scholarly journals Distribution of mean monthly surface/upper air parameters during July-August months of 1982-83 and 1987- 88

MAUSAM ◽  
2021 ◽  
Vol 57 (2) ◽  
pp. 255-270
Author(s):  
K. SEETHARAM
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Surface Parameters ◽  
Zonal Winds ◽  
Western Disturbances ◽  
E Region ◽  
Global Nature

Lkkj & Hkkjrh; xzh"edkyhu ekulwu dks leqnz vkSj /kjkry dh feyh&tqyh ok;qeaMyh; ifj?kVuk ekurs gq, bldk v/;;u HkweaMyh; izÑfr ds ifjn`’; esa fd;k x;k gSA bl v/;;u esa nks fo"ke ifjfLFkfr;ksa  esa ekulwu ds O;ogkj dks le>us ds fy, Øe’k% de vkSj vf/kd nksuksa rjg dh o"kkZ okys nks o"kksaZ ¼1982] 1987½] nks o"kksaZ ¼1983] 1988½ esa xzh"edkyhu ekulwu ds nks izeq[k eghuksa tqykbZ vkSj vxLr ds nkSjku 'kwU; va’k m- ls 40 va’k m-@40 va’k iw- ls 100 va’k iw- ds {ks= esa ek/; ekfld /kjkryh; izkpyksa ds forj.k dks fy;k x;k gSA blds vfrfjDr xzh"edkyhu ekulwu ij {kksHkeaMyh; if’peh gokvksa ds izHkko vkSj if’peh fo{kksHkksa dh xfrfof/k dk ewY;kadu djus ds fy, fuEu {kksHkeaMy dh dfVca/kh; iouksa ds forj.k vFkkZr~] tqykbZ] vxLr ds eghuksa esa 850 gSDVkikLdy vkSj 700 gSDVkikLdy ds Lrjksa tuojh] ebZ] tqykbZ vkSj vxLr ds eghuksa ds fy, 500 gSDVkikLdy ij HkwfLFkfrt Å¡pkb;ksa dk v/;;u fd;k x;k gSA bl v/;;u ls izkIr gq, ifj.kkeksa ij fopkj&foe’kZ fd;k x;k gSA  Indian summer monsoon is considered as an ocean-land-atmosphere coupled phenomenon and also of global nature. In present study, the distribution of mean monthly surface parameters within 0° N – 40° N / 40° E – 100° E region during the two representative months of summer monsoon, July and August,  in both deficient years (1982, 1987) and excess years (1983, 1988) was taken up to understand the behaviour of monsoon during two contrasting situations. Apart from this, the distribution of lower tropospheric zonal winds viz., 850 hPa and 700 hPa levels during July, August months, 500 hPa geopotential heights for the months of January, May, July and August months studied to assess the influence of tropospheric westerlies and  activity of Western Disturbances on the summer monsoon. The results discussed.

scholarly journals Revisiting the Possible Links between the Quasi-Biennial Oscillation and the Indian Summer Monsoon Using NCEP R-2 and CMAP Fields

2007 ◽  
Vol 20 (5) ◽  
pp. 773-787 ◽  
Author(s):  
Chantal Claud ◽  
Pascal Terray
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Indian Subcontinent ◽  
Rainfall Variability ◽  
Equatorial Indian Ocean ◽  
Boreal Winter ◽  
Convective Activity ◽  
Quasi Biennial Oscillation ◽  
Zonal Winds ◽  
Biennial Oscillation

Abstract In the past the stratospheric quasi-biennial oscillation (QBO) has sometimes been proposed to explain the tendency for the Indian summer monsoon (ISM) to alternate between strong and weak years. In this study, NCEP Reanalysis-2 (R-2) and Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) fields are statistically analyzed to assess the relationship between equatorial zonal winds in the stratosphere and ISM. In a first step, it is shown that zonal winds at 15 hPa during the preceding winter (January–February) are the best stratospheric predictor of the summer rainfall over the Indian subcontinent as a whole. This relationship mainly holds for August and September, or the late ISM. Surprisingly, the QBO pattern is not significantly associated with the rainfall variability during June–July or the early ISM. CMAP and NCEP R-2 fields corroborate these findings and show that westerly QBO years are associated with a deepening of the monsoon trough over the Gangetic plains and decreased convective activity in the eastern equatorial Indian region. However, further statistical analysis shows that the QBO–ISM link is complex since a westerly QBO phase at 15 hPa in boreal winter leads to a weaker monsoon surface circulation with, in particular, a weakening of the Somali jet at the beginning of the monsoon, but a much stronger circulation in September. At that time, the Tibetan high is reinforced, the tropical easterly jet at 200 hPa is stronger over India, and the local reversed Hadley circulation is also strengthened north of the equator. The mechanisms by which the QBO may affect ISM have been explored through, in particular, correlations between stratospheric winds and tropopause temperature and pressure fields. The results provide support for an out-of-phase behavior of convective activity between the Indian subcontinent and the equatorial Indian Ocean induced by the QBO phase, especially during the late ISM. During a westerly QBO phase, convective activity is, in September, enhanced over India, which brings higher precipitation, compared to the east phase. This work also suggests that the winter QBO at 15 hPa could have some skill in foreshadowing the late ISM.

VARIABILITY IN THE INDIAN SUMMER MONSOON PRECIPITATION AND LAKE LEVELS IN EASTERN TIBET

2016 ◽  
Author(s):  
Melanie Perello ◽  
◽  
Broxton W. Bird ◽  
Yanbin Lei ◽  
Pratigya J. Polissar ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Monsoon Precipitation ◽  
Lake Levels ◽  
Eastern Tibet

scholarly journals Tectonic and climatic drivers of Asian monsoon evolution

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
James R. Thomson ◽  
Philip B. Holden ◽  
Pallavi Anand ◽  
Neil R. Edwards ◽  
Cécile A. Porchier ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Asian Monsoon ◽  
Monsoon Rainfall ◽  
East Asian Monsoon ◽  
East Asian ◽  
Meridional Overturning Circulation ◽  
Great Debate ◽  
Climatic Drivers ◽  
Meridional Overturning

AbstractAsian Monsoon rainfall supports the livelihood of billions of people, yet the relative importance of different drivers remains an issue of great debate. Here, we present 30 million-year model-based reconstructions of Indian summer monsoon and South East Asian monsoon rainfall at millennial resolution. We show that precession is the dominant direct driver of orbital variability, although variability on obliquity timescales is driven through the ice sheets. Orographic development dominated the evolution of the South East Asian monsoon, but Indian summer monsoon evolution involved a complex mix of contributions from orography (39%), precession (25%), atmospheric CO2 (21%), ice-sheet state (5%) and ocean gateways (5%). Prior to 15 Ma, the Indian summer monsoon was broadly stable, albeit with substantial orbital variability. From 15 Ma to 5 Ma, strengthening was driven by a combination of orography and glaciation, while closure of the Panama gateway provided the prerequisite for the modern Indian summer monsoon state through a strengthened Atlantic meridional overturning circulation.

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