The Atacama Cosmology Telescope: Modeling Bulk Atmospheric Motion

TL;DR

This paper models atmospheric turbulence as moving layers to better understand and mitigate atmospheric noise in ground-based CMB observations, using data from ACT and satellite weather models.

Contribution

It introduces a pair-lag statistic to estimate atmospheric motion from observational data, linking it with satellite weather data for improved atmospheric noise modeling.

Findings

ACT-derived atmospheric motion estimates agree with satellite data.

Scan velocity influences the atmospheric noise spectrum predictably.

Pair-lag statistic offers new insights into atmospheric fluctuation impacts.

Abstract

Fluctuating atmospheric emission is a dominant source of noise for ground-based millimeter-wave observations of the CMB temperature anisotropy at angular scales $\gtrsim 0.5^{\circ}$. 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.