Guillermo Deferrari

Ozone and UV Radiation over Southern South America: Climatology and Anomalies

Abstract Ozone and UV radiation were analyzed at eight stations from tropical to sub-Antarctic regions in South America. Ground UV irradiances were measured by multichannel radiometers as part of the Inter American Institute for Global Change Radiation network. The irradiance channels used for this study were centered at 305 nm (for UV-B measurements) and 340 nm (for UV-A measurements). Results were presented as daily maximum irradiances, as monthly averaged, daily integrated irradiances and as the ratio of 305 nm to 340 nm. These findings are the first to be based on a long time series of semispectral data from the southern region of South America. As expected, the UV-B channel and total column ozone varied with latitude. The pattern of the UV-A channel was more complex because of local atmospheric conditions. Total column ozone levels of <220 Dobson Units were observed at all sites. Analysis of autocorrelations showed a larger persistence of total column ozone level than irradiance. A decreasing cross-correlation coefficient between 305 and 340 nm and an increasing cross-correlation coefficient between 305 nm and ozone were observed at higher latitudes, indicating that factors such as cloud cover tend to dominate at northern sites and that ozone levels tend to dominate at southern sites. These results highlight the value of long-term monitoring of radiation with multichannel radiometers to determine climatological data and evaluate the combination of factors affecting ground UV radiation.

Solar irradiances over Ushuaia (54.49° S, 68.19° W) and San Diego (32.45° N, 117.11° W) geographical and seasonal variation

Abstract The study of long-term variability in UV-B irradiance in places affected by the “ozone hole” and the comparison with undisturbed places is of interest for the atmospheric community, and is also useful from the biological and epidemiological points of view. Since some ecosystems are also sensitive to other bands of the solar spectrum, the study of UV-A and visible are also of interest. In this paper, we compare the irradiance in the UV-B, UV-A and visible at Ushuaia ( 54.49° S , 68.19° W ) and San Diego ( 32.45° N , 117.11° W ), going from instantaneous to year-integrated values. As some ecosystems are sensitive not only to the absolute value, but also to the relative changes, we also analyse the ozone and irradiance relative variations. The large variability in the total ozone column at Ushuaia combined with other parameters such as solar zenith angles, cloud cover and amount of daylight hours results in a wide variety of situations. For the ozone-sensitive bands, peaks of daily and daily-integrated maximum irradiance observed at Ushuaia during spring are remarkably higher than expected, although seldom reaching the maximum observed at San Diego. For the UV-A and visible, values at Ushuaia during the late spring and summer are very close to and, in a few cases, even exceed those at San Diego. The highest monthly integrated irradiance for the band 298.507–303.030 nm, at Ushuaia, was observed in December 1990, with a value well above the mean for that month. Relative ozone variation at Ushuaia presents the most important depletion and largest dispersion during the spring, as expected. While, for the ozone-sensitive bands, the largest relative irradiance increment is observed during the winter.

Simulation of Ozone Depletion Using Ambient Irradiance Supplemented with UV Lamps

Abstract In studies of the biological effects of UV radiation, ozone depletion can be mimicked by performing the study under ambient conditions and adding radiation with UV-B lamps. We evaluated this methodology at three different locations along a latitudinal gradient: Rimouski (Canada), Ubatuba (Brazil) and Ushuaia (Argentina). Experiments of the effect of potential ozone depletion on marine ecosystems were carried out in large outdoor enclosures (mesocosms). In all locations we simulated irradiances corresponding to 60% ozone depletion, which may produce a 130–1900% increase in 305 nm irradiance at noon, depending on site and season. Supplementation with a fixed percentage of ambient irradiance provides a better simulation of irradiance increase due to ozone depletion than supplementation with a fixed irradiance value, particularly near sunrise and sunset or under cloudy skies. Calculations performed for Ushuaia showed that, on very cloudy days, supplementation by the square-wave method may produce unrealistic irradiances. Differences between the spectra of the calculated supplementing irradiance and the lamp for a given site and date will be a function of the time of day and may become more or less pronounced according to the biological weighting function of the effect under study.

