The Indian Institute of Tropical Meteorology (IITM) is a scientific institution based in Pune, Maharashtra, India for expanding research in the tropical Indian Ocean with special reference to monsoon meteorology, and air-sea interaction of South Asian climate.[clarification needed] It is an Autonomous Institute of the Ministry of Earth Sciences, Government of India.
The socioeconomic impact of climate change on low- and medium-income tropical monsoonal countries is disproportionately high even though their historical contributions to greenhouse gas emissions are the least. Here, we address the climate change impacts on a few aspects of the South Asian monsoon not adequately addressed in previous studies. The dual impact of the increasing trend in the frequency and intensity of daily rainfall extremes and a rapidly increasing trend in the frequency and intensity of daily humid heat-stress extremes in recent decades is one such aspect. The two types of extremes occurring in two different phases of monsoon intraseasonal oscillations contribute to accelerating the socioeconomic impacts in the region. India alone accounts for half of the global potential productivity loss due to increased extreme heat stress, with ominous implications for the economic growth of the country. One of two silver linings in the bleak outlook is a westward expansion of the Indian monsoon due to climate change. With the decreasing trend in mean rainfall over Northeast India stabilizing in the coming decades, while that over Northwest India continues to increase, the potential for food production and water resources in the country remains optimistic. The other silver lining is related to the predictability of the seasonal mean climate. We argue that a global El Niño–Southern Oscillation (ENSO) predictor is required to assess the true ENSO–monsoon relationship, and unravel that it remains robust with the Indian monsoon remaining highly predictable even in the face of climate change, especially at longer lead times.
The 2024 Asian–Australian monsoon (AAM) year, defined as April 2024 to March 2025, was notable. Based on available data, a prolonged rainy season was observed in most parts of the AAM region, except for the Meiyu Region, which corresponds to the area affected by the second stage of the East Asian summer monsoon. The rainy season also featured elevated near-surface air temperatures, a boreal summer rainfall surplus of approximately 20
This study investigates the effect of depth-dependent salinity and potential temperature (PT) anomalies on the timing of monsoon onset over the Kerala (MoK) coast, utilizing the Estimating the Circulation and Climate of the Ocean Version 4 (ECCO4) reanalysis dataset for March-May (MAM) during 1992–2017. The monsoon onset years have been divided into four pentads—too early (P1), early (P2), normal (P3) and late (P4) onset years based on India Meteorological Department (IMD) reports. Analysis reveals a dominance of positive salinity anomalies up to 0.90 PSU during P1 and P2 years across the northern Indian Ocean (IO), specifically, in the regions feeding the Kerala coast. These conditions are consistent with elevated evaporation levels coinciding with intense southwesterlies and enhanced west-east moisture convergence over the Arabian Sea (AS). However, localized contrasting patterns appear over upper levels along the western/eastern coasts of India. Conversely, the P4 years appear to show negative salinity anomalies (-0.2 to -0.4 PSU), significant surface cooling of approximately − 0.75 °C, and weaker southwesterlies, particularly over the AS. Surface salinity anomalies exhibit a reversal over AS and adjoining regions across the onset pentads (from P1 to P4). A strong inverse relationship between salinity and PT at mixed layer depth (MLD) over the equatorial IO highlights the role of stratification in modulating onset timing. Furthermore, subsurface warming ( 0.75 °C) during P1-P2 years, while cooling of around − 0.90 °C during P4 years in the Bay of Bengal (BoB) and eastern IO, is evident. The resulting stratification/thermal structure modifies vertical mixing, affecting atmospheric convection and moisture availability. Overall, the depth-dependent salinity anomalies influence near-surface ocean stability and ocean-atmospheric interactions, necessary for monsoon progression and MoK. These findings highlight the importance of thermal observations and subsurface salinity in enhancing monsoon onset diagnostics.
This study examines the trends and variability of total column ozone (TCO) and explores its relationship with key atmospheric parameters. Extratropical regions show higher TCO concentrations in January compared to July, while tropical regions exhibit the opposite seasonal behaviour. Areas with relatively high mean TCO display declining trends, whereas regions with lower TCO levels show increasing trends. Meteorological Parameters during TCO surplus and deficit years over the equatorial Pacific show a pronounced asymmetry between January and July. In January, specific humidity is generally high across most regions during deficit TCO years. Surplus TCO in January is associated with downdrafts over the equatorial Pacific and updrafts over the equatorial Indian Ocean, with a contrasting pattern observed in July. Moreover, surplus TCO over the tropical Pacific is linked to strong vertical wind shear. Results show that ozone surplus years are associated with positive OLR anomalies, reduced cloudiness, suppressed deep convection, lower humidity, enhanced atmospheric stability, anomalous subsidence, and stronger zonal wind shear, conditions that favour ozone accumulation through limited convective dilution and enhanced dynamical transport. In contrast, ozone deficit years are characterized by negative OLR anomalies, increased moisture, active convection, upward motion, and reduced stability, promoting ozone loss via chemical depletion and vertical redistribution. Seasonal analysis reveals that these relationships are strongest during boreal winter and weaker during boreal summer.
The Indian Summer Monsoon (ISM) is a large-scale circulation pattern that influences worldwide weather and climate. The interannual variation of the ISM rainfall (ISMR) has a direct effect on millions of people living in the Indian subcontinent. The teleconnections of this variation have changed significantly since the major climatic shift in the late 1970s. The second dominant mode of the interannual variability for the recent four and a half decades after the late-seventies of ISMR shows an intriguing north–south dipole pattern, with in-phase loading centred over east India (including the central and eastern Gangetic Plains) and out-of-phase loading centred over south-east peninsular India. This variability arises from the complex interactions among the anomalous cooling of the sea surface temperature over the Indo-Pacific warm-pool (IPWP) and the gradient of surface air temperature between Iran and the Arabian landmass. The gradient of heating of the (Iran minus Arab) surface air temperature is compatible with an area of dipole surface pressure with low-pressure at Iran and high-pressure at Arab. This lower-level dipole pressure is accompanied by the northwesterlies over Saudi Arabia, converging and pulling the climatological background cross-equatorial monsoonal flow northward, further downstream curving cyclonically towards eastern India, supplying moisture towards the Gangetic Plains, producing flooding. Moreover, the cooling of the warm-pool region corresponds to an anomalous widespread surface high-pressure, also pushing the cross-equatorial monsoonal flow northward. Contrarily, as the monsoonal flow is shifted northwards in either of the cases, it is supplying less moisture towards the southern peninsular India, resulting in depressed rainfall. Thus, the surface temperatures of the Middle-East and IPWP are playing a decisive role in setting up the dipole rainfall pattern between the east and south peninsular India. This teleconnection could further be examined in the climate forecast models.
