Gerhard Kramm

A modified profile method for determining the vertical fluxes of NO, NO2, Ozone and HNO3 in the atmospheric surface layer.

A modified profile method for determining the vertical deposition (or/and exhalation) fluxes of NO, NO2, ozone, and HNO3 in the atmospheric surface layer is presented. This method is based on the generally accepted micrometeorological ideas of the transfer of momentum, sensible heat and matter near the Earths surface and the chemical reactions among these trace gases. The analysis (aerodynamic profile method) includes a detailed determination of the micrometeorological quantities (such as the friction velocity, the fluxes of sensible and latent heat, the roughness length and the zero plane displacement), and of the height-invariant fluxes of the composed chemically conservative trace gases with ‘group’ concentrations c1=[NO]+[NO2]+[HNO3], c2=[NO2]+[O3]+3/2·[HNO3], and c3=[NO]−[O3]−1/2·[HNO3]. The fluxes of the ‘individual’ species are finally determined by the numerical solution of a system of coupled nonlinear ordinary differential equations for the concentrations of ozone and HNO3 (‘decoding’ method). The parameterization of the fluxes is based on the flux-gradient relationships in the turbulent region of the atmospheric surface layer. The model requires only the vertical profile data of wind velocity, temperature and humidity and concentrations of NO, NO2, ozone, and HNO3.The method has been applied to vertical profile data obtained at Jülich (September 1984) and collected in the BIATEX joint field experiment LOVENOX (Halvergate, U.K., September 1989).

Modelling of the vertical fluxes of nitric acid, ammonia, and ammonium nitrate

Results from numerical investigations regarding the exchange of HNO3, NH3, and NH4NO3 between the atmosphere and the biosphere are presented. The investigations were performed with a modified inferential method which is based on the generally accepted micrometeorological ideas of the transfer of momentum, sensible heat and matter near the Earths surface and the chemical reactions among these nitrogen compounds. This modified inferential method calculates the micrometeorological quantities (such as the friction velocity and the fluxes of sensible and latent heat), the height-invariant fluxes of the composed chemically conservative trace species with ‘group’ concentrationsc1=[HNO3]+[NH4NO3] (total nitrate),c2=[NH3]+[NH4NO3] (total ammonia), andc3=[HNO3]-[NH3] as well as the fluxes of the ‘individual’ nitrogen compounds. The parameterization of the fluxes is based on the flux-gradient relationships in the turbulent region of the atmospheric surface layer. The modified inferential method requires only the data of wind velocity, temperature, humidity and concentrations (HNO3, NH3, and NH4NO3) measured at a reference height by stations of a monitoring network.

A SVAT scheme for NO, NO2, and O3 — Model description and test results

SummaryA soil/vegetation/atmosphere transfer (SVAT) scheme for determining the dry deposition and/or emission fluxes of NO, NO2, and O3 in the atmospheric surface layer over horizontally uniform terrain covered with fibrous canopy elements is presented and discussed. This transfer scheme is based on the micrometeorological ideas of the transfer of momentum, heat and matter near the Earths surface, where chemical reactions between these trace gases are included. The fluxes are parameterized by first-order closure principles. The uptake processes by vegetation and soil are described in accord with Deardorff (1978). The SVAT scheme requires only routine data of wind speed, dry- and wet-bulb temperatures, short wave and long wave radiation, and the concentrations of O3 and nitrogen species provided by stations of monitoring networks.First model results indicate that the dry deposition fluxes of NO, NO2, and O3 are not only influenced by meteorological and plant-physiological parameters, but also by chemical reactions between these trace species and by NO emission from the soil. Furthermore, a small displacement in the concentrations of NO, NO2, and O3 within in the range of the detection limits of the chemical sensors can produce large discrepancies in the flux estimates, which are manifested here by the shift from height-invariant fluxes substantiated by the photostationary state to strongly height-dependent fluxes caused by the departure from that state. Especially in the case of these nitrogen species the widely used ‘big leaf’ multiple resistance approach, which is based on the constant flux approximation seems to be inappropriate for computing dry deposition fluxes and deposition velocities.

