West Monsoon Research Articles

Agricultural drought monitoring and management at sub district level in Telangana

The weather or climate is considered as an important natural resource and basic input for better planning of crop and cropping system in agriculture particularly rainfed environments. Every plant process, related with growth, development and yield of a crop and each of in-season and off-season farm operations depends on weather. Amongst the various weather elements, temperatures, radiation and rainfall play crucial role in deciding the crop growth, development and yield levels. Precipitation is one of the important weather factors being responsible for atmospheric and soil moisture and therefore has more agricultural importance, especially in rainfed agriculture.
 Rainfed crops like jowar, maize, groundnut, greengram, blackgram and sunflower and one water-intensive crop like rice are mainly affected owing to drought. The drought conditions occur due to failure of South West Monsoon, delay in arrival of SW monsoon, and break monsoon conditions or early cessation of SW monsoon. Rainfed agriculture in India depends on onset of monsoon and the rainfall distribution during crop growth season. The amount of rainfall and the time of onset of monsoon decides the type of the crop to be grown. The timely onset and well distribution of monsoon rain in the month of June and July decides the area coverage of rainfed crops. Any deviation in the onset and distribution of southwest monsoon rainfall causes huge impact on agriculture and its dependent activities. Close monitoring of progress of monsoon and distribution of rainfall and its impact on sowing of rainfed crops is essential at sub district level to suggest time to time crop management strategies thereby to minimize the impact of aberrant seasonal conditions. In this paper a monitoring of drought at national, state and sub district (Mandal) level using indices like MAI, WRSI etc. were presented. Management strategies to reduce the impact of drought like optimum time of sowing, strategic irrigation, crop calendar, contingency crop planning etc. were discussed. Agromet advisories for communication of real time weather information for benefit of farming community were presented.

Variability in MODIS NDVI in Relation to Southwest Monsoon over Western Ghats, India

Eleven years (2000 to 2010) of Normalized Difference Vegetation Index (NDVI) data, derived from Moderate Imaging Spectroradiometer (MODIS) Terra with 250 m resolution is used in the present study to discuss the changes in the vegetal cover over Western Ghats, India. The NDVI over Western Ghats (number of test sites are 16) showed increasing tendency and the pronounced changes in NDVI have been studied in the context of southwest monsoon's distribution and activity. The NDVI progression is observed from June with a minimum value of 0.179 and yielded to a maximum at 0.565 during September/October, on an average. The study then relates NDVI with different rainy events to understand the connection between the ground vegetation and the south west monsoon. The results of the study inferred are as follows: i) NDVI, Antecedent Precipitation Index (API) are in good agreement throughout the monsoon which is evidenced by correlation; ii) NDVI maintained good correlation with a number of Light and Moderate Rainy days alternatively but not with the number of Heavy Rainy days; iii) Relation of NDVI with Isolated, Scattered distributions and active monsoons is substantial; and iv) Rate of Green Up is captured by the satellite during the crop growing season over the Western Ghats.

DINAMIKA DISSOLVED INORGANIC CARBON (DIC) DI EKOSISTEM LAMUN PULAU PARI

Coastal water represents 8% of the global ocean. The one of coastal ecosystem is seagrass ecosystem. The role of coastals ecosystem, such as seagrass ecosystem as source or sink carbondioxide (CO2) from atmospher to sea and dynamic of Dissolved Inorganic Carbon (DIC) has not been fully understood. The objective of study is analyzed DIC data and ancillary environmnet data in seagrass ecosystem at temporal represent west , east and trantition monsoon season as long as 2011 – 2012 in seawater and porewater. The higher DIC in seawater and porewater is east monsoon season. The lowest DIC in seawater and porewater is west monsoon season. Total alkalinity (TA) and partial pressure of CO2 (pCO2) have the same pattern with DIC, they are high in east monsoon season and low in west monsoon seasoon. Dynamic of DIC and (TA) every seasonin seawater are affected temperature, while in porewater is not visible factors affecting of DIC. Parameter of TA in porewater is influenced by total suspended solid (TSS). West monsoon season, seagrass ecosystem roles as CO2 sink with the flux is 3.237 mmolC/m2/day. East and trantition monsoon season, seagrass ecosystem plays a role as CO2 source with the flux of 11.669 mmolC/m2/hari.

