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1.
Recent extensive measurements of frequencies of free oscillation of the Sun have permitted a first direct estimate of the variation of sound speed and angular velocity throughout the Sun. The results hint that the answers to some tantalizing questions concerning the Sun's interior structure and its history are almost within grasp. Optimists like myself believe that in a few years a worldwide network of ground-based observing stations will give us important clues. However, it may be necessary to make observations from space before we can be sure of the answers.  相似文献   

2.
This contribution is mostly about phenomenology of what we see in space–time evolution of coronal green line brightness (CGLB), including its cyclic variations. Our own database (1943–2001) of the coronal Fe XIV 530.3 nm emission line intensities is used to display different aspects of the large-scale CGLB regularities and cyclic behaviour. Hemispheric asymmetry and relation of the longitudinal CGLB distribution to the rotational characteristics of the solar corona are particularly underlined.  相似文献   

3.
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.  相似文献   

4.
Precipitating electrons from the radiation belts with energies greater than from 150 keV to 5 MeV have been correlated with ozone data of a large number of stations located within 40–70° N. Energetic electrons have been collected by the low altitude polar Russian satellite METEOR while ozone data have been compiled from almost ninety (90) stations located all over the world within the latitude zone 40–70° N.  相似文献   

5.
Observations of the chromosphere with Deslandres’s spectroheliograph started at Paris Observatory in 1893 and were followed by systematic observations at Meudon since 1908. The solar collection of Hα and CaII K images is probably the longest available worldwide, with associated products such as synoptic maps and tables. Since 2018, Meudon spectroheliograph is the only instrument producing data-cubes of full line profiles of CaII H, CaII K and Hα, for each pixel of the solar disk. Slices of the cubes provide monochromatic images. We summarize in this paper the capabilities of the successive generations of the instrument, and explore the potential of the collection and products for analysis of rare events, investigations of past solar activity and studies of long term variability.  相似文献   

6.
Using daily temperature data available from radio-sonde measurements over Barajas (Madrid), La Coruña and Palma de Mallorca stations, for the time span 1971–1982 and an altitude range 100-30 mb, a study is made comparing temperatures at differents levels with the 10.7 cm flux in order to check whether radiation variability must be included in lower stratospheric models. At the latitude studied, stratospheric temperatures are uninfluenced by sudden warming phenomena avoiding difficulties of masking found in previous studies.  相似文献   

7.
We use the 8-year long satellite temperature data (2002–2010) from Atmospheric InfraRed Sounder (AIRS) and Atmospheric Microwave Sounding Unit (AMSU) on the Aqua satellite to identify temperature trends in the troposphere and low stratosphere over the Niño 3.4 region of the Tropical Pacific Ocean in the most recent 11-year solar cycle. Employing more extended sea surface temperature (SST) data for five solar cycles (1950–2009) in this region we show that the satellite trends reflect a typical decrease of the sea surface temperature (SST) in the Niño 3.4 region in the declining phase of the solar cycle. The magnitude of the SST decrease depends on the solar cycle and ranges between 0.07 K/yr and 0.27 K/yr for the last five solar cycles.  相似文献   

8.
The ionospheric total electron content (TEC) in the northern hemispheric equatorial ionization anomaly (EIA) crest region is investigated by using dual-frequency signals of the Global Positioning System (GPS) acquired from Rajkot (Geog. Lat. 22.29°N, Geog. Long. 70.74°E; Geom. Lat. 14.21°N, Geom. Long. 144.90°E), India. The day-to-day variability of EIA characteristics is examined during low solar activity period (F10.7∼83 sfu). It is found that the daily maximum TEC at EIA crest exhibits a day-to-day and strong semi-annual variability. The seasonal anomaly and equinoctial asymmetry in TEC at EIA is found non-existent and weaker, respectively. We found a moderate and positive correlation of daily magnitude of crest, Ic with daily F10.7 and EUV fluxes with a correlation coefficient of 0.43 and 0.33, respectively indicating an existence of a short-term relation between TEC at EIA and the solar radiation even during low solar activity period. The correlation of daily Ic with Dst index is also moderate (r = −0.35), whereas no correlation is found with the daily Kp index (r = 0.14) respectively. We found that the magnitude of EIA crest is moderately correlated with solar flux in all seasons except winter where it is weakly related (0.27). The magnitude of EIA crest is also found highly related with EEJ strength in spring (r = 0.69) and summer (r = 0.65) than autumn (0.5) and winter (r = 0.47), though EEJ is stronger in autumn than spring.  相似文献   

