scholarly journals Monsoon variability in recent years from synoptic scale disturbances and semi-permanent systems

MAUSAM ◽  
2021 ◽  
Vol 50 (2) ◽  
pp. 135-144
Author(s):  
J. RAJENDRA KUMAR ◽  
D. S. DESAI
Keyword(s):  
Monsoon Rainfall ◽  
Weighted Average ◽  
Recent Decade ◽  
Monsoon Trough ◽  
Summer Monsoon Rainfall ◽  
Average Value ◽  
Westerly Jet ◽  
Positive Side ◽  
Monsoon Variability ◽  
Interannual Scale

In the recent decade from 1987 to 1996, the Indian summer monsoon rainfall has shown less interannual variability in comparison with its earlier decade. Except 1987 and 1988, the area weighted average monsoon rainfall of all other years are within 10% (normal) of its long period average value over India. The paper discusses monsoon rainfall and several other associated circulations features with their variability in interannual scale during 1987-96. The results show that though the variability of monsoon rainfall is less during the decade, there is a significant interannual variation in the number of synoptic systems, their days, intensities and number of days of presence of monsoon trough and Tibetan anticyclone.   The years with positive side (negative side) of normal seasonal rainfall are characterised by more (less) number of days of synoptic disturbances and more (less) number of days of presence of monsoon trough and Tibetan anticyclone in their favourable positions. However, overall activity of heat low, tropical easterly jet and sub-tropical westerly jet in the season have no direct relation with seasonal monsoon rainfall. In addition, the dates of onset and withdrawal of monsoon over India and the number of days monsoon took to over all India also have no relation with the monsoon rainfall.  

scholarly journals Interannual Variation of the Summer Rainfall Center in the South China Sea

2017 ◽  
Vol 30 (19) ◽  
pp. 7909-7931 ◽  
Author(s):  
Tsing-Chang Chen ◽  
Jenq-Dar Tsay ◽  
Jun Matsumoto
Keyword(s):  
Summer Monsoon ◽  
Interannual Variation ◽  
Monsoon Rainfall ◽  
Monsoon Season ◽  
Summer Rainfall ◽  
The Philippines ◽  
Monsoon Trough ◽  
Summer Monsoon Rainfall ◽  
Tropical Depression ◽  
Easterly Wave

Abstract A northwest–southeast-oriented summer monsoon trough exists between northern Indochina and northwestern Borneo. Ahead of this the South China Sea (SCS) trough is located at a convergent center west of the Philippines, which provides an environment favorable for rain-producing synoptic systems to produce rainfall over this center and form the SCS summer rainfall center. Revealed from the x–t diagram for rainfall, this rainfall center is developed by multiple-scale processes involved with the SCS trough (TR), tropical depression (TY), interaction of the SCS trough with the easterly wave/tropical depression (EI), and easterly wave (EW). It is found that 56% of this rainfall center is produced by the SCS trough, while 41% is generated by the other three synoptic systems combined. Apparently, the formation of the SCS summer monsoon rainfall center is contributed to by these four rain-producing synoptic systems from the SCS and the Philippines Sea. The Southeast Asian summer monsoon undergoes an interannual variation and exhibits an east–west-oriented cyclonic (anticyclonic) anomalous circulation centered at the western tropical Pacific east of the Luzon Strait. This circulation change is reflected by the deepening (filling) of the SCS summer monsoon trough, when the monsoon westerlies south of 15°N intensify (weaken). This interannual variation of the monsoon westerlies leads to the interannual variation of the SCS summer monsoon rainfall center to follow the Pacific–Japan oscillation of rainfall. The rainfall amount produced over this rainfall center during the weak monsoon season is about two-thirds of that produced during the strong monsoon season. The rain-production ratio between TR and TY + EI + EW is 60:38 during the strong monsoon season and 47:49 during the weak monsoon season.

scholarly journals Daily summer monsoon rainfall over northeast India due to synoptic scale systems

MAUSAM ◽  
2021 ◽  
Vol 59 (1) ◽  
pp. 35-50
Author(s):  
M. MOHAPATRA ◽  
H. R. BISWAS ◽  
G. K. SAWAISARJE
Keyword(s):  
Summer Monsoon ◽  
Monsoon Rainfall ◽  
Rainfall Variability ◽  
Daily Rainfall ◽  
Northeast India ◽  
Monsoon Trough ◽  
Summer Monsoon Rainfall ◽  
Synoptic Scale ◽  
Data Set ◽  
The Mean

The summer monsoon rainfall over northeast India mostly depends on the synoptic systems over the region and neighbourhood and the convection due to the interaction of orography with the synoptic and sub-synoptic scale systems. Hence, an attempt is made to analyse the mean daily rainfall distribution over northeast India due to different synoptic systems like Low Pressure Systems (LPS) and cyclonic circulations (cycir) extending upto lower/middle tropospheric levels over different regions. The mean daily rainfall due to monsoon trough over various locations in northeast India is also analysed. For the above purpose, the rainfall data over 50 uniformly distributed stations in northeast India during summer monsoon season (June-September) for a period of 10 years (1991-2000) are considered. The principal objective of the study is to find out the contribution of the different synoptic systems to the spatial variability of monsoon rainfall over northeast India.   The developed synoptic analog maps may be useful to the forecasters for 24 hours rainfall forecast with the knowledge of location, intensity and movement of the synoptic systems. Based on larger data set, the results confirm the earlier findings (Srinivasan et al., 1972) with respect to rainfall due to monsoon trough and LPS. The Low Level Cycir (LLC) also plays significant role on the rainfall variability over northeast India, as the number of LLC days is significantly higher over the region, contrary to the days of occurrence of LPS. The study finds out the regions of excess/deficient rainfall and active/weak monsoon conditions due to different synoptic systems.

