In search of traceability : two decades of calibrated Brewer UV measurements in Sodankyla and Jokioinen

The two Brewer spectrophotometers of the Finnish Meteorological Institute at Jokioinen and Sodankyla have been operated according to the highest levels of the WMO/GAW (World Meteorological Organization/Global Atmosphere Watch) recommendations with rigorous quality control and quality assurance. The calibration of the instruments is based on annual recalibrations of primary standard lamps in the VTT MIKES Metrology National Standards Laboratory in Finland and an exhaustive measurement program with measurements of standard and working lamps in the on-site optical laboratories. Over the years, the maintenance of the calibration has produced data sets of approximately 2000 lamp scans for both instruments. An extensive re-examination of the lamp measurements and the response of the spectrophotometers was carried out. The primary standard lamps were found to age on an average rate of 0.3% per burn. The responsivity at wavelength 311 nm was found to exhibit both long-term and short-term changes. The overall long-term change was declining. In addition, abrupt changes of as large as 25% were detected. The short-term changes were found to fluctuate on time frames shorter than the interval between the measurements of the primary standard lamps. This underlines the importance of the use of more frequently measured working standard lamps.Peer reviewe

Data flow of spectral UV measurements at Sodankylä and Jokioinen

The data flow involved in a long-term continuous solar spectral UV irradiance monitoring program is investigated and structured to provide an overall view on the multiphase process from data acquisition to the final products. The program employing Brewer spectrophotometers as measuring instruments is maintained by the Finnish Meteorological Institute (FMI) ever since the 1990s at two sites in Finland: Sodankyla (67 degrees N) and Jokioinen (61 degrees N). It is built upon rigorous operation routines, processing procedures, and tools for quality control (QC) and quality analysis (QA) under continuous development and evaluation. Three distinct levels of data emerge, each after certain phase in the data flow: Level 0 denoting raw data, Level 1 meaning calibrated data processed in near-real time, and Level 2 comprising of postprocessed data corrected for all distinguishable errors and known inaccuracies. The final products disseminated to the users are demonstrated to result from a process with a multitude of separate steps, each required in the production of high-quality data on solar UV radiation at the Earth's surface.Peer reviewe

Surface UV Irradiance from OMI on EOS-Aura

ABSTRACT The Ozone Monitoring Instrument (OMI) onboard the NASA EOS Aura spacecraft is a nadir viewing spectrometer that measures solar reflected and backscattered light in a selected range of the ultraviolet and visible spectrum. The instrument has a 2600 km wide viewing swath and it is capable of daily, global contiguous mapping. We have developed and implemented a surface ultraviolet irradiance algorithm for OMI that produces noontime surface spectral UV irradiance estimates at four wavelengths (305, 310, 324, 380 nm). Additionally, noontime erythemal dose rate and the erythemal daily dose are estimated. The paper includes a brief overview of the OMI surface UV algorithm, current processing status, recent validation results and plans for further development of the surface UV algorithm. INTRODUCTION OMI is a nadir-viewing spectrometer designed to monitor ozone and other atmospheric species OMI SURFACE UV IRRADIANCE ALGORITHM, PROCESSING SYSTEM AND DATA PRODUCT Overview on the Current Operational OMI Surface UV Irradiance Algorithm Surface UV irradiance is estimated using a radiative transfer model whose input parameters are derived from the OMI measurements. The algorithm is similar to the TOMS UV algorithm developed by NASA OMUVB Processing System and the Processing Status Production of the OMUVB data is performed using the Sodankylä OMI UV Processing System (SOUPS). SOUPS ingests Level 2 OMTO3 total ozone product and generates Level 2 OMUVB surface UV irradiance product, both of which are in HDF5-EOS format. SOUPS communicates with the Sodankylä satellite data archive as an Oracle client. The processing is carried out in batches of a few thousand granules, which are initiated manually by the operator. There are additional postprocessing tools for archiving and gridding of data as well as for generation of overpass data. Currently, some 7000 granules out of the total 8000 ECS Collection 2 OMTO3 granules available have been processed. There are plans to reprocess all the OMI data as a completely new version of the OMTO3 data product become

Regional risks of wind damage in boreal forests under changing management and climate projections

We employed simulations by forest ecosystem (SIMA) and mechanistic wind damage (HWIND) models in upland boreal forests throughout Finland to study regional risks of wind damage under changing management preferences and climates (current, RCP4.5 and RCP8.5 scenarios) over 2010â 2099. We used a critical wind speed for the uprooting of trees as a measure of vulnerability, which together with the probability of such wind speed defined a level of risk. Based on that, we also predicted the stem volume of growing stock at risk and the amount of damage. In this work, medium fertility sites were planted to one of Scots pine, Norway spruce or silver birch, or to the tree species that was dominant before the final clear-felling. The vulnerability to wind damage, the volume of growing stock at risk and the amount of damage all increased and the most in the south, when the proportion of Norway spruce (with shallow rooting) of the growing stock increased. Under a severe climate warming, the proportion of Norway spruce decreased the most in the south, opposite to that of birch. This decreased the risk of damage in autumn (while birch is leafless), unlike in summer. The low risk of damage in the north was due to the large proportion of Scots pine.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

TOMS UV Algorithm: Problems and Enhancements

Satellite instruments provide global maps of surface ultraviolet (UV) irradiance by combining backscattered radiance measurements with radiative transfer models. The models are limited by uncertainties in input parameters of the atmosphere and the surface. We evaluate the effects of possible enhancements of the current Total Ozone Mapping Spectrometer (TOMS) surface UV irradiance algorithm focusing on effects of diurnal variation of cloudiness and improved treatment of snow/ice. The emphasis is on comparison between the results of the current (version 1) TOMS UV algorithm and each of the changes proposed. We evaluate different approaches for improved treatment of pixel average cloud attenuation, with and without snow/ice on the ground. In addition to treating clouds based only on the measurements at the local time of the TOMS observations, the results from other satellites and weather assimilation models can be used to estimate attenuation of the incident UV irradiance throughout the day. A new method is proposed to obtain a more realistic treatment of snow covered terrain. The method is based on a statistical relation between UV reflectivity and snow depth. The new method reduced the bias between the TOMS UV estimations and ground-based UV measurements for snow periods. The improved (version 2) algorithm will be applied to re-process the existing TOMS UV data record (since 1978) and to the future satellite sensors (e.g., Quik/TOMS, GOME, OMI on EOS/Aura and Triana/EPIC)

Variability of UV irradiance in Europe

The diurnal and annual variability of solar UV radiation in Europe is described for different latitudes, seasons and different biologic weighting functions. For the description of this variability under cloudless skies the widely used onedimensional version of the radiative transfer model UVSPEC is used. We reconfirm that the major factor influencing the diurnal and annual variability of UV irradiance is solar elevation. While ozone is a strong absorber of UV radiation its effect is relatively constant when compared with the temporal variability of clouds. We show the significant role that clouds play in modifying the UV climate by analyzing erythemal irradiance measurements from 28 stations in Europe in summer. On average, the daily erythemal dose under cloudless skies varies between 2.2 kJ m-2 at 70N and 5.2 kJ m-2 at 35N, whereas these values are reduced to 1.5–4.5 kJ m-2 if clouds are included. Thus clouds significantly reduce the monthly UV irradiation, with the smallest reductions, on average, at lower latitudes, which corresponds to the fact that it is often cloudless in the Mediterranean area in summer