Astronomi Laboratuvarı : Tamer ATAÇ

Soyadı, Adı: Ataç, Tamer

Adres: B.Ü. Kandilli Rasathanesi, 34684 Çengelköy - Istanbul

e-posta: atac@boun.edu.tr

Doğum Tarihi ve yeri : 25 Mart 1953, Bursa

Ortaöğrenim: 1972 Saint Benoit Fransız Lisesi.

Üniversite: 1977 İstanbul Üniversitesi, Fen Fakültesi, B.S

Y. Lisans: 1980 İstanbul Üniversitesi, Fen Fakültesi, M.S

Doktora: 1985 İ.Ü. Fen Fakültesi, Ph.D.

Ünvanı: Dr.

Ocak 2010’daki görevi: Boğaziçi Üniversitesi Kandilli Rasathanesi ve Deprem Araştırma Enstitüsü, Astronomi Laboratuvarı, Araştırmacı

İlgi Alanları: Güneş Fiziği, İyonosfer

Yayınlar

TÜBİTAK A Tipi :

- GIBSON, A.J., YILMAZ, U.M., TULUNAY, Y., EROL, C.B., ÖZGÜÇ A., and ATAÇ, T.
Characteristics of Fading of HF Signal and Noise Intensities
on Three Paths Between the UK and Turkey
Radio Science, 30, 649-658,1995

- ÖZGÜÇ, A., TULUNAY, Y., AND ATAÇ, T.
Examination of the Solar Cycle Variation of foF2 by Using Solar Flare Index for the Cycle 21
Advances in Space Research, 22, 139-142, 1998.

TÜBİTAK B Tipi :

- ÖZGÜÇ, A. and ATAÇ, T.
Periodic Behaviour of Solar Flare Index During Solar Cycles 20 and 21
Solar Phys., 123, 357-365, 1989

- ÖZGÜÇ, A. and ATAÇ, T.
The 73-day Periodicity of the Flare Index During the
Current Solar Cycle 22.
Solar Physics, 150, 339-346, 1994

- ÖZGÜÇ, A. and ATAÇ, T.
Confirmation of the 25.5-day Fundamental Period of the Sun Using North-South
Asymmetry of the Flare Index
Solar Physics, 163, 183-191, 1996

- ATAÇ, T. and ÖZGÜÇ, A.
North-South Asymmetry in the Solar Flare Index.
Solar Physics, 166, 201-208, 1996

- ATAÇ, T.,and ÖZGÜÇ, A.
Flare index of solar cycle 22
Solar Physics, 180, 397-407, 1998

- ATAÇ, T.,and ÖZGÜÇ, A.
Flare Index During the Rising Phase of Solar Cycle 23
Solar Physics, 198 (2):399-407, February 2001

- ÖZGÜÇ, A. , ATAÇ, T. , and RYBAK, J.
Flare index variability in the ascending branch of solar cycle 23
JGR-SPACE PHYSICS,10.1029/2001JA009080 ,30 July 2002

- ÖZGÜÇ, A. , ATAÇ, T. , and RYBAK, J.
Temporal Variability of the flare index (1966-2001)
Solar Physics, 214, 375-396, June 2003

TÜBİTAK C Tipi :

- ATAÇ,T.
Statistical Relationship Between Sunspots and Major Flares
Astrophys. and Space Sci.,129, 203-208, 1987

- ATAÇ,T.
Time variation of the flare index during the 21st solar cycle
Astrophys. and Space Sci.,135, 201-205, 1987

- ATAÇ,T.
On the short term variations of solar activity during solar cycle 21.
Earth, Moon and Planets, 47, 165-170, 1989

- ATAÇ,T.
Relation of the fluctuations of some of the solar activity indices
Astrophys. and Space Sci., 153, 173-176, 1989

- ATAÇ, T
On the SID durations
Astrophys. and Space Sci., 181, 157-159, 1991

Uluslararası Hakemli Dergiler :

- ÖZGÜÇ, A., ATAÇ, T., TULUNAY, Y., STANISLAWSKA, I.
The Ionospheric foF2 data over Istanbul and their response to solar activity for the
years 1964-1969 and 1993.
Studia Geoph. Geod., 42,112-118. 1998

