Characteristics of Monsoon Semipermanent Features in Changing Climate: An Environmental Approach

The Indian summer monsoon (ISM) spans four months beginning from June to September (JJAS) and produced extensive rainfall over Indian continents. The land-sea heating contrast is one of the major factors facilitating ISM. ISM is managed with the aid of several monsoon semi-permanent features (MSF) which include Pakistan heat low, cross-equatorial low-level jet over the Arabian Sea, and the tropical easterly jet over the Indian Ocean at 200 hPa, Mascarene High, and seasonal anti-cyclone over the Tibet. Any fluctuations in these SMF can strongly modulate Indian Summer Monsoon Rainfall (ISMR). Therefore, it is imperative that the structure and variability of MSF need to be examined in changing climate scenarios to assess its impact on the future monsoon. Further, ISM also experiences internal variability in terms of deficit and surplus years, therefore the impact of MSF on this variability also needs to be examined. The main objective of the study is to examine the variation of rainfall in JJAS over the Indian monsoon core region and the characteristics of SMF for two contrasting monsoon years. Based on the previous study observed that the monsoon core zone has an important role to play in the ISM so for the rainfall study take the monsoon core zone for the study purpose. The 5 th generation European Centre for Medium-Range Weather Forecasts (ERA5), India Meteorological Department (IMD) rainfall datasets from 1981-2020, and Coupled Model Intercomparison Project Phase 6 (CMIP6) 2015-2021 for four different SSP scenarios. In addition, to determine the changes in these MSF and their impact on rainfall for ISM. For the calculation of rainfall percentage departure of IMD and ERA5 and CMIP6 dataset following Rajeevan et al. (2010).