Impact of human interventions on nutrient biogeochemistry in the Pamba River, Kerala, India

Anthropogenic inputs nowadays are the major source of nutrients to the coastal area. While a wealth of data exists from high latitude regions, little is known on the amount and composition of nutrient fluxes from densely populated tropical catchments. The South Indian Pamba River is a prime example in this respect because of its manifold human interventions such as the Sabarimala pilgrimage, the largest pilgrim centre in the world and agricultural practices. In order (i) to identify direct cause-effect relationships, (ii) to quantify land use specific nutrient inputs and (iii) to assess the respective impacts water was sampled along the river course during the pre monsoon, south west monsoon and north east monsoon periods in 2010 to 2012. Sampling segments were chosen according to prevailing land use. A socioeconomic survey on agricultural practices was conducted to collect information on the type, time and quantity of fertilizer application.Our results indicate (i) little human activities in the forest segment resulted in a low nutrient yield; (ii) pilgrim activities led to high ammonium and phosphate yields in the temple segment; (iii) specific fertilizer management resulted in moderate and maximum nitrate yields in the respective agriculture segments. Annual NPK fertilizer inputs to the catchment were 95kgha−1yr−1.The average yield for the Pamba River catchment amounted to 3.5kgha−1yr−1 of DIN and 0.2kgha−1yr−1 of phosphate-P. As opposing predictions for densely-populated regions the N and P yields of the Pamba River are moderate to low on a global scale. It highlights the need for land use specific quantitative estimates from tropical regions in order to improve the global database and local water quality management.

Passive Acoustic Recognition of Fishing Vessel Activity in the Shallow Waters of the Arabian Sea: A Statistical Approach

The ambient noise system consisting of a vertical linear hydrophone array (VLA) with 12 elements was deployed in the waters of the Arabian Sea at a depth of 16[Formula: see text]m, off Goa, India, for extracting the ambient noise during the fishing season (March, April and May, 2013 before the onset of the south west monsoon). This study focuses on fishing vessel activity by finding the domination of the vessel and wind noise at two 12 hourly periodic cycles that start at midnight and noon, using the statistical analysis. It is performed using statistical parameters, like the mean, median, and standard deviation, skewness, percentile and spread of data. It is observed that the vessel noise dominates during the 12[Formula: see text]h period that starts at midnight and is an indication of the activity of fishing vessels while the wind generated noise is more during the 12[Formula: see text]h period that starts at noon, which is a sign of the domination of the sea breeze effects. This is the first time that a statistical analysis has been carried out to study the ambient noise data collected off Goa, in order to find the fishing vessel activity during the pre-monsoon season. The results are verified with the fishing information from the Directorate of Fisheries, Goa, ship traffic data from the Mormugao Port Trust and wind speed measurements.

KARAKTERISTIK GELOMBANG SIGNIFIKAN DI SELAT KARIMATA DAN LAUT JAWA BERDASARKAN RERATA ANGIN 9 TAHUNAN (2005-2013)

Karimata strait and the java sea is one of the most densely shipping lanes in the maritime country of Indonesia. Information of a significant wave is needed to safety navigation. The prediction of a significant wave mostly employs the modeling using wind as input data to produce an early warning warning prediction. Characteristic of a significant wave shows the maximum wave height in the strait and the java sea karimata occurs in west monsoon (January) and east season (August) every year. Especially at the peak of west monsoon (January) maximum wave height reach 1.5-3 meters in Karimata Strait, and reach 0.5-2.5 meters in Java Sea. The frequency of significant wave occurences mostly extend until February, where wave height in Java Sea will stay the same (0.5-2.5 meters), while in Karimata Strait is little bit decrease (1-2.5 meters). Recommended to all sea transportation users, in those regions during January and February, to avoid using ship with the hull is less than 3 meters height.Keywords: significant wave characteristic, Karimata Strait, Jawa Sea, Wind, Modeling

