The Earth’s atmosphere and oceans contain strongly swirling coherent structures. The sphericity of the Earth’s surface, which may be modelled by the beta-effect, is responsible for the motion of these vortices, and also for the existence of Rossby waves. This dissertation examines the evolution of distributed vortices on the beta-plane when the vortices are much stronger than the background beta-effect. There is a small nondimensional parameter ε , and a solution to the problem may be sought as an asymptotic expansion in ε. The near-field equation is then, to first order, a forced radial Rayleigh equation. For the nondivergent case, with no vortex stretching, a different dynamical balance holds in the far field. Chapter 2 derives an exact mode-one solution for the radial Rayleigh operator and completely solves the classical inviscid instability initial-value problem for mode-one disturbances to a circular basic state. Disturbances tend to a steady-state solution if the basic state circulation is nonzero, and grow algebraically without bound otherwise. Chapter 3 examines properties of the causal Green’s function for the far-field Rossby wave equation. Chapter 4 calculates the first-order solution to the global problem in the nondivergent case by the method of Matched Asymptotic Expansions. For zero circulation, there is no far field. The resulting trajectory of vortices is computed; several ways of identifying the centre of the vortices are presented. Trajectories are calculated for the Rankine and Gaussian vortices. Chapter 5 calculates the asymptotic behaviour of the second-order solution, and examines the nonuniformity of the asymptotic expansion. In the case of nonzero circulation, the expansion loses validity for times t = 0( ε -2/3 ) and spatial scales r = 0( ε -1/3 ), rather than t = 0( ε -1) and r = 0(1) respectively. Chapter 6 solves the divergent problem numerically to first order, and also analytically for asymptotically large Rossby radii of deformation. The order of breakdown is then t = 0( ε -1). Chapter 7 presents conclusions and suggestions for further research.

The overall aim of this thesis is to gain a better understanding of certain key attributes and processes in the Upper Troposphere/Lower Stratosphere (UTLS). This work involves exploring the interactions between radiation and dynamics which ultimately affect the destination of chemical constituents. A recently identified feature of the extratropical upper troposphere and lower stratosphere is a region of stable air located just above the tropopause known as the tropopause inversion layer (TIL) which appears as a peak in the stratification. The first main chapter of the thesis focuses on elucidating the large scale dynamical mechanisms which lead to the formation of the TIL by exploring the downward influence of the stratosphere on the UTLS region. Model experiments illustrate that the TIL can arise as a result of the dynamics and the wave driving leads to an upwelling structure that results in a TIL. The maximum value and the shape of the TIL peak vary considerable depending on how the observational data is processed. A common method involves averaging with respect to the tropopause. The details of this averaging are found to affect the shape and strength of the TIL. There exist a double peak in the radiative heating (and correspondingly in the upwelling) in the tropical lower stratosphere and radiative calculations reveal that part of it can be considered as imposed. Radiative process are usually thought of as relaxational with waves being regarded as driving the circulation. Idealised model experiments show that imposing a heating leads to an upwelling and the structure of the latter depends on the aspect ratio of the imposed heating. In such experiments, the waves form part of the response. The last core chapter looks at the relatively large annual cycle in temperatures at around 70 hPa in the UTLS. The annual cycle has peak to peak amplitude of about 7 K in observational data. Using radiative experiments that take into account the time evolution of trace gases, the effect of ozone and water vapour on temperatures is quantified. Water vapour is found to play a significant role in this region, especially lower down in the region of the cold point, with important non local influences on temperature. A further set of experiments reveals how the temperatures are affected by the interactions between the dynamics and radiation.

In this thesis, the broad topic of atmosphere chemistry over the Northern Atlantic is considered, especially using trace gas climatologies as indicators of the influence of continental outflow of anthropogenic pollutants on the composition and chemistry of this region. The data described were obtained during recent aircraft measurements campaigns conducted aboard the UK MRF C-130 Hercules platform, under the auspices of the UK-NERC ACSOE (Atmospheric Chemistry Studies in Oceanic Environment) and the EU MAXOX (MAXimum OXidation rates in the free troposphere) campaigns. Instruments mounted on this aircraft platform provided in situ measurements of the concentrations of O3, NOx, NOy, H2O2, CH3OOH, CO and HCHO in the free troposphere over the North Atlantic. This thesis describes, in part, the validation of measured modelled trace gas distributions via trace gas climatologies over the broad latitude range 20°N to 60°N by way of data bins ranging from 0-8 km. This climatological analysis provides an insight into the distribution of trace gas in this region, especially on a seasonal basis. Results suggest a number of photochemical tracers show pronounced seasonal variation over altitudes less than 8km. The exact nature of this seasonal variation is discussed, along with possible evidence of a wide spread photochemical source for a pronounced springtime ozone maximum in these environments. The validation of aircraft measurements has been investigated via model analysis. Climatology data has been compared to the outputs of a chemistry transport model. This work shows that for some tracers the model is able to reproduce measured values with a high degree of accuracy.

