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Research InterestsCoupled
climate and atmospheric chemistry modellingI am interested a number of topics in the area of climate-chemistry modelling, and in particular how these are influenced by natural year-to-year climate variations and under future climate change scenarios.
a) Inter-continental transport of tropospheric ozone Policy-makers
concerned with air quality standards of ground-level ozone, base their legislation around domestic emissions. However, emissions that are produced from natural sources
such as vegetation and lightning, and emissions whose origin is outside Europe
are unregulated by EU law. I am interested in modelling year-to-year variability and future changes in inter-continental transport and how these affect European ozone levels. Figure 1 shows the effect of a 1% decrease in anthropogenic NOx emissions over North America on NH winter surface ozone simulated with the STOCHEM-HadAM3 chemistry-climate model.
b) Quantifying uncertain processes and interactionsNatural emissions of ozone precursor species are linked to climate variables and are highly uncertain e.g. lightning NOx emissions vary with cloud height and precipitation location, isoprene emissions are strongly temperature and PAR sensitive, as well as dependent on plant species and their distribution. Convection exerts a strong influence on the vertical distribution of tropospheric ozone. We have shown that the role of deep convection on the global distribution
of tropospheric ozone to be completely different in two contemporary chemistry transport models (STOCHEM and MATCH-MPIC). Our research
highlighted differences in the strength and height of simulated convection as shown in Figure 2, as
well as differences in the chemistry of isoprene (Doherty et al., 2005 -click here) as the
sources of inter-model disagreement. I am interested in the combined use of model experiments and satellite measurements with the EOS MLS satellite to constrain the uncertainty in these processes and how they affect tropospheric ozone.
c) Climate-chemistry inter-anual variability and future changeYear-to year variability in tropospheric ozone in the tropics is controlled by the El Nino Southern Oscillation. Figure 3 shows simulations with the HadAM3-STOCHEM model of the change in tropospheric column ozone associated with a strong El Nino event (Doherty et al., 2006 -click here). With this model we also simulate an increase in ENSO-related
precipitation and consequently tropospheric ozone variability in the
future. In a recent multi-model comparison by Stevenson et al. (2006), higher water vapour amounts and an enhanced Brewer-Dobson circulation led to tropospheric ozone feedbacks. I am interested in how changes in convection, lightning NOx and isoprene emissions will affect future levels of tropospheric ozone.
Climate variability and its influence on regional climate I am interested in the influence of large scales climate phenomena and their influence on regional climate. In recent work for the CLIP project we have examined how well the Indian Ocean Dipole is simulated in different GCMs and its implications for modulating the short rainy season in East Africa. Masai herders and farmers (see image below) relate their experiences of their vulnerability to year-to-year variability in intensity the short rainy season in the Kilimanjaro region.
Climate change and variability impacts on ecosystemsIn recent and ongoing work we are examining the role of 20th century climate varaibility and climate change on ecosystem function and productivity using the LPJ ecosystem model. I am interested in exploring ecosystem uncertainty associated with the spatial and temporal scale of climate input. Future work with BIOSS colleagues will examine methods to representively sample and characterise uncertainty in ecosystem predictions associated with climate and soils input.
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