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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 115, A07308, doi:10.1029/2009JA015113, 2010
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GPS TEC response to the 22 July 2009 total solar eclipse in East
Asia
Feng Ding,1 Weixing Wan,1 Baiqi Ning,1 Libo Liu,1 Huijun Le,1 Guirong Xu,2
Min Wang,3 Guozhu Li,1 Yiding Chen,1 Zhipeng Ren,1 Bo Xiong,1,4 Lianhuan Hu,1
Xinan Yue,1,5 Biqiang Zhao,1 Fengqin Li,1 and Min Yang1
Received 18 November 2009; revised 28 January 2010; accepted 22 February 2010; published 15 July 2010.
[1] The longest total solar eclipse of this century occurred in East and South Asia on
22 July 2009. The eclipse was accompanied with a medium magnetic storm, whose main
phase onset occurred ∼27 min after the passage of the Moon’s umbral shadow. Using TEC
data from 60 GPS stations, we construct differential TEC maps to investigate the
ionosphere response to the solar eclipse in central China in the range of 26°N–36°N,
108°E–118°E (i.e., the magnetic latitude 15°N–25°N). During the eclipse’s totality, a
“shadow” in the ionosphere shown as TEC depletion area was formed ∼100 km south of
the Moon’s umbral path with a maximum decrease of 5 TECU. The TEC depletion area
moved eastward, following the movement of the totality area with a time lag of ∼10 min.
Enhancements of TEC due to the storm are observed after the main phase onset. The
relative drop of TEC due to the solar eclipse is evidently larger at lower latitudes than that
at higher ones and around noontime than that in the morning. By modeling work, we
find that the latitudinal dependence of the TEC response may result from latitudinal
variation of magnetic inclination, which influences the diffusion of ionization among
different layers. Besides, the local time dependence of TEC response is closely related to
the local time variation of background atmosphere density, which affects the electron loss
efficiency in the ionosphere.
Citation: Ding, F., et al. (2010), GPS TEC response to the 22 July 2009 total solar eclipse in East Asia, J. Geophys. Res., 115,
A07308, doi:10.1029/2009JA015113.
1. Introduction
[2] A total solar eclipse provides a good opportunity for
studying the ionospheric variations associated with the
photochemistry process and transportation process in the
ionosphere. During a solar eclipse, the decrease of solar flux
in the ionosphere due to the Moon’s shading leads to the
decrease of electron photoionization production, which
results in nearly synchronous drop of electron density in the
E layer and F1 layer. On the basis of the observation of
incoherent scatter radar [Salah et al., 1986], it is found that
the drop of electron density due to the solar eclipse could
reach 60% at maximum in F1 layer. The electron loss at
lower altitudes due to photochemical production loss is
transported by diffusion along magnetic field lines to higher
1
Beijing National Observatory of Space Environment, Institute of
Geology and Geophysics, Chinese Academy of Sciences, Beijing, China.
2
Institute of Heavy Rain, China Meteorological Administration,
Wuhan, China.
3
Institute of Earthquake Science, China Earthquake Administration,
Beijing, China.
4
Graduate School of the Chinese Academy of Sciences, Beijing, China.
5
University Corporation for Atmospheric Research, Boulder, Colorado,
USA.
Copyright 2010 by the American Geophysical Union.
0148‐0227/10/2009JA015113
altitudes. At the same time, the decrease of electron temperature leads to downward drift of the plasma in the topside
ionosphere, which partly compensates for the electron loss
at altitudes above F2 layer. The combined effects make the
electron density in topside ionosphere decrease very slowly
and relatively smaller to the low altitude. The maximum of
decrease, i.e., 10%–25%, appears about 1 h after the totality
in topside ionosphere [Korte et al., 2001; Adeniyi et al.,
2007]. Sometimes electron density even increases due to
the eclipse [Evans, 1965; Salah et al., 1986].
[3] A total eclipse occurred in East and South Asia in the
morning on 22 July 2009. Its totality lasted a maximum of
6 min 39 s. It is the longest total eclipse of this century, not to
be surpassed until year 2132. Detailed information of the eclipse
can be seen in the work of Espennak and Anderson [2008]
(http://eclipse.gsfc.nasa.gov/SEmono/TSE2009/TSE2009.
html). The Moon’s umbra passed through central China,
where the north boundary of the anomaly crest regions
locates. During this solar eclipse, the Institute of Geology
and Geophysics, Chinese Academy of Sciences initiated a
multi‐station and multi‐instrument observation campaign.
