Assessment and improvement of the Cloud Emission and Scattering Index (CESI) – an algorithm for cirrus detection

This study evaluates and improves the cirrus detection of the middle and low peak Weighting Function (WF) Cloud Emission and Scattering Index (CESI) by using the Visible Infrared Imaging Radiometer Suite (VIIRS) cloud mask product. Results show that CESI-3 (peak WF about 890 hPa) accurately detect cirrus with the Probability of detection (POD) value reaching 0.69 during both at day and nighttimes. The CESI-1 (peak WF about 550 hPa) falsely detects cirrus in the Sahara Desert, south of the Saudi Arabia, north of Tibetan Plateau and in Australia during the ascending process. More false alarm rates (FARs) are detected in the northern mid-latitude around 60° N because of the surface type and seasonal effects. Furthermore, the thresholds of middle and low peak WF CESIs for cirrus detection are determined and the performance is satisfactory. In addition, Linear Discriminant Analysis (LDA) is employed to train four combination types (combining CESI-1 and CESI-2, combining CESI-1 and CESI-3, combining CESI-2 and CESI-3, and combining CESI-1, CESI-2, and CESI-3). Accordingly, results elucidate that Comb-1-3 (combining CESI-1 and CESI-3) is appropriate to detect cirrus for the ascending process, increasing the POD by 11.2% as compared to CESI-3. However, Comb-1-2-3 (combining CESI-1, CESI-2 with peak WF around 790 hPa, and CESI-3) is most suitable for cirrus detection in the descending process, increasing the PODs by 8.5%. We also find that the POD of cirrus detection over the land increases relatively higher than over the sea. The most significant improvement of cirrus detection occurs over the land in the summer in the daytime with a 35% POD increase from 0.57 to 0.76.     

Satellite-retrieved vertical profiles of methane over the Indian region: impact of synoptic­scale meteorology

The altitude distribution of methane (CH₄) is the least addressed topic in the greenhouse gas assessment over the Indian region. In the absence of the in-situ measurements, the satellite-based retrievals of the vertical distribution of CH₄ using Atmospheric Infrared Sounder (AIRS) measurements during the period 2003–2015 were made use in this study for the first time to understand the 3D distribution (latitude-longitude-altitude) of CH₄ over Indian region. Significant regional and seasonal variations are observed in the vertical distribution of CH₄, even though it is a long-lived greenhouse gas and known to be well-mixed. Over most of the regions, the highest mixing ratio is observed during post-monsoon months and minimum in the pre-monsoon/monsoon season. The presence of a ‘high altitude peak’ in CH₄ (around 1880 ppbv) around 300 hPa–250 hPa was noted in post-monsoon which is caused by the monsoon-associated convective updrafts and the anti-cyclonic system. The vertical profiles show seasonal variations which are region as well as altitude-dependent. Over the oceanic region, the highest seasonal amplitude of CH₄ mixing ratio was observed over North–Arabian Sea due to the proximity of the source rich land regions. During the winter and pre-monsoon months, the latitudinal differences are absent throughout the troposphere. A consistent increasing trend in CH₄, ranging from 1 ppbv year^–1 to 6 ppbv year^–1 is seen at all the tropospheric altitudes, with faster growth rates at higher altitudes, maximizing at 300 hPa–150 hPa. An approximate estimate of direct forcing due to CH₄ lies in the range 0.80 W m^–2–0.83 W m^–2. The paper also presents a comparison of the in-situ measured upper tropospheric CH₄ mixing ratio from CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) flight data and AIRS retrievals.     

A theoretical exploration of the effect of fluorine and cyano substitutions in diketopyrrolopyrrole-based polymer donor for organic solar cells

A series of polymer donor materials 1-5 based on diketopyrrolopyrrole and thiophene unit which have been widely used in organic solar cells (OSCs) were investigated based on quantum chemical calculations. The effect of fluorine and cyano substitutions in polymer donor materials was focused on. Based on the investigation on electronic structures and optical properties of the reported molecules 1 and 2 and the analysis on some parameters relevant to charge dissociation ability at donor/acceptor interface constituted by 1 and 2 with PC₆₁BM such as intermolecular charge transfer and recombination, driving force and Coulombic bound energy, we explained why fluorine substitution can improve OPV efficiency through strengthening eletron-withdrawing ability from a theoretical perspective. Then we designed cyano-substituted polymers 3-5 with the aim of obtaining better photovoltaic donor materials. The results reveal that our attempt to design donor materials which can balance large open-circuit voltage (V_oc) and high short-circuit current (J_sc) in OSCs has worked out. It is worth noting that the substitutions of fluorine and cyano groups synergistically reduce energy gap and HOMO energy level of polymers 3 and 4. Moreover, 3/PC₆₁BM and 4/PC₆₁BM heterojunctions show over 10⁷ and 10⁴ times higher than 1/PC₆₁BM on the ratios of intermolecular charge transfer and recombination rates (k_inter-CT/k_inter-CR). Thus, our work here may provide an efficient strategy to design promising donor materials in OPVs and we hope it could be useful in the future experimental synthesis.     

