State of Climate 2011 - Global Ocean Phytoplankton

Phytoplankton photosynthesis in the sun lit upper layer of the global ocean is the overwhelmingly dominant source of organic matter that fuels marine ecosystems. Phytoplankton contribute roughly half of the global (land and ocean) net primary production (NPP; gross photosynthesis minus plant respiration) and phytoplankton carbon fixation is the primary conduit through which atmospheric CO2 concentrations interact with the ocean s carbon cycle. Phytoplankton productivity depends on the availability of sunlight, macronutrients (e.g., nitrogen, phosphorous), and micronutrients (e.g., iron), and thus is sensitive to climate-driven changes in the delivery of these resources to the euphotic zon

GOMOS O₃, NO₂, and NO₃ observations in 2002–2008

The Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument onboard the European Space Agency's ENVISAT satellite measures ozone, NO₂, NO₃, H₂O, O₂, and aerosols using the stellar occultation method. Global coverage, good vertical resolution and the self-calibrating measurement method make GOMOS observations a promising data set for building various climatologies and time series. In this paper we present GOMOS nighttime measurements of ozone, NO₂, and NO₃ during six years 2002–2008. Using zonal averages we show the time evolution of the vertical profiles as a function of latitude. In order to get continuous coverage in time we restrict the latitudinal region to 50° S–50° N. Time development is analysed by fitting constant, annual and semi-annual terms as well as solar and QBO proxies to the daily time series. Ozone data cover the stratosphere, mesosphere and lower thermosphere (MLT). NO₂ and NO₃ data cover the stratosphere. In addition to detailed analysis of profiles we derive total column distributions using the fitted time series. <br><br> The time-independent constant term is determined with a good accuracy (better than 1%) for all the three gases. The median retrieval accuracy for the annual and semi-annual term varies in the range 5–20%. For ozone the annual terms dominate in the stratosphere giving early winter ozone maxima at mid-latitudes. Above the ozone layer the annual terms change the phase which results in ozone summer maximum up to 80 km. In the MLT the annual terms dominate up to 80 km where the semiannual terms start to grow. In the equatorial MLT the semi-annual terms dominate the temporal evolution whereas in the mid-latitude MLT annual and semi-annual terms compete evenly. In the equatorial stratosphere the QBO dominates the time development but the solar term is too weak to be determined. In the MLT above 85 km the solar term grows significantly and ozone has 15–20% dependence on the solar cycle. For NO₂ below 32 km the annual summer maxima dominates at mid-latitudes whereas in the equatorial region a strong QBO prevails. In northern mid-latitudes a strong solar term appears in the upper stratosphere. For NO₃ the annual variation dominates giving rise to summer maxima. The NO₃ distribution is controlled by temperature and ozone

Assessing Greenhouse Gas Monitoring Capabilities Using SolAtmos End-to-End Simulator: Application to the Uvsq-Sat NG Mission

International audienceMonitoring atmospheric concentrations of greenhouse gases (GHGs) like carbon diox- ide and methane in near real time and with good spatial resolution is crucial for enhancing our understanding of the sources and sinks of these gases. A novel approach can be proposed using a con- stellation of small satellites equipped with miniaturized spectrometers having a spectral resolution of a few nanometers. The objective of this study is to describe expected results that can be obtained with a single satellite named Uvsq-Sat NG. The SolAtmos end-to-end simulator and its three tools (IRIS, OptiSpectra, and GHGRetrieval) were developed to evaluate the performance of the spectrometer of the Uvsq-Sat NG mission, which focuses on measuring the main GHGs. The IRIS tool was imple- mented to provide Top-Of-Atmosphere (TOA) spectral radiances. Four scenes were analyzed (pine forest, deciduous forest, ocean, snow) combined with different aerosol types (continental, desert, maritime, urban). Simulated radiance spectra were calculated based on the wavelength ranges of the Uvsq-Sat NG, which spans from 1200 to 2000 nm. The OptiSpectra tool was used to determine optimal observational settings for the spectrometer, including Signal-to-Noise Ratio (SNR) and integration time. Data derived from IRIS and OptiSpectra served as input for our GHGRetrieval simulation tool, developed to provide greenhouse gas concentrations. The Levenberg–Marquardt algorithm was applied iteratively to ne-tune gas concentrations and model inputs, aligning observed transmittance functions with simulated ones under given environmental conditions. To estimate gas concentrations (CO2 , CH4 , O2 , H2 O) and their uncertainties, the Monte Carlo method was used. Based on this analysis, this study demonstrates that a miniaturized spectrometer onboard Uvsq-Sat NG is capable of observing different scenes by adjusting its integration time according to the wavelength. The expected precision for each measurement is of the order of a few ppm for carbon dioxide and less than 25 ppb for methane

