The Solar-Terrestrial Environment

Hargreaves, J. K.

doi:10.1017/cbo9780511628924

Cited by 438 publications

(179 citation statements)

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“…Large amplitudes at high-latitudes during equinox can be associated with the highest efficiency in the interaction between the Earth and the solar wind that occurs during these periods (Hargreaves, 1992). The behaviour found at lower latitudes is opposite to that commonly found at middle latitudes and may explain the contradiction between our results and those by Lois et al (1990) and Jakowski et al (1991) at Havana, Cuba.…”

Section: Discussioncontrasting

confidence: 94%

Global morphology of night-time <i>Nm</i>F2 enhancements

2002

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Abstract. An overall statistical study of night-time enhancements of NmF2 has been carried out. All available foF2 observations since 1955 at 53 ionosonde stations distributed worldwide in the latitude range φ geom = 15 • − 60 • were used in the analysis. More than 200 000 station-nights of data were analysed. This large data base allowed us to study seasonal, solar cycle and spatial variations of the NmF2 nighttime enhancements. Both pre-midnight and post-midnight NmF2 peaks demonstrate distinct variations with geophysical conditions, indicating different physical mechanisms responsible for their formation.

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Section: Discussioncontrasting

confidence: 94%

Global morphology of night-time <i>Nm</i>F2 enhancements

2002

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“…taking place on the sun [5]. The solar cycle variations change the electronion production rates thus impacting on the electron density profiles of the ionosphere by a factor of 5 -6 and even more if there are energetic short period events [2].…”

Section: Introductionmentioning

confidence: 99%

A Novel Approach to Study Regional Ionospheric Variations Using a Real-Time TEC Model

Chakravarty¹

2014

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Since IGY (International Geophysical Year), through coordinated global observations, ionospheric research has been carried out by many countries. This effort primarily helped in the design and operation of HF radio wave communication systems. The Indian region covers a highly variable part of the equatorial electrojet and EIA (Equatorial Ionisation Anomaly) phenomena making its predictability difficult. With the advent of satellite communication and navigation, the need for accurate ionospheric TEC (Total Electron Content) models at global and regional scales has been stressed. The GAGAN (GPS Aided Geo Augmented Navigation) project jointly undertaken by the Indian Space Research Organisation (ISRO) and the Airport Authority of India (AAI) aims at effectively utilising the Global Navigational Satellite System (GNSS) to determine position coordinates accurately for aircraft precision landing applications. For this purpose the range errors are estimated by using a ground network of TEC stations spread over Indian region. The near simultaneous data collected from these dual frequency GPS stations can be used to generate the geo-referenced TEC values for various applications. The author has developed necessary algorithm and associated computer programmes for a real-time vertical TEC (VTEC) model based on TEC data collected from the GAGAN ground based network stations. The model has been tested and sample results presented here show that it adequately provides for the latitudinal resolution of 1˚ for the entire longitude span and also for two longitude blocks (73 -83 & 83 -93˚E) separately. Cubic spline and bilinear interpolation techniques are used for filling up temporal and spatial data gaps. The model provides tabulated output of hourly average VTEC data with latitude for ready use, as well as graphical displays of VTEC maps and contours for monitoring purpose. The real-time model and its extensions are also being used for detailed scientific studies; examples of these show small day to day variability of VTEC without any change in solar activity and indication of the change in the shape of the VTEC diurnal curve with season. The present model will be used for further studies to derive the monthly average variation of the diurnal pattern and the relationship between VTEC peak amplitudes with changes in solar activity. The new information generated can be fed back to improve the real-time model so that eventually the dependence of such models on ground based network stations data can be minimised.

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“…EOFs from Chapman profiles [16] were used to constrain the vertical profile to be physically meaningful. In contrast, Discrete Meyer (DM) wavelets and Spherical Harmonic (SH) basis functions were used to describe the horizontal variation of ionospheric structures.…”

Section: Resultsmentioning

confidence: 99%