20,636 research outputs found

    Linear retrieval and global measurements of wind speed from the Seasat SMMR

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    Retrievals of wind speed (WS) from Seasat Scanning Multichannel Microwave Radiometer (SMMR) were performed using a two-step statistical technique. Nine subsets of two to five SMMR channels were examined for wind speed retrieval. These subsets were derived by using a leaps and bound procedure based on the coefficient of determination selection criteria to a statistical data base of brightness temperatures and geophysical parameters. Analysis of Monsoon Experiment and ocean station PAPA data showed a strong correlation between sea surface temperature and water vapor. This relation was used in generating the statistical data base. Global maps of WS were produced for one and three month periods

    Precipitable water: Its linear retrieval using leaps and bounds procedure and its global distribution from SEASAT SMMR data

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    Eight subsets using two to five frequencies of the SEASAT scanning multichannel microwave radiometer are examined to determine their potential in the retrieval of atmospheric water vapor content. Analysis indicates that the information concerning the 18 and 21 GHz channels are optimum for water vapor retrieval. A comparison with radiosonde observations gave an rms accuracy of approximately 0.40 g sq cm. The rms accuracy of precipitable water using different subsets was within 10 percent. Global maps of precipitable water over oceans using two and five channel retrieval (average of two and five channel retrieval) are given. Study of these maps reveals the possibility of global moisture distribution associated with oceanic currents and large scale general circulation in the atmosphere. A stable feature of the large scale circulation is noticed. The precipitable water is maximum over the Bay of Bengal and in the North Pacific over the Kuroshio current and shows a general latitudinal pattern

    Structural ordering driven anisotropic magnetoresistance, anomalous Hall resistance and its topological overtones in full-Heusler Co2MnSi thin films

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    We report the evolution of crystallographic structure, magnetic ordering and electronic transport in thin films of full-Heusler alloy Co2_2MnSi deposited on (001) MgO with annealing temperatures (TAT_A). By increasing the TAT_A from 300^\circC to 600^\circC, the film goes from a disordered nanocrystalline phase to B2B2 ordered and finally to the L21L2_1 ordered alloy. The saturation magnetic moment improves with structural ordering and approaches the Slater-Pauling value of 5.0μB\approx 5.0 \mu_B per formula unit for TAT_A = 600^\circC. At this stage the films are soft magnets with coercive and saturation fields as low as \approx 7 mT and 350 mT, respectively. Remarkable effects of improved structural order are also seen in longitudinal resistivity (ρxx\rho_{xx}) and residual resistivity ratio. A model based upon electronic transparency of grain boundaries illucidates the transition from a state of negative dρ/dTd\rho/dT to positive dρ/dTd\rho/dT with improved structural order. The Hall resistivity (ρxy\rho_{xy}) derives contribution from the normal scattering of charge carriers in external magnetic field, the anomalous effect originating from built-in magnetization and a small but distinct topological Hall effect in the disordered phase. The carrier concentration (nn) and mobility (μ\mu) have been extracted from the high field ρxy\rho_{xy} data. The highly ordered films are characterized by nn and μ\mu of 1.19×\times 1029^{29} m3^{-3} and 0.4 cm2V1s1^2V^{-1}s^{-1} at room temperature. The dependence of ρxy\rho_{xy} on ρxx\rho_{xx} indicates the dominance of skew scattering in our films, which shows a monotonic drop on raising the TAT_A. The topological Hall effect is analyzed for the films annealed at 300^\circC. ......Comment: 10 pages, 9 figures, 1 tabl
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