- EROL, C.B., TULUNAY, Y., GIBSON, A.J., YILMAZ, U.M.
ÖZGÜÇ,A., and ATAÇ, T.
Characteristics of Fading of HF Signal and Noise
Intensities on Several Paths Between the UK and Kandilli and Göztepe,Turkey
Tr. J. of Physics, 18, 1155-1162, 1994

- TULUNAY,Y., BAYKAL, Ş.A. YİĞİT, Y.G., STANISLAWSKA, I., ROKICKI,A.
ZBYSZYNSKI, Z., ÖZGÜÇ, A., ATAÇ, T., ALTAŞ, L., BARLAS, O.
Spectral analysis of the foF2 data obtained at five PRIME sites
during a 15 minute campaign in June 1993
Annali di Geofisica, XXXIX, N.4, 863-875, 1996

Uluslararası Kitapta Bölüm:

- ROKICKI, A., STANISLAWSKA, I., ZBYSZYNSKI, Z., TULUNAY, Y.,
ÖZGÜÇ, A., ATAÇ,T., ALTAŞ,L., and BARLAS, O.
First Results from the Transportable Ionosonde Campaign
“PRIME Studies with Emphasis on TEC and Topside Modelling”
PRIME Cost 238 Graz Workshop, Part II, 297. 1993

- ÖZGÜÇ, A., ATAÇ, T., ALTAŞ, L.
Preparations for the Last Total Solar Eclipse of the Millennium in Turkey
ASP Conference Series, Vol.184, 348-352, 1999

- ÖZGÜÇ, A., ATAÇ, T., ALTAŞ, L.
The Last Total Solar Eclipse of the Millennium in Turkey
Contr. Skalnate Pleso Obs. XXVIII, N.3, 285-289, 1999

- ÖZGÜÇ, A., ATAÇ, T., ALTAŞ, L. RUSIN, V.
The Last Total Solar Eclipse of the Millennium in Turkey.
Proceeding 3rd advances in solar Physics Euroconference 22-26 Sep.
Potsdam, Germany, ASP Conf. Ser. 184, 349-352, 1998

- ÖZGÜÇ, A., ATAÇ, T., ANTALOVA, A.
Effects of hysteresis of some solar indices during the past three solar cycles 20,21 and 22
Proc. 1st Solar & Space Weather Euroconference,"The Solar Cycle and Terrestrial Climate".
Santa Cruz de Tenerife, Tenerife, Spain, 25-29 September 2000 (ESA SP-463, December 2000)

- ÖZGÜÇ, A., ATAÇ, T., ANTALOVA, A.
Effects of hysteresis of some solar indices
Recent Insights into the Physics of the Sun and Heliosphere: Highlights from SOHO and other Space
Missions, International Astronomical Union. Symposium no. 203. Manchester, England, August 2000.
2000IAUS..203E..72O

- ÖZGÜÇ, A., ATAÇ, T., RYBAK, J.
Long-Term Periodicities in the flare index between the years 1966-2001
Proc. 10th. European Solar Physics Meeting, 'Solar Variability: From Core to Outer Frontiers', Prague, Czech Republic, 9-14 September 2002 (ESA SP-506, December 2002)

Ulusal Kitapta Bölüm:

Kitap: Halley Kuyrukluyıldızı, DİZER, M., ÖZGÜÇ, A., ATAÇ,T., ALTAŞ,L., Boğaziçi Üniversitesi, 1986, Yayın No: 401

Ulusal Destekli Araştırma Projeleri:

Dar-band Sodyum Filtresi yapımı,
Proje yöneticisi
Boğaziçi Üniv. Araştırma Fonu.
1992 – 1993

Danjon Astrolabı ile Güneş çapının Ölçülmesi,
Proje Araştırıcısı
Boğaziçi Üniv. Araştırma Fonu
1993 – 1994

COST-238 PRIME,
Proje Araştırıcısı
TÜBITAK, Avrupa Topluluğu iletişim projesi
1.7.1992 – 1.3.1995

COST-238 PRIME'a destek I,
Proje Araştırıcısı
Boğaziçi Üniv. Araş. Fonu
1.1.1994 – 1.12.1994

