Ozone dec ease obse ed in he uppe a mosphe e ollowing he
May 11 h 2024 Mo he ’s day sola s o m.
Alexand e Winan 1, 2, Vi iane Pie a d1, 2, and Edi h Bo ek1
1Sola Wind, Space Physics and Sola -Te es ial Cen e o Excellence, Royal Belgian Ins i u e o Space Ae onomy
(BIRA-IASB), A enue Ci culai e 3, B ussels, Belgium
2Cen e o Space Radia ions (CSR), Ea h and Li e Ins i u e, Clima e Sciences ELI-C, Uni e si é Ca holique de Lou ain
(UCLou ain), Lou ain-la-Neu e, Belgium
Co espondence: Alexand e Winan (ale[email p o ec ed])
Abs ac . On May 11 h 2024, a succession o co onal mass ejec ions ha me ged oge he s uck he Ea h and induced la ge
scale pe u ba ions in he magne osphe e. Du ing his e en , sa elli e obse a ions showed a la ge sola ene ge ic p o on (SEP)
e en associa ed o an ex eme geomagne ic s o m. A he same ime, sa elli e obse a ions o a mosphe ic ozone ha e been
pe o med by AURA/MLS. In his wo k, we p esen he i s obse a ions o he e ec o he s o m o May and he ollowing
SEP o June 8 h on ozone concen a ion h oughou he a mosphe e. Obse a ions o he MLS show ha he e en o May lead5
o s onge deple ion o O3in he uppe pa o he a mosphe e han in June. This di e ence is explained by he ype o pa icle
p ecipi a ion ha occu ed du ing he wo e en s, wi h bo h p o ons and elec ons in May and only p o ons in June. Nei he
e en caused ozone deple ion in he s a osphe e while s ong dec eases a e obse ed in he mesosphe e. In May, mesosphe ic
ozone deple ion is obse ed du ing 18 days and eaches a maximum o 60%. In addi ion, he s o m o May also caused a
no iceable dec ease in ozone concen a ion (up o 20%) a al i udes abo e 90 km.10
1 In oduc ion
While sola cycle 25 is app oaching i s maximum ac i i y (p edic ed in 2025), he p obabili y o s ong sola e en s is also
expec ed o ise. Bo h he equency and he in ensi y o sola e en s inc ease a ound he maximum and he declining phase
o he cycle. The yea 2024 is loca ed a he end o he ascending phase o cycle 25, making i p one o be subjec ed o
la ge pe u ba ions o sola o igin. On he 11 h o May 2024, an ex eme geomagne ic s o m associa ed wi h a la ge Fo bush15
deac ease in galac ic cosmic ays we e obse ed on he g ound Ma omichalaki e al. (2024). The cause o he ex eme e en
o May 2024 is a succession o CMEs (Co onal Mass Ejec ions) ha me ged oge he and simul aneously s uck he Ea h,
which lead o an ex eme pe u ba ion o he magne osphe e Kwak e al. (2024). Mo eo e , a la ge Sola Ene ge ic Pa icle
(SEP) e en was obse ed in he icini y o he Ea h by space bo ne pa icle de ec o s Pie a d e al. (2024). This geomagne ic
s o m is he la ges obse ed in mo e han 20 yea s, eaching a minimum Dis u bed S o m ime index Ds min =−412 nT20
and a maximum Ba els plane a y index o geomagne ic ac i i y Kpmax = 9. The las obse a ion o an e en wi h a simila
magni ude da es back o he amous 2003 Halloween geomagne ic s o m wi h a minimum Ds mina ound −400 nT. The
geomagne ic s o m o May 11 h was esponsible o la ge a ia ions in he adia ion bel s o he Ea h, in which a empo a y 4
1
bel s s uc u e was obse ed a low Ea h o bi Pie a d e al. (2024). On he 8 h o June 2024, 27 days a e he ex eme e en
o May, ano he SEP e en has been obse ed nea Ea h.25
Enhanced geomagne ic ac i i y also leads o inc eased ene ge ic elec on p ecipi a ion (EEP) in he a mosphe e a high
la i ude which mainly consis o au o al elec ons o igina ing om he magne o ail and adia ion bel elec ons in he bounce
loss cone. Ene ge ic p o ons o sola o igin also p ecipi a e in he a mosphe e as hey a e guided owa d high la i udes by
