Chhattisgarh, Madhya Pradesh and western coast of Gujarat region. It is also found that the August-2020 heavy rainfall is mainly contributed by the synoptic (2-10 days) component of the total rainfall whereas the contribution of the large-scale intraseasonal oscillation (ISO) component (10-90 days) is quite less. Although the present operational Global Forecast System (GFS) T1534 (GFS T1534) is able to predict the anomalous high rainfall with day-1 lead time, it underestimates the magnitude of the synoptic variance. Further, the large-scale dynamical and thermodynamical parameters show anomalous behaviour in terms of strong low level (850 hPa) jet, vertical velocity and associated moisture convergence in the lower level. The GFS T1534 is able to forecast the above large-scale features reasonably well even with day-5 lead time. From energetics analysis, it is found that the mean kinetic energy (MKE) is stronger for August 2020 as compared to climatological value and the strong MKE efficiently transfers the energy to the synoptic scale, and hence the synoptic eddy kinetic energy is higher. Along with that, the ISO scale kinetic energy for August 2020 is less compared to the August climatological value. GFS T1534 model has some fidelity in capturing the energy conversion processes, but it has some difficulty in capturing the magnitude with increased lead time.

2021 ◽  
pp. SP515-2020-216
Author(s):  
Nupur Tiwari ◽  
P. Morthekai ◽  
K. Krishnan ◽  
Parth R. Chauhan

AbstractThe earliest occurrence of microliths in South Asia dates back to the Late Pleistocene at Mehtakheri (45 ka) and Dhaba (48 ka) in Central India, Jwalapuram 9 in Southern India (38 ka), Kana and Mahadebbara in Northeastern India (42-25 ka) and Batadomba-Lena (35-36 ka) and Fa Hien Lena (48 ka) in Sri Lanka. Microlithic technology is distributed across the entire Indian Subcontinent and chronologically continues up to the Iron Age and Early Historic periods. This paper discusses new data acquired from the first author's doctoral research in the two districts of Madhya Pradesh (Hoshangabad and Sehore), which fall within the central part of the Narmada Basin in central India. We present here the preliminary dates from key areas of distribution to understand the geo-chronological contexts of microliths at Pilikarar, Morpani, and Gurla-Sukkarwada. Initial dates from these respective occurrences range between 12.5 ka and 2.3 ka.


2015 ◽  
Vol 28 (24) ◽  
pp. 9583-9605 ◽  
Author(s):  
Xiangwen Liu ◽  
Song Yang ◽  
Jianglong Li ◽  
Weihua Jie ◽  
Liang Huang ◽  
...  

Abstract Subseasonal predictions of the regional summer rainfall over several tropical Asian ocean and land domains are examined using hindcasts by the NCEP CFSv2. Higher actual and potential forecast skill are found over oceans than over land. The forecast for Arabian Sea (AS) rainfall is most skillful, while that for Indo-China (ICP) rainfall is most unskillful. The rainfall–surface temperature (ST) relationship over AS is characterized by strong and fast ST forcing but a weak and slow ST response, while the relationships over the Bay of Bengal, the South China Sea (SCS), and the India subcontinent (IP) show weak and slow ST forcing, but apparently strong and rapid ST response. Land–air interactions are often less noticeable over ICP and southern China (SC) than over IP. The CFSv2 forecasts reasonably reproduce these observed features, but the local rainfall–ST relationships often suffer from different degrees of unrealistic estimation. Also, the observed local rainfall is often related to the circulation over limited regions, which gradually become more extensive in forecasts as lead time increases. The prominent interannual differences in forecast skill of regional rainfall are sometimes associated with apparent disparities in forecasts of local rainfall–ST relationships. Besides, interannual variations of boreal summer intraseasonal oscillation, featured by obvious changes in frequency and amplitude of certain phases, significantly modulate the forecasts of rainfall over certain regions, especially the SCS and SC. It is further discussed that the regional characteristics of rainfall and model’s deficiencies in capturing the influences of local and large-scale features are responsible for the regional discrepancies of actual predictability of rainfall.


2016 ◽  
Vol 144 (9) ◽  
pp. 3037-3055 ◽  
Author(s):  
Yangxing Zheng ◽  
M. M. Ali ◽  
Mark A. Bourassa

