West Monsoon Research Articles

Tropical coral reefs in Sri Lanka are threatened due to the fluctuation of seasonal and interannual sea surface temperature.

The thermal stress of oceans causes coral bleaching, which induces loss of life in coral reefs and makes them exposed to other threats which directly and indirectly affect millions of other species that inhabit the reef. However, studies focusing on how those thermal stresses affect Sri Lankan fringing reef ecosystems are scarce. Hence, the patterns of long-term and short-term fluctuations of sea surface temperature (SST) over the shallow reefs around the country were studied by separating them into different zones as the eastern coast (Passikudha, Kayankerni, Adukkuparu, Parrot Rock, and Pigeon Island), the southern coast (Beruwala Barbarian, Hikkaduwa, Unawatuna, Ahangama, Mirissa, Madiha, Polhena, and Devundara), and northern-northwestern coasts (Valiththoondal, Palk Bay, Mannar, Kalpitiya, Thalwila, and Uswatakeiyawa). The 1km Multiscale Ultrahigh Resolution (MUR) Level 4 SST dataset was used to analyze seasonal and interannual SST variability from 2005 to 2021. The data were correlated with the Indian Ocean Dipole (IOD), Ekman velocity, and wind stress curl. The annual, seasonal, and monthly variability of SST on different coasts is significantly different. Higher increasing trends of SST from 0.0324 to 0.0411 ℃/year are observed on different coasts, and most of the time higher positive anomalies are recorded after 2014. The First Inter Monsoon (IM-1) and the month of April are more critical since they reach the maximum SST, and the minimum is in the North West Monsoon (NWM) and January. Significant positive relationships are recorded between the Indian Ocean Dipole (IOD) index and the monthly average SST on different coasts, which was robust on the southern coast. Therefore, tropical coral reefs in Sri Lanka are severely threatened due elevation of SST by global warming and climate variability.

Sail technology on fishing vessel for blue swimming crab catching application - A review

The increase in fuel prices will gradually have an impact on the capture fisheries sub-sector, especially the fishermen. Sail technology is an alternative that can be used to save fuel oil, although it is realized that this technology cannot completely replace the diesel motor that is commonly used in fishing operations. This study will explain the application opportunities of sail technology on fishing vessels for blue swimming crab (Portunus pelagicus) in the deep waters of the Java Sea. This fishing ground is more than 12 nautical miles from the coast. Using sail technology on fishing vessels is very dependent on the characteristics of wind speed and direction. This discussion explores the relationship between the west and east monsoons in the Java Sea with the direction of fishing trip. Technological difficulties and current challenge in sail technology on fishing vessel for blue swimming crab are identified. The possible ideas for future research in this field are also discussed.

Study of Hydrodynamic Patterns of Tanjung Pasir Banten Waters to Support the NCICD Sea Wall Development Plan

Numerical modeling of hydrodynamics (HD) around the Tanjung Pasir Waters was carried out using MIKE 21 HD Flexible Mesh software to get the current velocity pattern conditions during the west and east monsoons. This activity is to support the NCICD sea wall construction plan. In addition, the results that will be obtained in this modeling are the conditions of the speed and direction of the current in various tidal conditions during spring and neap. The data used in this modeling include wind speed and direction, wave height, wave period, and wave direction. Based on the research that has been done, the validation value of Naotide tidal data on tidal field data is 93.8 %. HD MIKE 21 modeling results on field data have a validation value of 93.4 %. Extract points 4 and 5 which are the northernmost, have the highest current velocity values compared to the other points. In addition, when heading to the high tide phase, both spring and neap conditions, the current velocity value has the highest value.

Temperature, Salinity and Dissolved Oxygen West and East seasons in the waters of Amurang Bay, North Sulawesi

Observations of temperature, salinity, and dissolved oxygen have been carried out in Amurang Bay waters, North Sulawesi. This study aims to determine the temperature, salinity, and dissolved oxygen during the west and east seasonal monsoons. The statistical analysis results using the t-test showed that the temperature, salinity, and dissolved oxygen in the West monsoon with the east monsoon were significantly different. Temperature, salinity, and dissolved oxygen in the west monsoon are lower than in the east. Variations in temperature, salinity, and dissolved oxygen are influenced by atmospheric conditions, weather, rainfall, and current patterns. Implicitly, temperature and salinity can affect the solubility of oxygen in the East monsoon. The value of AOU (Apparent Oxygen Utilization) in the west monsoon is less than 0.00 mg/l (negative), which indicates that oxygen is very much needed for the process of respiration and decomposition of organic substances during the west monsoon.
 Keywords: oceanographic conditions, temperature, salinity, dissolved oxygen, Amurang Bay.