Introduction Semipermanent Features
Monsoons are a common feature of tropical and subtropical climates in many parts of the world, with wet summers and drier winters, as well as a seasonal reversal of the predominant wind.ISM exists specifically because of land-sea heating assessment among Indian Ocean and Asian land.The variable nature of ISM great impact on Indian socioeconomic growth because annual Indian Summer Monsoon rainfall (ISMR) contributes 70-80% of rainfall over the Indian continents.It is characterized via way of means of wind flow at the lower level (850 hPa) as a south-westerly jet and at the upper level (200 hPa) as an easterly jet and produced extensive rainfall over a significant land region of the Indian continent in 4 months beginning from June to September.ISM is specifically managed via way of means of semipermanent functions together with heat low over the northwest area of India, Tibetan High, Mascarene High, tropical easterly jet, and south-westerly jet.ISM is the maximum energetic and influential of all of the monsoon circulations over the globe (Pant and Rupa Kumar, 1997).The moisture transported from the Arabian Sea produced rainfall over the Indian Ocean to peninsular India and the Bay of Bengal.The annual cycle of ISM reveals variability on time scales starting from intra-seasonal to decadal (Webster et al., 1998).Low-Level Jet (LLJ) is a dominating characteristic of ISMR (Joseph and Sijikumar, 2004).The Somali Jet is the northern branch of the Indian Ocean's low-level crossequatorial flow, which travels over the Arabian Sea off the coast of Somalia in boreal summer and supplies the bulk of the moisture to the Indian monsoon.In July, the easterly flow concentrates south of the subtropical ridge across Asia forming a jet stream centered around roughly the latitude of Chennai at 150 hPa.The jet stream extends from Vietnam's east coast to Africa's west coast.The position is around 10° N over Africa.The upper-level large-scale circulation features in a composite of five years of Surplus were compared to the Normal and Deficit year of ISMR.It is anticipated that comparing upper-level circulation properties would be extremely beneficial in the research of Monsoons.Rao et al. (2004) observed that the strength of Tropical Easterly Jet (TEJ) throughout the Asian Summer Monsoon season indicates a sturdy reducing manner in recent years.
A deep low in mean sea-level pressure exists over Pakistan and northern India is known as the Pak-India low.It is frequently referred to as the "heat" and is kept low to emphasize the importance of surface thermal phenomena, which are thought to be vital for its formation.The current investigation is based on observations and diagnostics.The Pak-India low is impacted, according to models.Both regional and distant forces are at work.On a regional level, The Hindu Kush mountains have a bigger impactthan the effect of land-surface warming and its consequences.The monsoon trough (MT) is a salient semipermanent feature of the South Asian summer monsoon.MT is a low-pressure zone extending from north-western India and adjoining Pakistan towards the Gangetic plains, the Bay of Bengal.(e.g., Anjaneyalu 1969; Rao 1976; Koteswaram and Rao 1963; Krishnamurti and Surgi 1987;Sikka and Narasimha 1995;Wang 2004).
The importance of the east-west oriented MT in controlling the monsoon's active and break cycles, and hence seasonal and interannual rainfall variability throughout the Indian subcontinent.The Tibetan Plateau (TP), often known as the "third pole of the Earth" and "top of the planet," contains one of the world's most complicated geological characteristics.The TP operates directly on the middle troposphere as an elevated heat source, creating a substantial temperature difference with the nearby non-elevated atmosphere.During the monsoon season, the Tibetan High is a warm anticyclone in which winds change clockwise in the Northern Hemisphere and there is always an outflow of winds positioned above the Tibetan Plateau (central latitude 28˚N, longitude 98˚E) in the middle/upper troposphere.Mascarene high is an important semipermanent feature that acts as a powerhouse of the Asian Summer monsoon."High"refers to a high-pressure zone and is located between 25˚S-35˚S and 40˚E-90˚E near the Mascarene Island in the South-Indian Ocean.The planetary boundary layer is heated in a reasonable way.Knutson and Manabe (1995) observed that the Monsoonal flows and the tropical large-scale flow frequently weaken in international warming simulations.Stronger moisture convergence in a hotter environment dominates over weakening of the monsoon circulation, resulting in higher monsoonal precipitation, according to Douville et 2008) used a numerical model to investigate the variability of monsoon circulation under changing carbon dioxide levels, and analyzed monsoon circulation indices generated from simulated zonal-wind speeds in the upper and lower troposphere, as well as model precipitation rates.Douville et al. (2000) determined a good-sized unfold withinside the summertime season monsoon precipitation anomalies in spite of widespread weakening of the monsoon circulation.Monsoon fluctuation has significant sociological and economic consequences in the regions it affects, which account for more than 70% of the world's population.Monsoon study is therefore critical not only for understanding global atmospheric circulation and climate change but also for catastrophe prevention and mitigation, as well as for achieving long-term development.The Mascarene high over the southwestern Indian Ocean, Heat low over the arid regions of the middle east, Monsoon trough over India, Cross equatorial monsoon low-level jet, etc. are the most dominant surface features related to the south Asian monsoon.On the other hand, the upper troposphere has a Tibetan anticyclone located between Northern Subtropical Westerly Jet-stream (NSWJ) and Tropical Easterly Jet-stream (TEJ).These components of the monsoon system acting together form the monsoon vertical (Hadley) circulation.
Available online at: https://jazindia.com-2240 -Fig- 1Schematic view of the semi-permanent features during the Asian summer monsoon system (Krishnamurti and Bhalme, 1976) Air rises in convection over the Monsoon Trough, makes the Tibetan High above and as it moves south generates the Tropical easterly Jetstream, descends down at about latitude 30S to the Mascarene High.The return current is the Low-Level Jetstream.Monsoon Strong convection in Trough is followed by strong Tibetan High and TEJ, higher pressure in Mascarene High, and a strong LLJ and increased rainfall over India.The Monsoon Trough region loses conditional instability and the vertical circulation weakens as shown in Fig. 1.
Table 1 represents the different monsoon semipermanent features and their meteorological parameters like mean sea level pressure, surface air temperature, wind, etc at different pressure levels, location (where it forms), and duration (at which time it strengthens).

