scholarly journals Composite Structure of Monsoon Low Pressure Systems and Its Relation to Indian Rainfall

2010 ◽  
Vol 23 (16) ◽  
pp. 4285-4305 ◽  
Author(s):  
V. Krishnamurthy ◽  
R. S. Ajayamohan
Keyword(s):  
Monsoon Rainfall ◽  
Total Duration ◽  
Daily Rainfall ◽  
Central India ◽  
Low Pressure ◽  
Rainfall Pattern ◽  
Indian Rainfall ◽  
Northwest India ◽  
Monsoon Winds ◽  
Low Pressure Systems

Abstract The tropical disturbances formed in the Bay of Bengal and the Arabian Sea and over land points in central India, known as low pressure systems (LPSs), are shown to contribute significantly to the seasonal monsoon rainfall over India. Analyses of daily rainfall over India and statistics of the LPSs for the period of 1901–2003 show that the rainfall pattern when the LPSs are present captures the most dominant daily rainfall pattern that represents the active monsoon phase. The rainfall pattern when the LPSs are absent is similar to the pattern representing the break monsoon phase. The location, number, and duration of the LPSs are found to be closely related to the phases and propagation of the dominant intraseasonal modes of the Indian rainfall. The LPSs are also associated with the strengthening of the monsoon trough and low-level monsoon winds. The number of LPSs and their total duration and the corresponding rainfall during July and August exceed those in June and September. The LPS tracks reach up to northwest India during flood years, whereas they are confined to central India during drought years. However, the contribution of rainfall during the LPSs to the total seasonal rainfall is same during flood or drought years. Although the LPSs seem to play an important role in the monsoon rainfall, they alone may not determine the interannual variability of the seasonal mean monsoon rainfall.

An investigation of the bias in the median track of Monsoon Low Pressure Systems over the Indian subcontinent in CESM1.2.2 simulations

2021 ◽  
Author(s):  
Tresa Mary Thomas ◽  
Govindasamy Bala ◽  
Venkata Vemavarapu Srinivas
Keyword(s):  
Monsoon Rainfall ◽  
Indian Subcontinent ◽  
Low Pressure ◽  
Monsoon Trough ◽  
Tropospheric Temperature ◽  
Monsoon Period ◽  
Global Circulation Models ◽  
Extreme Precipitation Events ◽  
Latitudinal Shift ◽  
Low Pressure Systems

<p>Monsoon low pressure systems (LPS) are synoptic scale tropical disturbances that form in the Indian subcontinent over the quasi-stationary monsoon trough axis during the monsoon period (June to September). In a recent study, we showed that 60-70% of monsoon rainfall and 78% of extreme precipitation events in India are associated with LPS. Global circulation models (GCMs) have been used to understand the behavior of tropical disturbances in the past. It has been found that model resolution plays a key role in simulating the climatology of tropical storms, with finer resolution (of the order of 20-100km) required to better represent the genesis and propagation of these storms. As GCMs can be run at these finer resolutions today, various characteristics of LPS in the Indian subcontinent can be studied. It has been found that most CMIP5 GCMs show a southward latitudinal shift in the monsoon trough location and hence in the LPS tracks and associated characteristics. This shift has been attributed to a weaker simulated meridional tropospheric temperature gradient (MTG) in the models. However, the cause of weaker MTG in models is not known. In this study, we investigate the reason for the weaker MTG and hence the southward latitudinal shift of LPS tracks in the Climate Earth System Model (CESM1.2.2). A present-day control simulation is performed at 0.9°×1.25° horizontal resolution, and output is saved at 6-hourly intervals for LPS track analysis. We find that CESM is capable of simulating the general behavior of monsoon over the Indian subcontinent in terms of seasonality, propagation of monsoon rainfall, and mean monsoon winds. LPS are tracked in the CESM outputs by our recently proposed Automated Tracking Algorithm using Geopotential Criteria (ATAGC). A southward latitudinal shift is observed in the median track of LPS in CESM present-day simulations. The value of MTG is also significantly smaller compared to the observed MTG. The results from investigations on the likely causes for the weaker MTG in CESM will be presented at the meeting.</p>

scholarly journals Projected Changes in South Asian Monsoon Low Pressure Systems

2020 ◽  
Vol 33 (17) ◽  
pp. 7275-7287 ◽  
Author(s):  
Wenhao Dong ◽  
Yi Ming ◽  
V. Ramaswamy
Keyword(s):  
South Asian ◽  
Large Scale ◽  
Climate Model ◽  
Asian Summer Monsoon ◽  
Central India ◽  
Low Pressure ◽  
Geophysical Fluid Dynamics Laboratory ◽  
South Asian Summer Monsoon ◽  
Projected Changes ◽  
Low Pressure Systems

