Abstract
Fluctuating atmospheric emission is a dominant source of noise for ground-based millimeter-wave observations of the cosmic microwave background (CMB) temperature anisotropy at angular scales $\ensuremath{\gtrsim}0.5\ifmmode^\circ\else\textdegree\fi{}$. We present a model of the atmosphere as a discrete set of emissive turbulent layers that move with respect to the observer with a horizontal wind velocity. After introducing a statistic derived from the time-lag dependent correlation function for detector pairs in an array, referred to as the pair-lag, we use this model to estimate the aggregate angular motion of the atmosphere derived from time-ordered data from the Atacama Cosmology Telescope (ACT). We find that estimates derived from ACT's CMB observations alone agree with those derived from satellite weather data that additionally include a height-dependent horizontal wind velocity and water vapor density. We also explore the dependence of the measured atmospheric noise spectrum on the relative angle between the wind velocity and the telescope scan direction. In particular, we find that varying the scan velocity changes the noise spectrum in a predictable way. Computing the pair-lag statistic opens up new avenues for understanding how atmospheric fluctuations impact measurements of the CMB anisotropy.
Highlights
The cosmic microwave background (CMB) contains a wealth of information limited only by our ability to extract it
DATA SOURCES Our analysis draws on a number of sources, including Atacama Cosmology Telescope (ACT) [11], the ground-based weather station maintained by the Atacama Pathfinder EXperiment (APEX) Collaboration [e.g., [12]], NASA’s MERRA-2 database [13], the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis [14], the Cortees et al [15] synthesis of the precipitable water vapor (PWV) in the Cerro Chajnantor region, and the UdeC-UCSC 183 GHz radiometer next to ACT [16]
Temperature, and mass fraction of water vapor as determined by ERA5 and MERRA-2, we can obtain the mass density of water vapor as a function of height, and integrate over it to obtain an estimate for the total precipiRtable water vapor (PWV)
Summary
The cosmic microwave background (CMB) contains a wealth of information limited only by our ability to extract it. Of these two molecules, water is the most problematic: the concentration of water vapor is passively mixed and has an inhomogeneous, turbulent distribution [3]. S. [8] model the atmosphere as a two-dimensional frozen sheet of turbulence moving at a constant horizontal velocity to simulate the effects of wind This captures many aspects of the observations and is often quite effective but cannot comprehensively describe the three-dimensional atmosphere. ∞ 0 ρðh; tÞdh=ρH2O where h is a vertical line of sight through the atmosphere, ρ is the mass density of water vapor in the atmosphere, and ρH2O is the density of water
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