Indian summer monsoon rainfall (ISMR; June–September) has both temporal and spatial variability causing floods and droughts in different seasons and locations, leading to a strong or weak monsoon. Here, the authors present the contribution of all-India monthly, seasonal, and regional rainfall to the ISMR, with an emphasis on the strong and weak monsoons. Here, regional rainfall is restricted to the seasonal rainfall over four regions defined by the India Meteorological Department (IMD) primarily for the purpose of forecasting regional rainfall: northwest India (NWI), northeast India (NEI), central India (CI), and south peninsula India (SPIN). In this study, two rainfall datasets provided by IMD are used: 1) all-India monthly and seasonal (June–September) rainfall series for the entire Indian subcontinent as well as seasonal rainfall series for the four homogeneous regions for the period 1901–2013 and 2) the latest daily gridded rainfall data for the period 1951–2014, which is used for assessment at the extent to which the four regions are appropriate for the intended purpose. Rainfall during July–August contributes the most to the total seasonal rainfall, regardless of whether it is a strong or weak monsoon. Although NEI has the maximum area-weighted rainfall, its contribution is the least toward determining a strong or weak monsoon. It is the rainfall in the remaining three regions (NWI, CI, and SPIN) that controls whether an ISMR is strong or weak. Compared to monthly rainfall, regional rainfall dominates the strong or weak rainfall periods.


2010 ◽  
Vol 23 (8) ◽  
pp. 1979-1993 ◽  
Author(s):  
R. K. Yadav ◽  
J. H. Yoo ◽  
F. Kucharski ◽  
M. A. Abid

Abstract This study examines decadal changes of the El Niño–Southern Oscillation (ENSO) influence on the interannual variability of northwest India winter precipitation (NWIWP). The analysis is based on correlations and regressions performed using India Meteorological Department (IMD) records based on station data and reanalysis fields from 1950 to 2008. The authors find that the interannual variability of NWIWP is influenced by the ENSO phenomenon in the recent decades. This conclusion is supported by a consistency across the different observational datasets employed in this study and confirmed by numerical modeling. A physical mechanism for such an influence is proposed, by which western disturbances (WDs) are intensified over northwest India because of a baroclinic response due to Sverdrup balance related to large-scale sinking motion over the western Pacific during the warm phase of ENSO. This response causes an upper-level cyclonic circulation anomaly north of India and a low-level anticyclonic anomaly over southern and central India. The cyclonic circulation anomaly intensifies the WDs passing over northwest India.


2020 ◽  
pp. 323-332
Author(s):  
Deepak D. Ramteke ◽  
Steven R. Manchester ◽  
Vaishali D. Nagrale ◽  
Selena Y. Smith

A new bisexual flower, Singpuria kapgatei, gen. et sp. nov., is described from chert of latest Cretaceous age from the Deccan Intertrappean Beds at Singpur, Madhya Pradesh, in central India. The hypogynous, actinomorphic flower is ~1.6 mm wide, with distinct sepals and petals. The androecium consists of 18 tetrasporangiate, dithecal, basifixed anthers borne in radial pairs on nine bifurcate filaments. The gynoecium is superior and syncarpous, with pentagonal symmetry. Pollen from the stamens is tricolporate and microreticulate. The combined morphological features of this flower indicate that Singpuria is a eudicot with affinities in the Pentapetalae, but we have been unable to make a more precise assignment. Nevertheless, we consider it useful to place this rare fossil flower on record as an exemplary extinct member of the Deccan biota. Singpuria may represent a clade that was isolated on the Indian subcontinent and became extinct in response to environmental changes at the K/Pg boundary, or later in the Cenozoic as the land mass moved northward through new climate zones and collided with Eurasia.


2021 ◽  
pp. 1-13
Author(s):  
Naveena Neelam ◽  
Gubbala C. Satyanerayana ◽  
Kota S. Rao ◽  
Nandivada Umakantha ◽  
Dharma Raju

An assessment of temperature extremes is made for the Indian subcontinent to identify the changes since 1951 to 2015, and for the future climate periods till 2100 for all the 21 CMIP5 (Coupled Model intercomparision Project phase 5) models and the representative concentration pathways RCP4.5 and RCP8.5 were examined for the period from 1 March to 31 May to characterize the heat waves in future climates and mean maximum and mean minimum bias were evaluated for the Indian subcontinent. Later two highest recorded temperature regions were chosen Northwest & Central India (NW&CIN) and only central India (CIN) box and the features of heat waves such as intensity and frequency were evaluated up to 2100. Corresponding temperature predictions from historical runs for the period 1951–2005 of 21 global CMIP model outputs and statistics were performed with the India Meteorological Department (IMD) gridded maximum temperature data for validation. Statistical metrics of BIAS, RMSE and MAE have indicated low BIAS, high correlation and high IOA (Index of Agreement) validating CMIP climate simulations. By analyzing the statistics of all the 21 models with respect to the observational gridded data from IMD came to conclusion that among all the 21 models 5 models were performing well for Indian region and having good index of agreement with IMD. The frequencies of the days having thresholds of 40 ºC, 42 ºC and 45 ºC for the maximum temperature over India during the pre-monsoon are evaluated up to 21st century. All models are showing that the intensity and frequency of heat waves were increasing significantly for both RCP4.5 and RCP8.5. Specifically, the characteristics of heat waves in terms of intensity, duration and area extent are calculated and compared to heat waves of the current climate.


