Recent changes observed in column ozone concentrations over India

Ozone observations taken during the past 23-39 years by Dobson Spectrophotometers at Delhi, Varanasi, Pune and Kodikanal have been analysed to examine its long-term trend over Indian stations. An increasing trend of this species over the years has been noticed at all the places, except at Varanasi, where a decreasing trend has been found. The cause of these trends could be attributed, partly, to the trends of ozone in the troposphere. The results also indicate that there are certain recent changes in ozone levels at the Indian stations. These changes are less apparent in long-term trend analysis of total ozone data as the increase in tropospheric ozone has a compensating effect to the decrease in ozone at stratospheric levels.

Rate of change of total column ozone and monsoon rainfall - A co-variation with the variable component of 10.7 cm solar flux during pre-monsoon period

A critical analysis is done on the variation of the rate of change of Total Column Ozone (TCO) over Dum Dum (22° 38 N, 88° 26 E) and Total Monsoon Rainfall over Gangetic West Bengal with the variable component of 10.7 cm solar flux during different seasons for the period 1997- 2005. An anti-correlation is observed between the variable component with the rate of change of TCO during the pre-monsoon and monsoon period and significant positive correlations during the post-monsoon and winter seasons. Quite insignificant positive correlations are observed between the variable component and Total Monsoon Rainfall during different seasons for this period. A co-variation is observed with the increase in the variable component of 10.7 cm solar flux throughout the period of study only during the pre-monsoon season. Possible explanations are also presented.

Assessing the Influence of Inter Tropical Discontinuity on Total Column Ozone Variation Over West Africa

The focus of this study is to evaluate the influence of Intertropical Discontinuity (ITD) on the variation of Total column ozone (TCO). Relevant information is supplied on the temporal and spatial variability of TCO along the ITD zone, which is an important factor influencing the earth's atmosphere. Several studies over the years have established the relationship and influence several atmospheric processes have on TCO. However, the relationship between Intertropical discontinuity and TCO over West Africa has a gap. This study tends to examine the influence ITD has on TCO variation using the West Africa region as a case study. The study used Wind, ozone and dewpoint temperature data for the period between 1980-2019. To assess the variability and trend over the study region, several statistical methods were used, including Pearson correlation, Mann-Kendall, and linear regression model. The Mann-Kendall test shows an increasing trend throughout the months over the study region. Spatial analysis also revealed that regions North of the ITD has a higher concentration of TCO that the southern region of the ITD. however, ITD influence was more visible during the wet month of June to August (JJA) as the highest concentration of TCO was observed during this period across all latitude but more deviation was observed between latitude 100N to 180N, while the least occurrence is observed when ITD is at its minimum position in the month of December to February (DJF). The ACRV shows that 140N exhibit the highest variation with a value of 4.84, while the deviation is also at its highest with value of 13.65. The monthly position of ITD for Forty years was also analysed to observe the monthly deviation along the ITD region forty years and the spatial distribution of TCO was analysed from January to December. It’s of note that during the cause of this study, ozone hole which is designated by concentration less than or equal to 220DU was not recorded. The highest and the lowest value of TCO is 295DU and 227DU respectively with an average range of 68DU.

Stratospheric Ozone Response to Sulfate Aerosol and Solar Dimming Climate Interventions based on the G6 Geoengineering Model Intercomparison Project (GeoMIP) Simulations

