Ica us 361 (2021) 114394
A ailable online 24 Feb ua y 2021
0019-1035/© 2021 The Au ho s. Published by Else ie Inc. This is an open access a icle unde he CC BY-NC-ND license
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Jupi e ’s hi d la ges and longes -li ed o al: Colo changes and dynamics
N. Ba ado-Izagi e
a
,
*
, J. Lega e a
b
, A. S´
anchez-La ega
a
, S. P´
e ez-Hoyos
a
, R. Hueso
a
,
P. I˜
nu iga o
a
, J.F. Rojas
a
, I. Mendikoa
a
, I. O do˜
nez-E xebe ia
a
, he IOPW Team
c
a
Depa amen o de Física Aplicada I, Escuela de Ingenie ía de Bilbao, Uni e sidad del País Vasco UPV/EHU, Plaza To es Que edo 1, 48013 Bilbao, Spain
b
Depa amen o de Ingenie ía de Sis emas y Au om´
a ica, Escuela de Ingenie ía de Bilbao, Uni e sidad del País Vasco UPV/EHU, Plaza To es Que edo 1, 48013 Bilbao,
Spain
c
Escuela de Ingenie ía de Bilbao, Uni e sidad del País Vasco UPV/EHU, Plaza To es Que edo 1, 48013 Bilbao, Spain
ARTICLE INFO
Keywo ds:
Jupi e
A mosphe es dynamics
Jupi e a mosphe e
ABSTRACT
The ansi ion egion be ween he No h Equa o ial Band (NEBn) and No h T opical Zone (NT Z) in Jupi e is
home o con ec i e s o ms, sys ems o cyclones and an icyclones and a mosphe ic wa es. Zonal winds a e weak
bu ha e a s ong la i udinal shea allowing he o ma ion o cyclones ( ypically da k) and an icyclones ( ypically
whi e) ha emain close in la i ude. A la ge an icyclone o med in he yea 2006 a plane og aphic la i ude 19◦N
and pe sis s since hen a e a complex dynamic his o y, being possibly he hi d longes -li ed o al in he plane
a e Jupi e ’s G ea Red Spo and o al BA. This an icyclone has expe ienced close in e ac ions wi h o he o als,
me ging wi h ano he o al in Feb ua y 2013; i has also expe ienced colo changes, om whi e o ed (Sep embe
2013) and back o whi e wi h an ex e nal ed ing (2015–2016). The o al su i ed he e ec s o he closely
loca ed No h Tempe a e Bel Dis u bance, which occu ed in Oc obe 2016 and ully co e ed he o al, ende ing
i unobse able o a sho ime. When i became isible again a i s expec ed longi ude om i s p e ious lon-
gi udinal ack, i eappea ed as a whi e la ge o al keeping his colo and he same mo phology since 2017 a
leas un il he onse o he new con ec i e dis u bance in Jupi e ’s No h Tempe a e Bel in Augus 2020. He e
we desc ibe he his o ic e olu ion o he p ope ies o his o al. We use JunoCam and Hubble Space Telescope
(HST) images o measu e i s size ob aining a mean alue o (10,500 ±1000) x (5,800 ±600) km
2
and i s in e nal
o a ion inding a alue o -(2 ±1)⋅10
−5
s
−1
o i s mean ela i e o ici y. We also used HST and Plane Cam-
UPV/EHU mul i-wa eleng h obse a ions o cha ac e ize i s colo changes and Junocam images o un eil i s
de ailed s uc u e. The colo and he al i ude-opaci y indices show ha he o al is highe and has edde clouds
han i s en i onmen bu has lowe cloud ops han o he la ge o als like he GRS, and i is less ed han he GRS
and o al BA. We show ha in spi e o he d ama ic en i onmen al changes su e ed by he o al du ing all hese
yea s, i s main cha ac e is ics a e s able in ime and he e o e mus be ela ed wi h he a mosphe ic dynamics
below he obse able cloud decks.
