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 Relationship between Indian summer monsoon rainfall and sea surface temperature anomalies over equatorial central and eastern Pacific

MAUSAM ◽  
2021 ◽  
Vol 49 (2) ◽  
pp. 229-234
Author(s):  
V. THAPLIYAL ◽  
M. RAJEEVAN ◽  
S. R. PATIL
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Monsoon Rainfall ◽  
Indian Summer Monsoon Rainfall ◽  
Monsoon Season ◽  
Summer Monsoon Rainfall ◽  
Sea Surface ◽  
Sst Anomalies

Sea surface temperature (SST) variations over the three key regions over equatorial Pacific, viz., Nino (1+2), Nino 3 and Nino 4 and their relationships with Indian summer monsoon rainfall have been examined in this study. On monthly scale, SST anomalies over the three key regions show an oscillatory type of lagged correlations with Indian monsoon rainfall, positive correlations almost one year before the monsoon season (CC's are of the order of 0.3) which gradually change to significant negative correlation peaking in September/October during/after the monsoon season. The variations on seasonal scale also exhibit the same pattern of monthly variations but more smooth in nature. Composites of similar monsoon years show that during deficient (excess) monsoon years SST anomalies over all the three regions have warmer (cooler) trend which starts about 6 months prior to monsoon season. Tendencies of SST anomalies from previous winter (DJF) to summer (MAM) seasons over Nino 3 and Nino 4 regions are better predictors than EI-Nino categories currently being used in IMD's operational LRF model. By using tendency of SST over EI- Nino -4 region, in place of the category of EI-Nino, the 16 parameter operational Power Regression Model of IMD has been modified. The new forecast model shows better reduction in the forecast error.

scholarly journals Variability and Trends of Summer Monsoon Rainfall over Bangladesh

1970 ◽  
Vol 7 (1) ◽  
pp. 1-17 ◽  
Author(s):  
MN Ahasan ◽  
Md AM Chowdhary ◽  
DA Quadir
Keyword(s):  
Time Series ◽  
Time Scales ◽  
Summer Monsoon ◽  
Monsoon Rainfall ◽  
Monsoon Season ◽  
Rainfall Variability ◽  
Summer Monsoon Rainfall ◽  
Eastern Region ◽  
Strong Impact ◽  
South Central

In this paper, the updated rainfall data of 50 years (1961-2010) for 30 selected rain gauge stations of Bangladesh have been used. The data were analyzed to investigate the variability and trends of summer monsoon (June- September) rainfall over Bangladesh. The possible teleconnection of monsoon rainfall variability with ENSO has also been investigated. Annual profile of the station mean monthly rainfall of Bangladesh shows a unimodal pattern with high rainfall between June-September (monsoon season) with highest in July and low rainfall between December – February with lowest in January. All Bangladesh mean summer monsoon rainfall is 1769.14 mm, standard deviation 209.16 mm (coefficient of variance 11.82 %) and annual country average rainfall is 2456.38 mm. Summer monsoon rainfall widely varies over the geographical areas with lowest in central-western part and highest in southeastern part with next highest in northeastern part of the country. The trend analysis shows that the trend of the country average monsoon rainfall is decreasing (-0.53 mm/year). The spatial distribution of the trend values indicates that the summer monsoon rainfall exhibits increasing trends at the rate of 5-6 mm/year in the NW region and 3-4 mm/ year in the south-central and extreme SE region. The eastern region exhibits decreasing trends of about -2 to -7 mm/year with highest (-6 to -7 mm/year) in the east-central part. The time series plot of country average summer monsoon rainfall shows the inter-annual variability in the timescales of 2-3 years and 4-6 years. The time series of 5 year moving average reveals existence of low frequency variability of timescales of 9-14 years. The time series of Bangladesh monsoon rainfall shows that there were 11 strong monsoon years and 8 weak monsoon years within the periods of 1961-2010 (50 years). The analysis of the decadal mean rainfall shows that the decades 1961-1970 and 1981-1990 were wet and the decades 1971-1980, 1991-2000 and 2001-2010 were dry. Floods in Bangladesh result from the excess rainfall occurring both inside and outside the country. Summer monsoon rainfall is characterized by active and weak (break) spells, which are associated with the fluctuation of monsoon rainfall in the time scales of 20-25 and 40-50 days. Such fluctuations are caused due to north-south movement of the monsoon trough. The fluctuations in the time scales of 4-7 and 10-14 days are associated with the formation of low pressure systems over the head Bay. The possible atmospheric teleconnections of summer monsoon rainfall with ENSO have also been investigated. It is found that there is strong impact of ENSO on the monsoon system of subcontinent scale, though the relationship is weak in case of Bangladesh. The variability of Bangladesh rainfall has been investigated with respect to that for Nepal, Bhutan and the neighbouring sub-divisional regions of India. The results show that Bangladesh rainfall has positive correlation with that of the Indian regions of Naga-Monipur-Mizo-Tripura, Sub Himalayan West Bengal and Sikkim, and Bhutan. The above analysis shows the homogeneity of rainfall activities over these areas. Orissa shows negative correlation with Bangladesh. Keywords: Rainfall; Variability; Summer Monsoon; ENSO; TrendDOI: http://dx.doi.org/10.3126/jhm.v7i1.5612 JHM 2010; 7(1): 1-17

scholarly journals Variation of summer monsoon rainfall over India in El-Ninos

MAUSAM ◽  
2021 ◽  
Vol 48 (3) ◽  
pp. 413-420
Author(s):  
D.A. MOOLEY
Keyword(s):  
Summer Monsoon ◽  
Monsoon Rainfall ◽  
Monsoon Season ◽  
Percent Level ◽  
Central India ◽  
Summer Monsoon Rainfall ◽  
Sea Surface ◽  
Pacific Region ◽  
The Pacific ◽  
Second Category

