Unexpected self-lofting and dynamical confinement of volcanic plumes: the Raikoke 2019 case.

Recent research has provided evidence of the self-lofting capacity of smoke aerosols in the stratosphere and their self-confinement by persistent anticyclones, which prolongs their atmospheric residence time and radiative effects. By contrast, the volcanic aerosols-composed mostly of non-absorptive sulphuric acid droplets-were never reported to be subject of dynamical confinement. Here we use high-resolution satellite observations to show that the eruption of Raikoke volcano in June 2019 produced a long-lived stratospheric anticyclone containing 24% of the total erupted mass of sulphur dioxide. The anticyclone persisted for more than 3 months, circumnavigated the globe three times, and ascended diabatically to 27 km altitude through radiative heating of volcanic ash contained by the plume. The mechanism of dynamical confinement has important implications for the planetary-scale transport of volcanic emissions, their stratospheric residence time, and atmospheric radiation balance. It also provides a challenge or "out of sample test" for weather and climate models that should be capable of reproducing similar structures.

Changes in the total ozone content over the period 2006 to 2100 and the effects on the erythemal and vitamin D effective UV doses for South America and Antarctica.

Recent studies show that the ozone layer will recover by the middle part of this century. This is a significant result arising from the Montreal Protocol, and highlights the success of this environmental protection agreement. Climate change projections show that Total Ozone Content (TOC) levels will increase significantly by the end of this century, mainly at higher latitudes. This increase may result in a reduction of the adverse effects of UV radiation overexposure. By contrast, reduced UV radiation levels at the surface of the Earth can result in reduced levels of vitamin D synthesis among the inhabitants of these regions. In this study we provide estimates for the UVI, erythemal, and vitamin-D weighted daily doses for ten different locations in South America and Antarctica. Our calculations were based on ozone projections provided by climate models set forth in the last IPCC report. Results show that the increase of TOC levels in middle and high latitude regions may result in decreased UVI and UV doses throughout the century. In high latitudes, erythemal doses and vitamin D synthesis doses may be reduced by up to 22 and 39%, respectively, if anthropogenic emissions continue to rise throughout the century. Furthermore, there may be reductions of up to 9 and 12%, respectively, in mid-latitudes (20°S to 35°S). Significant variations at Equatorial sites were not observed. In most of South America, the attenuation in UVR caused by increases in TOC during the 21st century is neither enough to promote protective effects from this radiation, nor for the lack of UVR for vitamin D synthesis. The incidence of UVR in tropical and sub-tropical areas of the continent will continue to be a public health risk for the entire 21st century during all seasons, regardless of the climatic scenarios. Our results can be used as an important tool for health studies focusing on the excess and/or lack of sun exposure.

[Sun exposure at school: Evaluation of risk (erythema dose), benefits (vitamin-D synthesis) and behaviour among children in France]. / Exposition solaire en milieu scolaire : évaluation du risque (dose érythémale), du bénéfice (synthèse de vitamine D) et des comportements des enfants.

BACKGROUND: To better understand the potential risk associated with sun exposure during the school year, we decided to evaluate behaviour, risk [UV index (UVI), minimal erythema dose (MED)] and benefits (vitamin-D synthesis) of sun exposure in primary schoolchildren in France, as well as the various sun protection methods used for children. MATERIAL AND METHODS: We performed the study on a sunny day (July 24) in a school in Antony (France). Evaluation of UVI (with calculation of MED) and the amount of vitamin D synthesized according to exposed body surface area and phototype were performed every 15minutes from 9 a.m. to 5 p.m. The effects of albedo and shade on UVI were assessed in 8 different locations at the school. The sun-protection measures used by the children were systematically evaluated. RESULTS: Fifty-seven children were evaluated; the maximum UVI was 7.2 and the maximum temperature was 30.7°C. Irrespective of phototype and clothing, 1 MED was reached and an adequate level of vitamin D was synthesized in the skin before midday. Albedo had little impact on irradiation. The amount of protection afforded by shadow varied greatly, with the highest level occurring in the covered courtyard (99.5% reduction of UVI) and the lowest in the shadow of buildings (53.7% reduction of UVI). With strict sun protection measures concerning dress, children reached 1 MED before synthesizing 1000IU of vitamin D, but with clothing "suited to high temperatures", 1000IU of vitamin D were synthetized before 1 MED was reached. Compliance with photoprotection measures was poor. Regardless of duration of exposure during the day (minimal model: two play breaks+lunchtime break) and of skin phototype, at least 1.5 MED was reached during the day. STUDY LIMITATIONS: This was an experimental study ignoring children's actual behaviour (movement, sweating, application of sun protection products, etc.). Moreover, due to weather conditions, the study was performed at a recreation centre in July and not during the "standard" school year. CONCLUSION: Sun protection campaigns should naturally be directed chiefly towards children for several reasons relating to solar risk and learning. This study shows the complex link between UV, MED, vitamin D as well as the difficulties of implementing solar protection measures in schools in France.

Ground-based assessment of the bias and long-term stability of fourteen limb and occultation ozone profile data records.

