Atmospheric and Climate Sciences, 2013, 3, 475-480 Published Online October 2013 (
Variation of Total Ozone during 24 August 2005
Magnetic Storm: A Case Study
Gustavo A. Mansilla1,2
1Departamento de Física, Facultad de Ciencias Exactas y Tecnología, Universidad Nacional de Tucumán,
San Miguel de Tucumán, Argentina
2Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
Received June 11, 2013; revised July 13, 2013; accepted July 21, 2013
Copyright © 2013 Gustavo A. Mansilla. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This paper presents the longitudinal distribution of total ozone along several latitudinal circles from both hemispheres
during a strong geomagnetic storm that occurred on 24 August 2005 after a solar proton event (the maximum flux of
protons with energy > 10 MeV was 1.70 × 107 protons cm2·day1·sr1 on 23 August). For that, we use average daily
values of total ozone observations (=column ozone amount) in Dobson units for the period 18-25 August 2005 (ob-
tained from the Total Ozone Mapping Spectrometer, TOMS). The considered storm occurred after a relatively quiet
geomagnetic period and it is not superposed by another perturbation, which permit us to identify clearly the effects of
the geomagnetic storm on total ozone. The results show statistically significant decreases in ozone along the latitudinal
circles 70˚N and 70˚S (summer and winter), no statistically significant effects at middle latitudes (40˚S) and sparse sta-
tistically significant increases at low latitudes (20˚S). The role of some mechanisms to explain the features observed is
Keywords: Solar Proton Event; Geomagnetic Storm; Ozone; Hemispheres
1. Introduction
Solar Proton Events (SPEs) occur when protons with
very high energy are emitted by the Sun during solar
flares or coronal mass ejections (CME), sometimes to-
ward the Earth. High energy solar protons can penetrate
the Earth’s magnetic field near the poles. These protons
penetrate into the atmosphere, typically to the 40 to 80
km height. Only 12 - 15 events per solar cycle can be
recorded at the ground level [1]. In this way, they pro-
vide a direct connection between the Sun and the Earth’s
middle atmosphere [2]. Geomagnetic storms (temporary
disturbances of the Earth’s magnetic field) can be ex-
pected during solar flares and CMEs but not because of
the increase of charged particles into the Earth’s magne-
tosphere. They can occur when the interplanetary mag-
netic field (IMF) is southward and the solar wind crosses
the Earth for long duration of time or in shorter more
energetic bursts (flares/CMEs). When the IMF is south-
ward, a magnetic reconnection of the dayside magneto-
pause is produced, rapidly injecting magnetic and parti-
cle energy into the Earth’s magnetosphere.
Geomagnetic storms cause large disturbances in the
upper atmosphere (ionosphere and thermosphere) includ-
ing also the middle atmosphere and the troposphere [3,4].
Solar energetic particles which reach middle atmosphere
cause ionization of air molecules. As the ionized mole-
cules recombine, they produce nitrogen and hydrogen
oxides which can affect ozone through odd nitrogen NOy
and odd hydrogen HOx catalytic reactions (see e.g., [5]
for details). Decreases of ozone in the middle atmosphere
after large solar proton events have been predicted by
atmospheric models (e.g., Whole Atmosphere Commu-
nity Climate Model WACCM3), and also observed by
satellite measurements [6-8]. The stratospheric ozone
effects were caused by the odd nitrogen. Very large NOy
enhancements lasted for months in the middle and lower
stratosphere after some largest SPEs. Using a two-dimen-
sional chemistry and transport atmosphere model, [9]
compute the effects of gigantic SPEs in the stratosphere.
They obtained upper stratospheric ozone depletions >
10% to last for a few months after the SPEs. Moreover,
during the October-November 2003 series of solar proton
events, ozone depletion varying from 20% at 40 km alti-
tude to more than 95% at 78 km was found [10].
