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Dr Helen Kettle - Previous Research

CASIX PROJECT (2003 - 2006)
Mechanistic Modelling of Air-Sea Carbon Fluxes

Working with Chris Merchant, I investigated the sensitivity of estimates of air-sea fluxes of carbon dioxide to short-time-scale, small-vertical-scale variability. The air-sea interface is a very variable place, the fastest variations being associated with the diurnal cycle of sunshine and weather conditions. I have shown, for example, that neglecting the co-variability of wind and surface pressure leads to errors in flux estimates of order 10%, and there are many such co-factors to be accounted for. I have recently been examining the effects of the spectral resolution of light and phytoplankton photoadaptation on ocean carbon dynamics. These results will feed into a major hindcast of global ocean carbon flux that cannot explicitly account for these small-scale processes. This will be done at the Met Office as part of the Centre for observation of Air-Sea Interactions and fluXes (CASIX).

Papers from this project are listed on PUBLICATIONS

EMERGE PROJECT (2000 - 2003)
Statistical Modelling of Air and Water Temperatures at Remote Moutain Lakes

From 2000-2003 I worked with Prof. Roy Thompson in the Geology and Geophysics department on a multi-national EU fifth-framework project called EMERGE. The aim of this project was to assess the ecological status of Europe's remote mountain lakes.

My role in this project included the following:

1. Development of an empirical model for lake surface water temperatures and ice cover duration across Europe and Greenland based on air temperature and clear sky (theoretical) solar radiation.

2. Statistical downscaling of air temperature from data produced by General Circulation Models to weather stations located in remote mountain regions. The National Centers for Environmental Prediction and Atmospheric Research (NCEP & NCAR) have jointly produced a set of climate data known as Reanalysis Data available from 1958 that is homogeneous in time. Using long-term climate data available from a few mountain weather stations we can investigate whether it is possible to use the downscaled data to examine general changes in mountain climates over the past 40 years.

Papers from this project are listed on PUBLICATIONS

PHD PROJECT (1996 - 2000)
Numerical Modelling of Solute Dispersion in Rivers

My doctoral work on at Lancaster University, supervised by Prof. Keith Beven, focussed on the numerical modelling of soluble pollutant dispersion in rivers.

I developed a model which uses fuzzy logic rules to predict the turbulent fluctuations in the mean velocity field. These fluctuations are assumed to control the diffusion of the solute as molecular diffusion is considered negligible. The fuzzy rules are derived from time series velocity measurements taken around a dead zone in a laboratory flume for many different geometries and discharges. The rules are then included in a steady state hybrid finite volume advection-diffusion scheme. The implementation of the fuzzy rules in the scheme produces fuzzy numbers for the final spatial distribution of concentration. Thus the uncertainty in the turbulent field is directly incorporated into the solution. This model was applied to a hot water mixing experiment in a laboratory flume and to a dye tracer experiment in a natural dead zone on the River Severn.