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Microbase Profiles for ARM Sites

Clouds play a critical role in the earth's energy cycle through direct interactions with electromagnetic radiation and impacts through the hydrological cycle. Through these interactions, clouds provide a dominant feedback on the climate system that we must be able to define if we are to predict future climate states. Clouds may transmit, scatter or absorb radiant energy that impinges upon them. For a given cloud, the synergy of these processes depends on both cloud macrophysical (cloud height, cloud fraction, cloud thickness) and microphysical (phase, size and number density of cloud particles) properties. Therefore, in order to perform accurate calculations of the transfer of electromagnetic radiation through the atmosphere and to quantify the role clouds play in the earth's climate and climate change, vertical profiles of liquid and ice water, and the number and sizes of the cloud particles that contribute to this total water are needed.

The continuus baseline microphysical retrieval (MICROBASE) VAP uses a combination of observations from the millimeter cloud radar (MMCR), the ceilometer, the micropulse lidar (MPL), the microwave radiometer (MWR) and balloon-borne sounding profiles in order to determine the profiles of liquid/ice water content (L/IWC), liquid/ice cloud particle effective radius (re) and cloud fraction. The L/IWC is determined from the radar reflectivity values in the Active Remote Sensing of Clouds (ARSCL) VAP (Clothiaux et al. 2000). For liquid cloud layers (T > 0 °C) we use the radar reflectivity - LWC relationship derived by Liao and Sassen (1994). This quantity is vertically integrated to provide a liquid water path (LWP) which is then linearly scaled to match the LWP observed by the MWR, whenever the MWR value is smaller (last restriction for TWP only). Liquid cloud particle effective radii are computed assuming a log-normal droplet distribution with a width of σ = 0.35 and a mode radius given by the relationship derived by Frisch et al (1995). For ice cloud layers ( T <= -16 °C), the water content is determined using the Z-IWC relationship from Liu and Illingworth (2000), while the cloud particle effective radius is determined as a function of temperature from the relationship of Ivanova et al. (2001). For the mixed-phase region of the cloud (-16 °C < T < 0 °C) we assume a linear fractionation of ice/liquid where the ice fraction is equal to -T[°C]/16.

This baseline retrieval is calculated every 10 seconds and then averaged over twenty minute intervals with a vertical resolution of greater than 230 levels.

nsamicrobasepiavg: Instantaneous (averaged) Microbase Profiles for the North Slope of Alaska- January 2004 to December 2004
sgpmicrobasepiavg: Instantaneous (averaged) Microbase Profiles for the Southern Great Plains- March 2000 to February 2001
twpmicrobasepiavg: Instantaneous (averaged) Microbase Profiles for the Tropical Western Pacific (Manus)- November 2003 to October 2004

Contact: Mike Jensen at