Simulations of satellite Doppler wind observations

This study will involve two objectives: (1) to develop, through computer simulations, optimal satellite-based sensor scanning techniques for direct measurement of tropospheric winds on the meso- and synoptic scales; and (2) to construct simulations of remotely measured wind fields for assessing impact of such fields on the diagnosis and prognosis of atmospheric phenomena through the use of Observing System Simulation Experiments (OSSE). Using the LAWS Simulation Model (LSM), various global coverage scenarios have been investigated as part of an effort to define the optimal orbit, configuration and sampling strategies for observations of winds for use in global circulation models. Simulated data sets have been provided to GSFC, FSU and several LAWS team members. Particular emphasis has been on providing realistic cloud cover, cirrus backscatter, aerosol distribution and wind variance on scales less than 600 km. Progress is currently being made to incorporate other remote sensors (AIRS/AMSU, STIKSCAT) into the global OSSEs

B-field Determination from Magnetoacoustic Oscillations in kHz QPO Neutron Star Binaries: Theory and Observations

We present a method for determining the B-field around neutron stars based on observed kHz and viscous QPO frequencies used in combination with the best-fit optical depth and temperature of a Comptonization model. In the framework of the transition layer QPO model, we analyze magnetoacoustic wave formation in the layer between a neutron star surface and the inner edge of a Keplerian disk. We derive formulas for the magnetoacoustic wave frequencies for different regimes of radial transition layer oscillations. We demonstrate that our model can use the QPO as a new kind of probe to determine the magnetic field strengths for 4U 1728-42, GX 340+0, and Sco X-1 in the zone where the QPOs occur. Observations indicate that the dependence of the viscous frequency on the Keplerian frequency is closely related to the inferred dependence of the magnetoacoustic wave frequency on the Keplerian frequency for a dipole magnetic field. The magnetoacoustic wave dependence is based on a single parameter, the magnetic moment of the star as estimated from the field strength in the transition layer. The best-fit magnetic moment parameter is about (0.5-1)x 10^{25} G cm^3 for all studied sources. From observational data, the magnetic fields within distances less 20 km from neutron star for all three sources are strongly constrained to be dipole fields with the strengths 10^{7-8} G on the neutron star surface.Comment: 10 pages, 1 figure, accepted for the Astrophysical Journal Letter

Long-term Effects of Tillage on the Retention and Transport of Soil Water

Quantitative measurements were made of the physical and chemical properties of two virgin prairie soils, Crowley and Jay, that remain in their native Arkansas environments and of similar soils that had been tilled extensively. Comparisons were made of soil properties at several depths. When compared with the tilled soils the virgin soils had higher organic matter contents, saturated hydraulic conductivities and water retained at several applied pressures. Bulk densities and hydraulic resistances were lower in the virgin soils. For the Crowley silt loam, values of pH and elemental contents of the virgin soil were higher than those of the tilled soil. Determinations also were made of the effects of a 14-year addition of winter cover crops on a Dubbs-Dundee soil in continuous cotton production. In general, the winter cover crops tended to increase hydraulic conductivity~. ·porosity and organic matter content. These results indicated that the detrimental effects of long-term tillage on soil hydraulic properties could partially be overcome with the planting of these crops during the winter. However, the rate of improvement in the hydraulic properties was not dramatic

Photoionisation and Heating of a Supernova Driven, Turbulent, Interstellar Medium

The Diffuse Ionised Gas (DIG) in galaxies traces photoionisation feedback from massive stars. Through three dimensional photoionisation simulations, we study the propagation of ionising photons, photoionisation heating and the resulting distribution of ionised and neutral gas within snapshots of magnetohydrodynamic simulations of a supernova driven turbulent interstellar medium. We also investigate the impact of non-photoionisation heating on observed optical emission line ratios. Inclusion of a heating term which scales less steeply with electron density than photoionisation is required to produce diagnostic emission line ratios similar to those observed with the Wisconsin H{\alpha} Mapper. Once such heating terms have been included, we are also able to produce temperatures similar to those inferred from observations of the DIG, with temperatures increasing to above 15000 K at heights |z| > 1 kpc. We find that ionising photons travel through low density regions close to the midplane of the simulations, while travelling through diffuse low density regions at large heights. The majority of photons travel small distances (< 100pc); however some travel kiloparsecs and ionise the DIG.Comment: 10 pages, 13 figures, accepted to MNRA

Fermi LAT Gamma-ray Detections of Classical Novae V1369 Centauri 2013 and V5668 Sagittarii 2015

We report the Fermi Large Area Telescope (LAT) detections of high-energy (>100 MeV) gamma-ray emission from two recent optically bright classical novae, V1369 Centauri 2013 and V5668 Sagittarii 2015. At early times, Fermi target-of-opportunity observations prompted by their optical discoveries provided enhanced LAT exposure that enabled the detections of gamma-ray onsets beginning ~2 days after their first optical peaks. Significant gamma-ray emission was found extending to 39-55 days after their initial LAT detections, with systematically fainter and longer duration emission compared to previous gamma-ray detected classical novae. These novae were distinguished by multiple bright optical peaks that encompassed the timespans of the observed gamma rays. The gamma-ray light curves and spectra of the two novae are presented along with representative hadronic and leptonic models, and comparisons to other novae detected by the LAT are discussed.Comment: 13 pages, 6 figures, 4 tables, ApJ accepte

Two blowing concepts for roll and lateral control of aircraft

Two schemes to modulate aerodynamic forces for roll and lateral control of aircraft have been investigated. The first scheme, called the lateral blowing concept, consists of thin jets of air exiting spanwise, or at small angle with the spanwise direction, from slots at the tips of straight wings. For this scheme, in addition to experimental measurements, a theory was developed showing the analytical relationship between aerodynamic forces and jet and wing parameters. Experimental results confirmed the theoretically derived scaling laws. The second scheme, which was studied experimentally, is called the jet spoiler concept and consists of thin jets exiting normally to the wing surface from slots aligned with the spanwise direction