Clouds affect our daily weather and play key roles in the global climate. Through their ability to precipitate, clouds provide virtually all of the fresh water on Earth and are a crucial link in the hydrologic cycle. With ever-increasing importance being placed on quantifiable predictions – from forecasting the local weather to anticipating climate change – we must understand how clouds operate in the real atmosphere, where interactions with natural and anthropogenic pollutants are common. This textbook provides students – whether seasoned or new to the atmospheric sciences – with a quantitative yet approachable path to learning the inner workings of clouds. Developed over many years of the authors' teaching at Pennsylvania State University, Physics and Chemistry of Clouds is an invaluable textbook for advanced students in atmospheric science, meteorology, environmental sciences/engineering and atmospheric chemistry. It is also a very useful reference text for researchers and professionals.

No abstract

Instrumented aircraft and radar were used to investigate the microphysical, electrical, and dynamic evolution of the life cycle of a small thunderstorm which occurred in southeastern Montana. The observations commenced as precipitation development was just beginning, continued through the active stage of growth as the cloud produced graupel up to 8 to 9 mm diameter and reflectivities aloft of 45 dBZ, through the dissipation stage when only an anvil with a trail of light precipitation remained. The largest particles and the primary development of precipitation were found to occur in the fringes of the updraft. The electric fields inside the cloud did not exceed 100 V m−1 until 5 mm graupel, ice particle concentrations of 10 L−1, and reflectivities of 35 dBZ were already present, but then rapidly electrified to produce a single intracloud discharge 8 min later, near the peak of microphysical development. Early in the electrical development of the cloud when observed electric fields were only 200 V m−1, negative charge accumulation was observed near the 7 km (−20°C) level and was associated with the high reflectivity region. In the early stages of precipitation fallout, particle charge measurements near 4.5 km showed primarily negatively charged particles which appeared to be associated with precipitation falling from the cloud. Less than 5 to 10% of the observed particles larger than 100 μm were carrying charges larger than 5 pC, the detection limit of the instrument. These observations are discussed from the point of view of charge generation in thunderstorms, particularly, charge transfer between colliding ice particles.

No abstract

The condensation coefficient of water vapor on liquid water and the thermal accommodation coefficient of air on liquid water are poorly known despite their importance in many applications, such as cloud physics. We have developed a new technique for determining the condensation and thermal accommodation coefficients experimentally. The technique consists of simultaneously measuring the homogeneous nucleation rate of ice and the evaporation rate of liquid water droplets as a function of pressure (droplet Knudsen number). As the Knudsen number increases, surface kinetic processes limit mass and energy fluxes and, as a result, the equilibrium temperature of an evaporating droplet is a function of the condensation and thermal accommodation coefficients. The homogeneous freezing nucleation rate is used as a sensitive measure of the droplet temperature. The nucleation and evaporation rates are determined by observing the scattered light from evaporating water droplets suspended in an electrodynamic levitation system housed within a controlled environment. The observed rates are consistent with a condensation coefficient between 0.04 and 0.1, with 0.06 being most probable, and a thermal accommodation coefficient between 0.1 and 1, with 0.7 being most probable.