Synergetic use of POLDER and MODIS for multilayered cloud identification

The purpose of this study is to investigate the possibility of identifying overlapping clouds that contain thin cirrus overlying a lower-level water cloud by synergetic use of POLDER-3 (Polarization and Directionality of the Earth Reflectance) and MODIS (MODerate resolution Imaging Spectroradiometer) data. When thin cirrus clouds overlap the liquid cloud layer, the liquid information may be obtained by POLDER observations and the presence of the cirrus may be inferred from the MODIS CO₂-slicing technique. An initial comparison of the POLDER cloud phase and the MODIS cloud-top pressure for one scene over East Asia also shows that a large portion of clouds declared as liquid water clouds by POLDER-3 correspond to the lower cloud-top pressures derived from MODIS. As a result, an overlapped cloud identification method is proposed under the assumption that the multilayered cloud would be present if the POLDER cloud phase is liquid water and the MODIS cloud-top pressure is less than 500 hPa. For the studied scene, the comparison of the multilayered cloud identification results with CloudSat and CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) observations illustrates that the proposed method could detect multilayered clouds when the upper cirrus has a visible optical thickness of less than 2.0. Then the identification results are compared with the MODIS Cloud_Multi_Layer_Flag. It is indicated that the consistency between the multilayered clouds from the proposed synergy and MODIS-operational algorithm increases gradually from over 40% to nearly 100% with the increase of the confidence level of the MODIS multilayered clouds from the lowest to the highest. Further analysis suggests that the majority of multilayered clouds falsely classified as single-layered clouds by the proposed method may correspond to relatively thick cirrus covering lower-level water clouds. Additionally, an index by using the multilayered cloud detection differences from the two methods is proposed to provide some information on the optical thickness of the cirrus covering lower-level water cloud. Finally, quantitative comparisons are extended to four other scenes at different locations by using active measurements. The results also show that the mean visible optical thickness of the high-level clouds of the multilayered clouds detected by both methods (1.57) is remarkably less than that by only MODIS-operational method (2.84), which means that the differences between the results from the two methods are mainly caused by the different sensitivities to the visible optical thickness of the high-level cloud and could be used to indicate the range of the visible optical thickness of the cirrus clouds covering the lower-level water clouds.     

A direct numerical simulation of transition phenomena in a mixed convection channel flow

This study intends to provide an increased understanding of the laminar-turbulent transition phenomena for the buoyancy-assisted heated vertical channel flow during the early transient stage. The spectral method with weak formulation is applied in the direct numerical simulation. Initial disturbances consist of the finite-amplitude two-dimensional TS wave and a pair of three-dimensional oblique waves for the K-type disturbances. The results from the harmonic energy competitions of different wave modes show that for the buoyancy-assisted heated flow, the (k_x=1, k_z=1) or (1,1) and (1,0) modes would gain energy immediately and start to rise at almost the same rate. This phenomenon is different from that of the buoyancy-opposed flow, where the (1,1) mode decays slowly in the beginning until other modes gain enough energy and then it begins to grow quickly and overtakes the (1,0) mode after a short time period. These different transition patterns match with the experimental results that the flow transition is supercritical and subcritical for the buoyancy-assisted and -opposed flows, respectively. Buoyancy-assisted heated flow transition follows the general trend of an isothermal flow in the beginning, but the thermal-buoyant force is crucial in accelerating the instability and also causing notable differences during the subsequent transition process. All of the results for the vortex structures development, kinetic energy budget of the disturbances, flow visualization by tagged fluid particles, and the local temperature fluctuations are consistent in pointing to a clear pattern for the buoyancy-assisted heated flow transition.     

