The upper troposphere-lower stratosphere (UTLS) is a transition region between the troposphere and the stratosphere. During the boreal summer, the UTLS is dominated by large-scale anticyclonic circulations over the Asian and North American monsoon regions, exhibiting complex dynamical and chemical characteristics. Re-cent studies have emphasized the important role of the summer monsoon systemin stratosphere-troposphere exchange of water vapor and chemical species, which strongly influences the atmospheric chemistry and climate system. The transport in the UTLS region occurs in both directions, stratosphere-troposphere transport (STT)and troposphere-stratosphere transport (TST). For example, observational studies indicate localized maxima of tropospheric pollutants and stratospheric water vapor(SWV) in the UTLS, which are controlled by deep convection and large-scale circulation. Meanwhile, stratospheric ozone (O3) can fold into tropospheric air and entrain into the planetary boundary layer (PBL) via deep STT, and thus affect air quality at the surface. In this thesis, we aim at improving the understanding of the transport processes in the UTLS that are linked to monsoon dynamics using observations and modelling tools.<div><br></div><div>First, we investigate the TST transport in association with the Asian summer monsoon. We examine the simulation of SWV in the Community Earth System Model, version 1 with the Whole Atmosphere Community Climate Model as its atmospheric component [CESM1(WACCM)]. CESM1(WACCM) generally tends to simulate a SWV maximum over the central Pacific Ocean instead of over the Asian continent as observed, but this bias is largely improved in the high vertical resolution version. The high vertical resolution model with increased vertical layers in the UTLS is found to have a less stratified UTLS over the central Pacific Ocean compared with the low vertical resolution model. It therefore simulates a steepened potential vorticity gradient over the central Pacific Ocean that better closes the upper-level anticyclone and confines the SWV within the enhanced transport barrier.<br></div><div><br></div><div>We further study the transport pathways connecting the Northern Hemisphere sur-face and the North American (NA) UTLS by diagnosing Boundary Impulse Response idealized tracers implemented at the Northern Hemisphere surface during summer. In ensemble average, air masses enter the NA UTLS region above Central America, and then slowly mix into the higher latitudes. However, fast transport pathways with modal age around two weeks are evident in some tracer ensembles. For these rapid transport pathways, the tracers first reach the UTLS region over the eastern Pacific and the Gulf of Mexico as a result of enhanced deep convection and vertical advection, followed by horizontal transport over the United States by a strengthened UTLS anticyclone circulation.<br></div><div><br></div><div>To the end, we evaluate the downward transport of stratospheric O3via STT using simulation from a state-of-the-art chemistry climate model implemented with an artificial stratospheric ozone tracer (O3S). We find that O3transported from the stratosphere makes a significant contribution to the surface O3variability where back-ground surface O3exceeds 95thpercentile, especially over the western U.S. Maximum covariance analysis is applied to O3anomalies paired with stratospheric O3traceranomalies to identify the stratospheric intrusion and the underlying dynamical mechanism. The first leading mode corresponds to deep stratospheric intrusions in the western and northern tier of the U.S., and intensified north easterlies in the mid-to-lower troposphere along the west coast, which also facilitate the transport to the eastern Pacific Ocean. The second leading mode corresponds to deep intrusions over the Intermountain Regions. Both modes are associated with eastward propagating baroclinic systems, which are amplified near the end of the North Pacific storm tracks, leading to strong descents over the western United States.<br></div>

The stratosphere of Saturn is highly variable. With an axial tilt of 26.7°, Saturn experiences seasons like Earth and is currently approaching northern summer solstice in 2017. In addition to general seasonal change, previous studies have highlighted that Saturn's stratosphere is host to a range of dynamical phenomena. These processes have an observable effect on the vertical temperature profile and stratospheric concentrations of acetylene (C₂H₂) and ethane (C₂H₆), which may be determined or retrieved from thermal infrared observations of Saturn. This thesis presents an analysis of observations of Saturn acquired by Voyager's IRIS (Infrared Interferometer Spectrometer, 180 - 2500 ^cm-1, Hanel et al.,[1980]) instrument in 1980, Cassini's CIRS (Composite Infrared Spectrometer, 10 - 1400 ^cm-1, Flasar et al.,[2004]) instrument from 2005 to 2012 and the Celeste spectrometer (400 - 2000 ^cm-1, Moran et al.,[2007]) on NASA's IRTF (Infrared Telescope Facility) in 2012 in order to track seasonal and interannual changes in Saturn's stratosphere. The concentrations of C₂H₂ and C₂H₆ were seen to decrease at 15°S and increase at 25°N from 2005 to 2009/2010. These changes at 15°S and 25°N respectively indicate upward and downward branches associated with cross-equatorial seasonally-reversing Hadley circulation that has been predicted by a general circulation model [Friedson and Moses, 2012]. Strong cooling of up to 17 K at high-southern latitudes from 2005 to 2010 suggests an autumnal weakening of a vortex that appears to form at the pole of the summer hemisphere [Fletcher et al., 2008]. The emergence of a similar northern polar vortex as northern summer solstice approaches was yet to be observed in 2012. Interannual differences in the equatorial temperature structure between 1980 and 2009/2010 suggest Saturn's semiannual oscillation (or SSAO, Fouchet et al. [2008]; Orton et al. [2008]) has been captured in a different phase from one year to the next. This is puzzling since the oscillation would be expected to have undergone two cycles assuming its period is half a Saturn year (14.7 years). This contrast is suggestive that the period of the SSAO is more quasisemiannual.

