by Krushna Chandra Gouda, Iranna Gogeri & Aruna Singanahalli Thippa Reddy
The COVID-19 pandemic has created a major threat to human beings and huge losses over the globe. In order to control the pandemic spread, almost all parts of the world imposed lockdown. The imposed lockdown drastically impacted on reduction in the atmospheric pollutions and also resulted in net decrease in aerosol optical depth (AOD) in the atmosphere. In this study, the reduction in the AOD during the COVID-19 lockdown over the Indian subcontinent is being assessed using the moderate resolution imaging spectroradiometer (MODIS) satellite data available in Giovanni version 4.34 developed by NASA. The long-term mean analysis is computed considering 20 years (i.e., 2000–2019) data on Terra platform with a temporal resolution of daily and monthly and spatial resolution of 1 degree. The dataset of AOD with a temporal resolution of monthly was used for investigation of AOD anomaly for March, April and May 2020, and the seasonal variation (March to May 2020) is also assessed. Similarly, the daily scale dataset was used to investigate the percentage change in AOD during pre-lockdown and lockdown period with respect to long-term mean. The key findings in the present study show that reduction in AOD level over Indian subcontinent is approximately 14.75% during the lockdown period with spatial variation in the magnitude from region to region. The level of AOD is greatly reduced in the northern part of India (~ 22.53%), whereas changes in the southern part of India are much less (~ -0.31%); this may be due to ongoing anthropogenic activities during the lockdown period in this region. Furthermore, a positive AOD anomaly was observed in the eastern and central regions of India (i.e., over the states of Odisha, Chhattisgarh, Telangana, Jharkhand, West Bengal, Part of Maharashtra and Karnataka). However, negative AOD anomaly was observed in the north and northwest regions of India, whereas not much change in the AOD anomaly in other parts of the country. The overall assessment of the AOD level shows a net decrease over the Indian subcontinent during the lockdown period, i.e., March to May 2020. This kind of assessment study will surely help the government for the sustainable policy decisions for atmospheric pollution control by implementing proper lockdown procedures over various parts of the country.
Source: https://doi.org/10.1007/s10661-022-09855-3
by Smrutishree Lenka, Rani Devi, Chennemkeril Mathew Joseph & Krushna Chandra Gouda
There are several important large-scale oceanic and atmospheric processes like El Niño-Southern Oscillation (ENSO), Madden–Julian Oscillation (MJO), and Indian Ocean Dipole (IOD) which have significant impact on global weather and climate system. This article reviews the mechanism and dynamics of ENSO, MJO, and IOD processes and their impact on global and regional weather and climate particularly the Indian summer monsoon rainfall. Generally, these processes are coupled ocean–atmosphere phenomenon and associated dynamics control the global weather and climate system. Sea surface temperature (SST) anomaly in the central and equatorial pacific region respectively results the warm (El Niño) and cold (La Niña) events and it has strong impacts globally. Similarly, MJO is a dominant phase of intra-seasonal variability in the tropical region and also has significant impacts on the global system like strong wind, convective waves, extreme rainfall, cyclones, and ENSO. The IOD is often termed as the counterpart of pacific El Niño and La Niña in Indian Ocean which mainly measures the SST gradient between Arabian Sea and the eastern Indian Ocean. IOD also linked to ENSO and the shifting warm/cool pool results in the summer monsoon rainfall variability in the India Ocean as well as continental Indian region. All these phenomena have direct impact on the Indian monsoon circulation system, so in this work, these impacts are quantified using the India Meteorological Department (IMD) observed rainfall data over Indian subcontinent as a case study. This work also provides the review of the studies using observation and modelling to understand the dynamics of all the three processes. This review and analysis work will help in understanding the process feedback on the regional rainfall distribution and there is a need of near-future modelling research on these processes and their impacts on weather and climate system and associated sectors.
Source: https://doi.org/10.1007/s00704-021-03896-3