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![Location map of Kerala (8°–13°N, 75°–77.5°E) [Colour figure can be viewed at wileyonlinelibrary.com]](profile/A-V-Sreenath/publication/349123415/figure/fig1/AS:11431281245900523@1716258687873/Location-map-of-Kerala-8-13N-75-775E-Colour-figure-can-be-viewed-at.png)
Location map of Kerala (8°–13°N, 75°–77.5°E) [Colour figure can be viewed at wileyonlinelibrary.com]
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This study examined factors affecting wet and dry phases of monsoon rainfall over Kerala, using modern‐era retrospective analysis for research and applications (MERRA 2) data set. Based on circulation pattern, our study shows that the wet and dry phases of monsoon over Kerala are related to modulation of convective activity over the eastern equator...
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Citations
... A trend analysis of seasonal mean low-level winds for the period 1990-2020 indicates a shift in the wind patterns, particularly over the eastern Arabian Sea and regions of the equatorial Indian Ocean (IO) located to the south of peninsular India, i.e., southerly/southeasterly wind trends from the equatorial IO influencing the zonal wind intensity of the southern branch of LLJ reaching the Kerala region (Fig. 12b). This aligns well with the findings of Sreenath and Abhilash (2021), which highlight the significant role of the eastern equatorial Indian Ocean in regulating circulation and, consequently, rainfall over Kerala. A longitude-pressure cross section of the zonal wind trends (averaged over the latitude belt 8°N-12.5°N) ...
Earlier studies have shown a declining precipitation trend over the Indian state of Kerala during the southwest monsoon season since the early twentieth century. However, a notable change in trend is witnessed in this region during the 1990–2020 period relative to the previous decade. This study provides some insights using observations and ERA5 reanalysis. Seasonal rainfall amounts for the state of Kerala during the study period (1990–2020) show significant zonal variations, with rising trends over the midland (elevations 30–200 m asl) and highland (exceeding 400 m asl) regions and a falling trend over the lowland. In monthly data, near-compensating precipitation trends are noted from the first and second halves of the monsoon season (i.e., a negative precipitation trend during June and July, followed by a positive trend in August and September.). This pattern signals a slowing down of the overall declining trend in Kerala’s monsoon rainfall since the 1990s. Circulation trends appear to support this pattern, with June and July showing deficient moisture convergence over the Kerala region, while August and September exhibit enhanced moisture convergence. Additionally, increased moisture transport in August and September favors stronger ascent and deeper convective cloud development in the region. Observations also indicate a shift in Kerala’s rainfall patterns in recent decades relative to the 1960–1989 period. We investigated the climate change signals by decomposing precipitation changes into dynamic and thermodynamic contributions using a water vapor vertical advection budget framework. Our analysis demonstrates that the precipitation changes during 1990–2020 are predominantly driven by alterations in large-scale atmospheric circulation rather than by variations in moisture availability when compared with the earlier period. Contrary to earlier assessments in the scientific literature regarding highland rainfall in the Western Ghats, recent decades have shown greater rainfall variability and more frequent intense rain events in the highlands of Kerala. This also motivates the critical need for a larger observation network, particularly in mid- and highland regions of Kerala, to further understand the impact of complex mesoscale terrain on zonal variations in rainfall as the climate changes.
... For instance, west coast India has been experiencing decreased light/moderate rainfall days and increased heavy/very heavy rainfall days (Prathipati et al., 2019). The scientific evidence underscores the substantial role of offshore troughs (Viswanadhapalli et al., 2019), strong cross-equatorial flow over the Arabian Sea (Chaluvadi et al., 2021;Sreenath, 2021, Sreenath et al., 2022, and the low-pressure system over the Arabian Sea near Gujarat and Maharashtra coast for enhancing the precipitation amount along the west coast of India (Ray et al., 2019). ...
The inverse relationship between the warm phase of the El Niño Southern Oscillation (ENSO) and the Indian Summer Monsoon Rainfall (ISMR) is well established. Yet, some El Niño events that occur in the early months of the year (boreal spring) transform into a neutral phase before the start of summer, whereas others begin in the boreal summer and persist in a positive phase throughout the summer monsoon season. This study investigates distinct influences of exhausted spring El Niño (springtime) and emerging summer El Niño (summertime) on the regional variability of ISMR. The two ENSO categories were formulated based on the time of occurrence of positive SST anomalies over the Niño-3.4 region in the Pacific. The ISMR's dynamical and thermodynamical responses to such events were investigated using standard metrics such as the Walker and Hadley circulations, vertically integrated moisture flux convergence (VIMFC), wind shear and upper atmospheric circulation. The monsoon circulation features are remarkably different in response to the exhausted spring El Niño and emerging summer El Niño phases, which distinctly dictate regional rainfall variability. The dynamical and thermodynamical responses reveal that exhausted spring El Niño events favour excess monsoon rainfall over eastern peninsular India and deficit rainfall over the core monsoon regions of central India. In contrast, emerging summer El Niño events negatively impact the seasonal rainfall over the country, except for a few regions along the west coast and northeast India.
Large-scale transport of air mass modulates the weather by altering the cloud and precipitation microphysics of convective clouds. This study examines how oceanic and continental air mass advected into the convective cloud system determines hydrometeors' vertical distribution using in situ airborne observations from the Cloud-Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) during 2010. Maritime air mass from the Bay of Bengal favours a clean atmosphere (CA) that supports clouds with fewer droplets, and the effective radius crosses above 12 μm below the 10 °C temperature level. Thus CA is mainly characterised by moderate precipitation efficiency and broader hydrometeors size distribution spectra. The mixing of air mass from the Arabian sea, Bay of Bengal, and central Indian region results in a moderately polluted atmosphere (MPA), enhancing convective cloud depth and favours mixed-phase processes and equally strong updrafts and downdrafts. As the concentration of sea salt, dust particles, moisture content, and convective available potential energy (CAPE) increases, MPA profoundly supports the primary and secondary ice nucleation inside the convective system. Despite CA and MPA, wide hydrometeor size distribution is absent in a highly polluted atmosphere (HPA), primarily evolved from continental air mass. We noticed an absence of larger raindrops inside clouds developed in HPA, indicating reduced collisions, making them less efficient with the precipitation process. The raindrop size distribution under the three environmental conditions showed distinct characteristics, implying contrasting cloud microphysical processes and precipitation efficiency.