Weekly rainfall variability and probability analysis for resource planning at Hadagali, Karnataka

Daily rainfall data of 35 years (1978-2012) of Hadagali were used for weekly analysis to study the variability and the probability level of occurrence. The highest mean weekly rainfall (42.5 mm) was received during 39th SMW. The CV was less than 150 per cent during 22-33, 35 and 37-42 nd SMW, indicated that the rainfall was consistent during those weeks. The rainfall analysis showed that the crop could be recommended under dry land during 22-33, 35 and 37-42 nd SMW as the rainfall was more consistent during these periods as compared to 18 st to 21 st SMW, which also fell under south west monsoon period. The study indicated that rainfall amount of more than 20 mm of rainfall could be expected during 38-40 th SMW with 50 per cent probability, which hints for rain water harvesting.

Species Composition of Ants in Cashew Plantations and their Interrelationships with Cashew

In cashew plantations of south west Karnataka, India, foraging activity of 49 ants species belonging to 24 genera and 7 subfamilies were recorded. The study found that ants visited cashew trees regularly throughout the year. Myrmicinae ants were most dominant comprising 22 species followed by Formicinae with 13 species while, among Aenictinae and Dorylinae, only single species was found. Species richness was high in old cashew plantations recording 89.8 % of total species, while medium and young plantations recorded only 46.9 and 24.5 %. Dominance of different ant species was noticed on cashew canopy, trunk and soil in different aged cashew plantations. Old cashew plantations were characterized by Oecophylla smaragdina, followed by Anoplolepis gracillipes, while, Camponotus compressus and C. sericeus were dominant in young and medium aged plantations. Pit fall trap collection consisted mostly of Odontomachus haematodus, Lophomyrmex quadrispinosus, Technomyrmex albipes, Myrmicaria brunnea, Diacamma sp., C. compressus and C. sericeus. During flowering and fruiting period of cashew, foraging of up to 10 ant species was seen on the same tree at a time. Activities of most ant species were predominant during winter and summer which coincides with flowering and fruiting period of cashew (December–May), while during heavy down pour of south west monsoon, activities of only 10 species were seen. A significant positive correlation was found between number of ant species and maximum air temperature (0.842) and also with afternoon soil temperature (0.925).

Onset of the Rainy Seasons in the Eastern Indochina Peninsula

Abstract The onset dates of rainy season over the eastern Indochina Peninsula (8.5°–23.5°N, 100°–110°E) are objectively determined for individual years from 1958 to 2007 using the empirical orthogonal function (EOF) analysis. On average, the onset of the summer rainy season (SRS) determined by EOF1 is 6 May, with a standard deviation of 13 days. The autumn rainy season (ARS) indicated by EOF2 has a mean onset and standard deviation of 16 September and 12 days, respectively. The SRS onset is characterized by the evolution of summer monsoon westerlies and the northward propagation of strong convection from the equatorial region. Conversely, the withdrawal of the summer monsoon over northeastern Indochina in late summer–early autumn favors the ARS onset. Both onsets are strongly associated with intraseasonal oscillation on 30–60- and 10–20-day time scales. Examination of the precursory signals associated with the early/late onsets of both SRS and ARS implies that ENSO has a significant impact on their year-to-year variations. In La Niña years, the subsequent SRS tends to have early onsets. Simultaneously, the western Pacific subtropical high (WPSH) weakens and retreats eastward earlier. In contrast, advanced ARS onset generally occurs during an El Niño–developing autumn with weakened equatorial easterlies and suppressed convection over the central Indian Ocean from the preceding summer, as evident in weakened Walker circulation. However, robust precursory signals in SST are observed only from midsummer (July–August). An earlier ARS onset is also associated with the development of an anomalous Philippine Sea anticyclone and a westward-extended WPSH from midsummer. However, no coherent correlation is found between the late onset and La Niña.

