deletions | additions       diff --git a/observations.tex b/observations.tex  index 3303449..ffb0f10 100644  --- a/observations.tex  +++ b/observations.tex 
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\end{equation} with coefficients $a$ and $b$ derived from a set of observations.  Because it was clear that $W$ cannot vary with wind speed in a linear way, some autors tried to link $W$ with the cubed wind speed,   \begin{equation}  W = a({U}_{10} + b)^3 b)^3.  \end{equation}  According to Philips, in 1985, to obtain the whitecap fraction, one can refer to an average bubble persistence time $\tau_{bub}$ to obtain $W$:  \begin{equation}