Sky luminance distribution in the North of Iberian Peninsula during winter

This work is based on the study of outdoor daylight conditions during the winter period in Pamplona (the Iberian Peninsula). The 15 standard sky types proposed by the Commission Internationale de l’Eclairage (CIE) are used. The selected sky type in each moment is the one exhibiting the lowest root mean standard deviation (RMSD) when the theoretical and experimental luminance distributions in the sky hemisphere are compared. The selection was derived from luminance distribution data from 145 patches of the sky hemisphere and registered every 10 min from October to March from 2007 and 2008.The most frequent sky type observed in winter in Pamplona is V.5 (cloudless polluted with a broad solar corona), with a frequency of occurrence of 21%. Notwithstanding, the group of overcast skies exhibits a slightly higher frequency (40%) than the clear skies (37%). Seven out of the 15 standard sky types, i.e.V.5, I.1, III.4, II.1, IV.4, II.2 and III.3, are practically 80% of those under study. In order to provide a possible application in daylight climates studies, the frequency of occurrence of the 15 sky types is included in eleven intervals of solar elevation on the threshold corresponding to the time period and the location considered.     

A simple method for obtaining a continuous record of the presence and type of clouds in the sky during the day

Summary A photovoltaic cell or solar cell suitably mounted to look at a small portion of the sky and connected to a sensitive recorder yields considerable information as to the condition of the sky. The author has used such a simple device for many years and it is found that familiarity with the type of trace, which is in response to the changes in reflected light from clouds, will permit a good estimate of the type of clouds that are present. The presentation of such cloud information on a standard potentiometer or galvanometer type recorder is very convenient when correlating cloud conditions with other variables being recorded on similar types of recorders.     

GPS L1-Frequency Observations of Equatorial Scintillations and Irregularity Zonal Velocities

In this work, the climatology of ionospheric scintillations at global positioning system (GPS) L-band frequency and the zonal drift velocities of scintillation-producing irregularities were depicted for the equatorial observatory of São Luis (2.33°S; 44.21°W; dip latitude 1.3°S), Brazil. This is the first time that the hourly, monthly, and seasonal variations of scintillations and irregularity zonal drifts at São Luis were characterized during periods of different solar activity levels (from December 1998 to February 2007). The percentage occurrence of scintillations at different sectors of the sky was also investigated, and the results revealed that the scintillations are more probable to be observed in the west sector of the sky above São Luis, whereas the north–south asymmetries are possibly related to asymmetries in the plasma density distribution at off-equatorial latitudes. The scintillations on GPS signals occurred more frequently around solar maximum years, but it is also clear from the results of a strong variability in the scintillation activity in the years with moderate solar flux during the descending phase of the solar cycle. The equatorial scintillations occur predominantly during pre-midnight hours with a broad maximum near the December solstice months. In general, weak level of scintillations (S ₄ index between 0.2 and 0.4) dominated at all seasons; however, during the winter months around solar maximum years (although the scintillation occurrence is extremely low), stronger levels of scintillations (S ₄ > 0.6) may occur at comparable rate with the weak scintillations. The irregularity zonal velocities, as estimated from the GPS spaced-receiver technique, presented a different scenario for the two seasons analyzed; during the equinoxes, the magnitude of the zonal velocities appeared not to change with the solar activity, whereas during the December solstice months, the larger magnitudes were observed around solar maximum years. Other relevant aspects of the observations are highlighted and discussed.     

Messungen der Himmelsstrahlung und deren Polarisationsgrad während der Sonnenfinsternis am 15.2.1961 in Viareggio (Italien)

Summary On the occasion of the total solar eclipse in Viareggio (Italy) measurements of intensity of sky radiation and polarization have been carried out at 90 degrees vertical distance from the sun. UV-, green- and red-filters have been used. The results showed a diminution of the intensity during the eclipse of about 3 powers of ten. The sky brightness in the point 90 degrees distant during the total eclipse was similar to the brightness when sun is 7 degrees below the horizon. About one minute before the total eclipse the degree of polarization diminuished to zero. — Furthermore photos of nearly the total sky were made using two cameras with wide angle lenses.     

