Description: During two cruises wiht RV Sonne, SO234-2 from 8 to 19 July 2014 (Durban, South Africa to Port Louis, Mauritius) and SO235 from 23 July to 7 August 2014 (Port Louis, Mauritius to Malé, Maldives), within the SPACES (Science Partnerships for the Assessment of Complex Earth System Processes) and OASIS (Organic very short-lived Substances and their air sea exchange from the Indian Ocean to the Stratosphere) research projects, surface water samples were sampled from a continuous running pump in the hydrographic shaft of RV Sonne at a depth of 5 m. Deep water samples were taken from a Niskin-bottle rosette sampler. The samples were then analyzed for halogenated compounds using a purge and trap system onboard, which was attached to a gas chromatograph with an electron capture detector for surface water samples and a GC/MS Agilent 5975 for the deep water samples. An analytical reproducibility of 10% was determined from measuring duplicate water samples, detection limit was 0.2 pmol /L. Calibration was performed with several dilutions of a mixed-compound standard prepared in methanol.

Description: A quality assessment of the CFC-11 (CCl3F), CFC-12 (CCl2F2), HF, and SF6 products from limb-viewing satellite instruments is provided by means of a detailed intercomparison. The climatologies in the form of monthly zonal mean time series are obtained from HALOE, MIPAS, ACE-FTS, and HIRDLS within the time period 1991-2010. The intercomparisons focus on the mean biases of the monthly and annual zonal mean fields and aim to identify their vertical, latitudinal and temporal structure. The CFC evaluations (based on MIPAS, ACE-FTS and HIRDLS) reveal that the uncertainty in our knowledge of the atmospheric CFC-11 and CFC-12 mean state, as given by satellite data sets, is smallest in the tropics and mid-latitudes at altitudes below 50 and 20 hPa, respectively, with a 1sigma multi-instrument spread of up to ±5 %. For HF, the situation is reversed. The two available data sets (HALOE and ACE-FTS) agree well above 100 hPa, with a spread in this region of ±5 to ±10 %, while at altitudes below 100 hPa the HF annual mean state is less well known, with a spread ±30 % and larger. The atmospheric SF6 annual mean states derived from two satellite data sets (MIPAS and ACE-FTS) show only very small differences with a spread of less than ±5 % and often below ±2.5 %. While the overall agreement among the climatological data sets is very good for large parts of the upper troposphere and lower stratosphere (CFCs, SF6) or middle stratosphere (HF), individual discrepancies have been identified. Pronounced deviations between the instrument climatologies exist for particular atmospheric regions which differ from gas to gas. Notable features are differently shaped isopleths in the subtropics, deviations in the vertical gradients in the lower stratosphere and in the meridional gradients in the upper troposphere, and inconsistencies in the seasonal cycle. Additionally, long-term drifts between the instruments have been identified for the CFC-11 and CFC-12 time series. The evaluations as a whole provide guidance on what data sets are the most reliable for applications such as studies of atmospheric transport and variability, model-measurement comparisons and detection of long-term trends.

Description: Halocarbons, halogenated short-chained hydrocarbons, are produced naturally in the oceans by biological and chemical processes. They are emitted from surface seawater into the atmosphere, where they take part in numerous chemical processes such as ozone destruction and the oxidation of mercury and dimethyl sulfide. Here we present oceanic and atmospheric halocarbon data for the Peruvian upwelling obtained during the M91 cruise onboard the research vessel Meteor in December 2012. Surface waters during the cruise were characterized by moderate concentrations of bromoform (CHBr3) and dibromomethane (CH2Br2) correlating with diatom biomass derived from marker pigment concentrations, which suggests this phytoplankton group as likely source. Concentrations measured for the iodinated compounds methyl iodide (CH3I) of up to 35.4 pmol L-1, chloroiodomethane (CH2ClI) of up to 58.1 pmol L-1 and diiodomethane (CH2I2) of up to 32.4 pmol L-1 in water samples were much higher than previously reported for the tropical Atlantic upwelling systems. Iodocarbons also correlated with the diatom biomass and even more significantly with dissolved organic matter (DOM) components measured in the surface water. Our results suggest a biological source of these compounds as significant driving factor for the observed large iodocarbon concentrations. Elevated atmospheric mixing ratios of CH3I (up to 3.2 ppt), CH2ClI (up to 2.5 ppt) and CH2I2 (3.3 ppt) above the upwelling were correlated with seawater concentrations and high sea-to-air fluxes. The enhanced iodocarbon production in the Peruvian upwelling contributed significantly to tropospheric iodine levels.

Description: A comprehensive quality assessment of the ozone products from 18 limb-viewing satellite instruments is provided by means of a detailed inter-comparison. The ozone climatologies in the form of monthly zonal mean time series covering the upper troposphere to lower mesosphere are obtained from LIMS, SAGE I, SAGE II, UARS-MLS, HALOE, POAM II, POAM III, SMR, OSIRIS, SAGE III, MIPAS, GOMOS, SCIAMACHY, ACE-FTS, ACE-MAESTRO, Aura-MLS, HIRDLS, and SMILES within 1978-2010. The inter-comparisons focus on mean biases based on monthly and annual zonal mean fields, on inter-annual variability and on seasonal cycles. Additionally, the physical consistency of the data sets is tested through diagnostics of the quasi-biennial oscillation and the Antarctic ozone hole. The comprehensive evaluations reveal that the uncertainty in our knowledge of the atmospheric ozone mean state is smallest in the tropical middle stratosphere and in the midlatitude lower/middle stratosphere, where we find a 1σ multi-instrument spread of less than ±5%. While the overall agreement among the climatological data sets is very good for large parts of the stratosphere, individual discrepancies have been identified including unrealistic month-to-month fluctuations, large biases in particular atmospheric regions, or inconsistencies in the seasonal cycle. Notable differences between the data sets exist in the tropical lower stratosphere and at high latitudes, with a multi-instrument spread of ±30% at the tropical tropopause and ±15% at polar latitudes. In particular, large relative differences are identified in the Antarctic polar cap during the time of the ozone hole, with a spread between the monthly zonal mean fields of ±50%. Differences between the climatological data sets are suggested to be partially related to inter-instrumental differences in vertical resolution and geographical sampling. The evaluations as a whole provide guidance on what data sets are the most reliable for applications such as studies of ozone variability, model-measurement comparisons and detection of long-term trends. A detailed comparison versus SAGE II data is presented, which can help identify suitable candidates for long-term data merging studies.

