Total Column Ozone Amount Research Articles

Machine Learning-Based Retrieval of Total Ozone Column Amount and Cloud Optical Depth from Irradiance Measurements

Machine Learning-Based Retrieval of Total Ozone Column Amount and Cloud Optical Depth from Irradiance Measurements

Total ozone trends at three northern high-latitude stations

Abstract. After the decrease of ozone-depleting substances (ODSs) as a consequence of the Montreal Protocol, it is still challenging to detect a recovery in the total column amount of ozone (total ozone) at northern high latitudes. To assess regional total ozone changes in the “ozone-recovery” period (2000–2020) at northern high latitudes, this study investigates trends from ground-based total ozone measurements at three stations in Norway (Oslo, Andøya, and Ny-Ålesund). For this purpose, we combine measurements from Brewer spectrophotometers, ground-based UV filter radiometers (GUVs), and a SAOZ (Système d'Analyse par Observation Zénithale) instrument. The Brewer measurements have been extended to work under cloudy conditions using the global irradiance (GI) technique, which is also presented in this study. We derive trends from the combined ground-based time series with the multiple linear regression model from the Long-term Ozone Trends and Uncertainties in the Stratosphere (LOTUS) project. We evaluate various predictors in the regression model and found that tropopause pressure and lower-stratospheric temperature contribute most to ozone variability at the three stations. We report significantly positive annual trends at Andøya (0.9±0.7 % per decade) and Ny-Ålesund (1.5±0.1 % per decade) and no significant annual trend at Oslo (0.1±0.5 % per decade) but significantly positive trends in autumn at all stations. Finally we found positive but insignificant trends of around 3 % per decade in March at all three stations, which may be an indication of Arctic springtime ozone recovery. Our results contribute to a better understanding of regional total ozone trends at northern high latitudes, which is essential to assess how Arctic ozone responds to changes in ODSs and to climate change.

Ozone Variation during the Development of a Tropical Cyclone: Case Study

The aim of this work was to study the variation in the total ozone column amount (TOC) during the life cycle of the tropical cyclone (TC) that occurred over the northwest Indian Ocean from 14 to 25 October 2008. This goal was achieved through examining the behavior of the tropical cyclone tilt under vertically varying background flows in association with the cyclone development. Thus, the vertical wind shear (VWS) was estimated as one of the most important dynamical parameters related to TC formation and intensity changes. Moreover, we estimated the variations in the daily values of TOC during the period of cyclone activity. We found that the magnitude of VWS increased during the growth period, and VWS weakened during the decay period. Anomalies of daily TOC were found to reduce steadily before and during the cyclone formation, followed by an increasing trend after the dissipation of cyclone. It was also found that during the development of the tropical cyclone, an outflow developed in the upper levels, having high velocities that extended beyond the tropopause up to the lower stratosphere. As a result, the lowest value of TOC during the tropical cyclone was due to a large amount of injected water vapor from the troposphere into the stratosphere through the convection processes. This was mostly photo-dissociated into OH and atomic O by deep solar radiation in the upper and lower stratosphere, leading to a severe reduction in stratospheric ozone.

The Remarkably Strong Arctic Stratospheric Polar Vortex of Winter 2020: Links to Record‐Breaking Arctic Oscillation and Ozone Loss

AbstractThe Northern Hemisphere (NH) polar winter stratosphere of 2019/2020 featured an exceptionally strong and cold stratospheric polar vortex. Wave activity from the troposphere during December–February was unusually low, which allowed the polar vortex to remain relatively undisturbed. Several transient wave pulses nonetheless served to help create a reflective configuration of the stratospheric circulation by disturbing the vortex in the upper stratosphere. Subsequently, multiple downward wave coupling events took place, which aided in dynamically cooling and strengthening the polar vortex. The persistent strength of the stratospheric polar vortex was accompanied by an unprecedentedly positive phase of the Arctic Oscillation in the troposphere during January–March, which was consistent with large portions of observed surface temperature and precipitation anomalies during the season. Similarly, conditions within the strong polar vortex were ripe for allowing substantial ozone loss: The undisturbed vortex was a strong transport barrier, and temperatures were low enough to form polar stratospheric clouds for over 4 months into late March. Total column ozone amounts in the NH polar cap decreased and were the lowest ever observed in the February–April period. The unique confluence of conditions and multiple broken records makes the 2019/2020 winter and early spring a particularly extreme example of two‐way coupling between the troposphere and stratosphere.