he Ea h’s magne ic ield. As hey pene a e in o he a mosphe e, ene ge ic pa icles in e ac wi h he cons i uen s o he
a mosphe e inducing hei exci a ion, dissocia ion and ioniza ion Sinnhube e al. (2012); Mi ono a e al. (2015). Following30
he in e ac ion o he a mosphe e wi h he ene ge ic p ecipi a ing pa icles (EPP), complex chains o chemical eac ions ake
place in di e en laye s o he a mosphe e which can lead o he o ma ion o odd hyd ogen (HOx=H+HO+HO2)and odd
ni ogen (NOx=N+NO+NO2) ia ion-neu al chemis y Ve onen and Lehmann (2013). NOxa e mainly p oduced in he
uppe pa o he a mosphe e, in he mesosphe e (50 o 90 km) and lowe he mosphe e, whe e hei p oduc ion a e is inc eased
by EPP Sæ e e al. (2004). Those species a e long li ed in he a mosphe e, especially du ing pola win e . In he p esence o he35
pola o ex, NOxp oduced in he mesosphe e and lowe he mosphe e (MLT) egion can be e icien ly anspo ed downwa d
o he s a osphe e (10 o 50 km in a e age) and deple e he ozone in his egion o he a mosphe e Randall e al. (2007); Funke
e al. (2014, 2016). Mesosphe ic HOxle els ha e been obse ed o co ela e wi h he p ecipi a ion o elec ons om he
adia ion bel s Ve onen e al. (2011); Ande sson e al. (2012). HOxa e sho li ed, hus hei esponse o EPP is localized in
space and ime, whe e and when ioniza ion is inc eased Mi ono a e al. (2015). HOxand NOxcon ibu e o he deple ion o 40
ozone h ough ca aly ic eac ions La y (1997). Thus, he ne esul o EPP is o con ibu e o dec ease he ozone concen a ion
in he a mosphe e and can ha e epe cussion on clima e Rozano e al. (2012); Seppälä e al. (2014).
The esponse o ozone in he a mosphe e o EPP (o bo h p o ons and elec ons) has been ex ensi ely s udied o e he yea s.
Ene ge ic Elec on P ecipi a ions (EEP) ha e been ound o ha e a signi ican in luence on O3in he mesosphe e be ween 60 km
and 80 km, whe e i could be deple ed by 90% on a sho e m scale Ande sson e al. (2012). Because hey ha e he possibili y45
o ionize lowe laye s in he a mosphe e, ene ge ic sola p o ons may con ibu e o deple e ozone in he uppe s a osphe e.
Howe e , s ong e idence o SEP di ec ly deple ing s a osphe ic ozone a e sca ce. In he s udy o Jia e al. (2020), changes o
ozone we e obse ed by MLS a e SEPs be ween 2004 up o 2020. Al hough clea ozone deple ion can be obse ed a high
al i udes ollowing mul iple SEPs, only one e en was ound o ha e an e ec on he s a osphe ic ozone.
In his pape , we use obse a ions om he Mic owa e Limb Sounde (MLS) o in es iga e and p o ide a i s epo o he50
e ec o he ex eme sola and geomagne ic e en o May as well as he ollowing SEP o June on a mosphe ic ozone in he
pola egions.
2 Da a and me hods
2.1 Ozone obse a ions om AURA/MLS
The Mic owa e Limb Sounde (MLS) as pa o he Ea h Obse ing Sys em (EOS) E ans and G ee (2000) was launched in55
2004 onboa d he NASA sa elli e AURA on quasi-pola sun-synch onous o bi a 705 km o al i ude. This ins umen measu es
2
he mal adia ion om Ea h’s a mosphe e e ie ing e ical p o iles o he empe a u e and ace gases by scanning Ea h’s
limb in he plane o i s o bi . In his wo k, we mainly use ozone p o iles om he MLS ha a e de i ed om adiances
measu ed by he 240 GHz adiome e . Mo e speci ically, we use he la es e sion 5.0 o he MLS da a p oduc wi h a spa ial
co e age anging om -82° o 82° and ha has an inc eased e ical ange compa ed o p e ious e sions. Wi h 5.0, ozone60
obse a ions in he uppe mesosphe e a e a ailable o scien i ic s udies. In his wo k, we ha e applied all ecommenda ions
ega ding da a sc eening p o ided in he MLS Le el 2 Ve sion 5 Quali y Documen ha can be ound a (h ps://mls.jpl.nasa.
go /da a/ 5-0_da a_quali y_documen .pd ). Mo eo e , we only use high la i ude obse a ions, comp ised be ween 60° and 90°
in bo h hemisphe es and hen pe o m daily a e ages which a e necessa y o he highes al i udes in he mesosphe e. (Le el 2
ozone da a om MLS a e a ailable a h ps://disc.gs c.nasa.go /da ase s/ML2O3_005/summa y, las accessed on 29/10/2024)65
2.2 In si u obse a ions o ene ge ic pa icles
Fo he sola p o on luxes, we use he obse a ions om he Geos a iona y Ope a ional En i onmen al Sa elli e (GOES) which
is i ed wi h he Ene ge ic P o on, Elec on, and Alpha De ec o (EPEAD). This ins umen measu es he lux o p o ons in 7
ene gy channels spanning om 0.74 o 900 MeV. The da a used in his wo k consis s o in eg al p o on luxes wi h ene gies
>10 MeV, >30 MeV, >100 MeV which ha e a esolu ion o 5 minu es. (Da a a e accessible a : h ps://lasp.colo ado.edu/70
space-wea he -po al/, las accessed on 29/10/2024)
In o de o de e mine when ene ge ic elec ons om he adia ion bel s p ecipi a e in o he a mosphe e, we use he POES/MEPED
de ec o . The MEPED ins umen is composed o wo pai s o di ec ional de ec o s. The i s pai is dedica ed o he measu e-
men o p o ons wi h ene gies anging om 30 keV o 200 MeV. The second pai o de ec o s measu es he luxes o elec ons
o ene gies be ween 30 keV o 2500 keV in 3 in eg al channels. Fo a gi en ype o pa icles, he wo elescopes a e a anged75
pe pendicula o one ano he and a e e e ed o as he 0° elescope and he 90° elescope. On Me Op, he 0° elescope poin s
di ec ly o he zeni h and he 90° elescope poin s o he an i am di ec ion (i.e., opposi e o he eloci y ec o o he spacec a ).
A high la i udes, he 0° elescope mainly measu es pa icles in he Bounce Loss Cone (BLC) and hus p ecipi a ing in o he
a mosphe e.
2.3 Assessing he impac on ozone and empe a u e80
The main s a egy o quan i y he e ec o he May and June e en s on ozone h ough he a mosphe e is aking he a e age
p o ile o ozone be o e he e en (quie ozone p o ile), and compu ing i s di e ence ela i e o he daily p o iles o he es
o he mon h. The quie pe iod consis s o he i e daily p o iles obse ed be o e ei he he maximum p o on lux obse ed by
GOES o he minimum in he Ds index. Those p o iles a e hen a e aged on ime o p o ide he quie condi ions.
Ano he app oach used in his wo k is o i s compu e he long e m end in he p o iles obse ed by MLS. In o de o do85
so, a lowess (locally weigh ed sca e plo smoo hing) algo i hm was applied o he daily p o iles om MLS spanning om
Janua y 1s 2024 o June 30 h. Wi h he esul s o he lowess algo i hm, he daily de ended p o iles a e compu ed, e ealing
only he sho e m a ia ions which can hen be compa ed o daily a e aged geomagne ic ac i i y.
3
3 Resul s
Figu e 1 shows he daily a e aged MLS ozone p o iles a high la i udes om he beginning o 2024 o June 30 h. The op90
panel co esponds o he high sou he n la i udes comp ised be ween -60° and -90° o la i ude and he middle panel co esponds
o he no he n la i udes comp ised be ween 60° and 90°. The las panel o his igu e shows he geomagne ic ac i i y o he
pe iod, displaying bo h he Ds and Kp indices. The bo om panel o he igu e indica es ha du ing he beginning o he yea ,
he geomagne ic ac i i y is e y low, wi h he Kp index ba ely exceeding 4. I is only in Ma ch ha a no iceable geomagne ic
s o m was eco ded in bo h Ds and Kp. The nex big e en ook place in mid Ap il wi h a Ds below -100 nT and a Kp o 95
7. Fo m his poin onwa d, hese indices show ha he magne osphe e was epea edly dis up ed by in ense s o ms un il he
ex eme e en o May 11 occu ed wi h a minimum Ds alue ne e seen in 20 yea s o - 412 nT and a Kp o 9. Du ing he
eco e y phase o his majo e en , some o he in ense e en s ook place and he Ds index emained quie un il he end o June.
All along his pe iod, he AURA/MLS ins umen con inuously ca ied ou measu emen s o ozone h oughou he a mo-
sphe e. The i s panel o Fig. 1 clea ly illus a es he di e en ozone laye s ha exis in he a mosphe e. The main ozone laye 100
loca ed in he s a osphe e, he seconda y laye in he uppe mesosphe e and lowe he mosphe e (MLT) egion and inally he
e ia y laye in he mesosphe e whe e he maximum o ozone concen a ion is obse ed a a ound 75 km. Bo h he second
and hi d ozone laye s a e subjec ed o e y s ong seasonal a ia ions and a e mos ly deple ed du ing local summe due o
inc eased pho odissocia ion Ma sh e al. (2001); Smi h and Ma sh (2005); Smi h e al. (2018).
Thus in he no he n hemisphe e (NH), he ozone o ming he seconda y and e ia y laye s g adually ge s deple ed om105
win e o summe , when he mesosphe ic ozone is comple ely emo ed om he a mosphe e and he seconda y laye ozone is
educed om be ween 7 and 8 ppm o be ween 1 and 2 ppm . In he sou he n hemisphe e (SH) (middle panel o Fig. 1), he
si ua ion is e e sed and ozone s a s o accumula e in he mesosphe e and he lowe he mosphe e.
In addi ion o he s ong seasonal a ia ions o ozone, he i s and second panel o he igu e clea ly show ha he ozone
also expe iences sho e m a ia ions. Those a ia ions on smalle ime scales a e no linked o geomagne ic s o ms illus a ed110
by high peaks o geomagne ic ac i i y in he bo om panel, in any o he ozone laye s.
In o de o obse e a di ec e ec o sola ene ge ic pa icles (SEP) in he s a osphe ic ozone laye , he e mus be a signi ican
lux o p o ons wi h su icien ene gy o ionize he s a osphe e. Be ween Janua y and May, some mino SEP e en s did occu
bu hey had low luxes and a so spec um which could no ha e impac ed he s a osphe ic ozone. So p o ons can deposi
hei ene gy in he mesosphe e, and some apid dec eases in O3happened in he NH a e he pa icles injec ions a high115
al i udes, bu no always. A e he May 11 e en s, no ozone is le in he uppe pa o he a mosphe e so ha no ozone is los
u he . Despi e hei ha d spec um and high luxes, nei he he May no he June SEPs (see Fig. 2) ha e had any impac on
he NH main ozone laye . One o he easons migh be due o he weakening o he pola o ex in he NH du ing la e sp ing
and summe .
In he SH, in he beginning o he yea , no sho e m a ia ion o O3has been obse ed by MLS. Howe e , he middle panel120
o Fig. 1 clea ly shows a change o ozone concen a ion in he MLT egion (a ∼90 km) as well as in he mesosphe e (a ∼75
km) a e he e en o May. In he s a osphe e, no sign o he e en o May is disce nible in he igu e.
4
Figu e 1. Daily a e aged high la i ude ([60°, 90°]) ozone olume mixing a io p o iles om AURA/MLS as a unc ion o ime and al i ude
be ween Janua y 1s and June 30s 2024. Top: no he n hemisphe e. Middle: sou he n hemisphe e. Ozone olume mixing a ion is exp essed
in pa s pe million by olume (ppm ). Bo om: Geomagne ic ac i i y indices om he OMNI da abase be ween Janua y 1s and June 30 h.
The Dis u bed s o m ime (Ds ) index is ep esen ed in blue and he plane a y Kp index mul iplied by 10 is displayed in ed.
The lux o EPP be ween May 1s and June 30 h 2024 a e p esen ed on he wo panels o Fig. 2. On he op, GOES
obse a ions o he in eg al p o on luxes wi h di e en ene gy h eshold clea ly show he wo SEP e en s o May 11 h and
June 8 h. This panel e eals ha each o he wo SEPs ha e a double peak in p o ons o >10 MeV and >30 MeV bu no o 125
p o ons wi h ene gies >100 MeV. The p o on lux measu ed by GOES in June is e y simila o he lux o May (see Fig. 2
op panel), because hey o igina e om he same egion o he Sun and hey a e sepa a ed in ime by one sola o a ion.
The second panel o Fig. 2 displays he in eg al lux o elec ons wi h ene gies >30 keV obse ed by he MEPED 0°
elescope du ing he same pe iod as GOES. In his case, he elec on luxes a e p esen ed as a unc ion L, he McIlwain
pa ame e (uniquely iden i ying Ea h’s magne ic shells) and ime. Elec on luxes ha e been a e aged on L- ime bins o 0.1 L130
and 3 hou s. A high la i udes and hus high L alues, elec ons obse ed by he 0° elescope a e conside ed o p ecipi a e in o
he a mosphe e along he magne ic ield lines Rodge e al. (2010). Unlike SEP e en s, elec on p ecipi a ion in he a mosphe e
is a p ocess ha is cons an ly occu ing bu i is modula ed by geomagne ic ac i i y. Inc eased p ecipi a ion has been obse ed
du ing he main phase o he geomagne ic s o m o May 11 eaching he maximum lux o ∼1.2 106[cm2s s ]−1which is
ne e a ained again h oughou he whole pe iod.135
As ozone concen a ion in he a mosphe e is subjec o seasonal a ia ions and changes on longe ime scales such as he
sola cycle, we compu ed he long e m a ia ions in he MLS obse a ion in o de o ex ac only he ozone changes on small
5
Figu e 2. Top: In eg al p o on lux measu ed by GOES be ween May 01 and June 30, 2024 in h ee di e en ene gy channels. Bo om:
In eg al elec on lux wi h ene gy >30 keV measu ed by POES 0° elescope and a e aged in L- ime bins [0.1L - 3h] displayed as a unc ion
o ime and he McIlwain pa ame e o e he he same ime pe iod.
Figu e 3. Top panel: The plain lines ep esen he daily a e aged ozone m compu ed wi h AURA/MLS obse a ions om May 1s and
June 30 h in he Sou he n hemisphe e. The dashed lines a e he compu ed long e m ends in ozone m esul ing om he lowess algo i hm
applied on he obse a ions om Janu ay o June. Each colo co esponds o an al i ude le el. Bo om panel: The daily de ended ozone m .
Colo s a e he same as o he op panel. The black line ep esen s he daily a e aged Kp index mul iplied by 10 compu ed om omni da a.
ime scales be ween May 1s and June 30 h. The long e m end in MLS obse a ions was compu ed by applying he lowess
algo i hm on he daily ozone p o iles. To ensu e ha he esul s o he algo i hm could cap u e he seasonal a iabili y, we used
he da a om Janua y 1s o June 30 h o compu e he end. The esul o his da a ea men is shown in he op panel o Fig.140
3 oge he wi h he daily a e age ozone olume mixing a io ( m ). Each colo in he igu e ep esen s an al i ude le el anging
om 70 km o 97 km, co e ing he mesosphe e and lowe he mosphe e. The bo om panel o he igu e shows he de ended
6
ozone m (i.e., daily ozone m minus he long e m end) a each al i ude le el. The black cu e in his panel co esponds o
he daily a e aged Kp index(mul iplied by 10) compu ed om he OMNI da ase . F om his panel, i is clea ha , ollowing he
peak in he Kp index which indica es he main phase o he geomagne ic s o m o May 11 h, a apid dec ease in ozone m is145
obse ed by he MLS. I hen equi ed 18 days o he ozone m o egain he p e-s o m le els. In June, no majo geomagne ic
s o m ook place as shown by he daily Kp cu e. Howe e , he de ended ozone shows a no iceable dec ease on he 7 h o
June a 84 km. A highe al i udes, he dec ease in ozone occu s on he 9 h, a e he SEP e en ook place.
Figu e 4 displays he esul s o he ela i e di e ence in pe cen age be ween he p e-s o m (i.e. quie ) ozone m ( op panel),
as well as empe a u e p o ile (bo om panel) and all he daily p o iles measu ed om he s a o he pe iod un il he end o he150
mon h. The quie pe iod consis s o he ime a e ages o he daily p o iles be ween May 5 h and May 9 h. The eason o no
aking he p o iles be ween he 6 h and 10 h is ha , e en i he peak o he SEP lux and he main phase o he geomagne ic
s o m ook place on May 11 h, he lux o lowe ene gy p o ons (>10 MeV) has a i s peak on he 10 h o May. So ha May
10 h is nei he conside ed as a quie day no is he peak o he e en (when conside ing he p o on spec um and he geomagne ic
ac i i y). The op panel shows he ela i e di e ence compu ed wi h O3 m and he bo om panel wi h empe a u e.155
Figu e 4. Top panel: Rela i e di e ence in [%] be ween he mean quie condi ion ozone p o iles (Oq
3) and he daily ozone p o iles om
AURA/MLS, du ing he whole pe iod be ween May 05 and May 30 (O3). Bo om: same o empe a u e p o iles. Quie condi ions co espond
o he pe iod spanning om May 5 o May 9, 2024. The e ical black line displays he day when he daily Ds index eached i s minimal
alue, indica ing he end o he main phase o he geomagne ic s o m on May 11 also co esponding o he peak p o on lux o he e en .
F om he op panel o he igu e, i is ob ious ha some ozone was los du ing he pe iod o in e es . The e ical black
do ed line indica es he day du ing which he daily a e aged p o on lux and geomagne ic ac i i y a e he highes (i.e. May
11 h). The main ozone loss was obse ed a e he e en in he e ia y laye a a ound 75 km. Howe e , he day be o e, on
May 10 h, he ozone m a hose al i udes had al eady dec eased by 20%. This p ema u e dec ease migh be caused by he
pene a ion o he low ene gy p o ons measu ed by GOES on ha day, which e icien ly deposi hei ene gy a ound 70 km160
7
(see Fig. 1 o Sá o i e al. (2016)). Two days a e he main phase o he s o m, ozone m a 80 km dec eased by as much as
60%. This ozone de ici ela i e o p e-s o m le el emained un il May 29 h, oscilla ing be ween 30 % o 50%. Mo eo e , a e
he e en un il May 17 h, he loss in ozone was obse ed in he e ia y laye be ween 70 km and 80 km. A hose al i udes
howe e , only a ound 20% o he ozone is deple ed om he mesosphe e. This ozone dec ease is only obse ed down o 70 km
un il May 18 h. In addi ion o he mesosphe ic ozone loss, in he MLT egion abo e 90 km, a smalle deple ion is obse ed by165
MLS. As o he lowe al i udes, he dec ease o ozone m in he MLT seems o s a one day be o e he peak o he s o m.
Howe e , he ozone loss is ela i ely small, mainly emaining below 10%. None heless, he ozone deple ion eached 20% and
15% on May 13 h and 17 h espec i ely co esponding o pe iods o inc eased elec on p ecipi a ion (see Fig. 2 bo om panel).
Finally, no signi ican change in O3 m has been obse ed by MLS a e he s o m o May in he s a osphe e.
The bo om panel o Fig. 4 is he same as he op panel bu o he empe a u e measu emen s om MLS. The changes170
obse ed du ing his pe iod a e con ined be ween -5% and 5% h ough he en i e al i ude ange. Howe e , i is appa en in he
igu e ha a e he s o m and SEP o May 11 h, he en i e a mosphe e abo e 75 km hea s up while below his al i ude, he
gene al end is a cooling, excep om May 27 h o he 31 h be ween 45 km and 70 km. I is impo an o no e ha he wa ming
o he uppe a mosphe e s a s wo days be o e he e en . As o he ozone, his p ema u e a mosphe ic wa ming coincides wi h
he ea ly a i al o low ene gy p o ons in he a mosphe e, as well as an ea ly inc ease o elec on p ecipi a ion be o e he SEP175
ook place. Below 40 km, he empe a u e cons an ly dec eases om he e en onwa d. Howe e , his change in empe a u e is
caused by he seasonal a iabili y. The hea ing obse ed in he uppe pa o he a mosphe e is mos likely caused by pa icle
hea ing and joule hea ing. A pa o he ene gy o he EPP is los as hea in he a mosphe e and some o i s ene gy is dissipa ed
when hey mo e in he e ec i e elec ic ield o he Ea h Sinnhube e al. (2012).
