Good Monsoon Research Articles

Time series subsidence evaluation using NSBAS InSAR: a case study of twin megacities (Rawalpindi and Islamabad) in Pakistan

Ground deformation associated with natural and anthropogenic activities can be damaging for infrastructure and can cause enormous economic loss, particularly in developing countries which lack measuring instruments. Remote sensing techniques like interferometric synthetic aperture radar (InSAR) can thus play an important role in investigating deformation and mitigating geohazards. Rawalpindi and Islamabad are twin cities in Pakistan with a population of approximately 5.4 million, along with important government and private entities of national and international interest. In this study, we evaluate rapid paced subsidence in this area using a modified small baseline subset technique with Sentinel-1A imagery acquired between 2015 and 2022. Our results show that approximately 50 mm/year subsidence occurs in the older city of Rawalpindi, the most populated zone. We observed that subsidence in the area is controlled by the buried splays of the Main Boundary Thrust, one of the most destructive active faults in the recent past. We suggest that such rapid subsidence is most probably due to aggressive subsurface water extraction. It has been found that, despite provision of alternate water supplies by the district government, a very alarming number of tube wells are being operated in the area to extract ground water. Over 2017–2021, field data showed that near-surface aquifers up to 50–60 m deep are exhausted, and most of the tube wells are currently extracting water from depths of approximately 150–160 m. The dropping water level is proportional to the increasing number of tube wells. Lying downstream of tributaries originating from the Margalla and Murree hills, this area has a good monsoon season, and its topography supports recharge of the aquifers. However, rapid subsidence indicates a deficit between water extraction and recharge, partly due to the limitations inherent in shale and the low porosity near the surface lithology exposed in the area. Other factors amplifying the impacts are fast urbanization, uncontrolled population growth, and non-cultivation of precipitation in the area.

Impact of COVID-19 on Agriculture and Allied Sectors

Impact of Corona virus outbreak on mankind is serious. Apart from health issues and social life stand still, global economy has been affected drastically. Many sectors have been hit by this pandemic and agriculture and allied sectors are no exception. Issues such as shortage of labour, restricted access to markets have been tremendously affected this sector. Many of its frailties were exposed during the course but the resilient cultivation sector surfaced with some promising results after a good monsoon and aggressive response demonstrated by the government to support the sector. Government excluded several farming activities such as farm operations, agribusiness, dairy, poultry and fishery from lockdown limitations after the lockdown extended in May, 2020. Pandemic also presented a great opportunity to think over and evaluate the hidden potential of respective sectors. Solemn efforts are required for innovation and technical up gradation of agricultural operations to alleviate the impacts of the COVID-19 pandemic. As India struggles to uplift the distressed economy, government announced economic stimulus package worth INR 20, 00,000 crore under Atma Nirbhar Bharat Campaign. Long term impacts of this campaign are estimated to develop agriculture and allied sectors with major emphasis on quality products and increased exports of agriculture commodities.

Food Security Under The Era Of Climate Change Threat

Food Security Under The Era Of Climate Change Threat

Prolonged warming over the last ca. 11,700 cal years from the central Indian Core Monsoon Zone: Pollen evidence and a synoptic overview

Paleopalynological records of 1.1 m deep lacustrine sediment profile from the central Indian Core Monsoon Zone (CMZ) have provided a prolonged warming trend over the last ca. 11,700 years. Palynological evidence suggests that between ca. 11,700 and 8500 cal yr BP, a mixed tropical deciduous forest occurred in the region under a warm and humid climate with good monsoon precipitation. The forest expanded into a dense mixed tropical deciduous forest since ca. 8500 cal yr BP to the present, under warm and relatively more humid climatic conditions with further increase in monsoon precipitation. This warm climatic phase represents the Holocene Climate Optimum (HCO) or Holocene Thermal Maximum (HTM). Prior to the initiation of the long warm period, an open vegetation occurred in the region between ca.14,100 and 11,700 cal yr BP, under a cool and dry climate, probably indicating reduced monsoon precipitation, and partially matching with the Older Dryas stadial. The present study provides insights into the vegetation dynamics and associated climatic changes in response to the Indian Summer Monsoon (ISM) variability over the last ~14.1 ka from a poorly understood area of the tropics in South Asia, where rainfall is essentially controlled by the ISM. In addition, an account of the asynchronous warming during the Holocene from the central Indian CMZ, as well as other tropical regions of the Indian sub-continent, has been presented here. Global contextualization of the Holocene warming has also been summarized in this communication.