Validation of OMI-DOAS total ozone column amounts against ground-based measurements at an African equatorial belt site.

The total ozone column amount (TOCA) values from the Ozone Monitoring Instrument (OMI) derived from OMI/Aura ozone (O3) differential optical absorption spectroscopy (DOAS) V003 (OMDOAO3) have been validated against the ground-based TOCA values derived from Dobson and the Norwegian Institute for Air Research UV measurements in Kampala (0.31º N, 32.58º E, 1200 m), Uganda, for the period between 2005 and 2018. Under all-sky conditions, the OMI retrieval algorithm was found to underestimate the TOCA values with mean bias (MnB), root mean square error (RMSE), and correlation coefficient (r) values ranging from about -3.4% to -1.7%, 2.4% to 4.9%, and 0.73 to 0.90, respectively. When only days with a radiation modification factor greater than or equal to 65% were considered, the MnB, RMSE, and r values between TOCA values derived from ground-based and OMI measurements improved, and they ranged from -2.5% to -1.3%, 1.4% to 3.8%, and 0.8 to 0.91, respectively. A good agreement was found between TOCA values derived from Dobson measurements and those derived from OMI satellite measurements with MnB, RMSE, and r values of about -1.8%, 1.4%, and 0.91, respectively. This was due to the fact that Dobson measurements were taken only when the sky was perceived clear. The underestimation of TOCA values by the OMI retrieval algorithm was found to be due mainly to clouds and aerosols.

Ground-based measurements of total ozone column amount with a multichannel moderate-bandwidth filter instrument at the Troll research station, Antarctica.

Combining information from several channels of the Norwegian Institute for Air Research (NILU-UV) irradiance meter, one may determine the total ozone column (TOC) amount. A NILU-UV instrument has been deployed and operated on two locations at Troll research station in Jutulsessen, Queen Maud Land, Antarctica, for several years. The method used to determine the TOC amount is presented, and the derived TOC values are compared with those obtained from the Ozone Monitoring Instrument (OMI) located on NASA's AURA satellite. The findings show that the NILU-UV TOC amounts correlate well with the results of the OMI and that the NILU-UV instruments are suitable for monitoring the long-term change and development of the ozone hole. Because of the large footprint of OMI, NILU-UV is a more suitable instrument for local measurements.

Broadband dependence of atmospheric transmissions in the UV and total solar radiation

Atmospheric broadband transmissions of clouds, aerosols, and ozone in the erythemally weighted ultraviolet (EUV, 290–320 nm), total (spectrally integrated) ultraviolet (TUV, 290–363 nm), and total global solar (GS, 305–2800 nm) spectral regions were analysed with ground-based measurements in Seoul, Korea (37.57°N, 128.98°E) from March 2004 to February 2013. The annual average total transmission expressed as a fraction of the clear-sky irradiance was 77.6% in the EUV, 73.6% in the TUV, and 72.0% in the GS spectral regions. The corresponding values for cloud transmission were 78.4%, 73.9%, and 71.7%. In overcast cloudy conditions, atmospheric transmission was reduced by 45.9%, 50.2%, and 56.6% in the three spectral regions, respectively, indicating the dominant effect of clouds. Aerosol and ozone transmissions had almost the same annual average. Annual average atmospheric transmission effectively decreases with increasing wavelength from EUV to GS regions. However, we found that there was a difference in wavelength dependence of atmospheric transmission for monthly averages, which seems related to the monthly variation of total column ozone (TCO), aerosol, and cloud amount. It is also found that there is a critical value of TCO (TCO =370 DU) for the wavelength dependence of transmission. Higher ozone amount than this turnaround value can cause an increase in transmission from the EUV to GS regions. The monthly wavelength-dependent effects may be attributable more to the different climatological characteristics of the TCO rather than aerosols and clouds.