COST-238 PRIME'a Destek II,
Proje Araştırıcısı
Boğaziçi Üniv. Araş. Fonu
1.1.1995 – 1.12.1995

İlginç Güneş Olaylarının İncelenmesi
Proje Araştırıcısı
Boğaziçi Üniv. Araş. Fonu
1.1.1996 – 1.12.1996

Güneş Kromosferinin CCTV ile Gözlenmesi
Proje Araştırıcısı
Boğaziçi Üniv. Araş. Fonu
1.1.1996 – 1.12.1996

The Last Total Solar eclipse of the Millennium
Proje Araştırıcısı
Boğaziçi Üniv. Araş. Fonu
1998 – 1999

Magneto-Optik Filtre ile Güneş Gözlemleri
Proje Araştırıcısı
Boğaziçi Üniv. Araş. Fonu
1.1.2000 – 1.12.2000

NASA ADS Astronomy/Planetary Abstract Service

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Title:		Effects of hysteresis in solar cycle variations between flare index and cosmic rays
Authors:		Özgüç, A.; Ataç, T.
Affiliation:		AA(Kandilli Observatory and Earthquake Research Institute, Bogazic¸i University, C¸engelköy, 34684, Istanbul, Turkey), AB(Kandilli Observatory and Earthquake Research Institute, Bogazic¸i University, C¸engelköy, 34684, Istanbul, Turkey)
Journal:		New Astronomy, Volume 8, Issue 8, p. 745-750. (NewA Homepage)
Publication Date:		11/2003
Origin:		ELSEVIER
Abstract Copyright:		(c) 2003 Elsevier B.V.
Bibliographic Code:		2003NewA....8..745O

Abstract

We study the hysteresis effect between the solar flare index and cosmic ray intensity for the past 37 years from January 1, 1965 to December 31, 2001 on a daily basis. We show that smoothed time series of flare index and the daily Calgary Galactic Cosmic Ray intensity values exhibit significant solar cycle dependent differences in their relative variations during the studied period. The shapes of these differences vary from cycle to cycle. So we investigate the momentary time lags between the two time series for the odd and even cycles.

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Title:		Hysteresis phenomenon between flare index and cosmic rays
Authors:		Özgüç, Atila; Ataç, Tamer
Journal:		In: Solar variability as an input to the Earth's environment. International Solar Cycle Studies (ISCS) Symposium, 23 - 28 June 2003, Tatranská Lomnica, Slovak Republic. Ed.: A. Wilson. ESA SP-535, Noordwijk: ESA Publications Division, ISBN 92-9092-845-X, 2003, p. 687 - 689
Publication Date:		09/2003
Origin:		ARI
Keywords:		Solar Flares: Cosmic Rays
Abstract Copyright:		ESA
Bibliographic Code:		2003iscs.symp..687O

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Title:		Short-term periodicities in the flare index between the years 1966-2001
Authors:		Özgüç, A.; Ataç, T.; Rybák, J.
Journal:		In: Solar variability as an input to the Earth's environment. International Solar Cycle Studies (ISCS) Symposium, 23 - 28 June 2003, Tatranská Lomnica, Slovak Republic. Ed.: A. Wilson. ESA SP-535, Noordwijk: ESA Publications Division, ISBN 92-9092-845-X, 2003, p. 141 - 143
Publication Date:		09/2003
Origin:		ARI
Keywords:		Solar Photosphere, Solar Magnetic Fields
Abstract Copyright:		ESA
Bibliographic Code:		2003iscs.symp..141O

Abstract

A brief description and the results of the temporal variability of the flare index over the epoch of almost 4 cycles (1966-2001) are presented. Using Fourier and wavelet transforms the short-term periodicities in the daily flare index data for the total surface of the Sun are presented. A significant variability was found for all periods. The wavelet transform results show that the occurrence of flare index power is highly intermittent in time.