RAINFALL IMPLICATIONS FOR FOOD PRODUCTION IN INDIA: WHEN AND WHERE

Abstract. Early outlook on food production is important for policy making and can be formed on the basis of the recorded rainfall. Simplistically, a good monsoon produces a bumper harvest and scanty rainfall causes crop failure. Econometric modelling of past data shows that the reality is much more complex. Food production in a state is sensitive to rainfall in the state as well as other states depending on geography. Rainfall distribution in the growing season and pre-sowing months can matter significantly. Moreover, the rainfall effect can be favorable as well as adverse. In the sample period, sowing and growing season rainfall in the state had little favorable effect on area and yield in Punjab and its effect on Rice yield was even harmful in Punjab and West Bengal. Rainfall in Uttar Pradesh and Madhya Pradesh however had beneficial effects on the respective state’s and on each’s other production. Rainfall in the Himalayas is a powerful impact on food production resulting from river dynamics and water management but the dominance of adverse effect over beneficial ones is a sign of poorly managed upstream downstream linkages. Because production is sensitive also to economic variables, the government, which can modulate subsidies and support prices, also has control over food production. Improving efficiency of water distribution with an integrated geographical perspective can also be a potent public instrument for production planning.

SENTINEL-1&2 FOR NEAR REAL TIME CROPPING PATTERN MONITORING IN DROUGHT PRONE AREAS. APPLICATION TO IRRIGATION WATER NEEDS IN TELANGANA, SOUTH-INDIA

Abstract. Indian agriculture relies on monsoon rainfall and irrigation from surface and groundwater. The inter-annual variability of monsoon rainfalls is high, which forces South Indian farmers to adapt their irrigated area extents to local water availability. We are developing and testing an automatic methodology for monitoring spatio-temporal variations of irrigated crops in near real time based on Sentinel-1 and -2 data feed over the Telangana State, South India. These freely available radar and optical data are systematically acquired worldwide, over India since 2016, on a weekly basis. Their high spatial resolution (10–20 m) are well adapted to the small size field crops that is common in India. We have focused first on drought prone areas, North of Hyderabad. Crop fraction remains low and varies widely (from 10 to 60%, ISRO-NRSC, Bhuvan). Those upstream areas, mainly irrigated with groundwater, are composed by less than 20% of irrigated areas during the dry season (Rabi, December to March) and up to 60% of the surface is used for crop production during the Kharif (June to November), which includes rainfed cotton and drip irrigated maize crops and inundated rice. A machine learning algorithm, the Random Forest (RF) method, was automatically used over 6 growing seasons (January to March and July to November, from 2016 to 2018) from the Sentinel-1&2 data stacked for each season, to create crop mapping at 10 m resolution over a study area located in the north of Hyderabad (210 by 110 km). Six seasonal land cover field surveys were used to train and validate the classifier, with a specific effort on rice and maize field sampling. The lowest irrigated area extents were found for driest conditions in Rabi 2016 and Kharif 2016, accounting for 3.5 and 5% with moderate classification confusion. This confusion decreases with the increase of irrigated crops areas during Rabi 2017. For this season, 22% of rice and 9% of irrigated crops were detected after heavy rainfall events in September 2017, which have filled surface water tanks (3.4% of the surface area) and groundwater (Central Groundwater Board observations). From this abundance situation, the surface water detected for each season decreased regularly to less than 0.3% together with the rice and irrigated area extents respectively from 22 to 11% and 10 to 3%, despite a good monsoon 2017. Groundwater level show similar trends, with a drop from 20 meters depth in October 2016 and 2017 to more than 30 m in June 2018 (more recent available data). The deficit of the monsoon 2018 will certainly bring this situation to a hydrological drought at the beginning of 2019, probably similar to the Rabi 2016 situation. The estimated Irrigated Water Demand (IWD) varies from 51 to 310 mm/season, depending on water availability. This methodology shows the potential of automatically monitoring, in near real time, with standard computers, irrigated area extents presenting fast high resolution variability. As it is based on standard global satellite acquisitions, it is foreseen to be used for other regions, for any studies on farmer’s adaptation to climate and hydrological variability, as a proxy to estimate irrigation water needs and water resources availability. In Telangana for instance, it provides an inventory of crop production and irrigation practices before the implementation of mega project infrastructures funded by this new state: - the Kâkâtiya tank restoration program to enhance monsoon runoff capture or the Kaleshwaram project to divert Godavari river water toward upstream Telangana region through tunnels and canals in 20 giant reservoirs.