Revisiting ozone measurements as an indicator of tropical width

The total column ozone (TCO) amount varies with latitude, in part due to the difference in tropopause height between the tropics and midlatitudes. This dependency of TCO on latitude has been used to identify the latitudes of the tropical edges and to compute their variations in time. The previously reported poleward movement of the tropical edge latitudes computed from satellite TCO measurements over the past several decades is greater than 3° latitude per decade. This tropical widening rate is significantly larger than a number of independent estimates and if correct suggests a major deficiency in the representation of tropical widening in models. We revisit the previously used TCO tropical edge latitude diagnostic to extend it forward in time with a new data set and to assess its robustness through comparisons with independent tropical edge diagnostics. We find that the previous TCO-based tropical width timeseries contain a spurious jump, likely due to data inhomogeneities. After removal of this jump using an objective statistical breakpoint identification technique, TCO-based tropical widening is reduced to the point that it is not significantly different than other tropical widening estimates. The strong sensitivity of the TCO method to algorithmic choices, its out-of-phase seasonality in the Northern Hemisphere, and its lack of correlation with well-established tropical width metrics on interannual timescales support our conclusion that the TCO-based tropical width diagnostic as previously implemented is not a robust measure of tropical width.

Extensive validation of solar spectral irradiance meters at the World Radiation Center

A comprehensive uncertainty analysis validates a Solar Spectral Irradiance Meter (SolarSIM) for accurately resolving the spectral and broadband direct normal irradiances (DNI), spectral aerosol optical depth (AOD), precipitable water vapour and atmospheric total column ozone amounts. The derivation of these parameters from four SolarSIMs were compared to reference instrumentation at the Physikalisch-Meteorologisches Observatorium Davos and World Radiation Center (PMOD/WRC) in Davos, Switzerland in September 2015. The SolarSIMs are the first instruments to ever simultaneously participate in the 12th WMO International Pyrheliometer Comparison, Fourth Filter Radiometer Comparison, and First Spectroradiometer Comparison. The SolarSIMs’ DNI data were compared to the World Standard Group’s PMO2 absolute cavity radiometer, with World Radiometric Reference factors ranging from 0.999674 to 0.994610 for the best and the worst performing devices, respectively. In addition, the SolarSIMs’ spectral DNI data was compared against PMOD’s Precision Spectral Radiometer. The mean difference of the spectral DNI was found to be less than 5% for wavelengths above 400 nm. The SolarSIMs’ measurements of AOD data were compared against PMOD’s Precision Filter Radiometer triad. The median AOD differences and their standard deviations were found to be 0.0046 ± 0.0044, 0.0016 ± 0.0034, 0.0018 ± 0.0026, and 0.0041 ± 0.0022 for 368 nm, 412 nm, 500 nm, and 865 nm, respectively. The SolarSIMs’ measurements of precipitable water vapour were compared against PMOD’s Cimel CE318 sun photometer. The median difference and the corresponding standard deviation averaged 1 ± 0.2 mm for all SolarSIMs. Furthermore, the SolarSIMs’ measurements of total column atmospheric ozone were compared against PMOD’s Brewer MkIII spectrophotometer. The median difference and the corresponding standard deviation averaged 6 ± 7 DU for all SolarSIMs.

First Reprocessing of Southern Hemisphere Additional Ozonesondes (SHADOZ) Ozone Profiles (1998–2016): 2. Comparisons With Satellites and Ground‐Based Instruments