Dense distribution of GPS stations in this area makes it
possible to monitor the spatial and temporal variations of
TEC due to the solar eclipse at midlatitudes and low latitudes. In this paper, we use the TEC data from 60 GPS
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Figure 1. Map of East Asia showing the umbral and preumbral paths (thin blue curves) of the solar
eclipse on 22 July 2009. The paths are labeled with eclipse magnitudes. The thick solid curve shows
the central line of totality. Dotted curves represent contours of the universal time of the paths. Also presented in the figure is the location of GPS stations (black asterisks).
stations to build the two‐dimensional variation of differential TEC maps. The TEC response to the total solar eclipse is
investigated, and the variation of TEC associated with latitudes and local times is presented.
2. Two‐Dimensional GPS TEC Variations
[4] The exceptional long total eclipse began at 0053 UT in
India, shortly after sunrise. The Moon’s umbral shadow
traveled east northeast and entered China at 0105 UT (0905
Beijing standard time). It formed a path ∼244 km wide that
traveled nearly eastward through Central China along the
geographical latitude of ∼30°N (i.e., the magnetic latitude of
∼19°N) before crossing the south of Japan and the Pacific
Ocean. Figure 1 plots the umbral (total eclipse) and preumbral (partial eclipse) paths labeled with eclipse magnitudes. The total eclipse can be seen in several provinces in
Central China from about 0010 UT (0910 LT) to 0140 UT
(0940 LT) with the duration of 4–6 min. A partial eclipse is
seen in much broader area of north and south of China.
[5] Using the TEC data from 60 GPS stations as marked
in Figure 1, we adopt the least squares fit and triangle‐based
linear interpolation method to build the two‐dimensional
differential TEC (DTEC) maps in the range of 26°N–36°N,
108°E–118°E with the spatial resolution of 1° × 1° grid. The
GPS stations belong to several institutes and organizations,
including Wuhan Institute of Heavy Rain, China Earthquake
Administration, Institute of Geology and Geophysics, and
the International GNSS Service (IGS). We calculate DTEC
through subtracting the median value of TEC on reference
days from the TEC measured on 22 July. The reference days
are chosen to be 17–19 July, which are the geomagnetically
quietest days of that month.
[6] Figure 2 presents the sequence of DTEC maps during
the period of 0000–0230 UT on 22 July 2009. The maps are
plotted every 30 min during the periods of 0000–0100 UT
and 0200–0230 UT. To show more clearly the variation of
DTEC during the passage of the Moon’s umbral shadow, we
present the maps every 10 min from 0100 to 0140 UT. We
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Figure 2. Two‐dimensional maps of differential TEC (DTEC) on 22 July 2009 from 0000 to 0230 UT.
The value of the contours is DTEC in TECU. Black curves represent contours of the magnitude of the
eclipse at the moments. To show more clearly the variation of DTEC during the passage of the Moon’s
umbral shadow, the maps are plotted every 10 min from 0100 to 0140 UT. The maps are plotted every
30 min before or after this duration.
also plot contours of eclipse magnitude as black curves in
the maps.
[7] After the first contact (the time when the disk of the
Moon first touched the solar disk) at 0009 UT, the whole
area of 26°N–36°N, 108°E–118°E was in partial eclipse
with the magnitude of 0.1–0.3 at 0030 UT (Figure 2b).
Upon the arrival of the partial eclipse, TEC decreased
immediately following the increase of eclipse magnitude.
The nearly synchronous decrease of TEC during this period
is mainly due to the decrease of photochemical production,
which dominates in E and F1 layers. The time lag between
the lowering of solar radiation and the decrease of the
electron density is only 1–3 min in E and F1 layers, while it
can reach ∼1 h in topside ionosphere because of the domination of the dynamical process of that region, as reported
by many authors [Salah et al., 1986; Cheng et al., 1992;
Le et al., 2008]. The eclipse magnitude increased to 0.6–0.8
at 0100 UT (Figure 2c). Along with the increase of eclipse
magnitude, clear west‐east gradients of DTEC can be seen
(Figures 2b and 2c). There is a larger decrease in TEC at
lower latitudes than at higher ones due to large latitudinal
TEC gradient in this area, which makes the value of background TEC increase with the increase in the latitude.
