Physical Interpretation of the Spectral Radiative Signature in the Transition Zone Between Cloud-free and Cloudy Regions
|J.-Y. Christine Chiu||University of Reading|
|Alexander Marshak||NASA - Goddard Space Flight Center|
|Yuri Knyazikhin||Boston University|
|Warren Wiscombe||Brookhaven National Laboratory|
|Peter Pilewskie||University of Colorado|
Studies on aerosol direct and indirect effects demand a precise separation of cloud-free and cloudy areas. However, a separation between cloud-free and cloudy areas from remotely sensed measurements is ambiguous at any scale. Therefore, it is important to understand the transition zone where strong aerosol-cloud interactions are taking place. This paper uses one-second-resolution zenith radiance measurements from the Atmospheric Radiation Measurement Program’s new shortwave spectrometer (SWS) to study how aerosol and cloud properties change around cloud edges. We will demonstrate that in the transition zone, there is a remarkable linear relationship between the sum and difference of radiances at 870 and 1640 nm wavelengths. The intercept of the relationship is determined primarily by aerosol properties, and the slope by cloud properties. We also will show that this linearity can be predicted from simple theoretical considerations and furthermore that it supports the hypothesis of inhomogeneous mixing, whereby optical depth increases as a cloud is approached, but the effective drop size remains unchanged.
This poster will be displayed at ARM Science Team Meeting.