A re-evaluation of the Webb correction using density-weighted averages

Abstract Results from a re-evaluation of the flux correction suggested by Webb et al. ( Q. J. R. Meteorol. Soc. , 106, 85–100, 1980) are presented and discussed. This re-evaluation is based on the equation of continuity as well as the budget equations for dry air, water vapour and atmospheric trace species, where a density-weighted averaging procedure introduced by Hesselberg ( Beitr. Phys. fr. Atmos. , 12, 141–160, 1926) is used. This averaging procedure seems to be more appropriate than that of Reynolds, especially in the case of atmospheric trace species. The consequences of this flux correction as regards the exchange of atmospheric trace gases between the atmosphere and the ground (vegetation, soil and water) are pointed out.

On the dispersion of trace species in the atmospheric boundary layer: a re-formulation of the governing equations for the turbulent flow of the compressible atmosphere

Since especially the parameterisation of the vertical dispersion of trace species in the atmosphericboundary layer has controversially been discussed in the literature, the 1st-order balance equationsfor matter, momentum, and various energy forms were re-formulated with Hesselberg’sdensity-weighted averaging calculus to point out that this problem arises from averaging themacroscopic balance equations of matter, momentum and various energy forms in the sense ofReynolds, rather than from the parameterisation of the vertical dispersion by 1st-order closureprinciples, as this discussion seems to reflect. Results of the SANA field experiment “Eisd”presented here substantiate that in the case of chemically reactive trace constituents segregationeffects owing to turbulence cannot generally be neglected as usually performed in Eulerian airpollution models. Modelling such segregation effects, however, requires, at least, 2nd-orderclosureprinciples. Therefore, the 2nd-order balance equations for 2nd moments like the eddyflux densities of matter and momentum as well as covariances of scalar quantities were alsore-formulated by considering Hesselberg’s averaging procedure. This re-formulated set of governing1st-order and 2nd-order balance equations may be considered as most exact becausethe degree of simplification is reduced to a minimum. To distinguish between the Boussinesqapproximated equation set for the turbulent atmospheric flow, denoted as Boussinesq fluid, and our re-formulated one, the turbulent flow of the compressible atmosphere for which there-formulated governing balance equations are valid may be denoted as Hesselberg fluid. It isargued that averaging in the sense of Hesselberg reduces the risk to misinterpret turbulentatmospheric processes to a minimum. As exemplary shown on the basis of the balance equationsfor dry air, water vapour, and trace species, the so-called Webb correction will become insignificantif Hesselberg’s averaging calculus is considered. Based on the results obtained from the “Eisdorf” experiment and from sensitivity studies with a Seinfeld-type kinetic mechanism forphotochemical smog, it is argued that an evaluation and improvement of Eulerian air pollutionmodels require directly measured 2nd-order moments. Since the number of fast-responsephysico-chemical analysers for chemically reactive trace constituents is strongly limited, suchfast-response sensors have to be (further) developed to set-up a true platform for model evaluationthat implies not only a comparison of calculated and observed distributions of 1stmoments (necessary condition), but also a comparison of the calculated and observed distributionsof 2nd moments (sufficient condition).

Assessment of WRF/Chem to simulate sub–Arctic boundary layer characteristics during low solar irradiation using radiosonde, SODAR, and surface data

Abstract Data from a Doppler SOund Detection And Ranging (SODAR) device, twice–daily radiosondes, 33 surface meteorological and four aerosol sites were used to assess the ability of the Weather Research and Forecasting model inline coupled with a chemistry package (WRF/Chem) to capture atmospheric boundary layer (ABL) characteristics in Interior Alaska during low solar irradiation (11–01–2005 to 02–28–2006). Biases determined based on all available data from the 33 sites over the entire episode are 1.6 K, 1.8 K, 1.85 m/s, –5 o , and 1.2 hPa for temperature, dewpoint temperature, wind–speed, wind–direction, and sea–level pressure, respectively. The SODAR–data reveal that WRF/Chem over/under–estimates wind–speed in the lower (upper) atmospheric boundary layer. WRF/Chem captures the frequency of low–level jets well, but overestimates the strength of moderate low–level jets. Data from the four aerosol sites suggest large underestimation of PM 10 , and NO 3 at the remote sites and PM 2.5 at the polluted site. Difficulty in capturing the temporal evolution of aerosol concentrations coincides with difficulty in capturing sudden temperature changes, underestimation of inversion–strengths and timing of frontal passages. Errors in PM 2.5 concentrations strongly relate to temperature errors.

