25,441 research outputs found
Impact of upper-level jet-generated inertia-gravity waves on surface wind and precipitation
International audienceA meteorological case study for the impact of inertia-gravity waves on surface meteorology is presented. The large-scale environment from 17 to 19 December 1999 was dominated by a poleward breaking Rossby wave transporting subtropical air over the North Atlantic Ocean upward and north-eastward. The synoptic situation was characterized with an upper tropospheric jet streak passing Northern Europe. The unbalanced jet spontaneously radiated inertia-gravity waves from its exit region. Near-inertial waves appeared with a horizontal wavelength of about 200 km and an apparent period of about 12 h. These waves transported energy downwards and interacted with large-scale convection. This configuration is simulated with the nonhydrostatic Fifth-Generation Mesoscale Model. Together with simplified runs without orography and moisture it is demonstrated that the imbalance of the jet (detected with the cross-stream ageostrophic wind) and the deep convection (quantified with the latent heat release) are forcing inertia-gravity waves. This interaction is especially pronounced when the upper tropospheric jet is located above a cold front at the surface and supports deep frontal convection. Weak indication was found for triggering post-frontal convection by inertia-gravity waves. The realism of model simulations was studied in an extended validation study for the Baltic Sea region. It included observations from radar (DWDPI, BALTRAD), satellite (GFZGPS), weather stations (DWDMI) and assimilated products (ELDAS, MESAN). The detected spatio-temporal patterns show wind pulsations and precipitation events at scales corresponding to those of inertia-gravity waves. In particular, the robust features of strong wind and enhanced precipitation near the front appeared with nearly the same amplitudes as in the model. In some datasets we found indication for periodic variations in the post-frontal region. These findings demonstrate the impact of upper tropospheric jet-generated inertia-gravity waves on the dynamics of the boundary layer. It also gives confidence to models, observations and assimilation products for covering such processes. In an application for the Gotland Basin in the Baltic Sea, the implications of such mesoscale events on air-sea interaction and energy and water budgets are discussed
The Arizona Radio Observatory CO Mapping Survey of Galactic Molecular Clouds: III. The Serpens Cloud in CO J=2-1 and 13CO J=2-1 Emission
We mapped 12CO and 13CO J = 2-1 emission over 1.04 square deg of the Serpens
molecular cloud with 38 arcsec spatial and 0.3 km/s spectral resolution using
the Arizona Radio Observatory Heinrich Hertz Submillimeter telescope. Our maps
resolve kinematic properties for the entire Serpens cloud. We also compare our
velocity moment maps with known positions of Young Stellar Objects (YSOs) and
1.1 mm continuum emission. We find that 12CO is self-absorbed and 13CO is
optically thick in the Serpens core. Outside of the Serpens core, gas appears
in filamentary structures having LSR velocities which are blue-shifted by up to
2 km/s relative to the 8 km/s systemic velocity of the Serpens cloud. We show
that the known Class I, Flat, and Class II YSOs in the Serpens core most likely
formed at the same spatial location and have since drifted apart. The spatial
and velocity structure of the 12CO line ratios implies that a detailed
3-dimensional radiative transfer model of the cloud will be necessary for full
interpretation of our spectral data. The starless cores region of the cloud is
likely to be the next site of star formation in Serpens.Comment: 41 pages, 15 figure
Investigation and study of a multi-aperture antenna system final report, 1 jan. - 1 apr. 1964
Multiple aperture adaptive antenna system for telemetry reception from remote space vehicle
Development of mathematical techniques for the analysis of remote sensing data
There are no author-identified significant results in this report
Non-locality and Medium Effects in the Exclusive Photoproduction of Eta Mesons on Nuclei
A relativistic model for the quasifree exclusive photoproduction of
mesons on nuclei is extended to include both non-local and medium effects. The
reaction is assumed to proceed via the dominant contribution of the
S(1535) resonance. The complicated integrals resulting from the
non-locality are simplified using a modified version of a method given by
Cooper and Maxwell. The non-locality effects are found to affect the magnitude
of the cross section. Some possibilities reflecting the effects of the medium
on the propagation and properties of the intermediate S resonance are
studied. The effects of allowing the S to interact with the medium via
mean field scalar and vector potentials are considered. Both broadening of
width and reduction in mass of the resonance lead to a suppression of the
calculated cross sections.Comment: 19 pages, 7 figure
Generating Potent CāH PCET Donors: Ligand-Induced Fe-to-Ring Proton Migration from a Cp*Fe^(III)āH Complex Demonstrates a Promising Strategy
Highly reactive organometallic species that mediate reductive proton-coupled electron transfer (PCET) reactions are an exciting area for development in catalysis, where a key objective focuses on tuning the reactivity of such species. This work pursues ligand-induced activation of a stable organometallic complex toward PCET reactivity. This is studied via the conversion of a prototypical Cp*Fe^(III)āH species, [Fe^(III)(Ī·āµ-Cp*)(dppe)H]āŗ (Cp* = Cā
Meā
ā», dppe = 1,2-bis(diphenylphosphino)ethane), to a highly reactive, S = 1/2 ring-protonated endo-Cp*HāFe relative, triggered by the addition of CO. Our assignment of the latter ring-protonated species contrasts with its previous reported formulation, which instead assigned it as a hypervalent 19-electron hydride, [Fe^(III)(Ī·āµ-Cp*)(dppe)(CO)H]āŗ. Herein, pulse EPR spectroscopy (^(1,2)H HYSCORE, ENDOR) and X-ray crystallography, with corresponding DFT studies, cement its assignment as the ring-protonated isomer, [Fe^I(endo-Ī·ā“-Cp*H)(dppe)(CO)] āŗ. A less sterically shielded and hence more reactive exo-isomer can be generated through oxidation of a stable Fe0(exo-Ī·ā“-Cp*H)(dppe)(CO) precursor. Both endo- and exo-ring-protonated isomers are calculated to have an exceptionally low bond dissociation free energy (BDFE_(CāH) ā 29 kcal molā»Ā¹ and 25 kcal molā»Ā¹, respectively) cf. BDFE_(FeāH) of 56 kcal molā»Ā¹ for [Fe^(III)(Ī·āµ-Cp*)(dppe)H] āŗ. These weak CāH bonds are shown to undergo proton-coupled electron transfer (PCET) to azobenzene to generate diphenylhydrazine and the corresponding closed-shell [Fe^(II)(Ī·āµ-Cp*)(dppe)CO]āŗ byproduct
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