Effects of winter and summer-time irrigation over Gangetic Plain on the mean and intra-seasonal variability of Indian summer monsoon

The decreasing trend in rainfall in the last few decades over the Indo-Gangetic Plains of northern India as observed in ground-based observations puts increasing stress on groundwater because irrigation uses up to 70% of freshwater resources. In this work, we have analyzed the effects of extensive irrigation over the Gangetic Plains on the seasonal mean and intra-seasonal variability of the Indian summer monsoon, using a general circulation model and a very high-resolution soil moisture dataset created using extensive field observations in a state-of-the-art hydrological model. We find that the winter-time (November–March) irrigation has a positive feedback on the Indian summer monsoon through large scale circulation changes. These changes are analogous to a positive North Atlantic Oscillation (NAO) phase during winter months. The effects of the positive NAO phase persist from winter to spring through widespread changes in surface conditions over western and central Asia, which makes the pre-monsoon conditions suitable for a subsequent good monsoon over India. Winter-time irrigation also resulted in a reduction of low frequency intra-seasonal variability over the Indian region during the monsoon season. However, when irrigation is practiced throughout the year, a decrease in June–September precipitation over the Gangetic Plains, significant at 95% level, is noted as compared to the no-irrigation scenario. This decrease is attributed to the increase in local soil moisture due to irrigation, which results in a southward shift of the moisture convergence zone during the active phase of monsoon, decreasing its mean and intraseasonal variability. Interestingly, these changes show a remarkable similarity to the long-term trend in observed rainfall spatial pattern and low-frequency variability. Our results suggest that with a decline in the mean summer precipitation and stressed groundwater resources in the Gangetic Plains, the water crisis could exacerbate, with irrigation having a weakening effect on the regional monsoon.

Leveraging Policies for Self Sufficiency in Pulses in India

Although pulses are a major source of protein integral to the Indian diet, there has been a consistent demand–supply gap. Barring the last five years, total production of pulses remained stagnant at 12–14 million tonnes (mt) over the past five decades. Over the last 20 years, more than 550 improved varieties of different maturity periods and for different regions have been released by public research organisations, but the availability of quality seeds remained a serious concern, thereby resulting in yield uncertainty. The domestic supply fell short by 3–4 mt every year. Also, owing to increased consumption by the diet-conscious growing urban population in India, prices rose by 150 per cent to 200 per cent in recent years. The supportive trade policy has cooled down the pulses price during the deficit year, while encouraging price support policy and good monsoon helped in a big way to allocate 20 per cent more area to the crop, which resulted in record pulses production of 23 mt in 2016–2017. This article captures the influence of government policy on pulses production and suggests paradigm shift in strategy through short-, medium- and long-term plans to achieve self-sufficiency in pulses production and ensure nutritional security for population.