The Atmospheric Chemistry Experiment (ACE) is a satellite mission for remote sensing of the Earth's atmosphere using the solar occultation technique. The primary instrument on this satellite is the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). ACE-FTS retrievals are described with a focus on the creation of <em>a priori</em> temperature and pressure profiles. ACE-FTS measurements are then used to investigate the chemistry, transport and trends of chlorine, fluorine and water in the stratosphere, leading to an improved understanding of processes affecting both stratospheric ozone depletion and global climate change. <br /><br /> Total chlorine (Cl_TOT) in the stratosphere is determined using ACE-FTS measurements of eleven chlorine-containing species, supplemented by both other measurements and models, to determine Cl_TOT as a function of altitude in five latitude zones. All resulting Cl_TOT profiles are nearly linear, with a slight slope. Mean Cl_TOT for 2004 is determined to be 3. 65 ppbv for both the northern and southern midlatitudes (with a precision and estimated accuracy of ??0. 09 and ??0. 13 ppbv, respectively). A slightly lower value of mean Cl_TOT is determined for the tropics and slightly higher values at high latitudes. Total fluorine (F_TOT) in the stratosphere is also determined primarily from ACE-FTS measurements using a similar approach, resulting in stratospheric F_TOT profiles which are nearly linear with mean values ranging from 2. 50 to 2. 59 ppbv for each latitude zone (with a precision of 0. 04-0. 07 ppbv and an estimated accuracy of 0. 15 ppbv). The observed slopes and pattern of latitudinal variation are evidence of the beginning of a decline in global stratospheric chlorine and of the continuing increase in global stratospheric fluorine levels. <br /><br /> The abundance of water in the stratosphere is investigated for the northern hemisphere midlatitudes in 2004 using ACE-FTS measurements. Potential water is determined as [H₂O]+2[CH₄] and from [H₂O] versus [CH₄] correlations, resulting in a value of 7. 14??0. 05 ppmv, which is used to determine a value of 3. 65??0. 15 ppmv for the mean abundance of water entering the stratosphere. Both values are compared directly with historical data from the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument (1985-1994) and show a negligible change, implying that the increases observed by ATMOS and other long-term measurements from that time period have not continued. <br /><br /> The removal of stratospheric water in the Arctic vortex is investigated using ACE-FTS measurements. Using derived quantities from a meteorological data assimilation, northern hemisphere occultations from early 2004 are classified as vortex, vortex edge or extravortex. [CH₄] versus [N₂O] correlations are used to further classify the extravortex occultations as tropical, subtropical or midlatitude. Comparisons between profiles of [N₂O], [CH₄] and [H₂O] inside and outside the Arctic vortex, give estimates of upper stratospheric and lower mesospheric descent rates, indicating that descent in the winter 2004 Arctic vortex was rapid, with evidence of descent at higher altitudes than in past years. <br /><br /> The dehydration of air in the tropical tropopause layer and mechanisms for the entry of water vapor into the stratosphere are investigated by an analysis of ACE-FTS profiles of temperature, water vapor and [HDO]/[H₂O]. Month-to-month comparisons for 2004 and 2005 reveal a clear pattern of seasonal variation and a correlation between minimum temperature and maximum HDO depletion. Further interpretation indicates that the gradual dehydration mechanism accompanied by lofting of ice particles in the tropical troposphere is the most likely explanation for the observed seasonal variation and the shape of the [HDO]/[H₂O] profiles.