Stability and performance analysis of time‐delay LPV systems with brief instability

Linear parameter‐varying (LPV) systems provide a systematic framework for the study of nonlinear systems by considering a representative family of linear time‐invariant systems parameterized by system parameters residing in a compact set. The brief instability concept in such systems allows the linear system to be unstable for some trajectories of the LPV parameter set, so that instability occurs only for short periods of time. In the present paper, we extend the notion of brief instability to LPV systems with time delay in their dynamics. The results provide tools for the stability and performance analysis of such systems, where performance is evaluated in terms of induced ??₂‐gain (or so‐called ??_∞ norm). The main results of this paper illustrate that stability and performance conditions can be evaluated by examining the feasibility of parameterized sets of linear matrix inequalities (LMIs). Using the results of this paper, we then investigate analysis conditions to guarantee the asymptotic stability and ??_∞ performance of fault‐tolerant control (FTC) systems, in which instability may take place for a short period of time due to the false identification of the fault signals provided by a fault detection and isolation (FDI) module. The numerical examples are used to illustrate the qualification of the proposed analysis and synthesis results for addressing brief instability in time‐delay systems. Copyright © 2010 John Wiley & Sons, Ltd.     

The impact of assimilation of satellite derived wind observations for the prediction of a monsoon depression over India using a mesoscale model

The Penn State/NCAR mesoscale model (MM5) has been used in this study to ingest and assimilate the INSAT‐CMV (Indian National Satellite System‐Cloud Motion Vector) wind observations using analysis nudging (four‐dimensional data assimilation, FDDA) to improve the prediction of a monsoon depression which occurred over the Bay of Bengal, India during 28 July 2005 to 31 July 2005. To determine the impact of assimilation of INSAT‐CMV winds on the prediction of a monsoon depression, three sets of numerical experiments (NOFDDA, FDDA and FDDA CMV) were designed. While the FDDA CMV run assimilated satellite derived winds only, the FDDA run assimilated both satellite and conventional observations. The NOFDDA run used neither satellite nor conventional observations. The results of the study indicate that the simulated sea level pressure field from the FDDA run is more consistent with the sea level pressure field from NCEP‐FNL compared to the FDDA CMV and NOFDDA runs. The highest correlation and lowest rms error of the sea level pressure field are associated with the FDDA run, and this provides a quantitative verification of the improvement due to the assimilation of satellite derived winds and the conventional upper air observations for the prediction of monsoon depression. All the three model simulated winds are in good agreement with the analysis winds at 850 hPa, 500 hPa and 200 hPa levels. The simulated structure of the spatial precipitation pattern for the assimilation experiments (FDDA and FDDA CMV) are closer to the TRMM observations with more rainfall simulated over the east coast regions in the assimilation experiments. The rms errors of the wind speed for the FDDA run show lower values at 500 hPa for all the three model runs, with a reduction in all three levels of up to 0.8–1.4 m s^?1 for the FDDA run and 0.5–1.9 m s^?1 for the FDDA CMV run with respect to the NOFDDA run. The statistical significance of the sea level pressure and the precipitation differences between the FDDA and the NOFDDA as well as the differences between the FDDA CMV and the NOFDDA have been calculated using the two‐tailed Student's t‐test and were found to be statistically significant. The influence of varying the nudging coefficients in the FDDA experiment has been studied.     

Global distribution of tropospheric ozone and its precursors: a view from space

Satellite-borne tropospheric ozone measurements obtained from the tropospheric ozone residual (TOR) method, CO from the MOPITT (at 850 hPa level) measurements and NO₂ from the SCIAMACHY measurements for the three-year period 2003–2005 have been utilized to examine the distribution of the pollutant sources and long-range transport on a global scale. Elevated tropospheric ozone columns have been observed over regions of high NO₂ and CO concentrations in the northern and southern hemispheres. High levels of the tropospheric ozone column have been observed below about 5°S in the vicinity of the biomass burning regions and extend from continents out over the Atlantic during October. The seasonal distribution of tropospheric O₃ and its precursors in the southern hemisphere shows the strong correlation with the seasonal variation of biomass burning in Africa and South America. Northern hemisphere summer shows the widespread ozone and CO pollution throughout the middle latitudes. The inter-hemispheric gradient of ozone and CO found to be decreased during October. Large-scale transport of the ozone and CO over the Atlantic and Pacific Oceans has been clearly identified. Strong inter-continental transport has been observed to occur from west to east along with the mid-latitude winds in the northern hemisphere.     

