Search Results
Abstract
The time of onset of the initial electrification in a thunderstorm cell has been correlated with the appearance of the initial radar (3 cm) precipitation-echo. The results show that precipitation is a necessary, but not sufficient, condition for the onset of thunderstorm electrification. The presence of radar-detectable precipitation does not lead to thunderstorm electrification, unless the precipitation echo evidences rapid vertical development. When this condition is fulfilled, the appearance of the initial electrification is almost coincident with the appearance of the initial radar precipitation-echo. On days when no precipitation echoes were present, no electric fields significantly different from the fair-weather positive fields were observed, although the clouds noted ranged from small fair-weather cumulus to clouds of considerable depth and active convection.
Abstract
The time of onset of the initial electrification in a thunderstorm cell has been correlated with the appearance of the initial radar (3 cm) precipitation-echo. The results show that precipitation is a necessary, but not sufficient, condition for the onset of thunderstorm electrification. The presence of radar-detectable precipitation does not lead to thunderstorm electrification, unless the precipitation echo evidences rapid vertical development. When this condition is fulfilled, the appearance of the initial electrification is almost coincident with the appearance of the initial radar precipitation-echo. On days when no precipitation echoes were present, no electric fields significantly different from the fair-weather positive fields were observed, although the clouds noted ranged from small fair-weather cumulus to clouds of considerable depth and active convection.
Abstract
A description of the known physical properties of a thunderstorm reveals that active charge separation occurs during that stage of the storm's life-cycle in which the growth of graupel by the accretion of supercooled droplets is the dominant process. Laboratory experiments under simulated thunderstorm conditions show that a graupel pellet, growing by the accretion of supercooled droplets, acquires negative charge as a result of collisions with ice crystals. Other experiments show that when two ice formations are placed in rubbing contact, the ice which is warmer, or which contains trace amounts of contaminants, acquires negative charge. Further experiments suggest that the charge separation results from potential differences which arise during the resolidification of a liquid layer formed at the ice-ice contact.
Calculations indicate that the graupel pellets in a thunderstorm, as a result of the acquisition of the latent heat of supercooled droplets, will achieve temperatures several degrees warmer than coexisting ice crystals. Thus the graupel pellets will acquire negative charge as a result of rubbing contacts with ice crystals. The graupel pellets have much higher fall velocities than ice crystals, thus accounting for the polarity of the main thunderstorm dipole. Measurements suggest that the amount of charge separated per graupelcrystal collision is adequate to account for the magnitude of the charges of the main dipole.
Abstract
A description of the known physical properties of a thunderstorm reveals that active charge separation occurs during that stage of the storm's life-cycle in which the growth of graupel by the accretion of supercooled droplets is the dominant process. Laboratory experiments under simulated thunderstorm conditions show that a graupel pellet, growing by the accretion of supercooled droplets, acquires negative charge as a result of collisions with ice crystals. Other experiments show that when two ice formations are placed in rubbing contact, the ice which is warmer, or which contains trace amounts of contaminants, acquires negative charge. Further experiments suggest that the charge separation results from potential differences which arise during the resolidification of a liquid layer formed at the ice-ice contact.
Calculations indicate that the graupel pellets in a thunderstorm, as a result of the acquisition of the latent heat of supercooled droplets, will achieve temperatures several degrees warmer than coexisting ice crystals. Thus the graupel pellets will acquire negative charge as a result of rubbing contacts with ice crystals. The graupel pellets have much higher fall velocities than ice crystals, thus accounting for the polarity of the main thunderstorm dipole. Measurements suggest that the amount of charge separated per graupelcrystal collision is adequate to account for the magnitude of the charges of the main dipole.
Abstract
A case study of the effects of ship emissions on the microphysical, radiative, and chemical properties of polluted marine boundary layer clouds is presented. Two ship tracks are discussed in detail. In situ measurements of cloud drop size distributions, liquid water content, and cloud radiative properties, as well as aerosol size distributions (outside-cloud, interstitial, and cloud droplet residual particles) and aerosol chemistry, are presented. These are related to remotely sensed measurements of cloud radiative properties.
The authors examine the processes behind ship track formation in a polluted marine boundary layer as an example of the effects of anthropogenic particulate pollution on the albedo of marine stratiform clouds.
Abstract
A case study of the effects of ship emissions on the microphysical, radiative, and chemical properties of polluted marine boundary layer clouds is presented. Two ship tracks are discussed in detail. In situ measurements of cloud drop size distributions, liquid water content, and cloud radiative properties, as well as aerosol size distributions (outside-cloud, interstitial, and cloud droplet residual particles) and aerosol chemistry, are presented. These are related to remotely sensed measurements of cloud radiative properties.
The authors examine the processes behind ship track formation in a polluted marine boundary layer as an example of the effects of anthropogenic particulate pollution on the albedo of marine stratiform clouds.
Abstract
The effects of anthropogenic particulate emissions from ships on the radiative, microphysical, and chemical properties of moderately polluted marine stratiform clouds are examined. A case study of two ships in the same air mass is presented where one of the vessels caused a discernible ship track while the other did not. In situ measurements of cloud droplet size distributions, liquid water content, and cloud radiative properties, as well as aerosol size distributions (outside cloud, interstitial, and cloud droplet residual particles) and aerosol chemistry, are presented. These are related to measurements of cloud radiative properties. The differences between the aerosol in the two ship plumes are discussed;these indicate that combustion-derived particles in the size range of about 0.03–0.3-μm radius were those that caused the microphysical changes in the clouds that were responsible for the ship track.
The authors examine the processes behind ship track formation in a moderately polluted marine boundary layer as an example of the effects that anthropogenic particulate pollution can have in the albedo of marine stratiform clouds.
Abstract
The effects of anthropogenic particulate emissions from ships on the radiative, microphysical, and chemical properties of moderately polluted marine stratiform clouds are examined. A case study of two ships in the same air mass is presented where one of the vessels caused a discernible ship track while the other did not. In situ measurements of cloud droplet size distributions, liquid water content, and cloud radiative properties, as well as aerosol size distributions (outside cloud, interstitial, and cloud droplet residual particles) and aerosol chemistry, are presented. These are related to measurements of cloud radiative properties. The differences between the aerosol in the two ship plumes are discussed;these indicate that combustion-derived particles in the size range of about 0.03–0.3-μm radius were those that caused the microphysical changes in the clouds that were responsible for the ship track.
The authors examine the processes behind ship track formation in a moderately polluted marine boundary layer as an example of the effects that anthropogenic particulate pollution can have in the albedo of marine stratiform clouds.