1. In oduc ion
The ubiqui ous p esence o o ices a cloud le el is one o he mos
impo an cha ac e is ics o he me eo ology o he gian plane s along
wi h he zonal winds o ganized in a mul iple je sys em. Jupi e is he
mos p oli ic plane in showing a g ea a ie y o closed ci cula ion
o ices (Roge s, 1995). Vo ices wi h sizes abo e 2000 km a e obse ed
a all la i udes o he Jo ian disk excep e y close o he Equa o (Mac
Low and Inge soll, 1986; Mo ales-Jube ias e al., 2002a, 2002b; Li e al.,
2004). Recen obse a ions ob ained by he Juno mission show also
s able cyclones close o bo h poles (O on e al., 2017; Ad iani e al.,
2018, 2020; Taba aba-Vakili e al., 2020). The o ices can be isually
dis inguished by hei e lec i i y con as wi h espec o adjacen
clouds and by hei shape, showing an o al o m ha enci cles a egion
o closed o nea ly-closed o ici y. The su ounding cloud pa e ns
make hem appea as “b igh ” o “da k” o als wi h sizes anging om
one hund ed kilome e s o 40,000 km, he maximum size measu ed a
he end o he XIX cen u y o he la ges o al in Jupi e , he well-known
G ea Red Spo (GRS) (Simon e al., 2018a).
Vo ices a e classi ied acco ding o hei ela i e o ici y as cyclones
o an icyclones. In he No he n Hemisphe e, cyclones show an i-
clockwise o a ion while an icyclones o a e clockwise. An icyclones
* Co esponding au ho .
E-mail add ess: [email p o ec ed] (N. Ba ado-Izagi e).
Con en s lis s a ailable a ScienceDi ec
Ica us
jou nal homepage: www.else ie .com/loca e/ica us
h ps://doi.o g/10.1016/j.ica us.2021.114394
Recei ed 6 Oc obe 2020; Recei ed in e ised o m 16 Feb ua y 2021; Accep ed 18 Feb ua y 2021
Ica us 361 (2021) 114394
2
appea in a g ea numbe and a a ie y o sizes in he an icyclonic do-
mains o he Jo ian zonal wind p o ile, being mo e s able han cyclones
(Vasa ada and Showman, 2005), excep a pola la i udes whe e cy-
clones a e he s able o ices (Ad iani e al., 2018, 2020). The mos
appa en and well known o ices, due o hei longe i y and size, a e
he G ea Red Spo (GRS, plane og aphic mean la i ude 22◦S) and o al
BA (plane og aphic mean la i ude 33◦S) (Fig. 1), bo h an icyclones.
The essen ial p ope ies o unde s and a o ex a e i s o ici y dis-
ibu ion and i s ela ion wi h he en i onmen low shea (Dowling and
Inge soll, 1989; Ma cus, 1993). O he aspec s ha can be impo an in
Jo ian o ices a e hei colo , possible changes in ime, and in e ac ions
wi h o he o ices, which may include me ge s (cons uc i e in-
e ac ions) o des uc i e in e ac ions wi h eddies. In he gian plane s,
whe e he mechanisms powe ing he zonal winds a e mos ly unknown,
he in e ac ion be ween o ices, eddies and je s a e one o he mecha-
nisms p oposed o ha e an impo an ole in o cing and main aining he
zonal je s (Inge soll e al., 2004).
The i s o ici y measu emen s in Jupi e ’s a mosphe e we e ob-
ained o he GRS using g ound-based pho og aphic obse a ions
(Reese and Smi h, 1968; Hess, 1969). These we e la e much imp o ed
wi h p ecise measu emen s om he Voyage 1 and 2 lybys (Smi h and
21 colleagues, 1979a, 1979b) including accu a e measu emen s o he
de ailed low ield (Sada e al., 1996). The Voyage s also ob ained p e-
cise measu emen s o he local o ici y o Whi e O al BC (a 33◦S)
(Mi chell e al., 1981) and o a cyclone “ba ge” a 16◦N (Ha zes e al.,
1981). Images ob ained by he Galileo obi e allowed o measu e he
wind ield o he GRS (Choi e al., 2007) and a ew smalle o ices
(Vasa ada e al., 1998; Simon e al., 1998). Cu en ly, HST images can
also be used o e ie e he in e nal low ield o he la ges o ices such
as he GRS o o al BA (e.g. Hueso e al., 2009; Wong e al., 2011) and
JunoCam has p o ided da a wi h enough spa ial esolu ion and em-
po al sepa a ion o measu e he wind ield o he GRS (S´
anchez-La ega
e al., 2018) and pola o ices (Taba aba-Vakili e al., 2020).
When wo o ices o he same o ici y ype closely in e ac hey can
Fig. 1. The h ee longes -li ed and la ges Jupi e o als: GRS, o al BA and he NT O. Obse a ion om HST on 20 h o Sep embe 2012 in F763M il e .
