Solar rhythms in the characteristics of the Arctic frontal zone in the North Atlantic

Long-term changes of the Arctic frontal zone characteristics near the south-eastern coasts of Greenland were considered, the NCEP/NCAR reanalysis data being used. It was found that in the cold half of the year the temperature gradients in the layer 1000–500 hPa in the region under study reveal strong ∼10-yr and ∼22-yr periodicities that seem to be related to solar activity cycles. The results obtained suggest the influence of solar activity and cosmic ray variations on the structure of the temperature field of the troposphere resulting in the changes of the temperature contrasts in the Arctic frontal zone that, in turn, may affect the intensity of cyclogenesis at middle latitudes. The detected effects seem to indicate an important part of frontal zones in the mechanism of solar activity and cosmic ray variation influence on the development of extratropical baric systems. It is suggested that the variations of the temperature gradients revealed in the Arctic frontal zone are due to the radiative forcing of cloudiness changes which may be associated with geomagnetic activity and cosmic ray variations.     

27-day variation in solar-terrestrial parameters: Global characteristics and an origin based approach of the signals

The Earth and the near interplanetary medium are affected by the Sun in different ways. Those processes generated in the Sun that induce perturbations into the Magnetosphere-Ionosphere system are called geoeffective processes and show a wide range of temporal variations, like the 11-year solar cycle (long term variations), the variation of ～27?days (recurrent variations), solar storms enduring for some days, particle acceleration events lasting for some hours, etc.In this article, the periodicity of ～27?days associated with the solar synodic rotation period is investigated. The work is mainly focused on studying the resulting 27-day periodic signal in the magnetic activity, by the analysis of the horizontal component of the magnetic field registered on a set of 103 magnetic observatories distributed around the world. For this a new method to isolate the periodicity of interest has been developed consisting of two main steps: the first one consists of removing the linear trend corresponding to every calendar year from the data series, and the second one of removing from the resulting series a smoothed version of it obtained by applying a 30-day moving average. The result at the end of this process is a data series in which all the signal with periods larger than 30?days are canceled.The most important characteristics observed in the resulting signals are two main amplitude modulations: the first and most prominent related to the 11-year solar cycle and the second one with a semiannual pattern. In addition, the amplitude of the signal shows a dependence on the geomagnetic latitude of the observatory with a significant discontinuity at approx. ±60°.The processing scheme was also applied to other parameters that are widely used to characterize the energy transfer from the Sun to the Earth: F10.7 and Mg II indices and the ionospheric vertical total electron content (vTEC) were considered for radiative interactions; and the solar wind velocity for the non-radiative interactions between the solar wind and the magnetosphere. The 27-day signal obtained in the magnetic activity was compared with the signals found in the other parameters resulting in a series of cross-correlations curves with maximum correlation between 3 and 5?days of delays for the radiative and between 0 and 1?days of delay for the non-radiative parameters. This result supports the idea that the physical process responsible for the 27-day signal in the magnetic activity is related to the solar wind and not to the solar electromagnetic radiation.     

太阳活动与全球气候变化

太阳不断向地球辐射电磁波和粒子, 太阳辐射是地球气候系统最主要的能量来源. 地球气候系统对太阳活动的响应是一个复杂的过程, 包括辐射过程、动力学过程以及微观物理过程等. 根据太阳辐射的卫星观测结果和重建结果, 例举了古气候、温度、大气环流和云量等方面太阳影响气候的观测证据, 论述了太阳影响气候的三种可能机制, 即太阳总辐射变化可以影响地表温度, 并通过海-气耦合改变大气环流; 太阳紫外辐射通过调制平流层的温度和风场影响下面的对流层; 太阳通过行星际磁场调制银河宇宙线, 而银河宇宙线通过电离大气影响云量, 进而改变地球的能量收支.      

日冕扰动传播的数值模拟——(Ⅱ)热传导和辐射的影响

利用包含完全能量方程的磁流体力学方程组,数值研究了磁静力平衡基态下由于日面冷物质径向喷射所引起的日冕动力学响应。这些结果可以解释日珥的形成及伴随的日冕扰动传播。结果还表明,热传导和辐射损失对扰动传播的基本性质影响很小;对于日珥的形成,也未显出重要作用。      

