Abstract
The study of temporal and spatial distribution of ozone is very important for understanding the atmospheric chemistry and thereby its impact on environment, weather and climate. The intra-seasonal variability plays a major role in the inter-annual variability of weather parameters such as rainfall, temperature, pressure and atmospheric trace gas constituents such as atmospheric ozone. The strength of monsoon circulation and deep convection greatly modifies the atmospheric compositions and meteorological parameters such as rainfall amount, distributions of atmospheric trace gas concentrations and other weather parameters over the summer monsoon region. The daily total column ozone (TCO) measured over maritime station (Lakshadweep Island— 10°10'N & 73°30'E) and coastal station (Cochin—9°55'N and 76°16'E) using Microtop II Ozonometer were considered for the comparative study of seasonal and intra-seasonal variability for the year 2015. The annual average of total column ozone over Lakshadweep Islands and Cochin was 290 DU and 280 DU respectively for the year 2015. The greater concentrations in daily TCO measurements over Lakshadweep Islands for all seasons compared to Cochin lead to the speculations that, the surface ozone concentration is more because of pollution from the diesel burning emissions, since the whole Island’s population completely depends on diesel generator for the power supply. During winter season maritime station shows a decrease of ~30 DU in TCO over Lak-shadweep Island compared to coastal station Cochin (~18 DU) from the annual mean in the month of December. During pre-monsoon season TCO concentration is high over both locations. There is gradual increase of TCO concentration over Cochin from pre-monsoon to monsoon season and peak in the month of September, but decreasing TCO concentrations measured over Lakshadweep during July to August. In the analysis it was found that Intra-Seasonal Variability (ISV) in total column ozone over Lakshadweep Islands and Cochin during summer monsoon season was modulated by the monsoon dynamics and convection, thereby changes in the photochemistry of ozone production and distributions over the monsoon region. Two significant intra-seasonal oscillations (ISOs) such as Madden Julian Oscillation (MJO) and Quasi-Biweekly Oscillations (QBW) were identified in the TCO during monsoon season. The MJO shows higher periodicity (~54 days) over Lakshadweep Islands compared to the coastal station, Cochin (~48 days). Intra-seasonal variability of TCO over the maritime and coastal stations varies with geographic locations, marine boundary layer characteristics and also with seasons. The intra-seasonal variability or ISOs controls the interannual variability of TCO over a region. Hence deeper knowledge of ISOs in trace gases such as ozone helps us to understand more about the regional climate and air quality.
Highlights
Distribution and variability of ozone are vital to the atmospheric thermal structure as it can exert great influence on regional and global climate
The present analysis focused on the total column ozone variability during Indian summer Monsoon (ISM) season based on daily total column ozone measurements using Microtop II Ozonometer for the year 2015
The study reveals that total column ozone (TCO) undergoes seasonal and sub-seasonal variability (ISOs) with different time scales such as Madden Julian Oscillation (MJO) and quasi biweekly mode during the summer monsoon season
Summary
Distribution and variability of ozone are vital to the atmospheric thermal structure as it can exert great influence on regional and global climate. The region of the Earth’s atmosphere from ~10 to 50 kilometers above the surface, where the chemical compound ozone (~90%) plays a vital role in absorbing harmful ultraviolet radiations from the sun is called good ozone. During the past 20 years, concentrations of this important compound have been threatened by human-made gases released into the atmosphere, including those known as chlorofluorocarbons (CFCs). These chemical compounds as well as meteorological conditions in the stratosphere affect the concentration of stratospheric ozone. Ozone forms in the stratosphere when there is free oxygen in the atmosphere in the presence of ultraviolet radiations from the sun. It forms the same way it is renewed when extreme UV radiation breaks oxygen molecules into two oxygen atoms (atomic oxygen), and the oxygen atoms collide into oxygen molecules and form ozone
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