Particle backscatter and relative humidity measured across cirrus clouds and comparison with microphysical cirrus modelling

Advanced measurement and modelling techniques are employed to estimate the partitioning of atmospheric water between the gas phase and the condensed phase in and around cirrus clouds, and thus to identify in-cloud and out-of-cloud supersaturations with respect to ice. In November 2008 the newly developed balloon-borne backscatter sonde COBALD (Compact Optical Backscatter and AerosoL Detector) was flown 14 times together with a CFH (Cryogenic Frost point Hygrometer) from Lindenberg, Germany (52° N, 14° E). The case discussed here in detail shows two cirrus layers with in-cloud relative humidities with respect to ice between 50% and 130%. Global operational analysis data of ECMWF (roughly 1° × 1° horizontal and 1 km vertical resolution, 6-hourly stored fields) fail to represent ice water contents and relative humidities. Conversely, regional COSMO-7 forecasts (6.6 km × 6.6 km, 5-min stored fields) capture the measured humidities and cloud positions remarkably well. The main difference between ECMWF and COSMO data is the resolution of small-scale vertical features responsible for cirrus formation. Nevertheless, ice water contents in COSMO-7 are still off by factors 2–10, likely reflecting limitations in COSMO's ice phase bulk scheme. Significant improvements can be achieved by comprehensive size-resolved microphysical and optical modelling along backward trajectories based on COSMO-7 wind and temperature fields, which allow accurate computation of humidities, homogeneous ice nucleation, resulting ice particle size distributions and backscatter ratios at the COBALD wavelengths. However, only by superimposing small-scale temperature fluctuations, which remain unresolved by the numerical weather prediction models, can we obtain a satisfying agreement with the observations and reconcile the measured in-cloud non-equilibrium humidities with conventional ice cloud microphysics. Conversely, the model-data comparison provides no evidence that additional changes to ice-cloud microphysics – such as heterogeneous nucleation or changing the water vapour accommodation coefficient on ice – are required

Atmospheric Methane and Nitrous Oxide of the Late Pleistocene from Antarctic Ice Cores

International audienceThe European Project for Ice Coring in Antarctica Dome C ice core enables us to extend existing records of atmospheric methane (CH4) and nitrous oxide (N2O) back to 650,000 years before the present. A combined record of CH4 measured along the Dome C and the Vostok ice cores demonstrates, within the resolution of our measurements, that preindustrial concentrations over Antarctica have not exceeded 773 ± 15 ppbv (parts per billion by volume) during the past 650,000 years. Before 420,000 years ago, when interglacials were cooler, maximum CH4 concentrations were only about 600 ppbv, similar to lower Holocene values. In contrast, the N2O record shows maximum concentrations of 278 ± 7 ppbv, slightly higher than early Holocene values

Seasonal activity and distribution of cereal aphid parasitoids in Belgium

Activity of antagonists in winter and early spring as well as in late summer and autumn plays an important role in the control of cereal aphid populations. Indeed, parasitoids active early in the year are important to avoid high aphid densities. Late summer and autumn correspond to the transition period between two wheat cultures, and parasitoid activity would thus reduce aphid infestation. During these critical periods, other crops like rye-grass and red clover containing alternative hosts could play the role of parasitoid reservoirs. During 1996, parasitoid activity was measured by trap planting in wheat, rye-grass, red clover and fallow grassland. In each plot, early spring was characterized by an important parasitoid activity, while aphids remained at a low level. Later in spring, activity decreased, and aphid development began even during this period. During the summer, when aphids reached their-population peak, parasitoid activity rose again. Percentage of parasitism of aphids sampled was only important during summer in red clover and rye-grass. In wheat and fallow grassland, percentage of parasitism remained at a low level. The role of synchronization between parasitoid activity and aphid development is discussed