Arctic polar stratospheric cloud measurements by means of a four wavelength depolarization lidar

A four wavelength depolarization backscattering lidar has been operated during the European Arctic Stratospheric Ozone Experiment (EASOE) in Sodankyl, in the Finnish Arctic. The lidar performed measurements during the months of December 1991, January, February and March 1992. The Finnish Meteorological Institute during the same period launched regularly three Radiosondes per day, and three Ozone sondes per week. Both Mt. Pinatubo aerosols and Polar Stratospheric Clouds were measured. The use of four wavelengths, respectively at 355 nm, 532 nm , 750 nm, and 850 nm permits an inversion of the lidar data to determine aerosol particle size. The depolarization technique permits the identification of Polar Stratospheric Clouds. Frequent correlation between Ozone minima and peaks in the Mt. Pinatubo aerosol maxima were detected. Measurements were carried out both within and outside the Polar Vortex

The 1991 WMO ozone sonde intercomparison

The WMO ozone sonde intercomparison was held at Vanscoy, Saskatchewan from May 13 to May 24, 1991. The purpose of the intercomparison is to evaluate the performance of various ozone sonde types used operationally in the Global Ozone Observing System and to ensure that the accuracy and precision of the measurements are sufficient to detect long-term trends in stratospheric ozone. The intercomparison was sponsored by WMO and hosted by the Atmospheric Environment Service (AES) of Canada. It was attended by scientists from six countries: Canada, Finland, Germany, India, Japan and USA. A total of 10 balloon payloads were launched each carrying 7 or 8 sondes for a total of 67 successful ozone sonde flights. The payloads were carried to altitudes between 35 and 40 km where the flights terminated by balloon burst. Results of the profile measurements made during the series of the profile measurements made during the series of flight are used to determine statistically meaningful evaluations of the different sonde types. A description of the payload and the different ozone sondes is given. Preliminary results of the profile measurements and an evaluation of the performance of the sonde types are presented

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

PURE ROTATIONAL SPECTRA OF H217OH_{2}^{17}O AND H218OH_{2}^{18}O BETWEEN 50CM−150 CM^{-1} AND 730CM−1730 CM^{-1}

$^{1}$J. Kauppinen, Acta Univ. Oul. A38 (1975); Appl. Opt. 14, 1987 (1975). $^{2}$J. Kauppinen, Appl. Opt. 18, 1788 (1979).Author Institution:The pure rotational infrared spectrum of a mixture of $H_{2}^{16}O, H_{2}^{17}O$, and $H_{2}^{18}O$ was measured with a resolution of 0.010$cm^{-1}$. The spectrum was recorded on the Fourier transform spectrometer [1,2] constructed at the University of Oulu. The region $50 cm^{-1}-730$ $cm^{-1}$ was recorded in three parts using beam splitters $12\mu$ m, $5\mu$ m, and 2.5 $\mu m$ in thickness. The abundances of $H_{2}^{16}O, H_{2}^{17}O$, and $H_{2}^{18}O$ in the sample were about 47%, 24% 29% respectively. The accuracy of the observed line positions is better than 0.001$cm^{-1}$ for unblended lines. About 1100 lines were assigned in the spectrum. The measured frequencies of $H_{2}^{16}O$ were compared with frequencies calculated from rotational energy levels given in the literature. The measured line positions of $H_{2}^{17}O$ and $H_{2}^{18}O$ were compared with values calculated from the rotation and distortion constants given in the literature. In the case of $H_{2}^{17}O$, and $H_{2}^{18}O$ we found differences greater than $1 cm^{-1}$ between the observed and calculated wavenumbers. New rotation and distortion constants, and rotational energy levels for $H_{2}^{17}O$, and $H_{2}^{18}O$ were calculated from the Observed frequencies

PSC and volcanic aerosol observations during EASOE by UV-visible ground-based spectrometry

International audienceTwilight sky colour measurements were made using ground-based UV-visible SAOZ spectrometers at four stations along the Arctic circle during EASOE. The results show that volcanic aerosol from the Pinatubo eruption of June 1991 first appeared above the Arctic in September 1991. The aerosol layer thickened progressively during the autumn and had spread to all four stations, outside in the very low stratosphere, as well as inside the polar vortex, by mid-January. For the rest of the campaign, to mid-March, little further change was seen. The aerosol would have masked any PSCs that may have occurred at altitudes less than 22 km. However, PSCs at higher altitudes should have been detected, had their optical thickness exceeded 0.01. Only one was recorded during EASOE: on 28–29 December 1991, in contrast to their frequent occurrence in January and early February 1990

Ten years of NO2 comparisons between ground-based SAOZ and satellite instruments (GOME, SCIAMACHY, OMI)

