Thesis (Ph. D.)--University of Washington, 2005. / Vita. Includes bibliographical references (p. 97-103).

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Correlative and regression analyses of daily ERA-Interim reanalysis data for three separate solarmaximum periods confirm the existence of a temperature response to short-term (mainly ∼27 day) solarultraviolet variations at tropical latitudes in both the lower stratosphere and troposphere. The response,which occurs at a phase lag of 6–10 days after the solar forcing peak, consists of a warming in the lowerstratosphere, consistent with relative downwelling and a slowing of the mean meridional (Brewer-Dobson)circulation, and a cooling in the troposphere. The midtropospheric cooling response is most significant inthe tropical Pacific, especially under positive El Niño–Southern Oscillation conditions and may be relatedto a reduction in the number of Madden-Julian oscillation events that propagate eastward into the centralPacific following peaks in short-term solar forcing.

Lightning represents a key interaction with climate through its production of nitrogen oxides (NOx) which lead to ozone production. These NOx emissions are generally calculated interactively in chemistry-climate models but there has been little development of the representation of the lightning processes since the 1990s. In most models the parametrisation of lightning is based upon simulated cloud-top height. The aims of the thesis are: to explore existing schemes, and develop a new process-based scheme, to parametrise lightning; to use a new process-based lightning scheme to give insights regarding the role of lightning NOx in tropospheric chemistry; and to use alternative lightning schemes to improve the understanding of the response of lightning to climate change, and the consequent impacts on tropospheric chemistry. First, a new lightning parametrisation is developed using reanalysis data and satellite lightning observations which is based on upward cloud ice flux. This parametrisation is more closely linked to thunderstorm charging theory. It greatly improves the simulated zonal distribution of lightning compared to the cloud-top height approach, which overestimates lightning in the tropics. The new lightning scheme is then implemented in a chemistry-climate model, the UK Chemistry and Aerosol model (UKCA). It is evaluated against ozone sonde measurements with broad global coverage and improves the simulation of the annual cycle of upper tropospheric ozone concentration, compared to ozone simulated with the cloud-top height approach. This improvement in simulated ozone is attributed to the change in ozone production associated with the improved zonal distribution of simulated lightning. Subsequently, data from a chemistry-climate model intercomparison project (ACCMIP) are used to study the state-of-the-art in lightning NOx parametrisation along with its response to climate change. It is found that the models using the cloud-top height approach produce a very similar response of lightning NOx to changes in global mean surface temperature of +0.44± 0.05 TgNK-1, for a baseline emission of 5 TgN yr-1. However, two models using two alternative lightning schemes produce a weaker and a negative response of lightning to climate change. Finally, simulations in a future climate scenario for year 2100 in the UKCA model were performed with the cloud-top height and the ice flux parametrisations. The lightning response to climate change when using the cloud-top height scheme is in good agreement with the positive response found in the multi-model results of the cloud-top height approach. However, the new ice flux approach suggests that lightning will decrease in future. These opposing responses introduce large uncertainty into the projections of tropospheric ozone and methane lifetime in the future scenario. An analysis of the radiative forcing from these two species also shows the large uncertainty in the individual methane and ozone radiative forcings in the future. Due to the opposite effect that lightning NOx has on methane (loss) and ozone (production) the net radiative forcing effect of lightning in present-day and future is found to be close to zero. However, there is a small positive feedback suggested by the results of the cloud-top height approach, whereas no feedback is evident with the ice flux approach. These results show there are large and crucial uncertainties introduced by lightning parametrisation choice, not only in terms of the actual lightning distribution but also atmospheric composition and radiative forcing. The new ice-based parametrisation developed here offers a good alternative to the widely-used approach and can be used in future to model lightning and develop the understanding of associated uncertainties.

Hydroxyl radical HO plays a central role in controlling chemical processes in the troposphere. Current mechanisms are believed to accurately describe its formation, destruction and interaction with other atmospheric trace gases in clean air. Hydroperoxyl radical H0₂ is Iinked to HO in several chain processes and serves among other roles as a reservoir for HO. The relative concentration (H0₂/HO) in clean air is believed to be the order of 10². We here examine the conditions under which steady-state kinetics apply to HO₁ chemistry and derive simple relationships which can be used to predict HO and H0₂ concentration from measurable concentrations of the more stable trace gases. The equations assume a simple form for conditions where the ambient nitrogen oxide concentration is less than 1 ppb. These equations allow closed-form evaluation of the sensitivity of [HO] and [H0₂] to changes in the concentrations of the controlling species and allow assignment of uncertainty limits to the predictions of current tropospheric chemical models. Although most current efforts to test fast tropospheric photochemistry center upon measurements of ambient [HO], our equations indicate that tropospheric [H0₂] determinations may provide a more direct and accurate initial test of our knowledge of HO₁ chemistry in the unpolluted lower atmosphere. Overall the goal of this study is to benefit the experimenter by providing the information of insight and simple but reliable equations and to understand the conditions under which these measurements should be made and how best to interpret their results.

Thesis (Ph.D.)--University of Nevada, Reno, 2005. / "May 2005." Includes bibliographical references. Online version available on the World Wide Web.

It has been shown by Schlesinger and Mintz (1979) that the UCLA general circulation model (GCM) is able to simulate the observed negative correlation between the total amount of ozone in a vertical atmospheric column (the total ozone) and the eastward-propagating synoptic disturbances in the troposphere, with the total ozone maxima and minima located respectively at the troughs and ridges of the tropospheric waves. The goal of the present study was to understand how the GCM simulated this observed relationship. Our analysis shows that the transient-eddy total ozone disturbances were an omnipresent feature of the GCM January simulation in the northern hemisphere midlatitudes, just as they are in nature. It is also found that the transient-eddy total ozone disturbances in the northern hemisphere midlatitudes were closely related to the transient-eddy geopotential heights there throughout the entirety of the simulation. Furthermore, the correlations between these two quantities are negative up to the 72 mb level and attain their largest negative values at the 300 mb level. The analysis also shows that the transient-eddy disturbances in the stratosphere are out of phase with their counterparts in the troposphere, in accord with what would be expected from Dines compensation. In the GCM simulation there is a well-defined positive correlation between the total ozone and the ozone content in each of the model layers in the upper troposphere and lower and middle stratosphere. It is found that although layers 5-8 (19.3-150 mb) contain the largest percentage of the total ozone, it is predominantly layers 6-9 (37.3 -300 mb) that make the largest contribution to the temporal variations of total ozone. In accordance with the observations, a strong negative correlation is found between the simulated total ozone and the height of the simulated tropopause. However, changing the height of the tropopause cannot in itself change the total ozone, but rather only its partitioning between the stratosphere and the troposphere. Our analysis clearly shows that it is the ozone convergence and divergence in an atmospheric column, not the photochemical ozone production and destruction, which are responsible for the synoptic increases and decreases of total ozone. / Graduation date: 1988

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 169-184).