N. Ba ado-Izagi e e al.
Ica us 361 (2021) 114394
3
me ge (when hey a e o simila sizes), o i hey ha e e y di e en sizes
he smalle one migh ge abso bed o ally o pa ially. Vo ex me ge s
occu in di e en a eas o he plane wi h he bes well-known example
being he chain o la ge o ex me ge s in 1998 and 2000 ha esul ed in
o al BA (S´
anchez-La ega e al., 1999, 2001). The new whi e o al BA
u ned ed in Augus 2005 wi h a e y simila shade o ha o he GRS
(Naeye, 2006; Simon-Mille e al., 2006). Ex ensi e dynamic s udies
(Ga cía-Melendo e al., 2009; Hueso e al., 2009; Wong e al., 2011) did
no ind dynamical di e ences linked o colo . Acco ding o adia i e
ans e analysis models, he colo change esul ed om he di usion o
a colo ed compound ha in e ac ed wi h he sola pho ons a he uppe
le els o he o al (P´
e ez-Hoyos e al., 2009). Pa ial abso p ions ha e
been obse ed in Jupi e ’s G ea Red Spo in e ac ions wi h la ge o als
(S´
anchez La ega e al., 1998; S´
anchez-La ega, 2021).
Colo changes a e ela i ely common in Jupi e ’s a mosphe e. Colo
changes in he ed colo a ion o opical an icyclones ha e been
desc ibed in S´
anchez-La ega e al. (2013). Thei analysis o opical
o ices concluded ha he e ical s uc u e and dynamics o he an-
icyclones a e no he causes o hei colo a ion, and hey p opose ha
he ed ch omopho e o ms when he backg ound ma e ial is s i ed and
exposed o ul a iole adia ion o mixed wi h o he chemical com-
pounds inside he o ex. In addi ion, plane a y-scale dis u bances in he
Jo ian a mosphe e can modi y he zonal albedo pa e n o he plane as
o example in he cycle o he Sou h Equa o ial Bel (SEB) wi h
con ec i e Dis u bances, la ge-scale colo changes and Fades (S´
anchez-
La ega and G´
omez, 1996; Fle che e al., 2011; P´
e ez-Hoyos e al.,
2012). The No h Tempe a e Bel (NTB) also expe iences his kind o
e en leading o he en i e band becoming o ally dis u bed (Roge s,
1995; S´
anchez-La ega and G´
omez, 1996; S´
anchez-La ega e al., 2008).
The NTB Dis u bances (NTBD) s a wi h he ou b eak o one o mo e
con ec i e plumes seen as b igh spo s mo ing wi h a eloci y sligh ly
as e han he zonal wind ha in e ac s wi h he su ounding cloud
pa e ns al e ing hem and o ming u bulence in hei wake. The las
NTBD de eloped in Oc obe 2016 wi h an ou bu s o ou plumes
(S´
anchez-La ega e al., 2017) ha dis u bed he en i e la i udinal band
and led o he o ma ion o a e y di e en eddish band (P´
e ez-Hoyos
e al., 2020).
In his wo k, we ha e ollowed he e olu ion o a long-li ed an i-
cyclone loca ed in he bounda y be ween he No h T opical Zone
(NT Z) and he No h Equa o ial Bel (NEB) a 19◦N plane og aphic
la i ude (Figs. 1 and 2). This o al has been obse ed con inuously since
2008, bu he e a e e idences o ea lie obse a ions (Roge s, 2013).
The o al is in e es ing because o i s la ge size and longe i y ( hi d a e
he GRS and o al BA), i s colo changes be ween whi e and ed, and i s
in e ac ions wi h close o ices including a majo o ex me ge in
Feb ua y 2013, and by he in e ac ion wi h he NTBD in 2012, 2016 and
2020. In he ollowing, we will e e o his an icyclone as NT Z-O al
(NT O).
The a ea whe e his o ex is loca ed is also in e es ing, as his egion
is home o he o ma ion o se e al an icyclonic whi e o als, cyclonic
da k ba ges and a ew cases o small ed spo s (Bebee and Hockey, 1986;
S´
anchez-La ega and Quesada, 1988; Roge s, 1995). I is also he loca-
ion o wa e sys ems ha in e ac wi h he o als and migh be caused by
hem (Simon e al., 2018b). Ou goal is o unde s and how he en i-
onmen al changes a ec a long-li ed o al, ying o disce n which o i s
p ope ies can be aken as undamen al and which o he p ope ies a e
jus inciden al. Among he gene al p ope ies o a o ex we will s udy
mo phology, colo , zonal d i and o ici y.