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Title:		Temporal variability of the flare index (1966-2001)
Authors:		Özgüç, Atila; Ataç, Tamer; Rybák, Ján
Affiliation:		AA(Bogaziçi University, Kandilli Observatory and Earthquake Research Institute, Çengelköy, 34684, Istanbul, Turkey), AB(ozguc@boun.edu.tr), AC(Bogaziçi University, Kandilli Observatory and Earthquake Research Institute, Çengelköy, 34684, Istanbul, Turkey)
Journal:		Solar Physics, v. 214, Issue 2, p. 375-396 (2003). (SoPh Homepage)
Publication Date:		06/2003
Origin:		KLUWER
Abstract Copyright:		(c) 2003 Kluwer Academic Publishers
Bibliographic Code:		2003SoPh..214..375O

Abstract

A brief description and study of the temporal variability of the flare index over the epoch of almost 4 cycles (1966-2001) are presented. Using Fourier and wavelet transforms the long- and the intermediate-term periodicities in the daily flare index data for the total surface and for the northern and the southern hemispheres of the Sun are given in detail. A significant variability was found for all periods including those of 150 days and 1.3 years. The wavelet transform results show that the occurrence of flare index power is highly intermittent in time. A comparison of the results of the Fourier transform and the time-period wavelet transform of the flare index time series has clarified the importance of different periodicities, whether they are or are not the harmonics of the basic ones, as well as the temporal location of their occurrence.

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Title:		Long-term periodicities in the flare index between the years 1966 - 2001
Authors:		Özgüç, A.; Ataç, T.; Rybák, J.
Journal:		In: Solar variability: from core to outer frontiers. The 10th European Solar Physics Meeting, 9 - 14 September 2002, Prague, Czech Republic. Ed. A. Wilson. ESA SP-506, Vol. 2. Noordwijk: ESA Publications Division, ISBN 92-9092-816-6, 2002, p. 709 - 712
Publication Date:		12/2002
Origin:		ARI
Keywords:		Solar Activity, Sun, Periodicity
Abstract Copyright:		ESA
Bibliographic Code:		2002svco.conf..709O

Abstract

A brief description and the results of the temporal variability of the flare index over the epoch of almost 4 cycles (1966-2001) are presented. Using Fourier and wavelet transforms the long-term periodicities in the daily flare index data for the total surface and for the northern and the southern hemispheres of the Sun are presented. A significant variability was found for all periods. The wavelet transform results show that the occurrence of flare index power is highly intermittent in time.

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Title:		Flare index variability in the ascending branch of solar cycle 23
Authors:		Özgüç, A.; Ataç, T.; Rybák, J.
Journal:		Journal of Geophysical Research (Space Physics), Volume 107, Issue A7, pp. SSH 11-1, CiteID 1146, DOI 10.1029/2001JA009080 (JGRA Homepage)
Publication Date:		07/2002
Origin:		AGU
AGU Keywords:		Solar Physics, Astrophysics, and Astronomy: Flares, Solar Physics, Astrophysics, and Astronomy: Magnetic fields, Solar Physics, Astrophysics, and Astronomy: Solar activity cycle (2162), Solar Physics, Astrophysics, and Astronomy: Helioseismology, Solar Physics, Astrophysics, and Astronomy: Solar irradiance,
Abstract Copyright:		(c) 2002: American Geophysical Union
Bibliographic Code:		2002JGRA.107gSSH11O

Abstract

A brief description and the results of the determination of the flare index as a measure of solar activity on the ascending branch of cycle 23 up to 31 December 2000 are presented. The patterns of similar activity indices that arise under different physical conditions during the rising activity phase are compared with the flare index. All studied solar indices rise more slowly in the current cycle than the last one, except the total solar irradiance. The intermediate-term periodicities in the daily flare index data were studied using the Fourier transform, and it was found that the 35-, 62-, 116-, 198-, and 276-day periodicities are in operation during the ascending branch of cycle 23. Contrary to the previous three cycles, 155-, 73-, or 51-day periodicities were not detected by the Fourier transform in this branch of the cycle. The wavelet transform results show that the occurrence of flare index power is highly intermittent in time, and the most pronounced power peaks were found to be present at 35 days (the temporal locations at 1998.3, 1999.9, and 2000.5 years), 116 days (the temporal interval 1999.7-2000.4 years) and 276 days period (interval roughly from 1999.5 until the end of the flare index data). Comparison of the Fourier and wavelet transform results has clarified the importance of different periodicities, whether they are (62, 198 days) or are not (35, 116, 276 days) the harmonics of the basic ones, as well as the temporal location of their occurrence.