Some studies show that during intense geomagnetic
opyright © 2013 SciRes. ACS
storms the total ozone presents a pattern which is statis-
tically significant at the northern higher middle latitudes
only under very limited conditions [11]: in winter and
under the high solar activity and the East phase of the
QBO conditions. At around 50˚N latitudinal circle, but
not around 40˚N and 60˚N, the effect appears to be basi-
cally re-distribution of ozone (in the North Atlantic-
European it means an increase of the total ozone), neither
its loss, nor its production.
This short paper shows the short-term latitudinal dis-
turbances in the total ozone content as consequence of an
isolated geomagnetic storm occurred during the descen-
ding phase of solar cycle 23 (solar flux on storm day:
100.7). Since this storm came after a relatively quiet so-
lar/magnetic period and it is not superposed upon by an-
other perturbation, it is reasonable to assume that the
variations on total ozone during the considered storm
period are caused by the geomagnetic storm. In fact, the
selected geomagnetic storm was characterized by an SSC
(storm sudden commencement), which was preceded by
quiet days and without the arrival of a new solar rapid
flow during its phase of recovery, that is, a new storm is
not superimposed. Moreover, with the results obtained
here we can check the pattern of total ozone variation
during geomagnetic storm obtained by [11].
Case studies which consider several latitudes from
both hemispheres are rare but they are important for a
view of global space weather and also to know and/or
check the role of possible physical mechanisms. In addi-
tion, the ozone response to geomagnetic storms has not
been given adequate attention over Southern latitudes
We will first describe the datasets used for quantifying
the total ozone response to the geomagnetic storm. After
that, present our observations. Finally, a discussion and
the conclusion are given in Section 4.
2. Data
The database used in this study consists of average daily
values of total ozone observations (=column ozone
amount) in Dobson units for the period 18-25 August
2005, which were obtained from the Total Ozone Map-
ping Spectrometer (TOMS) (
ozone/ozone.html). We considered the measurements
obtained each 10˚ of geographic longitude, between
–180˚ and +180˚ (37 observations) at different latitu-
dinal circles of the Norhtern Hemisphere (NH) and the
Southern Hemisphere (SH): 20˚, 40˚, 60˚ and 70˚.
The Earth Probe EP-TOMS instrument measures back-
scattered ultraviolet radiance from Earth at wavelength
bands centered at 308.6, 313.5, 317.5, 322.3 331.2 and
360.4 nm. One significant difference in the EP-TOMS
series from the previous Nimbus-7 and Meteor 3 TOMS
is a change is the wavelength selection for the 6 channels
of the three new instruments. Four of the nominal band
center wavelengths remain the same on all TOMS. Chan-
nels measuring at 340 nm and 380 nm have been elimi-
nated in favor of 309 nm and 322 nm on the new TOMS.
Ozone retrieval at 309 nm is advantageous because of the
relative insensitivity to calibration errors, though retriev-
als are limited to equatorial regions. Ozone retrievals at
high latitudes are improved because 322 nm is a better
choice for the optical paths encountered there [13]. Total
column ozone is inferred from the differential absorption
of scattered sunlight in the ultraviolet using the ratio of
two wavelengths, 312 nm and 331 nm for instance,
where one wavelength is strongly absorbed by ozone
while the other is weakly absorbed. TOMS is subject to
errors and random uncertainties. Some of these errors
come from the instrument and others from environmental
phenomenon. Aside from some known problems at spe-
cific times and locations, accuracy is believed to be
within 3% - 4% of actual ozone levels.
The magnetic activity as represented by the geomag-
netic index Dst. The hourly values of Dst were obtained
from the world Data Center at the University of Kyoto
database (
3. Results
In August 2005, the Sun released a solar flare (M5/1N)
associated with a CME (Halo/22 1730). Consequently
the flux of particles toward the Earth’s atmosphere was
greatly enhanced. A solar proton event began on 22 Au-
gust 2005 at 2040 UT, reaching a maximum on the fol-
lowing day at 1045 UT. Figure 1 shows the daily meas-
urements of the proton fluence taken by the GOES-11
satellite during August 2005 (
ftpmenu/warehouse/2005.html. For the more important
proton event occurred during August 2005 it can be seen
that the protons with different energies are increased by
several orders of magnitude. The flux of the protons with
energy > 10 MeV was about 1.60 × 104 protons cm2·
day1·sr1 prior to the solar flare, and reached a maximum
of 1.70 × 107 protons cm2·day1·sr1 on 23 August.