This study assesses the impacts of sulfate aerosol intervention (SAI) and solar dimming on stratospheric ozone based on the G6 Geoengineering Model Intercomparison Project (GeoMIP) experiments, called G6sulfur and G6solar. For G6sulfur the stratospheric sulfate aerosol burden is increased to reflect some of the incoming solar radiation back into space in order to cool the surface climate, while for G6solar the global solar constant is reduced to achieve the same goal. The high emissions scenario SSP5-8.5 is used as the baseline experiment and surface temperature from the medium emission scenario SSP2-4.5 is the target. Based on three out of six Earth System Models (ESMs) that include interactive stratospheric chemistry, we find significant differences in the ozone distribution between G6solar and G6sulfur experiments compared to SSP5-8.5 and SSP2-4.5, which differ by both region and season. Both SAI and solar dimming methods reduce incoming solar insolation and result in tropospheric temperatures comparable to SSP2-4.5 conditions. G6sulfur increases the concentration of absorbing sulfate aerosols in the stratosphere, which increases lower tropical stratospheric temperatures by between 5 to 13 K for six different ESMs, leading to changes in stratospheric transport. The increase of the aerosol burden also increases aerosol surface area density, which is important for heterogeneous chemical reactions. The resulting changes in ozone include a significant reduction of total column ozone (TCO) in the Southern Hemisphere polar region in October of 10 DU at the onset and up to 20 DU by the end of the century. The relatively small reduction in TCO for the multi-model mean in the first two decades results from variations in the required sulfur injections in the models and differences in the complexity of the chemistry schemes, with no significant ozone loss for 2 out of 3 models. The decrease in the second half of the 21st century counters increasing TCO between SSP2-4.5 and SSP5-8.5 due to the super-recovery resulting from increasing greenhouse gases. In contrast, in the Northern Hemisphere (NH) high latitudes, only a small initial decline in TCO is simulated, with little change in TCO by the end of the century compared to SSP5-8.5. All models consistently simulate an increase in TCO in the NH mid-latitudes up to 20 DU compared to SSP5-8.5, in addition to 20 DU increase resulting from increasing greenhouse gases between SSP2-4.5 and SSP5-8.5. G6solar counters zonal wind and tropical upwelling changes between SSP2-4.5 and SSP5-8.5 but does not change stratospheric temperatures. Solar dimming results in little change in TCO compared to SSP5-8.5 and does not counter the effects of the ozone super-recovery. Only in the tropics, G6solar results in an increase of TCO of up to 8 DU compared to SSP2-4.5, which may counter the projected reduction due to climate change in the high forcing future scenario. This work identifies differences in the response of SAI and solar dimming on ozone, which are at least partly due to differences and shortcomings in the complexity of aerosol microphysics, chemistry, and the description of ozone photolysis in the models. It also identifies that solar dimming, if viewed as an analog to SAI using a predominantly scattering aerosol, would, for the most part, not counter the potential harmful increase in TCO beyond historical values induced by increasing greenhouse gases.

Ozone variations pertaining to dry and wet monsoon seasons over Indian region

’kq"d vkSj vknzZ ekulwu o"kkZsa ds nkSjku Vh-lh-vks- forj.k dk v/;;u djus ds fy, Hkkjrh; {ks+= esa o"kZ 1982]1983]1987 ,oa 1988 ds dqy dkWye vkstksu ¼Vh-lh-vks-½ ds ekfld vkSlr dk mi;ksx fd;k x;k gS A bl ’kks/k&Ik= esa mDr o"kksZa ds Hkkjr ds 13 LVs’kuksa ds Vh-lh-vks- vkadM+ksa dk v/;;u fd;k x;k gSA ’kq"d vkSj vknzZ ekulwu o"kksZa ds nkSjku Vh-lh-vks- forj.k dh rqyuk ls ;g irk pyk gS fd Vh-lh-vks- ds eku vknZz o"kksZa dh rqyuk esa ’kq"d o"kksZa esa vf/kd ik, x, gSaA Vh-lh-vks- esa ifjorZu gksuk ’kq"d ,oa vknzZ o"kksZa ds nkSjku laoguh; xfrfof/k esa fHkUurk dks ekuk tk ldrk gSA ’kq"d ¼vknzZ½ o"kksZa ds nkSjku laogu esa deh ¼o`f)½ Vh-lh-vks- dh ek=k dks c<+krh ?kVkrh gSA ’kq"d ,oa vknzZ o"kksZa ds chp ds ekulwu ds eghuksa ds nkSjku Vh-lh-vks- ds egRo dh tk¡p djus ds fy, lkaf[;dh; Vh--VsLV dk iz;ksx fd;k x;k gSA ;g varj nene dks NksM+dj vU; lHkh LVs’kuksa ds fy, lkaf[;dh; n`f"V ls 5 izfr’kr rd egRoiw.kZ gSA ,slk dgk tk ldrk gS fd Hkkjr esa xzh"edkyhu ekulwu eghuksa ds nkSjku vks-,y-vkj- rFkk Vh-lh-vks- ds chp vPNs laca/k jgs gSa D;ksafd bl vof/k ds nkSjku laogu dkQh izcy jgk gS A Monthly mean total column ozone (TCO) over Indian region for the years 1982, 1983, 1987 and 1988 has been utilized to study the TCO distribution during dry and wet monsoon years. TCO data for 13 Indian stations for the above years have been considered in the study. Comparison of TCO distribution during dry and wet monsoon years suggested that TCO values are found higher during dry years than those in wet years. The changes in TCO may be attributed to difference in convective activity during dry and wet years. The suppressed (enhanced) convection during dry (wet) years may lead to increase (decrease) in TCO. The statistical t-test is applied to test the significance of TCO difference during monsoon months between dry and wet years. The difference is statistically significant at 5% level of confidence for all stations except Dumdum. It can be said that the relation between OLR and TCO holds good during Indian summer monsoon months, as convection is stronger during this period.

