The variations of temperature, pressure and wind speedvalues: Effects on gravity waves

According to the theoretical studies, gravity waves, which are excited in the lower atmosphere, can transport momentum and energy on to the upper levels. Gravity waves are attenuated by interacting with the large-scale wind motions in the upper part of the middle atmosphere. Different meteorological parameters and atmospheric circulations are known as one of the sources of excitement of gravity waves. The main purpose of this paper is to analyze the onset of some gravity waves (GWs), and seasonal variations of gravity waves over Istanbul. Radiosonda data of Istanbul in troposphere and lower stratosphere (1000 hPa–30 hPa) between 1993 and 1997 is analyzed. Daily, monthly and annual variation of pressure heights, air temperature, horizontal wind speed and deviations from mean values are interpreted. Zonal and meridional wind speed variations show the effects of gravity waves for different pressure levels in the troposphere. These waves lead the meso-scale wave form structures in spring, autumn and winter

Wavelet transforms of meteorological parameters and gravity waves

The main purpose of this paper is to analyze some characteristics of gravity waves (GWs), and seasonal variations of atmospheric waves over Istanbul by using wavelet techniques. Daily radiosonda data of Istanbul in the troposphere and lower stratosphere (1000hPa-30hPa) between 1993 and 1997 have been considered. Wavelet analysis based on a computer simulation of data is generally close to the real data when Daubechies wavelet series are used. Daily, monthly, seasonal and annual variations of pressure heights, air temperature and deviations from mean values have been analyzed. Variations show the effects of gravity waves for different pressure levels in the troposphere. These waves lead to the meso-scale wave-form structures in spring, autumn and winter. As a result of this study, wavelet series and transforms for data construction, definition of some discontinuities and the local effects on the signal have been compared with the results of previous studies. The most similar structure between temperature, turbulence parameters and geo-potential height deviations has been defined at the 500-hPa pressure level

Harmonic analysis of precipitation, pressure and temperature over Turkey

Monthly averages of temperature, precipitation and pressure values from ground-based measurements for long-term data observed in different geographical regions in Turkey have been investigated. The main purpose of this study is to define the role of small- and large-scale phenomena (local and synoptic fluctuations) on precipitation, pressure and temperature variations and their periods. Hence, the Fourier transformation analysis of the monthly average value of meteorological parameters has been considered, and phase angles and amplitudes have been calculated. The first-order harmonics of temperature, precipitation and pressure values show large-scale effects, while higher-order harmonics show the effects of small-scale variations. The variations of first–sixth-order harmonic amplitudes and phases provide a useful means of understanding the large- and local-scale effects on meteorological parameters. The phase angle can be used to determine the time of the year when the maximum or minimum of a given harmonic occurs. The analysis helps us distinguish different precipitation, pressure and temperature regimes and transition regions. Local- and large-scale phenomena and some unusual seasonal patterns are also defined. This analysis also shows strong annual variations of precipitation in the Southern and Western part of Anatolia and that strong semi-annual fluctuations are predominant in the eastern part of Turkey. Strong annual influence on pressure variations is mostly observed in the coastal part of Turkey. The dominance of the first three harmonics of pressure is smaller over most of the terrestrial stations. Temperature variations are mostly influenced by the annual fluctuations in eastern and south-eastern Anatolia. The urban heat Island caused by developing metropolitan areas refers to local warming effects and heat islands. The local effects are observed in the western part of Turkey

Some results from the National Observatory of Turkey, Kazan State University, and Nikolaev Astronomical Observatory on small bodies of the solar system

A scientific collaboration between TÜBİTAK National Observatory (Turkey), Kazan State University (Russia) and Nikolaev Astronomical Observatory (Ukraine) involves observations of minor planets and near-Earth asteroids (NEAs) with the 1.5 m Russian-Turkish telescope (RTT150). Regular observations of selected asteroids in the range of 11-18 magnitudes began in 2004 with the view of determining masses of selected asteroids, improving the orbits of the NEAs, and studying physical characteristics of selected asteroids from photometric observations. More than 3000 positions of 53 selected asteroids and 11 NEAs have been obtained with an internal error in the range of 30-300 mas for a single determination. Photometric reductions of more than 4000 CCD frames are in progress. Masses of 21 asteroids were estimated through dynamical method using the ground-based optical observations, mainly from the RTT150 and Minor Planet Center. A comparison of the observational results from the RTT150 in 2004-2005 with observations of the same objects at other observatories allows us to conclude that RTT150 can be used for ground-based support in astrometry for the space mission GAIA. © 2008 Elsevier Ltd. All rights reserved

A comparative study of Meteosat, ECMWF and radiosonde wind vectors at Istanbul

Wind vector evaluation through Meteosat is useful for a continental belt such as Turkey, where nationwide radiosonde and aircraft data are suboptimal, especially from the point of view of numerical weather prediction (NWP). Towards this goal, investigations have been carried out on the Meteosat cloud motion winds (CMW) using IR imagery with collocated radiosonde data in and Istanbul with the eventual aim of extending this study to develop general circulation models in the Mediterranean region. The CMW analysis reveals correlation with the radiosonde data superior to that of the European Center for Medium range Weather Forecast (ECMWF) for the period of study. This study also confirms that Meteosat CMWs are subject to less severe speed biases, although there is a tendency to underestimate CMW speeds for low- speed scenarios, as opposed to high wind speeds as suggested in the past studies

First hours of the GRB 030329 optical afterglow

We present the first results of the observations of the extremely bright optical afterglow of gamma-ray burst (GRB) 030329 with the 1.5m Russian-Turkish telescope RTT150 (TUBITAK National Observatory, Bakyrlytepe, Turkey). RTT150 was one of the first 1.5m-class telescopes pointed to the afterglow. Observations were started approximately 6 hours after the burst. During the first 5 hours of our observations the afterglow faded exactly as a power law with index -1.19+-0.01 in each of the BVRI Bessel filters. After that, in all BVRI filters simultaneously we observe a steepening of the power law light curve. The power law decay index smoothly approaches the value ~= -1.9, observed by other observatories later. This power law break occurs at t-t_0 =0.57 days and lasts for +-0.1 days. We observe no variability above the gradual fading with the upper limits 10--1% on time scales 0.1--1000s. Spectral flux distribution in four BVRI filters corresponds to the power law spectrum with spectral index \alpha=0.66+-0.01. The change of the power law decay index in the end of our observations can be interpreted as a signature of collimated ultrarelativistic jet. The afterglow flux distribution in radio, optical and x-rays is consistent with synchrotron spectrum. We continue our observations of this unique object with RTT150.Comment: Astronomy Letters, Vol. 29, No. 9, p. 573; 6 pages, 5 figures; pagination corrected; the original Russian version can be found at http://hea.iki.rssi.ru/~br/030329/pfh030329.pd

A Note on Projective Klingenberg Planes over Rings of Plural Numbers

This paper deals with a certain class of projective Klingenberg planes over the local ring F[eta]/lteta^{m}gt with F an arbitrary field, known as the plural algebra of order m. In particular addition and multiplication of points on a line is defined geometrically and interpreted algebraically, by using the coordinate ring