Monitoring of Saharan dust over the Atlantic using Meteosat-VIS-data

The optical depth of Saharan dustclouds (a component of the radiation budget), which can be clearly seen in satellite images taken over the Atlantic, can be determined from the Meteosat VIS-data. ‘Favourable angles’ between sun, observed point and satellite are chosen so that the optical depth is determined with an inaccuracy of only about 20%.We present several clouds, their change over time, and some of their other interesting features. The results are discussed.     

Detection of aerosol pollution sources during sandstorms in Northwestern China using remote sensed and model simulated data

The present paper has used a comprehensive approach to study atmosphere pollution sources including the study of vertical distribution characteristics, the epicenters of occurrence and transport of atmospheric aerosol in North-West China under intensive dust storm registered in all cities of the region in April 2014. To achieve this goal, the remote sensing data using Moderate Resolution Imaging Spectroradiometer satellite (MODIS) as well as model-simulated data, were used, which facilitate tracking the sources, routes, and spatial extent of dust storms. The results of the study have shown strong territory pollution with aerosol during sandstorm. According to ground-based air quality monitoring stations data, concentrations of PM₁₀ and PM_2.5 exceeded 400?μg/m³ and 150?μg/m³, respectively, the ratio PM_2.5/PM₁₀ being within the range of 0.123–0.661. According to MODIS/Terra Collection 6 Level-2 aerosol products data and the Deep Blue algorithm data, the aerosol optical depth (AOD) at 550?nm in the pollution epicenter was within 0.75–1. The vertical distribution of aerosols indicates that the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) 532?nm total attenuates backscatter coefficient ranges from 0.01 to 0.0001?km^?1?×?sr^?1 with the distribution of the main types of aerosols in the troposphere of the region within 0–12.5?km, where the most severe aerosol contamination is observed in the lower troposphere (at 3–6?km). According to satellite sounding and model-simulated data, the sources of pollution are the deserted regions of Northern and Northwestern China.     

Remote sensing of aerosol and radiation from geostationary satellites

The paper presents a high-level overview of current and future remote sensing of aerosol and shortwave radiation budget carried out at the US National Oceanic and Atmospheric Administration (NOAA) from the US Geostationary Operational Environmental Satellite (GOES) series. The retrievals from the current GOES imagers are based on physical principles. Aerosol and radiation are estimated in separate processing from the comparison of satellite-observed reflectances derived from a single visible channel with those calculated from detailed radiative transfer. The radiative transfer calculation accounts for multiple scattering by molecules, aerosol and cloud and absorption by the major atmospheric gases. The retrievals are performed operationally every 30 min for aerosol and every hour for radiation for pixel sizes of 4-km (aerosol) and 15- to 50-km (radiation). Both retrievals estimate the surface reflectance as a byproduct from the time composite of clear visible reflectances assuming fixed values of the aerosol optical depth. With the launch of GOES-R NOAA will begin a new era of geostationary remote sensing. The Advanced Baseline Imager (ABI) onboard GOES-R will offer capabilities for aerosol remote sensing similar to those currently provided by the Moderate Resolution Imaging Spectroradiometer (MODIS) flown on the NASA Earth Observing System (EOS) satellites. The ABI aerosol algorithm currently under development uses a multi-channel approach to estimate the aerosol optical depth and aerosol model simultaneously, both over water and land. Its design is strongly inspired by the MODIS aerosol algorithm. The ABI shortwave radiation budget algorithm is based on the successful GOES Surface and Insolation Product system of NOAA and the NASA Clouds and the Earth’s Radiant Energy System (CERES), Surface and Atmospheric Radiation Budget (SARB) algorithm. In all phases of the development, the algorithms are tested with proxy data generated from existing satellite observations and forward simulations. Final assessment of the performance will be made after the launch of GOES-R scheduled in 2012.     

Long-term dynamics of the inner Jovian electron radiation belts

Long-term variations of total Jovian synchrotron emission are well known to vary slowly in time. Several hypotheses have been proposed to explain these variations, they can be solar wind driven and/or induced by the geometrical effect of the declination of the Earth in the jovicentric coordinates, D_E. However, until now, not any of them have been definitely proved. We propose here to investigate, this long-term dynamics based on appropriate simulation from a 3D model, Salammbô-3D. This model has been developed to study spatial distribution of electrons in the inner Jovian radiation belts. We will carry out two different approaches, the first one being based on synchrotron simulation from the Salammbô code and the second one being based on GALILEO EPD measurements. Two-dimensional images of Jupiter synchrotron emission can be obtained from our model, for any geometrical configuration (λ_III(CML), D_E). Comparisons show a good agreement between modeling results and VLA observations. With Salammbô-3D, we can also study long-term variations of total Jovian synchrotron emission. The role of the two geometrical factors, λ_III(CML) and D_E, will be analyzed. First, we will present beaming curves (evolution of Jovian synchrotron emission in terms of λ_III(CML)), resulting from the simulation to validate the geometry of the system in the code. Then, the evolution of the non-thermal flux density of synchrotron emission, in terms of D_E, joviographic declination of the Earth, will be studied. With the help of simulations resulting from Salammbô-3D, we will try to discriminate between geometrical induced variations and natural dynamics. On the other hand we will investigate on GALILEO EPD measurements from 1995 until now, restricted to 5–10 Rj, to find out any similarity with the long-term variations of non-thermal flux density of synchrotron emission.     

