Emanuel Christner

Processes controlling water vapor in the upper troposphere/lowermost stratosphere: An analysis of 8 years of monthly measurements by the IAGOS-CARIBIC observatory

An extensive set of in situ water vapor (H2O) data obtained by the IAGOS-CARIBIC passenger aircraft at 10–12 km altitude over 8 years (2005–2013) is analyzed. A multifaceted description of the vertical distribution of H2O from the upper troposphere (UT) via the extratropical tropopause mixing layer (exTL) into the lowermost stratosphere (LMS) is given. Compared to longer-lived trace gases, H2O is highly variable in the UT and exTL. It undergoes considerable seasonal variation, with maxima in summer and in phase from the UT up to ~4 km above the tropopause. The transport and dehydration pathways of air starting at the Earths surface and ending at 10–12 km altitude are reconstructed based upon (i) potential temperature (θ), (ii) relative humidity with respect to ice (RHi), and (iii) back trajectories as a function of altitude relative to the tropopause. RHi of an air mass was found to be primarily determined by its temperature change during recent vertical movement, i.e., cooling during ascent/expansion and warming during descent/compression. The data show, with great clarity, that H2O and RHi at 10–12 km altitude are controlled by three dominant transport/dehydration pathways: (i) the Hadley circulation, i.e., convective uplift in the tropics and poleward directed subsidence drying from the tropical tropopause layer with observed RHi down to 2%; (ii) warm conveyor belts and midlatitude convection transporting moist air into the UT with observed RHi usually above 60%; and (iii) the Brewer–Dobson shallow and deep branches with observed RHi down to 1%.

The Climatological Impacts of Continental Surface Evaporation, Rainout, and Subcloud Processes on δD of Water Vapor and Precipitation in Europe

All types of applications of stable water isotopes, e.g. for the reconstruction of paleotemperatures or for climate model validation, rely on a proper understanding of the mechanisms determining the isotopic composition of water vapor and precipitation. In this study, we use the isotope-enabled limited-area model COSMOiso to characterize the impacts of continental evapotranspiration, rainout, and subcloud processes on δD of European water vapor and precipitation. To this end, we first confirm a reliable implementation of the most important isotope fractionation processes in COSMOiso by comparing 5 years of modeled δD values with multi-platform δD observations from Europe (remote sensing observations of the δD of water vapor around 2.6 km a.g.l., in situ δD measurements in near-surface water vapor, and δD precipitation data from the Global Network of Isotopes in Precipitation). Based on six 15 year sensitivity simulations, we then quantify the climatological impacts of the different fractionation processes on the δD values. We find δD of European water vapor and precipitation to be most strongly controlled by rainout. Superimposed to this are the effect of subcloud processes, which especially affects δD in precipitation under warm conditions, and the effect of continental evapotranspiration, which exerts an important control over the δD of near-surface water vapor. In future studies, the validated COSMOiso model can be employed in a similar way for a comprehensive interpretation of European isotope records from climatologically different time periods.

Messungen von Wasserisotopologen von der planetaren Grenzschicht bis zur oberen Troposphäre zur Untersuchung des hydrologischen Kreislaufs

Konzentrationsverhaltnisse von Wasserisotopologen in der Atmosphare enthalten Information uber Phasenubergange und erlauben die Rekonstruktion von Dehydrierungs- und Transportprozessen. Mithilfe eines neuen lagrangeschen Isotopologenmodells werden die Anteile der europaischen Evapotranspiration quantifiziert. Flugzeuggestutzte in situ-Messungen von H216O und HDO mit CARIBIC belegen erstmals den Einfluss unterschiedlicher Transportprozesse auf die Isotopie der Feuchtigkeit in 11 km Hohe.

Regional Climate Simulations with COSMO-CLM: Ensembles, Very High Resolution and Paleoclimate

The IMK-TRO (KIT) presents in the HLRS annual report for 2016–2017 projects and their results using the CRAY XC40 “Hazel Hen”. The research focuses on the very high resolution regional climate simulations including the modeling of land surface processes and urban climate, the generation of ensemble projections, and regional paleoclimate (PALMOD). The simulations are performed with the regional climate model (RCM) COSMO-CLM (CCLM) and cover spatial resolutions from 50 to 2.8 km. Within the projects, the standard CCLM is enhanced; for the analysis of the impact of different soil-vegetation transfer schemes (SVATs) VEG3D is coupled via OASIS3-MCT to CCLM. For the PALMOD project, a special isotope-enabled version CCLMiso is used. To highlight the added value, the results of the higher resolution climate predictions are compared to those of simulations with coarser resolutions. In addition, the impact of different global driving data sets is investigated. Climate projections are performed for two future time slices, 2021–2050 and 2071–2100. The urban climate and its change are also investigated using very high resolution simulations to enable the energetic optimisation of buildings. The required Wall-Clock-Times (WCT) range from 9 to 2000 node-hours per simulated year.