Effect of Extreme ENSO and IOD on the Variability of Chlorophyll-a and Sea Surface Temperature in the North and South of Central Java Province

Chlorophyll-a (chl-a) and Sea Surface Temperature (SST) are important indicators of air-sea interaction and primary productivity. It has been widely known that the variability of chl-a and SST in the waters of Central Java Province (CJP) is influenced by the monsoonal cycle. Previous studies did not clearly describe the variability of chl-a and SST when compared to other cycles. This present study investigated the variability of chl-a and SST influenced by monsoonal cycles, IOD, and ENSO in both CJP waters. Our analysis is based on satellite observations and uses daily data to compile climatological data. The analysis found differences between the variability of chl-a and SST during the monsoonal cycle and ENSO-IOD extreme conditions. During the monsoonal cycle, the maximum (minimum) chl-a (SST) in northern CJP is 0.7 mg.L-1 (28.5ºC) is observed in the West Monsoon, and in the southern CJP is 1.5 mg.L-1 (25.5ºC) is observed in the East Monsoon. In addition, the analysis reveals that the ENSO and IOD extremes do not clearly alter the variability of chl-a and SST in the northern CJP. However, ENSO and IOD extremes have clearly altered the variability of chl-a and SST in the southern CJP. The highest impact to variability of chl-a and SST occurred during IOD+ extreme (2019), where the range of value chl-a (SST) in south CJP is 0,35–4,57 mg.L-1 (23,29 – 30,49ºC). The value of chl-a (SST) is greater than 4 mg.L-1 (less than 24ºC) are observed in the east monsoon. It is caused by the intensity of lifting the mass of water from deeper waters to the sea surface, which possibly supplies the nutrients in the surface waters. The result of the investigation showed that the increasing of chl-a and decreasing of SST in the northern CJP dominant by monsoonal cycle and southern CJP dominant by monsoonal cycle and ENSO – IOD.

Cycle of Potential Fishing Area of WPP-NRI 711 Year 2011-2020

This study discussed the cycle of potential fishing areas in WPP-NRI 711 based on the distribution of Sea Surface Temperature (SST) and distribution of chlorophyll-a concentration using MODIS Aqua satellite imagery. The distribution of Potential Fishing Areas (PFA) was determined based on the distribution of the thermal front which was processed using MGET (Marine Geospatial Ecology Tools) and chlorophyll-a. Determination of fluctuations and the emergence period of PFA for 10 years (2011-2020) is carried out using wavelets. The results showed that the average SST in WPP-NRI 711 was 29 °C. The highest average SST is 31 °C in May of the Transitional I Season, and the lowest average temperature is 27.9 °C in February of the West Monsoon Season. The average chlorophyll-a concentration was 0.6 mg/m3, the highest average chlorophyll-a concentration was 0.76 mg/m3 in December West Monsoon Season, and the lowest average was 0.53 mg/m3 in October Transitional II Season. The average PFA distribution area is 1.111 km2, the highest average area is 1.324 km2 in the West Monsoon Season, then the lowest area is 924 km2 in the Transitional II Season. Based on global spectrum and wavelet analysis, it is known that the period of the appearance of PFA is 3-6 months or Seasonal. then in the Northern Region segment of WPP-NRI 711, covering the Natuna Sea, the appearance of PFA is strongly influenced by Seasonal current movements. Meanwhile in the southern part, including the Karimata Strait, the emergence of PFA is strongly influenced by river runoff and changing Seasons.