High vertical resolution water vapour profiles in the upper troposphere and lower stratosphere retrieved from MAESTRO solar occultation spectra

An algorithm has been developed that retrieves water vapour profiles in the upper troposphere and lower stratosphere from optical depth spectra obtained by the Measurements of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation (MAESTRO) instrument onboard the SCISAT satellite as part of the Atmospheric Chemistry Experiment (ACE) mission. The retrieval relies on ro-vibrational absorption of solar radiation by water vapour in the 926–970 nm range. During the iterative inversion process, the optical depth spectra are simulated at the spectral resolution and sampling frequency of MAESTRO using the correlated-k approximation. The Chahine inversion updates the water vapour volume mixing ratio (VMR), adjusting all retrieval layers simultaneously, to match the observed differential optical depth due to absorption by water vapour and ozone at each tangent height. This approach accounts for significant line saturation effects. Profiles are typically obtained from ∼22 km down to the cloud tops or to 5 km, with relative precision as small as 3% in the troposphere. In the lower stratosphere, the precision on water vapour VMR is ∼1.3 μmol/mol in an individual retrieval layer (∼1 km thick). The spectral capability of MAESTRO allows for the clear separation of extinction due to water vapour and aerosol, and for the fitting quality to be quantified and used to determine an altitude-dependent convergence criterion for the retrieval. In the middle troposphere, interhemispheric differences in water vapour VMR are driven by oceanic evaporation whereas in the upper troposphere, deep convection dominates and a strong seasonal cycle is observed at high latitudes.     

Comparison of ground reflectance measurement with satellite derived atmospherically corrected reflectance: A case study over semi-arid landscape

Atmospheric corrections to satellite data are important for comparing multitemporal data sets over tropical regions with variable aerosol loading. In this study, we evaluated the potential of 6S radiative transfer model for atmospheric corrections of IRS-P6 AWiFS satellite data sets, in a semi-arid landscape. Ground measurements of surface reflectance representing different land use/land cover categories were conducted to relate IRS-P6 AWiFS top of atmospheric reflectance. The 6S radiative transfer model was calibrated for local conditions using ground measurements for aerosol optical depth, water vapor and ozone with a sun photometer. Surface reflectance retrieved from 6S code was compared with top of atmosphere (TOA) reflectance and ground based spectroradiometer measurements. Accurate parameterization of the 6S model using measurements of aerosol optical depth, water vapor and ozone plays an important role while comparing ground and satellite derived reflectance measurements.     

Validation of space-born Moderate Resolution Imaging Spectroradiometer remote sensors aerosol products using application of ground-based Multi-wavelength Radiometer

The measurements of aerosol optical properties were carried out during April 2006 to March 2011 over Mohal (31.9°N, 77.12°E) in the northwestern Indian Himalaya, using the application of ground-based Multi-wavelength Radiometer (MWR) and space-born Moderate Resolution Imaging Spectroradiometer (MODIS) remote sensors. The average (±standard deviation) values of aerosol optical depth (AOD) at 500 nm, Ångström exponent and turbidity coefficient during the entire measurement period were 0.25 ± 0.09, 1.15 ± 0.42 and 0.12 ± 0.06 respectively. About 86% AOD values retrieved from MODIS remote sensor were found within an uncertainty limit (Δτ_pλ = ±0.05 ± 0.15τ_pλ). In general, the MWR derived AOD values were higher than that of MODIS retrieval with absolute difference ∼0.02. During the entire period of measurement space-born MODIS remote sensor and ground-based MWR observation showed good correspondence with significant correlation coefficient ∼0.78 and root mean square difference ∼0.06. For daily observations the relative difference between these two estimates stood less than 9%. However, satellite-based and ground-based observation showed good correspondence, but further efforts still needed to eliminate systematic errors in the existing MODIS algorithm.     