Possible teleconnections between East and South Asian summer monsoon precipitation in projected future climate change

The present paper examined the teleconnections between two huge Asian summer monsoon components (South and East Asia) during three time slices in future: near-(2010–2039), mid-(2040–2069) and far-(2070–2100) futures under the RCP4.5 and RCP8.5 scenarios. For this purpose, a high-resolution atmospheric general circulation model is used and integrated at 40 km horizontal resolution. To get more insight into the relationships between the two Asian monsoon components, we have studied the spatial displaying correlation coefficients (CCs) pattern of precipitation over the entire Asian monsoon region with that of South Asia and three regions of East Asia (North China, Korea–Japan and Southern China) separately during the same three time slices. The possible factors responsible for these teleconnections are explored by using mean sea level pressure (MSLP) and wind fields at 850 hPa. The CC pattern of precipitation over South Asia shows an in-phase relationship with North China and an out-of-phase relationship with Korea–Japan, while precipitation variations over Korea–Japan and Southern China exhibit an out-of-phase relationship with South Asia. The CCs analysis between the two Asian blocks during different time slices shows the strongest CCs during the near and far future with the RCP8.5 scenario. The CC pattern of precipitation over Korea–Japan and Southern China with the wind (at 850 hPa) and MSLP fields indicate that the major parts of the moisture over Korea–Japan gets transported from the west Pacific along the western limb of NPSH, while the moisture over Southern China comes from the Bay of Bengal and South China Seas for good monsoon activity.

A Geospatial Technological Approach to Monitor Convection over Arabian Sea

In the land-atmosphere-ocean system, ocean acts as the heat reservoirs, thereby playing a role in weather and climate variability. Sea surface temperature variation across the ocean triggers heat exchange, initiating the deep convection resulting in the vertical movement of air parcels, leading to the formation of rain-bearing cloud systems. The local effect is seen in convection and resultant precipitation along coastal lines. In this study, an attempt is made to map the Sea Surface Temperature (SST), monitor the convection over Arabian Sea, analyse the SST variability over the latitude ranges of 0o N to 30oN and longitude ranges of 60oE to 95oE, so as to understand the relationship between the rainfall anomalies in the coastal Karnataka and the SST variability and convection in the Arabian Sea. The study showed that in the context of Karnataka state, during a good monsoon year (2013), the maximum convection zone (MCZ) was found to be hovering around 15 to 28 degrees north of the equator whereas, during a bad monsoon year (2016), the MCZ was below 15o north of the equator. The study also revealed that the maximum convection occurs in the Arabian Sea when the SST is above 27.5 degree Celsius in the summer and 28.5 degrees Celsius in winter months. The study reconfirms that the monsoon rainfall variability between a good and bad monsoon is dependent largely on the northward migration of the convection zone (i.e., the strength of the Hadley circulation).

Research Contribution for Rice Productivity Growth in Gujarat: As Reflected by TFP and RRI

The TFP growth of rice and its sources in Gujarat state from 1990–91 to 2011-12has been analyzed. The Tornqvist Theil Index has been used to calculate the total output, total input, and total factor productivity indices. Compound growth rates were worked out using semi-log trend equation. Two outputs and ten inputs have been used to construct output and input indices. The TFP growth of rice was stagnant (0.35percent) in 1990s, as both the input and output indices were increased at lower rates. But it moderately increased to around 1 percent per annum during the 2000s. With incorporation of technological change, rice output increased annually by 1.48 percent during 1990–91 to 2011–12. This has helped to keep the real cost of production near about stagnant from 2000s onwards, which was increased by 1.50 percent per annum in 1990s. The contribution of TFP to output growth for rice remained high about 92.16 percent during last two decades in Gujarat. This reveals that Gujarat has shown an outstanding performance of TFP growth in rice. This is credited to the release of popular varieties viz., GR-101 in 1984, GR-103 in 1990, GR-6 in 1991, Gurjari in 1997, Dandi and GR-7 in 2000, GR-8 in 2001, GR-12 in 2004, NAUR-1 in 2008, GAR-13 in 2009 and GAR-1 in 2010, in the state by the then GAU and SAUs, remarkably increased the productivity of paddy. The investment on paddy research generated annually 34.70 percent IRR found to be a high paying proposition in study period. The sources of productivity growth indicated that public investment in agricultural research, transfer of technology (extension), good monsoon and development of irrigation potential has constituted a significant source of TFP growth in rice.