Interannual Variability of the Australian Summer Monsoon Sustained through Internal Processes: Wind–Evaporation Feedback, Dynamical Air–Sea Interaction, and Soil Moisture Memory

Abstract In northern Australia (NAUS), mean rainfall during the Australian summer monsoon (AUSM) season exhibits distinct interannual variability despite weak influence from tropical sea surface temperature (SST) variability. The present study investigates mechanisms for the strong and persistent rainfall anomalies throughout the AUSM season. When the AUSM is stronger than normal, the low-level monsoonal circulation intensifies in response to the stronger convective activity over NAUS. The intensified surface westerlies over the tropical southeastern Indian Ocean (SEIO) enhance oceanic evaporation locally and downstream moisture transport into NAUS. This wind–evaporation feedback is verified through a moist static energy budget analysis. For this feedback to work effectively, SST cooling due to the stronger AUSM should be weak enough not to suppress the oceanic evaporation in the tropical SEIO. Our mixed layer heat budget analysis based on an ocean model hindcast experiment reveals that anomalous downwelling in the subsurface SEIO, which is induced dynamically by the intensified monsoon westerlies, partially offsets the SST cooling. The land surface evaporation over the continental inland area is also enhanced significantly in the middle and later portions of the monsoon season associated with increased soil moisture, suggesting its memory effect for the persistence of rainfall anomalies. The AUSM variability can therefore be regarded as a self-sustaining internal variability in the atmosphere–ocean–land surface coupled system, rather than just an atmospheric internal variability. Significance Statement We aim to understand why summer monsoon rainfall in northern Australia varies markedly from one year to another even under the weak influence of large-scale sea surface temperature fluctuations, such as El Niño/La Niña. Our analyses based mainly on observational datasets reveal that wind-induced changes in oceanic evaporation south of Java significantly modulates the water vapor transport into northern Australia. We also find that ocean dynamics helps this wind–evaporation feedback process and continental soil moisture may act to prolong anomalous rainfall by its memory effect. This study shows the self-sustaining nature of the Australian summer monsoon variability under the atmosphere–ocean–land surface interactions, which deepens our understandings of the monsoon system.

Rainfall based crop planning of Srikakulam district of A.P. under DAMU project

The District Agromet Unit (DAMU) under Gramin Krishi Mausam Sewa (GKMS) is the flagship programme of Govt. of India for weather related services to the farmers aiding in decision making on day-to-day agricultural operations. This scheme is extended to block level to address weather needs of farmers at micro-level. This is a joint effort of India Meteorological Department (IMD) and Indian Council of Agricultural Research (ICAR) with multi-organisational collaboration to implement various components and issuing crop and location specific weather based agro advisories for the benefit of farming community on every Tuesday and Friday and occurrence of extreme weather. The aim of the present study is to analyze the mandal wise rainfall data and the mandals were grouped based on the distribution of rainfall. Out of 38 plain mandals, 27 mandals received normal rainfall and 5 mandals received excess rainfall during South west monsoon period. Similarly, 7 agency mandals received normal rainfall and 4 agency mandal received excess rainfall during South West monsoon period as a whole. Month wise data showed that the distribution was either deficit or excess during the months of South West monsoon period i.e., June, July, August and September.

Strategies to cope with warming and reduced rainfall in green gram for northern transition zone of Karnataka, India

South West monsoon has become more erratic and unpredictable in the northern Transition Zone of Karnataka and in the coming decades this will continue further with warming. To cope with change in climate, agronomic adaptation strategies (optimum sowing window and application of irrigation at critical stages) are required to maintain higher yields of greengram. As a result, the DSSAT model was used to investigate the influence of climate change on greengram. The study included a combination of two temperature (+1 and +2 °C) and two reduced rainfall (˗10 and ˗20 %) scenarios in comparison with the baseline scenario (i.e., current climate). These scenarios were built for 32 years using historical weather data from 1985-2016. With regard to adaptation strategies, six dates of sowing; starting from June 1st week to July 2nd week at a weekly interval and four irrigation treatments each of 60 mm; one at pre-flowering stage, one at pod formation stage, one each at pre-flowering and pod formation stages, and no irrigation (rainfed) were included. Between sowing dates, the model's simulation of average grain yield across 32 years revealed that, 3rd (513 kg ha-1) and 4th (508 kg ha-1) week of June were found to be optimum under future climate. Irrigation at any of the critical stages increased the yield, but largest positive yield response was replicated with two irrigations: one at pre-flowering and the other during the pod formation stage (556 kg/ha). This study clearly showed that under future climates of 1 to 2 ℃ warming with reduced rainfall scenarios (-10 % & -20 %), sowing on 3rd and 4th week of June is best one, providing two irrigations (60 mm each) one at pre-flowering and the other at pod formation stage would more than compensate the loss in yield projected under changing climates in coming decades.