The 11 year solar-cycle component of climate variability is assessed in historical simulations of models taken from the Coupled Model Intercomparison Project, phase 5 (CMIP-5). Multiple linear regression is applied to estimate the zonal temperature, wind and annular mode responses to a typical solar cycle, with a focus on both the stratosphere and the stratospheric influence on the surface over the period ∼1850–2005. The analysis is performed on all CMIP-5 models but focuses on the 13 CMIP-5 models that resolve the stratosphere (high-top models) and compares the simulated solar cycle signature with reanalysis data. The 11 year solar cycle component of climate variability is found to be weaker in terms of magnitude and latitudinal gradient around the stratopause in the models than in the reanalysis. The peak in temperature in the lower equatorial stratosphere (∼70 hPa) reported in some studies is found in the models to depend on the length of the analysis period, with the last 30 years yielding the strongest response. A modification of the Polar Jet Oscillation (PJO) in response to the 11 year solar cycle is not robust across all models, but is more apparent in models with high spectral resolution in the short-wave region. The PJO evolution is slower in these models, leading to a stronger response during February, whereas observations indicate it to be weaker. In early winter, the magnitude of the modelled response is more consistent with observations when only data from 1979–2005 are considered. The observed North Pacific high-pressure surface response during the solar maximum is only simulated in some models, for which there are no distinguishing model characteristics. The lagged North Atlantic surface response is reproduced in both high- and low-top models, but is more prevalent in the former. In both cases, the magnitude of the response is generally lower than in observations.

The stratospheric and mesospheric wind field in winter is dominated by the stratospheric polar vortex, which reaches out up into the mesopause region and leads to strong westerlies there in winter. On the other hand, the tropospheric mean winter wind field is also connected with the polar vortex which thus can be considered as being extended from the surface up to the lower thermosphere. lt is found that the winter mesopause region zonal winds, as measured at the Collm Observatory of the University of Leipzig, are closely connected with the North Atlantic Oscillation (NAO) being an integrated measure for the northem hemispheric mean circulation. The NAO itself is found to be a measure for Central Europe winter temperatures. Thus also the mesopause region winds are closely correlated to the Central European winter surface temperatures. / Das stratosphärische und mesosphärische Windfeld wird im Winter wesentlich vom stratosphärischen Polarwirbel bestimmt, der von der Stratosphäre bis in die Mesopausenregion reicht und dort zu starken Westwinden führt. Auf der anderen Seite ist die mittlere troposphärische Zirkulation ebenfalls mit dem stratosphärischen Wirbel korreliert, so daß letzterer als von der Erdoberfläche bis in die untere Thermosphäre reichend betrachtet werden kann. Aus diesem Grund sind die mittleren Zonalwinde, gemessen am Observatorium Collm der Universität Leipzig, mit der Nordatlantikoszillation (NAO) korreliert. Andererseits hat die NAO einen starken Einfluß auf mitteleuropäische Wintertemperaturen, und damit ist der Wind im Mesopausenbereich ebenfalls mit den Wintertemperaturen korreliert.

The measurement of trace gases through remote sounding techniques has led to a better understanding of the processes controlling the structure and variability of the stratosphere. Differences between measurements over space and time are due to atmospheric variability and instrument errors: thus, comparison of measurements can be used to test our knowledge of both. Comparisons of measurements over long time periods are used to identify trends. Balloon-borne infrared emission radiometer instruments have been used to make measurements of midlatitude stratospheric HNO3 spanning a period of twelve years. The timing of the measurements is notable, since they occur before and well after the eruption of Mt. Pinatubo, which significantly perturbed HNO3 levels, complicating prior trend analyses. No significant differences are found between the HNO3 retrievals, although large measurement uncertainties preclude any conclusion concerning trends. Comparisons of measurements that are closely spaced in space and time are useful for satellite validation, where one aims to reduce the effect of atmospheric variability on the estimation of systematic and random errors. A novel technique for the estimation of systematic error, which differentiates between additive and multiplicative bias, is introduced. In a comparison of measurements by the ACE-FTS and Aura MLS instruments, significant multiplicative biases are identified and described. In order to validate the reported random errors (RREs) of measurements, satellite validation studies often focus on measurements in the tropical stratosphere, where variability is weak. The scatter in tropical measurements can then be used as an upper limit on instrument precision. In an analysis of tropical measurements by the ACE-FTS, scatter is found to be roughly consistent with the RREs for H2O and CO. The scatter in measurements of O3, HNO3, and N2O, while larger than the reported random errors, is roughly consistent with the variability simulated in the Canadian Middle Atmosphere Model. This work implies that the random error of the ACE-FTS measurements is smaller than the weak natural variability of the tropical stratosphere.