We focused the analysis on the geomagnetic storm that
took place two days after SPE. Figure 2 shows the geo-
magnetic index Dst for August 2005. It can be clearly
seen the only intense geomagnetic storm occurred that
month: the magnetic storm started on 24 August (kp =
46; Ap = 102) with a sudden commencement at 0613 UT.
An abrupt decrease is observed at about 11 - 12 UT that
day when Dst reached its minimum of –216 nT after
which started a relatively rapid recovery.
We selected ten magnetically quiet days of the month
of the storm to obtain an average pre-storm quiet level of
total ozone and calculate the average value and σ sepa-
rately for each latitudinal circle. The storm effect in the
Copyright © 2013 SciRes. ACS
1611 1621 26 31
> 1MeV> 10 M eV> 100 M eV
Figure 1. Daily values of proton fluence (protons/cm2/day/
sr) for August 2005, measured by GOES-11 satellite. Three
curves indicate protons with energies above 1, 10 and 100
12345678910 11 12 13 14 15 16 17 1819 20 21 22 23 24 25 26 27 28 29 30 31
Dst (n T )
Figure 2. Hourly variation of the geomagnetic index Dst for
August 2005. It can be observed the only intense storm oc-
curred that month.
total ozone may be considered as significant if the devia-
tion in individual storm days exceeds 2σ. This is the
usual criterion normally used to demonstrate the exis-
tence of a storm effect in variations of any geophysical
parameter [12]. Some cases with statistically significant
deviation (>2σ) and no statistically significant deviation
are shown in this paper.
Figures 3 and 4 display the longitudinal variation of
the total ozone at the latitudes 70˚N and 70˚S (summer
and winter hemispheres, respectively) for the storm pe-
riod 22-25 August together with ±2σ (thin curves). It can
be seen that the behavior of total ozone differs substan-
tially in the individual days and does not reveal any per-
sistent pattern. Statistically significant decreases in total
ozone are observed in the 30˚ - 120˚ longitude sector
(Northern Europe) on the storm day (24 August), and in
the longitude range 70˚ to 30˚ and 150˚ to 120˚ in
the Southern Hemisphere on 23 and 24 August. It can be
seen that individual days differ substantially and do not
reveal any persistent pattern.
Figure 5 shows the variation in total ozone at 60˚S
(winter). One can observe that the variations of total
ozone in the individual days show a similar trend. The
higher values of total ozone are observed in the east sec-
tor (about 60˚ - 120˚ longitude). Statistically significant
increases in total ozone are observed at longitudes be-
tween 120˚ and 60˚ and between +60˚ and +120˚ on
24-25 August, and statistically significant decreases at
higher longitudes (~ 150˚ - 180˚) in the west and the east
Latitude: + 70 degrees
Longit ude (degree s)
T otal ozone ( DU)
-2sig ma
Figure 3. Longitudinal variation of total ozone on 22-25
August 2005 along the latitudinal circle 70˚N for the geo-
magnetic storm occurred on 24 August. Thin curves indi-
cate +/2σ uncertainty.
Latitude: - 70 degrees
Longit u de ( deg re es)
T otal o z one (DU)
-2sig ma
Figure 4. Same as Figure 3 but for the latitudinal circle
Latitude: - 60 degrees
18015 01209060300-30-60-9 0-120-150-180
Longitude ( degr e es)
Total ozone (DU)
Figure 5. Same as Figure 3 but for the latitudinal circle
sectors. The total ozone at 60˚N in the summer hemi-
sphere (not shown here) reveals similar behavior that the
winter hemisphere.