scholarly journals Considerations of the Scale of Radiocarbon Offsets in the East Mediterranean, and Considering a Case for the Latest (Most Recent) Likely Date for the Santorini Eruption

Radiocarbon ◽  
2012 ◽  
Vol 54 (3-4) ◽  
pp. 449-474 ◽  
Author(s):  
Sturt W Manning ◽  
Bernd Kromer
Keyword(s):  
Time Horizon ◽  
Weighted Average ◽  
17Th Century ◽  
Data Sets ◽  
East Mediterranean ◽  
Average Value ◽  
Accuracy And Precision ◽  
Wide Range ◽  
The Impact ◽  
East Mediterranean Region

The debate over the dating of the Santorini (Thera) volcanic eruption has seen sustained efforts to criticize or challenge the radiocarbon dating of this time horizon. We consider some of the relevant areas of possible movement in the14C dating—and, in particular, any plausible mechanisms to support as late (most recent) a date as possible. First, we report and analyze data investigating the scale of apparent possible14C offsets (growing season related) in the Aegean-Anatolia-east Mediterranean region (excluding the southern Levant and especially pre-modern, pre-dam Egypt, which is a distinct case), and find no evidence for more than very small possible offsets from several cases. This topic is thus not an explanation for current differences in dating in the Aegean and at best provides only a few years of latitude. Second, we consider some aspects of the accuracy and precision of14C dating with respect to the Santorini case. While the existing data appear robust, we nonetheless speculate that examination of the frequency distribution of the14C data on short-lived samples from the volcanic destruction level at Akrotiri on Santorini (Thera) may indicate that the average value of the overall data sets is not necessarily the most appropriate14C age to use for dating this time horizon. We note the recent paper of Soter (2011), which suggests that in such a volcanic context some (small) age increment may be possible from diffuse CO2emissions (the effect is hypothetical at this stage and hasnotbeen observed in the field), and that "if short-lived samples from the same stratigraphic horizon yield a wide range of14C ages, the lower values may be the least altered by old CO2." In this context, it might be argued that a substantive “low” grouping of14C ages observable within the overall14C data sets on short-lived samples from the Thera volcanic destruction level centered about 3326–3328 BP is perhaps more representative of the contemporary atmospheric14C age (without any volcanic CO2contamination). This is a subjective argument (since, in statistical terms, the existing studies using the weighted average remain valid) that looks to support as late a date as reasonable from the14C data. The impact of employing this revised14C age is discussed. In general, a late 17th century BC date range is found (to remain) to be most likelyeven ifsuch a late-dating strategy is followed—a late 17th century BC date range is thus a robust finding from the14C evidence even allowing for various possible variation factors. However, the possibility of a mid-16th century BC date (within ∼1593–1530 cal BC) is increased when compared against previous analyses if the Santorini data are considered in isolation.

scholarly journals Water–food–energy nexus with changing agricultural scenarios in India during recent decades

2017 ◽  
Vol 21 (6) ◽  
pp. 3041-3060 ◽  
Author(s):  
Beas Barik ◽  
Subimal Ghosh ◽  
A. Saheer Sahana ◽  
Amey Pathak ◽  
Muddu Sekhar
Keyword(s):  
Food Production ◽  
Monsoon Rainfall ◽  
Central India ◽  
Recent Decade ◽  
High Energy ◽  
Western India ◽  
Groundwater Storage ◽  
Ganga Basin ◽  
Strong Negative Correlation ◽  
Food Energy

Abstract. Meeting the growing water and food demands in a densely populated country like India is a major challenge. It requires an extensive investigation into the changing patterns of the checks and balances behind the maintenance of food security at the expense of depleting groundwater, along with high energy consumption. Here we present a comprehensive set of analyses which assess the present status of the water–food–energy nexus in India, along with its changing pattern, in the last few decades. We find that with the growth of population and consequent increase in the food demands, the food production has also increased, and this has been made possible with the intensification of irrigation. However, during the recent decade (after 1996), the increase in food production has not been sufficient to meet its growing demands, precipitating a decline in the per-capita food availability. We also find a statistically significant declining trend of groundwater storage in India during the last decade, as derived from the Gravity Recovery and Climate Experiment (GRACE) satellite datasets. Regional studies reveal contrasting trends between northern and western–central India. North-western India and the middle Ganga basin show a decrease in the groundwater storage as opposed to an increasing storage over western–central India. Comparison with well data reveals that the highest consistency of GRACE-derived storage data with available well measurements is in the middle Ganga basin. After analysing the data for the last 2 decades, we further showcase that, after a drought, the groundwater storage drops but is unable to recover to its original condition even after good monsoon years. The groundwater storage reveals a very strong negative correlation with the electricity consumption for agricultural usage, which may also be considered as a proxy for groundwater pumped for irrigation in a region. The electricity usage for agricultural purposes has an increasing trend and, interestingly, it does not have any correlation with the monsoon rainfall as computed with the original or de-trended variables. This reveals an important finding that the irrigation has been intensified irrespective of rainfall. This also resulted in a decreasing correlation between the food production and monsoon rainfall, revealing the increasing dependency of agricultural activities on irrigation. We conclude that irrigation has now become essential for agriculture to meet the food demand; however, it should be judiciously regulated and controlled, based on the water availability from monsoon rainfall, specifically after the drought years, as it is essential to recover from the deficits suffered previously.

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