The measurement of trace gases through remote sounding techniques has led to a better understanding of the processes controlling the structure and variability of the stratosphere. Differences between measurements over space and time are due to atmospheric variability and instrument errors: thus, comparison of measurements can be used to test our knowledge of both. Comparisons of measurements over long time periods are used to identify trends. Balloon-borne infrared emission radiometer instruments have been used to make measurements of midlatitude stratospheric HNO3 spanning a period of twelve years. The timing of the measurements is notable, since they occur before and well after the eruption of Mt. Pinatubo, which significantly perturbed HNO3 levels, complicating prior trend analyses. No significant differences are found between the HNO3 retrievals, although large measurement uncertainties preclude any conclusion concerning trends. Comparisons of measurements that are closely spaced in space and time are useful for satellite validation, where one aims to reduce the effect of atmospheric variability on the estimation of systematic and random errors. A novel technique for the estimation of systematic error, which differentiates between additive and multiplicative bias, is introduced. In a comparison of measurements by the ACE-FTS and Aura MLS instruments, significant multiplicative biases are identified and described. In order to validate the reported random errors (RREs) of measurements, satellite validation studies often focus on measurements in the tropical stratosphere, where variability is weak. The scatter in tropical measurements can then be used as an upper limit on instrument precision. In an analysis of tropical measurements by the ACE-FTS, scatter is found to be roughly consistent with the RREs for H2O and CO. The scatter in measurements of O3, HNO3, and N2O, while larger than the reported random errors, is roughly consistent with the variability simulated in the Canadian Middle Atmosphere Model. This work implies that the random error of the ACE-FTS measurements is smaller than the weak natural variability of the tropical stratosphere.

Sprites, halos, and elves are members of a family of short-lived, luminous phenomena known as Transient Luminous Events (TLEs), which occur in the middle atmosphere. Sprites are vertical glows occurring at altitudes typically ranging from ~40 to 90 km. In video imagery they exhibit a red color at their top, with blue tendril-like structure at low altitudes. Elves are disk-like glows that occur at the base of the ionosphere, with diameters of ~100-300 km, and have very short lifetimes (~2-3 ms). Halos are diffuse glows that occur at low altitudes, have diameters <100 km, and have a duration that may last up to 10s of ms. A majority of the studies of TLEs have taken place over the Midwestern U.S. where they were first discovered. This area produces large thunderstorms, which in turn generate large lightning discharges that have been associated with the formation of TLEs. Studies have used the low frequency radiation that initiates with these strokes to study characteristics of these events. This low frequency radiation has been used to determine where large numbers of TLEs may occur. Extreme southern Brazil is a region of the globe believed to have many TLEs, but few studies on these phenomena. Two collaborative campaigns involving Utah State University proceeded in 2002-2003, and in 2006. Multiple TLE images were made, proving this is, indeed, a region of the globe where these types of events are prominent. In particular, one storm in February 2003 produced over 440 TLEs imaged by USU video cameras. Of these events, over 100 of them had associated halos. Statistical studies for halos previously had been performed in the U.S., but never abroad. Also, several events from the February storm have been associated with negative cloud to ground lightning, a surprising occurrence, as to date, less than a handful of such events have ever been witnessed or published. In analyzing the TLEs from this campaign, we have shown the halos are similar to those seen in the U.S., even though the storms may be somewhat different. Also, detailed analyses of the negative events show both temporal and spatial morphology heretofore never reported on.

