F. Hase

Dynamic Processes Governing Lower-Tropospheric HDO/H2O Ratios as Observed from Space and Ground

Cycling Around Water vapor is the most important greenhouse gas, and clouds are one of the most important components of climate, but the global hydrological cycle is still poorly-enough understood that the atmospheric cycling of water and cloud formation are inadequately represented in global climate models. As the transformation from liquid into vapor tends to deplete water of the isotope deuterium, Frankenburg et al. (p. 1374) were able to use satellite measurements of global “heavy” water abundances to provide a deeper understanding of atmospheric water dynamics. Tropospheric distributions of light and heavy water reveal previously unrecognized features of atmospheric circulation. The hydrological cycle and its response to environmental variability such as temperature changes is of prime importance for climate reconstruction and prediction. We retrieved deuterated water/water (HDO/H2O) abundances using spaceborne absorption spectroscopy, providing an almost global perspective on the near-surface distribution of water vapor isotopologs. We observed an unexpectedly high HDO/H2O seasonality in the inner Sahel region, pointing to a strong isotopic depletion in the subsiding branch of the Hadley circulation and its misrepresentation in general circulation models. An extension of the analysis at high latitudes using ground-based observations of δD¯ and a model study shows that dynamic processes can entirely compensate for temperature effects on the isotopic composition of precipitation.

Sensitivity of trace gas abundances retrievals from infrared limb emission spectra to simplifying approximations in radiative transfer modelling

The accuracy of trace gas abundances retrieved from spectrally resolved infrared limb emission measurements relies, among other things, on the appropriate modelling of radiative transfer through the actual atmosphere. We quantify the mapping of several commonly applied simplifications in radiative transfer modelling on the trace gas abundances retrieval error at the example of the Michelson interferometer for passive atmospheric sounding (MIPAS)/environmental satellite (ENVISAT) space borne Fourier transform infra-red limb emission experiment. The Karlsruhe optimized and precise radiative transfer algorithm (KOPRA) which was used as a tool for this study will be introduced. KOPRA supports accurate modelling of the particular instrument requirements of MIPAS and the observation scenarios during the ENVISAT mission, in particular with respect to its viewing direction and its altitude coverage of the atmosphere. We show that disregarding of horizontal temperature inhomogeneities and non-local thermodynamic equilibrium effects, insufficient accuracy in modelling of field-of-view and apodisation effects, and disregarding individual profiles of isotopic species play the key roles in radiative transfer modelling and lead to systematic retrieval errors which can by far exceed the expected random retrieval error caused by measurement noise.

Long‐term trends of inorganic chlorine from ground‐based infrared solar spectra: Past increases and evidence for stabilization

Long-term time series of hydrogen chloride (HCl) and chlorine nitrate (ClONO2) total column abundances has been retrieved from high spectral resolution ground-based solar absorption spectra recorded with infrared Fourier transform spectrometers at nine NDSC (Network for the Detection of Stratospheric Change) sites in both Northern and Southern Hemispheres. The data sets span up to 24 years and most extend until the end of 2001. The time series of Cl-y (defined here as the sum of the HCl and ClONO2 columns) from the three locations with the longest time-span records show rapid increases until the early 1990s superimposed on marked day-to-day, seasonal and inter-annual variability. Subsequently, the buildup in Cl-y slows and reaches a broad plateau after 1996, also characterized by variability. A similar time evolution is also found in the total chlorine concentration at 55 km altitude derived from Halogen Occultation Experiment (HALOE) global observations since 1991. The stabilization of inorganic chlorine observed in both the total columns and at 55 km altitude indicates that the near-global 1993 organic chlorine (CCly) peak at the Earths surface has now propagated over a broad altitude range in the upper atmosphere, though the time lag is difficult to quantify precisely from the current data sets, due to variability. We compare the three longest measured time series with two-dimensional model calculations extending from 1977 to 2010, based on a halocarbon scenario that assumes past measured trends and a realistic extrapolation into the future. The model predicts broad Cl-y maxima consistent with the long-term observations, followed by a slow Cl-y decline reaching 12-14% relative to the peak by 2010. The data reported here confirm the effectiveness of the Montreal Protocol and its Amendments and Adjustments in progressively phasing out the major man-related perturbations of the stratospheric ozone layer, in particular, the anthropogenic chlorine-bearing source gases. (Less)

Global CO2 fluxes inferred from surface air-sample measurements and from TCCON retrievals of the CO2 total column

We present the first estimate of the global distribution of CO_2 surface fluxes from 14 stations of the Total Carbon Column Observing Network (TCCON). The evaluation of this inversion is based on 1) comparison with the fluxes from a classical inversion of surface air-sample-measurements, and 2) comparison of CO_2 mixing ratios calculated from the inverted fluxes with independent aircraft measurements made during the two years analyzed here, 2009 and 2010. The former test shows similar seasonal cycles in the northern hemisphere and consistent regional carbon budgets between inversions from the two datasets, even though the TCCON inversion appears to be less precise than the classical inversion. The latter test confirms that the TCCON inversion has improved the quality (i.e., reduced the uncertainty) of the surface fluxes compared to the assumed or prior fluxes. The consistency between the surface-air-sample-based and the TCCON-based inversions despite remaining flaws in transport models opens the possibility of increased accuracy and robustness of flux inversions based on the combination of both data sources and confirms the usefulness of space-borne monitoring of the CO_2 column.

