CO2在中氣層與低熱氣層(MLT)中是了解此區域複雜動力機制的理想追蹤物件。此論述使用了搭載於TIMED衛星 (Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite)上SABER儀器 (Sounding of the Atmosphere using Broad Emission Radiometry instrument)的CO2觀測，作為2002至2015年追蹤大氣重力波導致的渦流擴散與大氣潮汐導致的平均運輸之物件。大氣重力波導致的渦流擴散與大氣潮汐導致的平均運輸在中氣層與低熱氣層(MLT)中扮演極重要的角色，但卻鮮少被觀測。 做為一個追蹤大氣重力波所致渦流擴散的追蹤物件，此研究計算了第一筆時間尺度長於一個太陽週期的衛星觀測全球平均渦流擴散係數。比較這些渦流擴散係數與自WACCM模型(Whole Atmosphere Community Climate Model)版與TIME-GCM (Thermosphere - Ionosphere - Mesosphere Electrodynamics - General Circulation Model)版本的參數化大氣重力波計算之係數，顯示出我們的係數可能與大氣重力波破碎所致的擴散有關，這提供了對於大氣重力波參數化史無前例的觀測支援。這項技術之後被使用於證明大氣動力波並沒有劇烈地影響熱氣層中性與電離層電子密度的季節變化。有著數據長於十年的優勢，我們可以看出在高度動態驅動的冬夏至日季節，破碎大氣重力波所致的渦流擴散與太陽週期呈現負相關。 做為一個追蹤大氣潮汐導致的平均運輸的追蹤物件，此研究證明了在春秋分時的熱帶，CO2有一個顯著的當地時間變化，接著它顯示WACCM模擬的類似當地時間變化。這讓WACCM資料輸出的使用顯示，這些熱帶CO2中的當地時間變化主要是由垂直與子午線方向的平流所驅使。這也讓我們看出了SABER溫度剖面分析所使用的一個反演方法，其假設CO2中所有顯著的當地時間變化都與用SABER CO2剖面反演出的SABER溫度剖面沒有清楚的差異。 這些大氣重力波參數化與潮汐餘流傳輸計算都是基於物理，此論述顯著地推進了我們對這些MLT區域中複雜波平均流動力背後物理機制的了解。此論述更高度推薦MLT區域的CO2觀測工作，因為這項研究彰顯了對於如大氣重力波與潮汐此類非常複雜動力機制，CO2能扮演相當良好的追蹤物件。 ;CO2 in the Mesosphere and Lower Thermosphere (MLT) is an ideal tracer for the numerous complicated dynamical motions in the region. This dissertation uses CO2 observations from the Sounding of the Atmosphere using Broad Emission Radiometry instrument (SABER) onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite (TIMED) from 2002 to 2015 as a tracer for eddy diffusion due to gravity waves and advective transport due to tides. Eddy diffusion due to gravity waves and advective transport due to tides are poorly observed but very important in the MLT region.
As a tracer for diffusive transport due to gravity waves, this work calculates the first satellite-based global-mean eddy diffusion coefficients that span more than a solar cycle. Comparing these eddy diffusion coefficients with coefficients calculated from gravity wave parameterizations in versions of the Whole Atmosphere Community Climate Model (WACCM) and in the Thermosphere - Ionosphere - Mesosphere Electrodynamics - General Circulation Model (TIME-GCM) suggest that our coefficients may correspond to diffusion due to breaking gravity waves. This provides first-ever observational support into these gravity wave parameterizations. These were then used to show that gravity waves do not significantly drive the seasonal variations in thermospheric neutral and ionospheric electron density. Taking advantage of the more than a decade long coverage of the data, it was also shown that eddy diffusion due to breaking gravity waves have a negative correlation to the solar cycle during the highly dynamically driven solstice season.
As a tracer for advective transport due to tides, this work proves that there is a significant local-time variation in CO2 over the tropics during equinox. It was then shown that WACCM simulates a similar local-time variation in CO2. This allowed the use of WACCM outputs to show that these local-time variations in tropical CO2 were driven primarily by vertical and meridional advection. It was then shown that SABER temperature profiles derived using a retrieval algorithm that assumes no significant local-time variation in CO2 has clear differences from SABER temperature profiles simultaneously retrieved with SABER CO2 profiles.
As these gravity wave parameterizations and tide-induced transport calculations are Physics-based, this dissertation significantly advances our understanding of the physical mechanisms behind these complicated wave-mean flow dynamics in the MLT region. This dissertation highly recommends more CO2 observations in the MLT region because this work demonstrates how great a tracer it is for very complicated dynamical motions like gravity waves and tides.
