Secular variations in the spectrum of solar p-modes

The solar p-mode spectrum of very low I is measured with high accuracy for a long enough period of time so as to allow the search for solar cycle variations. In this paper solar cycle variations of the frequency and energy of the modes are confirmed. Moreover, a slight variation,within errors, of its rotational splitting with the solar cycle, is suggested.     

VIDEO AND PHOTOGRAPHIC SPECTROSCOPY OF 1998 AND 2001 LEONID PERSISTENT TRAINS FROM 300 TO 930 nm

Spectra of persistent meteor trains were observed at wavelength between 300 and 930 nm. Two obtained train spectra during the 1998 and 2001 Leonid meteor showers are reported here. During the 1998 Leonids, one train was detected by a photographic camera with a spectrograph covering 370–640 nm region. On the other hand, during the 2001 Leonids, video observations were carried out using image intensified cameras in ultraviolet (UV), visible and near infrared (near-IR) wavelengths. Temperatures in persistent trains have been measured by atmospheric O₂ A(0,1) band at the wavelength near 864.5 nm. From a video spectrum obtained just 7 s after parent fireball’s flare, a rotational temperature of 250 K at altitude of 88.0±0.5 km was estimated. We can say that the cooling time scale of train strongly depends on the initial mass of its fireball at least for Leonids. Based on cooling constant calculated from our results, we estimated a temperature of ∼ ∼130 K as a final exothermic temperature at early stage of persistent trains.     

Some Aspects of Meteoric Head Echo Velocity Determination

Velocity determination of 131 head echoes recorded during Perseid meteor shower observations by the Canadian 2 MW radar, has been performed under the assumption of either their constant velocity or of its linear change with time. Even though the constant velocities concentrated at 60 km s-1 generally accepted for the Perseids, a substantial number of echoes had velocities either lower than 60 km s-1 or greater than this value. The inclusion of variable velocity into considerations led to surprising result that a great portion of the head echoes accelerated (3 possibly decelerating echoes in comparison with 33 accelerating cases on the level of relative standard deviations of output parameters not exceeding 10%). It seems that the allocation of the ionization responsible for the head echo is not entirely identical with the instantaneous meteoroid position. As a consequence, the velocity derived from the measured head echo coordinates can differ from the velocity of parent body. We are not able to explain this finding at present. This revised version was published online in July 2006 with corrections to the Cover Date.     

Bandwidth Effects in the 3G Photometric System

Bandwidth effects in the GAIA photometric system 3G are discussed. It is demonstrated that careful account for the bandwidth effects in any proposed GAIA photometric system has to be made, in order to determine the fundamental parameters of heavily reddened stars. This revised version was published online in July 2006 with corrections to the Cover Date.     

Diffuse Interstellar Band at 862 nm as a Reddening Tracer for GAIA

We investigate the plausibility of using diffuse interstellar band at862 nm for tracing interstellar extinction with the ESA's astrometric space mission GAIA. For this purpose we perform numerical tests to simulate the conditions of real observations, covering a wide range of stellar parameters and different amounts of interstellar extinction. Our simulations indicate that with the present Radial Velocity Spectrometer setup the uncertainty in color excess of σ_E(B-V)≤ 0.05 can be achieved only for the interstellar reddening tracers brighter than V ∼ 13. None of the plausible tracers can provide accurate color excesses (σ _E(B-V) ≤ 0.05) at the distances beyond 2 kpc. We therefore conclude that with the currently planned instrumentation onboard GAIA this method can not be used as a stand-alone approach for probing interstellar extinction on the Galactic distance scales within the framework of the GAIA mission. This revised version was published online in July 2006 with corrections to the Cover Date.     

GAIA Photometric System: Simultaneous 4-D Parameterization

We present a software package developed for the automatic 4-D stellar parameterization. The package can be adopted to virtually any multicolour photometric system. Procedure of simultaneous determination of T _eff, log g, [M/H] and E _B-V is very flexible and can be performed by applying various photometric parameters(magnitudes, colour indices etc.). Any changes of the photometric systems, weighting schemes or parameterization criteria can be implemented easily. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the stability of the zodiacal cloud

The problem of the stability of the zodiacal cloud is scrutinized. The central idea of the paper sticks in the theoretical treatment of the action of the solar electromagnetic radiation on small interplanetary dust particles (IDPs). It is suggested that the virtual problem of the (in-)stability of the zodiacal cloud originated from the physically incorrect application of the Poynting-Robertson effect on IDPs. Real particles are not of spherical shape and so the braking acceleration is not proportional to -v/c. Depending on the shape (and other optical properties) of the particle, also spiralling outward from the Sun may occur.     

An Analysis of Polar Coronal Hole Evolution: Relations to Other Solar Phenomena and Heliospheric Consequences

We use observations of the green corona low-brightness regions to construct a time series of a polar coronal hole area from 1939 to 1996, covering 5 solar cycles. We then perform a power-spectral analysis of the monthly data time series. Several persistent significant periodicities appear in the spectra, which are related with those found in solar magnetic flux emergence, geomagnetic storm sudden commencements and cosmic-ray flux at Earth. Of particular importance are the peak at around 1.6–1.8 yr recently found in cosmic-ray intensity fluctuations, and the peak at around 1 yr, also identified in coronal hole magnetic flux variations. Additional interesting features are the peaks close to 5 yr, 3 yr and the possible peak at around 30 yr, that were also found in other solar and interplanetary phenomena. Our results stress the physical connection between the solar magnetic flux emergence and the interplanetary medium dynamics, in particular the importance of coronal hole evolution in the structuring of the heliosphere.     

Triggering factors,behavior, and social impact of the January 2021 hail-debris flows at the Central Valley of Chile

Landslides - An extreme precipitation event produced catastrophic debris flows in central Chile during 29–31 January 2021 (austral summer). Our study focuses on the triggering factors and...     

Contribution of atmospheric processes to the degradation of air quality: case study (Sohar Industrial Area,Oman)

The impact of the air pollution generated by any industrial activities may be further aggravated if the location of the industrial area is exposed to certain atmospheric characteristics. Under such conditions, the likelihood of accumulation of local air pollution is high. This paper uses two approaches (statistical and numerical simulation) to investigate the contribution of atmospheric processes towards degradation of air quality. A case study of the two approaches was conducted over Sohar Industrial Area in the Sultanate of Oman. Measured wind data were used to account for specific atmospheric characteristics such as stagnation, ventilation, and recirculation using the statistical approach. In the second approach, numerical weather prediction model was used to simulate mesoscale circulation phenomena such as sea breeze and its contribution to the processes affecting the air quality. The study demonstrates that the atmospheric processes appear to contribute substantially to the degradation of air quality in the Sohar Industrial Area. The statistical analysis shows that the atmospheric dilution potential of Sohar Industrial Area is prone to stagnation and recirculation, rather than ventilation. Moreover, model simulation shows that there is a seasonal variation in the contribution of atmospheric processes to the degradation of the air quality at Sohar Industrial Area.