Water–food–energy nexus with changing agricultural scenarios in India during recent decades

Abstract. Meeting the growing water and food demands in a densely populated country like India is a major challenge. It requires an extensive investigation into the changing patterns of the checks and balances behind the maintenance of food security at the expense of depleting groundwater, along with high energy consumption. Here we present a comprehensive set of analyses which assess the present status of the water–food–energy nexus in India, along with its changing pattern, in the last few decades. We find that with the growth of population and consequent increase in the food demands, the food production has also increased, and this has been made possible with the intensification of irrigation. However, during the recent decade (after 1996), the increase in food production has not been sufficient to meet its growing demands, precipitating a decline in the per-capita food availability. We also find a statistically significant declining trend of groundwater storage in India during the last decade, as derived from the Gravity Recovery and Climate Experiment (GRACE) satellite datasets. Regional studies reveal contrasting trends between northern and western–central India. North-western India and the middle Ganga basin show a decrease in the groundwater storage as opposed to an increasing storage over western–central India. Comparison with well data reveals that the highest consistency of GRACE-derived storage data with available well measurements is in the middle Ganga basin. After analysing the data for the last 2 decades, we further showcase that, after a drought, the groundwater storage drops but is unable to recover to its original condition even after good monsoon years. The groundwater storage reveals a very strong negative correlation with the electricity consumption for agricultural usage, which may also be considered as a proxy for groundwater pumped for irrigation in a region. The electricity usage for agricultural purposes has an increasing trend and, interestingly, it does not have any correlation with the monsoon rainfall as computed with the original or de-trended variables. This reveals an important finding that the irrigation has been intensified irrespective of rainfall. This also resulted in a decreasing correlation between the food production and monsoon rainfall, revealing the increasing dependency of agricultural activities on irrigation. We conclude that irrigation has now become essential for agriculture to meet the food demand; however, it should be judiciously regulated and controlled, based on the water availability from monsoon rainfall, specifically after the drought years, as it is essential to recover from the deficits suffered previously.

Effect of changing tropical easterly jet, low level jet and quasi‐biennial oscillation phases on Indian summer monsoon

AbstractUsing the National Center for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR) reanalysis wind and homogeneous Indian summer monsoon (ISM) rainfall data during June, July, August and September (JJAS) for the period of 1953–2012, a long‐term trend has been extracted in the tropical easterly jet (TEJ) and lower level jet (Somali jet/LLJ) along with the rainfall trend over Indian region using empirical mode decomposition (EMD) technique. The zonal wind speed at 100 hPa shows an increasing trend, while a decreasing trend is observed at 850 hPa. The quasi‐biennial oscillation (QBO) phases, i.e. west and east phase, show a clear difference in wind anomalies at 100 and 850 hPa. A good (bad) monsoon year during the west (east) phase is confirmed on the basis of wind anomalies, velocity potential and divergent wind.

Demand Elasticities for Pulses and Public Policy Options

The case illustrates the application of the concepts of demand elasticities of an agricultural product with high protein content - pulses. It considers the current situation where a good monsoon has raised hopes for a bumper crop of pulses in India. From a deficit of about 20% met by imports, the county now is looking at attaining self-sufficiency. Public Policy options such as exports, imports or allowing domestic price adjustments or changing the minimum support price (MSP) in this regard are also considered.

