Radiative closure studies at the North Slope of Alaska ARM Climate Research Facility

The U.S. Department of Energy's Atmospheric Radiation Measurement Program (ARM) has been compiling an extensive dataset of surface-based radiometric and atmospheric state measurements at its Climate Research Facilities (ACRFs) since the mid-1990s. The ACRFs are an excellent venue from which to intercompare shortwave, longwave, and microwave observations with model calculations. Comparing observed and modeled radiances within a given spectral intervals can reveal whether or not specific physical processes are correctly represented in either the models or the characterization of the atmospheric state. Having the ability to diagnose issues with the representation of those physical processes ultimately leads to improvements in one of the three principal components of the closure analyses: characterization of the surface and atmospheric state, radiometric measurements, or radiative transfer models.

This presentation will summarize research initiatives aimed at improving our ability to model and measure atmospheric radiation at high latitudes. While great progress has been made in reconciling calculated and measured radiances and fluxes at the Southern Great Plains ACRF, the low integrated water vapor amounts above the NSA ACRF remain difficult to accurately measure by conventional water vapor radiometers. Results from an investigation aimed at simultaneously assessing the specification of the atmospheric water vapor profile and water vapor line parameters and continuum will be presented. Further related radiative closure analyses also allow an evaluation of the spectroscopic characterization of other important species, such as carbon dioxide, as well as cloud retrieval schemes.