Camtracker: a new camera controlled high precision solar tracker system for FTIR-spectrometers

Abstract. A new system to very precisely couple radiation of a moving source into a Fourier Transform Infrared (FTIR) Spectrometer is presented. The Camtracker consists of a homemade altazimuthal solar tracker, a digital camera and a homemade program to process the camera data and to control the motion of the tracker. The key idea is to evaluate the image of the radiation source on the entrance field stop of the spectrometer. We prove that the system reaches tracking accuracies of about 10 arc s for a ground-based solar absorption FTIR spectrometer, which is significantly better than current solar trackers. Moreover, due to the incorporation of a camera, the new system allows to document residual pointing errors and to point onto the solar disk center even in case of variable intensity distributions across the source due to cirrus or haze.

Karlsruhe optimized and precise radiative transfer algorithm. Part I: requirements, justification, and model error estimation

We present the Karlsruhe Optimized and Precise Radiative transfer Algorithm (KOPRA) which has been specifically developed for data analysis of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) going to be launched on ESAs polar-orbiting Environmental Satellite 1 (ENVISAT-1) in 1999. KOPRA has been designed to account for the particular instrument requirements of MIPAS and the observation scenarii during the ENVISAT mission, in particular with respect to the viewing direction and the altitude coverage of the atmosphere. The conceptual details of KOPRA, which reflect the requirements set up by the instrument design details, the observation scenarii, and the link to a retrieval concept with high flexibility, are presented. The forward model error due to discarding individual physical processes and properties of the atmosphere as well as an over-all error budget with respect to these parameters is assessed in order to demonstrate the improvements of retrieval accuracy expected by usage of KOPRA.

Karlsruhe optimized and precise radiative transfer algorithm: II. Interface to retrieval applications

The new Karlsruhe Optimized and Precise Radiative transfer algorithm (KOPRA) is a line-by-line model for use in retrieval processors for atmospheric observations. It simulates IR spectra by taking into account physical properties of the atmospheric observations. It simulates IR spectra by taking into account physical properties of the atmosphere and of the instrument. Besides spectrum calculation, KOPRA has the capability to determine the derivatives of the spectrum with respect to many retrieval parameters. Comparisons between analytical and numerical derivatives, which are generally within a few percent, demonstrate that approximates due to run time optimized implementations are small. Furthermore, a flexible scheme is presented for handling various parameterizations of atmospheric profiles as implemented in the code in order to support different retrieval approaches.

Column Amounts of ClONO2, HCl, HNO3, and HF from Ground-Based FTIR Measurements Made Near Kiruna, Sweden, in Late Winter 1994

Abstract During SESAME phase I ground-based FTIR measurements were performed atEsrange near Kiruna, Sweden, from 28 January to 26 March 1994. Zenith columnamounts of ClONO2, HCl, HF, HNO3,O3, N2O, CH4, and CFC-12 werederived from solar absorption spectra. Time series of ClONO2and HCl indicate a chlorine activation at the end of January and around 1March. On 1 March a very low amount of HCl of 2.09times; 1015molec. cm-2 was detected, probably caused by a second chlorineactivation phase starting from an already decreased amount of HCl. The ratioof column amounts of HCl to ClONO2 decreased inside the vortexfrom about 1 in January to 0.4 in late March compared to values of about 2outside the vortex. Although the Arctic stratosphere was rather warm in winter1993/94 and PSCs occurred seldom, chlorine partitioning into its reservoirspecies HCl and ClONO2 changed during that winter andClONO2 is the major chlorine reservoir at the end of thewinter as in cold winters like 1991/92 and 1994/95.

Atmospheric ray path modeling for radiative transfer algorithms

A new method for the determination of ray paths as well as resulting path segments and partial gas columns within a layered atmosphere is presented. Any singularity at the tangent point is avoided. No use is made of the gross spherical symmetry of the Earths atmosphere. Using this approach we examine the impact of the Earths oblate shape and horizontal atmospheric inhomogeneities on infrared limb spectra.

Mountain polar stratospheric cloud measurements by Ground Based FTIR Solar Absorption Spectroscopy

An analysis of mountain polar stratospheric cloud observations by solar absorption FTIR from Kiruna/Sweden was performed and compared with co-located airborne lidar measurements. The infrared cloud spectral signature and optical depth indicated water ice particles compatible with the high backscatter and depolarization ratio of the lidar signal. Retrieval of mean particle properties from the FTIR spectrum depend on the assumed width of the particle size distribution and range from 2.0 to 1.1 µm radius and from 1.9 to 5.1 cm−3 number density. The volume density is well determined with 63.8–60.2 µm³/cm³ equivalent to about 2.5 ppmv of condensed water at 20 hPa. Simulations of lidar backscatter ratio based on these results are consistent with the lidar observations.