9.
All possible changes of the solar activity can be expressed by the coronal index of solar activity that represents the averaged daily power of the green corona emitted from the Sun’s visible hemisphere. The representative character of this index allows us to study long-term, intermediate and short-term variations of the Sun as a star. This index can be expressed well as a function of other solar indices. As green line reflects the distribution of the photospheric magnetic fields in the solar corona, the dependence of this index on the solar magnetic field is confirmed by means of statistical analysis of these two parameters. Daily values of the coronal index, as well as of the magnetic field data obtained from the Wilcox Solar Observatory, has been analysed by Fast Fourier analysis and Wavelet Transform analysis for the time period 1966–1998 covering more than three solar cycles. Periodicities of 11.4, 3.2, 2.3, 1.7, 1, 0.29, 0.07 and 0.04 years have been found in both parameters that means once again that the coronal index is probably related to the underlying photospheric magnetic fields and can be used as a global index of solar activity useful for Space Weather studies.  相似文献   

10.
The Sun is the nearest astrophysical source with a very intense emission in the X-ray band. The study of energetic events, such as solar flares, can help us to understand the behaviour of the magnetic field of our star. There are in the literature numerous studies published about polarization predictions, for a wide range of solar flares models involving the emission from thermal and/or non-thermal processes, but observations in the X-ray band have never been exhaustive.The gas pixel detector (GPD) was designed to achieve X-ray polarimetric measurements as well as X-ray images for far astrophysical sources. Here we present the possibility to employ this instrument for the observation of our Sun in the X-ray band.  相似文献   

11.
We determine the spatial-time patterns of zonally averaged carbon monoxide (CO) in the middle atmosphere by applying Principle Component Analysis to the CO data obtained from the Microwave Limb Sounder (MLS) measurements on the Aura satellite in 2004–2012. The first two principal components characterize more than 90% of the CO variability. Both principal components are localized in the low thermosphere near the mesopause. The first principal component is asymmetric relative to the poles. It has opposite signs in the Northern and Southern Hemisphere at mid to high latitudes and strongly oscillates with an annual periodicity. The second principal component has the same sign in both hemispheres and oscillates mainly with a semi-annual frequency. Both principal components are modulated by the 11-year solar cycle and display short-term variations. To test possible correlations of these variations with the short term solar ultraviolet (UV) variability we use the simultaneous measurements of the UV solar radiance from the Solar-Stellar Irradiance Comparison Experiment (SOLSTICE) on the Solar Radiation and Climate Experiment (SORCE) satellite to investigate the correlation between CO in the middle atmosphere and solar UV in 2004–2012. Using a wavelet coherence technique a weak, intermittent 27-day signal is detected in high-frequency parts of the CO principal components.  相似文献   

12.
The measurements of gamma-activity of the 44Ti (T1/2 = 66.6 years) produced by spallation reaction of galactic cosmic rays (GCR) in Alfianello, Olivenza, Rio Negro, Dhajala and Torino meteorites, which fell in the time interval 1883 AD (Alfianello)-1988 AD (Torino), show a century scale modulation, connected to long-term solar-wind flux variations in the interplanetary space. The variation of the 44Ti activity with the time of fall of meteorites is qualitatively consistent with the Gleissberg solar cycle, but the amplitude is three-four times higher than expected (about 5%) for GCR flux modulated by solar activity, as determined solely by the sunspot number. The cosmogenic 44Ti is a suitable radioisotope for this investigation, but its activity in meteorites is very low. We performed these measurements in the underground low level counting station of Monte dei Cappuccini in Torino, by means of a big hyperpure Ge crystal (approximately 2 kg) in selective coincidence with a heavy NaI (T1) scintillation detector (approximately 28 kg). This system allows a reliable and non destructive measurement of 44Ti (44Sc) in meteorites of 200-1200 g in weight. The background is about 1 count per day in the gamma-peak at 1157 keV of 44Sc in equilibrium with its parent 44Ti. The high stability of the performance allows long-lasting runs (approximately 10(7) s) in order to attain results with a standard deviation up to about 10%.  相似文献   

13.
Diurnal, seasonal and latitudinal variations of Vertical Total Electron Content (VTEC) over the equatorial region of the African continent and a comparison with IRI-2007 derived TEC (IRI-TEC), using all three options (namely; NeQuick, IRI01-corr and IRI-2001), are presented in this paper. The variability and comparison are presented for 2009, a year of low solar activity, using data from thirteen Global Positioning System (GPS) receivers. VTEC values were grouped into four seasons namely March Equinox (February, March, April), June Solstice (May, June, July), September Equinox (August, September, October), and December Solstice (November, December, January). VTEC generally increases from 06h00 LT and reaches its maximum value at approximately 15h00–17h00 LT during all seasons and at all locations. The NeQuick and IRI01-corr options of the IRI model predict reasonably well the observed diurnal and seasonal variation patterns of VTEC values. However, the IRI-2001 option gave a relatively poor prediction when compared with the other options. The post-midnight and post-sunset deviations between modeled and observed VTEC could arise because NmF2 or the shape of the electron density profile, or both, are not well predicted by the model; hence some improvements are still required in order to obtain improved predictions of TEC over the equatorial region of the Africa sector.  相似文献   