High-resolution spectrometer for atmospheric studies

A high-resolution spectrometer (0.0014 nm at 313 nm) has been developed at the University of L’Aquila (Italy) for atmospheric spectroscopic studies. The layout, optics and software for the instrument control are described. Measurements of the mercury low-pressure lamp lines from 200 to 600 nm show the high performances of the spectrometer. Laboratory measurements of OH and NO₂ spectrums demonstrate that the system could be used for cross-section measurements and to detect these species in the atmosphere. The first atmospheric application of the system was the observation of direct solar and sky spectrums that shows a filling-in of the sky lines due to rotational Raman scattering. The measurements have been done with clear and cloudy sky and in both there was a strong dependence of the filling-in from the solar zenith angle whereas no dependence from the wavelengths was evident at low solar zenith angles (less than 85°).     

Solar forcing of the Northern hemisphere land air temperature: New data

It has previously been demonstrated that the mean land air temperature of the Northern hemisphere could adequately be associated with a long-term variation of solar activity as given by the length of the approximately 11-year solar cycle. Adding new temperature data for the 1990s and expected values for the next sunspot extrema we test whether the solar cycle length model is still adequate. We find that the residuals are now inconsistent with the pure solar model. We conclude that since around 1990 the type of Solar forcing that is described by the solar cycle length model no longer dominates the long-term variation of the Northern hemisphere land air temperature.     

Geometric properties of the coronal neutral surface

The interrelation between the density inhomogeneity and the magnetic field configuration in the solar corona has been studied. The situation of consistency with the regular cellular magnetic field organization, established by the authors based on polarization data, and helmet-shaped coronal structures has been analyzed. Consistency was found when coronal helmets appeared as projections on the plane of the sky of dense layer folds. It turned out that a dense layer on a regularly deformed neutral surface on a scale of 60° generates coronal shapes typical of solar activity minimum epochs. Threby, a weighty argument for the Molodenskii hypothesis that a dense layer is formed on the neutral surface has been obtained and it has been determined that one can find the 3D geometry of the coronal neutral surface based on modeling the visible shape of coronal helmets. The study of this geometry based on the observed coronal structures in the epoch of minimum and low solar activity indicated that the neutral surface longitudinal deformation scale remains stable and the surface latitudinal amplitude at the corona base reaches 50°–70° latitudes and tends to increase with increasing solar activity. This amplitude decreases as a power function with a variable index close to ?1 with increasing distance from the Sun. In addition, a 10° small-scale deformation of the studied surface with a predominant latitudinal flexure direction has been revealed.     

Statistical study of anomalous nighttime maximums in the <Emphasis Type="Italic">NmF</Emphasis> 2 diurnal variations in the region of appearance of the equatorial anomaly northern crest

The occurrence probabilities of the first and second anomalous nighttime local maximums in the diurnal variations in the electron density at a maximum of the ionospheric F ₂ layer (NmF2) in the region where the crest (hump) of the equatorial anomaly originates in the northern geographic hemisphere have been studied using the data of the stations for vertical sounding of the ionosphere (Paramaribo, Dakar, Quagadougou, Ahmedabad, Delhi, Calcutta, Chongoing, Guangzhou, Taipei, Chung-Li, Okinawa, Yamagawa, Panama, and Bogota) from 1957 to 2004. It has been demonstrated that the anomalous nighttime NmF2 maximums are least frequently formed at ～53° geomagnetic longitude. The calculations have indicated that the studied probabilities are independent of solar activity. Geomagnetic activity weakly affects the rate of occurrence of the first nighttime NmF2 maximum at geomagnetic longitudes of approximately 140° to 358°. At geomagnetic longitudes of approximately 16° to 70° (i.e., in the longitudinal zone of a decreased occurrence frequency of anomalous nighttime maximums), the occurrence probability of the first anomalous nighttime NmF2 maximum under geomagnetically quiet conditions is pronouncedly lower than under geomagnetically disturbed conditions. The dependence of the occurrence probabilities of the first and second anomalous nighttime NmF2 maximums on the month number in a year has been studied.     

