[1] The seasonal cycle of planetary boundary layer (PBL) depth is examined globally using observations from the Constellation Observing System for the Meteorology, Ionosphere, and Climate (COSMIC) satellite mission. COSMIC uses GPS radio occultation to derive the vertical profile of refractivity at high vertical resolution (~100 m). Here, we apply an algorithm to determine PBL top height and thus PBL depth from the maximum vertical gradient of refractivity. PBL top detection is sensitive to hydrolapses at nonpolar latitudes but to both hydrolapses and temperature jumps in polar regions. The PBL depths and their seasonal cycles compare favorably with selected radiosonde-derived estimates at tropical, midlatitude, and Antarctic sites, adding confidence that COSMIC can effectively provide estimates of seasonal cycles globally. PBL depth over extratropical land regions peaks during summer consistent with weak static stability and strong surface sensible heating. The subtropics and tropics exhibit a markedly different cycle that largely follows the seasonal march of the Intertropical Convergence Zone with the deepest PBLs associated with dry phases, again suggestive that surface sensible heating deepens the PBL and that wet periods exhibit shallower PBLs. Marine PBL depth has a somewhat similar seasonal march to that over continents but is weaker in amplitude and is shifted poleward. The maximum seasonal amplitude over oceans occurs over the Arctic. Over subtropical/tropical oceans there is seasonal asymmetry about the equator, with winter maxima in the Northern Hemisphere but fall maxima in the south. The seasonal march of PBL depth is largely modulated by the seasonal cycle of static stability in the extratropics and by the monsoon circulations at tropical and subtropical latitudes.Citation: Chan, K. M., and R. Wood (2013), The seasonal cycle of planetary boundary layer depth determined using COSMIC radio occultation data,
Using plasma-enhanced chemical vapor deposition (PECVD) based on fluorine chemistry, the limitations hindering the practical use of cubic boron nitride (cBN) films in mechanical applications have been overcome. The CVD method presented is characteristic with (a) the direct cBN growth on diamond without soft, noncubic BN interface layers, (b) the synthesis of cBN films with extraordinary adhesion to the substrates and high mechanical properties, and (c) the scalable process providing thick, large-area cBN films at high deposition rate even on rough and untreated surfaces. These prime technological properties open the route to the mechanical exploitation of cBN films, particularly in tribological and tool applications. The reduction of the bias voltage in the PECVD process presented to a value of −20V not only provides high-quality films, but also gives physical insight into the cBN growth mechanism.
We have studied the nucleation and growth of cubic boron nitride (cBN) films deposited on silicon and diamond-coated silicon substrates using fluorine-assisted chemical vapor deposition (CVD). These comparative studies substantiate that the incubation amorphous/turbostratic BN layers, essential for the cBN nucleation on silicon, are not vital precursors for cBN nucleation on diamond, and they are inherently eliminated. At vastly reduced critical bias voltage, down to -10 V, cBN growth is still maintained on diamond surfaces, and cBN and underlying diamond crystallites exhibit an epitaxial relationship. However, the epitaxial growth is associated with stress in the cBN-diamond interfacial region. In addition, some twinning of crystallites and small-angle grain boundaries are observed between the cBN and diamond crystallites because of the slight lattice mismatch of 1.36%. The small-angle grain boundaries could be eliminated by imposing a little higher bias voltage during the initial growth stage. The heteroepitaxial growth of cBN films on different substrate materials are discussed in the view of lattice matching, surface-energy compatibility, and stability of the substrate against ion irradiation.
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