Review on monitoring of water quality of the Jakarta Bay, Indonesia

Jakarta Bay is located in the north of Jakarta City and is potentially polluted by hazardous chemical substances. Monitoring of water quality in this bay was carried out in March (west monsoon) and August (east monsoon) by the government of Jakarta. This monitor aims toknow the quality of Jakarta Bay and the importance of marine organisms, recreation and port area importance. The water sample is taken by using a watersampler in 19 stations. Water quality parameters collected were temperature, acidity (pH), dissolved oxygen (DO), salinity, transparency, turbidity, phosphate, nitrate and heavy metals mercury (Hg), Lead (Pb), Cadmium (Cd), Copper (Cu), Zinc (Zn), Nickel (Ni), As, and Chromium (Cr), and we compare the data with seawater quality standards stated by Ministry of Environment of Indonesia. We determined the status of water quality using the Storet method. The results showed that, generally, the water quality in this water was insufficient to support the lifeof the marine organisms, recreation, and port area. According to the analysis ofwater quality status, this water was included in the C category (moderately polluted).

Development of Synoptic-Scale Disturbances over the Tropical Western North Pacific Associated with the Boreal Summer Intraseasonal Oscillation and the Interannual Pacific–Japan Pattern

The development mechanism of synoptic-scale disturbances over the tropical western North Pacific (WNP) associated with the boreal summer intraseasonal oscillation (BSISO) under different phases of the interannual Pacific-Japan (PJ) pattern is investigated. Intraseasonal convection is enhanced widely over the WNP for BSISO phases 5-7 in the positive PJ years, when seasonal-mean convective activity over the tropical WNP is enhanced. By contrast, developed convection is confined over the South China Sea in the negative PJ years. Similar features are also found in the horizontal distributions of eddy kinetic energy (K′) representing the activity of synoptic-scale disturbances and of tropical cyclone occurrences. The differences in location of intraseasonal convection and the activity of synoptic-scale disturbances between the positive and negative PJ years likely lead to different teleconnection to midlatitude East Asia. The non-PJ years show mixed features of the positive and negative PJ years. A K′ budget analysis reveals that the energy conversion from eddy available potential energy to K′ (PeKe) associated with synoptic convection primarily contributes to K′ generation during the convectively active phases of the BSISO. The barotropic energy conversion from mean kinetic energy to K′, KmKe, is the second largest contributor to the K′ increase in the lower troposphere, especially during the early stage of development of synoptic disturbances. Large K′ produced by PeKe and KmKe in the tropics is advected to the subtropics by the mean flow in the late to mature stages of development. There are two factors that can determine the different locations where synoptic disturbances develop associated with PeKe and KmKe. One is intraseasonal sea surface warming during convectively suppressed phases of the BSISO preceding the active phases. The other is convergence or shear of seasonal-mean horizontal winds associated with interannual fluctuations of monsoon westerlies over the WNP.

Determining Length of Growing Period for Crop Planning in East and South Eastern Coastal Plain Agroclimatic Zone of Odisha

The length of the growing period (LGP) refers to a number of days in a year during which the moisture at the root zone of crop plants is adequate to meet the crop water need. Information on LGP provides a basis for the selection of crops, cultivars (short / medium / long duration) and cropping/farming systems of a region.
 Aim: The study aims to estimate the length of crop growing season of the East and South Eastern Coastal Plain Agroclimatic Zone of Odisha in order to provide a basis for suitable crop planning for the region. 
 Methodology: The LGP for four districts (Jagatsinghpur, Kendrapara, Khordha and Puri) under East and South Eastern Coastal Plain Agroclimatic Zone of Odisha was estimated using rainfall data of 30 years (1991 to 2020). The growing season begins when the sum of daily rainfall (forward accumulation) reaches 75 mm (28 May, 29 May…15 Oct) and ends when backward accumulation (15 Oct, 14 Oct,……, 28 May) of 20 mm reach. The LGP was worked out by adding the duration of the rainy season with the sum of post-monsoon rainfall and the average water-holding capacity of soil divided by the post-monsoon PET of the district.
 Results: LGPs obtained by the above method varied from 173 to 192 days in this zone with Kendrapara district having the highest LGP (192 days) and Khordha the shortest (173 days). The date of onset and cessation of south west (SW) monsoon was 15-17 June and 13 October, respectively.
 Conclusion: Double cropping can be followed in Jagatsinghpur, Kendrapara and Puri districts where the length of the growing period >180 days except Khordha district where paira cropping can be followed as the length of the growing period <180 days.

