Abstract. Extensive airborne measurements of aerosol particles in a pristine marine region were made during the first Aerosol Characterization Experiment (ACE 1) from November 15 to December 14, 1995. During this study, high concentrations of condensation nuclei (CN) were frequently observed both near and within clouds. Near clouds, in the absence of liquid water, Clarke et al. [1998] have reported that high CN levels were from new particle formation by homogeneous nucleation. Here we show, however, that within clouds, elevated CN concentrations were not authentic, but instead a sampling artifact, likely related to fragmentation of cloud drops impacting the aerosol inlet. By themselves, these fragments were often indistinguishable from ambient particles. Spurious CN from fragmenting droplets were observed at temperatures down to roughly -20øC and spanned a broad size range, with diameters down to 3 nm. Comparison of two different sized isokinetic aerosol inlets showed that inlets with smaller openings produce higher droplet fragment concentrations. The mechanism for producing these particles is not completely understood. Although fragmentation appeared to be the primary mechanism, for one instrument, an additional spurious source, correlated with liquid water, was observed when ambient temperatures were below -5øC. These findings show that care must be taken when interpreting airborne aerosol measurements in regions of liquid water. This is particularly pertinent to studies of new particle formation by homogeneous nucleation in the vicinity of clouds.

[1] Previous tree ring based hydrologic studies in Mongolia have been regional in scale.Here, we present a large-scale summer drought reconstruction for Mongolia that reveals the main summer moisture patterns of the past. This reconstruction is based on a network of tree ring chronologies that span the country. The resulting drought model explains 61% of the variance and is extended to cover 1520-1993 by using a nested approach to modeling. Severe droughts and harsh winter conditions occurred in Mongolia from ∼1999-2002 and contributed to massive livestock mortality and economic loss. These droughts were extreme in the context of the past several hundred years. Significant periodicities are found at 40 (90%), 19.3-25 (99%), 11.6 (95%), 6.4-7.2 (95%), and 2.8 years (99%). This high-resolution drought reconstruction and associated tree ring chronologies supplement and extend the sparse meteorological data in Mongolia and can be used to better understand climate variability and potential forcings of climate.

A new method combining micro-X-ray computed tomography (μXCT) and volumetric digital image correlation (V-DIC) in conjunction with in-situ mechanical testing was used to probe three-dimensional (3D) deformation behavior in a friction stir blind rivet (FSBR) joint of carbon fiber reinforced polymer (CFRP) composite. Intrinsic microstructural features such as fibers, pores and metal inclusions enabled accurate volumetric strain calculation of dense fiber reinforced polymer composites using V-DIC without the need for highcontrast additives. Deformation calculated with V-DIC was employed to determine variation of local mechanical properties within the FSBR altered stir-zone microstructure. Unique deformation mechanisms such as internal interfacial shear and microstructure-dependent local buckling were observed in situ. The obtained 3D microscale strain maps revealed that the deformation behavior in joint-affected zones was fundamentally different from that of the bulk composite. Combined μXCT and V-DIC were shown to be effective for understanding 3D microscale deformations in composites.

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