AbstractThe Southern Hemisphere ADditional OZonesonde (SHADOZ) network was assembled to validate a new generation of ozone‐monitoring satellites and to better characterize the vertical structure of tropical ozone in the troposphere and stratosphere. Beginning with nine stations in 1998, more than 7,000 ozone and P‐T‐U profiles are available from 14 SHADOZ sites that have operated continuously for at least a decade. We analyze ozone profiles from the recently reprocessed SHADOZ data set that is based on adjustments for inconsistencies caused by varying ozonesonde instruments and operating techniques. First, sonde‐derived total ozone column amounts are compared to the overpasses from the Earth Probe/Total Ozone Mapping Spectrometer, Ozone Monitoring Instrument, and Ozone Mapping and Profiler Suite satellites that cover 1998–2016. Second, characteristics of the stratospheric and tropospheric columns are examined along with ozone structure in the tropical tropopause layer (TTL). We find that (1) relative to our earlier evaluations of SHADOZ data, in 2003, 2007, and 2012, sonde‐satellite total ozone column offsets at 12 stations are 2% or less, a significant improvement; (2) as in prior studies, the 10 tropical SHADOZ stations, defined as within ±19° latitude, display statistically uniform stratospheric column ozone, 229 ± 3.9 DU (Dobson units), and a tropospheric zonal wave‐one pattern with a 14 DU mean amplitude; (3) the TTL ozone column, which is also zonally uniform, masks complex vertical structure, and this argues against using satellites for lower stratospheric ozone trends; and (4) reprocessing has led to more uniform stratospheric column amounts across sites and reduced bias in stratospheric profiles. As a consequence, the uncertainty in total column ozone now averages 5%.

Brief overview of meteorological research in the late XX - early XXI century in Ukraine

In the paper the review of the meteorological research in Ukraine at the end of the 20-th century – the beginning of the 21-th century was made. Researches in the field of meteorology are performed mainly by the Ukrainian Hydrometeorological Institute of the State Service of Emergencies of Ukraine and National Academy of Sciences of Ukraine, Odessa State Environmental University (OSENU) and Taras Shevchenko National University of Kyiv (TSNUK).
 The studies of UkrHMI scientific schools headed by well-known scientists in the field of meteorology were devoted to the development of new theories, methods, models in the field of the weather forecasting and dangerous situations in Ukraine, radiation balance, agrometeorology, climate researches in the Ukraine, numerical modeling of cloud physics and active effects on clouds, numerical methods in analysis and forecast of natural and technogenic processes in the atmosphere.
 In OSENU, where two scientific schools are established, the scientists study the formation of severe weather and its forecast, diagnose and forecast mesoscale atmospheric circulations, identify nonlinear interaction between the main global structures, detect the features of circulation processes in high latitudes of the southern hemisphere, conduct systematic studies in the field of numerical modelling of physics and dynamics of atmospheric processes with the Enviro-HIRLAM and HARMONIE models.
 Scientists of TSNUK study changes in the total column ozone amount in the atmosphere of Antarctic Region and the mid-latitudes of Northern Hemisphere. The work on analyzing the state of climatic parameters and changing the current climate of Ukraine is being carried out at the KNU.

Aerosol optical depth determination in the UV using a four-channel precision filter radiometer

Abstract. The determination of aerosol properties, especially the aerosol optical depth (AOD) in the ultraviolet (UV) wavelength region, is of great importance for understanding the climatological variability of UV radiation. However, operational retrievals of AOD at the biologically most harmful wavelengths in the UVB are currently only made at very few places. This paper reports on the UVPFR (UV precision filter radiometer) sunphotometer, a stable and robust instrument that can be used for AOD retrievals at four UV wavelengths. Instrument characteristics and results of Langley calibrations at a high-altitude site were presented. It was shown that due to the relatively wide spectral response functions of the UVPFR, the calibration constants (V0) derived from Langley plot calibrations underestimate the true extraterrestrial signals. Accordingly, correction factors were introduced. In addition, the instrument's spectral response functions also result in an apparent air-mass-dependent decrease in ozone optical depth used in the AOD determinations. An adjusted formula for the calculation of AOD, with a correction term dependent on total column ozone amount and ozone air mass, was therefore introduced. Langley calibrations performed 13–14 months apart resulted in sensitivity changes of ≤ 1.1 %, indicating good instrument stability. Comparison with a high-accuracy standard precision filter radiometer, measuring AOD at 368–862 nm wavelengths, showed consistent results. Also, very good agreement was achieved by comparing the UVPFR with AOD at UVB wavelengths derived with a Brewer spectrophotometer, which was calibrated against the UVPFR at an earlier date. Mainly due to non-instrumental uncertainties connected with ozone optical depth, the total uncertainty of AOD in the UVB is higher than that reported from AOD instruments measuring in UVA and visible ranges. However, the precision can be high among instruments using harmonized algorithms for ozone and Rayleigh optical depth as well as for air mass terms. For 4 months of comparison measurements with the UVPFR and a Brewer, the root mean squared AOD differences were found < 0.01 at all the 306–320 nm Brewer wavelengths.

