scholarly journals Role and impact of Siberian High on the temporal variation of Indian northeast monsoon rainfall

MAUSAM ◽  
2021 ◽  
Vol 60 (4) ◽  
pp. 505-520
Author(s):  
B. GEETHA ◽  
Y. E. A. RAJ
Keyword(s):  
Bay Of Bengal ◽  
Tamil Nadu ◽  
Monsoon Rainfall ◽  
Northeast Monsoon ◽  
Peninsular India ◽  
Sea Level Pressure ◽  
Siberian High ◽  
Northeast Monsoon Rainfall ◽  
Latitudinal Position ◽  
The Relationship

The relation between the intensity of Siberian High, defined as the mean sea level pressure over the Siberian region bounded by 87.5 & 102.5° E longitudes and 47.5 & 52.5° N latitudes (PSH) and Indian northeast monsoon rainfall has been studied in antecedent and concurrent modes based on monthly/seasonal mean PSH and monthly/seasonal rainfall data of Tamil Nadu (NMR) for the 34 year period, 1971 to 2004. It has been found that a positive relationship exists between the PSH and NMR of October-November (ON) which is significant in the antecedent mode [PSH(AS/Sep)] and modest in concurrent mode. The relationship turns negative for NMR (Dec) with both PSH(Sep) (antecedent) and PSH(Dec) (concurrent).  By and large, negative anomaly profile of PSH during September-November (SON) followed by a positive PSH (Dec) anomaly is associated with a deficient NMR, but, a normal to positive PSH anomaly profile in SON becoming  negative in December is associated with an excess NMR. The manifestation of PSH on NMR has been shown to be by way of modulating the strength of low level easterlies over the Bay of Bengal off the southeast coast of peninsular India as well as the latitudinal positions of Sub Tropical Ridge at 200 hPa (STR) and Equatorial Trough at 850 hPa (ET) over India.  An intense PSH (Sep) is associated with strengthening of easterlies over the Bay of Bengal as well as southward location of STR/ET thereby favouring  a good NMR (ON).  During December, a weaker than normal PSH (Dec) is associated with northward location of ET from its normal latitudinal position near the equator which becomes conducive for good NMR(Dec). That a weaker than normal PSH in December is associated with good NMR(Dec) is comprehended from an analysis of time series of PSH.  It has been found that the PSH itself undergoes a phase change in December on most occasions, i.e., an intense PSH (Nov) is by and large, followed by a weaker than normal PSH (Dec) and vice versa.

scholarly journals Contrasting movement of wind based equatorial trough and equatorial cloud zone over Indian southern peninsula and adjoining Bay of Bengal during the onset phase of northeast monsoon

MAUSAM ◽  
2021 ◽  
Vol 58 (1) ◽  
pp. 33-48
Author(s):  
Y. E. A. RAJ ◽  
R. ASOKAN ◽  
P. V. REVIKUMAR
Keyword(s):  
Bay Of Bengal ◽  
Tamil Nadu ◽  
Southwest Monsoon ◽  
Monsoon Onset ◽  
Northeast Monsoon ◽  
Peninsular India ◽  
Zonal Winds ◽  
The North ◽  
Latitudinal Position ◽  
Onset Phase

ABSTRACT. The northeast monsoon sets in over southern parts of peninsular India after the retreat of southwest monsoon and in association with the southward movement of equatorial trough. The INSAT satellite imageries scrutinised during the past several years revealed that the cloud bands at the time of northeast monsoon onset moved from south Bay into the southern peninsula, a feature that contrasts with the north to south movement of the equatorial trough. The paper investigates this aspect based on a dataset of lower level upper winds of the peninsula, rainfall data and INSAT OLR data for the 20 year period 1981–2000. The super epoch profiles of zonal winds, latitudinal position of equatorial trough with reference to northeast monsoon onset dates have been derived and studied. The region with OLR values less than 230 W/m2 was defined as the equatorial cloud zone and the movement of northern limit of ECZ was studied based on the normal pentad OLR data and also the superposed epoch profiles. From these analysis it has been established that at the time of northeast monsoon onset, the wind based equatorial trough moves south of Comorin whereas the cloud zone in the Bay of Bengal moves from south to north. Reasons for the occurrence of such a contrasting feature have been ascribed to features such as decreasing strength of lower level easterlies from north to south over coastal Tamil Nadu, reversal of temperature gradient between Chennai and Thiruvananthapuram at the time of onset and the dynamics of 40-day oscillation. The northeast monsoon activity over coastal Tamil Nadu has been found to be negatively correlated with the low level zonal winds over the coast, the degree of relation decreasing from north to south and also from October to December. Based on the results derived in the study and also the other known features of northeast monsoon a thematic model of northeast monsoon onset listing the events that precede and succeed the onset has been postulated.

