Short‐period solar cycle signals in the ionosphere observed by FORMOSAT‐3/COSMIC

Liang, Mao‐Chang; Li, King Fai; Shia, Run‐Lie; Yung, Yuk L.

doi:10.1029/2008gl034433

Cited by 21 publications

(19 citation statements)

References 32 publications

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“…Periodograms of TEC at different individual sites were performed, but no strong 58.4 day peaks were found. A double of the 27 day solar rotation cycle giving a 54 day period in electron density was previously found [ Liang et al , 2008], but the 58.4 day peak is well defined. However, 58.4 days is approximately one sixth of the GPS orbital repeat period (∼351.4 days [ Ray et al , 2008]).…”

Section: Resultsmentioning

confidence: 83%

Higher‐order ionospheric effects on the GPS reference frame and velocities

et al. 2010

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[1] We describe how GPS time series are influenced by higher-order ionospheric effects over the last solar cycle (1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008) and examine implications for geophysical studies. Using 14 years of globally reprocessed solutions, we demonstrate the effect on the reference frame. Including second-and third-order ionospheric terms causes up to 10 mm difference in the smoothed transformation to the International Terrestrial Reference Frame (ITRF) 2005, with the Z translation term dominant. Scale is also slightly affected, with a change of up to ∼0.05 ppb. After transformation to ITRF2005, residual effects on vertical site velocities are as high as 0.34 mm yr −1 . We assess the effect of the magnetic field model on the second-order term and find a time-varying difference of 0-2 mm in the Z translation. We also assess the effect of omitting the third-order term. We find that while the second-order term is responsible for almost all the Z translation effects, it is the combination of the second-and third-order terms that causes the effect on scale. Comparison of our GPS reprocessing with ITRF2005 suggests that GPS origin rates may vary with time period. For example, we find Z translation rates of −0.82 ± 0.17 mm yr −1 for 1995-2008 and 0.17 ± 0.24 mm yr −1 for 1995-2005. If GPS were to contribute to origin rate definition for future ITRFs, higher-order ionospheric corrections would need to be applied due to their effect on translation parameters during solar maximum.

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Section: Resultsmentioning

confidence: 83%

Higher‐order ionospheric effects on the GPS reference frame and velocities

et al. 2010

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“…There is also usually a *27 day periodicity associated with solar rotation (see e.g. Liang et al 2008;Hocke 2008;Min et al 2009), together with seasonal variations in the activity of the ionosphere at different latitudes and heights (e.g. Liu et al 2009).…”

Section: Characteristics and Variabilitymentioning

confidence: 99%

A Review of Higher Order Ionospheric Refraction Effects on Dual Frequency GPS

et al. 2010

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Higher order ionospheric effects are increasingly relevant as precision requirements on GPS data and products increase. The refractive index of the ionosphere is affected by its electron content and the magnetic field of the Earth, so the carrier phase of the GPS L1 and L2 signals is advanced and the modulated code delayed. Due to system design the polarisation is unaffected. Most of the effect is removed by expanding the refractive index as a series and eliminating the first term with a linear combination of the two signals. However, the higher order terms remain. Furthermore, transiting gradients in refractive index at a non-perpendicular angle causes signal bending. In addition to the initial geometric bending term, another term allows for the difference that the curvature makes in electron content along each signal. Varying approximations have been made for practical implementation, mainly to avoid the need for a vertical profile of electron density. The magnetic field may be modelled as a tilted co-centric dipole, or using more realistic models such as the International Geomagnetic Reference Field. The largest effect is from the second term in the expansion of the refractive index. Up to several cm on L2, it particularly affects z-translation, and satellite orbits and clocks in a global network of GPS stations. The third term is at the level of the errors in modelling the second order term, while the bending terms appear to be absorbed by tropospheric parameters. Modelling improvements are possible, and three frequency transmissions will allow new possibilities.