Spectral and temporal characteristics of aerosol optical depth over a wet tropical location in North East India

A network of multi wavelength solar radiometer (MWR) stations has been in operation since the 1980s in India for measurement of aerosol optical depth (AOD). This network was augmented recently with the addition of a large number of stations located across the length and breath of India covering a variety of climate regimes. The spectral and temporal variations of aerosol optical depths observed over Dibrugarh located in the North East of India (27.3°N, 94.5°E) are investigated by analyzing the data obtained from a MWR during October 2001–September 2003 using the Langley technique. AOD varies with time of the day, month of the year and season. From January to April and October to December, aerosol optical depth decreases with wavelength whereas during May–September aerosol optical depth has been found to be nearly independent of wavelengths. AOD is higher during pre-monsoon season (March–May) and lower in the monsoon (June–September) season at about all wavelengths. The temporal variation of AOD over Dibrugarh have also been compared with those reported from selected locations in India.     

Single-event upset in geostationary transfer orbit during solar-activity maximum period measured by the Tsubasa satellite

This paper reports single-event upset (SEU) occurrence related to the space radiation environment in geostationary transfer orbit during solar-activity maximum period measured by the Tsubasa satellite. Most SEUs are measured in the inner radiation belt, indicating that they are mainly caused by trapped protons. Thus, the spatial distribution and the temporal variation of the SEU count correlate well with those of trapped protons. The peak SEU rate appears around L = 1.4. The transition point from SEUs caused by trapped protons to those caused by galactic cosmic rays is around L = 2.6. During the experiment period, increased SEU count was sometimes detected due to solar and geomagnetic events outside the inner radiation belt.     

Retrieval of aerosol optical characteristics from polarization measurements of reflected solar radiation above the oceans

The reflected near infrared solar radiation observed from space above the oceans is due mainly to the atmosphere scattering, as the ocean surface is nearly black. The molecular Rayleigh contribution is also minimized at infrared wavelengths and it can be evaluated. It is shown that the degree of polarization is much more sensitive to the aerosol properties than the radiance. Measurements of polarization at two wavelengths and with an angular scanning are simulated and an inversion algorithm is proposed. It aims at finding an “equivalent aerosol model,” which reproduces the optical thickness and the asymmetry factor of the actual aerosol at all wavelengths in the solar spectrum.     

Contribution of geometry of interaction between interplanetary and terrestrial magnetic fields into global magnetospheric state and geomagnetic activity

The paper presents results of our study of dependence of geomagnetic activity from geoeffective parameters taking into account mutual orientation of the interplanetary magnetic field, electric field of the solar wind and geomagnetic moment. We attract a reconnection model elaborated by us made allowance for changes of geometry of the solar wind–magnetosphere interaction during annual and diurnal motions of the Earth. We take as our data base the interplanetary magnetic field and solar wind velocity measured at 1 a.u. at ecliptic plane for the period of 1963–2005 and K_p, D_st, a_m indices. Taken as a whole a geoeffective parameter suggested by us explains 95% of observed variations of the indices. Changes of the geometric factor determined by mutual orientation of the solar wind electric field and geomagnetic moment explain larger than 75% of observed statistical variations of D_st and a_m indices. Based on our results we suggest a new explanation of semi-annual and UT variation of geomagnetic activity.     

On the station keeping of a solar sail in the elliptic Sun–Earth system

In this work we focus on the dynamics of a solar sail in the Sun–Earth Elliptic Restricted Three-Body Problem with solar radiation pressure. The considered situation is the motion of a sail close to the L₁ point, but displacing the equilibrium point with the sail so that it is possible to have continuous communication with the Earth. In previous works we derived a station keeping strategy for this situation but using the Circular RTBP as a model.     

太阳紫外辐射对星上光学膜层的影响

光学遥感是当前卫星遥感的重要手段, 而卫星温控和能源系统也广泛采 用光学膜层, 它们在空间环境条件下的性能对卫星应用任务的完成, 乃至卫星寿命、安全将起着非常重要的作用. 本文给出了太阳紫外辐射对星上光学膜层影响的主要机制, 分析了这一影响的主要规律和原子氧剥蚀、高能粒子和静电场的作用, 综述了太阳紫外辐射对星上光学系统表面膜层影响的测量结果, 最后提出了星上光学膜层污染防护中应重点关注的几个方面.      

Ozone variability related to several SEP events occurring during solar cycle no. 23

Data from geostationary operational environmental satellite (GOES) series were used to identify intense solar energetic particle (SEP) events occurred during the solar activity cycle no. 23. We retrieved O₃, NO, NO₂, HNO₃, OH, HCl and OHCl profiles coming from different satellite sensors (solar occultation and limb emission) and we looked for the mesospheric/stratospheric response to SEPs at high terrestrial latitudes. The chemistry of the minor atmospheric components is analysed to evaluate the associated odd nitrogen (NO_x) and odd hydrogen (HO_x) production, able to cause short (h) and medium (days) term ozone variations. We investigated the effects of SEPs on the polar atmosphere in three different seasons, i.e., January 2005, April 2002 and July 2000. The inter-hemispheric variability of the ozone, induced by the SEP series of January 2005, has been compared with the effects connected both to larger and quite similar events. We found that during SEP events: (i) solar illumination is the key factor driving SEP-induced effects on the chemistry of the polar atmosphere; (ii) even events with limited particle flux in the range 15–40 MeV are able to change the abundance of the minor constituents in the mesosphere and upper stratosphere.     

