We analytically compute the probability distribution function (PDF) of the local Reynolds stress ( $R$) for forced Hasegawa-Mima turbulence. With the assumption that the PDF tail is due to an instanton with the spatial form given by the modon solution, the tail of the PDF of $R$ is found to be a stretched, non-Gaussian exponential, with the specific form $\exp \left[{-cR}^{3/2}\right]$ ( $c$ is a constant). We relate the temporal localization of the instanton to the degree of “burstiness” of the momentum transport event.

• Received 3 August 2001

DOI:https://doi.org/10.1103/PhysRevLett.88.225002