Fractional bivariate exponential estimator for long-range dependent random field

Estimating long-range dependence parameter of a random field, which provides a measure for the extent of long-range dependence, is a challenging problem. Fractional Bivariate EXponential (FBEXP) estimator is proposed for long-range dependence parameter estimation in random fields observed on a regular lattice. FBEXP is a generalized version of the commonly used FEXP estimator in time series. FBEXP estimator belongs to the class of broadband semiparametric estimators, which makes it free from the optimal bandwidth selection problem, present in other semiparametric estimators. The behavior of FBEXP estimator depends on the model order of bivariate exponential model. Three data-driven model order selection criteria are introduced to serve as a guide in appropriate choice of model order for efficient estimation of long-range dependence using FBEXP. The finite sample performance of the FBEXP estimator and model order selection criteria are illustrated via simulation study. FBEXP estimator provides an efficient estimate for the long-range dependence parameter, especially when the spectral density is sufficiently smooth everywhere except at the points of singularities. Total column ozone amounts in Europe and Mediterranean region illustrate the applicability of FBEXP estimator in providing efficient estimates for direction specific long-range dependence parameters and the spectral density of the process.

Comparison of ozone retrievals from the Pandora spectrometer system and Dobson spectrophotometer in Boulder, Colorado

Abstract. A comparison of retrieved total column ozone (TCO) amounts between the Pandora #34 spectrometer system and the Dobson #061 spectrophotometer from direct-sun observations was performed on the roof of the Boulder, Colorado, NOAA building. This paper, part of an ongoing study, covers a 1-year period starting on 17 December 2013. Both the standard Dobson and Pandora TCO retrievals required a correction, TCOcorr = TCO (1 + C(T)), using a monthly varying effective ozone temperature, TE, derived from a temperature and ozone profile climatology. The correction is used to remove a seasonal difference caused by using a fixed temperature in each retrieval algorithm. The respective corrections C(TE) are CPandora = 0.00333(TE-225) and CDobson = -0.0013(TE-226.7) per degree K. After the applied corrections removed most of the seasonal retrieval dependence on ozone temperature, TCO agreement between the instruments was within 1 % for clear-sky conditions. For clear-sky observations, both co-located instruments tracked the day-to-day variation in total column ozone amounts with a correlation of r2 = 0.97 and an average offset of 1.1 ± 5.8 DU. In addition, the Pandora TCO data showed 0.3 % annual average agreement with satellite overpass data from AURA/OMI (Ozone Monitoring Instrument) and 1 % annual average offset with Suomi-NPP/OMPS (Suomi National Polar-orbiting Partnership, the nadir viewing portion of the Ozone Mapper Profiler Suite).

Influence of cloud fraction and snow cover to the variation of surface UV radiation at King Sejong station, Antarctica

This study investigated how cloud fraction and snow cover affect the variation of surface ultraviolet (UV) radiation by using surface Erythemal UV (EUV) and Near UV (NUV) observed at the King Sejong Station, Antarctica. First the Radiative Amplification Factor (RAF), the relative change of surface EUV according to the total-column ozone amount, is compared for different cloud fractions and solar zenith angles (SZAs). Generally, all cloudy conditions show that the increase of RAF as SZA becomes larger, showing the larger effects of vertical columnar ozone. For given SZA cases, the EUV transmission through mean cloud layer gradually decreases as cloud fraction increases, but sometimes the maximum of surface EUV appears under partly cloudy conditions. The high surface EUV transmittance under broken cloud conditions seems due to the re-radiation of scattered EUV by cloud particles. NUV transmission through mean cloud layer also decreases as cloud amount increases but the sensitivity to the cloud fraction is larger than EUV. Both EUV and NUV radiations at the surface are also enhanced by the snow cover, and their enhancement becomes higher as SZA increases implying the diurnal variation of surface albedo. This effect of snow cover seems large under the overcast sky because of the stronger interaction between snow surface and cloudy sky.