Impact of Natural Processes and Human Activities on Groundwater Quality in the Negombo-Muthurajawela Region in Sri Lanka

Groundwater is an essential and finite resource in the world. Numerous knowledge gaps remain in the understanding of groundwater resources in Sri Lanka, mainly due to the lack of accurate data. The purpose of this study is to assess the water quality in groundwater and its spatial distribution in Negombo-Muthurajawela area in Sri Lanka. The data collection was conducted at the beginning and at the end of south west monsoon (May and September, respectively) in 2013. A pilot survey was carried out using 116 dug wells. A total of thirty-one dug wells were selected for physiochemical analysis. In situ field testing of electrical conductivity (EC), salinity, and pH were carried out and laboratory tests were performed for HCO3−, Na+, K+, Ca2+, Cl−, SO42−, Mg2−, PO43−, NO3−, and total hardness (TH). Principal component analysis (PCA) was performed to assess water quality and interpolation technique in ArcGIS was performed to analyze and prepare spatial distribution maps of water. Sri Lankan standards for drinking water were used to determine the threshold levels of physiochemical parameters. The results of the PCA reveal that thirty-one observation wells can be classified under three main components: the first based on the impact on EC, HCO3−, Na−, K+, Cl−, Mg2−, and TH; the second component considering the pH, HCO3, Ca2+, SO42−, PO43−, and TH; and the third component based on NO3−. These three components evidence the role of salt water intrusion, the influence of Muthurajawela wetlands, and the anthropogenic discharges on groundwater quality in the Negombo-Muthurajawela area.

Global effect of climate change and food security with respect to Nepal

The effect of global climate change in Nepal could be observed by glacier retreat in the Himalaya region and change in the pattern of the south west monsoon which is the only reliable source of water for farming. Climate change has been occurred in Terai, hills and mountain of Nepal resulting change in agriculture systems leading to the emergence of new insect, pest and disease of crops and animals. There are frequent losses of lives, crops and, human settlements due to occurrence of flash floods, droughts, typhoon and hurricanes in the world mainly due to climate change. Global food production and trade have been affected by the negative consequences of climate change as a result countries like Nepal are also victimized due to the negative effect of climate change. Increase in C02concentration in the atmosphere and change in precipitation are being the main cause of floods, droughts, glacier retreat, and melting of snows, hence, change in the flora and fauna globally. To address such measures of climate change, Nepal has been trying to develop some adoptive ways such as development of climate resilient technology including crop varieties, animal breeds; agronomic practices that could address vagaries of climate change and sustain food and nutritional security. In Nepal, the effect of climate change is more pronounced in hills and mountains with respect to increase in temperature than that of Terai. This paper tries to address issue of global climate change with respect to food security of Nepal by applying some of the pragmatic adoptive measures to follow in agriculture for sustaining food security in Nepal.

Analysis of Rainfall Probabilities for Strategic Crop Planning in Raipur District of Chhattisgarh State

Rainfall data of recent forty three years (1971-2013) of Labhandi station, Indira Gandhi Krishi Vishwavidhyalaya Raipur, Chhattisgarh was analysed with the method of incomplete gamma probability. The data revealed that the average rainfall of labhandi station is 1202 mm spread over 61 rainy days. Out of this 1055, 68, 53 and 27 mm received from south west monsoon (June-September), north east (October-December), summer (March-May) and winter season (January -February) respectively. Probability for receiving more than 100 mm of rainfall can be expected only at 25% probability level and that too in four weeks which is leading to the interpretation that rainfed rice production is a challenging task in this region. it has been found that at 75 per cent assured probability level rainfall of more than 200 mms can be expected only in July and August months and this rainfall is hardly sufficient for meeting the water requirement in upland situations. However at 50 per cent probability which is equivalent to average condition, cultivation of rice is possible under well water management conditions. On seasonal basis rainfall at assured probability level of 75% is not sufficient as the quantity is 795 mm rainfall in south-western monsoon season.