ABSTRACT. El Ninos which occurred during 1871-1990 are divided into two categories of events. The first category, EW, consists of the El Ninos in which the equatorial southeast (ESE) Pacific region (0-10° S; 80°W-180°W) experienced a Warn1ing phase as defined by suitable objective criteria, and the second category, E, consists of El Ninos in which the ESE Pacific region did not experience the warming phase. Sea surface temperature rise as well as anomaly over the Pacific region, summer monsoon rainfall over India and over its meteorological sub-divisions, in the categories EW and E are compared. Area-averaged rainfall of India for the summer monsoon season and for each of the months July and September are significantly (at 0.1 percent level) lower in EW events in comparison to those in E events. The summer monsoon rainfall of each of the 12 sub-divisions, from northwest and central India constituting about 50 per cent of the Indian plains, is significantly lower in EW events than that in E events, the highest rainfall deficiency in EW events being in the westernmost sub-divisions, i.e., West Rajasthan and Saurashtra-Kutch. Possible causes for the same have also been discussed.    

scholarly journals The association between the north Indian Ocean and summer monsoon rainfall over India

MAUSAM ◽  
2021 ◽  
Vol 49 (3) ◽  
pp. 325-330
Author(s):  
O. P. SINGH
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
Arabian Sea ◽  
Monsoon Rainfall ◽  
Monsoon Season ◽  
Meteorological Data ◽  
Summer Monsoon Rainfall ◽  
North Indian Ocean ◽  
The North ◽  
The Mean

Utilizing the marine meteorological data of the period 1961-81, the sea level pressure (SLP) and sea surface temperature (SST) distributions have been obtained on a 5° grid-mesh over the north Indian Ocean area bounded by  0°- 25°N, 50°- l00°E for each individual year. It has been found that the SLP and SST fields for the month of May provide predictive indications of subsequent summer monsoon rainfall over India. Significant negative correlations have been found between the mean SLPs of May over the latitudinal belts 5°-10°, 10°- 15°, 15°-20° and 20°-25°N of Arabian Sea and Bay of Bengal and all India rainfall departures of succeeding summer monsoon season. The mean SST gradient over the Arabian Sea between 7.5°- 17 .5°N during May has been found to have significant positive correlation with all India rainfall of subsequent monsoon. The study suggests that certain functions of SLP and SST of May over the north Indian Ocean can prove to be useful predictors for subsequent summer monsoon rainfall over India.

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 Timing of El Niño–Related Warming and Indian Summer Monsoon Rainfall

2008 ◽  
Vol 21 (11) ◽  
pp. 2711-2719 ◽  
Author(s):  
Chie Ihara ◽  
Yochanan Kushnir ◽  
Mark A. Cane ◽  
Alexey Kaplan
Keyword(s):  
Summer Monsoon ◽  
El Niño ◽  
Monsoon Rainfall ◽  
El Nino ◽  
Southern Oscillation ◽  
Monsoon Season ◽  
Summer Monsoon Rainfall ◽  
Equatorial Pacific ◽  
Central Pacific ◽  
Eastern Equatorial Pacific

Abstract The relationship between all-India summer monsoon rainfall (ISMR) and the timing of (El Niño–Southern Oscillation) ENSO-related warming/cooling is investigated, using observational data during the period from 1881 to 1998. The analysis of the evolutions of Indo-Pacific sea surface temperature (SST) anomalies suggests that when ISMR is not below normal despite the co-occurrence of an El Niño event, warming over the eastern equatorial Pacific starts from boreal winter and evolves early so that the western-central Pacific and Indian Ocean are warmer than normal during the summer monsoon season. In contrast, when the more usual El Niño–dry ISMR relationship holds, the eastern equatorial Pacific starts warming rapidly only about a season before the reference summer so that the western-central Pacific and Indian Oceans remain cold during the monsoon season.

scholarly journals Activity of Madden Julian Oscillation during 2002 and 2006 – A comparative analysis

MAUSAM ◽  
2021 ◽  
Vol 59 (3) ◽  
pp. 321-326
Author(s):  
MEDHA KHOLE
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Seasonal Variability ◽  
Monsoon Rainfall ◽  
Indian Summer Monsoon Rainfall ◽  
Monsoon Season ◽  
Rainfall Variability ◽  
Summer Monsoon Rainfall ◽  
Equatorial Region ◽  
Madden Julian Oscillation

The Indian summer monsoon is characterized by very significant intra-seasonal variability. Madden-Julian Oscillation (MJO) is one of the dominant modes of the intra-seasonal variability of the Indian summer monsoon rainfall.  The activity of Madden Julian Oscillation during the monsoon seasons of the two years of contrasting intra-seasonal rainfall variability has been examined in terms of rainfall activity over India and eastward propagation of convection in the near-equatorial region. The study shows the contrasting nature, viz., in the monsoon season of 2002, eastward mode dominated whereas in 2006, it remained suppressed.

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