@PhDThesis{Essien:2021:StMeTr,
author = "Essien, Patrick",
title = "Study on mediumscale traveling ionospheric disturbances observed
in the South American equatorial region/Estudo sobre
dist{\'u}rbios ionosf{\'e}ricos itinerantes de m{\'e}dia escala
na regi{\~a}o equatorial da Am{\'e}rica do Sul",
school = "Instituto Nacional de Pesquisas Espaciais (INPE)",
year = "2021",
address = "S{\~a}o Jos{\'e} dos Campos",
month = "2020-08-27",
keywords = "medium-scale traveling ionospheric disturbances, equatorial
ionosphere, detrending TEC map, secondary and tertiary gravity
waves, intertropical convergence zone, dist{\'u}rbios
ionosf{\'e}ricos propagantes de m{\'e}dia-escala, ionosfera
equatorial, mapa de TEC de {"}detrend{"}, ondas de gravidade
secund{\'a}rias e terci{\'a}rias, zona de converg{\^e}ncia
intertropical.",
abstract = "Using data collected by GNSS (GPS and GLONASS specifically) dual
frequency receivers network, detrended TEC maps were generated to
identify and characterize the medium-scale traveling ionospheric
disturbances (MSTIDs) over the South American equatorial region
(latitude: 0 to 15S and longitude: 30 to 55W ) during solar cycle
24 (from January 2014 to December 2019). Among 742 MSTIDs that
were observed, 712 of them representing 96% were observed during
geomagnetic quiet condition and 30 events indication 4% were
observed during geomagnetic disturbed condition. The observed
MSTIDs show strong positive correlation with the solar activity.
The positive correlation might have been caused by gravity waves
dissipation due to high viscosity in the thermosphere as a result
of low and high thermospheric temperature during solar minimum and
maximum respectively. The predominant daytime MSTIDs representing
70% of the total observation occurred in winter with the secondary
peak in equinox, while the evening time MSTIDs which is 28% of the
entire events occurred in summer and equinox, while the remaining
2% of the MSTIDs were observed during nighttime. The local time
dependency of the MSTIDs was attributed to the mechanisms
generating them and/or the medium at which they propagated while
the seasonal variation could be as results of wind filtering and
dissipation effect during winter and summer. The horizontal
wavelengths of the MSTIDs were concentrated between 300 and 1400
km, with the mean value of 667±131 km. The observed periods were
ranging from 20 to 60 min with the mean value of 36±7 min. The
observed horizontal phase speeds were distributed around 100 to
700 m/s, with the corresponding mean of 301±75 m/s. The MSTIDs in
winter solstice and equinoctial months preferentially propagated
northeastward and northwestward. Meanwhile, during summer solstice
they propagated in all directions. The anisotropy of the
propagation direction might be due to several reasons: the wind
and dissipative filtering effects, ion drag effects, the primary
source region and the presence of the secondary or tertiary
gravity waves in the thermosphere. Atmospheric gravity waves from
strong convective sources originated from the equatorial and
Amazon region might be the primary precursor of the northeastward
and northwestward propagating MSTIDs during summer solstice and
autumn equinox. Nevertheless, strong cold front emanating from low
latitude might have been the primary source for the northeastward
and northwestward MSTIDs during winter solstice and spring
equinox. In all the seasons, we noted that the MSTIDs propagating
southeastward were probably excited by the likely gravity waves
that was generated by the intertropical convergence zone (ITCZ).
