Description:
<jats:p>Using firn-core data from ten widely spread Antarctic sites, the dependence
of firnification on temperature, wind and accumulation rate has been examined with
two empirical models. One model relates the square of the porosity to the
logarithm of the overburden pressure, and yields good fit to data through the
first stage of firnification up to around 0.70-0.75 Mg m <jats:sup>−3</jats:sup>,
beyond which it severely overestimates density. All three meteorological factors
enter into this model, with higher temperatures and stronger winds increasing
firnification rates, whilst higher accumulation rates have the opposite effect at
any given depth. A temperature increase of 10°C has the equivalent effect to a
wind-speed increase of 5 m s<jats:sup>−1</jats:sup>, or an accumulation rate
decrease of 0.10 m a<jats:sup>−1</jats:sup> w.e. A second model equates the
logarithm of the porosity to overburden pressure and gives a much better fit to
field data at higher densities where values asymptote to the bubble-free density
of pure ice. This model generally yields a poor match to field data in the upper
layers, with surface densities generally overestimated. Annual mean wind speed
appears to be the least important of the local variables in this case, consistent
with the success of the model at greater depth in matching data profiles.</jats:p>