2018 ◽  
Vol 31 (17) ◽  
pp. 6985-7002 ◽  
Author(s):  
Yong Wang ◽  
Guang J. Zhang ◽  
Yiquan Jiang

The Plant–Craig (PC) stochastic convective parameterization scheme is modified by linking the stochastic generation of convective clouds to the change of large-scale vertical pressure velocity at 500 hPa with time so as to better account for the relationship between convection and the large-scale environment. Three experiments using the National Center for Atmospheric Research (NCAR) Community Atmosphere Model, version 5 (CAM5), are conducted: one with the default Zhang–McFarlane deterministic convective scheme, another with the original PC stochastic scheme, and a third with the modified PC stochastic scheme. Evaluation is focused on the simulation of the Indian summer monsoon (ISM), which is a long-standing challenge for all current global circulation models. Results show that the modified stochastic scheme better represents the annual cycle of the climatological mean rainfall over central India and the mean onset date of ISM compared to other simulations. Also, for the simulations of ISM intraseasonal variability for quasi-biweekly and 30–60-day modes, the modified stochastic parameterization produces more realistic propagation and magnitude, especially for the observed northeastward movement of the 30–60-day mode, for which the other two simulations show the propagation in the opposite direction. Causes are investigated through a moisture budget analysis. Compared to the other two simulations, the modified stochastic scheme with an appropriate representation of convection better represents the patterns and amplitudes of large-scale dynamical convergence and moisture advection and thus corrects the monsoon cycle associated with their covariation during the peaks and troughs of intraseasonal oscillation.


2008 ◽  
Vol 65 (5) ◽  
pp. 1549-1569 ◽  
Author(s):  
R. Chattopadhyay ◽  
A. K. Sahai ◽  
B. N. Goswami

Abstract The nonlinear convectively coupled character of the summer monsoon intraseasonal oscillation (ISO) that manifests in its event-to-event variations is a major hurdle for skillful extended-range prediction of the active/break episodes. The convectively coupled character of the monsoon ISO implies that a particular nonlinear phase of the precipitation ISO is linked to a unique pattern of the large-scale variables. A methodology has been presented to capture different nonlinear phases of the precipitation ISO using a combination of a sufficiently large number of dynamical variables. This is achieved through a nonlinear pattern recognition technique known as self-organizing map (SOM) involving six daily large-scale circulation indices. It is demonstrated that the nonlinearly classified states of the large-scale circulation isolated at the SOM nodes without involving any information on rainfall are strongly linked to different phases of evolution of the rainfall ISO, including the active and break phases. While a lower SOM classification involving 9 different states identify the composite phases of the rainfall ISO, a higher SOM classification involving 81 states can identify different shades of composite phase of the rainfall ISO. The concept of isolating the nonlinear states, as well as the technique of doing so, is robust as almost identical phases of precipitation ISO are identified by the large-scale circulation indices derived from two different reanalysis datasets, namely, the 40-yr ECMWF Re-Analysis (ERA-40) and the NCEP–NCAR reanalysis. The ability of the SOM technique to isolate spatial structure and evolutionary history of nonlinear convectively coupled states of the summer monsoon ISO opens up a new possibility of extended-range prediction of summer monsoon ISO. This knowledge is used to develop an analog technique for predicting different phases of monsoon ISO. Skillful four-pentad lead prediction of rainfall over central India is demonstrated with the model using only large-scale circulation fields. A major strength of the model is that it can easily be used for real-time extended-range prediction of monsoons.


2000 ◽  
pp. 50-61 ◽  
Author(s):  
S. V. Osipov ◽  
V. P. Verkholat

Two territories on the western coast of Peter the Great Bay were mapped in the large scale. The geobotanical mapping means revealing and displaying the essential regularities of vegetation cover. Both the spatial and temporal regularities of vegetation under natural and anthropogenic influences are well pronounced in the territory under consideration. The concept of the vegetation spatial unit (vegetation complexes) was applied as a basis for mapping. The maps and their legend were worked out as a system of vegetation combination types (vegetation combination is a spatial unit of the supracoenotic level). Such categories, as vegetation of tops and slopes, lowlands and river valleys, sea coasts reflect maximal contrasts in vegetation cover, so they are the highest level divisions of the map legend. Types of succession series and stages of series are developed for construction of the second and third levels of the legend. Communities, similar in ecotope, total species composition, saplings and some other characteristics, are referred to one type of series. 5 types of series have been distinguished: dry, fresh, moist, very moist, wet. The main factor of dynamics in considered territory is fire and the series are mainly pyrogeneous. Series are presented as sequences of vegetation stages. The vegetation stages for tops and slopes are: closed low forest — open low woodland — shrub thicket with saplings — meadow with saplings, for lowlands and river valleys they are: open low woodland — thicket of saplings — meadow or mire with saplings.


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