Wavelet Analysis of Cirrus Multiscale Structures from Lidar Backscattering: A Cirrus Uncinus Complex Case Study

Abstract

Although cirrus cloud structures play an important role in dynamics issues, cloud radiative calculations, and cloud parameter retrievals from satellite measurements, fully understanding cirrus cloud structures still remains a challenge. A case study of a cirrus containing mesoscale uncinus complexes (MUC) with a two-layer structure observed by a high-resolution lidar is presented using the method based on wavelet transform. The results indicate that dynamical processes play a leading role in determining cloud multiscale structures. The uncinus cells with a length scale on the order of ?1 km, embedded in both the top and lower layers, have similar spectral features and are probably produced by a similar mechanism?thermal perturbation generated by heating and cooling effects associated with phase changes of water (i.e., adiabatic heating) and radiative processes. However, the mesoscale cloud patches are probably involved in different dynamics processes, suggesting that understanding of the interaction of cloud-scale convective activities with 2D turbulence and propagating gravity waves in cirrus cloud systems should receive more attention in future model simulations. The study also demonstrates the utility of the continuous and discrete wavelet transform to objectively and quantitatively analyze the properties of cirrus cloud structures, which is a useful supplement to the traditional Fourier transform method.