GPS TEC response to the 22 July 2009 total solar eclipse in East Asia

GPS TEC response to the 22 July 2009 total solar eclipse in East Asia
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                                                            altitudes. At the same time, the decrease of electron tem-
                                                                           perature leads to downward drift of the plasma in the topside
  [2] A total solar eclipse provides a good opportunity for
                                                                           ionosphere, which partly compensates for the electron loss
studying the ionospheric variations associated with the
                                                                           at altitudes above F2 layer. The combined effects make the
photochemistry process and transportation process in the
                                                                           electron density in topside ionosphere decrease very slowly
ionosphere. During a solar eclipse, the decrease of solar flux
                                                                           and relatively smaller to the low altitude. The maximum of
in the ionosphere due to the Moon’s shading leads to the
                                                                           decrease, i.e., 10%–25%, appears about 1 h after the totality
decrease of electron photoionization production, which
                                                                           in topside ionosphere [Korte et al., 2001; Adeniyi et al.,
results in nearly synchronous drop of electron density in the
                                                                           2007]. Sometimes electron density even increases due to
E layer and F1 layer. On the basis of the observation of
                                                                           the eclipse [Evans, 1965; Salah et al., 1986].
incoherent scatter radar [Salah et al., 1986], it is found that
                                                                             [3] A total eclipse occurred in East and South Asia in the
the drop of electron density due to the solar eclipse could                morning on 22 July 2009. Its totality lasted a maximum of
reach 60% at maximum in F1 layer. The electron loss at
                                                                           6 min 39 s. It is the longest total eclipse of this century, not to
lower altitudes due to photochemical production loss is
                                                                           be surpassed until year 2132. Detailed information of the eclipse
transported by diffusion along magnetic field lines to higher              can be seen in the work of Espennak and Anderson [2008]
   1
                                                                           (http://eclipse.gsfc.nasa.gov/SEmono/TSE2009/TSE2009.
     Beijing National Observatory of Space Environment, Institute of       html). The Moon’s umbra passed through central China,
Geology and Geophysics, Chinese Academy of Sciences, Beijing, China.
   2
     Institute of Heavy Rain, China Meteorological Administration,         where the north boundary of the anomaly crest regions
Wuhan, China.                                                              locates. During this solar eclipse, the Institute of Geology
   3
     Institute of Earthquake Science, China Earthquake Administration,     and Geophysics, Chinese Academy of Sciences initiated a
Beijing, China.                                                            multi‐station and multi‐instrument observation campaign.
   4
     Graduate School of the Chinese Academy of Sciences, Beijing, China.
   5
     University Corporation for Atmospheric Research, Boulder, Colorado,
                                                                           Dense distribution of GPS stations in this area makes it
USA.                                                                       possible to monitor the spatial and temporal variations of
                                                                           TEC due to the solar eclipse at midlatitudes and low lati-
Copyright 2010 by the American Geophysical Union.                          tudes. In this paper, we use the TEC data from 60 GPS
0148‐0227/10/2009JA015113

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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 pre-
         sented in the figure is the location of GPS stations (black asterisks).

stations to build the two‐dimensional variation of differen-       [5] Using the TEC data from 60 GPS stations as marked
tial TEC maps. The TEC response to the total solar eclipse is    in Figure 1, we adopt the least squares fit and triangle‐based
investigated, and the variation of TEC associated with lati-     linear interpolation method to build the two‐dimensional
tudes and local times is presented.                              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
2. Two‐Dimensional GPS TEC Variations                            GPS stations belong to several institutes and organizations,
                                                                 including Wuhan Institute of Heavy Rain, China Earthquake
  [4] The exceptional long total eclipse began at 0053 UT in     Administration, Institute of Geology and Geophysics, and
India, shortly after sunrise. The Moon’s umbral shadow           the International GNSS Service (IGS). We calculate DTEC
traveled east northeast and entered China at 0105 UT (0905       through subtracting the median value of TEC on reference
Beijing standard time). It formed a path ∼244 km wide that       days from the TEC measured on 22 July. The reference days
traveled nearly eastward through Central China along the         are chosen to be 17–19 July, which are the geomagnetically
geographical latitude of ∼30°N (i.e., the magnetic latitude of   quietest days of that month.