Re-examination of tropical cyclone formation in monsoon troughs over the western North Pacific

The monsoon trough (MT) is one of the large-scale patterns favorable for tropical cyclone (TC) formation over the western North Pacific (WNP). This study re-examines TC formation by treating the MT as a large-scale background for TC activity during May–October. Over an 11-year (2000–10) period, 8.3 TC formation events on average per year are identified to occur within MTs, accounting for 43.1% of the total TC formation events in the WNP basin. This percentage is much lower than those reported in previous studies. Further analysis indicates that TC formation events in monsoon gyres were included at least in some previous studies. The MT includes a monsoon confluence zone where westerlies meet easterlies and a monsoon shear line where the trade easterlies lie north of the monsoon westerlies. In this study, the large-scale flow pattern associated with TC formation in the MT is composited based on the reference point in the confluence zone where both the zonal and meridional wind components are zero with positive vorticity. While previous studies have found that many TCs form in the confluence zone, the composite analysis indicates that nearly all of the TCs formed in the shear region, since the shear region is associated with stronger low-level relative vorticity than the confluence zone. The prevailing easterly vertical shear of zonal wind and barotropic instability may also be conducive to TC formation in the shear region, through the development of synoptic-scale tropical disturbances in the MT that are necessary for TC formation.

CMIP5 model-simulated onset, duration and intensity of the Asian summer monsoon in current and future climate

A number of significant weaknesses existed in our previous analysis of the changes in the Asian monsoon onset/retreat from coupled model intercomparison project phase 3 (CMIP3) models, including a lack of statistical significance tests, a small number of models analysed, and limited understanding of the causes of model uncertainties. Yet, the latest IPCC report acknowledges limited confidence for projected changes in monsoon onset/retreat. In this study we revisit the topic by expanding the analysis to a large number of CMIP5 models over much longer period and with more diagnoses. Daily 850 hPa wind, volumetric atmospheric precipitable water and rainfall data from 26 CMIP5 models over two sets of 50-year periods are used in this study. The overall model skill in reproducing the temporal and spatial patterns of the monsoon development is similar between CMIP3 and CMIP5 models. They are able to show distinct regional characteristics in the evolutions of Indian summer monsoon (ISM), East Asian summer monsoon (EASM) and West North Pacific summer monsoon (WNPSM). Nevertheless, the averaged onset dates vary significantly among the models. Large uncertainty exists in model-simulated changes in onset/retreat dates and the extent of uncertainty is comparable to that in CMIP3 models. Under global warming, a majority of the models tend to suggest delayed onset for the south Asian monsoon in the eastern part of tropical Indian Ocean and Indochina Peninsula and nearby region, primarily due to weakened tropical circulations and eastward shift of the Walker circulation. The earlier onset over the Arabian Sea and part of the Indian subcontinent in a number of the models are related to an enhanced southwesterly flow in the region. Weak changes in other domains are due to the offsetting results among the models, with some models showing earlier onsets but others showing delayed onsets. Different from the analysis of CMIP3 model results, this analysis highlights the importance of SST warming patterns over both the tropical Pacific and Indian Oceans in affecting the modelling results. The increased atmospheric moisture content offsets some effects of the delayed onset and results in increased rainfall intensity during the active monsoon period. The deficiencies of using rainfall alone in assessing the potential changes of the monsoon system are also shown in this study.

Role of Tropical Cyclones along the Monsoon Trough in the 2011 Thai Flood and Interannual Variability