[8] The Moon’s umbra entered the selected area at
0115 UT. It moved east northeastward and left the area at
0133 UT. During this period, a “shadow” in the ionosphere
shown as TEC depletion maximum was formed ∼100 km
south of the umbral path. The depletion maximum area then
moved eastward (Figures 2d–2g), following the movement
of the totality area with a time lag of ∼10 min. After the
totality (∼0133 UT), the solar flux began to recover, but
TEC remained decreasing until ∼0140 UT, when TEC
depletion reached its maximum of −5 TECU. This is
because the decrease of electron density in F2 region and
topside ionosphere became effective during this time, since
there is a time lag of up to 1 h between the decrease of solar
eclipse and the decrease of electron density in topside ionosphere, and the eclipse had been in progress for more than
1 h. A second depletion maximum of TEC was seen in the
northeast of the area in Figures 2f and 2g. It may be caused
by local variation of TEC. After 0140 UT, TEC began to
recover from the west to the east following the recovery of
the solar radiation and returned to original level afterward
(Figures 2h and 2i).
3. Latitudinal Dependence
[9] Previous studies have shown that the ionosphere
response to solar eclipses has distinct latitudinal dependence. The diffusion process is more effective in topside
ionosphere at midlatitudes than at low latitudes because of
larger geomagnetic inclination at higher latitudes. As a
consequence, diffusion tends to smooth out differences in
the behavior of the layer at different heights and cause the
similar electron density responses at all heights in the top F2
layer at midlatitudes [Rishbeth, 1968]. This was addressed
by the simulation of Le et al. [2009]. At low latitudes, the
ionization transports poleward from the equator along magnetic lines and influences the variation of the low‐latitude
electron density in the top F2 layer. As a result, the topside
ionosphere and F2 layer is controlled more by fountain
effect than by solar eclipses. Earlier observations of Cheng
et al. [1992] shows that the response of electron density in
F2 layer around the equatorial anomaly region during a solar
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Figure 3. Temporal variation of the relative change of TEC (RTEC) observed at five pairs of GPS
stations with the maximum eclipse magnitude of (a, b) ∼1.0, (c, d) ∼0.83, (e, f) ∼0.77, (g, h) ∼0.63,
and (i, j) ∼0.47. RTEC is the DTEC divided by the reference TEC observed from GPS satellite number
PRN 22. The code of each station and its geographical longitude and latitude are marked in each subplot. Also marked in the plots are the eclipse magnitudes M at the stations. Vertical dotted lines mark
the time of the first, second, and fourth contacts of the solar eclipse in central China.
eclipse is not controlled by local solar radiation at EIA
region but by that at the magnetic equator.
[10] The observation results of latitudinal variation of
TEC response to the solar eclipse is presented in Figure 3.
We draw the temporal variation of the relative change of
TEC (RTEC) observed at five pairs of GPS stations, where
they share the maximum eclipse magnitude of ∼1.0 (a, b),
∼0.83 (c, d), ∼0.77 (e, f), ∼0.63 (g, h), and ∼0.47 (i, j),
respectively. RTEC is the DTEC divided by the reference
TEC observed from GPS satellite number PRN 22, which
has the highest elevation angles (greater than 80°) around
the time of totality. The code of each station, as well as its
geographical longitude and latitude, is marked in each
subplot. Also marked in the panel are the eclipse magnitudes
M at the stations. Each pair of the stations locates symmetrically with respect to the umbral path. The criteria for us
to choose these stations is that, for each pair of stations, the
difference of their maximum eclipse magnitudes should be
less than 0.02 and their longitudinal difference should be
within 5°. Thus we avoid the contamination of the influence
of eclipse magnitude variation and local time variation on
RTEC when analyzing its latitudinal dependence.
[11] As shown in Figure 3, the maximum drop of RTEC
decreases from 26% in umbral path to 5% in the region with
eclipse magnitude M equals ∼0.48. It is indicated that the
decrease of the drop of RTEC is mainly controlled by the
change of solar flux radiation. Comparing the RTEC series
in the left panel with that in the right, we can see that the
drop of RTEC is larger at low‐latitude stations than at
midlatitudes ones. The drop of RTEC remains almost
unchanged from the umbral path to the partial eclipse region
at lower latitude with M equals 0.82 (Figures 3a and 3c),
while it decreases from 26% in the umbral path to 20% at
higher latitude with M equals 0.84 (Figures 3b and 3d).
