New Technique Used to Measure Ice and Liquid in Clouds

 
Published: 31 December 2004

A mirror angled at 45 degrees inside the "winglet" viewing port deflects sunlight to the optical fiber and into the detector housed inside the "Great White" shelter at Barrow.

Difficulties in modeling the effects of clouds on climate arise largely from the insufficient number of observations needed to sufficiently understand cloud processes. Science collaborators at the National Oceanic and Atmospheric Administrations (NOAA) Aeronomy Laboratory have developed a cost effective technique that uses measurements of sunlight scattered by clouds, at various near-infrared wavelengths, to infer the amount of liquid and ice within the clouds. During the Spectral Water Phase IOP—conducted in September and October 2004 at the ARM Climate Research Facility North Slope of Alaska (NSA) site in Barrow—NOAA researchers measured the zenith spectral radiance during daylight hours. Using data obtained from those measurements, they will be able to estimate the amount of liquid and ice in the clouds and compare the values to similar estimates obtained by other ARM instrumentation. Specifically, the liquid and ice retrievals from the Spectral Water Phase IOP are being compared with the values obtained by the microwave radiometer and atmospheric emitted radiance interferometer during the Mixed-Phase Arctic Cloud Experiment (M-PACE) conducted in parallel at the NSA.

During the IOP, the NOAA instrumentation was located in the “Great White” facility—a large shelter used to house most of the computers for ARM instruments at Barrow. An optical fiber was passed through the wall of the facility to the zenith-pointing viewing port mounted outside the shelter. Data was acquired nearly continuously during daylight hours between September 12 and October 22, 2004.

By conducting the Spectral Water Phase IOP in conjunction with the larger M-PACE effort, the researchers are now able to compare the current best techniques for measuring the water phase in various clouds, as well as to compare the liquid and ice abundances. Preliminary qualitative comparisons of liquid water estimated from the spectral observations and the microwave radiometer are encouraging. Because clouds are key factors to our current understanding and prediction of climate change, the comparisons will increase scientific understanding of the radiative properties of clouds, leading to improvements in both weather and climate models.