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.

Evaluation of Version 3 Total and Tropospheric Ozone Columns From Earth Polychromatic Imaging Camera on Deep Space Climate Observatory for Studying Regional Scale Ozone Variations

Discrete wavelength radiance measurements from the Deep Space Climate Observatory (DSCOVR) Earth Polychromatic Imaging Camera (EPIC) allows derivation of global synoptic maps of total and tropospheric ozone columns every hour during Northern Hemisphere (NH) Summer or 2 hours during Northern Hemisphere winter. In this study, we present version 3 retrieval of Earth Polychromatic Imaging Camera ozone that covers the period from June 2015 to the present with improved geolocation, calibration, and algorithmic updates. The accuracy of total and tropospheric ozone measurements from EPIC have been evaluated using correlative satellite and ground-based total and tropospheric ozone measurements at time scales from daily averages to monthly means. The comparisons show good agreement with increased differences at high latitudes. The agreement improves if we only accept retrievals derived from the EPIC 317 nm triplet and limit solar zenith and satellite looking angles to 70°. With such filtering in place, the comparisons of EPIC total column ozone retrievals with correlative satellite and ground-based data show mean differences within ±5-7 Dobson Units (or 1.5–2.5%). The biases with other satellite instruments tend to be mostly negative in the Southern Hemisphere while there are no clear latitudinal patterns in ground-based comparisons. Evaluation of the EPIC ozone time series at different ground-based stations with the correlative ground-based and satellite instruments and ozonesondes demonstrated good consistency in capturing ozone variations at daily, weekly and monthly scales with a persistently high correlation (r2 &gt; 0.9) for total and tropospheric columns. We examined EPIC tropospheric ozone columns by comparing with ozonesondes at 12 stations and found that differences in tropospheric column ozone are within ±2.5 DU (or ∼±10%) after removing a constant 3 DU offset at all stations between EPIC and sondes. The analysis of the time series of zonally averaged EPIC tropospheric ozone revealed a statistically significant drop of ∼2–4 DU (∼5–10%) over the entire NH in spring and summer of 2020. This drop in tropospheric ozone is partially related to the unprecedented Arctic stratospheric ozone losses in winter-spring 2019/2020 and reductions in ozone precursor pollutants due to the COVID-19 pandemic.

Decreases in wintertime total column ozone over the Tibetan Plateau during 1979–2017

We use the ozone dataset from the Copernicus Climate Change Service (C3S) during 1979–2017 to investigate the long-term variations of the total column ozone (TCO) and the relative total ozone low (TOL) over the Tibetan Plateau (TP) during different seasons. Based on various regression models, the wintertime TCO over the TP decreases overall during 1979–2017 with ongoing decreases since 1997. We perform multivariate regression analysis to quantify the influence of dynamical and chemical processes responsible for the long-term TCO variability over the TP. We use both piecewise linear trend (PWLT) and equivalent effective stratospheric chlorine loading (EESC)-based regression models that include explanatory variables such as the 11-year solar cycle, quasi-biennial oscillation (QBO) at 30 hPa and 10 hPa and the geopotential height (GH) at 150 hPa. The 150 hPa GH is found to be a major dynamical contributor to the total ozone variability (8 %) over the TP in wintertime. We also find strong correlation between TCO in DJF and the following JJA, indicating that negative/positive anomalies in the wintertime build up persist into summer. We also use the TOMCAT/SLIMCAT 3-D chemical transport model to investigate the contributions of different factors to the ozone variations over the TP. Using identical regression model on simulated TCO time series, we obtain consistent results with C3S-based data. We perform two sensitivity experiments with repeating dynamics of 2004 and 2008 to further study the role that the GH at 150 hPa plays in the ozone variations over the TP. The GH differences between the two years show an obvious, negative centre near 150 hPa over the TP in DJF. Composite analysis show that GH fluctuations associated with Inter Tropical Convergence Zone, ENSO events or Walker circulation play a key role in controlling TCO variability in the lower stratosphere.

Quantifying the impact of synoptic circulations on ozone variations in North China from April–October 2013–2017

The ozone variation characteristics and the impact of synoptic and local meteorological factors in North China were analysed quantitively during the warm season from 2013 to 2017 based on multi-city, in-situ ozone and meteorological data, as well as meteorological reanalysis. The domain-averaged maximum daily 8-h running average O3 (MDA8 O3) concentration was 122 ± 11 μg m−3 with an increase rate of 7.88 μg m−3 year−1, and the three most highly-polluted months were June (149 μg m−3), May (138 μg m−3) and July (132 μg m−3), which was closely related to synoptic circulation variations. Twenty-six synoptic circulation types (merged into 5 weather categories) were objectively identified using the Lamb-Jenkinson method. The highly-polluted weather categories included S-W-N directions, LP (low-pressure related circulation patterns) and C (cyclone type), and corresponding domain-averaged MDA8 O3 concentration were 122, 126 and 128 μg m−3, respectively. Based on the frequency and intensity changes of synoptic circulations, 39.2 % of the inter-annual domain-averaged O3 increase from 2013 to 2017 was attributed to synoptic changes, and intensity of synoptic circulations was the dominant factor. Using synoptic classification and local meteorological factors, the segmented synoptic-regression approach was established to evaluate and forecast daily ozone variations on an urban scale. The results showed that this method is practicable in most cities, and that the dominant factors are the maximum temperature, southerly winds, relative humidity in the previous and in the same day, and total cloud cover. Overall, 43–64 % of the day-to-day variability of MDA8 O3 concentrations was due to local meteorological variations in most cities over North China, except for QHD~32 % and ZZ~25 %. Our quantitative exploration on synoptic and local meteorological factors influencing both on inter-annual and day-to-day ozone variations will provide the scientific basis for evaluating emission reduction measures, since the national and local governments have implemented a series of measures to mitigate air pollution in North China in these five years.