Similarly, the drop of RTEC is larger at low‐latitude stations
than at midlatitude ones in the regions with M equals ∼0.63
(Figures 3e and 3f) and ∼0.77 (Figures 3g and 3h). The result
shows an obvious tendency that TEC response to the solar
eclipse is more intense at low latitudes than at mid ones. The
tendency is unnoticeable in the region with eclipse magnitude
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Figure 4. Modeling results of the (a) change of electron temperature, (b) change of the field‐aligned ion
drift velocity, (c) change of plasma flux, and (d) percentage change in electron density at 0130 UT along
the meridian of 120°E associated with the solar eclipse. The change of these parameters is obtained by
subtracting the values in reference day from those on 22 July 2009. Dotted lines mark the latitude range
of umbral path at 0130 UT.
of less than 0.5, either because TEC is influenced by low‐
latitude background disturbances (Figure 3i) or because the
background TEC is too low to show its variation associated
with the eclipse (Figure 3j).
[12] To further investigate the cause of the latitudinal
dependence of TEC associated with the eclipse, we use a
midlatitude and low‐latitude theoretical ionospheric model
to simulate the latitudinal variation of the ionosphere during
the eclipse on 22 July 2009. The model, which is known as
the Theoretical Ionospheric Model of the Earth in Institute
of Geology and Geophysics, Chinese Academy of Sciences
(TIME‐IGGCAS), was developed by Liu et al. [1999], Lei
et al. [2004a, 2004b], and Yue et al. [2008]. Figure 4 presents the simulation results of the change of electron temperature (Figure 4a), change of the field‐aligned ion drift
velocity (Figure 4b), change of plasma flux (Figure 4c), and
percentage change in electron density (Figure 4d) at 0130 UT
along the meridian of 120°E. The change of these parameters is obtained by subtracting the values in reference day
from those on 22 July 2009.
[13] The geomagnetic inclination is about 45° in the
umbral path at 30°N (i.e., the magnetic latitude of 19°N). As
seen in Figure 4a, the maximum decrease of electron temperature stretches along the geomagnetic field lines from
300 km altitude in the umbral path to 1000 km altitude at
∼20°N (i.e., the magnetic latitude of ∼9°N). The decrease of
electron temperature causes the contraction of the ionosphere, which leads to downward drift of plasma along the
magnetic field lines from lower latitudes to the region in the
umbral path (Figure 4b). Figure 4b shows that the largest
field‐aligned drift occurs in the latitude range of 17°N–25°N
at the altitude 800–1000 km. The drift causes downward
plasma flux from topside ionosphere to F2 layer, as illustrated in Figure 4c. The plasma flux compensates for the
plasma loss in F2 layer and leads to a slight increase of
electron density in F2 layer in the umbral path (Figure 4d).
As shown in Figure 4d, in topside ionosphere, the drop of
electron density is considerably larger in south of the umbral
path than in the north during the solar eclipse. Besides the
major maximum drop of electron density (up to 60%) in F1
layer in the umbral path, which is due to the photochemical
loss, a minor maximum drop of electron density (about
25%) is found in topside ionosphere with an altitude range of
850–1000 km at ∼10°N–20°N. It is inferred from Figure 4
that, owing to diffusion of plasma along magnetic field
lines, TEC measured at lower latitudes (in the south of
∼30°N) is expected to decrease more than that measured at
higher ones (in the north of ∼30°N). This is in good
agreement with our observations in Figure 3.
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Figure 5. Longitudinal dependence of the maximum drop
of RTEC during the eclipse observed at stations within the
umbra (circles), at low‐latitude stations with the eclipse
magnitude of 0.68 (plus signs), and at midlatitude stations
with the eclipse magnitude of 0.75 (asterisks).
[14] The latitudinal dependence of TEC response to the
solar eclipse at midlatitudes and low latitudes differs from
the result of Afraimovich et al. [1998], who analyzed TEC
response to the 9 March 1997 total eclipse at mid‐ and high‐
latitude stations around Irkutsk and found that the depression of TEC is independent of the latitude in the range of
52°N ± 6°N. The difference of two results may be caused by
the difference of the geomagnetic inclination at two regions.