Why are the Indian monsoon transients short‐lived and less intensified during droughts vis‐à‐vis good monsoon years? An inspection through scale interactive energy exchanges in frequency domain

ABSTRACTThe interannual variability of Indian summer monsoon rainfall (ISMR) is largely dictated by the continental tropical convergence zone (CTCZ), characterized by the frequent cyclogenetic tendency associated with the transitory low pressure systems (LPS(s) or monsoon transients) such as lows, depressions, cyclonic storms etc. A good monsoon is characterized by more intense and sustainable transients having longer westward propagation in comparison with the LPS(s) during weak monsoon. Now the questions arise from the energetics aspects – how does the energy favour the CTCZ to be more cyclogenetic during the good monsoon years? From where the monsoon transients are gaining energy to intensify and to sustain for longer durations during good monsoons compared with those in weak monsoons? The non‐linear scale interactions may possibly be the dynamical reason for the intensification and maintenance of LPS(s), but, the quantification of non‐linear interactions among the seasonal mean, low frequency oscillations, and synoptic scales are not revealed so far in previous studies. First time, the scale interactive energy exchanges in frequency domain have been explored to unravel the causes of weak LPS(s) during droughts vis‐à‐vis good monsoon years. It may be inferred from this study that the seasonal mean may play a crucial role for the generation of low and high frequency oscillations through mean–wave interaction whereas the wave–wave interactions have a significant contribution in intensification as well as the maintenance of monsoon transients. The dominant transfer of kinetic energy from the low frequency oscillations to synoptic scale observed over the large region of CTCZ favours the synoptic systems to intensify, survive for longer duration over that region before dissipation causing CTCZ to be more cyclogenetic during the good monsoon period with respect to those in weak monsoons attributing to the rainfall variability over the Indian landmass in contrasting monsoon seasons.

Predictive Simulation of Seawater Intrusion in a Tropical Coastal Aquifer

AbstractThe solute transport in a tropical, coastal aquifer of southern India is numerically simulated considering the possible cases of aquifer recharge, freshwater draft, and seawater intrusion using numerical modeling software. The aquifer considered for the study is a shallow, unconfined aquifer with lateritic formations having good monsoon rains up to about 3,000 mm during June to September and the rest of the months almost dry. The model is calibrated for a two-year period and validated against the available dataset, which gave satisfactory results. The groundwater flow pattern during the calibration period shows that for the month of May a depleted water table and during the monsoon month of August a saturated water table was predicted. The sensitivity analysis of model parameters reveals that the hydraulic conductivity and recharge rate are the most sensitive parameters. Based on seasonal investigation, the seawater intrusion is found to be more sensitive to pumping and recharge rates compared to ...

Spatio-temporal variability of net ecosystem productivity over India and its relationship to climatic variables

The net ecosystem productivity (NEP) represents net carbon exchange between the terrestrial ecosystem and the atmosphere that plays a crucial role on the control of the atmospheric CO2 in different time scales. The present study examined the spatial and temporal variability of NEP over India during 1981–2006 in relation to the climatic variables using the Carnegie–Ames–Stanford Approach (CASA) terrestrial ecosystem model and regional databases on the land surface-vegetation characteristics and the climatic parameters. At national scale the NEP exhibits semi-annual cycle with primary positive values up to 80 TgC month−1 during August–December, secondary positive values up to 15 TgC month−1 during January–March and negative values up to −70 TgC month−1 during April–July. The estimated long-term NEP budget for the country is 10 TgC year−1. It had undergone substantial inter-annual change in response to the climate variability. In the early 1980s, the Indian terrestrial biosphere remained a source and later became a sink of carbon during four pentad periods. The NEP budgets are positive for all the extreme years with severe flood and drought conditions except 1982. The normal years have either positive or negative NEP budgets. The precipitation-induced reduction of the net primary production (NPP) dominates the NEP variability in dry years, whereas in good monsoon years the precipitation-induced enhancement of the soil respiration (Rh) dominates the NEP variability.