On the variation of solar radiation and blueness of the sky during the eclipse of June 30, 1954 at Athens

Summary This paper presents the study of variations of the solar radiation and the blueness of the sky during the eclipse of June 30, 1954 at Athens. The comparison of the solar radiation march during the eclipse day to that of the two preceding and the two following days of the eclipse-all five days were almost identical from the standpoint of weather—proved that the direct solar radiation and the total (sky and sun) radiation underwent a considerable decrease during the phenomenon. The blueness of the sky also underwent a significant change, especially at the maximum of the eclipse.     

Atmospheric Broadband Model for Computation of Solar Radiation at the Earth’s Surface. Application to Mediterranean Climate

—This paper deals with a new broadband atmospheric model designed for predicting the total and diffuse solar radiation incident on the earth’s surface in medium or large-sized coastal or near-coastal cities, under a clear or cloudy sky. The revised solar spectrum is used. The atmospheric transmittance of each atmospheric parameter contributing to solar radiation depletion, water vapor, ozone, uniformly mixed gases, molecules and aerosols, is calculated using parameterized expressions resulting from integrated spectral transmittance functions. The beam and diffuse radiation components are obtained as a function of the specific atmospheric transmittances. The model requires the following parameters as inputs: total water vapor and ozone amount in a vertical column, sunshine duration and the surface albedo. The model has been used for validation purposes at two stations with slightly different characteristics (NOA and Penteli) in the Athens basin, where total and diffuse radiation measurements are available, for a period of 34 months for NOA and 23 for Penteli. The NOA station is located on a small hill (107 m a.m.s.l.) near the center of Athens, while the Penteli station (500 m a.m.s.l.) is situated in a relatively less polluted area in northern Athens. The clear sky part of the model was tested for 70 individual “clear” days with 2-minute intervals, while the whole model was checked with monthly “mean” days and mean hourly values. A close agreement between the calculated and the measured values of total and diffuse solar radiation is observed.     

An evaluation of illuminance measurements at Valladolid (Spain)

Data used in this study are obtained from a solar radiation station sited at the Low Atmospheric Research Center, CIBA, at Valladolid (Spain). Measurements from different sensors have been collected and put together in order to analyze different types of correlations. Results from two data sets, corresponding to years 2003 and 2004, are shown in this work. Data are firstly divided into eight categories according to the clearness of the sky. Then each category is analyzed independently in order to get conclusions about the parameter of interest, the solar illuminance. Here, an attempt to model hourly global horizontal illumination data is made; the year 2003 is used for calibration and 2004 for validation of the model.     

Manifestation of 22-year solar magnetic cycle in the imbalance between positive and negative photospheric magnetic fluxes

Time variations in strong and weak photospheric magnetic fields have been considered based on synoptic maps from the Kitt Peak observatory for 1976?C2003. The magnetic fields of positive and negative polarities of the Northern and Southern hemispheres of the Sun and their imbalance were studied. It has been indicated that different groups of magnetic fields vary with 11-or 22-year periods depending on their values. The difference between positive and negative fluxes for each hemisphere always varies with a 22-year period. For weak fields, the 22-year cycle is related to the manifestation of the global solar magnetic field. For strong fields, the imbalance between positive and negative fluxes reflects the predominant role of leading sunspots in a given solar hemisphere. It has been detected that the total magnetic flux over the entire solar disk varies with an 11-year period in antiphase with the solar activity cycle for the weakest magnetic fields (0?C5 G).     