Climatological Study of Ozone over Saudi Arabia

In this work, analysis of the variability of total column ozone (TCO) over the Kingdom of Saudi Arabia (KSA) has been conducted during the 1979–2020 period based on the ECMWF-ERA5 dataset. It is found that the highest values of TCO appear in the spring and winter months especially over north KSA, while the lowest values of TCO occur in the autumn months. The highest values of the coefficient of variation (COV) for TCO occur in winter and spring as they gradually decrease southward, while the lowest COV values appear in summer and autumn. The Mann–Kendall test indicates that the positive trend values are dominant for the annual and seasonal TCO values over KSA, and they gradually increase southward. The study of long-term variability of annual TCO at KSA stations shows negative trend values are the dominant behavior during the 1979–2004 period, while positive trend values are the dominant behavior during the 2004–2020 period. The Mann–Whitney test assessed the abrupt change of the annual TCO time series at 28 stations in KSA and confirmed that there is an abrupt change towards increasing values around 2000, 2005, and 2014. The climatological monthly mean of the ozone mass mixing ratio (OMR) is studied at three stations representing the north, middle, and south of KSA. The highest values of OMR are found in the layer between 20 and 4 hPa with the maximum in summer and early autumn, while the lowest values are found below 100 hPa.

Total column ozone measurements by the Dobson spectrophotometer at Belsk (Poland) for the period 1963–2019: homogenization and adjustment to the Brewer spectrophotometer

The total column ozone (TCO3) measurements by the Dobson spectrophotometer (serial no. 84) have been carried out at Belsk station (51∘50′ N, 20∘47′ E), Poland, since 23 March 1963. In total, ∼115 000 intraday manual observations were made by 31 December 2019. These observations were performed for different combinations of double wavelength pairs in the ultraviolet range and observation types, i.e., direct sun (DS), zenith blue (ZB), and zenith cloudy (ZC) depending on weather conditions. The long-term stability of the instrument was supported by frequent (almost every 4 years) intercomparisons with the world standard spectrophotometer. Trend analyses, based on the monthly and yearly averaged TCO3, can be carried out without any additional corrections to the intraday values. To adjust these data to the Brewer spectrophotometer observations, which were also performed at Belsk, a procedure is proposed to account for less accurate Dobson observations under low solar elevation, presence of clouds, and the temperature dependence of ozone absorption. The adjusted time series shows that the Brewer–Dobson monthly averaged differences are in the range of about ±0.5 %. The intraday TCO3 database, divided into three periods (1963–1979, 1980–1999, and 2000–2019), is freely available at https://doi.org/10.1594/PANGAEA.919378 (Rajewska-Więch et al., 2020).