Application of Gaussian Error Propagation Principles for Theoretical Assessment of Model Uncertainty in Simulated Soil Processes Caused by Thermal and Hydraulic Parameters

Statistical uncertainty in soil temperature and volumetric water content and related moisture and heat fluxes predicted by a state-of-the-art soil module [embedded in a numerical weather prediction (NWP) model] is analyzed by Gaussian error-propagation (GEP) principles. This kind of uncertainty results from the indispensable use of empirical soil parameters. Since for the same thermodynamic and hydrological surface forcing and mean empirical parameters a soil module always provides the same mean value and standard deviation, uncertainty is first theoretically analyzed using artificial data for a wide range of soil conditions. Second, NWP results obtained for Alaska during a July episode are elucidated in relation to the authors’ theoretical findings. It is shown that uncertainty in predicted soil temperature and volumetric water content is of minor importance except during phase transition. Then the freeze–thaw term dominates and leads to soil temperature and moisture uncertainties of more than 15.8 K and 0.212 m 3 m 3 in mineral soils. Heat-flux uncertainty is of the same order of magnitude as typical errors in soil-heat-flux measurements. Uncertainty in the pore-size distribution index dominates uncertainty for all state variables and soil fluxes under most conditions. Uncertainties in hydraulic parameters (saturated hydraulic conductivity, pore-size distribution index, porosity, saturated water potential) affect soil-temperature uncertainty more than those in thermal parameters (density and specific heat capacity of dry soil material). Based on a thermal conductivity approach alternatively used, it is demonstrated that GEP principles are indispensable for evaluating parameterized soil-transfer processes. Generally, statistical uncertainty decreases with depth. Close beneath the surface, the uncertainty in predicted soil temperature, volumetric water content, and soil-moisture and heat fluxes undergoes a diurnal cycle.

On the parameterization of ice microphysics in a mesoscale α weather forecast model

Abstract Numerical experiments with a 3-D-dimensional mesoscale α weather forecast model are performed to investigate the sensitivity of the model to different parameters and the parameterized microphysics. The parameterization considers condensation and deposition of water vapor, sublimation, evaporation of both cloud water and rainwater, riming of ice crystals by cloud water, rainwater formation by autoconversion, accretion and melting as well as the sedimentation of rain and ice crystals. The results of the simulations are discussed on the basis of the analysis, estimations of skill and uncertainty, satellite data as well as observed precipitation data. These results show that the dynamics of the troposphere and the cloud microphysics can be described more realistically and that the model performance can be improved if ice processes are included. It is substantiated by all of these simulations that the relative humidity and water substance mixing ratio fields were only strongly altered by turning off the ice phase or the riming process.

Lectures in Meteorology

Introduction.- Thermodynamics.- Clouds and Precipitation.- Atmospheric Radiation.- Atmospheric Chemistry.- Dynamics and Synoptic.- Climate and Climatology.

On the Meaning of Feedback Parameter, Transient Climate Response, and the Greenhouse Effect: Basic Considerations and the Discussion of Uncertainties

Da mittlerweile verschiedene Versionen des zitierten Kommentars von Link und Ludecke existieren, haben wir uns entschlossen, zunachst nur auf die erste Version dieses Kommentars zu antworten, die am 15. Dezember 2010 auf der EIKE-Webseite erschien. Zwischenzeitlich existierte auf der Webseite des Autors Link eine dritte Version, die am 16. Dezember 2010 verfugbar war, nun aber wiederum durch eine andere Version ersetzt wurde. Hinzu kommt noch, das eine weitere Version auf der EIKE-Webseite existiert, die als Version 14 bezeichnet wird. Da dieses vorerst die jungste Version zu sein scheint, werden wir kurz darauf eingehen. Wir uberlassen es dem Leser, dieses merkwurdige Verhalten der Autoren Link und Ludecke zu wurdigen.