Date of Award
Doctor of Philosophy (PhD)
Physics and Astronomy
Jens Oberheide, Committee Chair
This dissertation investigates the impact of nonmigrating tides on the energy budget of the thermosphere and its two major infrared (IR) emissions that govern the cooling of the region, nitric oxide (NO) at 5.3 µm and carbon dioxide (CO2) at 15 µm using Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) observations and a photochemical modeling. The focus is on the DE2 and DE3, two important nonmigrating tides that originate near the Earth's surface. The overarching goal is to understand the coupling between the tropospheric weather system and the thermospheric IR budget. The results provide additional tidal information in the height regime where no temperature observations are possible.
Vertical wave coupling due to atmospheric tides is key to a better understanding of the connection between meteorology and space weather. Atmospheric tides are global-scale oscillations in temperature, wind fields and density that are forced by the periodic absorption of solar energy in the lower atmosphere. When propagating upward, tides grow exponentially and often dominate the dynamics, chemistry and electrodynamics of the middle and lower thermosphere (MLT) through net deposition of energy and momentum. In particular, nonmigrating tides can propagate all the way into the upper thermosphere and impose a substantial longitudinal and local time variability similar to the one in MLT. Forced by global-scale heat release in the deep convective clouds in the tropics, nonmigrating tides are also known to impact various ionospheric parameters, for example, F-region plasma through the modulation of E-region winds. Past studies have mostly been focused on the dynamical and electrodynamical effects of nonmigrating tides. Their magnitude in the dynamical and ionospheric fields suggests that significant nonmigrating tidal variations may be present in other parameters important to the aeronomy of the thermosphere-ionosphere system, for example, in energetics. Little work has been done in this field such that the coupling mechanism in the infrared energy budget is not well understood.
The major findings of this dissertation can be summarized as (i) tides caused by tropospheric weather impose a substantial seasonal -and in the NO 5.3 µm case solar cycle dependent-modulation of the infrared cooling, mainly due to the tidal temperature, (ii) NO cooling rate tides become very important for the longitudinal modulation of energy budget of the lower thermosphere during solar maximum above 135 km (DE3) and 120 km (DE2) as compared to CO2 but remain largely unimportant during solar minimum, (iii) NO cooling rate tidal spectra show unexpectedly large signals for several westward propagating tidal components (DW5, DW2, SW6, and SW3) and zonally symmetric diurnal oscillation D0 that cannot be explained by upward tidal propagation from the lower thermosphere, and (iv) observed tides in the infrared cooling are a suitable proxy for tidal activity including its solar cycle dependence in a part of Earth's atmosphere where direct global temperature observations are lacking.
Nischal, Nirmal, "Nonmigrating Tidal Impact on the Energy Budget of the Lower Thermosphere" (2019). All Dissertations. 2441.