We p esen he e a ull epo o he obse ed cha ac e is ics o he
NT O (excluding he in e ac ions wi h he 2020 NTBD aking place in
Jupi e a he ime o his w i ing). Th oughou his pape we will use
plane og aphic la i ude (S´
anchez-La ega, 2011) and Sys em III longi-
udes (Da ies e al., 1986). This pape is s uc u ed in he ollowing way.
We de ail he obse a ions used in Sec ion 2. We de ail he his o ical
e olu ion o he mo phology o he o al, i s wind ield and colo e o-
lu ion om 2012 o 2019 in Sec ion 3. Finally, we p esen ou conclu-
sions in Sec ion 4.
2. Obse a ions
This wo k is based on he analysis o se e al da a se s. These include:
(i) images acqui ed wi h g ound-based elescopes using lucky-imaging
echniques ha allow high-spa ial esolu ion obse a ions using small
elescopes (Mousis e al., 2014) and a ailable in public da abases such as
PVOL (Hueso e al., 2010a, 2018); (ii) pho ome ically calib a ed ob-
se a ions wi h he Plane Cam ins umen (Mendikoa e al., 2016,
2017); (iii) HST obse a ions when a ailable and e ie ed om he HST
a chi e. In addi ion, we used an obse a ion o he o al ob ained a e y
high spa ial esolu ion by he JunoCam ins umen (Hansen e al., 2014)
on he Juno mission. Fig. 3 shows ep esen a i e examples o hese
obse a ions (excep o he JunoCam image ha will be p esen ed
la e ). These se s o images a e e y di e en om each o he bu allow
us o ob ain a nea ly comple e empo al co e age o he pe iod o in-
e es . The obse a ions used a e summa ized in Table 1. We he e de ail
Fig. 2. Zonal wind p o ile o Jupi e and loca ion o he NT O. The zonal wind p o ile is om Ba ado-Izagi e e al., (2013) and he ellipse shows he loca ion and
app oxima e size o he NT O wi hin i .
N. Ba ado-Izagi e e al.
Ica us 361 (2021) 114394
4
he main cha ac e is ics o hese da a se s.
The images om small elescopes we e ob ained by ama eu as-
onome s who con ibu e wi h hei obse a ions o he Plane a y
Vi ual Obse a o y and Labo a o y (PVOL) da abase a h ps://p ol2.
ehu.eus. This da abase s a ed as a da abase o obse a ions o he
gian plane s om he In e na ional Ou e Plane s Wa ch (IOPW)
collabo a ion (Hueso e al., 2010a) and cu en ly encompasses images o
all sola sys em plane s (Hueso e al., 2018). PVOL s o es cu en ly mo e
han 33,000 images o Jupi e acqui ed since he yea 2000 wi h con-
ibu o s om mo e han 30 coun ies. The quali y and e ec i e spa ial
esolu ion o hese images depend on se e al pa ame e s: plane
appa en size (which depends on he ime o obse a ions wi h espec o
opposi ion da e), a mosphe ic condi ions (seeing), elescope diame e ,
plane ele a ion wi h espec o he ho izon, came a used and de ails o
Fig. 3. Examples o images used in his wo k. (a) Obse a ions om ama eu as onome s a ailable in he PVOL da abase. Indi idual obse e s a e indica ed in he
igu e. (b) Plane Cam obse a ion in a Johnson I il e showing a pho ome ic (unp ocessed) image. (c) HST (F658N).
N. Ba ado-Izagi e e al.
Ica us 361 (2021) 114394
5
he image p ocessing. The g ea es s eng h o hese obse a ions is hei
empo al esolu ion wi h ens o images pe day a ailable in he days
a ound Jupi e ’s opposi ion. The images a e gene ally high-pass p o-
cessed e sions o he o iginal da a, wi h a la ge ac ion o hem being
RGB colo composi es. Howe e , hey canno gene ally be used o
adia i e ans e analysis o colo cha ac e iza ion. We also pa icipa e
as da a supplie s wi h obse a ions acqui ed wi h a 28-cm elescope
om he Aula EspaZio acili y a he School o Enginee s o he Uni-
e si y o he Basque Coun y UPV/EHU (S´
anchez-La ega e al., 2014)
and om a obo ic 35-cm elescope om ou uni e si y si ua ed a Cala
Al o obse a o y.
We also egula ly un obse a ion campaigns ( ypically 2 campaigns
o 4 nigh s pe yea ) wi h he Plane Cam-UPV/EHU ins umen (Men-
dikoa e al., 2016) a he 2.2 m elescope in Cala Al o obse a o y.