Spatial Coherence of winds and waves over the Arabian Sea and Bay of Bengal and their evolution during SW Monsoon: a novel application of along-track Radar Altimeter measurements from Space

Abstract. We have examined, for the first time, the spatial coherence of oceanic parameters, namely, the ocean surface wind and significant wave height (SWH), using near-instantaneous along-track sampling over vast oceanic tracks provided by Poseidon-2 Radar Altimeter onboard Jason-1. The spatial coherence length scales over the Arabian Sea and the Bay of Bengal regions, derived using Auto correlation analysis, display interesting characteristics in relation to onset and evolution of SW Monsoon over India. The estimated spatial coherence scales are found to be of the order of 100–500 km. Generally, SWH coherence lengths over Arabian Sea are observed to increase from June to July during good monsoon year (2012). This trend is not followed for the poor monsoon year (2002). Similar trend is observed for spatial coherence scales for wind speed. The temporal evolution of analyzed spatial coherence scales of winds and waves over Arabian Sea clearly brings out the distinction between a "good" (2012) and a "poor" (2002) monsoon year. The spatial coherence lengths of these parameters over the Bay of Bengal are found to be shorter and do not show any systematic relation to onset and evolution of SW monsoon. Anisotropy in coherence lengths is also analyzed by treating ascending and descending tracks separately. Generally, the descending tracks measurements show higher spatial coherence lengths than the ascending ones. Like the spatial coherence scales, the anisotropy of the coherence scales over the Arabian Sea also mimics the behaviour of the strength of SW Monsoon.

Examining pathways for modulation of Indian Summer Monsoon Rainfall by extratropical tropospheric temperature pattern

ABSTRACTIn this article, role of extratropical circulation features in modulating Indian Summer Monsoon Rainfall (ISMR) is examined. Principal component (PC) analysis of extratropical tropospheric temperature data of the monsoon season for 1951–1980 and 1981–2010 years was performed separately. Analysis revealed that a PC (PC 3) of the first period and two PCs (PC 2 and PC 6) of the second period had significant correlation with the ISMR. Composite geopotential height anomaly of middle and upper troposphere, for the dates when extratropical tropospheric temperature anomaly pattern was similar to that of Eigen Vector of the PC 3 of the first period and PC 6 of the second period, highlighted presence of standing waves in the extratropics. These waves had trough over northwestern/northern parts of the Indian subcontinent and adjoining extratropics and ridge eastwards. Such circulation anomaly pattern of the extratropics apparently reduced the north‐south tropospheric temperature gradient required for good monsoon flow. This led to weak monsoon currents, resulting subdued ISMR activity during the period. This pathway of interaction of the extratropical circulation anomalies and the ISMR was reported by earlier studies also. Composite geopotential height anomaly of the middle and upper troposphere, for the dates when extratropical tropospheric temperature anomaly pattern was similar to that of Eigen Vector of the PC 2 (explaining larger variance of the temperature data) of the second period also depicted presence of standing waves. These waves were of relatively large amplitude and wavelength and were located at more northern latitudes. The configurations had warm high/ridge with centre over higher latitudes to the north of India and cold low/trough eastwards. Further analysis highlighted a new pathway of modulation of the ISMR by the extratropical circulation anomalies with above features.

Space–Time Scales of Northward Propagation of Convection during Boreal Summer

Abstract This study uses precipitation estimates from the Tropical Rainfall Measuring Mission to quantify the spatial and temporal scales of northward propagation of convection over the Indian monsoon region during boreal summer. Propagating modes of convective systems in the intraseasonal time scales such as the Madden–Julian oscillation can interact with the intertropical convergence zone and bring active and break spells of the Indian summer monsoon. Wavelet analysis was used to quantify the spatial extent (scale) and center of these propagating convective bands, as well as the time period associated with different spatial scales. Results presented here suggest that during a good monsoon year the spatial scale of this oscillation is about 30° centered around 10°N. During weak monsoon years, the scale of propagation decreases and the center shifts farther south closer to the equator. A strong linear relationship is obtained between the center/scale of convective wave bands and intensity of monsoon precipitation over Indian land on the interannual time scale. Moreover, the spatial scale and its center during the break monsoon were found to be similar to an overall weak monsoon year. Based on this analysis, a new index is proposed to quantify the spatial scales associated with propagating convective bands. This automated wavelet-based technique developed here can be used to study meridional propagation of convection in a large volume of datasets from observations and model simulations. The information so obtained can be related to the interannual and intraseasonal variation of Indian monsoon precipitation.