@Article{EssienWrPaMeBuTa:2018:SeChSm,
author = "Essien, Patrick and Wrasse, Cristiano Max and Paulino, I. and
Medeiros, A. F. and Buriti, R. A. and Takahashi, Hisao",
affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)} and {Instituto
Nacional de Pesquisas Espaciais (INPE)} and {Universidade Federal
de Campina Grande (UFCG)} and {Universidade Federal de Campina
Grande (UFCG)} and {Universidade Federal de Campina Grande (UFCG)}
and {Instituto Nacional de Pesquisas Espaciais (INPE)}",
title = "Seasonal characteristics of small- and medium-scale gravity waves
in the mesosphere and lower thermosphere region over brazilian
equatorial region",
journal = "Annales Geophysicae",
year = "2018",
volume = "36",
number = "3",
pages = "899--914",
month = "jun.",
keywords = "Atmospheric composition and structure (airglow and aurora) –
electromagnetics (wave propagation) – history of geophysics
(atmospheric sciences).",
abstract = "This work reports the seasonal characteristics of small- and
medium-scale gravity waves in the mesosphere and lower
thermosphere region observed in the OH NIR airglow images over Sao
Joao do Cariri (7.4oS, 36.5oW). Observations were made from
September 2000 to December 2010, which corresponded to a total of
1496 nights. To investigate medium-scale gravity waves, sequences
of images observed in each night was used to create 701 keograms.
Two techniques were used to calculate for gravity waves
parameters: Keo-FFT analysis for medium-scale gravity waves
(MSGWs) and Fourier cross spectrum for small-scale gravity waves
(SSGWs). The two analytical techniques resulted in 537 and 2343
MSGWs and SSGWs events respectively. The horizontal wavelengths of
MSGWs were concentrated between 100 to 150 km, while that of the
SSGWs were between 10 to 15 km. The observed periods for MSGWs
ranged from 20 to 40 minutes, while the SSGWs had a maximum peak
around 5 to 10 min. The observed horizontal phase speed of MSGWs
was distributed between 60 to 80 10 m/s while the SSGWs showed a
peak around 20 to 40 m/s. Except spring, which the wave events
propagated in all directions, in summer, fall and winter were
northeast and southeast. The horizontal propagation direction of
MSGWs and SSGWs show clear seasonal variations based on the
influence of the background atmospheric conditions such as wind.
The anisotropy observed in the total propagation directions of
MSGWs was northeast which can be attributed to either the source
location of the gravity waves or the filtering process due to the
wind system which depends fundamentally on the seasonal
variations. However, there was no clear anisotropy in the total
propagation direction of the SSGWs which could be due to uniformly
distribution of the sources or filtering processes by the wind
system. Critical level theory for gravity wave filtering was
applied to study the effects of middle atmospheric winds on the
propagation path of the wave events while the average of daily
mean Outgoing Long-wave Radiation (OLR) was used to study the
possible seeding mechanism of the gravity waves. The SSGWs were
found to be filtered out by the mean flow due to their least phase
velocities. Deep Convection is the possible seeding mechanism for
both MSGWs and SSGWs in the summer and fall over the Brazilian
equatorial sector. MSGWs were found to be less susceptible to wind
filtering effects due to their high phase velocities.",
doi = "10.5194/angeo-36-899-2018",
url = "http://dx.doi.org/10.5194/angeo-36-899-2018",
issn = "0992-7689",
language = "en",
targetfile = "essien_seasonal.pdf",
urlaccessdate = "15 jun. 2024"
}