Literature Review
During the Indian summer monsoon season, semi-permanent features (SMF) such as the Heat Low (HL), Monsoon Trough (MT), Tibetan Anticyclone (TA), Tropical Easterly Jet (TEJ), and Low-Level Jet (LLJ) or Somali jet can be seen over the Indian subcontinent (June through September).These SMFs are crucial in determining the overall intensity of the Indian summer monsoon rainfall (ISMR).The Himalayas and Tibet regions may lead to setting westerly flow which may lead to the weakening of easterly jet in a warmer climate.The relative strength of anticyclonic flow in the Arabian Sea at 850 nline at: le o b ila Ava -2241 -hPa and anomalous westerly flow at 200 hPa over the Indian Ocean can be responsible for the change in spatial distribution and magnitude of mean ISMR.In summer, surplus years, a stronger Somali jet indicates a stronger monsoon circulation.The TEJ is weak across northern India, but it flows stronger in a southwest to the west direction at lower latitudes, increasing the monsoon circulation.Furthermore, during the wet years, the center of the Somali jet moves eastward, creating increased circulation and ISMR.The multi-model ensemble results for the period 2005-2099 reveal a weakened Somali Jet in the early twenty-first century (2010-2040), the strongest Somali Jet in the middle twenty-first century (2050-2060), and the weakest Somali Jet at the end of the twenty-first century (2070-2090).The intensity of Somali Jet is weakening in general compared to 1976-1999, and it reaches its lowest point at the close of the twenty-first century.The cross-equatorial LLJ crosses the equator as a southerly current near the East African coast, and it crosses India as a westerly current in latitudes spanning from the equator to 25 N.The center of the LLJ flows over peninsular India near latitude 15N due to inactive monsoon conditions.In the latitude region from the equator to 10 N, the LLJ from the central Arabian Sea flows south-eastward and passes eastward near Sri Lanka during break monsoon conditions.A weaker LLJ axis may be detected through north India at about latitude 25N at this time.

Data
Different datasets are taken from multiple sources for this study.The main dataset used in this study consists of atmospheric and surface variables from the ERA-5 atmospheric reanalysis (https://www.ecmwf.int/en/forecasts/datasets/reanalysis-datasets/era5),IMD observational data (https://www.imdpune.gov.in/Clim_Pred_LRF_New/Grided_Data_Download.html), and CMIP6 model output datasets(https://cds.climate.copernicus.eu)for the time period of 1981 to 2020 and 2015-2024 respectively.Characteristics of mean ISMR in JJAS, monthly mean wind in JJAS at 850 hPa and 200 hPa, the monthly mean surface temperature in JJAS, and monthly mean sea level pressure during the period of 1981-2020.The horizontal resolution of ERA-5 reanalysis (0.25°×0.25°) and IMD (0.25°×0.25°) is used in this paper which is shown in Table 2.The monthly averages of the OLR (W/m2) dataset with a spatial grid resolution of 2.5º*2.5ºwith the diurnal temporal resolution was obtained from the National Oceanic and Atmospheric Administration (NOAA), (https://psl.noaa.gov/data/reanalysis).The monthly OLR (W/m2) data analyzed in this study from 1981 to 2020 is 2.5˚*2.5˚spatial resolution.The Scenario Model Intercomparison Project (Scenario-MIP) is the primary activity of Phase 6 of the Coupled Model Intercomparison Project (CMIP6), which will provide multi-model climate projections based on alternative scenarios of future emissions and landuse changes generated with integrated assessment models.Scenario-MIP experiment consists of a set of the light pathway of future emission and concentration.The scenario describes the possible future development of anthropogenic drivers of climate change.ISM is mainly controlled by semipermanent features.

Methodology
• The monsoon core zone indicated in Fig. 1 will be used for the purpose of the rainfall study because it was found in a previous study that it is crucial to the Indian summer monsoon.The core region is roughly from 18° N to 28° N, and 65° E to 88° E (Rajeevanet al.2010).
• For the monsoon core region, IMD and ERA identify rainfall shortage and surplus years.

