In the Arctic winter 2003, in-situ measurements of the long-lived trace gases N2O, CFC-11 (CCl3F), H-1211 (CBrClF2), CH4, O3 and H2O have been performed on board the high-altitude aircraft M55 ...Geophysica. The data are presented and used to study transport into the lowermost stratosphere (LMS). The LMS can be regarded as a mixture of fractions of air originating in (i) the troposphere, (ii) the extra-vortex stratosphere above 400 K and (iii) the Arctic vortex above 400 K. These fractions are determined using a simple mass balance calculation. The analysis exhibits a strong tropospheric influence of 50% ± 15% or more in the lowest 20 K of the high-latitude LMS. Above this region the LMS is dominated by air masses having descended from above 400 K. Below the Arctic vortex region at potential temperatures above 360 K, air in the LMS is a mixture of extra-vortex stratospheric and vortex air masses. The vortex fraction increases from about 40% ± 15% at 360 K to 100% at 400 K for equivalent latitudes >70° N. This influence of air masses descending through the bottom of the polar vortex increases over the course of the winter. By the end of winter a significant fraction of 30% ± 10% vortex air in the LMS is found even at an equivalent latitude of 40° N. Since the chemical and dynamical history of vortex air is distinct from that of mid-latitude stratospheric air masses, this study implies that the composition of the mid- to high-latitude LMS during late winter and spring is significantly influenced by the Arctic vortex.
We present a climatology of O3, CO, and H2O for the upper troposphere and lower stratosphere (UTLS), based on a large collection of high‐resolution research aircraft data taken between 1995 and 2008. ...To group aircraft observations with sparse horizontal coverage, the UTLS is divided into three regimes: the tropics, subtropics, and the polar region. These regimes are defined using a set of simple criteria based on tropopause height and multiple tropopause conditions. Tropopause‐referenced tracer profiles and tracer‐tracer correlations show distinct characteristics for each regime, which reflect the underlying transport processes. The UTLS climatology derived here shows many features of earlier climatologies. In addition, mixed air masses in the subtropics, identified by O3‐CO correlations, show two characteristic modes in the tracer‐tracer space that are a result of mixed air masses in layers above and below the tropopause (TP). A thin layer of mixed air (1–2 km around the tropopause) is identified for all regions and seasons, where tracer gradients across the TP are largest. The most pronounced influence of mixing between the tropical transition layer and the subtropics was found in spring and summer in the region above 380 K potential temperature. The vertical extent of mixed air masses between UT and LS reaches up to 5 km above the TP. The tracer correlations and distributions in the UTLS derived here can serve as a reference for model and satellite data evaluation.
In this study we report measurements of hydrogen peroxide (H2O2), methyl hydroperoxide* (MHP* as a proxy of MHP based on an unspecific measurement of total organic peroxides) and formaldehyde (HCHO) ...from the HOx OVer EuRope (HOOVER) project (HOx = OH+HO2). HOOVER included two airborne field campaigns, in October 2006 and July 2007. Measurement flights were conducted from the base of operation Hohn (Germany, 54° N, 9° E) towards the Mediterranean and to the subpolar regions over Norway. We find negative concentration gradients with increasing latitude throughout the troposphere for H2O2 and CH3OOH*. In contrast, observed HCHO is almost homogeneously distributed over central and northern Europe and is elevated over the Mediterranean. In general, the measured gradients tend to be steepest entering the Mediterranean region, where we also find the highest abundances of the 3 species. Mixing ratios of these tracers generally decrease with altitude. H2O2 and CH3OOH* show maxima above the boundary layer at 2–5 km, being more distinct over southern than over northern Europe. We also present a comparison of our data with simulations by two global 3-D-models, MATCH-MPIC and EMAC, and with the box model CAABA. The models realistically represent altitude and latitude gradients for both HCHO and hydroperoxides (ROOH). In contrast, the models have problems reproducing the absolute mixing ratios, in particular of H2O2. Large uncertainties about retention coefficients and cloud microphysical parameters suggest that cloud scavenging might be a large source of error for the simulation of H2O2. A sensitivity study with EMAC shows a strong influence of cloud and precipitation scavenging on the budget of H2O2 as simulations improve significantly with this effect switched off.