∼19°N) before crossing the south of Japan and the Pacific          [6] Figure 2 presents the sequence of DTEC maps during
Ocean. Figure 1 plots the umbral (total eclipse) and pre-        the period of 0000–0230 UT on 22 July 2009. The maps are
umbral (partial eclipse) paths labeled with eclipse magni-       plotted every 30 min during the periods of 0000–0100 UT
tudes. The total eclipse can be seen in several provinces in     and 0200–0230 UT. To show more clearly the variation of
Central China from about 0010 UT (0910 LT) to 0140 UT            DTEC during the passage of the Moon’s umbral shadow, we
(0940 LT) with the duration of 4–6 min. A partial eclipse is     present the maps every 10 min from 0100 to 0140 UT. We
seen in much broader area of north and south of China.


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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      depletion reached its maximum of −5 TECU. This is
the maps.                                                       because the decrease of electron density in F2 region and
  [7] After the first contact (the time when the disk of the    topside ionosphere became effective during this time, since
Moon first touched the solar disk) at 0009 UT, the whole        there is a time lag of up to 1 h between the decrease of solar
area of 26°N–36°N, 108°E–118°E was in partial eclipse           eclipse and the decrease of electron density in topside ion-
with the magnitude of 0.1–0.3 at 0030 UT (Figure 2b).           osphere, and the eclipse had been in progress for more than
Upon the arrival of the partial eclipse, TEC decreased          1 h. A second depletion maximum of TEC was seen in the
immediately following the increase of eclipse magnitude.        northeast of the area in Figures 2f and 2g. It may be caused
The nearly synchronous decrease of TEC during this period       by local variation of TEC. After 0140 UT, TEC began to
is mainly due to the decrease of photochemical production,      recover from the west to the east following the recovery of
which dominates in E and F1 layers. The time lag between        the solar radiation and returned to original level afterward
the lowering of solar radiation and the decrease of the         (Figures 2h and 2i).
electron density is only 1–3 min in E and F1 layers, while it
can reach ∼1 h in topside ionosphere because of the domi-       3. Latitudinal Dependence
nation of the dynamical process of that region, as reported
by many authors [Salah et al., 1986; Cheng et al., 1992;          [9] Previous studies have shown that the ionosphere
Le et al., 2008]. The eclipse magnitude increased to 0.6–0.8    response to solar eclipses has distinct latitudinal depen-
at 0100 UT (Figure 2c). Along with the increase of eclipse      dence. The diffusion process is more effective in topside
magnitude, clear west‐east gradients of DTEC can be seen        ionosphere at midlatitudes than at low latitudes because of
(Figures 2b and 2c). There is a larger decrease in TEC at       larger geomagnetic inclination at higher latitudes. As a
lower latitudes than at higher ones due to large latitudinal    consequence, diffusion tends to smooth out differences in
TEC gradient in this area, which makes the value of back-       the behavior of the layer at different heights and cause the
ground TEC increase with the increase in the latitude.          similar electron density responses at all heights in the top F2
  [8] The Moon’s umbra entered the selected area at             layer at midlatitudes [Rishbeth, 1968]. This was addressed
0115 UT. It moved east northeastward and left the area at       by the simulation of Le et al. [2009]. At low latitudes, the
0133 UT. During this period, a “shadow” in the ionosphere       ionization transports poleward from the equator along mag-
shown as TEC depletion maximum was formed ∼100 km               netic lines and influences the variation of the low‐latitude
south of the umbral path. The depletion maximum area then       electron density in the top F2 layer. As a result, the topside
moved eastward (Figures 2d–2g), following the movement          ionosphere and F2 layer is controlled more by fountain
of the totality area with a time lag of ∼10 min. After the      effect than by solar eclipses. Earlier observations of Cheng
totality (∼0133 UT), the solar flux began to recover, but       et al. [1992] shows that the response of electron density in
TEC remained decreasing until ∼0140 UT, when TEC                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 sub-
         plot. 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          of eclipse magnitude variation and local time variation on
region but by that at the magnetic equator.                        RTEC when analyzing its latitudinal dependence.
