INTERACTIONS - SOLAR AND LASER-BEAMS IN STRATUS CLOUDS, FRACTALS AND MULTIFRACTALS IN CLIMATE AND REMOTE-SENSING STUDIES

Recent research on cloud structure and cloud-radiation interaction at NASA's Goddard Space Flight Center is presented as a show case of inte rdisciplinary work where fractals and multifractals play a central rol e. Focus has been primarily on stratocumulus because of their first-or der effect on the Earth's energy balance (hence the global climate) du e to their unusual horizontal extension and persistence. These cloud l ayers have quasi-flat upper/lower boundaries and appear to be quite un iform but are highly variable inside. The general strategy has been: u tilization of spatial statistics of in situ and remotely sensed data p ertaining to cloud structure to constrain stochastic cloud models used in turn for radiative transfer simulations where artificial radiation fields are generated; these fields are compared to actual measurement s, and so on, until a degree of closure is achieved. The major trends have been: i) computation and understanding of cloud-radiative propert ies from the large scales of interest to Global Climate Models (over 1 0(2) km) down to the smallest observable scales (less than 10 m); ii) from predicting the outcome of ''ideal'' measurements to those of ''re al'' ones with limited accuracy, sampling and averaging; iii) from pas sive to active remote-sensing methods; and iv) shifting from standard to wavelet-based analysis/modeling techniques. In terms of potential f or impact on geophysical research at large, the most important contrib utions are: a) criteria for and measures of nonstationarity and interm ittency in scale-invariant data; b) so-called ''bounded'' multifractal cascade models having a continuously variable degree of nonstationari ty; c) a parameterization of the bulk effect of fractal variability on large-scale planetary albedo; and d) the basic scaling theory of radi ative ''smoothing'' that explains non-trivially related multiple scatt ering phenomena in both solar-and lidar-based remote sensing. The last item also suggests new methods of observing clouds and new ways of pr ocessing cloud radiance data to retrieve physical cloud properties.