Modeling of effect of polarization on UV sky radiance during twilight

The spatial distribution of the vector of the Stokes parameters characterizing the radiance intensity and the radiance polarization describes the radiation field in the atmosphere. A simplified treatment of light as the scalar has only restricted application. A few studies compared previously results of the vector and scalar radiative transfer models and showed that scalar models are in error by up to 10% for many cases. Though several observational conditions were exploited, an effect of polarization on modeling of UV radiance has not been investigated yet for twilight. The paper presents a preliminary study of modeled UV radiance during twilight taking into account polarization. The intensity and the degree of linear polarization of the scattered UV radiance for two cases of the ground-based observations are discussed. In the first case, radiation incoming from the zenith for the solar zenith angles (SZA) from 90° to 98° is under investigation. Radiation in the solar principal plane for the beginning of twilight (SZA = 90.1°) was calculated in the second case. The study showed that the UV radiation field in the twilight atmosphere can be handled correctly only using the vector theory. The errors of scalar radiative transfer strongly depend on wavelength, line of an observation and solar position. The revealed distortion of the zenith radiance caused by using of the scalar approximation reaches maximum of 15% at 340 nm for the solar zenith angle (SZA) equal to 98°. The shorter wavelengths have the smaller errors, about 5% at 305 nm for SZA = 98°, due to the larger part of the single scattered radiance. The error of the scalar modeling may be as large as −17% for radiance incoming from the horizon for SZA = 90.1°. Scalar radiative transfer models underestimate the integral intensity in the principal plane up to 3–4% ± 0.5% at SZA = 90.1° for wavelengths from 320 to 340 nm. This should be taken into account in problems of radiative budget estimation and remote sensing of the atmosphere exploiting the twilight period.     

Viewing radiation signatures of solar energetic particles in interplanetary space

A current serious limitation on the studies of solar energetic particle (SEP) events is that their properties in the inner heliosphere are studied only through in situ spacecraft observations. Our understanding of spatial distributions and temporal variations of SEP events has come through statistical studies of many such events over several solar cycles. In contrast, flare SEPs in the solar corona can be imaged through their radiative and collisional interactions with solar fields and particles. We suggest that the heliospheric SEPs may also interact with heliospheric particles and fields to produce signatures which can be remotely observed and imaged. A challenge with any such candidate signature is to separate it from that of flare SEPs. The optimum case for imaging high-energy (E > 100 MeV) heliospheric protons may be the emission of π⁰-decay γ-rays following proton collisions with solar wind (SW) ions. In the case of E > 1 MeV electrons, gyrosynchrotron radio emission may be the most readily detectible remote signal. In both cases we may already have observed one or two such events. Another radiative signature from nonthermal particles may be resonant transition radiation, which has likely already been observed from solar flare electrons. We discuss energetic neutrons as another possible remote signature, but we rule out γ-ray line and 0.511 MeV positron annihilation emission as observable signatures of heliospheric energetic ions. We are already acquiring global signatures of large inner-heliospheric SW density features and of heliosheath interactions between the SW and interstellar neutral ions. By finding an appropriate observable signature of remote heliospheric SEPs, we could supplement the in situ observations with global maps of energetic SEP events to provide a comprehensive view of SEP events.     

Investigation of natural and artificial stimulation of the ionospheric Alfvén resonator at high latitude

A brief review is provided of recent progress in understanding the ionospheric Alfvén resonator (IAR) at high latitude. Firstly, naturally occurring resonances of the IAR as detected by pulsation magnetometers in the auroral zone at Sodankylä and in the polar cap at Barentsburg are considered. The characteristics of the IAR in the two regions are broadly similar, although the effects of solar illumination are less clear at the higher latitudes. Secondly we review recent attempts to stimulate the IAR through high-power radio frequency experiments both in the auroral zone at Tromsø with the European Incoherent SCATter (EISCAT) heater, and within the polar cap at Longyearbyen with the Space Plasma Exploration by Active Radar (SPEAR) facility. In the auroral zone at, Tromsø the stimulated IAR has been observed by ground-based magnetometers, and through electron acceleration observed on the FAST spacecraft. At SPEAR in the polar cap, the stimulated IAR has been investigated, with ground magnetometers, with the first results indicative of a positive detection.     

Solar cycle evolution of the contrast of small photospheric magnetic elements

Solar irradiance variations produced on the solar rotation time-scale are known to be driven by the passage of active regions while, during the last years, the origin of variations on the solar cycle time-scale has been under debate. Nowadays, there is an agreement that the magnetic network has an important contribution to these long-term variations, although it has not been fully quantified. This important role motivated us to study its physical properties along the solar cycle, such as contrast and population. We combine magnetograms and intensity images from the MDI instrument on board the SOHO spacecraft to analyze the radiative properties of small magnetic elements. We determine the contrast of faculae and network elements as a function of position over the disk, magnetic flux and time, finding that these elements exhibit a very different center-to-limb variation of the contrast. This implies that their contribution to irradiance variability is distinct. By extending this analysis through the rising phase of solar cycle 23, we conclude that the functional dependence of the contrast of small elements results to be time independent, implying that the physical properties of the underlying flux tubes may not vary with time. We decompose magnetograms into two structures identifying both faculae and network features and we examine their populations along the solar cycle.     