14.
This paper studies the efficiency of geomagnetic solar flare effects (gsfe) in X solar flare detection; so during the period 1999–2007 a comparison between solar flare (sf) observed by satellites of the Geostationary Operational Environmental Satellite (GOES) programme and gsfe published by the Service International des Indices Geomagnetiques (SIIG) is made.  相似文献   

15.
An understanding of observed global chemistry and climate changes caused by solar activity changes is a high priority in modern geosciences. Here, we discuss the influence of the ultraviolet spectral irradiance variability during solar cycle on chemical composition of the stratosphere and mesosphere with chemistry-climate model that fully describes the interactions between chemical and thermo-dynamical processes. We have performed several 20-year long steady-state runs and found a significant influence of solar irradiation on the chemical composition in the stratosphere and mesosphere. An enhanced photolysis during solar maximum results in destruction of methane, nitrous oxide and CFCs providing an increase in the chemical activity of the atmosphere with more pronounced effects in the mesosphere. In the mesosphere, an increase of HOx caused by more intensive water vapor photolysis results in significant ozone depletion there. More intensive methane oxidation gives statistically significant rise to the stratospheric humidity. The influence of dynamical perturbations has been identified over high latitude areas. The response of OH is found to be in a good agreement with observation data. The response of the other species is hard to validate, because of the lack of theoretical and observational studies.  相似文献   

16.
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 (NOx) and odd hydrogen (HOx) 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.  相似文献   

17.
Primary photoionisation of major ionospheric constituents is calculated from satellite-borne solar EUV measurements. Number densities of the background atmosphere are taken from the NRLMSISE-00 climatology. From the calculated ionisation rates, a proxy termed EUV-TEC, which is based on the global total ionisation is calculated, and describes the ionospheric response to solar EUV and its variability. The proxy is compared against the global mean ionospheric total electron content (TEC) derived from GPS data. Results show that the EUV-TEC proxy provides a better overall representation of global TEC than conventional solar indices like F10.7 do. The EUV-TEC proxy may be used for scientific research, and to describe the ionospheric effects on radio communication and navigation systems.  相似文献   

18.
This work aims to investigate far-UVC light at 222 nm as a new microbial reduction tool for planetary protection purposes which could potentially be integrated into the spacecraft assembly process. The major advantage of far-UVC (222 nm) compared to traditional germicidal UVC (254 nm) is the potential for application throughout the spacecraft assembly process in the presence of humans without adverse health effects due to the limited penetration of far-UVC light into biological materials. Testing the efficacy of 222-nm light at inactivating hardy bacterial cells and spores isolated from spacecraft and associated surfaces is a necessary step to evaluate this technology. We assessed survival of Bacillus pumilus SAFR-032 and Acinetobacter radioresistens 50v1 exposed to 222-nm light on proxy spacecraft surfaces simulated by drying the bacteria on aluminum coupons. The survival fraction of both bacteria followed a single stage decay function up to 60 mJ/cm2, revealing similar susceptibility of both species to 222-nm light, which was independent of the exposure rate. Irradiation with far-UVC light at 222 nm is an effective method to decontaminate the proxy spacecraft materials tested in this study.  相似文献   

19.
The Sun provides unique opportunities to study particle acceleration mechanisms using data from detectors placed on the Earth’s surface and on board spacecrafts. Particles may gain high energies by several physical mechanisms. Differentiating between these possibilities is a fundamental problem of cosmic ray physics. Energetic neutrons provide us with information that keeps the signatures of the acceleration site. A summary of some representative solar neutron events observed on the Earth’s surface, including associated X and γ-ray observations from spacecrafts is presented. We discuss evidence of acceleration of particles by the Sun to energies up to several tens of GeV. In addition, a recent solar neutron event that occurred on September 7th 2005 and detected by several observatories at Earth is analyzed in detail.  相似文献   

20.
This paper attempts to examine the control of electron density and solar activity on the F-region electron temperature. This is achieved by obtaining coefficients relating electron temperature with electron density and solar activity by using incoherent scatter radar measurements at Arecibo for the period August 1966 to May 1977. These coefficients are then used to construct an empirical model of F-region electron temperature. The model values are compared with measurements at other locations and show reasonable agreement.  相似文献   

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