Plane Cam is a as dual came a acqui ing images in he isible (380
nm–1.0
μ
m) and SWIR (1.0–1.7
μ
m) ha uses he “lucky imaging”
me hod o ob ain high- esolu ion images (Law e al., 2006). Obse a-
ions a e calib a ed in absolu e e lec i i y by obse ing s anda d
e e ence s a s (Mendikoa e al., 2017). Plane Cam allows obse a ions
in na ow- il e images including il e s in he me hane abso p ion
bands and nea -ul a iole , which can hen be used o pe o m he colo
index calcula ions la e desc ibed in Subsec ion 3.4.
We analyzed six se s o images acqui ed by HST using he Wide Field
Came a 3 (WFC3) and e ie ed om he public a chi e (see Table 1).
The spa ial esolu ion o hese images is on a e age a ac o 10 highe
(0.04′′/pixel) han mos ypical images in he PVOL da abase. This
ansla es in e ec i e spa ial esolu ions a Jupi e opical la i udes o
150 km/pixel app oxima ely. Un o una ely, HST images co espond o
epochs in which he o al appea ed whi e, as he e a e no HST obse -
a ions o Jupi e when he o al was ed. We used images acqui ed on
19–20 Sep embe 2012 o calcula e he in e nal wind ield in he o al
and images ob ained on Janua y 2015, Feb ua y 2016, Feb ua y and
Ap il 2017, and Ap il 2018 o measu e he in e nal wind ield and also o
e alua e colo indices o di e en ea u es.
All he images p esen ed so a need o be na iga ed, i.e. he longi-
ude and la i ude plane a y coo dina es o each pixel (x, y) o he image
mus be compu ed. To na iga e HST and g ound-based obse a ions, we
used he so wa e LAIA, based in he VICAR code (Video Image
Communica ion And Re ie al, Duxbu y and Jensen, 1994.; see Ga cía-
Melendo and S´
anchez-La ega, 2001 o de ails).
Finally, JunoCam obse ed he NT Z o al a h ee pe ijo es: PJ9
(2017 Oc obe 24), PJ16 (2018 Oc obe 29) and PJ21 (2019 July 21). In
PJ16, obse a ions did no ully co e he o al, bu in PJ9, and espe-
cially in PJ21, hey co e ed he o al in high- esolu ion wi h he bes
Fig. 4. E olu ion o he o al and i s aspec in di e en pe iods. (a) The wo o als Z and A ha me ged o o m he whi e o al; (b) Immedia e esul o he me ge
(Whi e Spo Z); (c) A sample o he o al du ing i s ed phase (Red O al Z); (d) T ansi ional phase wi h a ed/pink ing; (e) Cu en s a e o he o al. (Fo in e p e a ion
o he e e ences o colo in his igu e legend, he eade is e e ed o he web e sion o his a icle.)
Table 1
Summa y o he HST, PVOL and Juno obse a ions used in his wo k. Mos o he
PVOL images a e RGB composi es (wa eleng h ange om~400 o 700 nm) o
IR (685 o 700 high-pass).
Ins umen Da e Numbe o
images
Fil e s
HST 2012/09/20 6 F275W, F763M
2015/01/19 8 F658N, F502N, FQ889N,
F275W
2016/02/
9–10
10 F631N, F658N, F502N,
FQ889N, F275W
2016/12/11 4 F631N
2017/01/11 4 F631N
2017/04/03 10 F631N, F658N, F502N,
FQ889N, F275W
2018/04/17 4 F631N
IOPW F om 2012 o
2019
<900 RGB, MT
PLANETCAM 2013/12 12 B, R, M3, UV
JUNO 2019/07/21 1 RGB
N. Ba ado-Izagi e e al.
Ica us 361 (2021) 114394
6
images eaching e ec i e spa ial esolu ions o 25 km/pixel a he o al.
We ans o med an o iginal JunoCam image o a cylind ically p ojec ed
map using Juno’s ajec o y in o ma ion om SPICE ke nels and he
In eg a ed So wa e o Image s and Spec ome e s (ISIS3) so wa e o
he U.S. Geological Su ey.
3. Analysis
3.1. His o y and mo phology
The NT O has been p esen in he plane since 2008 and possibly
be o e ha (Roge s, 2013). Un il 2012 i was one o he many di e en
o als p esen in he NEB-NT Z egion and was known as whi e o al Z
ollowing he con en ion o naming di e en spo s wi h le e s. How-
e e , in Ap il 2012 a con ec i e dis u bance in he NTB de eloped. This
dis u bance s a ed close o Jupi e ’s sola conjunc ion and he e a e
only a ew images ha eco ded his e en (Roge s and Adamoli, 2019).