Description: We present the first comprehensive intercomparison of currently available satellite ozone climatologies in the upper troposphere/lower stratosphere (UTLS) (300-70hPa) as part of the Stratosphere-troposphere Processes and their Role in Climate (SPARC) Data Initiative. The Tropospheric Emission Spectrometer (TES) instrument is the only nadir-viewing instrument in this initiative, as well as the only instrument with a focus on tropospheric composition. We apply the TES observational operator to ozone climatologies from the more highly vertically resolved limb-viewing instruments. This minimizes the impact of differences in vertical resolution among the instruments and allows identification of systematic differences in the large-scale structure and variability of UTLS ozone. We find that the climatologies from most of the limb-viewing instruments show positive differences (ranging from 5 to 75%) with respect to TES in the tropical UTLS, and comparison to a zonal mean ozonesonde climatology indicates that these differences likely represent a positive bias for p100hPa. In the extratropics, there is good agreement among the climatologies regarding the timing and magnitude of the ozone seasonal cycle (differences in the peak-to-peak amplitude of 〈15%) when the TES observational operator is applied, as well as very consistent midlatitude interannual variability. The discrepancies in ozone temporal variability are larger in the tropics, with differences between the data sets of up to 55% in the seasonal cycle amplitude. However, the differences among the climatologies are everywhere much smaller than the range produced by current chemistry-climate models, indicating that the multiple-instrument ensemble is useful for quantitatively evaluating these models.

Description: Monthly zonal mean climatologies of atmospheric measurements from satellite instruments can have biases due to the non-uniform sampling of the atmosphere by the instruments. We characterize potential sampling biases in stratospheric trace gas climatologies of the Stratospheric Processes and their Role in Climate (SPARC) Data Initiative using chemical fields from a chemistry climate model simulation and sampling patterns from 16 satellite-borne instruments. The exercise is performed for the long-lived stratospheric trace gases O3 and H2O. Monthly sample biases for O3 exceed 10% for many instruments in the high latitude stratosphere and in the upper troposphere/lower stratosphere, while annual mean sampling biases reach values of up to 20% in the same regions for some instruments. Sampling biases for H2O are generally smaller than for O3, although still notable in the upper troposphere/lower stratosphere and Southern Hemisphere high latitudes. The most important mechanism leading to monthly sampling bias is the non-uniform temporal sampling of many instruments, i.e., the fact that for many instruments, monthly means are produced from measurements which span less than the full month in question. Similarly, annual mean sampling biases are well explained by non-uniformity in the month-to-month sampling by different instruments. Non-uniform sampling in latitude and longitude are shown to also lead to non-negligible sampling biases, which are most relevant for climatologies which are otherwise free of sampling biases due to non-uniform temporal sampling.

Description: Within the SPARC Data Initiative, the first comprehensive assessment of the quality of 13 water vapor products from 11 limb-viewing satellite instruments (LIMS, SAGE II, UARS-MLS, HALOE, POAM III, SMR, SAGE III, MIPAS, SCIAMACHY, ACE-FTS, and Aura-MLS) obtained within the time period 1978-2010 has been performed. Each instrument's water vapor profile measurements were compiled into monthly zonal mean time series on a common latitude-pressure grid. These time series serve as basis for the ‘climatological’ validation approach used within the project. The evaluations include comparisons of monthly or annual zonal mean cross-sections and seasonal cycles in the tropical and extra-tropical upper troposphere and lower stratosphere averaged over one or more years, comparisons of inter-annual variability, and a study of the time evolution of physical features in water vapor such as the tropical tape recorder and polar vortex dehydration. Our knowledge of the atmospheric mean state in water vapor is best in the lower and middle stratosphere of the tropics and mid-latitudes, with a relative uncertainty of ±2-6% (as quantified by the standard deviation of the instruments’ multi-annual means). The uncertainty increases towards the polar regions (±10-15%), the mesosphere (±15%), and the upper troposphere/lower stratosphere below 100 hPa (±30-50%), where sampling issues add uncertainty due to large gradients and high natural variability in water vapor. The minimum found in multi-annual (1998-2008) mean water vapor in the tropical lower stratosphere is 3.5 ppmv (±14%), with slightly larger uncertainties for monthly mean values. The frequently used HALOE water vapor dataset shows consistently lower values than most other datasets throughout the atmosphere, with increasing deviations from the multi-instrument mean below 100 hPa in both the tropics and extra-tropics. The knowledge gained from these comparisons and regarding the quality of the individual datasets in different regions of the atmosphere will help to improve model-measurement comparisons (e.g. for diagnostics such as the tropical tape recorder or seasonal cycles), data merging activities, and studies of climate variability.