Northern Alaska Site Science: Cloud and precipitation microphysical studies at the Northern Alaska ARM facilities

Description

The results of cloud and precipitation microphysical studies using remote sensors (emphasizing radars) available at the ARM Oliktok Point and Barrow facilities will be presented. The dual-frequency (Ka-W bands) scanning ARM cloud radar (SACR) provides measurements of dual-wavelength ratio (DWR) which can be used for retrieving characteristic sizes of ice hydrometeor populations. The DWR was evaluated theoretically and using SACR observations and its dependence on hydrometeor shapes was analyzed. It was shown that while there is a significant correlation between radar reflectivity and DWR, a combination of these two variables provides valuable information on hydrometeor shapes. In addition, ground based-microphysical retrievals of ice cloud and precipitation microphysical profiles were compared with the spaceborne CloudSat radar retrievals during satellite overpasses over the Oliktok Point site. Some significant discrepancies exist in retrieved microphysical parameters such as characteristic particle size, ice water content and snow rate even though both ground-based and spaceborne measurements were closely matched in space and time. The CloudSat overpasses also allowed for evaluating the SACR absolute calibration. The corresponding SACR and CloudSat reflectivity comparisons will be presented. Taking a regional perspective, we will also review a comparison of cloud and radiation measurements at the two ARM sites on the North Slope of Alaska. While these sites have similar synoptic backgrounds, the Oliktok Point site is close to the polluted area of Prudhoe Bay oil fields. Cloud and radiation parameters observed at the Barrow and Oliktok Point sites were analyzed in order to evaluate the effects of different aerosol properties. In addition to ARM data, the satellite measurements from the spaceborne Moderate Resolution Imaging Spectroradiometer (MODIS) were used to quantify aerosol effects. Finally, we will show results related to the processing of Oliktok Point Ka-band ARM zenith looking radar (KAZR) spectra. This processing helps to identify multiple peaks and the isolation of spectral peaks as needed to distinguish among different hydrometeor species in mixed-phase clouds. Spectral moments estimated from standard ARM spectral processing routines can be misleading because they assume a single hydrometeor population. The results of the new processing algorithm will be presented. They can be used for in depth studies of mixed-phase cloud microphysics.