Surplus and Deficit
During June-September (Jun to Sep), the Indian summer monsoon rainfall (ISMR) contributes around 80% of the yearly precipitation.The consistency, unpredictability, and extremes of summer monsoon rains have a substantial impact on India's agricultural output, economy, and overall well-being.Because of its complexities and impact on the general population, the study of Indian summer monsoon variability is a prominent socially relevant scientific topic (Webster et al. 1998).For the study of rainfall examine raw data and anomaly of IMD and ERA5 rainfall data and find out the composite of five years of deficit and surplus year using both IMD and ERA5 for the monsoon core zone.For the study of rainfall, I have taken common years composite of five deficit (1982,1985,1986,1987,2002)   (C) TEJ: Over southern Asia and northern Africa, the TEJ is a distinctive and prominent characteristic of the northern hemisphere summer between 5° and 20°N.From June to the beginning of October, it maintains a consistent direction and intensity.Its latitude varies between 5 and 20 degrees north.The TEJ runs 6-9 kms from east to west over peninsular India and the Northern African area.The creation of TEJ causes a reversal of upper air circulation patterns [high-pressure changes to low-pressure] and the beginning of monsoons to occur quickly.According to recent findings, the amount of rainfall in India during the monsoons is directly related to the intensity and duration of heating on the Tibetan Plateau.The TEJ is observed in the upper troposphere during the monsoon season.This jet has also been analyzed to understand its variability and impact on the surplus and deficit phases of the monsoon.The mean position of the TEJ is displayed of easterly winds along 5-20° N at 200 hPa.The core of this jet is located west of southern India over the Arabian Sea, with a maximum wind speed of more than 22 m/s over a larger area, which increases the Indian monsoon (figure 7 a).During surplus years, strong anticyclonic circulation is recorded across higher latitudes, and the wind vector is also bigger, indicating higher wind magnitude.In the illustration (7 b) The core of this jet is located west of southern India over the Arabian Sea in a deficit year, with maximum wind speeds exceeding 22 m/s across a narrower area, not strengthening the Indian monsoon.During deficit years, strong anticyclonic circulation is found across higher latitudes, and the wind vector is also reduced, indicating a lower wind magnitude.
In figure (7 c).In the (Surplus-Deficit) year, there was a positive wind anomaly in central India along 20N-30N spreading from east to west, as well as a bigger positive anomaly in the western section of the Arabian Sea with a magnitude greater than 3 m/s.There is a negative anomaly in the Bay of Bengal's southern section.The Mascarene High (MH), is a high-pressure area located between 20°S-40°S and 45°E-100°E near the Mascarene Islands in the Southern Indian Ocean (SIO) and is also called the Indian Ocean subtropical high.It also contributes to the inter-hemispheric circulation between the Indian Ocean and the subcontinental landmass in the north.During the boreal summer, the high-pressure system deepens, while a low-pressure area forms in the northern hemisphere due to severe solar heating of the subcontinental landmass.This establishes a strong pressure gradient between the northern and southern hemispheres and creates a cross-equatorial wind between the two regions and a strong oceanic monsoon current over the Arabian Sea.The MH's anticyclonic circulation and related cross-equatorial winds bring moisture from the SIO to South Asia, forming a link between the MH and the Indian monsoon trough (Fig. 8a).This, in turn, has an impact on the commencement of the monsoon in India and rainfall in East Asia.In Figure 8, Surplus year, we have seen that the is a high-pressure area located between 20°S-40°S and 45°E-100°E, and anticyclonic circulation is shown by the wind vector because of the passage of the migratory low-pressure system of the coast of South Africa and contour show the value of wind magnitude is 2m/s at the center of the high-pressure region and anticlockwise circulation because the passage of migratory low-pressure system of the coast of South Africa and circulation are less strong.In figure (8b) In deficit year, we have seen that the strength of high pressure is more and in a small area has pressure greater than 1028 hPa and wind vector is larger which shows that the wind magnitude is higher (> 2 m/s) than a surplus year and anticlockwise circulation is also stronger.It means that in the increasing year of climate change scenario strength of Mascarene high is decreasing.In To investigate ISMR using raw data and calculate rainfall percentage anomalies using IMD and ERA5 and different scenarios of CMIP6 rainfall data to determine the deficit and surplus years using SSP2.6(a),SSP4.5(b),SSP7.5(c),SSP8.5(d),IMD(e), and ERA5(f) for the monsoon core zone depicted in Figure 10.For the study of rainfall, I have taken individual common deficit years (2018) and surplus years (2020) for the study.The anomaly is found by subtracting the climatology mean from the respective year mean and dividing it by the climatology mean as shown in Table :3 which represents the common surplus and deficit years from the different data sets.
The Deficit year rainfall percentage anomaly shown in SSP4.5-ERA5(a) and SSP4.5-IMD(b) in Figure11(a-d) shows a similar result because underestimated rainfall comes over the Western Ghat and Southern Peninsular, including some parts of West Bengal, Jharkhand, and Uttar Pradesh, but it is less strong in SSP4.5-IMD (b).Overestimated rainfall occurs in Jammu and Kashmir, Maharashtra, and Chattisgarh, but it is more intense in the SSP4.5-IMDzone (b).SSP8.5-ERA5(c) demonstrates that rainfall across the monsoon core zone is underestimated, although this is more pronounced in SSP8.5-IMD (d).Both SSP4.5-IMD(e) and SSP4.5-ERA5(f) show a similar underestimation of the entire southwest region and an overestimation of the Jammu and Kashmir region in the Normal year.SSP8.5-IMD(g)and SSP8.5-ERA5(h) both show a negative anomaly over a smaller portion of the Western Ghat and all Eastern regions such as Bihar, Jharkhand, and West Bengal, but SSP8.5-ERA5(g) is stronger, and it is known that SSP4.5 shows less rainfall in the Western Ghat in both Deficit and Normal years, but SSP8.5 shows less rainfall in the Eastern part of India.The wind is weaker across the Indian continent region because it is mostly blown over the BOB, which absorbs more moisture.The south-westerly jet of 20-22 m/s in the ERA5 is an overestimation jet.This is depicted in Figure 12(d-f).In a normal year, SSP4.5(d) has the stronger jet, although SSP8.5(e) is more active over the Arabian Sea region and the lower part of Sri Lanka (70E-90E,5-7N) and less so over the Indian continent.In the Deficit year, SSP8.5 shows a stronger jet than in a normal year.In a deficit year, the jet is stronger over the Arabian Sea than in a normal year, but more wind passes through the BoB in a deficit year, therefore more moisture does not reach the Indian continent region, resulting in a stronger jet in a deficit year.

