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>

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>

scholarly journals ISO-Modulating Effects on the East Asian Summer Monsoon Circulation Patterns Associated with Southern Taiwan’s Monsoon Rainfall

2014 ◽  
Vol 142 (9) ◽  
pp. 3163-3177 ◽  
Author(s):  
Ken-Chung Ko ◽  
Po-Sheng Chiu
Keyword(s):  
Summer Monsoon ◽  
Monsoon Rainfall ◽  
Southern China ◽  
Low Pressure ◽  
Monsoon Trough ◽  
Central China ◽  
Monsoon Circulation ◽  
Circulation Patterns ◽  
Southern Taiwan ◽  
Southern Flank

In this study, the circulation patterns of the summer monsoon associated with monsoon rainfall in southern Taiwan were analyzed and two types of monsoon patterns were defined. The first type was characterized by a broad low pressure area extending northeastward from a low pressure center near southern China to southern Japan. Strong southwesterly flows were observed over the southern flank of the monsoon trough. The second type of monsoon pattern was characterized by a strong westward-extending anticyclone in the area north of Taiwan (including central China, South Korea, and Japan), and a weaker east–west-elongated monsoon trough south of Taiwan, driving the easterly flow to southern Taiwan. The modulating effect of intraseasonal oscillations (ISOs) on these monsoon flow patterns indicates that as ISOs propagate northwestward toward southern China, they create favorable conditions for developing and strengthening southwesterly flows and convection. However, because of the latitudinal limit of northwestward-propagating ISOs, only the edge of the strongest convection over the southern flank of the ISO cyclonic circulation reaches southern Taiwan during the westerly phase. Thus, although the westerly ISO pattern appears to be stronger than the easterly pattern, it brings less rainfall to southern Taiwan. Through the tightening of pressure gradients, the ISO typically generates anomalous cyclones (anticyclones) that can affect the southwesterly and northeasterly flows near its southern (northern) and northern (southern) rims. Therefore, fluctuations in the low-frequency background flow can exert a notable effect on the monsoon rainfall and associated circulation systems near Taiwan.

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.

Statistics of Monsoon Low Pressure Systems in the Indian Subcontinent and Estimation of Related Extreme Rainfall Risk

2020 ◽  
Author(s):  
Tresa Mary Thomas ◽  
Govindasamy Bala ◽  
Srinivas Venkata Vemavarapu
Keyword(s):  
Extreme Precipitation ◽  
Activity Index ◽  
Indian Subcontinent ◽  
Central India ◽  
Extreme Rainfall ◽  
Low Pressure ◽  
Height Anomaly ◽  
Historical Period ◽  
New Approach ◽  
Low Pressure Systems

<p>Indian monsoon, which spans through the months of June-September, brings in copious rain for the agriculture dependent country India. Monsoon low pressure systems (LPS) are the major rain bearers during the season. Apart from being a lifeline, they are also cited as a cause of disastrous floods in the country. Various approaches have been attempted to locate and track these LPS. Inconsistency exists among  them in statistics of LPS not only for the historical period, but also in future projections of these systems. We have developed an improved tracking scheme in this study. . The new approach takes into consideration geopotential height anomaly condition and is  named Automated Tracking algorithm using geopotential criteria (ATAGC). The approach is validated by comparing characteristics of LPS identified by it with those identified in previous studies. On average, around 14 LPS  each year are identified by the new approach, which comprise 9 lows, 4 depressions and about one deep depression. Further, the annual average number for LPS days is estimated as 68. The LPS mostly form over north part of Bay of Bengal and move north-westwards. Synoptic Activity Index, which quantifies LPS risk at a location in terms of both frequency and intensity of the system, shows that locations in the coastal regions of central India are highly affected by LPS. But the effect in terms of extreme rainfall is not localized near  the coast. Even though contribution of LPS towards total monsoon rainfall and total extreme precipitation has been analyzed in previous studies, the risk in terms of extreme rainfall due to LPS has not been assessed. In this study, extreme rainfall risk map in terms of average extreme precipitation and 90 percentile precipitation observed at a location in the vicinity of an LPS is determined. An average extreme rainfall of 60-100mm/day and 90 percentile extreme rainfall of 150-250mm/day is estimated at many locations in Central Indian region due to LPS. While analyzing continuous spells of rainfall, it is found  that along with LPS, topography of a region has considerable effect on the duration of the spells.</p>

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.

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