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>

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.

scholarly journals Synoptic study of extremely heavy rainfall events over lower Yamuna catchment : Some cases

MAUSAM ◽  
2021 ◽  
Vol 64 (2) ◽  
pp. 265-280
Author(s):  
MEHFOOZ ALI MEHFOOZALI ◽  
U.P. SINGH ◽  
D. JOARDAR ◽  
NIZAMUDDIN NIZAMUDDIN
Keyword(s):  
Bay Of Bengal ◽  
Heavy Rainfall ◽  
Extreme Rainfall ◽  
Low Pressure ◽  
Crop Damage ◽  
Local Conditions ◽  
Rainfall Events ◽  
Synoptic Conditions ◽  
Heavy Rainfall Events ◽  
Low Pressure Systems

vR;f/kd o"kkZ gksus ds dkj.k HkwL[kyu gksrk gS vDlekr ck<+ vk tkrh gS vkSj Qly dks {kfr igq¡prh gSA lekt] vFkZO;oLFkk vkSj i;kZoj.k ij bldk cgqr nq"izHkko iM+rk gSA i;kZoj.kh; vkSj flukWfIVd fLFkfr;ksa ds mRiUu gksus ls  vR;f/kd vFkok cgqr Hkkjh o"kkZ gksus ds dkj.k Hkkjr esa nf{k.k if’peh ekulwu _rq ds nkSjku vf/kdk¡’kr% ck<+ vkrh gSA bl 'kks/k i= esa izeq[k flukWfIVd dkj.kksa dk irk yxkus dk iz;kl fd;k x;k gS tks y?kq vof/k iwokZuqeku ds {ks= esa fodflr iwokZuqeku rduhd vkSj vk/kqfud izs{k.kkRed izkS|ksfxdh ij vk/kkfjr o"kZ 1998&2010 dh vof/k dh bl o"kkZ  vkSj ok;qeaMyh; iz.kkfy;ksa ds e/; laca/kksa ds fo’ys"k.k ds ek/;e ls ;equk ds fupys tyxzg.k {ks= ¼,y-okbZ-lh-½ esa vR;f/kd Hkkjh o"kkZ dh ?kVukvksa ds fy, mRrjnk;h gSA bl v/;;u ls ;g irk pyk gS fd  bl {ks= esa caxky dh [kkM+h esa fuEu nkc iz.kkfy;ksa dk cuuk izeq[k dkjd gS fuLlansg ;fn LFkkuh; fLFkfr;k¡ izHkkoh gks tSlsa fd xehZ dk c<+uk rks ogk¡ ij Hkkjh o"kkZ gksrh gSA lkekU;r% caxky dh [kkM+h esa fuEu vcnkc iz.kkfy;k¡ ¼pØokr] vonkc] fuEu vonkc {ks= vkfn tSls ¼,y-ih-,l-½ fodflr gqbZ tks if’pe ls mRrjh  if’peh fn’kk dh vksj c<+h rFkk ;equk ds fupys tyxzg.k ¼,y-okbZ-lh-½ {ks= esa igq¡phA ,slh ?kVukvksa ds fy, mRrjnk;h mifjru  ok;q pØokrh ifjlapj.k ¼lkblj½ ds izHkko ls ogha ij ,y- ih- ,l- Hkh cu ldrk gSA ,slh iz.kkyh ls bDds&nwDds LFkkuksa ij vR;f/kd Hkkjh o"kkZ dh ?kVuk,¡ ¼lkekU;r% iz.kkyh ds nf{k.k if’pe {ks= esa½ vkSj dqN LFkkuksa ij Hkkjh ls cgqr Hkkjh o"kkZ gqbZ ftlds dkj.k ck<+ vkbZA ;fn ;equk ds fupys tyxzg.k ¼,y-okbZ-lh-½ {ks= esa ,y-ih-,l- fuf"Ø; ;k /khek iM+ tkrk gS rks bl izdkj dh o"kkZ dh ?kVukvksa dh laHkkouk c<+ ldrh gSA ,y-ih-,l- ds vkxs c<+us dk lgh iwokZuqeku nsus ds fy, vkj-,l-,e-lh- ¼Hkkjr ekSle foKku foHkkx½ ubZ fnYYkh ds iwoZuqeku :i js[kk ds ,u-MCY;w-ih- mRikn@72] 48 vkSj 24 ?kaVksa ds iou pkVZ lgh lk/ku ik, x, gSaA vR;f/kd o"kkZ dh ?kVukvksa ds iwokZuqeku esa bl izdkj dh lwpuk nsus ls iwokZuqekudrkvksa dks fuf’pr :i ls lgh iwokZuqeku feysxk rkfd ftyk izkf/kdkjh le; jgrs vkink dh rS;kjh ds fy, vko’;d ewyHkwr lqfo/kk,¡ miyC/k djk ldsaA  Extreme rainfall results in landslides, flash flood and crop damage that have major impact on society, the economy and the environment. During southwest monsoon season, flood mostly occurs in India due to extremely or very heavy rain that originates from environmental and   synoptic conditions. An attempt has been made to identify the main synoptic reasons, which are responsible for extremely heavy rainfall events over Lower Yamuna catchment (LYC) through the analysis of the relationship between this rainfall and atmospheric systems for the period 1998-2010 based on modern observational technology and developed forecasting technique in the field of short range prediction. The finding of this study show that the major factor have is the arrival of Bay of Bengal low pressure systems in this region, of course if the ascent local conditions such as heat occur, causing the heaviest rains there. The low pressure systems (LPS like, Cyclone, depression, low pressure area etc.) developed generally over Bay of Bengal moved in west to north-westwards direction and reached over the LYC region. Also LPS may be formed in situ under the influence of upper air cyclonic circulation (cycir) responsible for such events. Such system yield extremely heavy rainfall events (generally in the south-west sector of the system) at isolated places and heavy to very heavy rainfall at a few places and there by caused flood situation. The possibility of occurrence of such type of rainfall would be higher if the LPS is either stagnate or slow over LYC region. The NWP products of RSMC (IMD) New Delhi forecast contours / wind charts for 72, 48 & 24 hrs were found good tool for accurate forecast position of the movement of the LPS. Such information certainly facilitate to forecaster in prediction of extreme rainfall events more accurately so that district authorities may set up necessary infrastructures for disaster preparedness in time.