Abstract The atmospheric circulation patterns that were responsible for the heavy flooding that occurred in Thailand in 2011 are examined. This paper also investigates the interannual variation in precipitation over Indochina over a 33-yr period from 1979–2011, focusing on the role of westward-propagating tropical cyclones (TCs) over the Asian monsoon region. Cyclonic anomalies and more westward-propagating TCs than expected from the climatology of the area were observed in 2011 along the monsoon trough from the northern Indian subcontinent, the Bay of Bengal, Indochina, and the western North Pacific, which contributed significantly to the 2011 Thai flood. The strength of monsoon westerlies was normal, which implies that the monsoon westerly was not responsible for the seasonal heavy rainfall in 2011. Similar results were also obtained from the 33-yr statistical analysis. The 5-month total precipitation over Indochina covaried interannually with that along the monsoon trough. In addition, above-normal precipitation over Indochina was observed when enhanced cyclonic circulation with more westward-propagating TCs along the monsoon trough was observed. Notably, the above-normal precipitation was not due to the enhanced monsoon westerly over Indochina. Therefore, the 2011 Thai flood was caused by the typical atmospheric circulation pattern for an above-normal precipitation year. It is noteworthy that the effect of sea surface temperature (SST) forcing over the western North Pacific and the Niño-3.4 region on total precipitation during the summer rainy season over Indochina was unclear over the 33-yr period.

Siltation and Coastal Erosion at Shoreline Harbours

One of the major maintenance problems encountered by the shoreline harbours along east coast of India is siltation of approach channels due to huge longshore sediment movement by wave action along the coast. Wave induced longshore sediment transport rates along east coast of India at selected major shoreline harbours Chennai, Visakhapatnam and Paradip have been estimated using an energy flux method. The direction of littoral drift is generally from south to north during the period March to October when southwest monsoon blows over Bay of Bengal and reverses its direction from north to south during the period November to February during northeast monsoon season. The rates of sediment transport however vary from one shoreline harbour to another depending upon the wave climate and other near shore features. While the littoral drift rates are high during south west monsoon season from March to October at Visakhapatnam and Paradip harbours, the Chennai harbour on the other hand experiences high rates of littoral drifts during north east monsoon months particularly from November to January due to storm waves along the coast. The estimated sediment transport rates have been compared with the available dredging quantities to know their accuracies. The problems of siltation and coastal erosion have become severe over the years due to deepening of the harbour channels as a part of expansion and modernization of ports. Hence, a detailed study on siltation problems faced by the shoreline harbours will definitely useful not only for dredging management plan for existing ports but also for planning new port locations along the coast. The historical problems of the shoreline harbours due to construction of harbour installations at selected important ports along east coast of India have been discussed briefly.

Application of Geophysical and Hydrogeochemical Tracers to Investigate Salinisation Sources in Nagapatinam and Karaikal Coastal Aquifers, South India

Groundwater in coastal aquifers of Nagapattinam and Karaikal regions are characterized by large saline variations with Conductivity levels up to (12,430.0μS/cm). The high salinity collective with deterioration in water level creates a serious threat to current groundwater quality for human consumption. An integrated electrical resistivity and hydrogeochemical investigations were carried out to isolate the saline sources of groundwater. The Vertical Electrode Spacing isolated resistivity ranges between 0.5 to 1.5μ m as saline intruded up to a stretch of 20km inland along the eastern parts of the study area. A total of 122 groundwater samples were collected twice during summer and south west monsoon seasons and analyzed for 14 different water quality parameters using standard procedures. Results demarcate higher Conductivity (12,430.0μS/cm), Cl− (5060.0mg/L) and Na+ (1330.0mg/L) indicating the saline nature of groundwater. The multi-rectangular diagram suggests groundwater influenced by recharge during south west monsoon and increasing salinity during SUM. The disseminate plots for various ions suggest saline water intrusion along the coastal tracts, cation exchange and rock water interaction along the south western and north western parts of the study area. Anthropogenic influences like sewage effluents and agricultural activities dominate south western parts of the study area. Higher Mn, Zn and Pb indicate influence from anthropogenic activities.

The Climatology and Interannual Variability of East Asian Summer Monsoon in CMIP5 Coupled Models: Does Air–Sea Coupling Improve the Simulations?