Bifurcations and buffet of transonic flow past flattened surfaces

Turbulent transonic flow past flattened aerodynamic surfaces is investigated numerically using the RANS equations. The study is focused on: (★) a buffet onset caused by instability of the shock wave/boundary layer interaction, (★★) instability of the entire flow structure and related flow bifurcations.For a symmetric airfoil at zero angle of attack, computations reveal both bifurcations and buffet in a range of the freestream Mach number M_∞. At nonzero angles of attack, α=±1°, there are two ranges of M_∞ in which the buffet onset takes place. For a Whitcomb type airfoil, computations demonstrate instability of the flow structure only at negative α. Axisymmetric flow past axisymmetric bodies is also considered, and instability of the flow structure at certain freestream Mach numbers is shown.     

Measuring and modelling CO2 effects on sugarcane

In order to fully capture the benefits of rising CO₂ in adapting agriculture to climate change, we first need to understand how CO₂ affects crop growth. Several recent studies reported unexpected increases in sugarcane (C₄) yields under elevated CO₂, but it is difficult to distinguish direct leaf-level effects of rising CO₂ on photosynthesis from indirect water-related responses. A simulation model of CO₂ effects, based purely on changes in stomatal conductance (indirect mechanism), showed transpiration was reduced by 30% (initially) to 10% (closed canopy) and yield increased by 3% even in a well-irrigated crop. The model incorporated the results of a field experiment, and a glasshouse experiment designed to disentangle the mechanisms of CO₂ response: whole-plant transpiration and stomatal conductance were both 28% lower for plants growing with high-frequency demand-based watering at 720 vs 390 ppm CO₂, but there was no increase in biomass, indicating that indirect mechanisms dominate CO₂ responses in sugarcane.     

On the bounds of the trajectories of differential systems†

The behaviour of differential systems is investigated by considering the stability and instability of such systems with respect to certain sub-sets of the state space These Sets may in general be time-varying, and their properties do not only yield information about the stability of a system but also estimates of the bounds of the system trajectories. In all cases the results which are established yield sufficient conditions for stability and instability, and in general involve the existence of Lyapunov-like functions which do not appear to possess the usual definiteness requirements on V and [Vdot].

The developed theory is applied to two special cases: in one case, only time-invariant sub-sets are considered: in the second case, the time interval [t₀, ∞) over which the systems me defined is truncated to [t ₀, t _a  + T), T < ∞, So the that case of stability over a finite time interval may be considered.     

Simulation of a thermonuclear target drive at the 1 MJ laser energy level

The objective of this study was by use of mathematical simulation methods to create an opportunity of a thermonuclear target (k _f ) gain of the order of 1 at the 1 MJ laser energy level. The calculations were performed in two codes with a comparison of their results. It is shown that in the direct drive mode it is possible to obtain a neuron yield an order higher than that obtained in experiments on the NIF (LLNL, the United States) installation in the indirect drive target.     

Stability and l2‐gain of discrete‐time switched systems with unstable modes

This paper addresses stability and l₂‐gain for discrete‐time switched systems with unstable modes based on slow/fast mode‐dependent average dwell time (MDADT) switching strategies. Firstly, by employing a class of multiple discontinuous Lyapunov functions (MDLFs) and developing a kind of alternative switching signals, the sufficient conditions on stability are established for the system without external disturbances under a slow/fast MDADT switching scheme with a tighter bounds on the dwell time. Furthermore, by defining indicator functions and exploring the features of slow/fast MDADT switching, the weighted l₂‐gain conditions are achieved for the system with external disturbances. Particularly, the criteria of stability and l₂‐gain are also established for the corresponding discrete‐time switched linear systems with unstable modes via the MDLFs method and the slow/fast MDADT switching strategy. Finally, two numerical examples are presented to illustrate the advantages of the proposed methods.     

Analysis of the aging characteristics of SnO2 gas sensors

Two types of tin oxide (SnO₂) gas sensors were synthesized, which consist of spherical SnO₂ nanoparticles and SnO₂ nanorods mixed at different ratio, and their aging processes were studied. Using the Complex Impedance Spectroscopy method the electrical properties that are related to the microscopic structure of the samples were investigated. The evolution of absorption current was measured to analyze the ionic conductance that reflects the charging states of the samples. The results indicate that devices of optimal long-term stability can be obtained by sintering the mixture of SnO₂ nanorods and spherical nanoparticles (1:1 weight ratio) at 850 °C. In the samples’ impedance data considerable fluctuation could be seen during the early stage of the aging process, which gradually disappeared after several days. The aging process, which is revealed by the changes in both grain-boundary resistance and capacitance, indicates the corresponding changes in the grain-boundary barrier height and the width of depletion layer. We suggest the DC-field-induced migration of ions within the grain boundaries as the probable cause of the phenomenon.     

