Abstract The susceptibility of rain formation to aerosol emissions is a key aspect of aerosol-cloud-precipitation interactions. Using aircraft observations and a detailed cloud model with a state-of-the-art particle-based representation of microphysics, it is shown that the enhancement of drop collision-coalescence from turbulent flow in clouds -- which is neglected in current climate models -- leads to earlier onset of rain in warm cumulus clouds and significantly dampens the precipitation susceptibility to aerosol loading. Enhanced drop coalescence from turbulence substantially increases the production of embryonic drizzle drops just above cloud base, which in turn act as seeds that accelerate rain drop growth at mid and upper cloud levels even in highly polluted conditions. In contrast, pollution aerosols strongly inhibit rainfall when the commonly assumed gravitational-only collision kernel is used in the model and turbulent coalescence is neglected. There is also a large impact of turbulent drop coalescence on the mean cloud water amount and optical depth. Overall, turbulence-enhanced drop coalescence strongly influences the response of warm cumulus clouds and precipitation to aerosol loading, suggesting that the effects of turbulent coalescence should be included in climate model representations of aerosol-cloud-precipitation interactions and aerosol indirect radiative forcing.

clouds, but can only produce very light precipitation on its own. Species cumulus humilis – These are small detached fair-weather cumuliform clouds that In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, ice crystals, or other particles, suspended in the atmosphere of a planetary body or similar space. Water, primarily, comprises the droplets and crystals. On Earth, clouds are formed as a result of saturation of the air when it is cooled to its dew point, or when it gains sufficient moisture, usually i Species cumulus congestus – Increasing airmass instability can cause free-convective cumulus to grow very tall to the extent that the vertical height from base to top is greater than the base-width of the cloud. The cloud base takes on a darker gray coloration and the top commonly resembles a cauliflower. This cloud type can produce moderate to heavy showers and is designated Towering cumulus (Tcu) by the International Civil Aviation Organization (ICAO). Genus cumulonimbus (Cb) – This genus type is a heavy, towering, cumulonimbiform mass of free-convective cloud with a dark-gray to nearly black base and a very high top in the form of a mountain or huge tower. Cumulonimbus can produce thunderstorms, local very heavy downpours of rain that may cause flash floods, and a variety of types of lightning including cloud-to-ground that can cause wildfires. Other convective severe weather may or may not be associated with thunderstorms and include heavy snow showers, hail, strong wind shear, downbursts, and tornadoes. Of all these possible cumulonimbus-related events, lightning is the only one of these that requires a thunderstorm to be taking place since it is the lightning… When the precipitation reaches the ground without completely evaporating, it is designated as the feature praecipitatio. This normally occurs with altostratus opacus, which can produce widespread but usually light precipitation, and with thicker clouds that show significant vertical development. Of the latter, upward-growing cumulus mediocris produces only isolated light showers, while downward growing nimbostratus is capable of heavier, more extensive precipitation. Towering vertical clouds have the greatest ability to produce intense precipitation events, but these tend to be localized unless organized along fast-moving cold fronts. Showers of moderate to heavy intensity can fall from cumulus congestus clouds. Cumulonimbus, the largest of all cloud genera, has the capacity to produce very heavy showers. Low stratus clouds usually produce only light precipitation, but this always occurs as the feature praecipitatio because this cloud genus lies too close to the ground to allow the formation of virga.

Abstract. A double moment warm rain scheme that includes the effects of turbulence on droplet collision rates has been implemented in a large-eddy model to investigate the impact of turbulence effects on clouds and precipitation. Simulations of shallow cumulus and stratocumulus show that different precipitation-dynamical feedbacks occur in these regimes when the effects of turbulence are included in the microphysical processes. In both cases, inclusion of turbulent microphysics increases precipitation due to a more rapid conversion of cloud water to rain. In the shallow convection case, the greater water loading and latent heating in the upper cloud levels reduces the buoyancy production of turbulent kinetic energy and the entrainment. The stratocumulus case on the other hand shows a positive precipitation feedback, with enhanced rainwater producing greater evaporation, stronger circulations and more turbulence. Sensitivity studies where the cloud droplet number was varied show that greater number concentrations suppress the stratocumulus precipitation leading to larger liquid water paths. This positive second indirect aerosol effect was produced in all of the simulations except for the case using the turbulent microphysics with the highest droplet number, which suggests a limit on the amount of liquid water that can be produced. While the sign of the second indirect effect is negative in the shallow convection case whether the effects of turbulence are considered or not, the magnitude of the effect is doubled when the turbulent microphysics are used.