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GCM. The physical processes that are responsible for structures seen in the MBL cloud fields are not fully understood, but recent research has indicated that the occurrence of drizzle may play a key role in forming and sustaining the observed structures. Observational studies have investigated pockets of open cells (POCs) that are embedded in otherwise uniform stratocumulus, and resemble broader regions of open mesoscale cellular convection typically found farther offshore ( Stevens et al. 2005
GCM. The physical processes that are responsible for structures seen in the MBL cloud fields are not fully understood, but recent research has indicated that the occurrence of drizzle may play a key role in forming and sustaining the observed structures. Observational studies have investigated pockets of open cells (POCs) that are embedded in otherwise uniform stratocumulus, and resemble broader regions of open mesoscale cellular convection typically found farther offshore ( Stevens et al. 2005
cloud had lower concentrations of larger droplets with a broader spectrum and more drizzle drops. The first two characteristics areattributed to the lower cloud condensation nuclei (CCN) concentrations that were measured near the clean cloud.The greater droplet spectral broadness may just be a manifestation of the usual observation of broader dropletspectra for larger droplet sizes but it may also be related to the higher slope of the CCN spectra that was observedin the cleaner air mass. The larger
cloud had lower concentrations of larger droplets with a broader spectrum and more drizzle drops. The first two characteristics areattributed to the lower cloud condensation nuclei (CCN) concentrations that were measured near the clean cloud.The greater droplet spectral broadness may just be a manifestation of the usual observation of broader dropletspectra for larger droplet sizes but it may also be related to the higher slope of the CCN spectra that was observedin the cleaner air mass. The larger
therefore the cloud albedo (e.g., Albrecht 1989 ; Savic-Jovcic and Stevens 2008 ). Indeed, over the cold regions of the eastern subtropical and tropical oceans, observations of marine stratocumulus sheets reveal a striking relationship between the mode of mesoscale cellular convection and the occurrence of drizzle, with open cells frequently associated with strong drizzle and closed cells less frequently so ( Stevens et al. 2005 ; Comstock et al. 2007 ; Wood et al. 2008 ). Over warmer regions of the
therefore the cloud albedo (e.g., Albrecht 1989 ; Savic-Jovcic and Stevens 2008 ). Indeed, over the cold regions of the eastern subtropical and tropical oceans, observations of marine stratocumulus sheets reveal a striking relationship between the mode of mesoscale cellular convection and the occurrence of drizzle, with open cells frequently associated with strong drizzle and closed cells less frequently so ( Stevens et al. 2005 ; Comstock et al. 2007 ; Wood et al. 2008 ). Over warmer regions of the
, clear trends or patterns in how the structure of the boundary layer changes under the influence of drizzle have yet to emerge; thus the target, or object, of any theoretical development of the subject is itself outstanding. In this context, a number of missions, flown as part of the Second Dynamics and Chemistry of Marine Stratocumulus (DYCOMS-II; Stevens et al. 2003a ) field study, offer the possibility of expanding our understanding of the basic phenomenology of precipitating boundary layers. The
, clear trends or patterns in how the structure of the boundary layer changes under the influence of drizzle have yet to emerge; thus the target, or object, of any theoretical development of the subject is itself outstanding. In this context, a number of missions, flown as part of the Second Dynamics and Chemistry of Marine Stratocumulus (DYCOMS-II; Stevens et al. 2003a ) field study, offer the possibility of expanding our understanding of the basic phenomenology of precipitating boundary layers. The
that produces heavy rainfall. This is accompaniedby the production of a large amount of drizzle in the middle levels of the cloud. An increase in the drop growthrate within cloud cells above zones of low level convergence, as well as drop recirculation, influence efficientproduction of a "drizzle pool".1. Introduction The longevity and severity of cloud disturbances canbe observed in differing cloud systems. The line cloudsystem has been investigated by many workers. Squalllines at midlatitudes