SAOZ (Systeme d'Analyse par Observations Zenithales) is a ground-based UV-Visible zenith-sky spectrometer installed between 1988 and 1995 at a number of NDSC stations at various latitudes on the globe. The instrument is providing ozone and NO2 vertical columns at sunrise and sunset using the Differential Optical Absorption Spectroscopy (DOAS) technique in the visible spectral range. The ERS-2 GOME Ozone Monitoring Experiment (GOME) in 1995 was the first satellite mission to provide a global picture of atmospheric NO 2 with reasonable spatial and temporal resolution. It was then followed by SCanning ImAging spectroMeter for Atmospheric ChartographY (SCIAMACHY) onboard ENVISAT in 2002, and Ozone Monitoring Instrument (OMI) onboard EOS-AURA in 2004, with a similar capacity to monitor total NO 2. All these instruments are nadir viewing mapping spectrometers, applying the DOAS technique in the visible for deriving the NO2 total column. Here we present the results of NO2 long-term comparisons between GOME and SAOZ for the whole period of GOME operation since 1995 at all latitudes - tropics, mid-latitudes and polar regions - in both hemispheres. Comparisons are also shown with the most recently available SCIAMACHY and OMI data in 2004-2005. Overall, the daytime satellite measurements (around noon) are found consistent with sunrise ground-based data, with an average smaller difference at the tropics and mid-latitudes than in the polar areas in the summer. The agreement is even improved after correcting for the NO2 photochemical change between sunrise and the satellite overpass using a box model. However, some seasonal dependence of the difference between ground-based and satellite total NO2 still remains, related to the accuracy of photochemical simulations and the set of NO2 air mass factors used in the retrievals of both systems

Carbon dioxide balance of a fen ecosystem in northern Finland under elevated UV-B radiation

The effect of elevated UV-B radiation on CO2 exchange of a natural flark fen was studied in open-field conditions during 2003-2005. The experimental site was located in SodankylA in northern Finland (67 degrees 22'N, 26 degrees 38'E, 179 m a.s.l.). Altogether 30 study plots, each 120 cm x 120 cm in size, were randomly distributed between three treatments (n=10): ambient control, UV-A control and UV-B treatment. The UV-B-treated plots were exposed to elevated UV-B radiation level for three growing seasons. The instantaneous net ecosystem CO2 exchange (NEE) and dark respiration (R-TOT) were measured during the growing season using a closed chamber method. The wintertime CO2 emissions were estimated using a gradient technique by analyzing the CO2 concentration in the snow pack. In addition to the instantaneous CO2 exchange, the seasonal CO2 balances during the growing seasons were modeled using environmental data measured at the site. In general, the instantaneous NEE at light saturation was slightly higher in the UV-B treatment compared with the ambient control, but the gross photosynthesis was unaffected by the exposure. The R-TOT was significantly lower under elevated UV-B in the third study year. The modeled seasonal (June-September) CO2 balance varied between the years depending on the ground water level and temperature conditions. During the driest year, the seasonal CO2 balance was negative (net release of CO2) in the ambient control and the UV-B treatment was CO2 neutral. During the third year, the seasonal CO2 uptake was 43 +/- 36 g CO2-C m(-2) in the ambient control and 79 +/- 45 g CO2-C m(-2) in the UV-B treatment. The results suggest that the long-term exposure to high UV-B radiation levels may slightly increase the CO2 accumulation to fens resulting from a decrease in microbial activity in peat. However, it is unlikely that the predicted development of the level of UV-B radiation would significantly affect the CO2 balance of fen ecosystems in future

Ozone profiles in the high-latitude stratosphere and lower mesosphere measured by the Improved Limb Atmospheric Spectrometer (ILAS)-II: Comparison with other satellite sensors and ozonesondes

A solar occultation sensor, the Improved Limb Atmospheric Spectrometer (ILAS)-II, measured 5890 vertical profiles of ozone concentrations in the stratosphere and lower mesosphere and of other species from January to October 2003. The measurement latitude coverage was 54–71°N and 64–88°S, which is similar to the coverage of ILAS (November 1996 to June 1997). One purpose of the ILAS-II measurements was to continue such high-latitude measurements of ozone and its related chemical species in order to help accurately determine their trends. The present paper assesses the quality of ozone data in the version 1.4 retrieval algorithm, through comparisons with results obtained from comprehensive ozonesonde measurements and four satellite-borne solar occultation sensors. In the Northern Hemisphere (NH), the ILAS-II ozone data agree with the other data within ±10% (in terms of the absolute difference divided by its mean value) at altitudes between 11 and 40 km, with the median coincident ILAS-II profiles being systematically up to 10% higher below 20 km and up to 10% lower between 21 and 40 km after screening possible suspicious retrievals. Above 41 km, the negative bias between the NH ILAS-II ozone data and the other data increases with increasing altitude and reaches 30% at 61–65 km. In the Southern Hemisphere, the ILAS-II ozone data agree with the other data within ±10% in the altitude range of 11–60 km, with the median coincident profiles being on average up to 10% higher below 20 km and up to 10% lower above 20 km. Considering the accuracy of the other data used for this comparative study, the version 1.4 ozone data are suitably used for quantitative analyses in the high-latitude stratosphere in both the Northern and Southern Hemisphere and in the lower mesosphere in the Southern Hemisphere

Coordinated ground-based validation of ENVISAT atmospheric chemistry with NDSC network data : Commissioning phase report

International audienceIn the framework of the coordinated project called CINAMON, a list of ground-based stations associated with the Network for the Detection of Stratospheric Change (NDSC) contribute to the quasi-global validation of ENVISAT atmospheric chemistry data. This paper reports on such activities performed during the Commissioning Phase (CP) of the satellite. After a description of the correlative database generated during this period, preliminary ground-based studies relying on this database give a first picture of the quality of SCIAMACHY ozone and nitrogen dioxide columns, and GOMOS and MIPAS ozone profiles. Illustration of the global mapping of MIPAS ozone profile data is also presented. The paper concludes with perspectives for the Main Validation Phase of ENVISAT