scholarly journals The effect of ENSO / Anti ENSO on northeast monsoon rainfall

MAUSAM ◽  
2021 ◽  
Vol 50 (4) ◽  
pp. 343-354
Author(s):  
U. S. DE ◽  
R. K. MUKHOPADHYAY
Keyword(s):  
Tamil Nadu ◽  
Arabian Sea ◽  
Monsoon Rainfall ◽  
Southern Oscillation ◽  
Northeast Monsoon ◽  
Monsoon Precipitation ◽  
Peninsular India ◽  
Enso Events ◽  
The North ◽  
Northeast Monsoon Rainfall

Northeast monsoon precipitation data of 5 meteorological sub-divisions in India, spanning the period 1901-97, were analysed to identify the effect of ENSO/Anti ENSO events on the rainfall over southern peninsular India. ENSO/Anti ENSO years were selected on the basis of seasonal Southern Oscillation Index (SOI). The analysis revealed that ENSO years were generally associated with enhanced northeast monsoon precipitation while there was reduced precipitation during Anti ENSO years, the reduction in Anti ENSO years being significant for Tamil Nadu (at 0.1% level), for Kerala (at 1% level) and for South Peninsular India (at 1% level). Of 22 ENSO years, 18 years were found to be either flood or wet years, while 11 years out of 15 Anti ENSO years were found to be either drought or dry years.   During ENSO years, the Sea Surface Temperature (SST) anomalies both over the Arabian Sea and the Bay of Bengal were positive during the months October to December, while the reverse was the case during Anti ENSO years. A concurrent significant positive correlation was noted between SST over east central Arabian Sea and the north central Bay regions and northeast monsoon rainfall.   The cyclonic systems were observed to form relatively at lower latitudes during ENSO years as compared to those during Anti ENSO years. These systems were also found to move in a more westerly direction, hit Tamil Nadu and south Andhra coast, thus giving more rain over peninsula during ENSO years. The ridge line at 200 hPa level during ENSO years was located 3° south as compared to its location during Anti ENSO years.

scholarly journals Relation between southern oscillation index and Indian northeast monsoon as revealed in antecedent and concurrent modes

MAUSAM ◽  
2021 ◽  
Vol 59 (1) ◽  
pp. 15-34
Author(s):  
Y. E. A. RAJ ◽  
B. GEETHA
Keyword(s):  
Southern Oscillation Index ◽  
Monsoon Rainfall ◽  
Southern Oscillation ◽  
Negative Relationship ◽  
Positive Temperature ◽  
Northeast Monsoon ◽  
Temperature Anomalies ◽  
Northeast Monsoon Rainfall ◽  
Latitudinal Position ◽  
The Relationship

The relation between Southern Oscillation Index (SOI) and Indian northeast monsoon has been studied in antecedent and concurrent modes based on monthly /seasonal mean SOI  and monthly/seasonal rainfall data of Tamil Nadu for the 104 year period, 1901 to 2004. It has been found that a good negative relationship exists between the SOI and Indian northeast monsoon in antecedent and concurrent modes, the former being stronger than the later. In the concurrent mode, a strong negative relationship exists during the beginning of the season  which changes as the season advances and turns positive during the fag end of the season. Such a changing nature of relationship is explained through the variation of latitudinal positions of 200 hPa Sub Tropical Ridge (STR) / Equatorial Trough (ET) and the location of these with reference to the latitudinal location of the area benefited by the northeast monsoon. It has been shown that a positive (negative) SOI shifts the STR north(south)wards throughout the year. The relationship between latitudinal position of STR and the Indian northeast monsoon rainfall (NMR) is negative during the beginning of the season and turns positive during the fag end of the season, which is similar to the relationship between SOI and NMR. The relation between upper tropospheric wind/temperature anomalies and NMR also shows a similar change in relationship.  Westerly wind and negative temperature anomalies in October changing to easterly wind and positive temperature anomalies in January are by and large associated with good northeast monsoon activity.  The reversal in the relationship between latitudinal position of STR and NMR as the season advances has also been partly explained based on theoretical considerations by invoking the tilting term of the vorticity equation. Thus the SOI appears to manifest itself on Indian northeast monsoon rainfall by way of modulating the latitudinal positions of STR. An analysis based on Australian “Rainman” software on winter monsoon rainfall of some Sri Lankan and southeast Asian stations  has substantiated the changing nature of relationship. A study of dates of onset and withdrawal of Indian northeast monsoon in relation to SOI has revealed that negative (positive) SOI in September is associated with early (late) onset. But, continuation of negative SOI throughout the season favours early and abrupt withdrawal. Positive SOI during the fag end of the season is frequently associated with extension of the monsoon into January of the next year. 