Quantifying the role of solar radiative forcing over the 20th century

The 20th century temperature anomaly record is reproduced using an energy balance model, with a diffusive deep ocean. The model takes into account all the standard radiative forcings, and in addition the possibility of a non-thermal solar component. The model is parameterized and then optimized to produce the most likely values for the climate parameters and radiative forcings which reproduce the 20th century global warming. We find that the best fit is obtained with a negligible net feedback. We also show that a non-thermal solar component is necessarily present, indicating that the total solar contribution to the 20th century global warming, of ΔT_solar = 0.27 ± 0.07 °C, is much larger than can be expected from variation in the total solar irradiance alone. However, we also find that the largest contribution to the 20th century warming comes from anthropogenic sources, with ΔT_man = 0.42 ± 0.11 °C.     

利用6S进行月光条件下遥感器信号模拟研究

以太阳为光源的卫星遥感器,可以采用6S或MODTRAN等辐射传输计算软件对其入瞳处的辐亮度进行计算。而在微光或月光条件下,遥感器是对观测目标反射的月亮辐射进行遥感观测,因此在进行辐射传输计算时需要代入月球的辐照度数据。可以利用已公布的月球表面反射率和已知的大气层外太阳辐照度来计算月球辐照度,并对6S辐射传输计算进行适当的修改进行计算。通过对月球辐照度计算原理进行了详细的描述并计算得到了波长在0.250μm~1.500μm范围内的月球表面辐照度,并给出了一个宽波段遥感器的微光动态范围。     

The large-scale solar variability through the cycle

Observational evidence for solar variability along the cycle has been considered. Two fundamental questions for the understanding of the solar structure and evolution are addressed :One concerning the detection of the large - scale dynamics of the convective zone which may be responsible for the generation and the maintenance of the solar differential rotation. There is evidence of a large - scale axisymmetric pattern (rolls) by observations of the meridional circulation and the transport of angular momentum by fluid motion. The rolls are time - dependent and are related to the torsional wave pattern.The second important question addresses the variability of the convective zone structure (radius and luminosity). Several independent observations favour a pulsation of the convective envelope, through cyclic variations of the radius and luminosity exhibiting the same periodicities as the magnetic sunspot cycle.It is suggested that we are in the presence of two strongly coupled cycles, a magnetic cycle and a convective pulsating cycle. The axisymmetric rolls (and related torsional oscillations) could be the main convective influence on the production of the magnetic field.     

The radial velocity of the sun as a star and the solar cycle

Radial velocity measurements of the sun as a star using a resonant scattering spectrometer have been obtained at Izaña (Tenerife) during long observing seasons from 1976 to 1985. Its analysis shows that except for the global oscillations with periods shorter than one day there are stable signals with longer periods: at ∼13 days with mean amplitude of ∼ 3 m/s (it changes with the solar cycle) and another one of ∼ 15 m/s amplitude which shows a temporal variation of various years related to the solar cycle. The first signal has a partial explanation as an effect produced by the passage of active regions through the visible surface of the sun but it does not completely explain the observed signal. The second one, related to the limb shift, is probably due to changes in the convection zone in connection with the solar cycle.     

用半经验模型研究耀斑大气的能量耗散

本文利用南京大学太阳塔多波段光谱资料推求出的两个耀斑(一个SB级,一个2B级)的半经验模型;计算了耀斑不同时刻的辐射损失速率,并与电子束轰击和X线作用下的产能率作了比较.结果表明,耀斑不同时刻的色球辐射损失变化可达一个量级以上;耀斑脉冲相前后电子束轰击加热相当有效;耀斑强度极大时,电子束轰击和X线加热都有作用;耀斑主相时,X线加热更能有效地平衡辐射损失.但是,尤其是对大耀斑来说,色球低层和光球上层的加热既不能用电子束轰击,也不能用X线的作用来解释;可能存在某种把能量从色球上层向低层转移的机制.研究也表明,耀斑随时间变化的半经验模型为研究耀斑的能量耗散过程提供了很好的工具.      

Determination of Angular Distribution Models for Indian desert scene: Comparison with other desert models

In this paper, the shortwave and longwave anisotropy for clear sky Indian desert scene has been estimated using long-term surface data, radiative transfer calculations and Helmholtz reciprocity for missing values. This study is important in the perspective of the low inclination satellites like Megha–Tropiques (MT) mission, carrying Scanner for Radiation Budget (ScaRaB) payload, which will provide broadband radiative fluxes at the top of the atmosphere (TOA). Due to low inclination angle, the angular models for clear sky land scenes for the MT-ScaRaB orbits will be dominated by desert points.The Angular Distribution Models (ADMs) determined in this study were compared with existing desert models. It is observed that for longwave radiation, the largest disagreement is observed for higher values of viewing zenith angle, especially for the summer season, where the difference in flux can reach up to 13 W/m². For the shortwave radiation, higher values of both solar zenith angle and viewing zenith angle cause largest incongruity in the computed albedo from the different models, suggesting the need of caution in interpretation of the flux computations from these bins. In fact at the higher solar zenith angle bin, the disparity in albedo can go up to 6.4%.     