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Small-scale structure of the thermosphere is studied at high-latitudes for its important role in ion-neutral coupling. Four Fabry-Perot Interferometers (FPIs) in Scandinavia are primarily used. These are supplemented by a range of other instruments, including the Spectrograph Imaging Facility, radars, magnetometers, all-sky cameras, and satellite data. The FPIs measure the atomic oxygen emission line at 6300 A, from 240 km altitude. Emission intensities, thermospheric line of sight wind speeds, and neutral temperatures are obtained. Comparisons of electron densities from tomography data and EISCAT (European Incoherent SCATter) radar with FPI intensities allow the investigation whether dissociative recombination is the dominant production mechanisms of the nighttime 6300 A oxygen line. Cross correlations indicate that the thermosphere varies on short temporal scales. Altitude variations have less effect due to the broad (-50 km) emission height band. Atmospheric gravity waves in the thermosphere have been detected for the first time in ground-based FPI data using Lomb-Scargle analysis. Joule heating from electrojet currents, and particle precipitation in the auroral oval, have been identified as the primary source mechanisms using two case study nights. High time resolution data shows a limit to the variability of the thermosphere to be approximately 1-minute. Statistical studies of the gravity waves from 567 nights of FPI data show that the length of the night and time resolution are the most important influences on the number and periods of waves detected. Greater numbers of short period waves are detected in the rapidly responding intensities than in the winds and temperatures. Little variation with geomagnetic activity or solar cycle is observed. Periods at particular harmonics of the length of the night are preferred between October and February. Comparisons of mainland and Svalbard data show that the shorter period waves that are formed equatorward in the auroral oval mostly dissipate before reaching Svalbard.

Cold air pools (CAPs) over complex terrain have rarely been investigated in hilly regions that are typical across the UK. This thesis gives a detailed account of CAP observations gained during the COLd air Pooling EXperiment (COLPEX), conducted in the Clun Valley region of Shropshire, England. A short 9–month climatology study reveals that weak CAPs, defined as temperature inversions larger than 1◦C across a valley depth of ∼170m, occur 45% of all nights. Strong CAPs, defined as temperature inversions larger than 4◦C, occur 12% of all nights. Strong CAPs are found to occur when the following “ideal” conditions are met: (1) mean sea level pressures >1029 hPa, (2) pressure gradients <1.5 Pa km−1, (3) mean night-time ambient wind speeds <3 m s−1, (4) mean night-time ambient wind directions from the N, (5) low values of Flw, i.e., <0.80, where Flw is the ratio of incoming to outgoing LW radiation. Using this criteria a case study investigation is conducted. The case study highlights the sensitivity of CAPs to nocturnal phenomena, which have rarely been documented before. The CAP is disturbed by; a gravity wave, an acceleration of the ambient wind (∼4.6 x 10−4 m s−2) and by an increase in the ambient wind speed associated with a developing nocturnal low level jet (NLLJ). The final breakup of the CAP occurred some 3.5hrs after local sunrise and the NLLJ appears to play a role. Further investigations indicate that NLLJs occur during other CAP nights also. A wind climatology study is conducted investigating the relationship between ambient winds and valley winds. Four forcing mechanisms for valley winds are proposed by Whiteman & Doran (1993), and these are; forced channeling, downward momentum transport, pressure driven channeling and thermally driven flows. Downward momentum transport preferentially occurs in less sheltered regions and forced channeling in narrow valley regions. The valley wind behaviour is notably different from day to CAP nights, with thermally driven down-valley winds prominent during CAP nights. Pressure driven channeling and daytime thermally driven flows (anabatic winds) are not seen. High resolution model simulations of five CAP nights, show that drainage flows develop frequently. However, the timing, structure and strength of drainage flows differs from case to case. Two regimes stand out: (1) For low ambient wind speed nights the development of strong drainage flows leads to increased mixing in valley bottom regions, resulting in weaker stability. (2) For high ambient wind speed nights, weaker drainage flows form initially, which result in stronger stability and stronger temperature gradients in valley bottom regions. This result suggest a negative feedback on near surface stability caused by stronger drainage flows that preferentially form during strong CAP nights. This highlights a potential misunderstanding of CAP characteristics in valleys. Here it is shown that stronger CAPs do not have stronger near surface temperature gradients. An investigation into the affects of ambient wind on local sheltering/decoupling in valley bottom regions is conducted. Results suggest that quantifying the amount of sheltering/ decoupling of valley bottom regions can be a useful indicative tool for understanding the timing and amount of cooling that is occurring during CAP formation. However, future attempts to use NH/U as a downscaling tool should endeavour to integrate other factors, such as; changes in the ambient wind, drainage flows, gravity waves and NLLJs.