AbstractMonsoon low pressure systems (MLPSs) are among the most important synoptic-scale disturbances of the South Asian summer monsoon. Potential changes in their characteristics in a warmer climate would have broad societal impacts. Yet, the findings from a few existing studies are inconclusive. We use the Geophysical Fluid Dynamics Laboratory (GFDL) coupled climate model CM4.0 to examine the projected changes in the simulated MLPS activity under a future emission scenario. It is shown that CM4.0 can skillfully simulate the number, genesis location, intensity, and lifetime of MLPSs. Global warming gives rise to a significant decrease in MLPS activity. An analysis of several large-scale environmental variables, both dynamic and thermodynamic, suggests that the decrease in MLPS activity can be attributed mainly to a reduction in low-level relative vorticity over the core genesis region. The decreased vorticity is consistent with weaker large-scale ascent, which leads to less vorticity production through the stretching term in the vorticity equation. Assuming a fixed radius of influence, the projected reduction in MLPSs would significantly lower the associated precipitation over north-central India, despite an overall increase in mean precipitation.

Simulation of Monsoon trough and low pressure systems in CMIP6 models

2020 ◽  
Author(s):  
Praveen Veluthedathekuzhiyil ◽  
Ajayamohan Ravindran ◽  
Sabeerali Cherumadanakadan Thelliyil
Keyword(s):  
Climate Models ◽  
Monsoon Rainfall ◽  
Indian Monsoon ◽  
Low Pressure ◽  
Monsoon Trough ◽  
Warming Scenario ◽  
Wide Range ◽  
Future Warming ◽  
Dynamical Features ◽  
Low Pressure Systems

<p>Monsoon low pressure systems (LPS) contributes to more than half of the Indian monsoon rainfall. However most climate models fail to capture the characteristics of low pressure systems realistically. This aspect is scrutinized in a wide range of available CMIP6 model simulations using an objective LPS tracking algorithm. Broader features such as monsoon trough over which these systems forms are also analyzed. It has been found that, majority of the models fail to realistically represent these two important features. However few models that were able to capture these events in CMIP5 are able to simulate them in CMIP6 as well. We examine the dynamical features that lead to realistic simulation of LPS in these set of models. Selected good models are then used to study the characteristics of LPS in a future warming scenario. This study will help in judging the performance of models and for any future improvements.</p>

Intraseasonal and Seasonally Persisting Patterns of Indian Monsoon Rainfall

2007 ◽  
Vol 20 (1) ◽  
pp. 3-20 ◽  
Author(s):  
V. Krishnamurthy ◽  
J. Shukla
Keyword(s):  
Monsoon Rainfall ◽  
Indian Monsoon ◽  
Singular Spectrum Analysis ◽  
Daily Rainfall ◽  
Central India ◽  
North India ◽  
Peninsular India ◽  
Rainfall Analysis ◽  
Intraseasonal Oscillations ◽  
Rainfall Anomalies

Abstract The space–time structure of the active and break periods of the Indian monsoon has been studied using 70-yr-long high-resolution gridded daily rainfall data over India. The analysis of lagged composites of rainfall anomalies based on an objective categorization of active and break phases shows that the active (break) cycle, with an average life of 16 days, starts with positive (negative) rainfall anomalies over the Western Ghats and eastern part of central India and intensifies and expands to a region covering central India and parts of north India during the peak phase, while negative (positive) anomalies cover the sub-Himalayan region and southeast India. During the final stage of the active (break) period, the positive (negative) rainfall anomalies move toward the foothills of the Himalayas while peninsular India is covered with opposite sign anomalies. The number of days on which lows and depressions are present in the region during active and break periods is consistent with the rainfall analysis. The number of depressions during the active phase is about 7 times that during the break phase. Using multichannel singular spectrum analysis of the daily rainfall anomalies, the seasonal monsoon rainfall is found to consist of two dominant intraseasonal oscillations with periods of 45 and 20 days and three seasonally persisting components. The 45- and 20-day oscillations are manifestations of the active and break periods but contribute very little to the seasonal mean rainfall. The seasonally persisting components with anomalies of the same sign, and covering all of India, have a very high interannual correlation with the total seasonal mean rainfall. These results support a conceptual model of the interannual variability of the monsoon rainfall consisting of seasonal mean components and a statistical average of the intraseasonal variations. The success in the prediction of seasonal mean rainfall depends on the relative strengths of the seasonally persisting components and intraseasonal oscillations.

scholarly journals Excess and deficient summer monsoon rainfall over Orissa in relation to low pressure systems

MAUSAM ◽  
2021 ◽  
Vol 60 (1) ◽  
pp. 25-38
Author(s):  
M. MOHAPATRA ◽  
U. C. MOHANTY
Keyword(s):  
Bay Of Bengal ◽  
Andhra Pradesh ◽  
West Bengal ◽  
Monsoon Rainfall ◽  
Low Pressure ◽  
Summer Monsoon Rainfall ◽  
Cyclonic Storm ◽  
Normal Number ◽  
Different Characteristics ◽  
Low Pressure Systems

