The Earth, a tiny pale blue dot in the universe is the only place known to harbor life. Earth’s atmosphere is a thin envelope of gases surrounding the planet that keeps Earth naturally warm enough to sustain life on it through the processes (e.g. greenhouse effect), filtering out the deadly cosmic rays, absorbing harmful ultraviolet radiation from the sun and burn external bodies (e.g. meteors) which collision course with Earth to prevent living organisms from extinction.The Earth’s atmosphere. The composition of the atmosphere largely made up of oxygen, nitrogen and a small number of other gases and aerosols.
Although the atmosphere is homogeneous on a small scale, the atmosphere itself is not physically uniform but has significant variations in pressure and temperature with altitude. Due to the continuous interactions between motions of air, rotation of the Earth and the radiation from the sun create a complicated fluid dynamical system that has not completely understood yet. Processes in the atmosphere also have a societal impact through a number of different social, cultural, and natural resources. For example, infrastructure, electric power industry, global communication, navigation, national security and day-to-day lives structured around climate conditions and their operations adversely affected by conditions in the space environment. Thus, better understanding the physics, chemistry and dynamical process that govern the atmosphere via observations and numerical models are vitally important to improve our current understanding.
Our knowledge about the atmosphere has vastly improved over the last six decades due to the advancement of satellite observations, measurements from weather balloons, ground-based radar, rocketsondes and modeling capabilities with the advancement of computing power. Mathematical models constructed using primitive equations to simulate and compare to the observations are an invaluable tool that can offer new insight into the atmospheric dynamics and global characteristics.
The Mesosphere and Lower Thermosphere (MLT) region (~60-120 km) form the boundary between the lower atmosphere (i.e. troposphere and stratosphere) and the upper atmosphere. The MLT region is one of the less-studied regions of the Earth’s atmosphere and is understood to be dominated by wave-wave and wave mean flow interactions driven by atmospheric waves of various scales (e.g. tides, planetary waves, and gravity waves). Atmospheric tides are persistent global oscillations which have periods that are integer fractions of the solar or lunar day and mainly generated due to the absorption of solar radiation in the troposphere and stratosphere. Gravity waves (internal gravity or buoyancy waves) are restored by buoyancy forces and have very short term periodicity. Planetary waves are also global oscillations with longer periods (2 ~ 30 days) result from the conservation of potential vorticity and are influenced by the Coriolis force and pressure gradient. These waves play a very important role in the dynamics of the MLT region by dissipation and deposit momentum and energy to the large-scale flow (Holton, 1982; Lindzen, 1981; Miyahara et al., 1992; Salby, 1984).
A major science goal of this decade in the Atmosphere-Ionosphere-Magnetosphere Interactions (AIMI) is to “understand how tropospheric weather influences space weather”. Numerous observational and modeling studies revealed that the most variabilities (local-time, seasonal-latitudinal, day to day) of the Earth's thermosphere and ionosphere (TI) during “quiet time” periods (geomagnetic quiet conditions and medium solar conditions) owes much to the perturbations originating from the lower atmosphere which transferred momentum and energy through propagation and generation of waves (Akmaev, 2011; Forbes et al., 2000; H. ‐L. Liu, 2016; Rishbeth & Mendillo, 2001; Yamazaki et al., 2017; Yamazaki & Maute, 2017).
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