Osteoblastic cells in long-term culture undergo a phenotypic maturation process leading to extracellular matrix (ECM) production and bone nodule (BN) formation. Cell-to-cell communication via gap ...junctions (GJC) can be detected between osteoblastic cells within 24 h of plating. We evaluated, in long-term cultures of osteoblastic cells, the effect of inhibiting GJC on the phenotypic maturation process and the expression of specific genes associated with this process. MC3T3-E1 cells were plated, and, after 24 h (day 0), cells were exposed to 18-α-glycyrrhetinic acid (AGA), a nontoxic reversible inhibitor of GJC. GJC, alkaline phosphatase (AP) activity, BN formation, and the relative level of transcripts encoding osteocalcin (OC), bone sialoprotein (bSP), osteopontin (OP), collagen α1 type I (α1ICol), and elongation factor-1a (EF1a) were evaluated on day 0 and every 4–7 days thereafter through day 30. GJC was assessed by fluorescent dye transfer. Gene expression was analyzed by northern blot and semiquantitative reverse transcription-polymerase chain reaction. GJC was detectable at day 0 and increased with time in culture. AGA (100 μmol/L) strongly inhibited GJC at all timepoints tested. Moreover, AGA-exposed cells showed a dose-dependent decrease in AP activity and a delay in the appearance of BN. This delayed phenotypic expression coincided with an inhibitory effect on the expression of the osteoblast-specific genes OC and bSP. Expression of α1ICol mRNA was also affected, but to a lesser extent, whereas OP and EF1a were not affected. Similar results were obtained with oleamide, an additional reversible inhibitor of GJC. In contrast, cells exposed to either vehicle or 100 μmol/L glycyrrhizic acid (a noninhibitory glycoside of 18-β-glycyrrhetinic acid) were indistinguishable from untreated cells for all parameters evaluated. We conclude that GJC inhibition interferes with the maturation process of osteoblastic cells in culture, possibly by affecting signals regulating the expression of genes involved in the maturation/differentiation of the osteoblastic phenotype.
Acquiring accurate measurements of water vapor at the low mixing ratios (< 10 ppm) encountered in the upper troposphere and lower stratosphere (UT/LS) has proven to be a significant analytical ...challenge evidenced by persistent disagreements between high‐precision hygrometers. These disagreements have caused uncertainties in the description of the physical processes controlling dehydration of air in the tropical tropopause layer and entry of water into the stratosphere and have hindered validation of satellite water vapor retrievals. A 2011 airborne intercomparison of a large group of in situ hygrometers onboard the NASA WB‐57F high‐altitude research aircraft and balloons has provided an excellent opportunity to evaluate progress in the scientific community toward improved measurement agreement. In this work we intercompare the measurements from the Midlatitude Airborne Cirrus Properties Experiment (MACPEX) and discuss the quality of agreement. Differences between values reported by the instruments were reduced in comparison to some prior campaigns but were nonnegligible and on the order of 20% (0.8 ppm). Our analysis suggests that unrecognized errors in the quantification of instrumental background for some or all of the hygrometers are a likely cause. Until these errors are understood, differences at this level will continue to somewhat limit our understanding of cirrus microphysical processes and dehydration in the tropical tropopause layer.
Key Points
Agreement among in situ measurements of UT/LS water vapor is improved
Scientifically significant disagreements between instruments still exist
Abstract Marrow-isolated adult multilineage inducible (MIAMI) cells were differentiated in vitro to neuronal cells in a neurotrophin-dependent fashion. After induction, the cells revealed ...electrophysiological features similar to those observed in mature neurons. Primary early passage human MIAMI cells without any type of co-cultures with other cell types were used. The developmental program involved a multi-step process requiring the concerted action of brain-derived neurotrophic factor, nerve growth factor and depended on neurotrophin-3, after basic fibroblast growth factor withdrawal. MIAMI-derived neuron-like cells sequentially expressed the neuronal markers, developed a complex neurite outgrowth and arborization, and acquired electrophysiological characteristics similar to those observed in mature neurons. The young and old MIAMI-derived neuronal cells developed both inward and outward currents upon depolarization, similar to those observed in normal neurons. These results represent the earliest evidence that neurotrophin-3 can direct the differentiation of non-neural stem cells from human adult bone marrow stroma to neuron-like cells in vitro . Supplementing the aforementioned multi-step process with sonic hedgehog, fibroblast growth factor 8, and retinoic acid increased the expression of molecules involved in dopaminergic differentiation and of tyrosine hydroxylase, the rate limiting enzyme of dopamine synthesis. MIAMI cells from young and old individuals represent autologous human cell populations for the treatment of disorders of the skeletal and nervous systems and for applications in cell therapy and reparative medicine approaches.
The frequency of occurrence of cirrus clouds and contrails, their life time, ice crystal size spectra and thus their radiative properties depend strongly on the ambient distribution of the relative ...humidity with respect to ice (RHice). Ice clouds do not form below a certain supersaturation and both cirrus and contrails need at least saturation conditions to persist over a longer period. Under subsaturated conditions, cirrus and contrails should dissipate. During the mid-latitude aircraft experiment CONCERT 2008 (CONtrail and Cirrus ExpeRimenT), RHice and ice crystals were measured in cirrus and contrails. Here, we present results from 2.3/1.7 h of observation in cirrus/contrails during 6 flights. Thin and subvisible cirrus with contrails embedded therein have been detected frequently in a subsaturated environment. Nevertheless, ice crystals up to radii of 50 μm and larger, but with low number densities were often observed inside the contrails as well as in the cirrus. Analysis of the meteorological situation indicates that the crystals in the contrails were entrained from the thin/subvisible cirrus clouds, which emerged in frontal systems with low updrafts. From model simulations of cirrus evaporation times it follows that such thin/subvisible cirrus can exist for time periods of a couple of hours and longer in a subsaturated environment and thus may represent a considerable part of the cirrus coverage.
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