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Temporal-Spatial Variation of Global GPS-Derived Total Electron Content, 1999-2013.

Guo J, Li W, Liu X, Kong Q, Zhao C, Guo B - PLoS ONE (2015)

Bottom Line: The fitting results of a quadratic polynomial show that the effect of solar activity on TEC is stronger in low latitudes than in mid-high latitudes, and stronger in the southern hemisphere than in the northern hemisphere.The effect of solar activity on TECs was analyzed with the cross wavelet analysis and the wavelet coherence transformation, and we found that there appears to be a strong coherence in the period of about 27 days.So TECs decrease over most areas year by year, but TECs over the Arctic around Greenland maintained a rising trend during these 15 years.

View Article: PubMed Central - PubMed

Affiliation: College of Geodesy and Geomatics, Shandong University of Science and Technology, Qingdao, 266590, China; State Key Laboratory of Mining Disaster Prevention and Control Co-founded by Shandong Province and Ministry of Science & Technology, Shandong University of Science and Technology, Qingdao, 266590, China.

ABSTRACT
To investigate the temporal-spatial distribution and evolutions of global Total Electron Content (TEC), we estimate the global TEC data from 1999 to 2013 by processing the GPS data collected by the International Global Navigation Satellite System (GNSS) Service (IGS) stations, and robustly constructed the TEC time series at each of the global 5°×2.5° grids. We found that the spatial distribution of the global TEC has a pattern where the number of TECs diminishes gradually from a low-latitude region to high-latitude region, and anomalies appear in the equatorial crest and Greenland. Temporal variations show that the peak TEC appears in equinoctial months, and this corresponds to the semiannual variation of TEC. Furthermore, the winter anomaly is also observed in the equatorial area of the northern hemisphere and high latitudes of the southern hemisphere. Morlet wavelet analysis is used to determine periods of TEC variations and results indicate that the 1-day, 26.5-day, semi-annual and annual cycles are the major significant periods. The fitting results of a quadratic polynomial show that the effect of solar activity on TEC is stronger in low latitudes than in mid-high latitudes, and stronger in the southern hemisphere than in the northern hemisphere. But the effect in low latitudes in the northern hemisphere is stronger than that in low latitudes in the southern hemisphere. The effect of solar activity on TECs was analyzed with the cross wavelet analysis and the wavelet coherence transformation, and we found that there appears to be a strong coherence in the period of about 27 days. So the sunspot as one index of solar activity seriously affects the TEC variations with the sun's rotation. We fit the TEC data with the least squares spectral analysis to study the periodic variations of TEC. The changing trend of TEC is generally -0.08 TECu per year from 1999 to 2013. So TECs decrease over most areas year by year, but TECs over the Arctic around Greenland maintained a rising trend during these 15 years.

No MeSH data available.


Related in: MedlinePlus

Dependence of the daily mean TEC on SSN in 1999–2013.the daily averages of mean TEC are averaged in both hemispheres at low latitudes (0°-30°), middle latitudes(30°-60°) and high latitudes(60°-87.5°). The superscripts N, S denote the northern hemisphere, southern hemisphere, respectively, the subscripts l, m, and h denote low, middle, and high latitudes. The variable S denotes sunspot number. The red curves denote the fitting results.
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pone.0133378.g010: Dependence of the daily mean TEC on SSN in 1999–2013.the daily averages of mean TEC are averaged in both hemispheres at low latitudes (0°-30°), middle latitudes(30°-60°) and high latitudes(60°-87.5°). The superscripts N, S denote the northern hemisphere, southern hemisphere, respectively, the subscripts l, m, and h denote low, middle, and high latitudes. The variable S denotes sunspot number. The red curves denote the fitting results.

Mentions: The daily mean TEC over different latitudes in both hemispheres from 1999 to 2013 are plotted as a function of the SSN in Fig 10. The second-order polynomial is applied to fit the function to show the effect of solar activity on the daily mean TEC averaged on three latitude bands. The red curve denotes the fitting results in Fig 10. We will focus on the coefficient of the first-order polynomial that represents the strength of the effect between SSN and TEC. As shown in Fig 10, the coefficients of the first-order polynomial at three latitude bands have a negative relation with latitude. For example, the coefficients at low latitudes, middle latitudes, and high latitudes in the northern hemisphere are 0.417, 0.164, and 0.118, respectively. The coefficient at low latitude is two to three times larger than that at mid-high latitudes. The variation tendency is also observed in the southern hemisphere, which indicates TECs over low latitudes are more sensitive to solar activity than those over mid-high latitudes. Furthermore, the mean TEC sensitivity to solar activity at the same latitude in both hemispheres is somewhat different. The coefficients at middle latitudes in the northern hemisphere and the southern hemisphere are 0.164 and 0.204, respectively, and at high latitudes, they are 0.118 and 0.148. It is clear that TECs in the southern hemisphere are more sensitive to solar activity than those in the northern hemisphere at mid-high latitudes. However, the change rule at low latitudes is unique, and the coefficient in the northern and southern hemispheres are 0.417, 0.389, respectively, which shows that the solar activity sensitivity of TEC is stronger in the northern hemisphere than in the southern hemisphere.


