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Bradley, P. A.
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Bradley, P. A.
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9 results
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- PublicationOpen AccessFurther tests of the IRI and DGR model ionospheres(1994-05)
; ; ; ; ; ;Kecic, K. J.; Geomagnetic Institute, Grocka, Belgrade, Yugoslavia ;Bradley, P. A.; Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, U.K. ;Cander, L. R.; Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, U.K. ;Dick, M. I.; Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, U.K. ;Zolesi, B.; Istituto Nazionale di Geofisica, Roma, ItalyIstituto Nazionale di Geofisica, Roma, Italy; ; ; ; The present study discusses and compares the IRI and DGR ionospheric models using N(h) profiles obtained during a high solar activity period at South Uist ionosonde station. After inversion, N(h) profiles obtained from ionograms at South Uist have been compared with those derived from the IRI-90 and DGR ionospheric models. A small data set has been selected such that both geomagnetically quiet and disturbed conditions are represented. The importance of further comparisons with additional sets of N(h) profiles under different solar-geophysical conditions and at more stations has been recognized.148 247 - PublicationOpen AccessStatus of available N(h) model profiles(1996-08)
; ; ; ;Cander, L. R.; Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, U.K ;Zolesi, B.; Istituto Nazionale di Geofisica, Roma, Italy ;Bradley, P. A.; Istituto Nazionale di Geofisica, Roma, Italy; ; This paper attempts to highlight progress in the ionospheric electron-density height profile modelling made during the last few years. It consists of a brief review of some major aspects associated with available theoretical, parameterised and empirical N(h) models. Emphasis is placed on pointing out the key issues in the areas that are relevant for the COST 238 PRIME project.140 221 - PublicationOpen AccessFurther study of fOF2 and M(3000)F2 in different solar cycles(1994-05)
; ;Bradley, P. A.; Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, U.K.Measured monthly median fOF2 and M(3000)F2 for Slough over six solar cycles from 1932 onwards are examined for a selection of hours and months. Data are shown as a function of twelve-monthly smoothed sunspot number. Comparisons are made for the different solar cycles and for the rising and falling halves of each cycle. Measurements for individual cycles are compared with best-fit parabolic regression lines over all cycles to investigate possible systematic long-term effects.125 172 - PublicationOpen AccessInternational activities in HF sky-wave field-strength estimation (period 1956-1991)(1998-11)
; ;Bradley, P. A.; Consultant, Slough, Berks SL2 3ES,U.K.Methods for the determination of the strengths of radio signals reflected from the ionosphere and propagated to distant locations are required for service planning and circuit operation. Efforts are described following World War II to arrive at agreed procedures and some of the features of the various empirical prediction methods that have been formulated over the years are discussed. The problems are highlighted of determining a "best" method from among those available. Measurement data collected for this purpose are reviewed and attention is drawn to their limitations of accuracy and coverage. Even comparison of predicted and measured values is not straightforward, and the techniques that have been developed to do this are considered.123 365 - PublicationOpen AccessImpact of COST 271(2004)
; ; ;Bradley, P. A.; Pandora, Scotlands Drive, Farnham Common, Slough, Berks, U.K. ;Reinisch, B. W.; Environmental, Earth, and Atmospheric Sciences Department, Center for Atmospheric Research, University of Massachusetts, Lowell, MA, U.S.A.; This article discusses the significance of the achievements of the COST 271 Action on science and technology for space weather and telecommunications in Europe and the world. The Action's work has impacted national and international projects and the decision processes. The key words encompassed in the title of COST 271 are «space weather». But as the reader of this Final Report will appreciate, many more topics were addressed during the Action by the large team of workers from a wide range of countries and organisations than this wording would suggest. Relevant to the performance of telecommunication systems that rely on the presence of the ionosphere for propagation support, or that are affected by transmission through it, there have been investigations among other items of solar and magnetosphere disturbances on the ionosphere, satellite and ground-based measurements of the ionosphere, assembly of near-real-time databases of ionosphere information on the Web, studies of planetary and gravity waves in the ionosphere, ionosphere modelling, mapping and forecasting, long-term changes, ray-path deviations in the presence of irregularities, channel-scattering functions, and scintillations on Earth-space paths. The impact of all this work on the outside communities can be considered within three broad headings as follows.144 109 - PublicationOpen AccessThe impact of space weather on communication(2004)
; ; ;Tulunay, Y. K.; Faculty of Aeronautics and Astronautics, Istanbul Technical University (?ITÜ), Maslak, Istanbul, Turkey ;Bradley, P. A.; Pandora, Scotlands Drive, Farnham Common, Slough, Berks, U.K.; As a preliminary to the studies conducted by the individual Working Groups, a review has been undertaken of topics which are relevant to the space-weather phenomena that can occur. The ways in general that these can influence the state of the ionosphere are discussed. The various changes in propagation parameters that arise on Earth-space and terrestrial radio paths via the ionosphere are listed. International procedures for frequency allocation and assignment are explained and the extent to which these are influenced by propagation factors is addressed. The role of mitigation techniques to improve radio-system performance is also identified.218 258 - PublicationOpen AccessExtreme values in ionospheric radio propagation(2002)
; ;Bradley, P. A.; Pandora, Farnham Common, Slough, Berks, U.KProposals are made for Earth-space and space-space paths to apply the term ‘propagation degradation probability’, analogous to ‘basic circuit reliability’ adopted within the Radiocommunication Sector of the International Telecommunication Union (ITU-R) to quantify the performance of HF terrestrial ionospheric radio circuits. The principal elements characterising propagation impairments are described and formulae and a table given by the ITU-R are reproduced relating many of these effects to the path total electron content. Expressions are provided enabling estimates of the probabilities of occurrence of user-specified extreme values to be estimated in terms of their median quantities and day-to-day variabilities. The need is stressed for additional data collection and analyses both to refine the median values and to derive the required reference variability factors.165 194 - PublicationOpen AccessProposed terminology for the classification and parameters for the quantification of variability in ionosphere morphology(2002)
; ; ;Bradley, P. A.; Pandora, Farnham Common, Slough, Berks, U.K ;Cander, L. R.; Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, U.K; Much uncertainty currently exists in the use by different workers of the term ‘variability’ in describing the results of statistical analyses applied to ionospheric measurement data sets and in their relationships with various existing or new ionospheric models. Often it is not clear whether data for different time periods or different geographical areas, and if so which, are being used to formulate results. Terms are presented in the Annex which it is suggested should be used, at least once in every publication addressing this topic, to describe unambiguously what is talked about. The background to the proposed terminology is discussed. Options for variability parameters are also addressed.145 147 - PublicationOpen AccessThe ionospheric storm studies: further development of the mapping technique(1996-08)
; ; ; ; ; ;Kutiev, I.; Geophysical Institute, Bulgarian Academy of Sciences, Sofia, Bulgaria ;Samardjiev, T.; Geophysical Institute, Bulgarian Academy of Sciences, Sofia, Bulgaria ;Bradley, P. A.; Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, U.K ;Dick, M. I.; Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, U.K ;Cander, L. R.; Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, U.K; ; ; ; The technique of using instantaneous maps for ionospheric storm studies is further developed. Integral parameters are introduced characterizing the main features of each map. These parameters are the net volumes of Δf0F2, ΔM(3000)F2and their gradients. The magnetic storm 1-2 March, 1982 was considered and it was found that before the storm commencement and in recovery phase the Net Gradient (NG) is directed steadily to the East, while in the main phase it turns southward. NG shows where the changes of the F-layer come from. The net volume of Δf0F2 (NF) correlates well with Dst and AE indices.127 159