Towards a robust estimate of the global lightning nitrogen oxides source using in situ and remote sensing data and model results
Ulrich Schumann(3), Hans Schlager(1), Heidi Huntrieser(2), Christian Kurz(3) and Andreas Richter(4)
(1) DLR, Oberpfaffenhofen , 82230 Wesling, Germany
(2) DLR, Oberpfaffenhofen, 82230 Wesling, Germany
(3) DLR, Oberpfaffenhofen, 82234 Wessling, Germany
(4) University of Bremen, P.O. Box 33 04 40, 28334 Bremen, Germany
A weighted least square fit method is introduced which provides best estimates for the annually mean global source strength S of lightning induced nitrogen oxides (LNOx) together with random and systematic error bounds. The method is applied to data measured in-situ with airborne instruments near deep convection over a tropical continent at altitudes up to 20 km in Southern Brazil in February 2004 and 2005 during the project “Tropical Convection, Cirrus, and Nitrogen Oxides Experiment” (TROCCINOX). Several different global chemical transport models simulating air chemistry for these periods are used which provided results for at least two values of S. Robust LNOx estimates are obtained not only from NO mixing ratio data measured close to thunderstorms with fresh LNOx sources, but also from O3, CO and possibly CH4 data with LNOx sensitivity due to tropospheric photochemistry during the chemical life-time of theses species. The best LNOx source estimate computed for the given data is S = 4 +- 2 Tg/a (in mass units of nitrogen per year) for the best fitting model. The random errors are smaller than any systematic errors. The robustness of the results with respect to various parameter variations is shown. The value obtained from TROCCINOX itself is just a preliminary result. Inclusion of data from (in-situ or remote sensing) measurements at other periods and latitudes may still change this result.
In order to come to the best practically achievable result we are now rerunning the models for a period of ten years (1996-2005). With the given method, the model results are analysed together with existing measurements in various regions of the world and at various times during that decade. The data include high quality airborne measurements of chemical composition, data from the global ozone sonde systems, and from remote sensing results from satellite sensors such as SCIAMACHY, MOPITT and others.
Finally we indicate that the present method may also be applied to determine other parameters of Earth system models. For example, if models were run with two set of aviation emissions, the best fitting emission rate may be determine by a similar study using data mainly from the mid-latitudes. Even more important, such a study would reveal the consistency of state-of- the-art photochemical models in representing aviation effects. If the models simulate an aviation NOx impact on NOx, O3, and CO concentrations consistent with the data and among each other (see section 5.5), then this provides some validation for the suitability of the models for aviation related assessments. If however, the consistency is weak, this would indicate that important processes are still to be included into the models. By careful analysis of the discrepancy and further parameter studies one should be able to detect “missing chemistry” such as heterogeneous chemical processes. Hence, this approach opens a whole new venue for research and assessments.
Keywords: ESA European
Space Agency - Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,