The ozone profile records of a large number of limb and occultation satellite instruments are widely used to address several key questions in ozone research. Further progress in some domains depends on a more detailed understanding of these data sets, especially of their long-term stability and their mutual consistency. To this end, we made a systematic assessment of fourteen limb and occultation sounders that, together, provide more than three decades of global ozone profile measurements. In particular, we considered the latest operational Level-2 records by SAGE II, SAGE III, HALOE, UARS MLS, Aura MLS, POAM II, POAM III, OSIRIS, SMR, GOMOS, MIPAS, SCIAMACHY, ACE-FTS and MAESTRO. Central to our work is a consistent and robust analysis of the comparisons against the ground-based ozonesonde and stratospheric ozone lidar networks. It allowed us to investigate, from the troposphere up to the stratopause, the following main aspects of satellite data quality: long-term stability, overall bias, and short-term variability, together with their dependence on geophysical parameters and profile representation. In addition, it permitted us to quantify the overall consistency between the ozone profilers. Generally, we found that between 20-40 km the satellite ozone measurement biases are smaller than ±5 %, the short-term variabilities are less than 5-12% and the drifts are at most ±5% decade-1 (or even ±3 % decade-1 for a few records). The agreement with ground-based data degrades somewhat towards the stratopause and especially towards the tropopause where natural variability and low ozone abundances impede a more precise analysis. In part of the stratosphere a few records deviate from the preceding general conclusions; we identified biases of 10% and more (POAM II and SCIAMACHY), markedly higher single-profile variability (SMR and SCIAMACHY), and significant long-term drifts (SCIAMACHY, OSIRIS, HALOE, and possibly GOMOS and SMR as well). Furthermore, we reflected on the repercussions of our findings for the construction, analysis and interpretation of merged data records. Most notably, the discrepancies between several recent ozone profile trend assessments can be mostly explained by instrumental drift. This clearly demonstrates the need for systematic comprehensive multi-instrument comparison analyses.

Evaluation of tourists' UV exposure in Paris.

BACKGROUND: Ultraviolet (UV) exposure is one of the most important risk factor for skin cancers. If UV hazard has been evaluated in tropical countries or in some population - children, outdoor activities - little information is available about UV hazard in high latitude towns like Paris, considered as the most 'charismatic city' in the world. OBJECTIVE: To evaluate UV exposure in Paris in spring, in sun and shade, in real life conditions. METHODS: We evaluated erythemal UV exposure, during four sunny days in May-June in eight Paris touristic sites during peak hours (2 days), and during two walks in touristic downtown of Paris. Measures were performed in sun and shade. UV radiation exposure was evaluated with UV index performed with a 'Solarmeter ultraviolet index (UVI)' and UV dose with 'standard erythema dose' (SED) and 'minimal erythema dose' (MED) calculations. RESULTS: Despite 'average' UVI in sunny conditions, a 4-h sun exposure reaches 13-20 SED and 3-10 MED according to phototype. Clouds were inefficient to protect against UV. Shade of places reduces moderately UVI (50-60%) in forecourts. Exposure during 1-h walk reach at least one MED in real life conditions for skin phototypes I-IV. CONCLUSIONS: UV risk for tourist is quite high in spring in Paris. UVI remains high despite high cloud fraction. Shade reduces UVI, but UV protection factor is only 2-3 in large places such as Place Notre Dame and Place Charles de Gaulle. So sun protection campaigns should be proposed, and sun protective strategies could be integrated in urban planning.

Outdoor sports and risk of ultraviolet radiation-related skin lesions in children: evaluation of risks and prevention.

BACKGROUND: Excessive ultraviolet (UV) radiation exposure can cause skin cancers, skin photoageing and cataracts. Children are targeted by sun-protection campaigns because high sun exposure and sunburn in childhood increase the risk of melanoma in adulthood. Little information is available about UV radiation risk and exposure in children who take part in outdoor sports. OBJECTIVE: To evaluate the risk of developing UV radiation-induced skin lesions run by children who practise outdoor sports, and UV radiation exposure and sun-protection measures during a soccer tournament. METHODS: Firstly, we evaluated the relationship between melanocytic naevus - a skin lesion linked with exposure to UV radiation - and outdoor sports in 660 11-year-old children. Secondly, we used the occasion of a 1-day soccer tournament held in the spring to evaluate UV radiation-protective measures used by soccer players and the public. We also evaluated the UV radiation index and cloud cover during the tournament, and calculated the UV radiation dose and minimal erythema dose depending on skin phototype. RESULTS: The naevus count and acquired naevus count measured over the 2 years of the study were higher in the 344 children who practised outdoor sports. Sun-protective measures were insufficient for soccer players and the public. CONCLUSIONS: This study shows that outdoor sports increase the risk of developing UV radiation-induced skin lesions in childhood. During a 1-day soccer tournament held in the spring, children and their parents were inadequately protected against the sun. These results suggest that sun-protection campaigns should be aimed at children who practise popular outdoor sports.

Systematic DIAL lidar monitoring of the stratospheric ozone vertical distribution at Observatoire de Haute-Provence (43.92 degrees N, 5.71 degrees E).

Long term stratospheric DIAL (Differential Absorption Lidar) ozone lidar (Light Detection and Ranging) measurements have been performed at the Observatoire de Haute-Provence (OHP) since 1985 and as part of the Network for the Detection of Stratospheric Changes (NDSC) since 1991. This paper provides a detailed description of the DIAL lidar instrument implemented at OHP and a discussion of the ozone retrieval analysis. The instrument includes the detection of atmospheric nitrogen Raman scattering wavelengths, which is required for ozone measurements in the presence of strong volcanic aerosol loading. A comprehensive evaluation of the error budget in the 10-50 km altitude range is performed with particular emphasis on the bias associated with background and volcanic stratospheric aerosol. This bias is evaluated using ancillary measurements of the aerosol size distribution obtained from 1991 to 1999 after the Mount Pinatubo volcanic eruption. Results show that the bias associated with background aerosols is smaller than 1% above 13 km while the bias due to volcanic aerosols reaches a maximum of 5% above 15 km in the DIAL Raman ozone retrieval. In background aerosol conditions the total accuracy of the DIAL ozone vertical distribution at OHP ranges from 5% below 20 km to 15-30% above 45 km with a vertical resolution varying from 0.5 km to 5 km.