Modelling the impact of solar variability on climate

Computer simulations of the impact on climate of solar variability generally fall into four categories. First, there are lower atmosphere GCM experiments, in which enhanced solar activity is represented by changes in spectrally integrated solar constant. Secondly, there are GCM studies of the dynamical response of the middle atmosphere to changes in solar ultraviolet, mainly concentrating on the northern hemisphere winter, and how these impact the troposphere. These studies have been instructive in providing an understanding of some of the mechanisms involved but, because of the very different nature of the assumptions made, give rather different suggestions as to potential patterns of change. In particular predicted zonal mean temperature changes in the lower stratosphere are usually of opposite sign in these two types of experiment. None of these GCM studies include interactive photochemistry and the third category of modelling work is concerned with the photochemical response of the middle atmosphere to enhanced solar ultraviolet. These generally employ 2D models to predict changes in ozone and other gaseous species. Recently it has been realised that the responses (to a variety of external forcings) of the lower and middle atmospheres are linked through both radiative and dynamical mechanisms and should not be viewed in isolation from each other. Thus the fourth type of modelling study, which is still in its infancy, attempts to represent solar variability by realistic changes in both irradiance and ozone concentrations. In this paper these various modelling studies are reviewed and some new results presented which confirm previous theoretical suggestions that, in the northern hemisphere winter, the atmosphere may respond to solar changes in a similar way as to the injection of volcanic aerosol. The implications of the results of the model studies for the detection of solar-induced climate change are discussed.     

Actinometric measurements of total solar radiation at normal incidence and its spectral distribution at Giza

Summary Measurements of the total solar radiation at normal incidence and its spectral distribution have been undertaken for clear sky conditions, at Giza, from March 1961 to February 1962. A Linke-Feussner actinometer no 113 supplied with two standard Schott filters OG₁ and RG₂ has been used.The results obtained for a whole year have been presented graphically and studied as function of the air mass and as diurnal variation.     

Asymmetry in the form of solar spots

We have analyzed the geometric characteristics of sunspots. The form of sunspots has been studied by sunspot image normalization to obtain the average profile of spots and the profile relative to the position of cores. The deviation of the sunspot form from the axisymmetric configuration has been studied. We have found that the spots of leading and trailing polarities have a drop shape. The cores of leading and trailing sunspots are shifted toward the western and eastern edges of the photosphere–penumbra boundary, respectively. The strength of the magnetic field of the cores of leading spots in the eastern hemisphere exceeds the field strength in the western hemisphere. We considered the tilt of the form of sunspots as a function of size. The form of spots of a large area (S > 1000 ppm of solar hemisphere) is elongated along the magnetic axis of the bipole of a group of sunspots.     

Inference of total ozone from photometric measurements of sky radiation

Summary Ground-based photometric measurements of spectral sky radiation have been made using a simple filter instrument. Sky radiation intensities measured in the solar vertical at =3200 Å and 3600 Å are compared to infer total ozone. A model of multiple scattering Rayleigh atmosphere serves as a primary reduction parameter. Spectral measurements of all-sky radiance distribution are used to study the effects of haze and clouds on the inference of total ozone. The brightness distribution of clear and overcast sky in ultraviolet is also described.     

不同起源地磁扰动期间极光沉降能量的统计研究

尽管对极光沉降能量(HP)的研究已经开展很久,但是关于不同行星际扰动源对HP影响的研究仍然很少.本文基于2001—2008年NOAA极轨卫星数据,对三类不同扰动源,即盔状冕流共转相互作用区(CIRs)、伪冕流CIRs和行星际日冕物质抛射(ICMEs)驱动的中等磁暴期间HP的变化进行时序叠加统计分析,讨论了相关太阳风背景参数、地磁活动强度以及耦合函数的有效性;研究了三类磁暴事件期间HP的南北半球不对称性.结果表明,在磁暴之前盔状冕流CIR磁暴的HP明显低于伪冕流CIR磁暴和ICME磁暴,盔状冕流"磁暴前的平静期"与Newell耦合函数关系密切,而与Russell-McPherron效应关系较小.盔状冕流CIR磁暴主相HP高于伪冕流CIR磁暴和ICME磁暴,可能与盔状冕流相应行星际|B_z|和太阳风数密度均较高有关.此外,在Kp≤4时,冬夏季半球HP的差别随着Kp增加而增加,相应的变化规律符合电导率反馈机制的预测;在Kp>4时,盔状冕流磁暴和ICME磁暴冬季半球的HP大于夏季半球的,伪冕流磁暴事件夏季半球的HP大于冬季半球的或与冬季半球的相近.     