Aerobic Capacity of Steel Workers in India

Abstract

Seventy-six workers, aged 21–43 y. drawn from three major steel plants—two located in the eastern and one in the central region of India (referred to as Group A, Group B and Group C respectively)—were studied on the bicycle ergometer to determine their aerobic capacity ([Vdot]_O2max), Both the direct and indirect methods were employed, the direct one being used only in the case of the workers in Group C. The mean [Vdot]_O2max of these workers was found to be 42·6 cm³ kg^?1 with a standard error of ± 0·71 cm³ kg^?1 min^?1. The highest values were observed among the workers in Group B (mean 47·0± 1·35 (S.E.)cm³kg^?1 min^?1) who are ethnically distinct and have a high level of customary activity, and the lowest among workers in Group C (mean: 39·0±0·74(S.E.) cm³kg^?1 min^?1).

As expected, the [Vdot]_O2max was found to be correlated positively with body weight, and negatively with age in a multiple regression analysis. Furthermore, the active Group B has values for [Vdot]_O2max that are significantly higher than those for the other Groups, a difference that is not attributable to weight or age.     

Theory and design of robust direct and indirect adaptive-control schemes

A general approach for designing and the theory for analysing robust direct and indirect adaptive-control schemes for continuous-time plants is presented. The design approach involves the development of a general robust adaptive law and the use of the certainty equivalence principle to combine it with robust model reference and pole placement control structures. The global stability properties and robustness of the developed adaptive control schemes are established by using a general theory which relates the properties of signals in the mean sense over intervals of time. The developed theory and design approach are used to analyse and compare the robustness properties and performance of a wide class of robust adaptive laws which employ a dead-zone, fixed-σ, ε₁, and a switching-σ modification as well as their variations.     

Liapunov functions and stability criteria for nonlinear systems with multiple critical eigenvalues

Efficient criteria are derived via explicit construction of Liapunov functions for local asymptotic stability inference of nonlinear systems, whose linearizations possessc 2 critical modes at an equilibrium point. The stability criteria are obtained in the context of two novel notions, relaxed definiteness and relaxed stability. A real symmetricc×c matrixQ isrelaxed negative definite ifw ^TQw<0 for any 0w ₊ ^c , ₊=[0, ); a matrixR isrelaxed stable if there is aP>0 such thatPR+R ^TP is relaxed negative definite. The construction leads to some characterizations of the nonlinear system's local structure,in the sense of Liapunov, and the so-called stability characteristic matrices and tensors. It is shown that a nonlinear system with multiple critical modes is locally asymptotically stable generically if the stability characteristic matrix is relaxed stable and less generically if the stability characteristic tensor is trivial or degenerate in certain way and the perturbed stability characteristic matrix is relaxed stable.     

Estimation and distribution of near-surface meteorological elements over complex terrains: a case study in the Tibetan areas of West Sichuan Province,China

ABSTRACT

Meteorological elements are important for various fields related to human activities, including scientific research. Using the Tibetan Areas of West Sichuan Province (TAOWS) as an example, this study examined the estimation methods for near-surface air temperature (T_a), vapour pressure deficit (VPD), and atmospheric pressure (P) and their distribution characteristics in areas with complex terrains and sparse stations. An improved satellite-based approach, combining an artificial neural network and inverse distance weighting (ANN-IDW), is proposed for estimating T_a and VPD with high-accuracy under all weather conditions from Moderate Resolution Imaging Spectroradiometer (MODIS) data. The data of 41 meteorological stations in TAOWS and its adjacent areas were used for the training and validation of the ANN-IDW. For T_a and VPD, the mean absolute errors (MAEs) of the ANN-IDW are 1.45°C to 2.15°C and 0.54 hPa to 0.87 hPa, respectively. Also, the detailed features of the distribution of the estimated T_a and VPD are prominent and closely related to the terrain. The accuracy of the method was also verified indirectly. In addition, the improved method based on the existing method was applied for estimating P. The results confirm that (1) the ANN-IDW is suitable for estimating T_a and VPD in areas with complex terrain and sparse stations under all weather conditions; (2) the improved method is more suitable for estimating P at high-elevation. Moreover, the distribution characteristics of meteorological elements in TAOWS were also analysed. These elements influence agricultural production and animal husbandry and have a high application value. The results further show that topography is the most important factor affecting the spatial distribution and complexity of meteorological elements over complex terrains, but the degree of influence of topography varies greatly across different seasons.