Figure 6 shows the behavior in total ozone at the lati-
tude 40˚S. As at higher latitudes, the total ozone values at
mid latitudes differ each day and they do not reveal any
regular pattern. A statistically significant effect of the in-
tense geomagnetic storm in ozone is observed only be-
tween 120˚ and 100˚ of the Southern Hemisphere.
Similar result (not shown here) is observed for 40˚N.
Figure 7 presents the variation in total ozone along the
latitudinal circle 20˚S (winter). Statistically significant
increases can be observed between 60˚ and 150˚ on
24-25 August. The rest of the longitudinal sectors do not
present any evident effect of the geomagnetic storm on
total ozone.
In order to determine a possible longitudinal re-dis-
tribution of total ozone during a geomagnetic storm, we
calculated “the mean zonal total ozone” TO3-zonal. This
Copyright © 2013 SciRes. ACS
parameter was defined as follows: the quotient between
the difference of the average of the measurements taken
each 10 degrees during the storm days in each longitudi-
nal circle and the average pre-storm values above men-
tioned, and the average pre-storm values (in percentage).
Figures 8 and 9 show the results for the summer and
Latitude: - 40 degrees
18015012 09060300-30-6 0-90-120-150-180
Longitude ( deg r ee s)
T otal oz on e ( DU )
Figure 6. Same as Figure 3 but for the latitudinal circle
Latitud e: - 20 degrees
Longitude (degrees)
Total ozone (DU)
+2sig ma
Figure 7. Same as Figure 3 but for the latitudinal circle
Nort hern Hem isphere
22 2324 25
TO3-zonal (%)
20 40 60 70
Figure 8. Relative variation of the zonal mean total ozone
along several latitudinal circles (20˚, 40˚, 60˚ and 70˚) for
the Northern Hemisphere during the storm period 22-25
August 2005.
Southern Hemisphere
22 23 24 25
TO3-zonal (% )
-20 -40 -60 -70
Figure 9. Same as Figure 8 but for the Southern Hemi-
winter hemispheres respectively. At the Northern Hemi-
sphere (summer), the larger decrease is produced at 60˚N
(<5%); at higher latitudes (70˚N) the decrease is lower in
association with statistically significant decreases, while
at middle and low latitudes no substantial change is ob-
served (<1%). At the Southern Hemisphere (winter) the
larger decrease occurs in the high latitude region (<5%)
also in association with statistically significant decreases,
whereas at low latitude there is a small increase. The
magnitude of the changes in both hemispheres seems to
indicate that at 60˚N in the summer hemisphere and at
higher latitudes from the winter hemisphere there is a
decrease in ozone, while at the other latitudes would oc-
cur zonal re-distribution in ozone.
4. Discussion and Conclusions
This paper reports the longitudinal variation of the total
ozone measured along different latitudinal circles at the
Northern and Southern Hemispheres during the isolated
geomagnetic storm occurred on 24 August 2005.
The main observational results can be roughly summa-
rized as follows:
Along the latitudinal circles 70˚N and 70˚S statisti-
cally significant decreases in total ozone are observed
in the Northern Europe (30˚- 120˚ longitude sector)
on the storm day, and in the longitude range 70˚ to
30˚ and 150˚to 120˚ in the Southern Hemisphere.
Along the latitudinal circle 60˚S statistically signifi-
cant increases in total ozone are produced at longi-
tudes between 120˚ and 60˚ and between 60˚ and
120˚ and decreases at higher longitudes in the west
and east sectors on 24 August.
At mid latitudes (40˚S) no statistically significant
effect of geomagnetic storm in ozone is observed,
while at low latitudes (20˚S) they are sparse.