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Title:		Effects of Hysteresis in Solar Cycle Variations Between Flare Index and some Solar Activity Indicators
Authors:		Özgüç, A.; Ataç, T.
Journal:		Solar-Terrestrial Magnetic Activity and Space Environment, Proceedings of the COSPAR Colloquium held in the NAOC in Beijing, China, September 10-12, 2001. Edited by Huaning Wang and Ronglan Xu. 1st ed. Boston: Pergamon, 2002. COSPAR colloquia series; v. 14, p.447
Publication Date:		00/2002
Origin:		ADS
Bibliographic Code:		2002stma.conf..447O

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Title:		Flare Index During the Rising Phase of Solar Cycle 23
Authors:		Ataç, Tamer; Özgüç, Atila
Affiliation:		AA(atac@boun.edu.tr), AB(atac@boun.edu.tr)
Journal:		Solar Physics, v. 198, Issue 2, p. 399-407 (2001). (SoPh Homepage)
Publication Date:		02/2001
Origin:		KLUWER
Abstract Copyright:		(c) 2001 Kluwer Academic Publishers
Bibliographic Code:		2001SoPh..198..399A

Abstract

A brief description and results of the flare index (FI) as a measure of solar activity for cycle 23 are given. The calculation of the daily flare index was determined using the final solar flare tables from the National Geophysical Data Center A. The final data of FI are presented in graphical form over the rising activity phase of solar cycle 23. Daily calculated values are available for general use in Kandilli observatory's and NGDC's anonymous ftp servers. The pattern of similar activity indices that arise under different physical conditions during the rising activity phase are compared with the flare index. The north-south asymmetry in the daily flare index data was studied.

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Title:		Observations of Hysteresis Between Flare Index and Some Solar Indices
Authors:		Özgüç, A.; Ataç, T.
Affiliation:		AA(Kandilli Observatory, Istanbul, Turkey)
Journal:		Recent Insights into the Physics of the Sun and Heliosphere: Highlights from SOHO and Other Space Missions, Proceedings of IAU Symposium 203, edited by Pål Brekke, Bernhard Fleck, and Joseph B. Gurman. Published by Astronomical Society of the Pacific, ISBN: 1-58381-069-2, 2001, p. 125
Publication Date:		00/2001
Origin:		ADS
Bibliographic Code:		2001IAUS..203..125O

Abstract

During the past two cycles, researchers have been monitoring solar irradiance at many selected wavelengths in addition to maintaining more traditional indices such as sunspot number and the 10.7cm flux. Certain pairs of these indices exhibit hysteresis, solar cycle dependent differences in their relative variations. We study this hysteresis effect by using smoothed time series of some indices of solar activity including the solar flare index and LDE flare index. The solar flare index and LDE flare index are newly calculated by the authors for the cycles 21 and 22. Further we try to find that hysteresis effect is indeed a feature of solar activity during the past two cycles.

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Title:		Preparations for the Last Total Solar Eclipse of the Millenium in Turkey
Authors:		Özgüç, A.; Ataç, T.; Altas, L.; Rusin, V.
Journal:		Third Advances in Solar Physics Euroconference: Magnetic Fields and Oscillations, ASP Conference Series vol.184, p. 348-352. Eds. B. Schmieder, A. Hofmann, J. Staude. ISBN: 1-58381-010-2(1999)
Publication Date:		09/1999
Origin:		AUTHOR
Keywords:		SUN, SOLAR ECLIPSE
Bibliographic Code:		1999tasp.conf..348O

Abstract

The last total solar eclipse of the millennium will be observed from Turkey which bridges two continents and has been the cradle of so many past civilizations. Among the countries from which the eclipse will be visible, Turkey seems to be one of the most suitable countries in terms of its climate and observational facilities. Kandilli Observatory and Earthquake Research Institute has organised a survey along the eclipse path to determine the suitable sites for the observations. The shadow of the moon will be first seen from the Black Sea coast at 14:20 L.T. It will then pass through central Anatolia and will leave Turkey from south-east at 14:42 L.T. A list of the suitable observing sites along the eclipse path is given.