A total ozone‐dependent ozone profile climatology based on ozonesondes and Aura MLS data

AbstractOzone profiles measured with the Aura Microwave Limb Sounder (MLS) and ozonesondes are used to create a new ozone climatology that can be used for satellite retrievals and radiative transfer studies. The climatology is binned according to total column ozone amount and latitude rather than with season. Because of high correlation between ozone profile shape and total ozone, the ozone profiles in this climatology capture ozone variations well, especially near the tropopause. This climatology has been constructed from nearly a million individual MLS ozone profile measurements taken between 2004 and 2013 as well as over 55,000 ozonesonde measurements from 1988 to 2011. The MLS profiles were sorted by total column ozone as measured by Ozone Monitoring Instrument in observations that were coincident with the MLS measurements. The data from the sondes were used in the troposphere and lower stratosphere and MLS in the middle and upper stratosphere. These two data sets were blended together between 13 and 17 km (~159–88 hPa). This climatology consists of average ozone profiles as a function of total ozone for six 30° latitude bands covering altitudes between 0 and 75 km (in Z* pressure altitude coordinates) as well as the corresponding standard deviations for each layer. There is no seasonal component. This new climatology shows some remarkable and somewhat unexpected correlations between the total column ozone and the ozone amount at some layers, particularly in the lower and middle troposphere in some latitude bands.

New neural-network-based method to infer total ozone column amounts and cloud effects from multi-channel, moderate bandwidth filter instruments.

A new method is presented based on a radial basis function neural network (RBF-NN) to analyze data obtained by ultraviolet (UV) irradiance instruments. Application of the RBF-NN method to about three years of data obtained by a NILU-UV device, which is a multi-channel, moderate bandwidth filter instrument, revealed that compared to the traditional Look-up table (LUT) method, the RBF-NN method yielded better agreement with a 1% decrease in relative difference and an increase of 0.03 in correlation with total ozone column (TOC) values obtained from the Ozone Monitoring Instrument (OMI). Furthermore, the RBF-NN method retrieved more valid results (daily average values within a meaningful range (200-500 DU)) than the LUT method. Compared with RBF-NN retrievals, TOC values obtained from the OMI are underestimated under cloudy conditions. This finding agrees with conclusions reached by Anton and Loyola (2011).

Chemical ozone loss and ozone mini-hole event during the Arctic winter 2010/2011 as observed by SCIAMACHY and GOME-2

Abstract. Record breaking loss of ozone (O3) in the Arctic stratosphere has been reported in winter–spring 2010/2011. We examine in detail the composition and transformations occurring in the Arctic polar vortex using total column and vertical profile data products for O3, bromine oxide (BrO), nitrogen dioxide (NO2), chlorine dioxide (OClO), and polar stratospheric clouds (PSC) retrieved from measurements made by SCIAMACHY (Scanning Imaging Absorption SpectroMeter for Atmospheric CHartography) on-board Envisat (Environmental Satellite), as well as total column ozone amount, retrieved from the measurements of GOME-2 (Global Ozone Monitoring Experiment) on MetOp-A (Meteorological Experimental Satellite). Similarly we use the retrieved data from DOAS (Differential Optical Absorption Spectroscopy) measurements made in Ny-Ålesund (78.55° N, 11.55° E). A chemical transport model (CTM) has been used to relate and compare Arctic winter–spring conditions in 2011 with those in the previous year. In late winter–spring 2010/2011 the chemical ozone loss in the polar vortex derived from SCIAMACHY observations confirms findings reported elsewhere. More than 70% of O3 was depleted by halogen catalytic cycles between the 425 and 525 K isentropic surfaces, i.e. in the altitude range ~16–20 km. In contrast, during the same period in the previous winter 2009/2010, a typical warm Arctic winter, only slightly more than 20% depletion occurred below 20 km, while 40% of O3 was removed above the 575 K isentrope (~23 km). This loss above 575 K is explained by the catalytic destruction by NOx descending from the mesosphere. In both Arctic winters 2009/2010 and 2010/2011, calculated O3 losses from the CTM are in good agreement to our observations and other model studies. The mid-winter 2011 conditions, prior to the catalytic cycles being fully effective, are also investigated. Surprisingly, a significant loss of O3 around 60%, previously not discussed in detail, is observed in mid-January 2011 below 500 K (~19 km) and sustained for approximately 1 week. The low O3 region had an exceptionally large spatial extent. The situation was caused by two independently evolving tropopause elevations over the Asian continent. Induced adiabatic cooling of the stratosphere favoured the formation of PSC, increased the amount of active chlorine for a short time, and potentially contributed to higher polar ozone loss later in spring.

