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 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.

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 Influence of some circulation anomalies on Indian northeast monsoon rainfall

MAUSAM ◽  
2021 ◽  
Vol 49 (4) ◽  
pp. 443-448
Author(s):  
G. P. SINGH ◽  
J. CHATTOPADHYAY
Keyword(s):  
Tamil Nadu ◽  
Direct Relationship ◽  
Monsoon Rainfall ◽  
Southern Oscillation ◽  
Rainfall Series ◽  
Northeast Monsoon ◽  
Equatorial Pacific Ocean ◽  
Northeast Monsoon Rainfall ◽  
June July ◽  
Sst Anomalies

The relationship between Indian northeast monsoon rainfall over Tamil Nadu (TNR) and southeast India (SER) as well as two indices of southern oscillation (SOI), and sea surface temperature (SST) anomalies over different Nino regions of equatorial Pacific Ocean and seven tropical circulation indices (TCI), have been studied for different periods. The study indicates that northeast monsoon rainfall (TNR) shows significant inverse relationship with SOI (I-D) during previous MAM (March- April-May) season. significant direct relationship with SST anomalies over Nino-4 region during previous JJA (June-July- August) and significant direct relationship with TCI (C-N) during previous DJF, The SOI (I-D), MAM correlates I significantly and negatively with both the northeast monsoon rainfall series, the TNR rainfall series displaying the better correlation. The strongest correlation is observed during 1961-90. For SSTA, the strongest correlation is during 1964-85 and for TCI, the highest correlation is observed during 1958-82.

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

scholarly journals Spatial variation of clouding / rainfall over southeast Indian peninsula and adjoining Bay of Bengal associated with active and dry spells of northeast monsoon as derived from INSAT OLR data

MAUSAM ◽  
2021 ◽  
Vol 67 (3) ◽  
pp. 559-570
Author(s):  
B. AMUDHA ◽  
Y. E. A. RAJ ◽  
R. ASOKAN
Keyword(s):  
Spatial Variation ◽  
Tamil Nadu ◽  
Active Phase ◽  
Wave Radiation ◽  
Northeast Monsoon ◽  
Peninsular India ◽  
North East ◽  
The North ◽  
Northern Latitudes ◽  
Dry Spells

South Peninsular India (SPI) benefits largely from the rainfall (RF) realised during the North East Monsoon (NEM) season that prevails from October to December spilling over to January in some of the years.  Salient aspects of clouding / RF over SPI associated with 13 NEM seasons from 2000-01 to 2012-13 have been analysed using estimates of Outgoing Long wave Radiation (OLR) at 1° × 1° resolution derived from the radiance observations in the infra-red channel onboard the geostationary operational Indian satellite (INSAT) radiometers. OLR is considered as a proxy indicator for convective activity with the value of 230 Wm-2  as the threshold for RF occurrence. Year-to-year mean OLR patterns of the NEM season along with the latitudinal and longitudinal variabilities were analysed for dry, light and active phases of NEM. Based on rigorous analysis of INSAT OLR data for the above 13 years, it has been shown that during the active phase of NEM, Coastal Tamil Nadu (CTN) receives more RF while over BoB the RF is lower and decreases sharply over interior Tamil Nadu. This is a reiteration of a similar result from an earlier study based on 3 years (1996-98) OLR data from polar orbiting NOAA satellites. The spatial variation in OLR over the latitudes of 10.5, 12.5 and 14.5° N along  the longitudes of 75.5-85.5° E  has revealed the feature that  north of 10.5° N, values of OLR are higher with decrease in RF from south to north.  During dry phase of NEM in December and January, higher OLR is observed over northern latitudes of BoB than southern latitudes. It has been comprehended that in the southern latitudes of BoB, where higher sea surface temperatures (SST) are prevalent, more moisture is generated and pumped in to upper levels of the atmosphere leading to lower values of OLR compared to northern latitudes.  

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 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.

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