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.

Evaluation and Projection of Extreme Precipitation over Northern China in CMIP5 Models

2020 ◽  
Author(s):  
Xi Lu
Keyword(s):  
Extreme Precipitation ◽  
Northeast China ◽  
Climate Models ◽  
Extreme Rainfall ◽  
Northern China ◽  
Northwest China ◽  
Cmip5 Models ◽  
Historical Period ◽  
Extreme Precipitation Indices ◽  
Group 1

&lt;p&gt;This study evaluates 32 climate models from CMIP5 compared with a daily gridded&lt;br&gt;observation dataset of extreme precipitation indices including total extreme precipitation (R95p),&lt;br&gt;maximum consecutive five days of precipitation (RX5day) and wet days larger than 10 mm of&lt;br&gt;precipitation (R10mm) over Northern China during the historical period (1986&amp;#8211;2005). Results show&lt;br&gt;the majority models have good performance on spatial distribution but overestimate the amplitude of&lt;br&gt;precipitation over Northern China. Most models can also capture interannual variation of R95p and&lt;br&gt;RX5d, but with poor simulations on R10mm. Considering both spatial and temporal factors, the best&lt;br&gt;multi-model ensemble (Group 1) has been selected and improved by 42%, 34%, and 37% for R95p,&lt;br&gt;RX5d, and R10mm, respectively. Projection of extreme precipitation indicates that the fastest-rising&lt;br&gt;region is in Northwest China due to the enhanced rainfall intensity. However, the uncertainty&lt;br&gt;analysis shows the increase of extreme rainfall over Northwest China has a low confidence level.&lt;br&gt;The projection of increasing extreme rainfall over Northeast China from Group 1 due to the longer&lt;br&gt;extreme rainfall days is more credible. The weak subtropical high and southwest winds from Arabian&lt;br&gt;Sea lead to the low wet biases from Group 1 and the cyclonic anomalies over Northeast China, which&lt;br&gt;result in more extreme precipitation.&lt;/p&gt;

scholarly journals Evaluation and Projection of Extreme Precipitation over Northern China in CMIP5 Models

Atmosphere ◽  
2019 ◽  
Vol 10 (11) ◽  
pp. 691 ◽  
Author(s):  
Xiaoqiang Rao ◽  
Xi Lu ◽  
Wenjie Dong
Keyword(s):  
Extreme Precipitation ◽  
Northeast China ◽  
Climate Models ◽  
Extreme Rainfall ◽  
Northern China ◽  
Northwest China ◽  
Cmip5 Models ◽  
Historical Period ◽  
Extreme Precipitation Indices ◽  
Group 1

This study evaluates 32 climate models from CMIP5 compared with a daily gridded observation dataset of extreme precipitation indices including total extreme precipitation (R95p), maximum consecutive five days of precipitation (RX5day) and wet days larger than 10 mm of precipitation (R10mm) over Northern China during the historical period (1986–2005). Results show the majority models have good performance on spatial distribution but overestimate the amplitude of precipitation over Northern China. Most models can also capture interannual variation of R95p and RX5d, but with poor simulations on R10mm. Considering both spatial and temporal factors, the best multi-model ensemble (Group 1) has been selected and improved by 42%, 34%, and 37% for R95p, RX5d, and R10mm, respectively. Projection of extreme precipitation indicates that the fastest-rising region is in Northwest China due to the enhanced rainfall intensity. However, the uncertainty analysis shows the increase of extreme rainfall over Northwest China has a low confidence level. The projection of increasing extreme rainfall over Northeast China from Group 1 due to the longer extreme rainfall days is more credible. The weak subtropical high and southwest winds from Arabian Sea lead to the low wet biases from Group 1 and the cyclonic anomalies over Northeast China, which result in more extreme precipitation.

scholarly journals Increasing Trend of Synoptic Activity and Its Relationship with Extreme Rain Events over Central India

2010 ◽  
Vol 23 (4) ◽  
pp. 1004-1013 ◽  
Author(s):  
R. S. Ajayamohan ◽  
William J. Merryfield ◽  
Viatcheslav V. Kharin
Keyword(s):  
Activity Index ◽  
Central India ◽  
Extreme Rainfall ◽  
Strong Connection ◽  
Activity Increase ◽  
Extreme Rainfall Events ◽  
Rainfall Events ◽  
Increasing Trend ◽  
Extreme Rain ◽  
Rain Events

Abstract The nature of the increasing frequency of extreme rainfall events (ERE) in central India is investigated by relating their occurrence to synoptic activity. Using a long record of the paths and intensities of monsoon synoptic disturbances, a synoptic activity index (SAI) is defined whose interannual variation correlates strongly with that in the number of ERE, demonstrating a strong connection between these phenomena. SAI furthermore shows a rising trend that is statistically indistinguishable from that in ERE, indicating that the increasing frequency of ERE is likely attributable to a rising trend in synoptic activity. This synoptic activity increase results from a rising trend in relatively weak low pressure systems (LPS), and it outweighs a declining trend in stronger LPS.

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