  The classical EMD algorithm has been used extensively in the literature to
decompose signals that contain nonlinear waves. However when a signal contain
two or more frequencies that are close to one another the decomposition might
fail. In this paper we propose a new formulation of this algorithm which is
based on the zero crossings of the signal and show that it performs well even
when the classical algorithm fail. We address also the filtering properties and
convergence rate of the new algorithm versus the classical EMD algorithm. These
properties are compared then to those of the principal component algorithm
(PCA). Finally we apply this algorithm to the detection of gravity waves in the
atmosphere.