As a esul o his dis u bance, he o al changed i s d i eloci y s a ing
o mo e ela i e o he chain o o als a close la i udes. A e wa ds, in
Feb ua y 2013, he NT O me ged wi h ano he whi e o al, named A.
The la e was somewha slowe as i was loca ed a 19◦N while Z was a
19.5◦N, whe e he winds a e a li le bi as e . The me ge led o a e y
simila whi e o al (see Figs. 4 and 5) ha con inued he same eloci y
endency as i had be o e as o al Z and was widely known in he ama eu
communi y as Whi e O al Z (WOZ).
Some mon hs la e , in Sep embe 2013, a d ama ic change ook
place: he o al u ned ed (Fig. 4) and looked b igh e in he me hane
band il e images as we will discuss in Sec ion 3.4. I s ayed ed o mo e
han a yea , and was some imes named Red O al Z (ROZ), bu suddenly,
in Feb ua y 2015, i dimmed a me hane band il e images and eco -
e ed i s ini ial whi e colo a ion excep o a pinkish ing.
I emained wi h ha isual aspec un il Oc obe 2016, when an
ou bu s o ou plumes in he NTB ga e ise o he 2016 NTBD (S´
anchez-
La ega e al., 2017), again du ing he sola conjunc ion. When he
dis u bance ceased, he mo phology o he whole NTB had changed. In
Decembe 2016, HST obse a ions e ealed he pe sis en p esence o
he NT O, bu la e images in Janua y and Feb ua y 2017 did no clea ly
show he o al, as he la i udes whe e he o al was became e y blu y
and he o al appa en ly disappea ed (Fig. 5). A ca e ul ack o he o al
in PVOL images made i possible o dis inguish he o al om he
backg ound and ollow i s posi ion un il Decembe 2017 e en hough
he NT Z and NTB we e o ally dis u bed. In Janua y 2019, and due o
he p oximi y o sola conjunc ion, he o al was no dis inguishable in
he ew images a ailable in he ama eu eco d. Howe e , on Feb ua y
18 h i appea ed again a i s expec ed longi ude o 250◦(sys em III). By
ha da e many new o als had appea ed in he NT Z possibly as a
consequence o he 2016 NTBD. The new o als we e bo h cyclones and
an icyclones, wi h he NT O being he la ges and mos conspicuous o
all hese ea u es.
Juno obse ed he o al on di e en o bi s, bu gene ally unde poo
obse ing condi ions. Howe e , Juno passed abo e he NT O on i s
pe ijo e 21 on 21 July 2019 and ob ained images o he an icyclone a
e y high spa ial esolu ion. Fig. 6 shows a cylind ical map p ojec ion
based on he Junocam image JNCR_2019202_21C00021 wi h an e ec-
i e spa ial esolu ion abo e he o al o ~25 km. The o al appea s as a
la ge-scale ea u e wi h a whi e co e and a eddish ing ha ex ends in o
he en i onmen wi h uzzy bounda ies. The mean size o he eddish
ing is an ellipse wi h a mean size o (10,500 ±1000) x (5,200 ±400)
km
2
and he inne whi e egion has a mean size o (5800 ±200) x (4,500
±200) km
2
. He e measu emen s and e o s come om he s a is ical
analysis o di e en size es ima ions o he o al a e i ing ellipses o i s
di use bounda ies. B igh and da k pa ches in he inne whi e co e ha e
ypical sizes o 210 ±45 km. The mo phology o he no h and sou h
b anches o he o al a e di e en , possibly ela ed wi h he e y
di e en me idional shea o he en i onmen zonal winds, which is
much s onge in he no he n hemisphe e. Small-scale b igh ea u es
Fig. 5. NT O in de ail be o e and a e he 2016 NTBD e en . All images om
HST in F658N il e .
N. Ba ado-Izagi e e al.
Ica us 361 (2021) 114394
7
(~150 km) a 21.2◦plane og aphic la i ude ( ead on he igh axis o
Fig. 6), in he ansi ion be ween he ou e ed ing and he en i onmen
whi e clouds. This is a egion o s ong me idional shea o he zonal
wind wi h he ela i e o ici y o he mean zonal wind being −
∂
u/
∂
y =
(4.0 ±0.8) ×10
−5
s
−1
. Simila -sized ea u es in he no h side o he
whi e o al a e loca ed a 20◦. The ansi ion in he sou h b anch o he
o al om he eddish ing o he whi e en i onmen a 16.5◦la i ude
occu s in a egion o low wind shea wi h −
∂
u/
∂
y =(0.6 ±0.8) ×10
−5
s
−1
. The winds and o ex ci cula ion canno be di ec ly measu ed on
he Junocam images due o he small ime-sepa a ion be ween consec-
u i e images (2 min).
3.2. D i eloci y and acking o he o al
The NT O is loca ed in he bounda y be ween he No h T opical
Zone (NT Z) and he No h Equa o ial Band (NEB) o Jupi e a 19◦N
plane og aphic la i ude. This is an an icyclonic a ea whe e he zonal
eloci y is nea 0 m/s (Fig. 2), so he o al should be quasi-s a iona y.
Howe e , he wind shea in ha a ea is so p onounced ha a small
change o less han a deg ee in la i ude leads o a la ge change in zonal
eloci y. Mo eo e , sou h o i s la i ude, he local wind p oduces s ong
cyclonic o ici y and a small change in i s la i ude could esul in he
o al des uc ion by he in e ac ion wi h he wind. The longe i y o he
NT O in his a ea, wi h such a high wind shea (see Fig. 2), equi es a
s ong inne ci cula ion. La ge and long-li ed s able o ices like he
GRS and o al BA sha e also a posi ion in a s ongly shea ed je .
We ha e measu ed he d i eloci y o he NT O acking i s posi ion
since Augus 2011 un il No embe 2019. Measu emen s o e mo e han
300 images a e shown in Fig. 7. Changes in he slope o he plo ep e-
sen changes in he d i a e o he o al, i.e. i s zonal wind speed. Such
changes a e p obably ela ed o small changes in la i ude. Gi en e o s
a e ob ained om he s anda d de ia ion o he indi idual
measu emen s.
A he beginning o he acking pe iod, he e is a no iceable eloci y
change p obably ela ed wi h he NTBD ha ook place in Ap il 2012.
Al hough only a ew images show he Whi e O al Z in his pe iod, he
long ime di e ence be ween hem makes i possible o measu e he
eloci y change ha goes om 0.2 ±0.2 m/s be o e he NTBD o 13.3 ±
0.5 m/s a e wa ds.
A he end o 2012, Whi e O al Z app oached a simila o al a a e y
close la i ude, (Whi e O al A in Fig. 2). The acking o his ea u e is
also shown in Fig. 7. Whi e O al Z was a 19.7 ±0.6◦mo ing a a e-
loci y o 11.5 ±0.5 m/s, while o al A was loca ed a 19.1 ±0.4◦and
mo ed a a eloci y o 5.3 ±0.7 m/s. These eloci ies co espond o
hose o he zonal wind p o ile a hei espec i e mean la i ude. Thei
longi udinal dis ance in Decembe 2012 was 35◦and a e wo mon hs,
hey con e ged and me ged in o a unique o ex, NT O ha ollowed he
d i endency o Z (Fig. 6). Be o e and a e his me ge bo h o ices
we e whi e and showed no colo changes.
A e he me ge , he d i eloci y om Feb ua y 2013 o Sep embe
2013 was abou 6.5 m/s, while om Sep embe 2013 o No embe 2014
i su e ed a decele a ion and he d i eloci y was a ound 2.9 m/s and
no as uni o m as in he i s pe iod, when he linea i was almos
pe ec . We also no e ha hese changes ollow e y well he shape o he
wind p o ile o he a ea because he la i ude o he o al also changed
e y sligh ly. The colo change happened a ha e y same ime. F om
Augus 2014 o Decembe 2016 he o al was in a nea ly s a iona y si -
ua ion, wi h i s la i ude e y close o 19◦N again, wi h i s d i a e
ma ching he zonal wind p o ile a i s la i ude.
In Oc obe 2016, an ou bu s o con ec i e plumes in he NTB
dis u bed he NTB and NT Z (S´
anchez-La ega e al., 2017). The isual
p ope ies o he o al did no change in his pe iod bu in he acking
p esen ed in Fig. 6 we obse e ha some days a e he e up ion o he
plumes he ack eloci y o he o al changed subs an ially, inc easing
Fig. 6. The Whi e T opical O al and i s en i onmen om JunoCam obse a ions on June 21, 2019. The image was o iginally p ojec ed in plane ocen ic co-
o dina es. The inse shows zonal winds as measu ed du ing he Cassini lyby (Po co e al., 2003) in black o in 2011 (Ba ado-Izagi e e al., 2013) in pu ple wi h only
mino changes in his la i ude ange. (Fo in e p e a ion o he e e ences o colo in his igu e legend, he eade is e e ed o he web e sion o his a icle.)
