Effects of Atmospheric Emission on Ground-based Microwave Background Measurements

Abstract

We present an analysis of multifrequency measurements ofatmospheric emission in the Rayleigh-Jeans portion of the cosmicmicrowave background spectrum (1-90 GHz) taken since 1986 from WhiteMountain, CA, and from the South Pole. Correlations of simultaneous dataat 10 and 90 GHz and accurate low-frequency measurements show goodagreement with model predictions for both sites. Our data from the SouthPole 1989 campaign combined with real-time measurements of the localatmospheric profiles provide accurate verification of the expectedindependent contributions of H2O and O2 emission. We show that variationson the order of 10 percent of the oxygen emission (both resonant andnonresonant components) are present on timescales of hours to days,mainly due to the evolution of the atmospheric pressure profile. Oxygenemission fluctuations appear larger than previously expected and may havesignificant consequences for ground-based cosmic microwave backgroundexperiments.