Effects of the large-scale circulation on temperature and water vapor distributions in the Π Chamber

Abstract

Abstract. Microphysical processes are important for the development of clouds and thus Earth's climate. For example, turbulent fluctuations in the water vapor mixing ratio, r, and temperature, T, cause fluctuations in the saturation ratio, S. Because S is the driving factor in the condensational growth of droplets, fluctuations may broaden the cloud droplet size distribution due to individual droplets experiencing different growth rates. The small-scale turbulent fluctuations in the atmosphere that are relevant to cloud droplets are difficult to quantify through field measurements. We investigate these processes in the laboratory using Michigan Tech's Π Chamber. The Π Chamber utilizes Rayleigh–Bénard convection (RBC) to create the turbulent conditions inherent in clouds. In RBC it is common for a large-scale circulation (LSC) to form. As a consequence of the LSC, the temperature field of the chamber is not spatially uniform. In this paper, we characterize the LSC in the Π Chamber and show how it affects the shape of the distributions of r, T, and S. The LSC was found to follow a single roll with an updraft and downdraft along opposing walls of the chamber. Near the updraft (downdraft), the distributions of T and r were positively (negatively) skewed. At each measuring position, S consistently had a negatively skewed distribution, with the downdraft being the most negative.

An Intercomparison of Large‐Eddy Simulations of a Convection Cloud Chamber Using Haze‐Capable Bin and Lagrangian Cloud Microphysics Schemes

“…Because of the positive feedback, activation and deactivation rates in haze-capable cases are significantly larger than the aerosol injection rate, but the net activation rate is still statistically equal to the aerosol injection rate such that the whole chamber reaches a steady state. We also find that the net activation rate oscillates every few minutes, which might be linked to oscillations from the large-scale circulation in the convection chamber (Anderson et al, 2021;Niedermeier et al, 2018).…”

“…It is also worth mentioning that the net activation rate oscillates every few minutes. This phenomenon might be linked to oscillation related to the large‐scale circulation in the convection chamber (Anderson et al., 2021; Niedermeier et al., 2018). Further studies are needed to complete our understanding of the fluctuation of the net activation rate and its potential link to large‐scale dynamics, which are beyond the scope of this study.…”

Scaling of Turbulence and Microphysics in a Convection–Cloud Chamber of Varying Height

“…The 3D outputs are separated temporally by 5 min. The sampling distance is chosen to avoid any wall effects, and the sampling time is chosen to avoid any correlation effects due to turbulence (Anderson et al., 2021; Niedermeier et al., 2018). At least 3.68 × 10 5 , 1.47 × 10 6 , and 4.92 × 10 8 grid boxes have been sampled for 1‐m, 2‐m and 4‐m chambers, respectively to produce the PDFs.…”

Contactless optical hygrometry in LACIS-T

“…Such a need for a contactless sampling was recognized following the reports from other laboratory experiments (e.g. Anderson et al, 2021, observed that the position of sensor holders inside the Pi chamber affects the orientation of the principal circulation) and taking into account the relatively small size of the central section of LACIS-T.…”