SOLAR INFLUENCE ON METEOROLOGICAL PARAMETERS IN THE EARTH’S LOWER ATMOSPHERE

Abstract

In the present thesis, Sun and its activities on a seasonal and longer time scale (solar cycle with ~11 years’ time period) and its influence on meteorological parameters such as on temperature, wind, relative humidity and surface pressure for the Indian landmass and its isles have been extensively studied using data from several locations. Data used over locations, which are confined over India and its isles Lakshadweep (Arabian sea side) and Andaman and Nicobar (Bay of Bengal side). The study has been divided into three major areas, first being the study of solar insolation and its influence on particle pollution over Delhi, India. The motivation for this area lies in the fact that particle pollution (PM2.5) is rising at an alarming rate specially in the capital city, Delhi. We aimed at studying the probable reasons for rise in high pollution episodes in New Delhi, especially during winter and its dispersion with incoming solar radiation. This objective was successfully achieved in our study and we aim to dig deeper into the reasons obtained and the necessary actions that can be taken by us to reduce the high pollution episodes. The concentration of PM2.5 presented using a Compact and Useful PM2.5 Instrument (CUPI) from Nov 2018 to Oct 2019. A high-time resolution data (~2 min interval) was recorded at Dwarka (West Delhi), New Delhi, to investigate difference in the concentration of ambient particulate matter outdoor as well as indoor. Association between diurnal variation of solar irradiance and dispersion of PM2.5 is clearly seen, decrease in PM2.5 is well linked with rise in solar irradiance. Diurnal variation of solar radiation showed a consistent increase from 9 am to 2 pm, while relative humidity declined considerably from 10 am to 4 pm (local time); these two factors correspond to less concentration in both indoor and outdoor environments. However, there is no significant difference between outdoor and indoor concentration during summer and monsoon season. This has been described in chapter 3 of thesis. The second objective of our study was focussed on understanding the solar influence on meteorology for six stations in India viz. Delhi, Kolkata, Mumbai, Chennai, Kochi and Trivandrum during 1981-2021. For this, we made use of MERRA-2 data and tried to understand the role of solar sun spots on temperature, wind and surface pressure for these stations and presented the results in chapter 4. We were able to interpret the implications sun has on our troposphere, some being direct and some indirect. It turns out that the Sun does play a crucial role in atmospheric dynamics, however, it is not the sole force responsible in driving the dynamics of atmosphere. Decrease in wind speed with the sun spot numbers decline coincides suggesting a relationship, however, this is found more on latitude dependent confining around 10-150N. We expanded it further in the next chapter 5 which is performed during 1981-2021 using datasets from MERRA-2 over several stations. The third subject is the extension of the preliminary findings (second subject). While the second subject’s core analysis was directed towards understanding meteorological parameters such as wind speed decline, temperature rise etc. in major metro cities of India over a given period. However, the third subject majorly explores oceanic and land studies (Andaman and Nicobar Islands in Bay of Bengal, Lakshadweep Islands in Arabian Sea and Coastal Areas and small cities in land areas of different topography). This is mentioned in details in chapter 5. v It helped us to understand the role of atmospheric dynamics in the context of Indian region and a very striking feature gained our attention. It is the atmosphere-ocean dynamics which comes into play when our islands climatology is taken into consideration. This objective was successfully achieved using datasets and the outcomes which indeed helped us understand the role of Sun in the atmospheric dynamics for Indian region. We aim to advance our research in such a manner that it will be beneficial to the society to upgrade the living standards in which environment, environmental health and human health will remain of prime importance. The dynamics of energy emissions from the sun and its varying magnetic field makes it the fundamental energy source of Earth. The amount of energy that we receive from the Sun just outside the Earth’s atmosphere is defined as the total solar irradiance containing every possible solar wavelength. Past studies have shown that the sunspots correlate with the solar radiation, in fact, the concentrations of solar magnetic fields occurring at the photosphere are known as sunspots. These are identified by an umbra dark zone in the centre having a vertical field and surrounded by penumbra with a horizontal field. During the Small Ice Age period no sunspots were observed, in the wake of sunspots absence, there has been a suspicion that the solar cycle has an influence on Earth’s climate. Furthermore, sun is the main source of energy on Earth’s surface, thus it is liable to influence Earth even by a small fluctuation. Hence, we aimed to study the influence of solar cycle on meteorological parameters over the Indian region. Sun-climate connection has been the most debated topic, which is helping to upgrade the understanding on the natural variability of climate and its atmospheric components vis-a-vis anthropogenic factors. To elaborate this thought further, we investigated changes in temperature, wind, and relative humidity, and their association with El- Nino Southern Oscillation (ENSO) and sunspot numbers patterns etc. in the Indian region. ENSO and Sun spot numbers are two such natural variations, which have the significant influence over atmospheric and meteorological parameters, which is selective and more prominent in different latitudes and altitudes. Quasi-periodic fluctuations in temperature (which is linearly rising) closely relates with the ENSO parameter (correlation coefficient ‘r’ using 6 locations spread over Arabian sea and Andaman and Nicobar ranged from ~ 0.20 to 0.34; which is statistically significant and larger towards Andaman Islands). The value of ‘r’ increased considerably (> 0.5) during 2000-2021, confirming rapid increase in temperature along with ENSO linear rise with synchronized quasi-periodic fluctuations. Wind speed, in general, showed larger magnitude over Andaman and Nicobar Islands (~ 5.0 m/s yearly averaged) in comparison to Arabian sea (~ 4.0 m/s) and also over landmass (~ 2.2 m/s). Solar cycle (sun spot numbers) and wind speed reflects a weak positive correlation coefficient (< ~ 0.40) though it is statistically significant while no consequential correlation found between solar cycle and relative humidity. Detailed analysis suggests that relative humidity decreased over landmass as well islands during 2000-2021, temperature increased more rapidly between latitudes 7.03ºN and 12.91ºN post 2000 in comparison to other stations located above 15ºN. Increase in temperature in the lower latitudes (< 15ºN) seems thoroughly controlled by the ENSO signal. These findings are displaying a complex interplay between meteorological parameters and ocean-atmosphere interaction. Future course of action is also proposed and described in chapter 6, which can prove a significant improvement in our understanding and set a new narrative for the policy makers and scientific community.