Models of Venus neutral upper atmosphere: Structure and composition

Models of the Venus neutral upper atmosphere, based on both in-situ and remote sensing measurements, are provided for the height interval from 100 to 3,500 km. The general approach in model formulation was to divide the atmosphere into three regions: 100 to 150 km, 150 to 250 km, and 250 to 3,500 km. Boundary conditions at 150 km are consistent with both drag and mass spectrometer measurements. A paramount consideration was to keep the models simple enough to be used conveniently. Available observations are reviewed. Tables are provided for density, temperature, composition (CO₂, O, CO, He, N, N₂, and H), derived quantities, and day-to-day variability as a function of solar zenith angle on the day- and nightsides.Estimates are made of other species, including O₂ and D. Other tables provide corrections for solar activity effects on temperature, composition, and density. For the exosphere, information is provided on the vertical distribution of normal thermal components (H, O, C, and He) as well as the hot components (H, N, C, O) on the day- and nightsides.     

Scaling and universality of the thermal conductivity of liquid 4He near the superfluid transition and in restricted geometries

We present measurements of the thermal conductivity λ(t, P, L) = l/ρ(t, P, L) near the superfluid transition of ⁴He at saturated vapor pressure and confined in cylindrical geometries with radii L = 0.5 and 1.0 μm (t ≡ T/T_λ(P) − 1). For L = 1.0 μm measurements at six pressures P are presented. At and above T_λ the data are consistent with a universal scaling function F(X) = (L/ξ_o)^x/ν(ρ/ρ₀), X = (L/ξ_o)^1/νt valid for all P (ρ₀ and x are the pressure-dependent amplitude and effective exponent of the bulk resistivity ρ(t, P, ∞) = ρ₀t^x and ξ = ξ₀t^−ν is the correlation length). Indications of breakdown of scaling and universality are observed below T_λ.     

X射线脉冲星自主导航的卫星运动方程

基于X射线脉冲星的卫星自主导航模型中, 无论从理论上还是从测量精度方面考虑, 光子到达时间测量方程(观测方程)和卫星运动方程(状态方程)应在同一参考系中讨论. 在DSX体系中太阳系质心系是惯性系, 可以使用现行时间测量方程, 但卫星摄动加速度中除了地球多极矩、日月引力摄动和太阳光压三项外, 还应考虑相对论修正项, 计算表明该修正项导致卫星位置误差在10m量级. 而地心系是非惯性系, 在此系中卫星运动方程中的相对论效应导致卫星误差在10 cm量级, 因而可以忽略, 但要将BCRS的时间测量方程转换到GCRS中. 在此基础上建立的导航模型较为精确和完整.      

Direct radiative forcing from black carbon aerosols over urban environment

There is growing evidence that the earth’s climate is changing and will likely continue to change in the future. It is still debated whether these changes are due to natural variability of the climate system or a result of increases in the concentration of greenhouse gases in the atmosphere. Black carbon (BC) has become the subject of interest for a variety of reasons. BC aerosol may cause environmental as well as harmful health effects in densely inhabited regions. BC is a strong absorber of radiation in the visible and near-infrared part of the spectrum, where most of the solar energy is distributed. Black carbon is emitted into the atmosphere as a byproduct of all combustion processes, viz., vegetation burning, industrial effluents and motor vehicle exhausts, etc. In this paper, we present results from our measurements on black carbon aerosols, total aerosol mass concentration and aerosol optical depth over an urban environment namely Hyderabad during January to May, 2003. Diurnal variations of BC indicate high BC concentrations during 6:00–9:00 and 19:00–23:00 h. Weekday variations of BC concentrations increase gradually from Monday to Wednesday and gradually decrease from Thursday to Sunday. Analysis of traffic density along with meteorological parameters suggests that the primary determinant for BC concentration levels and patterns is traffic density. Seasonal variations of BC suggest that the BC concentrations are high during dry season compared to rainy season due to the scavenging by air. The fraction of BC to total mass concentration has been observed to be 7% during January to May. BC showed positive correlation with total mass concentration and aerosol optical depth at 500 nm. Radiative transfer calculations suggests that during January to May, diurnal averaged aerosol forcing at the surface is −33 Wm² and at the top of the atmosphere (TOA) above 100 km it is observed to be +9 Wm⁻². The results have been discussed in detail in the paper.