Interpreting millimeter-wave radiances over convective clouds

Abstract

Attempts to interpret the measurements of millimeter-wave radiometers over tropical storms must overcome the difficulty of modeling the scattering signatures of hydrometeors at these frequencies. Approaches to date try to retrieve surface precipitation, to which the observations are not directly sensitive. Millimeter wavelengths are most sensitive to the scattering from hydrometeors in the cloud upper levels. Millimeter-wavelength radiometers have a definite advantage over the lower frequency radiometers in that they have finer spatial resolution to resolve deep convection. Preliminary analyses indicate that the measurements are indeed sensitive to the depth and intensity of convection. The challenge is to derive a robust approach to estimate the characteristics of the convection directly from the observations, and conversely to derive a robust forward representation of the dependence of the radiances on the underlying moisture fields. This is done in a two-step semi-empirical approach.