N. Ba ado-Izagi e e al.
Ica us 361 (2021) 114394
8
Fig. 7. T acking o he NT O o al om Augus 2011 o No embe 2019. Top panel: Longi udes. Middle panel: La i udes. In black, he measu emen s o he o al when
i was whi e, ed do s when he o al looks ed and pink ci cles o si ua ion wi h a whi e cen e enci cled by a pinkish ing. The wo NTB dis u bances occu ed du ing
his pe iod a e ma ked wi h g ey a eas. Bo om panel: The posi ion o he o al o e he wind p o ile. (Fo in e p e a ion o he e e ences o colo in his igu e legend,
he eade is e e ed o he web e sion o his a icle.)
N. Ba ado-Izagi e e al.
Ica us 361 (2021) 114394
9
om being nea ly s a iona y o a eloci y o 5.54 ±0.07 m/s o he Eas .
This beha io is equi alen o he one ha had been obse ed 7 yea s
be o e a he simila 2012 e up ion. In bo h cases, he NT O mo ed in
la i ude om 19◦ o 19.5◦leading o a egion o he zonal wind p o ile
wi h highe eloci ies.
3.3. Ro a ion eloci y and o ici y
We selec ed HST images o he NT O o measu e he in e nal low
ield in he o al. We selec ed images om Sep embe 2012 be o e he
me ge happened, when he o al was whi e, and om Janua y 2015 and
Feb ua y 2016 when he o al was whi e a e i s ed phase and s ill had a
pink ing su ounding i , p io o he 2016 NTBD. We selec ed images
om Janua y 2017, Ap il 2017 and Ap il 2018 o cha ac e ize i s
p ope ies a e he NTBD.
We used he PICV (Pa icle Image Co ela ion Velocime y) 2-dimen-
sional image co ela ion so wa e (Hueso e al., 2009) o analyze image
pai s and s udy mo ions in he NT O. We selec ed images o he same
a ea ob ained wi h a ypical ime sepa a ion o 10 h and we na iga ed
and p ojec ed hem in o cylind ical coo dina es. The so wa e allows
selec ing egions o he images whe e image co ela ion is used o
iden i y cloud ace s and hei mo ions. Because o he limi ed esolu-
ion o he images, each measu emen was “ alida ed” by a human
ope a o ha examined he cloud ea u e iden i ied by he so wa e in
bo h images and i s co ela ion map. We also manually measu ed ea-
u es in di e en da a se s o e alua e he e ec i eness o he co ela o
o his pa icula o al, as he size and con as o he cloud ea u es may
a ec he esul s.
In bo h cases, zonal u and me idional eloci ies a e calcula ed om
he displacemen s in longi ude λ and plane ocen ic la i ude θ espec-
i ely. u and a e gi en by he exp essions:
u= −
π
180 R(θ)cosθ Δλ
Δ (1)
=
π
180 R(θ)Δθ
Δ (2)
Fig. 8. Examples o measu ed wind ield in NT O in 2012 and 2017. These esul s we e ob ained wi h he image co ela ion so wa e esul ing in a dense ne wo k o
measu emen s. These measu emen s we e la e in e pola ed o e a egula g id.
Table 2
NT O’s measu ed alues o di e en yea s.
Yea a (◦) b (◦) V
T
(m/s) ζ (s
−1
)
2012 4.9 2.4 −60 ±30 (−3 ±1)⋅10
−5
2015 4.4 2.9 −35 ±20 (−1.6 ±0.9)⋅10
−5
2016 3.2 2.1 −33 ±10 (−2.1 ±0.7)⋅10
−5
2017 4.9 2.1 −34 ±20 (−2 ±1)⋅10
−5
2018 4.0 3.0 −40 ±20 (−1.9 ±0.9)⋅10
−5
2019
a
4.0 2.1 – –
No es: a is hal he eas -wes ex ension o he o al, while b is hal he no h-sou h
ex ension, V
T
is he angen ial eloci y o he ex e nal con ou o he o al and ζ is
he ela i e o ici y measu ed wi h eq. 7. E o s associa ed o his measu emen
a e ob ained wi h eq. 9.
a
Measu emen s ob ained o e he JunoCam image.
N. Ba ado-Izagi e e al.