In general, the longitudinal distribution in total ozone
shows small loss in both hemispheres during SPE
event on 22 August 2005. At the NH the maximum
loss is observed around the 60˚N latitudinal circle
(~5%); around the longitudinal circles corresponding
at 40˚ N and 70˚ the loss is of the order 1% - 2%. At
the SH no significant production in total ozone is ob-
served at around the 20˚ longitudinal circle (~1% -
2%), almost no changes at 40˚S and 60˚S, and at 70˚
loss in the total ozone (~5%) the day of the greater
proton fluence. These results seem to suggest a redis-
tri- bution of the total ozone only in some latitudinal
cir- cles, where the relative deviation of the “zonal
total ozone” is lower than 1% - 2%. It might owe to
changes in the stratospheric storm-time circulation
which could produce redistribution of ozone along
longitudinal circles.
The results obtained here suggest that total ozone is
affected by geomagnetic disturbances. According to [11],
Copyright © 2013 SciRes. ACS
the Northern Hemisphere is not under all the favourable
conditions for a significant ozone response during the
considered event because NH is in the summer season.
Analyzing 5 strong geomagnetic storms occurred in
July-August for the period 1982-1991, [12] found that
contrary to the Northern Hemisphere, detectable effects
of geomagnetic storms on total ozone do not occur at the
Southern Hemisphere higher middle latitudes. On the
contrary, we found longitudinal variations at 60˚ - 70˚ in
winter in the Southern Hemisphere.
Some total ozone column depletions are observed near
the south boundary of the Atlantic South magnetic
anomaly and close to the boreal geomagnetic pole which
suggests that geomagnetic field longitude seems to play
an important role in ozone variation. The ozone change
in the South Atlantic anomaly agrees with [14], who ob-
served mesospheric ozone depletion in that region.
There is an evident depletion of total ozone (~5%) dur-
ing the strong geomagnetic storm in the 60˚N and 70˚S
longitudinal circles. During both quiet and disturbed
conditions the Antarctic polar vortex creates ozone de-
pletion. A speculative and no verifiable explanation is
that the polar vortex plays a significant role in the loss of
ozone at high latitudes of the winter hemisphere during
the storm. However, satellite observations taken during
polar winter in the Antarctic indicate NOx enhancements,
which occur in good correlation with levels of enhanced
high-energy particle precipitation (associated with SPEs)
and/or geomagnetic activity (e.g., [6,15]).
A possible explanation of the depletion of ozone in the
Northern Hemisphere could be related with changes in
HOx and NOx. In fact, upper stratospheric enhancements
in NOx were measured at northern high latitudes during
storms [16,17]. Measurements from the UARS HALOE
and NOAA 14 SBUV/2 instruments indicate short-term
(~day) middle mesospheric ozone decreases for over
70% caused by short-lived HOx during a SPE with a
longer-term (several days) upper stratospheric ozone
depletion of up to 9% caused by longer-lived NOx.
Unfortunately no available study about the changes of
NOx in the middle atmosphere in the case of this SPE has
been found, which prevents the confirmation of that as-
The ozone depletion observed in summer differs from
the results obtained by other authors who found that sig-
nificant effects of geomagnetic storms on total ozone
(redistribution in ozone, not ozone production or loss)
have been observed only in winter and for strong storms
(Ap > 40) and only under specific conditions [11,18,19].
Because each storm has its individual characteristics we
believe that actual patterns of response are not consistent
yet because deviations from the model pattern are ob-
served. For that reason more case studies are necessary to
obtain some common/consistent storm-time features.
In summary, we analyzed the short-term response of
the total ozone content to an isolated geomagnetic storm
along several latitudinal circles from both hemispheres
(summer and winter). The total ozone content exhibits
redistribution at middle and low latitudes (20˚ - 40˚) in
both hemispheres and decreases at higher latitudes (in
winter and summer) the days of great proton fluence.
This result is a new one and can be considered as the
main contribution of this paper to current community
knowledge on total ozone storm effects because it differs
from obtained by other authors [12]. It is clear that the
present results may be significant and could have impor-
tant implications for the study of the behavior of the at-
mosphere during geomagnetic storms, contain little sta-
tistical information. Because of the discrepancy of the
results for the different authors, it is evident that it is nec-
essary to perform further analysis of satellite measure-
ments in order to infer a statistics about the standards of
behavior of the total ozone during disturbed periods.
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