Multichannel radiometer calibration: a new approach.

The error in irradiance measured with Sun-calibrated multichannel radiometers may be large when the solar zenith angle (SZA) increases. This could be particularly detrimental in radiometers installed at mid and high latitudes, where SZAs at noon are larger than 50 degrees during part of the year. When a multiregressive methodology, including the total ozone column and SZA, was applied in the calculation of the calibration constant, an important improvement was observed. By combining two different equations, an improvement was obtained at almost all the SZAs in the calibration. An independent test that compared the irradiance of a multichannel instrument and a spectroradiometer installed in Ushuaia, Argentina, was used to confirm the results.

Effect on irradiance of the eruption of the Cordon Caulle (Chile) at different altitudes in the Nahuel Huapi National Park (Patagonia, Argentina)

Volcanic eruptions inject ash and non-ash particles into the atmosphere, modifying regional Aerosols Optical Depth (AOD) and aerosols size distribution, which affect irradiance at the earth’s surface. In this paper, we analyze the effect of the eruption of Puyehue-Cordon Caulle (Chile) on irradiance in the area of the Nahuel Huapi National Park (NHNP) (~100 km southeast of Puyehue-Cordon Caulle), at different altitudes. In this paper we only included the results for direct and AOD obtained during field campaigns at two consecutive years, before and after the eruption. Three days presented clear skies during most of the day in 2011. Two of those days, showed AOD similar to the values in 2010. On the third days, at the lowest altitude site (804m.s.l.), AOD were near 200% larger than in 2010. The largest decreases observed, at noon, in the direct irradiance was ~30% at 380 nm and 25% at 500nm, increasing with Solar Zenith Angle (SZA). The effect was less pronounced at the site at highest altitude (1930 m.s.l.), where the AODs increase was near 90% and the direct noon irradiance decrease 10% at 380 nm and 7% at 500nm.

Calibrating six years of multiband UV measurements at Ushuaia and Marambio for model and satellite comparisons

An Antarctic UV-monitoring network established in 1999 as a Spanish-Finnish-Argentinian co-operation consists of multiband filter radiometers located at Belgrano, Marambio, and Ushuaia. To provide with quality controlled and assured calibrated groundbased Antarctic UV data, bi-weekly lamp tests were used on every site and visits of travelling reference instruments on two of the sites. Along the six years of operation, the sensitivity in some of the instrument channels was found to drift up to 61%. In both stations, always the same channels showed the best stability or worst instability. The rigorous quality assurance programme ensured that reliable time series of solar data could be produced, however. The most recent Antarctic ozone depletion period of 2005/2006 was studied by comparing OMI satellite-based erythemally weighted daily doses with the measured polynomial corrected data for August 2005-March 2006 for Ushuaia and Marambio. The root mean square (RMS) of difference between the groundbased and satellite-retrieved daily doses was on monthly basis smaller for Ushuaia (19 - 28 %) than for Marambio (17-58 %), possibly due to e.g. bigger heterogeneity of the ground albedo, and variability of the cloudiness. Our final task of combining the polynomial corrected lamp calibration factors and the traveling reference calibration factors, to produce the final calibrated Antartic UV data, is discussed, too.