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“…Our results are consistent with other studies. For instance, Liang et al [2008] analyzed ionospheric electron density profiles retrieved from FORMOSAT‐3/COSMOC radio occultation observations and found that at 2.5°N and 355 km the ∼27 day signal of electron density had a peak‐to‐peak variation of about 10%–25%, corresponding to a NSD of ∼3.5%–8.8%.…”

Section: Discussionmentioning

confidence: 99%

“…In this paper, we focus on the morphology and mechanisms of the ∼27 day variation of N m F 2 . There have been many studies of N m F 2 variations with this periodicity [e.g., Bartels , 1950; Titheridge , 1973; Kane et al , 1995; Forbes et al , 2000; Rishbeth and Mendillo , 2001; Pancheva et al , 2002; Rich et al , 2003; Prabhakaran Nayar et al , 2004; Wang et al , 2007; Oinats et al , 2008; Astafyeva et al , 2008; Afraimovich et al , 2008; Liang et al , 2008; Hocke , 2008; Min et al , 2009; Borries and Hoffmann , 2010]. However, the latitudinal, seasonal, local time, and solar cycle changes of this variation are not fully understood.…”

Section: Introductionmentioning

confidence: 99%

The effect of ∼27 day solar rotation on ionospheric F₂ region peak densities (N_mF₂)

Ma¹,

Xu²,

Wang³

et al. 2012

J. Geophys. Res.

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[1] Ionospheric F 2 region peak electron densities (N m F 2 ) observed from 11 ionosonde stations in the East Asian-Australian sector from 1969 to 1986 have been used to investigate the effect of $27 day solar rotation on the ionosphere. These stations were located from the magnetically equatorial regions to the middle latitudes in both hemispheres. We found that, averaged over all stations and for 18 years, the normalized standard deviation of the midday $27 day variations of N m F 2 was 8% and that of the midnight variations was 10%. We applied different data analysis methods, including Fourier transform, band-pass filter, and multiple linear regression analysis, to determine quantitatively the sources of the observed $27 day variations of N m F 2 and their relative contributions to these variations. Our results show that the $27 day variations in solar radiation and geomagnetic activity, caused by solar rotation, are the main drivers of the ionospheric $27 day variations. They accounted for more than 85% of the variations seen in the N m F 2 $27 day variation, and their contributions became about 95% at higher latitudes. At geomagnetically low latitudes, the contribution of the $27 day variation in solar EUV radiation was greater than that of the $27 day variation in geomagnetic activity. However, the contribution from geomagnetic activity became more significant and was even larger than the contribution of solar radiation at higher latitudes, especially at midnight. At all latitudes the correlation between the $27 day variations of N m F 2 and solar radiation was evidently positive, whereas that between N m F 2 and geomagnetic activity was positive at geomagnetically low latitudes and became negative at higher middle latitudes. We did not found large seasonal or solar cycle changes in the $27 day variations of N m F 2 . These variations, however, did show significant differences between the two hemispheres.

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Short‐period solar cycle signals in the ionosphere observed by FORMOSAT‐3/COSMIC

Cited by 21 publications

References 32 publications

Higher‐order ionospheric effects on the GPS reference frame and velocities

Higher‐order ionospheric effects on the GPS reference frame and velocities

A Review of Higher Order Ionospheric Refraction Effects on Dual Frequency GPS

The effect of ∼27 day solar rotation on ionospheric F₂ region peak densities (N_mF₂)

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Short‐period solar cycle signals in the ionosphere observed by FORMOSAT‐3/COSMIC

Cited by 21 publications

References 32 publications

Higher‐order ionospheric effects on the GPS reference frame and velocities

Higher‐order ionospheric effects on the GPS reference frame and velocities

A Review of Higher Order Ionospheric Refraction Effects on Dual Frequency GPS

The effect of ∼27 day solar rotation on ionospheric F2 region peak densities (NmF2)

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The effect of ∼27 day solar rotation on ionospheric F₂ region peak densities (N_mF₂)