The upper mesosphere/lower thermosphere (MLT) is an important transition region. However, it remains poorly understood relative to other parts of the Earth’s atmosphere, largely due to a lack of observations. Metal species, produced by meteoric ablation act as useful tracers of upper atmospheric dynamics and chemistry. Of these meteoric metals, K has long been an enigma. Limited lidar data at extra-tropical latitudes shows that the K layer displays a semi-annual seasonal variation rather than the annual pattern seen in other metals such as Na and Fe. This is a rather surprising feature as both Na and K are Group 1 alkali metals and, thus, should exhibit similar behaviour. The aim of this thesis was to produce the first near-global K retrieval which could be used to evaluate this unusual behaviour, as well as providing a new dataset with which to test our understanding of the MLT region. The K retrieval uses dayglow measurements of K at ~770 nm from the Optical Spectrograph and InfraRed Imager System (OSIRIS) instrument on-board the Odin satellite. This retrieval is shown to be capable of retrieving K number density profiles with a 2 km vertical resolution and a typical peak layer error of ±15%. It is shown to compare well with the limited available lidar data. A first near-global look at the global K layer is presented, which shows that the unusual semi-annual seasonal behaviour is global in extent. The OSIRIS data is used to validate the National Center of Atmospheric Research (NCAR) Whole Atmosphere Community Climate Model (WACCM) modelled K layer; showing good overall agreement and providing support for a new K chemistry scheme which is included in the model. Both OSIRIS and WACCM datasets are used to examine the response of the Na and K metal layers to the 11-year solar cycle. Unlike Na, K shows an anti-correlation with the 11-year solar cycle. The associated temperatures appear to be the predominant source of this anti-correlation. Finally, the response of the WACCM modelled K, Na and Fe layers is examined with respect to longer-term (50-year) changes within the MLT region. K is the only metal to demonstrate a pronounced response to the recent cooling temperature trend.

In this thesis, the TOMCAT and HadGEM2-ES models are used to improve the understanding of the complex interactions between tropospheric ozone and the global biosphere. The focus is on the impacts of surface ozone on crops, impacts of land surface vegetation changes on tropospheric ozone and the effects of vegetation ozone damage on tropospheric chemistry through changes in dry deposition and BVOC emissions. This thesis presents the first estimates of the impact of ozone precursor emissions from each of the northern hemisphere’s major industrialised regions (N America, SE Asia and Europe) on crop yields globally and in continents downwind of each region. Using a range of ozone crop damage metrics, 100% reductions in SE Asian anthropogenic NOx emissions tend to produce the greatest global reduction in crop production losses (42.3-95.2 %). A 100% reduction in N American anthropogenic NOx emissions produces the largest transboundary impact, resulting in European production loss reductions of between 14.2% and 63.2 %. Preindustrial model tropospheric ozone distributions are shown to be sensitive to the model vegetation coverage and representation of biosphere atmosphere processes. Simulations with HadGEM2-ES indicate a pre-industrial ozone burden which ranges from 200.4 Tg to 220.9 Tg with the variation resulting from differences in the model land vegetation distribution, the CO2 mixing ratio the vegetation was exposed to and the model climate setup. The change in pre-industrial to present day ozone burden ranged from 71.9 Tg to 92.5 Tg translating into an estimated radiative forcing of 0.227Wm−2 to 0.244Wm−2. The response of ozone concentrations to land cover changes is greater than the response to changes in the CO2 mixing ratio the vegetation is exposed to. The ozone distribution is shown to be more sensitive to changes in the rates of isoprene emissions than to changes in dry deposition processes. The effects of ozone damage have a self limiting effect on ozone and NOy dry deposition leading to a rise in surface ozone concentrations. Depending on plant sensitivity to ozone damage, mean total stomatal uptake was shown to decline by 0.22 to 0.42 mmolO3m−2 resulting in average surface ozone concentrations rising by 0.02 to 0.03 ppbv, with local increases of up to 14 ppbv. The effects of ozone damage on photosynthesis is to reduce isoprene emissions, producing slight drops in ozone over the more polluted regions offsetting the rise in concentrations due to the dry deposition effect. The inclusion of both effects resulted in a net rise in surface ozone concentrations indicating the dry deposition response to ozone damage dominates over the effects on isoprene emissions.