Descriptive study of solar activity sudden increase and Halloween storms of 2003

During the declining phase of the last three solar cycles, secondary peaks have been detected 2–3 years after the main peak of sunspot number. The main peak of cycle 23 was in 2001, but a sudden increase of the solar activity occurred during the period October 17 to November 10, 2003 (the so-called Halloween storms). A similar storm occurred 1 year later, during the period October 3 to November 13, 2004. These events are considered as secondary peaks during the declining phase of cycle 23. Secondary peaks during declining phase of the last 10 solar cycles were detected by Gonzalez and Tsurutani [1990. Planetary and Space Science 38, 181–187]. During Halloween storm period, the sunspot area increased up to 1.11×10^?9 hemisphere on October 19, and grow up to 5.69×10^?9 hemisphere on October 30, 2003. Then it decreased to 1.11×10^?9 hemisphere on November 4, 2003. Also, the radio flux of λ=10.7 cm increased from 120 sfu on October 19, to 298 sfu on October 26, 2003, then decreased to 168 sfu on November 4, 2003. Two eruptive solar proton flares were released on 26 and 28 October 2003, the latter being the most eruptive flare recorded since 1976 (values reaching X17/4B).The aim of this study is to follow the morphological and magnetic changes of the active region before, during, and after the production of high-energy flares. Furthermore, the causes of release of these eruptive storms have been discussed for the period, October–November 2003, during the declining phase of the solar cycle 23.     

Stratospheric ozone response to a solar proton event: Hemispheric asymmetries

Ozone depression in the polar stratosphere during the energetic solar proton event on 4 August 1972 was observed by the backscattered ultraviolet (BUV) experiment on the Nimbus 4 satellite. Distinct asymmetries in the columnar ozone content, the amount of ozone depressions and their temporal variations above 4 mb level (38 km) were observed between the two hemispheres. The ozone destroying solar particles precipitate rather symmetrically into the two polar atmospheres due to the geomagnetic dipole field These asymmetries can be therefore ascribed to the differences mainly in dynamics and partly in the solar illumination and the vertical temperature structure between the summer and the winter polar atmospheres. The polar stratosphere is less disturbed and warmer in the summer hemisphere than the winter hemisphere since the propagation of planetary wave from the troposphere is inhibited by the wind system in the upper troposphere, and the air is heated by the prolonged solar insolation. Correspondingly, the temporal variations of stratospheric ozone depletion and its recovery appear to be smooth functions of time in the (northern) summer hemisphere and the undisturbed ozone amount is slighily, less than that of its counterpart. On the other hand, the tempotal variation of the upper stratospheric ozone in the winter polar atmosphere (southern hemisphere) indicates large amplitudes and irregularities due to the disturbances produced by upward propagating waves which prevail in the polar winter atmosphere. These characteristic differences between the two polar atmospheres are also evident in the vertical distributions of temperature and wind observed by balloons and rocker soundings.     

Relations of field line resonances and upstream waves and the winter attenuation of pulsations

Using data on the occurrence frequency of geomagnetic pulsations of different periods from three observatories in Central Europe, conclusions are drawn about the occurrence of field line resonances and pulsations directly driven by upstream waves at L-values below 3. It was found that both types occur during the interval studied (first 6 months of the year 1991), but both the occurrence frequency of the two types and the characteristic period of the field line resonance change significantly as compared to other intervals. During Northern winter, pulsation activity is severely damped in solar maximum years, including the year 1991. The decrease in the activity of the pulsations is more significant at shorter periods.