Supergiant Fast X-ray Transients in outburst: new Swift observations of XTE J1739−302, IGR J17544−2619 and IGR J08408−4503

We report on new X-ray outbursts observed with Swift from three Supergiant Fast X-ray Transients (SFXTs): XTE J1739−302, IGR J17544−2619 and IGR J08408−4503. XTE J1739−302 underwent a new outburst on 2008 August 13, IGR J17544−2619 on 2008 September 4 and IGR J08408−4503 on 2008 September 21. While the XTE J1739−302 and IGR J08408−4503 bright emission triggered the Swift /Burst Alert Telescope, IGR J17544−2619 did not, thus we could perform a spectral investigation only of the spectrum below 10 keV. The broad-band spectra from XTE J1739−302 and IGR J08408−4503 were compatible with the X-ray spectral shape displayed during the previous flares. A variable absorbing column density during the flare was observed in XTE J1739−302 for the first time. The broad-band spectrum of IGR J08408−4503 requires the presence of two distinct photon populations, a cold one (∼0.3 keV) most likely from a thermal halo around the neutron star and a hotter one (1.4–1.8 keV) from the accreting column. The outburst from XTE J1739−302 could be monitored with a very good sampling, thus revealing a shape which can be explained with a second wind component in this SFXT, in analogy to what we have suggested in the periodic SFXT IGR J11215−5952. The outburst recurrence time-scale in IGR J17544−2619 during our monitoring campaign with Swift suggests a long orbital period of ∼150 d (in a highly eccentric orbit), compatible with what previously observed with INTEGRAL .     

The determination of cloud altitudes using SCIAMACHY onboard ENVISAT

This letter shows first results for the application of a recently developed semianalytical cloud retrieval algorithm for the determination of cloud top heights from space. The technique is based on the measurements of the top-of-atmosphere reflectance in the oxygen A-band. The depth of the band depends on the cloud top height and its geometrical thickness. The data obtained are compared to ground-based measurements of the cloud top height using a cloud-profiling radar.     

The cloud phase discrimination from a satellite

A new technique to identify mixed-phase clouds but also clouds with supercooled water droplets using satellite measurements is proposed. The technique is based on measurements of the backscattered solar light at wavelengths 1.55 and 1.67 /spl mu/m in combination with cloud brightness temperature measurements at 12 /spl mu/m. For the first time, the concept of the phase index-temperature correlation plot (the P-T diagram) is introduced in the cloud remote sensing. Retrievals of cloud temperature and cloud phase index are performed using data from the Advanced Along Track Scanning Radiometer (AATSR) and Scaning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) both onboard the Envisat platform.     

The New SCIAMACHY Reference Solar Spectral Irradiance and Its Validation

This paper describes a new reference solar spectrum retrieved from measurements of the satellite instrument SCIAMACHY in the wavelength region from \(0.24~\upmu\mbox{m}\) to \(2.4~\upmu\mbox{m}\) and its comparison with several other established solar reference spectra. The SCIAMACHY reference spectrum was recorded early in the mission before substantial optical degradation due to the harsh space environment sets in. The radiometric calibration of SCIAMACHY, applied in this study, includes a physical model of the scanner unit. Furthermore, SCIAMACHY’s internal white light source (WLS) is used to correct for on-ground to in-flight changes. The resultant calibrated solar spectrum from SCIAMACHY is in good agreement with several available solar spectral irradiance (SSI) references in the visible spectral range. Strong throughput losses due to detector icing in the near infrared (NIR) are now adequately accounted for. Nevertheless, a deficit with respect to the ATLAS-3 composite and SORCE/SIM SSI is observed in the NIR. However, the SCIAMACHY solar reference spectrum agrees well with the recently re-evaluated SOLAR/SOLSPEC-ISS and recent ground measurements taken at Mauna Loa in the NIR.     

Modelling tidal stream power potential

In recent years, there has been an increase in interest in renewable energy sources for a number of reasons. A particular interest in tidal energy has developed within the UK due to its numerous sites of high current velocity. In this article a development, based upon previous work, of an existing hydrodynamic computational model is shown which is used to study the potential generation and the physical impacts of tidal stream farms. An idealised geometry is used to study the impacts of installed capacity and general layout of tidal stream farms and a realistic UK west coast model is used to examine the potential of presently proposed in-stream farms.     

Calibration of SCIAMACHY Using AATSR Top-of-Atmosphere Reflectance Over a Hurricane

This letter investigates the synergy between the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) and the Advanced Along Track Scanning Radiometer (AATSR) onboard the ENVISAT platform for reflectance calibration purposes. This calibration study was mainly performed over a portion of a hurricane corresponding to fully cloudy SCIAMACHY and AATSR pixels. Results show that SCIAMACHY underestimates the top-of-atmosphere (TOA) reflectance by up to 23% (at 870 nm) as compared to AATSR for a nadir viewing geometry. Specifically, considering AATSR calibration as accurate, which is confirmed by comparison with the Medium Resolution Imaging Spectrometer, the SCIAMACHY TOA reflectances should be multiplied by 1.21, 1.19, 1.23, and 1.10 for wavelengths at 550, 670, 870, and 1600 nm, respectively, ahead of satellite retrieval schemes based on the measurements of TOA reflectance     

Lattice Boltzmann simulations of the transient shallow water flows

A two-dimensional lattice Boltzmann model (LBM) is presented for transient shallow water flows. The model is based on the shallow water equations coupled with the large eddy simulation model. In order to obtain accurate results efficiently, a multi-block lattice scheme is applied at the area where a local finer grid is needed for strong change in physical variables. The model is verified by applying to five cases with transient processes: (a) a tidal wave over steps; (b) a perturbation over a submerged hump; (c) partial dam break flow; (d) circular dam break flow; (e) interaction between a dam break surge and four square cylinders. The objectives of this study are to validate the two-dimensional LBM in transient flow simulation and provide the detailed transient processes in shallow water flows.     

Efficient Calibration/Uncertainty Analysis Using Paired Complex/Surrogate Models

The use of detailed groundwater models to simulate complex environmental processes can be hampered by (1) long run‐times and (2) a penchant for solution convergence problems. Collectively, these can undermine the ability of a modeler to reduce and quantify predictive uncertainty, and therefore limit the use of such detailed models in the decision‐making context. We explain and demonstrate a novel approach to calibration and the exploration of posterior predictive uncertainty, of a complex model, that can overcome these problems in many modelling contexts. The methodology relies on conjunctive use of a simplified surrogate version of the complex model in combination with the complex model itself. The methodology employs gradient‐based subspace analysis and is thus readily adapted for use in highly parameterized contexts. In its most basic form, one or more surrogate models are used for calculation of the partial derivatives that collectively comprise the Jacobian matrix. Meanwhile, testing of parameter upgrades and the making of predictions is done by the original complex model. The methodology is demonstrated using a density‐dependent seawater intrusion model in which the model domain is characterized by a heterogeneous distribution of hydraulic conductivity.