SCIENTIFIC SPONSORSHIP STATEMENT ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ This document describes the spectral measurement of UV radiation (1991 to present) and total ozone column (2000 to present) at Reading and total ozone column in Manchester (2000 - present). The University of Manchester* is responsible for instruments at both sites, observations at Reading are made on behalf of the UK Department for Environment, Food and Rural Affairs (DEFRA). Spectral Global Irradiance at Reading (51.44N 0.94W) ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ The early spectral data for the Reading site are from Optronic Laboratories 742 spectroradiometers.Two virtually identical spectroradiometers, maintained as distinct entities, were used in the data collection. The majority of the data were collected with a single instrument, but this was exchanged for significant periods when repair or other demands on the main monitoring instrument deemed the change necessary. The two instruments were calibrated on the same sources, and operated in the same manner, and no distinction is made between the two in the data record. The Optronics data should be regarded in two sections, pre- and post-1993, for other reasons. Pre-1993 measurements were made on an intermittent basis, predominantly under clear sky conditions, with an instrument transported to the measurement site before each set of measurements, infrequently calibrated, and with incomplete temperature stabilisation. The format of the scans and data files had not been standardised, and much of the data was gathered using the original Optronics diffuser mounted on the spectroradiometer body. These early data are subject to greater uncertainties than the later measurements, and will not be discussed here. Details are available on request. Since January 1993 the monitoring spectroradiometer has been deployed in the following fashion. The body of the spectroradiometer, which includes the photomultiplier tube detector, is mounted in a temperature stabilised chamber, (to within ħ 0.2şC). The temperature sensitivity of the instrument is approximately 1% per şC. The chamber is mounted on a jacking system and raised up beneath the roof of the monitoring hut. A 1 metre quartz fibre light guide, mounted in a retractable tube, connects the entrance port of the spectroradiometer with a teflon diffuser mounted on the roof of the hut. For calibration the whole chamber-fibre-diffuser assembly is lowered to the floor of the hut and secured in a calibration jig which provides a fixed geometry between diffuser and calibration lamp. Calibration in situ was made with 200W lamps, operated with a horizontal filament and fixed in a calibration mount supplied by Optronic Laboratories, which was in turn mounted over the diffuser in the calibration jig. The 200W lamps are transfer standards, calibrated in Manchester against 1000W FEL lamps traceable to the US National Institute of Standards and Technology (NIST) with calibration by Optronics. A calibration check is performed every 2-3 weeks using the 200W lamp, which is itself calibrated every 6 months, or more frequently if required. A suite of 200W calibration lamps has now been employed, since the main calibration laboratory has moved from the Reading site. The wavelength alignment of the spectroradiometer is checked before each calibration using a mercury lamp. The wavelength control setting is in steps of 0.1nm, and is repeatable within one step. The wavelength setting of the instrument, within these constraints, has proved very stable. Throughout 1993, the wavelength alignment was set before every scan by reference to the Fraunhofer lines of the sun. However, this process can be disturbed in changing cloud conditions (which occur frequently), resulting in an erroneous wavelength setting for the following scan. Data affected in this way are relatively easy to identify, but the procedure was leading to significant loss of data and was eventually discontinued. All spectra recorded have been passed through the SHICrivm quality assurance process (Slaper et al, 1995), which corrects spectra for wavelength dependent wavelength shifts and calculates a standardised spectrum for a 1nm FWHM triangular slit function. Furthermore, any spectra with low irradiance levels, spikes and other spectral anomolies are identified and flagged. The process spectra are then passed through the SHICrivm algorithm a second time and only those with favourable (only green and yellow) flags are retained, before the files are converted to WOUDC format. The Optronics spectroradiometer ceased operation in 2003 (last data submitted to WOUDC is for 2002), but since 1999 a new instrument, a Bentham DM-150, was run alongside it. This period of overlap allowed the data series to be homogenised to account for the poorer cosine response for the Optronics global irradiance diffuser, resulting in a wavelength and SZA independent increase of 11%. The DM-150 instrument is run in a similar fashion to the Optronics. It is housed in a temperature stabilised envirobox, with a fibre optic leading to the roof mounted global irradiance optics. This optical head is connected to a closed system whereby air is pumped continuously through a desiccant trap. This desiccant is checked daily at 0900UTC; at the same time the optics are cleaned. The instrument is calibrated in situ with 200W lamps every month, these being calibrated in Manchester against 1000W FEL lamps traceable to NIST on a c. annual basis. A wavelength calibration was carried out before each absolute calibration for the early years' data, but more recently this adjusted with reference to the output from SHICrivm. As with the Optronics data, all spectra are passed through the SHICrivm algorithm twice, once to produce the standardised spectra for a 1nm FWHM triangular slit function, with any wavelength shifts adjusted (beforehand these are typically < 0.02nm), and a second time to check the quality of the processed spectra. Again only those spectra with the highest quality flags for all aspects are formatted and submitted to WOUDC. Further the Bentham DM-150 instrument uses adaptive integration rather then fixed time intervals to reduce noise at the shortest wavelengths. For both spectral instruments the timestamp is the time that the first wavelength was measured, typically on the half hour. Total Ozone Column at Manchester (53.47N 2.23W) and Reading (51.44N 0.94W) ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ In 2000, Brewer MkIV spectrophotometer #075 was installed at the Reading site. This instrument was formerly based at Cambourne, under the stewardship of the UK Meteorological Office. In the same year Brewer MkIII spectrometer #172 was installed at Manchester, with its initial calibration being carried out by the manufacturers. The two instruments then have the same calibration history, briefly this is as follows: May 2002 Manchester, UK Apr 2004 Manchester, UK Sep 2005 El Arensillo, Spain Sep 2007 El Arensillo, Spain The total ozone column data uses interpolated values for the ETCs and datum standard lamp ratios where possible, except in cases of a known step change. Daily variations in the standard lamp are corrected and individual measurements rejected with standard deviations greater than 2.5DU (DS), or 4.0DU (ZS), or for airmass values greater than 4.0 (for the single monochromator #075), or 6.0 (for the double monochromator #172). 24 July 2008 References ŻŻŻŻŻŻŻŻŻŻ Slaper,H., Reinen,HAJM., Blumthaler,M. Huber,M. and Kuik,F. (1995) Comparing ground-level spectrally resolved solar UV measurements using various instruments: A technique resolving effects of wavelength shift and slit width. Geophys Res Lett 22, 2721-2724. _______________________________ * Support and responsibility for the monitoring was originally based at Reading, but moved to UMIST in 1995. In 2004 UMIST became part of the University of Manchester. Procedures now undertaken at (and refered to as) the University of Manchester were conducted at Reading until mid-1995.