Rainfall Precipitation Pattern from 2001-2021 over Andhra Pradesh Region in India

The research focuses on a key meteorological variable, precipitation, in order to analyze the changing trend of rainfall in Andhra Pradesh, India. The State highly depends on rainfall for its agricultural activities, but the occurrence of rainfall is unprecedent and variable, causing adverse implications on the cropping system as well as negative effects on natural water resources. Daily data from the years 2001 to 2021 were analyzed to determine monthly, seasonal and yearly rainfall variability using statistical methods such as mean, standard deviation (SD) and coefficient variability (CV). District wise monthly, seasonal and annual rainfall trends have been drawn using 21-year daily data. The statistical analysis of whole reference time series data reveals that maximum mean South West Monsoon (SWM) rainfall is received in the north and central coastal districts of Srikakulam, Visakhapatnam, Vizianagaram, East Godavari, West Godavari and Krishna. North East Monsoon (NEM) rainfall contributes significantly in mean annual rainfall of southern coastal district and Rayalaseema sub division of the State.

Spatial Distribution, Material Composition and Provenance of Loess in Xinjiang, China: Progress and Challenges

The loess in the arid area of Xinjiang is located at the eastern end of the Central Asia Loess Belt, and paleoclimate research about it is of great importance for understanding the mechanism of interaction of the Eurasian Westerly monsoon system and the aridity of Central Asia. This review focuses on recent progress concerning the spatial distribution, material composition and provenance of loess in Xinjiang and points out the shortcomings of and challenges to provenance and dust circulation. Field investigation and previous studies indicate that loess sediments have been mainly distributed on the river terraces and windward piedmont of the Tianshan Mountains and the Kunlun Mountains since the late Pliocene (mainly late Pleistocene). Grain size and age data show that Xinjiang loess deposits at some locations are rapid and discontinuous or sedimentary hiatus. The Siberian High system largely controlled dust mobilization and loess accumulation in northern Xinjiang but not southern Xinjiang. In southern Central Asia, the intensity of dust activity may be determined by the Caspian Sea–Hindu Kush Index (CasHKI) and local circulation. However, there is not enough evidence that the CasHKI index can affect the Tarim Basin area. Consequently, ascertaining the driving mechanism of mid-latitude Westerly winds and the dynamic process of loess deposition in Xinjiang is a specific suggestion for critical future research. Many indicators have shown that the loess dust sources in Xinjiang are composed of mainly proximal materials plus some remote materials. Alluvial plains and local proluvial fans contributed more to loess deposition, while Central Asian deserts comprise a small proportion of loess deposition in northern Xinjiang. In future provenance research, new technologies and new methods should be continuously tested to facilitate an objective understanding of the provenance of the loess in Xinjiang.

Comparative analysis of Sub division wise rainfall INSAT-3D vs Ground based observations