Temporal-Spatial Variation of Global GPS-Derived Total Electron Content, 1999-2013.

Guo J, Li W, Liu X, Kong Q, Zhao C, Guo B - PLoS ONE (2015)

Dependence of the daily mean TEC on SSN in 1999–2013.the daily averages of mean TEC are averaged in both hemispheres at low latitudes (0°-30°), middle latitudes(30°-60°) and high latitudes(60°-87.5°). The superscripts N, S denote the northern hemisphere, southern hemisphere, respectively, the subscripts l, m, and h denote low, middle, and high latitudes. The variable S denotes sunspot number. The red curves denote the fitting results.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4508092&req=5

pone.0133378.g010: Dependence of the daily mean TEC on SSN in 1999–2013.the daily averages of mean TEC are averaged in both hemispheres at low latitudes (0°-30°), middle latitudes(30°-60°) and high latitudes(60°-87.5°). The superscripts N, S denote the northern hemisphere, southern hemisphere, respectively, the subscripts l, m, and h denote low, middle, and high latitudes. The variable S denotes sunspot number. The red curves denote the fitting results.
Mentions: The daily mean TEC over different latitudes in both hemispheres from 1999 to 2013 are plotted as a function of the SSN in Fig 10. The second-order polynomial is applied to fit the function to show the effect of solar activity on the daily mean TEC averaged on three latitude bands. The red curve denotes the fitting results in Fig 10. We will focus on the coefficient of the first-order polynomial that represents the strength of the effect between SSN and TEC. As shown in Fig 10, the coefficients of the first-order polynomial at three latitude bands have a negative relation with latitude. For example, the coefficients at low latitudes, middle latitudes, and high latitudes in the northern hemisphere are 0.417, 0.164, and 0.118, respectively. The coefficient at low latitude is two to three times larger than that at mid-high latitudes. The variation tendency is also observed in the southern hemisphere, which indicates TECs over low latitudes are more sensitive to solar activity than those over mid-high latitudes. Furthermore, the mean TEC sensitivity to solar activity at the same latitude in both hemispheres is somewhat different. The coefficients at middle latitudes in the northern hemisphere and the southern hemisphere are 0.164 and 0.204, respectively, and at high latitudes, they are 0.118 and 0.148. It is clear that TECs in the southern hemisphere are more sensitive to solar activity than those in the northern hemisphere at mid-high latitudes. However, the change rule at low latitudes is unique, and the coefficient in the northern and southern hemispheres are 0.417, 0.389, respectively, which shows that the solar activity sensitivity of TEC is stronger in the northern hemisphere than in the southern hemisphere.

Bottom Line: The fitting results of a quadratic polynomial show that the effect of solar activity on TEC is stronger in low latitudes than in mid-high latitudes, and stronger in the southern hemisphere than in the northern hemisphere.The effect of solar activity on TECs was analyzed with the cross wavelet analysis and the wavelet coherence transformation, and we found that there appears to be a strong coherence in the period of about 27 days.So TECs decrease over most areas year by year, but TECs over the Arctic around Greenland maintained a rising trend during these 15 years.

View Article: PubMed Central - PubMed

Affiliation: College of Geodesy and Geomatics, Shandong University of Science and Technology, Qingdao, 266590, China; State Key Laboratory of Mining Disaster Prevention and Control Co-founded by Shandong Province and Ministry of Science & Technology, Shandong University of Science and Technology, Qingdao, 266590, China.

ABSTRACT
To investigate the temporal-spatial distribution and evolutions of global Total Electron Content (TEC), we estimate the global TEC data from 1999 to 2013 by processing the GPS data collected by the International Global Navigation Satellite System (GNSS) Service (IGS) stations, and robustly constructed the TEC time series at each of the global 5°×2.5° grids. We found that the spatial distribution of the global TEC has a pattern where the number of TECs diminishes gradually from a low-latitude region to high-latitude region, and anomalies appear in the equatorial crest and Greenland. Temporal variations show that the peak TEC appears in equinoctial months, and this corresponds to the semiannual variation of TEC. Furthermore, the winter anomaly is also observed in the equatorial area of the northern hemisphere and high latitudes of the southern hemisphere. Morlet wavelet analysis is used to determine periods of TEC variations and results indicate that the 1-day, 26.5-day, semi-annual and annual cycles are the major significant periods. The fitting results of a quadratic polynomial show that the effect of solar activity on TEC is stronger in low latitudes than in mid-high latitudes, and stronger in the southern hemisphere than in the northern hemisphere. But the effect in low latitudes in the northern hemisphere is stronger than that in low latitudes in the southern hemisphere. The effect of solar activity on TECs was analyzed with the cross wavelet analysis and the wavelet coherence transformation, and we found that there appears to be a strong coherence in the period of about 27 days. So the sunspot as one index of solar activity seriously affects the TEC variations with the sun's rotation. We fit the TEC data with the least squares spectral analysis to study the periodic variations of TEC. The changing trend of TEC is generally -0.08 TECu per year from 1999 to 2013. So TECs decrease over most areas year by year, but TECs over the Arctic around Greenland maintained a rising trend during these 15 years.

No MeSH data available.


Related in: MedlinePlus