RESUMO: Usando dados coletados pela rede de receptores GNSS de
dupla frequ{\^e}ncia (especificamente GPS e GLONASS),
obt{\^e}m-se mapas de TEC perturbado com o objetivo de
identificar e caracterizar os MSTIDs (sigla em ingl{\^e}s para
Medium-Scale Traveling Ionospheric Disturbances) na regi{\~a}o
equatorial da Am{\'e}rica do Sul (latitude: 0 to 15S and
longitude: 30 to 30W ) durante o ciclo solar 24 (Janeiro de 2014 e
dezembro de 2019). Entre os 742 MSTIDs observados, 712 deles,
representando 96%, foram observados durante a condi{\c{c}}{\~a}o
geoman{\'e}ticas calmas e 30 eventos, 4% durante
per{\'{\i}}odos geomagneticamente perturbadas. Os MSTIDs
observados mostram uma forte correla{\c{c}}{\~a}o positiva com a
atividade solar. Essa correla{\c{c}}{\~a}o pode ter sido causada
pela dissipa{\c{c}}{\~a}o das ondas de gravidade devido {\`a}
alta viscosidade na termosfera, e como resultado da baixa e alta
temperatura termosf{\'e}rica durante m{\'{\i}}nima e
m{\'a}xima solar, respectivamente. Os MSTIDs ocorrem predominante
durante o dia, 70% da observa{\c{c}}{\~a}o total, com pico no
inverno e pico secund{\'a}rio no equin{\'o}cio, enquanto que os
MSTIDs noturnos, 28% de todos os eventos, ocorrem no ver{\~a}o e
no equin{\'o}cio, enquanto os 2% restantes dos MSTIDs foram
observados durante a noite. A depend{\^e}ncia do hora local dos
MSTIDs foi atribu{\'{\i}}da aos mecanismos que os geraram e/ou
ao meio em que se propagam. A varia{\c{c}}{\~a}o sazonal pode
ser resultado dos efeitos de filtragem das ondas atrav{\'e}s do
vento e dissipa{\c{c}}{\~a}o, durante o inverno e o ver{\~a}o.
Os comprimentos de onda horizontais dos MSTIDs variam entre 300 e
1400 km, com valor m{\'e}dio de 667±131 km. Os per{\'{\i}}odos
observados variam de 20 a 60 min, com valor m{\'e}dio de 36±7
min. As velocidades de fase horizontal observadas foram observados
entre 100 e 700 m/s, com a m{\'e}dia de 301±75 m/s. Os MSTIDs
durante os solst{\'{\i}}cio de inverno e nos meses de
equin{\'o}cio se propagam preferencialmente para noroeste , norte
e nordeste. Enquanto isso, durante o solst{\'{\i}}cio de
ver{\~a}o, eles se propagavam em todas as dire{\c{c}}{\~o}es. A
anisotropia da dire{\c{c}}{\~a}o da propaga{\c{c}}{\~a}o pode
ser devida aos efeitos de filtragem do vento, efeitos
dissipativos, efeitos de arrasto de {\'{\i}}ons, al{\'e}m da
regi{\~a}o de fonte prim{\'a}ria e por fim, a presen{\c{c}}a
das ondas de gravidade secund{\'a}ria ou terci{\'a}ria na
termosfera. As fontes de convec{\c{c}}{\~a}o troposf{\'e}rica
originadas da regi{\~a}o equatorial e amaz{\^o}nica podem ser o
precursor prim{\'a}rio dos MSTIDs que se propagam para nordeste e
noroeste durante o solst{\'{\i}}cio de ver{\~a}o e o
equin{\'o}cio de outono. Por outro lado, uma frente fria que
emana de altas latitudes pode ser sido a principal fonte para os
MSTIDs que se propagam para nordeste e noroeste durante o
solst{\'{\i}}cio de inverno e o equin{\'o}cio da primavera. Em
todas as esta{\c{c}}{\~o}es, observamos que os MSTIDs que se
propagam para o sudeste provavelmente s{\~a}o originadas por
ondas de gravidade geradas pela Zona de Converg{\^e}ncia
Intertropical (ZCIT).",
committee = "Pimenta, Alexandre Alvares (presidente) and Takahashi, Hisao
(orientador) and Figueiredo, Cosme Alexandre Oliveira Barros
(orientador) and Souza, Jonas Rodrigues de and Rabiu, Akeem
Babatunde and Silva, Igo Paulino da",
englishtitle = "Estudo sobre dist{\'u}rbios ionosf{\'e}ricos itinerantes de
m{\'e}dia escala na regi{\~a}o equatorial da Am{\'e}rica do
Sul/Study on mediumscale traveling ionospheric disturbances
observed in the South American equatorial region",
language = "en",
pages = "167",
ibi = "8JMKD3MGP3W34R/432JP4S",
url = "http://urlib.net/ibi/8JMKD3MGP3W34R/432JP4S",
targetfile = "publicacao.pdf",
urlaccessdate = "28 abr. 2024"
}