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Title:		The last total solar eclipse of the millennium in Turkey
Authors:		Ozguc, A.; Atac, T.; Altas, L.
Journal:		Contributions of the Astronomical Observatory Skalnate Pleso, vol. 28, no. 3, p. 285-289. (CoSka Homepage)
Publication Date:		03/1999
Origin:		COSKA
Keywords:		THE SUN, SOLAR ECLIPSE
Bibliographic Code:		1999CoSka..28..285O

Abstract

The last total solar eclipse of the millennium will be observed from Turkey which bridges two continents and has been the cradle of so many past civilizations. Wouldn't you like to witness this magnificent event in the mystic ambiance of central Anatolia which offers its guests Turkish hospitality and a lot of historical examples of paganism, Christianity and Islam. Among the countries from which the eclipse will be visible, Turkey seems to be one of the most suitable countries in terms of its climate and observational facilities. Kandilli Observatory and Earthquake Research Institute has arranged fieldwork on the eclipse path to determine the suitable points for the observations. The shadow of the moon will be first seen from the Black Sea coast at 14:20 L.T. It will then pass through central Anatolia and will leave Turkey from south-east at 14:42 L.T.

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Title:		Flare Index of Solar Cycle 22
Authors:		Atac, Tamar; Ozguc, Atila
Journal:		Solar Physics, v. 180, Issue 1/2, p. 397-407. (SoPh Homepage)
Publication Date:		06/1998
Origin:		KLUWER
Bibliographic Code:		1998SoPh..180..397A

Abstract

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Title:		Examination of the solar cycle variation of foF2 by using solar flare index for the cycle 21
Authors:		Özgüç, A.; Tulunay, Y.; Ataç, T.
Affiliation:		AA(Kandilli Observatory, Bog&breve;azi çi University, Çengelköy Istanbul, Turkey), AB(Middle East Technical University, Dept. of Aeronautical Eng. 06531 Ankara, Turkey), AC(Kandilli Observatory, Bog&breve;aziçi University, Çengelköy Istanbul, Turkey)
Journal:		Advances in Space Research, Volume 22, Issue 1, p. 139-142. (AdSpR Homepage)
Publication Date:		00/1998
Origin:		ELSEVIER
Abstract Copyright:		(c) 1998 Elsevier Science B.V. All rights reserved.
Bibliographic Code:		1998AdSpR..22..139O

Abstract

For solar cycle 21 (1976 - 1986) the variation of monthly mean values of noon-time foF2 at Slough, Rome, and Manila are examined by using solar flare index and geomagnetic Ap index. A single regression analysis for dependence of foF2 on solar flare index shows better matching. Moreover, less hysteresis effect is seen when we use solar flare index instead of other solar indices. Thus, for making prediction, one needs to take into account just the solar flare index and not the solar flare index and geomagnetic Ap index simultaneously.

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Title:		North-South Asymmetry in the Solar Flare Index
Authors:		Atac, Tamer; Ozguc, Atila
Journal:		Solar Physics, v. 166, p.201 (SoPh Homepage)
Publication Date:		06/1996
Origin:		ADS
Bibliographic Code:		1996SoPh..166..201A

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Title:		Confirmation of the 25.5-Day Fundamental Period of the Sun Using the North-South Asymmetry of the Flare Index
Authors:		Ozguc, Atila; Atac, Tamer
Journal:		Solar Physics, v. 163, p. 183-191. (SoPh Homepage)
Publication Date:		01/1996
Origin:		KLUWER
Bibliographic Code:		1996SoPh..163..183O

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Title:		Characteristics of fading of HF signal and noise intensities on three paths between the United Kingdom and Turkey
Authors:		Gibson, A. J.; Yilmaz, U. M.; Tulunay, Y.; Erol, C. B.; Özgüç, A.; Ataç, T.
Journal:		Radio Science, Volume 30, Issue 3, May 1995, pp.649-658 (RaSc. Homepage)
Publication Date:		05/1995
Origin:		AIP
Bibliographic Code:		1995RaSc...30..649G

