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Gandrud, Bruce

Publications and source records attributed to Gandrud, Bruce.

In Situ Observations of PSCs Generated by Gravity Waves

During SOLVE, the bulk of the in-situ observations of PSCs are of large scale extended structures associated with synoptic scale cooling. The nature of these structures is also determined by layers of high relative NOy that have been stretched into thin layers by advective processes. Some of the in situ observations, however, are clearly correlated with gravity wave signatures. The first goal of this work is to examine these cases and evaluate gravity wave parameters. In particular, we are interested in the intrinsic periods of the waves and their temperature amplitude, which are key ingredients in the nucleation process. Secondly, we will examine some rudimentary properties of the particle size distributions and composition, comparing these with in situ observations of the more extended PSC features. Finally, we will attempt to ascertain the mechanism which generates the gravity waves.

Pfister, Leonhard↗

How do Polar Stratospheric Clouds Form?

SOLVE measurements have been compared with results from a microphysical model to understand the composition and formation of the polar stratospheric clouds (PSCs) observed during SOLVE. Evidence that the majority of the particles remain liquid throughout the winter will be presented. However, a small fraction of the particles do freeze, and the presence of these frozen particles can not be explained by current theories, in which the only freezing mechanism is homogeneous freezing to ice below the ice frost point. Alternative formation mechanisms, in particular homogeneous freezing above the ice frost point and heterogeneous freezing, have been explored using the microphysical model. Both nitric acid trihydrate (NAT) and nitric acid dihydrate (NAD) have been considered as possible compositions for the solid-phase nitric acid aerosols. Comparisons between the model results and the SOLVE measurements will be used to constrain the possible formation mechanisms. Other effects of these frozen particles will also be discussed, in particular denitrification.

Drdla, Katja↗

An intercomparison of airborne PAN measurements

Results are reported on the performance of the NASA and NCAR PAN measurement instruments during the NASA Global Tropospheric Experiment Chemical Instrumentation Test and Evaluation 2 (CITE 2) mission in August-September 1986. Both PAN instruments employ the electron-capture gas chromatography approach for detection and are calibrated using a liquid PAN standard in a diffusion tube. Details of the instrument design, experimental protocols, and CITE 2 test flights are discussed, and the results are presented in extensive tables and graphs. It is found that the NASA and NCAR instruments agreed to within about 17 parts per trillion by volume (pptv) when the PAN mixing ratio was below 100 pptv and to within about 25 percent when the mixing ratio was 100-300 pptv.

Gregory, Gerald L.↗