Europa, tidally heated oceans, and habitable zones around giant planets.

Tidal dissipation in the satellites of a giant planet may provide sufficient heating to maintain an environment favorable to life on the satellite surface or just below a thin ice layer. In our own solar system, Europa, one of the Galilean satellites of Jupiter, could have a liquid ocean which may occasionally receive sunlight through cracks in the overlying ice shell. In such case, sufficient solar energy could reach liquid water that organisms similar to those found under Antarctic ice could grow. In other solar systems, larger satellites with more significant heat flow could represent environments that are stable over an order of Aeons and in which life could perhaps evolve. We define a zone around a giant planet in which such satellites could exist as a tidally-heated habitable zone. This zone can be compared to the habitable zone which results from heating due to the radiation of a central star. In our solar system, this radiatively-heated habitable zone contains the Earth.     

Degradation of thermal control materials under a simulated radiative space environment

A spacecraft with a passive thermal control system utilizes various thermal control materials to maintain temperatures within safe operating limits. Materials used for spacecraft applications are exposed to harsh space environments such as ultraviolet (UV) and particle (electron, proton) irradiation and atomic oxygen (AO), undergo physical damage and thermal degradation, which must be considered for spacecraft thermal design optimization and cost effectiveness. This paper describes the effect of synergistic radiation on some of the important thermal control materials to verify the assumptions of beginning-of-life (BOL) and end-of-life (EOL) properties. Studies on the degradation in the optical properties (solar absorptance and infrared emittance) of some important thermal control materials exposed to simulated radiative geostationary space environment are discussed. The current studies are purely related to the influence of radiation on the degradation of the materials; other environmental aspects (e.g., thermal cycling) are not discussed. The thermal control materials investigated herein include different kind of second-surface mirrors, white anodizing, white paints, black paints, multilayer insulation materials, varnish coated aluminized polyimide, germanium coated polyimide, polyether ether ketone (PEEK) and poly tetra fluoro ethylene (PTFE). For this purpose, a test in the constant vacuum was performed reproducing a three year radiative space environment exposure, including ultraviolet and charged particle effects on North/South panels of a geostationary three-axis stabilized spacecraft. Reflectance spectra were measured in situ in the solar range (250–2500 nm) and the corresponding solar absorptance values were calculated. The test methodology and the degradations of the materials are discussed. The most important degradations among the low solar absorptance materials were found in the white paints whereas the rigid optical solar reflectors remained quite stable. Among the high solar absorptance elements, as such the change in the solar absorptance was very low, in particular the germanium coated polyimide was found highly stable.     

Solar variability effects studied by tree-ring data wavelet analysis

The global change approach to study the Sun-Earth system gives a growing amount of evidences that climate dynamics is affected by a large number of factors. The solar variability is very likely to be among them. Natural records, such as tree ring data, can be investigated to study the past global and regional climate, which was influenced by the solar radiative output variations, associated to solar activity. Wavelet transform analysis was applied to sunspot number and tree ring width time series from 1837 to 1996 at Concórdia, Brazil. The amplitude and cross-amplitude spectral representation in the time-frequency domain allowed us to detect the occurrence of predominant periodicities and the relationship between the sunspot number and the tree ring time series. The Morlet complex wavelet analysis was used to study the most important variability factors on time scales ranging from from 2 to 100 years, and their stability in time, which is shown in both time series studied. We also applied the cross-wavelet spectral analysis to evaluate time delay among different tree ring time series, and between tree ring and sunspot number time series.     

Cyclone regeneration in the North Atlantic intensified by energetic solar proton events

Atmospheric effects of energetic solar proton events (SPE) were studied in the North Atlantic region, for particle energies above 90 MeV, using NCEP/NCER reanalysis data and weather charts. A significant lowering of the pressure levels in the troposphere accompanied by an increase of the cyclonic vorticity was found near the south-eastern coast of Greenland on days following the event onsets. According to the weather charts, the detected effects are caused by the re-deepening (the regeneration) of well developed cyclones that seems to be intensified during the SPE under study. A joint analysis of the pressure and temperature variations showed a noticeable decrease of the temperature in the rear of the deepening cyclones that may be due to the cold advection increase. The results obtained suggest the influence of energetic SPE on the cyclone development as well as the importance of the frontal zone situated near the Greenland coast for this influence. The physical mechanism may involve the increase of cold advection due to changes in the temperature gradients in this region, resulting from radiative forcing and/or latent heat release related to variations of cloudiness.