Conclusion
We have found the 10 deficit years and 12 surplus years from ERA5 and 8 deficit years and 8 surplus years from IMD after calculating the rainfall percentage departure over the period of 1981-2020.After taking 5 common surplus years and 5 common deficit years to see how these MSF are behaving in the respective year.We found that in Somali jet wind magnitude over Somalia region is high (stronger jet) by the number of 22m/s over the larger circular area in surplus year comparison with deficit year.So, it means that the Somali Jet is stronger in the Surplus year to take more moisture from the ocean to the Indian Continents.In Mascarene high, the mean sea level pressure is low in the surplus year and high in the deficit year because more surplus year is a recent year but the deficit year belongs to the previous year and changes in the western Pacific (WP) due to the Indonesian Through flow have an impact on it (ITF).The core of the Tropical Easterly Jet is located west of southern India over the Arabian Sea with a maximum wind speed greater than 22 m/s over a larger area which gives strengthens the Indian monsoon in the surplus year and Strong anticyclonic circulation is observed.The TEJ is weakened over northern India but stronger flow over the lower latitudes in the southwest to west direction, strengthening the monsoon circulation.When heating of land surface is more and sensible heating is stronger, the Pak-India low is at its deepest, triggering the Indian summer monsoon.In the difference plot of Surplus and Deficit year, we found a positive anomaly over Western Ghat and the Southern part of India, and North-west India which enhance the monsoon triggering toward the Indian monsoon because it creates the pressure gradient more during monsoon season.In the Monsoon trough, there is a patch of OLR in the axis of Northwest to southeast direction originating from Rajasthan to West Bengal and the lesser value of OLR represent the deep convection in the surplus year and a higher OLR value in the Deficit year having low convection which leads to a lesser amount of cloud and rainfall.nline at: le o b ila Ava -2253 -Bar plot of SSP2.6, SSP4.5, SSP7.5, SSP8.5, IMD, and ERA5 represent the rainfall anomaly departure, and the projection of rainfall with different scenarios provides some good results having rainfall amount in the difference of SSP4.5-IMD and SSP4.5-ERA5 found that overestimated rainfall over mid of Chattisgarh and Madhya Pradesh because SSP4.5 scenario shows more rainfall in that region and SSP8.5-IMD shows underestimated rainfall in the monsoon core region in the Deficit year.In the Normal year, SSP4.5-ERA5 and SSP4.5-IMD show a shift in underestimated rainfall from the monsoon core zone to the Western Ghat, but SSP8.5-ERA5 and SSP8.5-IMD show underestimated rainfall migrated from the monsoon core zone to the Central Northeast region.SSP4.5 shows a good result with respect to mean sea level pressure and anticlockwise circulation and its intensity of Mascarene is high with respect to ERA5 and IMD in both deficit and normal years.SSP8.5 shows that the rainfall is stronger in the Deficit year because the impact of the forcing is more in the Deficit year.In SSP8.5 Somali low-level jet has less strong in deficit year and even lesser stronger in Normal year but it is intense in the Somalia region.SSP4.5 shows a good result with respect to ERA5 because the Deficit year is less deepening but in the Normal year, it is more deepening which provides the situation of good rainfall in a normal year.SSP8.5 shows the temperature and pressure show the opposite result of Pakistan heat low in deficit year and Normal year in comparison with ERA5.In SSP8.5 TEJ is less strong in the deficit year and TEJ is stronger in the normal year which provides the information about the monsoon is stronger in the normal year.SSP8.5 shows a good result with observed data of IMD over the monsoon core zone and Peninsular India and Northwest India in deficit and Normal year.

