scholarly journals Importance of meridional winds in. forecasting sub-regional summer monsoon rainfall

MAUSAM ◽  
2021 ◽  
Vol 47 (3) ◽  
pp. 275-280
Author(s):  
DHANNA SINGH ◽  
SUMAN GOYAL ◽  
C.V.V. BHADRAM ◽  
G. S. MANDAL
Keyword(s):  
Monsoon Rainfall ◽  
Temporal Stability ◽  
Correlation Coefficients ◽  
Meridional Wind ◽  
Northeast India ◽  
Summer Monsoon Rainfall ◽  
Temporal Behaviour ◽  
Sliding Windows ◽  
Meridional Winds ◽  
Level Of Significance

ABSTRACT. Based on 35 years' (1959-1993) data, the zonal and meridional wind components of selected Indian RS/RW statiomupto 100 hPa level were analysed for the pre-monsoon months of April and May in order to associate them with sub-regional monsoon rainfall of northeast India. Composite values of monsoon rainfall and meridional components for May for excess and deficient yean have revealed that anomaly of meridional components for the middle and upper troposphere is northerly/southerly preceding excees/deficient monsoon year. The meridional winds at most of the levels of Delhi and some of the levels of Jodhpur Nagpur, Bombay and Madras for the month of May showed significant correlations (significant at 0.1% to 5% level of significance) with sub-divisional monsoon rainfall in northeast India. The temporal behaviour of correlation coefficients for Punjab and Haryana for 16 and 20-year sliding windows has exhibited rasonable temporal stability except for first few years. Multiple rearession equations for 30 and 35 year period for Haryana, Punjab and contiguous northweat India were also developed. The regression model for Punjab sub-division has shown quite good  results for the independent period.  

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 Zonal wind variations in the stratosphere and mesosphere over the equatorial region of Asia and possible association with Indian summer monsoon rainfall

MAUSAM ◽  
2021 ◽  
Vol 50 (3) ◽  
pp. 243-250
Author(s):  
U. S. DE ◽  
K. RATNAM ◽  
R. K. MUKHOPADHYAY
Keyword(s):  
Summer Monsoon ◽  
Annual Cycle ◽  
Lower Stratosphere ◽  
Monsoon Rainfall ◽  
Correlation Coefficients ◽  
Summer Monsoon Rainfall ◽  
Equatorial Region ◽  
Seasonal Rainfall ◽  
Wind Data ◽  
Zonal Winds

Behaviour of stratospheric and mesospheric zonal winds in the equatorial region of Asia has been studied using rocket wind data from 921 flights for the period from 1970 to 1993 over Thumba (India) and upper wind data in the lower stratosphere over Singapore (S.E. Asia) from 1970 to 1997. Monthly means of these zonal winds are subjected to spectrum analysis. It is inferred that the quasi-biennial oscillation (QBO) with periodicity of 22 to 30 months and annual cycle with periodicity of 11 to 12 months dominate in the lower stratosphere over Thumba, while the semi-annual cycle is predominant in the upper stratosphere and mesosphere. QBO in the lower stratosphere over Singapore has been observed to be significant with periodicity of 22 to 28 months, whereas the annual cycle has no significance.   There exists a prognostic value between easterly & westerly phases of QBO over Thumba during the antecedent months of January to May and the performance of succeeding summer monsoon rainfall over India with strong easterlies favouring decreased rainfall and westerlies or light easterlies favouring increased rainfall over the country a s a whole. Correlation coefficients are statistically significant between the seasonal rainfall over India and zonal winds at 10 hPa (30 km) during winter months and also zonal winds at 30 hPa (24 km) during pre-monsoon months. However, there is an improvement in correlation if combined circulation of zonal winds at 10 hPa during winter and at 30 hPa during pre-monsoon is considered. Zonal winds at 50 hPa (20 km) and 30 hPa (24 km) over Singapore during monsoon months show diagnostic value with seasonal rainfall over India having significant concurrent correlation coefficients; however winds during winter and pre-monsoon do not show significant correlation with Indian monsoon. Thus, this could be used to monitor the progress of south-west monsoon performance but not in predicting it.   Over Thumba, the mean zonal winds at 30 hPa during ENSO and anti- ENSO years differ significantly in the annual feature.

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