  [10] The observation results of latitudinal variation of           [11] As shown in Figure 3, the maximum drop of RTEC
TEC response to the solar eclipse is presented in Figure 3.        decreases from 26% in umbral path to 5% in the region with
We draw the temporal variation of the relative change of           eclipse magnitude M equals ∼0.48. It is indicated that the
TEC (RTEC) observed at five pairs of GPS stations, where           decrease of the drop of RTEC is mainly controlled by the
they share the maximum eclipse magnitude of ∼1.0 (a, b),           change of solar flux radiation. Comparing the RTEC series
∼0.83 (c, d), ∼0.77 (e, f), ∼0.63 (g, h), and ∼0.47 (i, j),        in the left panel with that in the right, we can see that the
respectively. RTEC is the DTEC divided by the reference            drop of RTEC is larger at low‐latitude stations than at
TEC observed from GPS satellite number PRN 22, which               midlatitudes ones. The drop of RTEC remains almost
has the highest elevation angles (greater than 80°) around         unchanged from the umbral path to the partial eclipse region
the time of totality. The code of each station, as well as its     at lower latitude with M equals 0.82 (Figures 3a and 3c),
geographical longitude and latitude, is marked in each             while it decreases from 26% in the umbral path to 20% at
subplot. Also marked in the panel are the eclipse magnitudes       higher latitude with M equals 0.84 (Figures 3b and 3d).
M at the stations. Each pair of the stations locates sym-          Similarly, the drop of RTEC is larger at low‐latitude stations
metrically with respect to the umbral path. The criteria for us    than at midlatitude ones in the regions with M equals ∼0.63
to choose these stations is that, for each pair of stations, the   (Figures 3e and 3f) and ∼0.77 (Figures 3g and 3h). The result
difference of their maximum eclipse magnitudes should be           shows an obvious tendency that TEC response to the solar
less than 0.02 and their longitudinal difference should be         eclipse is more intense at low latitudes than at mid ones. The
within 5°. Thus we avoid the contamination of the influence        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‐       ∼20°N (i.e., the magnetic latitude of ∼9°N). The decrease of
latitude background disturbances (Figure 3i) or because the      electron temperature causes the contraction of the iono-
background TEC is too low to show its variation associated       sphere, which leads to downward drift of plasma along the
with the eclipse (Figure 3j).                                    magnetic field lines from lower latitudes to the region in the
  [12] To further investigate the cause of the latitudinal       umbral path (Figure 4b). Figure 4b shows that the largest
dependence of TEC associated with the eclipse, we use a          field‐aligned drift occurs in the latitude range of 17°N–25°N
midlatitude and low‐latitude theoretical ionospheric model       at the altitude 800–1000 km. The drift causes downward
to simulate the latitudinal variation of the ionosphere during   plasma flux from topside ionosphere to F2 layer, as illus-
the eclipse on 22 July 2009. The model, which is known as        trated in Figure 4c. The plasma flux compensates for the
the Theoretical Ionospheric Model of the Earth in Institute      plasma loss in F2 layer and leads to a slight increase of
of Geology and Geophysics, Chinese Academy of Sciences           electron density in F2 layer in the umbral path (Figure 4d).
(TIME‐IGGCAS), was developed by Liu et al. [1999], Lei           As shown in Figure 4d, in topside ionosphere, the drop of
et al. [2004a, 2004b], and Yue et al. [2008]. Figure 4 pre-      electron density is considerably larger in south of the umbral
sents the simulation results of the change of electron tem-      path than in the north during the solar eclipse. Besides the
perature (Figure 4a), change of the field‐aligned ion drift      major maximum drop of electron density (up to 60%) in F1
velocity (Figure 4b), change of plasma flux (Figure 4c), and     layer in the umbral path, which is due to the photochemical
percentage change in electron density (Figure 4d) at 0130 UT     loss, a minor maximum drop of electron density (about
along the meridian of 120°E. The change of these para-           25%) is found in topside ionosphere with an altitude range of
meters is obtained by subtracting the values in reference day    850–1000 km at ∼10°N–20°N. It is inferred from Figure 4
from those on 22 July 2009.                                      that, owing to diffusion of plasma along magnetic field
  [13] The geomagnetic inclination is about 45° in the           lines, TEC measured at lower latitudes (in the south of
umbral path at 30°N (i.e., the magnetic latitude of 19°N). As    ∼30°N) is expected to decrease more than that measured at
seen in Figure 4a, the maximum decrease of electron tem-         higher ones (in the north of ∼30°N). This is in good
perature stretches along the geomagnetic field lines from        agreement with our observations in Figure 3.
300 km altitude in the umbral path to 1000 km altitude at

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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 effi-
Figure 5. Longitudinal dependence of the maximum drop              ciency in the ionosphere.
of RTEC during the eclipse observed at stations within the
umbra (circles), at low‐latitude stations with the eclipse         5. Discussion
magnitude of 0.68 (plus signs), and at midlatitude stations          [17] What makes TEC response complicated is that a
with the eclipse magnitude of 0.75 (asterisks).                    medium magnetic storm occurred during the solar eclipse.
