Relationship between clear-sky atmospheric greenhouse effect and deep convection during the Central Equatorial Pacific Experiment: Model calculations and satellite observations

This study investigates the relation between tropical convection and the atmospheric greenhouse effect using data collected during the Central Equatorial Pacific Experiment (CEPEX). We present calculations of total clear-sky greenhouse effect and its partitioning between the lower, middle, and upper troposphere using high-quality balloon soundings of temperature and humidity as input to a radiative transfer model. The soundings were taken from a ship every 6 hours from March 7 to 20, 1993, in the central Pacific. We examine the influence on atmospheric greenhouse effect due to changes in humidity and lapse rate and investigate the relationship between atmospheric greenhouse effect, water vapor, and deep convection. Our observations indicate that periods of active or suppressed convection with timescales of the order of days can produce large spatial gradients in clear-sky atmospheric greenhouse trapping in warm, climatologically convective regions. While the sea surface temperature (SST) decreased by 2 K from west to east, temperatures above 850 mbar showed considerably less variation. Accordingly, lapse rate changes occurred primarily in the boundary layer and such changes account for 80% of the gradient in boundary layer greenhouse effect. The column-integrated water vapor content from the surface to 850 mbar was nearly constant in each of the regimes. Conversely, large variations in column-integrated water vapor above 850 mbar and particularly above 500 mbar account for nearly all the gradient in the greenhouse effect in the middle and upper troposphere. Coincident outgoing longwave radiation (OLR) analyses derived from satellite observations show active deep convection in areas with high clear-sky greenhouse trapping and upper level moisture and generally clear, suppressed conditions elsewhere. In addition, the surface net flux and outgoing flux emitted to space decreased with increased SST. The reduced cooling of the ocean-atmosphere system is consistent with a supergreenhouse effect operating in regions of deep convection

Local Ferroelectricity in SrTiO_3 Thin Films

The temperature-dependent polarization of SrTiO_3 thin films is investigated using confocal scanning optical microscopy. A homogeneous out-of-plane and inhomogeneous in-plane ferroelectric phase are identified from images of the linear electrooptic response. Both hysteretic and non-hysteretic behavior are observed under a dc bias field. Unlike classical transitions in bulk ferroelectrics, local ferroelectricity is observed at temperatures far above the dielectric permittivity maximum. The results demonstrate the utility of local probe experiments in understanding inhomogeneous ferroelectrics.Comment: 8 pages, 3 figures, accepted for publication in PR

Photonic excess noise and wave localization

This is a theory for the effect of localization on the super-Poissonian noise of radiation propagating through an absorbing disordered waveguide. Localization suppresses both the mean photon current I and the noise power P, but the Fano factor P/I is found to remain unaffected. For strong absorption the Fano factor has the universal value 1+3f/2 (with f the Bose-Einstein function), regardless of whether the waveguide is long or short compared to the localization length.Comment: 3 pages including 3 figure

Handling qualities of a wide-body transport airplane utilizing Pitch Active Control Systems (PACS) for relaxed static stability application

Piloted simulation studies have been conducted to evaluate the effectiveness of two pitch active control systems (PACS) on the flying qualities of a wide-body transport airplane when operating at negative static margins. These two pitch active control systems consisted of a simple 'near-term' PACS and a more complex 'advanced' PACS. Eight different flight conditions, representing the entire flight envelope, were evaluated with emphasis on the cruise flight conditions. These studies were made utilizing the Langley Visual/Motion Simulator (VMS) which has six degrees of freedom. The simulation tests indicated that (1) the flying qualities of the baseline aircraft (PACS off) for the cruise and other high-speed flight conditions were unacceptable at center-of-gravity positions aft of the neutral static stability point; (2) within the linear static stability flight envelope, the near-term PACS provided acceptable flying qualities for static stabilty margins to -3 percent; and (3) with the advanced PACS operative, the flying qualities were demonstrated to be good (satisfactory to very acceptable) for static stabilty margins to -20 percent

EGRET Observations of the Diffuse Gamma-Ray Emission in Orion: Analysis Through Cycle 6

We present a study of the high-energy diffuse emission observed toward Orion by the Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma-Ray Observatory. The total exposure by EGRET in this region has increased by more than a factor of two since a previous study. A simple model for the diffuse emission adequately fits the data; no significant point sources are detected in the region studied ($l = 195^\circ$ to $220^\circ$ and $b = -25^\circ to -10^\circ$) in either the composite dataset or in two separate groups of EGRET viewing periods considered. The gamma-ray emissivity in Orion is found to be $(1.65 \pm 0.11) \times 10^{-26} {s sr}^{-1}$ for E > 100 MeV, and the differential emissivity is well-described as a combination of contributions from cosmic-ray electrons and protons with approximately the local density. The molecular mass calibrating ratio is $N(H_2)/W_{CO} = (1.35 \pm 0.15) \times 10^{20} cm^{-2} (K km/s)^{-1}$.Comment: 16 pages, including 5 figures. 3 Tables as three separate files. Latex document, needs AASTEX style files. Accepted for publication in Ap