Rainfall monitoring during south west monsoon season both are very important ad crucial activity. It is important mainly because it is a boon for agriculture, a mirror for future for both social and economic activities and crucial for its measurements (ground as well as remote). In this current works authors made an attempt to know the performance of recently Space Application Centre (SAC), ISRO developed INSAT-3D improved rainfall algorithms (Hydro Estimator and corrected IMSARA) with actual ground based rainfall data by calculating the bias (Actual –Satellite) for each sub-division. The analysis is done for the southwest monsoon season -2021 in by calculating weekly, monthly and seasonal bias for each subdivisions of Indian domain. It is seen that both the algorithms behave similar fashion (both show increase or decrease, simultaneously) with actual data and mostly satellite overestimate with actual data ranges from ~ 20-40 mm. In some subdivisions bias reached within the range 40 -70 mm (except Konkan & Goa ). Almost 40 % of the subdivisions have bias within 0 to 20 mm range, however the variation on weekly, monthly or seasonal differs subdivision and magnitude-wise. Overall, both the algorithms captures and performance well the trends in weekly, monthly and seasonal accumulated rainfall values. Corrected IMSRA (IMC) algorithm perform slightly better (15-20 %) except heavy rainfall episodes during the monsoon season -2021. In both the heavy and very heavy rainfall cases Hydro Estimators pick up well and performs better (~ 10 -12 %) than IMC algorithm especially over orographic areas. In extremely heavy rainfall cases both the algorithms behave in the same manner and captures the events although it is differing magnitude wise. Seasonal analysis of monsoon 2021 rainfall shows that 8 subdivisions have negative biases in the range of 50-60 mm) and 24 subdivisions have negative biases in the range of 0-20 mm, except Konkan Goa, Coastal Karnataka & A & N Islands have positive biases. Therefore, there is need to strengthen the actual observation rainfall measuring network and re-examine the performance of algorithms with larger data sets so that current algorithms retuned as per changing scenario.

Nocturnal Southerly Moist Surge Parallel to the Coastline Over the Western Bay of Bengal

AbstractThe role of the diurnal atmospheric circulation cycle around the eastern Indian subcontinent, leeward of the monsoon westerlies, on the hydroclimate of South Asia remains unknown. Here, we reveal that low‐level moist southerlies are greatly enhanced at night parallel to the coastline over the western Bay of Bengal (BoB), and then flow onto the Gangetic Plain enhancing onshore moisture flux and nocturnal precipitation over the Himalayas and the Meghalaya Plateau. This nocturnal surge is strongly controlled by the diurnal cycle of dynamic and thermodynamic effects around the subcontinent. At night, nocturnal westerly low‐level jets appear over the subcontinent. Strong low‐level southwesterly flow with a low‐level jet structure also appears parallel to the coastline over the western BoB, extending from the west of Sri Lanka. The low‐level westerlies from the subcontinent and the low‐level southwesterlies merge into a single strong southwesterly flow, forming the low‐level moist surge.

Influences of Spring Land Surface Thermal Anomalies over West Asia on Indian Early Summer Monsoon Activity and Its Pathway

Abstract Exploring the premonsoonal land thermal predictor of the Indian summer monsoon is a hot topic under the background of global warming, and West Asia is one of the regions with the most significant warming in spring. In this study, we investigated the impact of anomalous spring land surface warming over West Asia on early summer (June) Indian monsoon precipitation as well as its possible mechanisms based on statistical analysis and numerical simulations. It has been found that spring land surface anomalous warming over West Asia corresponds to the enhancement of the leading mode of early summer precipitation in the Indian subcontinent, especially in its northern part. Further analysis indicates that an anomalously warm land surface over West Asia can advance the transition of atmospheric conditions toward the warm season by heating the atmosphere above. The increased land–sea meridional thermal contrast favors the intensification of the low-level jet and monsoon trough, further inducing anomalous moisture convergence and ascending motion over northern India. Additionally, the heat-driven anomalous upper-tropospheric anticyclone over West Asia favors the intensification of the tropical easterly jet and the northwestward development of the South Asian high (SAH). The enhanced SAH dynamically couples with the lower- to middle-level cyclonic circulation over northern India, resulting in a stronger monsoon and increased precipitation. These findings are helpful for better understanding and prediction of Indian early summer monsoon. Significance Statement The land surface thermal condition is critical to the monsoon activity and exploring the premonsoonal land thermal predictor of Indian summer monsoon remains a hot topic. The purpose of this study is to explore how spring land surface thermal anomalies over West Asia impact Indian monsoon activity in early summer (June). The anomalous land surface warming over West Asia can lead to a stronger Indian monsoon in early summer by heating and driving the atmosphere, which benefits the precipitation increase over northern India. Our results provide a further scientific basis for the prediction of early summer Indian precipitation.