A study has been undertaken to find out different characteristics like frequency, intensity, movement, region of occurrence etc. of low pressure systems (LPS) including low, depression and cyclonic storm etc. developing over Orissa and neighbouring sea and land regions during excess and deficient monsoon  rainfall months (June – September) over Orissa. The study is based on data of 20 years (1980-1999). The principal objective of this study is to find out the contribution of LPS to extreme monsoon rainfall activity over Orissa.   The number of LPS days rather than frequency of formation of LPS over different regions better explain the excess and deficient rainfall over Orissa. The excess rainfall over Orissa during June is not significantly related with the number of LPS days. Significantly less than normal number of LPS days over northwest (NW) Bay of Bengal and Gangetic West Bengal (GWB) and higher number of LPS days over west central (WC) Bay off north coastal Andhra Pradesh (NCAP) cause deficient rainfall over Orissa during June. While significantly higher than normal number of LPS days over NW Bay and Orissa leads to excess rainfall during July, less than normal number of LPS days over WC Bay off NCAP is associated with excess rainfall during August. The less number of LPS days over Orissa due to less frequent movement of LPS across Orissa from the Bay of Bengal leads to deficient rainfall over Orissa during both July and August. Significantly higher/less than normal number of LPS days over NW Bay leads to excess/deficient rainfall over Orissa during September.

scholarly journals Multiscale interactions between monsoon intra-seasonal oscillations and low pressure systems that produce heavy rainfall events of different spatial extents

2021 ◽  
pp. 1-36
Author(s):  
Akshaya C Nikumbh ◽  
Arindam Chakraborty ◽  
G.S. Bhat ◽  
Dargan M. W. Frierson
Keyword(s):  
Large Scale ◽  
Thermodynamic Characteristics ◽  
Central India ◽  
Low Pressure ◽  
Monsoon Trough ◽  
The Other ◽  
Rainfall Events ◽  
Other Hand ◽  
Seasonal Oscillations ◽  
Low Pressure Systems

AbstractThe sub-seasonal and synoptic-scale variability of the Indian summer monsoon rainfall are controlled primarily by monsoon intra-seasonal oscillations (MISO) and low pressure systems (LPS), respectively. The positive and negative phases of MISO lead to alternate epochs of above-normal (active) and below-normal (break) spells of rainfall. LPSs are embedded within the different phases of MISO and are known to produce heavy precipitation events over central India. Whether the interaction with the MISO phases modulates the precipitation response of LPSs, and thereby the characteristics of extreme rainfall events (EREs) remains unaddressed in the available literature. In this study, we analyze the LPSs that produce EREs of various spatial extents viz., Small, Medium, and Large over central India from 1979 to 2012. We also compare them with the LPSs that pass through central India and do not give any ERE (LPS-noex). We find that thermodynamic characteristics of LPSs that trigger different spatial extents of EREs are similar. However, they show differences in their dynamic characteristics. The ERE producing LPSs are slower, moister and more intense than LPS-noex. The LPSs that lead to Medium and Large EREs tend to occur during the positive phase of MISO when an active monsoon trough is present over central India. On the other hand, LPS-noex and the LPSs that trigger Small EREs occur mainly during the neutral or negative phases of the MISO. The large-scale dynamic forcing, intensification of LPSs, and diabatic generation of low-level potential vorticity due to the presence of active monsoon trough help in the organization of convection and lead to Medium and Large EREs. On the other hand, the LPSs that form during the negative or neutral phases of MISO do not intensify much during their lifetime and trigger scattered convection, leading to EREs of small size.

scholarly journals Secular variations and trends in the occurrence of monsoon synoptic systems and its impact on central India rainfall

MAUSAM ◽  
2021 ◽  
Vol 60 (3) ◽  
pp. 309-316
Author(s):  
D. M. RASE ◽  
M. P. SHEVALE ◽  
S. I. M. RIZVI
Keyword(s):  
Central India ◽  
Low Pressure ◽  
Indian Region ◽  
Regular Pattern ◽  
Annual Variability ◽  
Secular Variations ◽  
Monsoon Depressions ◽  
Using Data ◽  
Low Pressure Systems

Importance of monsoon depressions, Low Pressure Systems (LPS) and the number of LPS days on rainfall and hence indirectly on agriculture and hydrology, is well recognized.      In this paper the pattern of annual variability in these systems have been examined using data from 1901-2000. The above mentioned parameters have been subjected to decadal analysis to detect presence of any regular pattern. An attempt has been made to find its tendency with time.  Impact of these systems on central India rainfall has been determined and discussed.     The study endorses the earlier findings that there is a   decreasing trend in the frequency of depressions which has been compensated with increase in LPS days over Indian region in recent years.  The rainfall over central India is more significantly related with a number of LPS days over Indian region.

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