Abstract The climatology and interannual variability of the East Asian summer monsoon (EASM) simulated by 34 coupled general circulation models (CGCMs) from phase 5 of the Coupled Model Intercomparison Project (CMIP5) are evaluated. To estimate the role of air–sea coupling, 17 CGCMs are compared to their corresponding atmospheric general circulation models (AGCMs). The climatological low-level monsoon circulation and mei-yu/changma/baiu rainfall band are improved in CGCMs from AGCMs. The improvement is at the cost of the local cold sea surface temperature (SST) biases in CGCMs, since they decrease the surface evaporation and enhance the circulation. The interannual EASM pattern is evaluated by a skill formula and the highest/lowest eight models are selected to investigate the skill origins. The observed Indian Ocean (IO) warming, tropical eastern Indian Ocean (TEIO) rainfall anomalies, and Kelvin wave response are captured well in high-skill models, while these features are not present in low-skill models. Further, the differences in the IO warming between high-skill and low-skill models are rooted in the preceding ENSO simulation. Hence, the IO–western Pacific anticyclone (WPAC) teleconnection is important for CGCMs, similar to AGCMs. However, compared to AGCMs, the TEIO SST anomaly is warmer in CGCMs, since the easterly wind anomalies in the southern flank of the WPAC reduce the climatological monsoon westerlies and decrease the surface evaporation. The warmer TEIO induces the stronger precipitation anomaly and intensifies the teleconnection. Hence, the interannual EASM pattern is better simulated in CGCMs than that in AGCMs.

Variability of zonal currents in the eastern equatorial Indian Ocean on seasonal to interannual time scales

This study examines equatorial zonal current variations in the upper layers of eastern Indian Ocean in relation to variations in the Indian Ocean Dipole (IOD). The analysis utilizes data from the Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) and the European Centre for Medium-Range Weather Forecasts-Ocean Reanalysis System 4 (ECMWF-ORAS4). Surface currents are characterized by semiannual eastward flowing Wyrtki jets along the equator in boreal spring and fall, forced by westerly monsoon transition winds. The fall jet intensifies during negative IOD (NIOD) events when westerlies are anomalously strong but significantly weakens during positive IOD (PIOD) events when westerlies are anomalously weak. As zonal wind stress weakens during PIOD events, sea surface height becomes unusually low in the eastern basin and high in the west, setting up an anomalous pressure force that drives increased eastward transport in the thermocline. Opposite tendencies are evident during NIOD events in response to intensified equatorial westerlies. Current transport adjustments to anomalous zonal wind forcing during IOD events extend into the following year, consistent with the cycling of equatorial wave energy around the basin. A surface layer mass budget calculation for the eastern sea surface temperature (SST) pole of the IOD indicates upwelling of ∼2.9±0.7 Sv during normal periods, increasing by 40–50% during PIOD events and reducing effectively to zero during NIOD events. IOD-related variations in Wyrtki jet and thermocline transports are major influences on these upwelling rates and associated water mass transformations, which vary consistently with SST changes.

Spatio-temporal Identification of Regions with Anomalous Values of 222Rn in Groundwater of Madurai District, Tamilnadu, India

Measurement of dissolved radon (222Rn) activity concentration in groundwater samples from private and public hand pumps, and in bore wells located at Madurai district of Tamilnadu, India, are presented. The study attempts to identify the background value of 222Rn in groundwater of hard rock terrain and the main aquifer contributing 222Rn, and to determine if any correlation exists with observed field parameters. Measured parameters included pH, TDS, Temperature and 222Rn in 42 samples for two seasons (South West Monsoon [SWM] and North East Monsoon [NEM]). The results show that the 222Rn activity concentration of the samples ranged from 0.049 to 59.952 Bq/L in South west monsoon and 0.12 to 211.60 Bq/L in North east monsoon. The higher activity was noted in NEM and the highest 222Rn concentrations were observed in granitic terrains in both seasons. The average values of the parameters studied shows that there is a general decrease of TDS and Temperature, but an increase in 222Rn and pH during NEM. The spatial representation of the activity shows that maximum values are in the north eastern part of the study area. Further, correlations between the measured parameters show that temperature has a negative correlation to the samples of charnockite formation during both seasons; pH and TDS also show negative relationships to 222Rn during SWM.