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Title:		The 73-DAY Periodicity of the Flare Index during the Current SOLAR-CYCLE-22
Authors:		Ozguc, A.; Atac, T.
Journal:		SOLAR PHYSICS V.152, NO. 1/JUN, P.318, 1994 (SoPh Homepage)
Publication Date:		06/1994
Origin:		KNUDSEN
Bibliographic Code:		1994SoPh..152..318O

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Title:		The 73-day periodicity of the flare index during the current solar cycle 22
Authors:		Ozguc, Atila; Atac, Tamer
Affiliation:		AA(Bogazici University, Istanbul, Turkey), AB(Bogazici University, Istanbul, Turkey)
Journal:		Solar Physics, vol. 150, no. 1-2, p. 339-346 (SoPh Homepage)
Publication Date:		03/1994
Category:		Solar Physics
Origin:		STI
NASA/STI Keywords:		GAMMA RAY ASTRONOMY, GAMMA RAY BURSTS, LIGHT (VISIBLE RADIATION), PERIODIC VARIATIONS, PHOTOSPHERE, SOLAR ACTIVITY, SOLAR CORONA, SOLAR CYCLES, SOLAR FLARES, SOLAR PROTONS, SOLAR X-RAYS, SUNSPOTS, X RAY ASTRONOMY, BRIGHTNESS, CORRELATION, FALSE ALARMS, FOURIER ANALYSIS, FOURIER TRANSFORMATION, POWER SPECTRA, PROBABILITY THEORY, RANDOM NOISE, SPECTRUM ANALYSIS, TIME SERIES ANALYSIS
Bibliographic Code:		1994SoPh..150..339O

Abstract

The flare index of the current solar cycle 22 is analysed to detect periodicities. Power spectral analysis of the time series of solar flare index data reveals a periodicity around 73 and 53 days. We find that a periodicity of 73 days was in operation from November 1988 to the end of December 1991. We also find that when the 73-day periodicity or the 154-day periodicity is in operation the flare index is well correlated with the relative sunspot numbers.

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Title:		On the SID durations
Authors:		Atac, Tamer
Affiliation:		AA(Kandilli Observatory, Istanbul, Turkey)
Journal:		Astrophysics and Space Science (ISSN 0004-640X), vol. 181, no. 1, July 1991, p. 157-159. (Ap&SS Homepage)
Publication Date:		07/1991
Category:		Geophysics
Origin:		STI
NASA/STI Keywords:		SOLAR FLARES, SOLAR TERRESTRIAL INTERACTIONS, SOLAR X-RAYS, SUDDEN IONOSPHERIC DISTURBANCES, D REGION, GOES SATELLITES, SOLAR PHYSICS
Bibliographic Code:		1991Ap&SS.181..157A

Abstract

This Letter is based on analysis of data on SID listed in Solar Geophysical Data. The mean durations of 1272 SIDs taken from the SGD lists were calculated with respect to their associated X-ray flares. In general, all of the present calculated mean durations showed a large scatter in the mean values. The comparison of the present values by the estimated Solar Geophysical Data Center SID durations indicated an apparent discrepancy in the mean duration relative to that estimated by SGD for the case of low levels of SID importance. This apparent discrepancy suggests a need for a correction in SGD's assumptions in the importance range from -1 to +1.

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Title:		On the short term variations of solar activity during solar cycle 21
Authors:		Atac, Tamer
Affiliation:		AA(Kandilli Observatory, Cengelkoy, Turkey)
Journal:		Earth, Moon, and Planets (ISSN 0167-9295), vol. 47, Nov. 1989, p. 165-170. (EM&P Homepage)
Publication Date:		11/1989
Category:		Solar Physics
Origin:		STI
NASA/STI Keywords:		SOLAR ACTIVITY, SOLAR CYCLES, TEMPORAL DISTRIBUTION, FORBIDDEN TRANSITIONS, SOLAR CORONA, SOLAR FLARES, VARIABILITY
Bibliographic Code:		1989EM&P...47..165A

Abstract

Short-term variations of the last solar activity cycle were studied by the flare and coronal indices using Gleissberg method. Systematic short-term variations are found from their course during the 21st solar activity cycle. Comparison of their autocorrelograms constructed by the new set of data obtained from the magnitude of the fluctuations showed the existence of the phase shift between the temporal variations of the two indices.