Table: 1 Fig: 2
Fig:2 Monsoon core zone (black color box) is taken to identify the Surplus, Deficit, and Normal Year for the time period (1981-2020) rainfall (mm/day) during the boreal summer monsoon is shown.
and five surplus years(2007,2011,2013,2019,2020)  from IMD and ERA5 for further study.The anomaly (Fig-4) is found by subtracting the climatology mean from the respective year mean divided by the climatology mean.Table:3 represents the five common surplus and five common deficit years from the IMD and ERA5datasets.The difference in IMD(4-a) in the observed JJAS rainfall distribution reveals overestimated rainfall in Madhya Pradesh (greater positive anomaly), the monsoon core zone, and the Southeastern region, and underestimated rainfall in the North-eastern part of India.The difference in ERA5(4-b)in the observed JJAS rainfall distribution shows a positive anomaly in the central part of the monsoon core zone (maximum positive anomaly) and the Southeastern part and Western Ghat and Gujarat during the surplus-deficit year.nline at:

Fig: 7
Fig:7 ERA5 composite of five years of Surplus(a), Deficit(b), Surplus-Deficit(c), respectively and the color bar showing positive anomaly and contour represent negative anomaly of wind magnitude(m/s) and vector are wind direction (D) Mascarene High:The Mascarene High (MH), is a high-pressure area located between 20°S-40°S and 45°E-100°E near the Mascarene Islands in the Southern Indian Ocean (SIO) and is also called the Indian Ocean subtropical high.It also contributes to the inter-hemispheric circulation between the Indian Ocean and the subcontinental landmass in the north.During the boreal summer, the high-pressure system deepens, while a low-pressure area forms in the northern hemisphere due to severe solar heating of the subcontinental landmass.This establishes a strong pressure gradient between the northern and southern hemispheres and creates a cross-equatorial wind between the two regions and a strong oceanic monsoon current over the Arabian Sea.The MH's anticyclonic circulation and related cross-equatorial winds bring moisture from the SIO to South Asia, forming a link between the MH and the Indian monsoon trough (Fig.8a).This, in turn, has an impact on the commencement of the monsoon in India and rainfall in East Asia.In Figure8, Surplus year, we have seen that the is a high-pressure area located between 20°S-40°S and 45°E-100°E, and anticyclonic circulation is shown by the wind vector because of the passage of the migratory low-pressure system of the coast of South Africa and contour show the value of wind magnitude is 2m/s at the center of the high-pressure region and anticlockwise circulation because the passage of migratory low-pressure system of the coast of South Africa and circulation are less strong.In figure (8b) In deficit year, we have seen that the strength of high pressure is more and in a small area has pressure greater than 1028 hPa and wind vector is larger which shows that the wind magnitude is higher (> 2 m/s) than a surplus year and anticlockwise circulation is also stronger.It means that in the increasing year of climate change scenario strength of Mascarene high is decreasing.In Figure(12c) In (Surplus-Deficit) year, negative anomalies were seen near the Madagascar region and overall Indian ocean and Arabian sea region over a latitude(45E-75E) and longitude(10N-40S) which shows that high pressure occurs in the deficit year and low pressure occurs in the surplus year and positive anomaly in Northern Indian continental region.