Relatively smaller inclination in midlatitude and low‐latitude
region such as Central China leads to enhanced horizontal
diffusion along the magnetic field lines, which results in
obvious latitudinal variation of TEC during the solar eclipse.
While larger magnetic inclination at higher latitudes tends to
smooth out differences in the behavior at different heights,
as stated by Le et al. [2009], which in turn weakens the
latitudinal variation of TEC response to the eclipse.
4. Local Time Dependence
[15] During this solar eclipse, the umbral path crossed
Central China with the latitudinal range of no more than 5°.
This enables us to study the local time dependence of TEC
response to the eclipse from the observation of stations that
locate in the umbral path. Figure 5 illustrates longitudinal
variation of the maximum drop of RTEC observed at the
stations located in the umbral path (circles), in the partial
eclipse area at midlatitude (asterisks), and in the partial
eclipse area at low latitude (plus signs). The solid line is the
curve fitting of the data of RTEC from stations in umbral
path. The midlatitude stations are chosen to be DLHA
(37.4°N, 97.4°E) and BJFS (39.6°N, 115.9°E), both of
which endured the same eclipse magnitude of 0.71. The
low‐latitude stations are MMNS (20.9°N, 97.7°E) and
GUAN (23.2°N, 113.3°E), with the eclipse magnitude of
0.77. Since each group of stations has almost the same
eclipse magnitude as well as similar latitude, we can exclude
the influence of latitudinal and eclipse magnitude on RTEC
from our result.
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[16] Figure 5 indicates that the drop of RTEC is larger in
the east of the area than in the west. As the eclipse occurred
in the morning sector, the result exhibits a tendency that the
more the area is close to local noon, the more intense TEC
response is. The tendency is mostly obvious at the stations
in the umbral area. It is also clear in partial eclipse regions,
but much weaker. Our observation validates the simulation
results of Le et al. [2008], who modeled the response of
ionosphere to solar eclipses at various local times and found
that the decrease of NmF2 is larger around the midday than
in the morning. In F2 layer, the electron loss coefficient b is
proportional to the molecular N2 density. Larger N2 density
at noontime leads to a larger value of b, which then results
in more distinct decrease of NmF2 during the solar eclipse.
Therefore, the local time dependence of TEC response is
closely related to the local time variation of background
atmosphere density, which affects the electron loss efficiency in the ionosphere.
5. Discussion
[17] What makes TEC response complicated is that a
medium magnetic storm occurred during the solar eclipse.
Figure 6 presents temporal variation of horizontal component of magnetic field (Bh) observed at Shumagin (55.4°N,
199.5°E) in Alaska, USA (Figure 6a), as well as at Beijing
(40.3°N, 116.2°E) (Figure 6b), and the variation of AU and
AL indices (Figure 6c) from 2000 UT on 21 July to 1200 UT
on 22 July. Vertical dashed lines mark the time of the first
contact, the time of the second contact (start of the totality),
and the time of the fourth contact (end of the eclipse) in the
area of Central China. Beijing is the nearest geomagnetic
observatory to our selected area, and Shumagin is an
observatory near the auroral oval. It is seen from Figures 6a
and 6b that the storm began its gradual commencement at
∼0040 UT on 22 July, 40 min after the first contact. Then, its
initial phase lasted from ∼0040 to ∼0200 UT. After the onset
of the main phase at ∼0200 UT, the value of Bh began to
drop abruptly. The drop of AL index indicates that a substorm occurred during this period, with its growth phase
beginning at ∼0040 UT and its expansion phase beginning at
∼0200 UT (Figure 6c). AL index reached its minimum at
∼0410 UT.
[18] Though the storm began its initial phase during the
occurrence of the eclipse, the Moon’s umbral shadow left
the area of Central China at 0133 UT, which is 27 min prior
to the storm’s main phase onset. As stated by Thomas and
Venables [1966] and Zhao et al. [2007], the onset of auroral input into the ionosphere occurred most strongly after
the main phase onset of storm. This can be addressed by
Figures 6a and 6b. As a consequence, clear eclipse‐related
DTEC variation is seen before the main phase onset
(0200 UT) (Figures 2b–2h). The storm seemed to have little
influence on TEC variation before 0200 UT, while it began to
influence our observation after 0200 UT. As we can see from
Figures 2i and 2h, slight enhancement of DTEC appears in
some areas at 0200 UT and 0230 UT. Obvious increase of
TEC occurred after 0300 UT at some low‐latitude stations, as
shown in Figure 3. This indicates the coming of a positive
ionospheric storm.