The Atmospheric Chemistry Experiment (ACE) is a satellite mission for remote sensing of the Earth's atmosphere using the solar occultation technique. The primary instrument on this satellite is the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). ACE-FTS retrievals are described with a focus on the creation of <em>a priori</em> temperature and pressure profiles. ACE-FTS measurements are then used to investigate the chemistry, transport and trends of chlorine, fluorine and water in the stratosphere, leading to an improved understanding of processes affecting both stratospheric ozone depletion and global climate change. <br /><br /> Total chlorine (Cl_TOT) in the stratosphere is determined using ACE-FTS measurements of eleven chlorine-containing species, supplemented by both other measurements and models, to determine Cl_TOT as a function of altitude in five latitude zones. All resulting Cl_TOT profiles are nearly linear, with a slight slope. Mean Cl_TOT for 2004 is determined to be 3. 65 ppbv for both the northern and southern midlatitudes (with a precision and estimated accuracy of ±0. 09 and ±0. 13 ppbv, respectively). A slightly lower value of mean Cl_TOT is determined for the tropics and slightly higher values at high latitudes. Total fluorine (F_TOT) in the stratosphere is also determined primarily from ACE-FTS measurements using a similar approach, resulting in stratospheric F_TOT profiles which are nearly linear with mean values ranging from 2. 50 to 2. 59 ppbv for each latitude zone (with a precision of 0. 04-0. 07 ppbv and an estimated accuracy of 0. 15 ppbv). The observed slopes and pattern of latitudinal variation are evidence of the beginning of a decline in global stratospheric chlorine and of the continuing increase in global stratospheric fluorine levels. <br /><br /> The abundance of water in the stratosphere is investigated for the northern hemisphere midlatitudes in 2004 using ACE-FTS measurements. Potential water is determined as [H₂O]+2[CH₄] and from [H₂O] versus [CH₄] correlations, resulting in a value of 7. 14±0. 05 ppmv, which is used to determine a value of 3. 65±0. 15 ppmv for the mean abundance of water entering the stratosphere. Both values are compared directly with historical data from the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument (1985-1994) and show a negligible change, implying that the increases observed by ATMOS and other long-term measurements from that time period have not continued. <br /><br /> The removal of stratospheric water in the Arctic vortex is investigated using ACE-FTS measurements. Using derived quantities from a meteorological data assimilation, northern hemisphere occultations from early 2004 are classified as vortex, vortex edge or extravortex. [CH₄] versus [N₂O] correlations are used to further classify the extravortex occultations as tropical, subtropical or midlatitude. Comparisons between profiles of [N₂O], [CH₄] and [H₂O] inside and outside the Arctic vortex, give estimates of upper stratospheric and lower mesospheric descent rates, indicating that descent in the winter 2004 Arctic vortex was rapid, with evidence of descent at higher altitudes than in past years. <br /><br /> The dehydration of air in the tropical tropopause layer and mechanisms for the entry of water vapor into the stratosphere are investigated by an analysis of ACE-FTS profiles of temperature, water vapor and [HDO]/[H₂O]. Month-to-month comparisons for 2004 and 2005 reveal a clear pattern of seasonal variation and a correlation between minimum temperature and maximum HDO depletion. Further interpretation indicates that the gradual dehydration mechanism accompanied by lofting of ice particles in the tropical troposphere is the most likely explanation for the observed seasonal variation and the shape of the [HDO]/[H₂O] profiles.

Recent observational and modeling studies indicate a robust dynamical coupling between the stratosphere and troposphere during boreal winter. This coupling occurs in association with the Northern Annular Mode (NAM), which itself accounts for a significant fraction of the variability of the extratropical circulation. While monthly NAM dynamics have been studied previously, the mechanisms that give rise to NAM variability on short intraseasonal timescale are still unclear. We perform regression analyses, case studies, and composites based on periods of dynamical growth/decay to investigate the roles of the different proposed mechanisms in driving the atmospheric variability observed in association with the NAM on short intraseasonal timescales. More specifically, lag-regression analyses are used to identify the mean canonical structures present during the evolution of a typical NAM event. Illustrative case studies of robust stratospheric NAM events but with different tropospheric signals are contrasted in order to identify the underlying dynamical reasons for the observed differences. Finally, composite analyses of NAM tendencies are performed to isolate the structural and dynamical evolution of NAM events. Zonal-mean and three-dimensional eddy-flux diagnoses are used to examine the role of eddy-mean flow interaction in driving the wind tendencies characteristic of the NAM. In particular, Plumb flux analyses are employed to quantify the contribution of regional stationary wave anomalies toward the zonal mean wind tendency field. Potential vorticity inversions are also used to determine the role of stratospheric anomalies in inducing tropospheric circulations. The case study analyses indicate that preexisting tropospheric PV anomalies can mask the downward penetration of an initial stratospheric NAM signal into the troposphere. PV inversions further suggest that a minimum requirement for a direct downward stratospheric influence is that the stratospheric NAM signal be robust in the lower stratosphere. The dynamical composites show a remarkable degree of reverse symmetry between the zonal-mean dynamical evolution of positive and negative NAM events. Anomalous Eliassen-Palm fluxes are observed in the troposphere and stratosphere, consistent with index of refraction considerations and an indirect downward influence of the stratosphere on the troposphere. The patterns of anomalous wave driving, primarily due to low-frequency planetary scale waves, provide the main forcing of the zonal mean wind tendency field. Regional wave activity fluxes indicate that the wave driving pattern represents the manifestation of planetary scale anomalies over the North Atlantic.