Jordi Badosa

Interactive effects of UV radiation and water availability on seedlings of six woody Mediterranean species

To assess the effects of UV radiation and its interaction with water availability on Mediterranean plants, we performed an experiment with seedlings of six Mediterranean species (three mesophytes vs three xerophytes) grown in a glasshouse from May to October under three UV conditions (without UV, with UVA and with UVA+UVB) and two irrigation levels (watered to saturation and low watered). Morphological, physiological and biochemical measures were taken. Exposure to UVA+UVB increased the overall leaf mass per area (LMA) and the leaf carotenoids/chlorophyll a + b ratio of plants in relation to plants grown without UV or with UVA, respectively. In contrast, we did not find a general effect of UV on the leaf content of phenols or UVB-absorbing compounds of the studied species. Regarding plant growth, UV inhibited the above-ground biomass production of well-watered plants of Pistacia lentiscus. Conversely, under low irrigation, UVA tended to abolish the reduction in growth experienced by P. lentiscus plants growing in a UV-free environment, in accordance with UVA-enhanced apparent electron transport rate (ETR) values under drought in this species. UVA also induced an overall increase in root biomass when plants of the studied species were grown under a low water supply. In conclusion, while plant exposition to UVA favored root growth under water shortage, UVB addition only gave rise to photoprotective responses, such as the increase in LMA or in the leaf carotenoids/chlorophyll a + b ratio of plants. Species-specific responses to UV were not related with the xerophytic or mesophytic character of the studied species.

Using a Parameterization of a Radiative Transfer Model to Build High-Resolution Maps of Typical Clear-Sky UV Index in Catalonia, Spain

To perform a climatic analysis of the annual UV index (UVI) variations in Catalonia, Spain (northeast of the Iberian Peninsula), a new simple parameterization scheme is presented based on a multilayer radiative transfer model. The parameterization performs fast UVI calculations for a wide range of cloudless and snow-free situations and can be applied anywhere. The following parameters are considered: solar zenith angle, total ozone column, altitude, aerosol optical depth, and single-scattering albedo. A sensitivity analysis is presented to justify this choice with special attention to aerosol information. Comparisons with the base model show good agreement, most of all for the most common cases, giving an absolute error within 0.2 in the UVI for a wide range of cases considered. Two tests are done to show the performance of the parameterization against UVI measurements. One uses data from a high-quality spectroradiometer from Lauder, New Zealand [45.04°S, 169.684°E, 370 m above mean sea level (MSL)], where there is a low presence of aerosols. The other uses data from a Robertson–Berger-type meter from Girona, Spain (41.97°N, 2.82°E, 100 m MSL), where there is more aerosol load and where it has been possible to study the effect of aerosol information on the model versus measurement comparison. The parameterization is applied to a climatic analysis of the annual UVI variation in Catalonia, showing the contributions of solar zenith angle, ozone, and aerosols. High-resolution seasonal maps of typical UV index values in Catalonia are presented.

Two Methods for Retrieving UV Index for All Cloud Conditions from Sky Imager Products or Total SW Radiation Measurements

Cloud effects on UV Index (UVI) and total solar radiation (TR) as a function of cloud cover and sunny conditions (from sky images) as well as of solar zenith angle (SZA) are assessed. These analyses are undertaken for a southern‐hemisphere mid‐latitude site where a 10‐years dataset is available. It is confirmed that clouds reduce TR more than UV, in particular for obscured Sun conditions, low cloud fraction (<60%) and large SZA (>60°). Similarly, local short‐time enhancement effects are stronger for TR than for UV, mainly for visible Sun conditions, large cloud fraction and large SZA. Two methods to estimate UVI are developed: (1) from sky imaging cloud cover and sunny conditions, and (2) from TR measurements. Both methods may be used in practical applications, although Method 2 shows overall the best performance, as TR allows considering cloud optical properties. The mean absolute (relative) differences of Method 2 estimations with respect to measured values are 0.17 UVI units (6.7%, for 1 min data) and 0.79 Standard Erythemal Dose (SED) units (3.9%, for daily integrations). Method 1 shows less accurate results but it is still suitable to estimate UVI: mean absolute differences are 0.37 UVI units (15%) and 1.6 SED (8.0%).

How large and how long are UV and total radiation enhancements

Enhancement of solar radiation, which happens when solar irradiance at the surface is greater than the expected clear-sky value, is mainly caused by partial cloudy conditions. This effect has been extensively observed and investigated in the past, both on solar total radiation (TR) and on ultraviolet (UV) radiation. Characterization of the enhancements is relevant to better understand the radiative effects of clouds and solar radiation variability on the ground. We analyse this effect with a 10-years dataset obtained in Lauder, New Zealand, that contains TR and UV radiation measurements, cloud observations from a sky camera, and aerosol information from a four channel SPO2 solar-tracking radiometer, all at 1 min resolution. This great wealth of high-resolution measurements allows novel analyses and robust results about the typology of the radiation enhancements, in particular in terms of their duration, intensity and the associated atmospheric conditions.

A method to estimate erythemal UV from total solar irradiance measurements based on 9 years of 1-minute data at Lauder, New Zealand

The radiative effect of clouds on the incident surface solar radiation highly depends on the spectral band of the solar spectrum that is considered. In particular, cloud effects are known to be different for the broadband erythemal ultraviolet (hereafter, UVE) irradiance and the total global solar irradiance (TR) due to the much more important molecular (Rayleigh) scattering on the UV than on the visible and near infrared wavelengths. In this work we investigate these differences by analyzing 9 years (2000-2008) of 1-minute UVE and TR measured at Lauder (45.04S, 169.68E, 370m asl), New Zealand. Clear sky models for UVE and TR are considered and their performances are tested. Effective cloud transmittance, also known as cloud modification factor (CMF) is calculated as the ratio between the 1-minute measurements and the clear sky estimation from modeling, both for UVE (CMF(UV)) and TR (CMF(TR)). The two CMF are then compared. The analyses are undertaken as a function of solar zenith angle (SZA), and Sun vis...