Retrieval of atmospheric parameters from GOMOS data

International audienceThe Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument on board the European Space Agency's ENVISAT satellite measures attenuation of stellar light in occultation geometry. Daytime measurements also record scattered solar light from the atmosphere. The wavelength regions are the ultraviolet-visible band 248-690 nm and two infrared bands at 755-774 nm and at 926-954 nm. From UV-Visible and IR spectra the vertical profiles of O3, NO2, NO3, H2O, O2 and aerosols can be retrieved. In addition there are two 1 kHz photometers at blue 473-527 nm and red 646-698 nm. Photometer data are used to correct spectrometer measurements for scintillations and to retrieve high resolution temperature profiles as well as gravity wave and turbulence parameters. Measurements cover altitude region 5-150 km. Atmospherically valid data are obtained in 15-100 km. In this paper we present an overview of the GOMOS retrieval algorithms for stellar occultation measurements. The low signal-to-noise ratio and the refractive effects due to the point source nature of stars have been important drivers in the development of GOMOS retrieval algorithms. We present first the Level 1b algorithms that are used to correct instrument related disturbances in the spectrometer and photometer measurements The Level 2 algorithms deal with the retrieval of vertical profiles of atmospheric gaseous constituents, aerosols and high resolution temperature. We divide the presentation into correction for refractive effects, high resolution temperature retrieval and spectral/vertical inversion. The paper also includes discussion about the GOMOS algorithm development, expected improvements, access to GOMOS data and alternative retrieval approaches

GOMOS data characterization and error estimation

International audienceThe Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument uses stellar occultation technique for monitoring ozone and other trace gases in the stratosphere and mesosphere. The self-calibrating measurement principle of GOMOS together with a relatively simple data retrieval where only minimal use of a priori data is required, provides excellent possibilities for long term monitoring of atmospheric composition. GOMOS uses about 180 brightest stars as the light source. Depending on the individual spectral characteristics of the stars, the signal-to-noise ratio of GOMOS is changing from star to star, resulting also varying accuracy to the retrieved profiles. We present the overview of the GOMOS data characterization and error estimation, including modeling errors, for ozone, NO2, NO3 and aerosol profiles. The retrieval error (precision) of the night time measurements in the stratosphere is typically 0.5-4% for ozone, about 10-20% for NO2, 20-40% for NO3 and 2-50% for aerosols. Mesospheric O3, up to 100 km, can be measured with 2-10% precision. The main sources of the modeling error are the incompletely corrected atmospheric turbulence causing scintillation, inaccurate aerosol modeling, uncertainties in cross sections of the trace gases and in the atmospheric temperature. The sampling resolution of GOMOS varies depending on the measurement geometry. In the data inversion a Tikhonov-type regularization with pre-defined target resolution requirement is applied leading to 2-3 km resolution for ozone and 4 km resolution for other trace gases

Simultaneous measurements of OClO, NO₂ and O₃ in the Arctic polar vortex by the GOMOS instrument

International audienceWe present the first nighttime measurements of OClO from a limb-viewing satellite instrument in the Arctic polar vortex. The relationship between OClO, NO2 and O3 slant column densities in the Arctic polar vortex are analyzed from the GOMOS measurements. The retrieval process is based on a differential optical absorption spectroscopy (DOAS) method applied on the weighted median GOMOS transmittances. A study of the longitudinal distributions of OClO, NO2 and O3 above 65° north in January 2008 is presented. It shows a strong halogen activation in the lower stratosphere and a strong denoxification in the entire stratosphere inside the Arctic polar vortex. Time series of temperatures and OClO, NO2 and O3 slant column densities for the winters 2002/2003 to 2007/2008 are also presented. They highlight the correlation between temperature, OClO and NO2. The GOMOS instrument appears to be a very suitable instrument for the monitoring of OClO, NO2 and O3 in the stratosphere during nighttime

Global measurement of the mesospheric sodium layer by the star occultation instrument GOMOS

International audienceWe present the first global measurement of the sodium mesospheric layer obtained from the processing of about 100 000 star occultations by the GOMOS instrument onboard the ENVISAT satellite. The retrieval method is developed on the basis of a simple DOAS retrieval applied to averaged transmittances. The vertical inversion of the sodium slant path optical thickness is performed by using a modified Gaussian extinction profile. A global climatology is derived by using monthly bins of 20 degrees in latitude. The high variability of the sodium layer is confirmed on a global scale as well as the presence of an important modulation in the annual cycle. Also, we present some evidence for the existence of a diurnal cycle characterized by an increase of the sodium concentration in daylight