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Title: Model sensitivities and stratosphere-troposphere interactions
Author: Flint, Alice
ISNI:       0000 0004 2728 5608
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2012
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In recent years it has been shown that the troposphere is affected by changes in the climate of the stratosphere as well as vice versa. Investigating the downward influence has implications for understanding not only past climate but also for predicting future climate. A simplified, Newtonian-forced general circulation model is used to investigate the impact of changes in the stratosphere on the tropospheric circulation. First the sensitivity of tropospheric climate, tropospheric climate variability and response to stratospheric forcing to the surface temperature relaxation timescale are investigated. Changes to this parameter are shown to have significant impact on the model’s climatology, influencing both the thermal structure of the lower troposphere and the position of the eddy driven mid-latitude jet. The change in mean tropospheric climate influences the annular variability, including its timescale. A strong relationship between this timescale and the magnitude of response to forcing is found, which is consistent with the fluctuation – dissipation theorem. The tropospheric response for both the surface parameter experiments and stratospheric temperature forcings is shown to be remarkably similar. This indicates that the same dynamical feedbacks are triggered, and thus resulting in the same annular mode-like response. Further, the impact of an improved representation of the stratosphere (in a model of greater vertical extent) and its effect on the response to a range of stratospheric heating perturbations is investigated. The extent of the heating perturbations, both in latitude and altitude, are shown to have a significant impact on the tropospheric response. These experiments further reveal an influence of the tropospheric eddy response back onto the stratospheric forcing region which modifies the direct stratospheric response to the heating. This suggests a strong two way coupling between the lower stratosphere and the tropospheric jets and storm track eddies.
Supervisor: Haigh, Joanna Sponsor: Imperial College London
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral