The present study aims to understand the influence of the Madden–Julian oscillation (MJO) on the seasonal and diurnal characteristics (amplitude and phase) of rainfall over the Indian subcontinent (lat. 10°S–38°N, long. 60°–100°E). The study is conducted for the period 1998–2015 and for each Indian season. To accomplish this, the Tropical Rainfall Measuring Mission (TRMM) data set (3B42, version 7) is examined using indices quantifying rainfall frequency percentage and rainfall octet contribution, respectively. The real‐time multivariate (RMM) index developed by Wheeler and Hendon (2004) is used to partition the MJO into active, weak and suppressed phases. The results show that during active and weak phases (suppressed), positive (negative) rainfall anomalies are observed and the frequency of rainfall events is enhanced (lessened) over the most of the geometrically distinct regions. This finding is common to all seasons but is most prominent for weak phases (restricted to RMM phases 2–5) of the MJO during the monsoon season. Results suggest that the eastward propagation of the MJO over the Indian Ocean modulates rainfall across the India and neighbouring seas and countries – irrespective of the RMM index amplitude. Most works previously published focuses on the diurnal rainfall characteristics of the Indian summer monsoon (JJAS). The present study extends current understanding by investigating diurnal variation in rainfall related to the mean, active, weak and suppressed phases of MJO for each Indian season. Possible drivers of the diurnal cycle of rainfall over the oceans and continental regions were explored using recently reported observational and modelling studies. Our findings help understand rainfall processes for the Indian subcontinent and have practical application for numerical weather prediction, flood forecasting and water resource management regionally.
This study aims to quantify the interannual variations of groundwater storage changes (GWSCs) over India. GWSCs are derived from the gravity recovery and climate experiment (GRACE) and global land data assimilation system (GLDAS)-Noah life safety model (LSM) for the period 2003-2015. Estimated GWSCs are validated with the satellite altimetry over the six lake stations. The variability of GWSC and altimetry water-level heights are assessed with the cross-correlation and plotting analysis. Annual trends of GWSC and GRACE in terrestrial water storage (TWS) were estimated using the non-parametric Mann-Kendall test and Sen's slope method. Results suggest that GWSC and TWS have declined in northern India at the rate of ∼1.6 cm yr −1 and in southern and western central India at the rate of ∼0.5 cm yr −1. Impacts of short-term climate perturbations such as El Niño and La Niña for the GWSCs are assessed. During the El Niño period, the decline of GWSC over northern India enhanced, whereas during the La Niña period, the recovery of GWSC is evident. These interannual variations of GWSCs over India are attributed by interannual precipitation changes. Under the global warming scenario, the occurrences of El Niño events are likely to enhance in the future, and our findings help the water resource management policy makers for necessary actions during such short-term climate perturbations.
The relationship between extreme rainfall events (ERE) and the Madden-Julian Oscillation (MJO) over the Indian Subcontinent is intriguing. In this regard, the study investigates in detail the association between the ERE and the MJO. Daily Tropical Rainfall Measuring Mission (TRMM) data were used for the period 1998-2015. The real-time multivariate MJO index was applied to classify active and suppressed phases of the MJO. The percentile-based threshold indices, change in probability, logistic regression models and composite analysis were used to understand the statistical and atmospheric circulation features. The results suggest that the frequency and rainfall contribution of the ERE were found to be higher during the active phases of the MJO across the seasons over the geographically distinct regions. The profound influence of the MJO on the ERE was found during the post-monsoon over the southern Indian peninsula and Bay of Bengal regions. During the Indian Summer Monsoon (ISM), the prominent signals of the MJO are limited to the south of 20 N. The logistic regression and cumulative probability changes affirm the above results. The composite analysis of various diagnostic parameters reveals the background synoptic conditions during the post-monsoon and the propagation of the Rossby convective lobe during the ISM might facilitate the occurrences of the ERE during the active phases of the MJO. The study highlights the space-time evolution of the ERE and the relative influence of the MJO across the seasons.Besides, its insights have practical implications for the understanding and prediction of sub-seasonal rainfall extremes over the Indian Subcontinent.
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