[19] It should also be noted that the storm effect is not
included in our model results of Figure 4. However, the
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Figure 6. Temporal variation of horizontal component of magnetic field (Bh) observed at (a) Shumagin
(55.4°N, 199.5°E) in Alaska, USA and (b) Beijing (40.3°N, 116.2°E) and (c) the variation of AU and AL
indices from 2000 UT on 21 July to 1200 UT on 22 July. Vertical dashed lines mark the time of the first,
second, and fourth contacts of the solar eclipse in central China.
latitudinal trends of ionosphere response to solar eclipse in
Figure 4 is fundamentally reliable, as we simulate the variation of ionosphere at 0130 UT, which is 30 min before the
storm’s main phase onset.
6. Summary
[20] The longest total eclipse of this century occurred in
East and South Asia on 22 July 2009. The eclipse was
accompanied with a medium magnetic storm, whose main
phase onset occurred ∼27 min after the passage of the
Moon’s umbral shadow in the area of central China.
[21] Using TEC data from 60 GPS stations in East Asia,
we build differential TEC maps to examine the two‐
dimensional TEC variations during the solar eclipse in the
range of 26°N–36°N, 108°E–118°E, where the north
boundary of the EIA region is. Because the solar eclipse
occurred mainly during the storm’s initial phase, it seems
that the storm did not influence the drop and recovery of
TEC until 0200 UT, when the onset of the main phase
began. Before 0200 UT, a “shadow” in the ionosphere
shown as TEC depletion area was formed ∼100 km south of
the Moon’s umbral path. The TEC depletion area, with a
maximum decrease of 5 TECU, moved eastward following
the movement of the totality area with a time lag of ∼10 min.
Enhancement of TEC due to the storm is observed after the
fourth contact.
[22] TEC response to the solar eclipse shows evident
latitudinal and local time dependence. By comparing the
relative change of TEC observed at different stations with
similar eclipse magnitude, we find that TEC response is
more intense at low latitudes than at mid ones. By modeling
work, we find that, owing to a latitudinal change of the
downward diffusion of topside plasma, the drop of electron
density in topside ionosphere is larger in the south of the
umbral path than in the north during the solar eclipse. It is
inferred that the latitudinal dependence of the TEC response
may result from latitudinal variation of magnetic inclination,
which influences the diffusion of ionization among different
layers. Besides, the relative drop of TEC due to the solar
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eclipse is larger around noontime than in the morning. This
validates the modeling results in the work of Le et al.
[2008], which indicates that the local time dependence of
TEC response is closely related to the local time variation of
background atmosphere density, which affects the electron
loss efficiency in the ionosphere.
[23] Acknowledgments. We acknowledge all the colleagues of the
observation team around this solar eclipse. We are grateful to the Scripps
Orbit and Permanent Array Center (SOPAC) and IGS, Wuhan Institute
of Heavy Rain, and China Earthquake Administration for providing GPS
network data. We also thank INTERMAGNET for promoting high standards of magnetic observatory practice (http://www.intermagnet.org). This
work is supported by the National Natural Science Foundation of China
(grants 40974089, 40774090, and 40636032), the National Important Basic
Research Project (2006CB806306), the National Science and Technology
Basic Work Program (2008FY120100), and the Heavy Rain Research
Open Project of IHR, CMA (grant IHR2007G01).
[24] Robert Lysak thanks Jan Lastovicka and another reviewer for their
assistance in evaluating this paper.
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W. Wan, M. Yang, and B. Zhao, Beijing National Observatory of Space
Environment, Institute of Geology and Geophysics, Chinese Academy of
Sciences, 52 Sanlihe Rd., Beijing 100864, China. ([email protected])
M. Wang, Institute of Earthquake Science, China Earthquake
Administration, No. 63 Fuxing Ave., Beijing 100036, China.
B. Xiong, Graduate School of the Chinese Academy of Sciences,
52 Sanlihe Rd., Beijing 100864, China.
G. Xu, Institute of Heavy Rain, China Meteorological Administration,
No. 46, Zhongguancun Nandajie, Haidian District, Beijing 100081, China.
X. Yue, University Corporation for Atmospheric Research, PO Box
3000, Boulder, CO 80307‐3000, USA.
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