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>

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 Indian Monsoon Low-Pressure Systems Feed Up-and-Over Moisture Transport to the Southwestern Tibetan Plateau

2017 ◽  
Vol 122 (22) ◽  
pp. 12,140-12,151 ◽  
Author(s):  
Wenhao Dong ◽  
Yanluan Lin ◽  
Jonathon S. Wright ◽  
Yuanyu Xie ◽  
Fanghua Xu ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Moisture Transport ◽  
Indian Monsoon ◽  
Low Pressure ◽  
Low Pressure Systems

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 On the Relationship between Mean Monsoon Precipitation and Low Pressure Systems in Climate Model Simulations

2015 ◽  
Vol 28 (13) ◽  
pp. 5305-5324 ◽  
Author(s):  
V. Praveen ◽  
S. Sandeep ◽  
R. S. Ajayamohan
Keyword(s):  
Summer Monsoon ◽  
Climate Models ◽  
Climate Model ◽  
Low Pressure ◽  
Tracking Algorithm ◽  
Monsoon Precipitation ◽  
Model Simulations ◽  
Detection And Tracking ◽  
Climate Model Simulations ◽  
Low Pressure Systems

Abstract The north-northwest-propagating low pressure systems (LPS) are an important component of the Indian summer monsoon (ISM). The objective detection and tracking of LPS in reanalysis products and climate model simulations are challenging because of the weak structure of the LPS compared to tropical cyclones. Therefore, the skill of reanalyses and climate models in simulating the monsoon LPS is unknown. A robust method is presented here to objectively identify and track LPS, which mimics the conventional identification and tracking algorithm based on detecting closed isobars on surface pressure charts. The new LPS tracking technique allows a fair comparison between the observed and simulated LPS. The analysis based on the new tracking algorithm shows that the reanalyses from ERA-Interim and MERRA were able to reproduce the observed climatology and interannual variability of the monsoon LPS with a fair degree of accuracy. Further, the newly developed LPS detection and tracking algorithm is also applied to the climate model simulations of phase 5 of the Coupled Model Intercomparison Project (CMIP5). The CMIP5 models show considerable spread in terms of their skill in LPS simulation. About 60% of the observed total summer monsoon precipitation over east-central India is found to be associated with LPS activities, while in model simulations this ratio varies between 5% and 60%. Those models that simulate synoptic activity realistically are found to have better skill in simulating seasonal mean monsoon precipitation. The model-to-model variability in the simulated synoptic activity is found to be linked to the intermodel spread in zonal wind shear over the Indian region, which is further linked to inadequate representation of the tropical easterly jet in climate models. These findings elucidate the mechanisms behind the model simulation of ISM precipitation, synoptic activity, and their interdependence.

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 Downstream and In Situ Genesis of Monsoon Low‐Pressure Systems in Climate Models

2021 ◽  
Vol 8 (9) ◽  
Author(s):  
K. S. S. Sai Srujan ◽  
S. Sandeep ◽  
E. Suhas
Keyword(s):  
Climate Models ◽  
Low Pressure ◽  
Low Pressure Systems
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