Fig: 8 Fig: 9
Fig:8 ERA5 composite of five years of Surplus(a), Deficit(b), Surplus-Deficit(c), respectively and colorbar represent mean sea level pressure(hPa) and contour represent wind magnitude(m/s) and vector are wind direction (E) Pakistan Heat Low: The Pakistan heat low in sea-stage strain is from May to September over Pakistan and north-western India.It is frequently referred to as the ''heat low'' to deliver the importance of surface heating results appraised to be essential for it.From May to July, a wide dynamic range of low pressure (1,002 hPa) runs from the Arabian sea to the Indian continent, with the Pak-India low's core marked by the lowest pressure closed contour (998 hPa).The heat low is over the Indus River plain, with the Hindu Kush Mountain range on its western border.The summertime evolution of the Pak-India low is shown in Fig. 9, along with surface air temperature (SAT) and mean sea level pressure.In Pakistan and northern India, an extended low with a clear core is present, with SAT temperatures reaching 32°C across most of the Indian subcontinent and even 34°C in southern Pakistan and the northwestern portion of Rajasthan.With the closed 1002 hPa contour defining its core, the low deepens significantly and is about synchronous with the warmest SAT region >34C.The relevance of surface thermal forcing in the deepening of the low can be seen in these distributions.In a surplus year (Fig:9 a), The core deepens in southern Pakistan and central India, as well as the Indian peninsular region, where the pressure (1002 hPa) is low, allowing for the formation of low pressure across the Indian Subcontinents, enhancing the pressure gradient force and triggering the Indian summer monsoon.In the deficit year (Fig 9: b) the coreless deepens seen in the southern part of Pakistan and central part of India, and the Indian peninsular region over which the pressure is relatively high.In figure(16c) In the Surplusdeficit year, positive anomaly over the Indian region including southern Pakistan, and a negative anomaly over the small region of the Southern part of Pakistan.

Fig: 12 Fig: 14
Fig:12 Mean JJAS winds (ms−1) at 850 hPa and shaded color depict the mean wind speed(ms−1) in the Deficit year (2018) with SSP4.5(a),SSP7.5(b),SSP8.5(c), and ERA5(d) and in the Normal year (2020) with SSP4.5(e),SSP7.5(f),SSP8.5(g), and ERA5(h) as shown in the above figure respectively.(B)Mascarene HighMascarene High acts as a Powerhouse of the ISM system.In Figure13(a-c) In the deficit year, projection of SSP4.5(a) in the MSLP of Mascarene high is showing the low pressure (less than 1025hPa) area.It means that the establishment of high pressure over the Madagascar region is not accomplished.The high-pressure zone (higher than 1025hPa) in SSP8.5(b) is distributed across a larger area in the deficit year, indicating a stronger high-pressure gradient between the Southern Ocean and Northern Continental portion, although it is not identical to ERA5(c), which is used as a validation benchmark.In deficit years, SSP4.5 produces similar results to ERA5, but in normal years, SSP8.5 produces better results.In comparison to SSP8.5 and ERA5, figure13(d-f) SSP4.5(d) displays a very high-pressure zone.SSP4.5(d) depicts high pressure in the Normal year, implying that in the future, there will be a wider area of high pressure.In the normal year, SSP8.5 has a similar consequence to ERA5 in that the area of high pressure is reduced and it confines in concentric patterns.A mixed layer heat budget research reveals the primary role of heat advection in the observed warming trend.During the warming age, stronger zonal currents transport warm waters from the Western Pacific (WP) to the MH region.The sea level pressure in the MH is reduced as a result of the warming which creates a slight pressure differential between the MH and the mainland of the northern hemisphere.As a result, the crossequatorial winds in the western Indian Ocean diminish.

Table : 1
It represents the semipermanent features and their meteorological parameters, location,

Table : 2
Description of the different datasets used for this study Characteristics of Monsoon Semipermanent Features in Changing Climate: An Environmental ApproachAvailable online at: https://jazindia.com-2242 - Characteristics of Monsoon Semipermanent Features in Changing Climate: An Environmental Approach