Calibration improvement of the IAI Network for the measurement of UVR: multichannel instruments

The IAI Network for the measurement of ultraviolet radiation in Chile, Argentina and Puerto Rico is composed of ten multi-channel radiometers (GUV 511, Bisopherical Instruments Inc.), which are periodically sun calibrated with a traveling reference GUV (RGUV). The RGUV is calibrated under solar light against a SUV100 spectroradiometer. This calibration is then transferred to each instrument in the network through the RGUV. A previous multi-regression model proved to be suitable to derive narrowband irradiance from broadband irradiance, ozone column and solar zenith angles (SZA). A recent modification of the existing multi-regression model improved the multi-channel instrument sun calibration against spectroradiometers. In this approach, the narrowband irradiance is the SUV spectral irradiance and the broadband is the multi-channel GUV irradiance. We included the azimuth angle as a parameter into the multi-regression equation and we applied a non-linear function, instead of a single coefficient, to correct for SZA. In this paper, the new multi-regression approach is applied to both steps of a GUV calibration: SUV - RGUV and RGUV - GUV and the results are compared with traditional calibration methods. Important improvements are observed in the calibration, in particular for SZA larger than 50°.

Improving multichannel radiometer calibration and data quality

When a multi-channel radiometer is calibrated using the sun as calibration source, the error in the calculated calibration constants may be large when solar zenith angles increase. A multi-regression model has proved to be suitable to derive narrowband irradiance from broadband irradiance, ozone column and solar zenith angles (SZA). In this paper, a modification of this model is being proposed to improved the multi-channel instrument sun calibration against spectroradiometers, considering a channel of a multi-channel radiometers as a broadband instrument. The errors in the GUV irradiance, compared to the spectroradiometer irradiance, diminished considerably at all channels for SZA larger than 50a, then, this technique could be particularly beneficial to calibrate radiometers installed at high latitudes, where SZA during winter, even at noon, are larger than 50a.

Spatial abundance models and seasonal distribution for guanaco (Lama guanicoe) in central Tierra del Fuego, Argentina

Spatially explicit modelling allows to estimate population abundance and predict species’ distribution in relation to environmental factors. Abiotic factors are the main determinants of a herbivore´s response to environmental heterogeneity on large spatiotemporal scales. We assessed the influence of elevation, geographic location and distance to the coast on the seasonal abundance and distribution of guanaco (Lama guanicoe) in central Tierra del Fuego, by means of spatially explicit modelling. The estimated abundance was 23,690 individuals for the non-breeding season and 33,928 individuals for the breeding season. The factors influencing distribution and abundance revealed to be the elevation for the non-breeding season, and the distance to the coast and geographic location for the breeding season. The southwest of the study area presented seasonal abundance variation and the southeast and northeast presented high abundance during both seasons. The elevation would be the driving factor of guanaco distribution, as individuals move to lower areas during the non-breeding season and ascend to high areas during the breeding season. Our results confirm that part of the guanaco population performs seasonal migratory movements and that the main valleys present important wintering habitats for guanacos as well as up-hill zones during summer. This type of study would help to avoid problems of scale mismatch and achieve better results in management actions and is an example of how to assess important seasonal habitats from evaluations of abundance and distribution patterns.

UV measurements at Marambio and Ushuaia during 2000–2010

Kaisa Lakkala1,2, Alberto Redondas3, Outi Meinander1, Laura Thölix1, Britta Hamari1, Antonio Fernando Almansa3, Virgilio Carreno3, Guillermo Deferrari4,5, Hector Ochoa6, Germar Bernhard7, Ricardo Sanchez8, and Gerardus de Leeuw1 1Finnish Meteorological Institute, Climate Research, Helsinki, Finland 2Finnish Meteorological Institute, Arctic Research, Sodankylä, Finland 3Izaña Atmospheric Research Center, Agencia Estatal de Meteorología, Tenerife, Spain 4Centro Austral de Investigaciones Cientificas (CADIC/CONICET), Ushuaia, Argentina 5Universidad Nacional de Tierra del Fuefo, Ushuaia, Argentina 6Dirección Nacional del Antártico-Instituto Antártico Argentino, Buenos Aires, Argentina 7Biospherical Instruments, Inc., San Diego, U.S.A 8Servicio Meteorológico Nacional, Argentina Correspondence to: Kaisa Lakkala (kaisa.lakkala@fmi.fi)