Dietmar J. Baumgartner

Aircraft measurements of photolysis rate coefficients for ozone and nitrogen dioxide under cloudy conditions

Atmospheric chemistry is mainly driven by photodissociation of trace gases. Especially the photolysis of ozone, which is a major source of OH radicals and the photolysis of nitrogen dioxide, which is the primary step in ozone production are essential quantities for atmospheric chemistry calculations. As part of the EU-funded project Scientific Training and Access to Aircraft for Atmospheric Research Throughout Europe (STAAARTE) measurements of the photolysis rate coefficients for ozone and nitrogen dioxide were performed on board the research aircraft FALCON 20-E5 of DLR (German Aerospace Center, Oberpfaffenhofen, Germany). Additional measurements of basic meteorological parameters, global irradiance, trace gas concentrations and particles were conducted. The influence of clouds on the vertical profile of the photolysis rate coefficients was analyzed in combination with radiative transfer model calculations. Compared to clear-sky values the actinic flux is generally lower below clouds, but shows an increase inside and an enhancement above clouds. This work presents some of the results from the flight experiments that were performed in the summer 1998 over southern Austria.

Investigation of the effect of contrails on direct and diffuse irradiance

In the present study we investigate the effect of contrails on global shortwave radiation. This investigation is performed using continuous hemispherical fish eye photographs of the sky, diffuse and direct shortwave measurements. These measurements have been performed at the solar observatory Kanzelhohe (1540 m.a.s.l) located in the southern part of Austria during a period of one and half year. The time resolution of the measurements is one minute, which allows to accurately follow the formation-eventually the disappearance or the movement - of the contrails in the sky. Using the fish eye photographs we identified clear sky days with a high contrail persistence. We especially look at situations where the contrails were obstructing the sun. First results show that contrails moving between sun and observer/sensor may reduce the global radiation by up to 68%. In general we however observe that during days with a high contrail persistence the diffuse irradiance is slightly increased. Finally a statistic of th...

A comparison of long-term parallel measurements of sunshine duration obtained with a Campbell-Stokes sunshine recorder and two automated sunshine sensors

In recent decades, automated sensors for sunshine duration (SD) measurements have been introduced in meteorological networks, thereby replacing traditional instruments, most prominently the Campbell-Stokes (CS) sunshine recorder. Parallel records of automated and traditional SD recording systems are rare. Nevertheless, such records are important to understand the differences/similarities in SD totals obtained with different instruments and how changes in monitoring device type affect the homogeneity of SD records. This study investigates the differences/similarities in parallel SD records obtained with a CS and two automated SD sensors between 2007 and 2016 at the Kanzelhöhe Observatory, Austria. Comparing individual records of daily SD totals, we find differences of both positive and negative sign, with smallest differences between the automated sensors. The larger differences between CS-derived SD totals and those from automated sensors can be attributed (largely) to the higher sensitivity threshold of the CS instrument. Correspondingly, the closest agreement among all sensors is found during summer, the time of year when sensitivity thresholds are least critical. Furthermore, we investigate the performance of various models to create the so-called sensor-type-equivalent (STE) SD records. Our analysis shows that regression models including all available data on daily (or monthly) time scale perform better than simple three- (or four-) point regression models. Despite general good performance, none of the considered regression models (of linear or quadratic form) emerges as the “optimal” model. Although STEs prove useful for relating SD records of individual sensors on daily/monthly time scales, this does not ensure that STE (or joint) records can be used for trend analysis.