Total Ozone Column Trends over Five Iraqi Selected Provinces Using TOMS Data

Monthly and annual values of the total column ozone(TOC) amount have been analyzed for five stations of Iraq for the period from 1979 to 2012 employing Total ozone Mapping Spectrometer (TOMS) data point, It is found that ozone variation is function of latitude, where the higher values of total ozone column occurs at the northern station which represented by Mosul station, it decreases gradually from northern station (Mosul) passing by middle region stations (Biji, Baghdad and Rutba) to southern station (Basra). The values of Total ozone column start to increase gradually from November to reach its maximum at March then it decreases gradually to reach its minimum values at October. The analysis of the spatial distribution of the monthly average of total ozone column for each month of the year has been made. It is found that the largest of total ozone column amounts occurs systematically over the northern regions during winter whereas in spring and early summer months the maximum values of total ozone column directed to the northwestern regions of the country, The overall period (1979-2012) Trend Analysis presented negative trends for all months in five considered stations except Baghdad station during July and August gives a strong positive trend which refer to a notable enhancement of TOC which reaches to (0.443) DU/Year, Whereas the first period (1979-1992) showed a clear negative trend for all months also for all stations except Baghdad station which presented a weak positive trend during late autumn station, the second period (1997-2012) trends analysis presented negative trends for all months in five considered station except Baghdad station during all months gives a strong positive trend. Finally the results of the second period trend analysis indicated that the ozone layer may be responding as expected to the reducing on ozone-depleting substances imposed by the Montreal Protocol.

The effect of ozone and aerosols on the surface erythemal UV radiation estimated from OMI measurements

Surface erythemal UV radiation is mainly affected by total column ozone, aerosols, clouds, and solar zenith angle. The effect of ozone on the surface UV radiation has been explored many times in the previous studies due to the decrease of ozone layer. In this study, we calculated the effect of aerosols on the surface UV radiation as well as that of ozone using data acquired from Ozone Monitoring Instrument (OMI). First, ozone, aerosol optical depth (AOD), and surface erythemal UVB radiation measured from satellite are compared with those from ground measurements. The results showed that the comparison for ozone was good with r2 of 0.92. For aerosol, there was difference between satellite measurements and surface measurements due to the insufficient information on aerosol in the retrieval algorithm. The r2 for surface erythemal UV radiation was high (∼0.94) but satellite measurements showed about 30% larger values than surface measurements on average by not considering the effect of absorbing aerosols in the retrieval process from satellite measurements. Radiative amplification factor (RAF) is used to access the effect of ozone and aerosol quantitatively. RAF for ozone was 0.97∼1.49 with solar zenith angle. To evaluate the effect of aerosol on the surface UV radiation, only clear-sky pixel data were used and solar zenith angle and total column amount of ozone were fixed. Also, RAF for aerosol was assessed according to the single scattering albedo (SSA) of aerosols. The results showed that RAF for aerosol with smaller SSA ( 0.90). The RAF for aerosol was 0.09∼0.22 for the given conditions which was relatively small compared to that for ozone. However, considering the fact that aerosol optical depth can change largely in time and space while the total column amount of ozone does not change very much, it needs to include the effect of aerosol to predict the variations of surface UV radiation more correctly.