                                                                   Figure 6 presents temporal variation of horizontal compo-
  [14] The latitudinal dependence of TEC response to the           nent of magnetic field (Bh) observed at Shumagin (55.4°N,
solar eclipse at midlatitudes and low latitudes differs from       199.5°E) in Alaska, USA (Figure 6a), as well as at Beijing
the result of Afraimovich et al. [1998], who analyzed TEC          (40.3°N, 116.2°E) (Figure 6b), and the variation of AU and
response to the 9 March 1997 total eclipse at mid‐ and high‐       AL indices (Figure 6c) from 2000 UT on 21 July to 1200 UT
latitude stations around Irkutsk and found that the depres-        on 22 July. Vertical dashed lines mark the time of the first
sion of TEC is independent of the latitude in the range of         contact, the time of the second contact (start of the totality),
52°N ± 6°N. The difference of two results may be caused by         and the time of the fourth contact (end of the eclipse) in the
the difference of the geomagnetic inclination at two regions.      area of Central China. Beijing is the nearest geomagnetic
Relatively smaller inclination in midlatitude and low‐latitude     observatory to our selected area, and Shumagin is an
region such as Central China leads to enhanced horizontal          observatory near the auroral oval. It is seen from Figures 6a
diffusion along the magnetic field lines, which results in         and 6b that the storm began its gradual commencement at
obvious latitudinal variation of TEC during the solar eclipse.     ∼0040 UT on 22 July, 40 min after the first contact. Then, its
While larger magnetic inclination at higher latitudes tends to     initial phase lasted from ∼0040 to ∼0200 UT. After the onset
smooth out differences in the behavior at different heights,       of the main phase at ∼0200 UT, the value of Bh began to
as stated by Le et al. [2009], which in turn weakens the           drop abruptly. The drop of AL index indicates that a sub-
latitudinal variation of TEC response to the eclipse.              storm 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
4. Local Time Dependence                                           ∼0410 UT.
  [15] During this solar eclipse, the umbral path crossed            [18] Though the storm began its initial phase during the
Central China with the latitudinal range of no more than 5°.       occurrence of the eclipse, the Moon’s umbral shadow left
This enables us to study the local time dependence of TEC          the area of Central China at 0133 UT, which is 27 min prior
response to the eclipse from the observation of stations that      to the storm’s main phase onset. As stated by Thomas and
locate in the umbral path. Figure 5 illustrates longitudinal       Venables [1966] and Zhao et al. [2007], the onset of auro-
variation of the maximum drop of RTEC observed at the              ral input into the ionosphere occurred most strongly after
stations located in the umbral path (circles), in the partial      the main phase onset of storm. This can be addressed by
eclipse area at midlatitude (asterisks), and in the partial        Figures 6a and 6b. As a consequence, clear eclipse‐related
eclipse area at low latitude (plus signs). The solid line is the   DTEC variation is seen before the main phase onset
curve fitting of the data of RTEC from stations in umbral          (0200 UT) (Figures 2b–2h). The storm seemed to have little
path. The midlatitude stations are chosen to be DLHA               influence on TEC variation before 0200 UT, while it began to
(37.4°N, 97.4°E) and BJFS (39.6°N, 115.9°E), both of               influence our observation after 0200 UT. As we can see from
which endured the same eclipse magnitude of 0.71. The              Figures 2i and 2h, slight enhancement of DTEC appears in
low‐latitude stations are MMNS (20.9°N, 97.7°E) and                some areas at 0200 UT and 0230 UT. Obvious increase of
GUAN (23.2°N, 113.3°E), with the eclipse magnitude of              TEC occurred after 0300 UT at some low‐latitude stations, as
0.77. Since each group of stations has almost the same             shown in Figure 3. This indicates the coming of a positive
eclipse magnitude as well as similar latitude, we can exclude      ionospheric storm.
the influence of latitudinal and eclipse magnitude on RTEC           [19] It should also be noted that the storm effect is not
from our result.                                                   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   began. Before 0200 UT, a “shadow” in the ionosphere
Figure 4 is fundamentally reliable, as we simulate the var-     shown as TEC depletion area was formed ∼100 km south of
iation of ionosphere at 0130 UT, which is 30 min before the     the Moon’s umbral path. The TEC depletion area, with a
storm’s main phase onset.                                       maximum decrease of 5 TECU, moved eastward following
                                                                the movement of the totality area with a time lag of ∼10 min.