Figu e 5. Top panel: Rela i e di e ence in [%] be ween he mean quie condi ion ozone p o iles (Oq
3) and he daily ozone p o iles om
AURA/MLS, du ing he whole pe iod be ween June 02 and June 30 (O3). Bo om: same o empe a u e p o iles. Quie condi ions co espond
o he pe iod spanning om June 02 o June 07, 2024. The e ical black line displays he day o peak p o on lux o his e en .
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The wo panels o Fig. 5 a e simila o hose o Fig. 4 bu o MLS obse a ions jus be o e and a e he SEP o June180
8 h. Again, he op panel shows he esul s o ozone. Despi e being mo e in ense han in May, his SEP had no in luence
on he s a osphe ic ozone. A a ound 50 km, he ozone m g adually dec eases om he ime o he SEP onwa d. Below
his al i ude, no no iceable change was obse ed by MLS. The slow ozone deple ion a 50 km can be explained by long e m
(seasonal) a ia ions a he han he e ec o EPP (see Fig. 1 middle panel). The day ollowing he p o on injec ion o June,
AURA/MLS measu emen s show a deple ion o 60% in ozone m a 80 km. Al hough no as in ense as a 80 km, he deple ion185
in O3 m occu ed be ween 70 km and 90 km and was o abou 20%. In he MLT egion, no change in ozone is disce nible in
he obse a ions.
The bo om panel o he igu e shows he ela i e di e ence in a mosphe ic empe a u e. The maximum changes in em-
pe a u e obse ed in June a e limi ed be ween -2% and 2%, which is qui e less ha in May. As in May, below 40 km, he
empe a u e obse a ions show a s eady dec ease caused by seasonal a ia ions as win e s a s in he SH. Be ween 40 km and190
80 km, he gene al beha io o he a mosphe e is a small wa ming which is las ing o he whole pe iod as is no likely o be
linked o he p o on p ecipi a ion.
4 Discussion and conclusions
In his wo k, we p esen ed he i s obse a ions o he a mosphe ic ozone esponse o he ex eme geomagne ic s o m and SEP
ha ook place on May 11 h and June 8 h 2024. We mainly used AURA/MLS obse a ions which p o ided measu emen s o 195
ozone and empe a u e p o iles a high la i ude in bo h hemisphe es due o i s low Ea h o bi .
The esponses o ozone and empe a u e o he e en o May 11 h and June 8 h a e qui e di e en . Much s onge and longe
las ing ozone deple ion is obse ed h ough he a mosphe e in May han in June. Howe e , his is easily explained by he
di e ence in he lux o EPP du ing he wo e en s. In May, an o e lap be ween ene ge ic sola p o ons obse ed by GOES
and s ongly enhanced elec on luxes om he adia ion bel s obse ed by POES ha e p ecipi a ed in he a mosphe e. In June,200
elec on p ecipi a ion is obse ed he day be o e he SEP eached he Ea h, bu does no con inue due o he lack o s ong
geomagne ic dis u bances o his e en .
Aside he seasonal a ia ions, he e is a clea di e ence in he beha io o ozone in he no he n and sou he n hemisphe e
a e he p ecipi a ion o ene ge ic pa icles in he high la i ude a mosphe e. Du ing he e en o May 11 h, MLS obse a ions
show a clea dec ease o ozone in he sou he n pola mesosphe e. In he no he n hemisphe e howe e , only wo sho li ed205
dec eases in ozone ook place in he MLT egion abo e 90 km, on May 13 h and on he 17 h, each o hem las ing o
wo days. These in e -hemisphe ic di e ences a e s ongly linked o he local season. Fo geomagne ic ac i i y, hence elec on
p ecipi a ion, Mi ono a e al. (2023) showed h ough a one dimensional Radia i e-Con ec i e Pho ochemical model ha ozone
deple ion in he mesosphe e we e only possible du ing local sp ing, win e and all, wi h he s onges one only aking place in
win e . Those conclusions also apply o sola p o ons as shown wi h MLS obse a ions be ween 2004 and 2024 by Do onin210
e al. (2024) and by Xiong e al. (2023) o he se e e SEP o Janua y 2012. In ou obse a ions o he June SEP, no signi ican
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