On the Predictability of Northeast Monsoon Rainfall over South Peninsular India in General Circulation Models

2013 ◽  
Vol 170 (11) ◽  
pp. 1945-1967 ◽  
Author(s):  
Archana Nair ◽  
Nachiketa Acharya ◽  
Ankita Singh ◽  
U. C. Mohanty ◽  
T. C. Panda
Keyword(s):  
General Circulation ◽  
Monsoon Rainfall ◽  
General Circulation Models ◽  
Northeast Monsoon ◽  
Peninsular India ◽  
Northeast Monsoon Rainfall

On the recent strengthening of the relationship between ENSO and northeast monsoon rainfall over South Asia

2006 ◽  
Vol 28 (6) ◽  
pp. 649-660 ◽  
Author(s):  
Pankaj Kumar ◽  
K. Rupa Kumar ◽  
M. Rajeevan ◽  
A. K. Sahai
Keyword(s):  
South Asia ◽  
Monsoon Rainfall ◽  
Northeast Monsoon ◽  
Northeast Monsoon Rainfall ◽  
The Relationship

scholarly journals OUTLOOK ON NORTHEAST MONSOON RAINFALL OF TAMIL NADU

MAUSAM ◽  
2021 ◽  
Vol 44 (1) ◽  
pp. 19-22
Author(s):  
Y.E.A. RAJ ◽  
P. N. SEN ◽  
S. M. JAMADAR
Keyword(s):  
Multiple Regression ◽  
Tamil Nadu ◽  
Monsoon Rainfall ◽  
Northeast Monsoon ◽  
Northeast Monsoon Rainfall ◽  
The Mean ◽  
In The Beginning

The mean monthly wind vectors at 850, 500 and 150 hPa levels over Thiruvananthapuram (TRV) and Madras (MDS) for August. and September have been subjected to stepwise screening. The objective is to develop a scheme capable of providing an outlook of .northeast monsoon rainfall of Tamil Nu in the beginning of October. A multiple regression scheme of S1K predictors has been identified. The scheme developed from 23•year data performed well when te.ted in an independent five-year period.

scholarly journals A scheme for advance prediction of northeast monsoon rainfall of Tamil Nadu

MAUSAM ◽  
2021 ◽  
Vol 49 (2) ◽  
pp. 247-254
Author(s):  
Y. E. A. RAJ
Keyword(s):  
Tamil Nadu ◽  
Monsoon Rainfall ◽  
Southern Oscillation ◽  
Weighted Average ◽  
Test Period ◽  
Northeast Monsoon ◽  
Subtropical Anticyclone ◽  
Northeast Monsoon Rainfall ◽  
The Individual ◽  
June July

Monthly means of winds. contour height and temperature of seven standard isobaric levels of ten well distributed Indian upper air stations for the months of April, June. July, August and September were subjected to correlation analysis to detect parameters that have predictive value to forecast in advance the northeast monsoon rainfall of Tamil Nadu. The period 1965-87 was taken as developmental period and 1988-94 as test period. Six predictors, out of which three were completely new, were identified. The final forecast of rainfall was obtained as the weighted average of the individual forecasts based on the six predictors by employing a screening technique different from the conventional ones. The system explained between 65-77% variation of the predict and with standard error of 13-18% and provided reasonably correct forecasts during the test period. The physical significance of the predictors has been explained based on the intensity of the subtropical anticyclone over India. The possibility of extending the study to include global parameters in the context of proven negative and significant relationship between Southern Oscillation Index (SOl) and the Indian northeast monsoon has been discussed. Scope for further studies on the topic has been spelt out.

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