Effect of Interdecadal Variation in Southern Indian Ocean SST on the Relationship Between ENSO and Summer Precipitation in the Asian‐Pacific Monsoon Region

AbstractThe relationships between the El Niño‐Southern Oscillation (ENSO), Asian‐Pacific region summer precipitation and its corresponding atmospheric circulations exhibit interdecadal changes. From the early 1990s to the early 2000s, these relationships were significant. Therefore, we divided this time frame into three periods for analysis: 1979–1991 (P1), 1992–2005 (P2), and 2006–2019 (P3). The possible mechanism underlying these relationships is as follows: the southern Indian Ocean sea surface temperature (SST) over the east of Madagascar exhibits interdecadal variation. During P2, the SST was relatively cold, which induced an anomalously high mascarene high (MH). The strengthened MH enhanced the Somali jet and Indian monsoon westerlies, which intensified the strong center of the Indian Ocean Walker circulation. Therefore, owing to the strength and location changes of the Indian Walker circulation and the Walker circulation, the connection between the ENSO and the western Pacific vertical motions strengthened, resulting in the close relationship of the ENSO with the atmospheric circulation over the Asian‐Pacific region. Hence, ENSO can influence a north‐south tripole pattern of precipitation over the Asian‐Pacific monsoon region through local vertical activities and meridional Hadley circulation over western Pacific. Numerical experiments using an atmospheric general circulation model, with prescribed three times southern Indian Ocean SST anomalies of 1995–2005 relative to 1979–2019, also lend support to the southern Indian Ocean SST's contribution to modulating the relationship between ENSO and summer precipitation over the Asian‐Pacific monsoon region.

Seasonal changes in East Asian monsoon-westerly circulation modulated by the snow-darkening effect of mineral dust

The snow-darkening forcing of dust (SFD) is known to occur when dust-covered snow reduces surface albedo and absorbs more radiation, which causes snowmelt and surface warming. To date, few studies have focused on how SFD affects atmospheric circulation. In this study, we used a climate model to evaluate the influence of the SFD on seasonal changes in coupled monsoon westerlies over East Asia. The results indicate that the SFD causes anomalies in temperature, precipitation, and atmospheric circulation over East Asia. In December and January (DJ), the temperature increase over the Tibetan Plateau is significant, and the anomalous anticyclonic circulation causes a weakening of the westerly circulation during this period. In February, March, and April (FMA), the SFD causes an increase in temperature over the plateau and its eastern flank and widespread anomalous cooling to the north, which can be attributed to diabatic cooling of the upper atmosphere. These changes in thermal conditions lead to enhanced westerly winds and weakened East Asian winter monsoons during FMA. The enhanced westerly winds bring more precipitation to the East Asian continent. In May, June, and July (MJJ), only the Tibetan Plateau is significantly warmed in East Asia. At this time, the westerly circulation weakens, and the East Asian summer monsoon strengthens. The low-level atmospheric circulation shows anomalous westerly winds over South Asia. The anomalous westerly winds from Central Asia bring dry air and result in reduced precipitation over India.

Association of Different Satellite Driven Products with Evapotranspiration in Tamil Nadu, India (2010-2020)

Evapotranspiration is an important phenomenon of hydrological cycle mainly influenced by meteorological factors and other vegetation characteristics. In this study, the relationship between Actual Evapotranspiration (AET) with Normalized Difference Vegetation Index (NDVI) and Land Surface Temperature (LST) were analysed using Moderate Resolution Imaging Spectroradiometer (MODIS) TERRA satellite data products with the help of Geographic Information System (GIS) software. The duration of study was during South West Monsoon (SWM) season from June to September, over a period of ten years (2011 to 2020) for all seven Agro Climatic Zones (ACZ) of Tamil Nadu, India. The results showed that moderate to strong positive correlation were observed between AET and NDVI (r= 0.3 to 0.9) in all seven ACZ. The AET and LST showed a weak to strong negative correlation (r= -0.4 to -0.7) in six ACZs except High Rainfall Zone (HRZ) which might be due to lower LST and high NDVI values recorded in the HRZ which exhibited a weak positive relationship (r=0.2). Relationship between AET, LST and NDVI are highly useful for parametrizing evapotranspiration in different climatic conditions, analyzing different crop growth and production and helps in planning water management strategies at regional scale.