6. Summary                                                      Enhancement of TEC due to the storm is observed after the
                                                                fourth contact.
  [20] The longest total eclipse of this century occurred in      [22] TEC response to the solar eclipse shows evident
East and South Asia on 22 July 2009. The eclipse was            latitudinal and local time dependence. By comparing the
accompanied with a medium magnetic storm, whose main            relative change of TEC observed at different stations with
phase onset occurred ∼27 min after the passage of the           similar eclipse magnitude, we find that TEC response is
Moon’s umbral shadow in the area of central China.              more intense at low latitudes than at mid ones. By modeling
  [21] Using TEC data from 60 GPS stations in East Asia,        work, we find that, owing to a latitudinal change of the
we build differential TEC maps to examine the two‐              downward diffusion of topside plasma, the drop of electron
dimensional TEC variations during the solar eclipse in the      density in topside ionosphere is larger in the south of the
range of 26°N–36°N, 108°E–118°E, where the north                umbral path than in the north during the solar eclipse. It is
boundary of the EIA region is. Because the solar eclipse        inferred that the latitudinal dependence of the TEC response
occurred mainly during the storm’s initial phase, it seems      may result from latitudinal variation of magnetic inclination,
that the storm did not influence the drop and recovery of       which influences the diffusion of ionization among different
TEC until 0200 UT, when the onset of the main phase             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                       Le, H., L. Liu, X. Yue, and W. Wan (2008), The mid‐latitude F2 region
validates the modeling results in the work of Le et al.                             during solar eclipses: Observations and modeling, J. Geophys. Res.,
                                                                                    113(A8), A08309, doi:10.1029/2007JA013012.
[2008], which indicates that the local time dependence of                         Le, H., L. Liu, X. Yue, W. Wan, and B. Ning (2009), Latitudinal depen-
TEC response is closely related to the local time variation of                      dence of the ionospheric response to solar eclipses, J. Geophys. Res.,
background atmosphere density, which affects the electron                           114(A7), A07308, doi:10.1029/2009JA014072.
                                                                                  Lei, J., L. Liu, W. Wan, and S. R. Zhang (2004a), Modeling the behavior of
loss efficiency in the ionosphere.                                                  ionosphere above Millstone Hill during the September 21–27, 1998
                                                                                    storm, J. Atmos. Sol. Terr. Phys., 66, 1093–1102.
                                                                                  Lei, J., L. Liu, W. Wan, and S. R. Zhang (2004b), Model results for the
   [23] Acknowledgments. We acknowledge all the colleagues of the                   ionospheric lower transition height over mid‐latitude, Ann. Geophys.,
observation team around this solar eclipse. We are grateful to the Scripps          22, 2037–2045.
Orbit and Permanent Array Center (SOPAC) and IGS, Wuhan Institute                 Liu, L., W. Wan, J. N. Tu, Z. T. Bao, and C. K. Yeh (1999), Modeling
of Heavy Rain, and China Earthquake Administration for providing GPS                study of the ionospheric effects during a total solar eclipse, Chin. J.
network data. We also thank INTERMAGNET for promoting high stan-                    Geophys., 42(3), 296–302.
dards of magnetic observatory practice (http://www.intermagnet.org). This         Rishbeth, H. (1968), Solar eclipses and ionospheric theory, Space Sci. Rev.,
work is supported by the National Natural Science Foundation of China               8(4), 543–554.
(grants 40974089, 40774090, and 40636032), the National Important Basic           Salah, J. E., W. L. Oliver, J. C. Foster, and J. M. Holt (1986), Observations
Research Project (2006CB806306), the National Science and Technology                of the May 30, 1984, Annular Solar Eclipse at Millstone Hill, J. Geophys.
Basic Work Program (2008FY120100), and the Heavy Rain Research                      Res., 91(A2), 1651–1660.
Open Project of IHR, CMA (grant IHR2007G01).                                      Thomas, L., and F. H. Venables (1966), The onset of the F region distur-
   [24] Robert Lysak thanks Jan Lastovicka and another reviewer for their           bance at middle latitudes during magnetic storms, J. Atmos. Terr. Phys.,
assistance in evaluating this paper.                                                28, 599–605.
                                                                                  Yue, X., W. Wan, L. Liu, H. Le, Y. Chen, and T. Yu (2008), Development
                                                                                    of a middle and low latitude theoretical ionospheric model and an obser-
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