SEMINAR
6 jun. 2020 9am – 10am Horário Padrão de Brasília – Fortaleza
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Título: Atmospheric gravity wave dynamics and coupling processes: A particular emphasis on MLT region and ionosphere.
Palestrante: Dr. Mani Sivakandan – Nagoya University – Japan.
Informações de participação Entrar com o Google Meet
meet.google.com/awr-rjov-zbo
Tel
+1 502-414-3877 (Número de identificação pessoal (PIN): 573560083)
•
douglas@df.ufcg.edu.br- organizador
The mesosphere and lower thermosphere (MLT) region is influenced by the insolation (such as electromagnetic radiation, and energetic particle precipitation) from the topside and lower atmospheric forcing due to gravity wave, planetary waves, and tidal waves associated momentum and energy deposition from the bottom side. Previously, it was believed that the ionosphere thermosphere (IT) system was fully controlled by the solar forcing. However, recent investigations show that in addition to the solar forcing, lower atmospheric waves and tides also have significant role in the variability of the IT region neutral dynamics, as well as the electrodynamics.
Gravity waves are generated in the lower atmosphere by variety of sources such as tropospheric convection, wind shear, jets and fronts, topography, etc. Under conducive
background these waves can propagate to the middle and upper atmosphere. Most of these waves break/dissipate in the MLT region due to the inherent instability. On breaking these waves deposit their energy and momentum to the ambient atmosphere. Therefore, it can alter the background wind, temperature, composition, concentration and associated dynamics (i.e. middle atmospheric circulation). Sometimes, the wave which are not breaking in the MLT
region can propagate further and it can act as a seed perturbation for the equatorial plasma bubble (EPB) and mid latitude medium-scale traveling ionospheric disturbances (MSTIDs).
During the post sunset hours, large depletions in the electron density are observed over the geomagnetic equatorial ionosphere and extends to the low-latitudes. These structures are called as EPBs or Spread-F. EPBs are aligned parallel to the geomagnetic filed lines and drift
toward east (mostly) or west (rarely). These structures are commonly referred as ionospheric irregularities and have adverse effect on the satellite based navigation communication systems. Similarly, in the mid-latitude ionosphere north-west to south-east aligned phase
front structures moving south westward are called MSTIDs. Recent investigations suggests that nighttime electrified MSTIDs are one of the prime source for the generation of midnight EPBs during summer in lower solar activity. The present talk focuses on the gravity waves in the MLT region and their plausible role on the generation of EPB and MSTIDs through coupling processes. This talk is intended to lend an insight into these phenomena.