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Title:		Relation of the fluctuations of some of the solar activity indices
Authors:		Atac, T.
Affiliation:		AA(B.U. Kandilli Observatory, Istanbul, Turkey)
Journal:		Astrophysics and Space Science (ISSN 0004-640X), vol. 153, no. 1, March 1989, p. 173-176. (Ap&SS Homepage)
Publication Date:		03/1989
Category:		Solar Physics
Origin:		STI
NASA/STI Keywords:		SOLAR ACTIVITY, SOLAR CORONA, CORRELATION COEFFICIENTS, SOLAR ATMOSPHERE, SUNSPOTS
Bibliographic Code:		1989Ap&SS.153..173A

Abstract

The fluctuation curves from the differences of unsmoothed and smoothed values of the different solar activity indices are obtained. The patterns of fluctuations of these curves are compared. Using monthly mean values of each index, the degree of correlation between the pairs of indices during the selected time intervals is studied.

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Title:		Periodic behavior of solar flare index during solar cycles 20 and 21
Authors:		Ozguc, Atila; Atac, Tamer
Affiliation:		AA(Kandilli Observatory, Istanbul, Turkey), AB(Kandilli Observatory, Istanbul, Turkey)
Journal:		Solar Physics (ISSN 0038-0938), vol. 123, no. 2, 1989, p. 357-365. (SoPh Homepage)
Publication Date:		00/1989
Category:		Solar Physics
Origin:		STI
NASA/STI Keywords:		PERIODIC VARIATIONS, SOLAR CYCLES, SOLAR FLARES, FACULAE, SOLAR ACTIVITY, SUNSPOT CYCLE
Bibliographic Code:		1989SoPh..123..357O

Abstract

Short-term periodicities of solar activity were studied with the flare index by using Discrete Fourier Transform for the time interval 1966-1986. Two noticeable periodicities (18.5 and 5 months) have been found. The existence of these periodicities comparing with the early findings is discussed.

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Title:		Time variation of the flare index during the 21st solar cycle
Authors:		Atac, T.
Affiliation:		AA(B. U. Kandilli Observatory, Istanbul, Turkey)
Journal:		Astrophysics and Space Science (ISSN 0004-640X), vol. 135, no. 1, July 1987, p. 201-205. (Ap&SS Homepage)
Publication Date:		07/1987
Category:		Solar Physics
Origin:		STI
NASA/STI Keywords:		PERIODIC VARIATIONS, SOLAR CYCLES, SOLAR FLARES, CHROMOSPHERE, SOLAR ACTIVITY, SOLAR TERRESTRIAL INTERACTIONS, SPATIAL DISTRIBUTION
Bibliographic Code:		1987Ap&SS.135..201A

Abstract

In this study, the flare index during the solar activity cycle 21 is calculated for every day from January 1, 1976 to March 31, 1986. It is determined that the chromospheric activity for the whole disc was significantly higher during the 21st solar cycle as compared to the preceding cycle. It is found that the activity began and reached its maximum earlier on the northern hemisphere. Finally, it is determined that the time variation of the flare indices for the eastern and western hemispheres are in good agreement.

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Title:		Statistical relationship between sunspots and major flares
Authors:		Atac, T.
Affiliation:		AA(B.U. Kandilli Observatory, Istanbul, Turkey)
Journal:		Astrophysics and Space Science (ISSN 0004-640X), vol. 129, no. 1, Jan. 1987, p. 203-208. (Ap&SS Homepage)
Publication Date:		01/1987
Category:		Solar Physics
Origin:		STI
NASA/STI Keywords:		SOLAR FLARES, STATISTICAL ANALYSIS, SUNSPOTS, MAGNETIC FLUX, SOLAR CYCLES
Bibliographic Code:		1987Ap&SS.129..203A

Abstract

In this study, the statistical relationship between sunspots and major flares observed in the descending branch of the 20th and in the ascending branch of the 21st solar cycle is evaluated. It is found that the sunspots which produced these major flares are of the type Dki or Eki with magnetic class D and the largest magnetic field strength between 1600 and 2500 G.