that produces heavy rainfall. This is accompaniedby the production of a large amount of drizzle in the middle levels of the cloud. An increase in the drop growthrate within cloud cells above zones of low level convergence, as well as drop recirculation, influence efficientproduction of a "drizzle pool".1. Introduction The longevity and severity of cloud disturbances canbe observed in differing cloud systems. The line cloudsystem has been investigated by many workers. Squalllines at midlatitudes
surface of the earth associated with an increase in aerosols. Aerosols do not independently affect the microphysical characteristics of clouds since precipitation processes can influence aerosol concentrations that can further affect the microphysics of the clouds. For example, in precipitating boundary layer clouds, CCN spectra can be modified by collision and coalescence processes associated with drizzle, even if drizzle droplets do not reach the surface. One possible explanation for the presence of
surface of the earth associated with an increase in aerosols. Aerosols do not independently affect the microphysical characteristics of clouds since precipitation processes can influence aerosol concentrations that can further affect the microphysics of the clouds. For example, in precipitating boundary layer clouds, CCN spectra can be modified by collision and coalescence processes associated with drizzle, even if drizzle droplets do not reach the surface. One possible explanation for the presence of
can occur with drizzle, freezing drizzle, or light snow, the weather may be reported as “clear” by the ASOS. These issues are mitigated at airports that still maintain a human observer who can augment and correct the automated observations. The ASOS sites are classified into service levels ( FAA 2017 ) that help to identify whether a human observer exists at the site and the extent to which they can modify the ASOS observations. Service level A and B airports, for example, have full-time human
can occur with drizzle, freezing drizzle, or light snow, the weather may be reported as “clear” by the ASOS. These issues are mitigated at airports that still maintain a human observer who can augment and correct the automated observations. The ASOS sites are classified into service levels ( FAA 2017 ) that help to identify whether a human observer exists at the site and the extent to which they can modify the ASOS observations. Service level A and B airports, for example, have full-time human
group according toTcc~ and PB. The physical basis of TccL and PB to implicitly represent a period of time for coalescence toproduce supercooled drizzle and raindrops is discussed. The technique performed well at forecasting the occurrenceand height of a_qernoon convective clouds. Aircraft measurements of supercooled raindrop concentrations showedthat a discriminator function, dependent only on Tccc and PB, gave a good indication oftbe presence or absenceof supercooled drizzle and raindrops in the
group according toTcc~ and PB. The physical basis of TccL and PB to implicitly represent a period of time for coalescence toproduce supercooled drizzle and raindrops is discussed. The technique performed well at forecasting the occurrenceand height of a_qernoon convective clouds. Aircraft measurements of supercooled raindrop concentrations showedthat a discriminator function, dependent only on Tccc and PB, gave a good indication oftbe presence or absenceof supercooled drizzle and raindrops in the
short, this simple model of nucleation, condensation, and coalescence—the warm rain process—is insufficient to explain the rapid growth of precipitation-sized droplets in observations. The bottleneck in the classical theory is the development of sufficient droplets in the ∼20–25- μ m range. Giant CCN (GCCN; 1 < r < 10 μ m) have been suggested as one mechanism that may serve to “short circuit” the coalescence bottleneck. More precisely, GCCN may be responsible for the development of drizzle
short, this simple model of nucleation, condensation, and coalescence—the warm rain process—is insufficient to explain the rapid growth of precipitation-sized droplets in observations. The bottleneck in the classical theory is the development of sufficient droplets in the ∼20–25- μ m range. Giant CCN (GCCN; 1 < r < 10 μ m) have been suggested as one mechanism that may serve to “short circuit” the coalescence bottleneck. More precisely, GCCN may be responsible for the development of drizzle
besides CloudSat ( Stephens et al. 2002 ). Although other satellites in the A-train will carry a wealth of different sensors, cloud retrieval algorithms that use only radar reflectivity need to be developed for special uses (e.g., nighttime spaceborne radar retrievals). One important problem for radar-only retrievals in stratiform liquid clouds is caused by drizzle-size drops. Almost all marine ( Fox and Illingworth 1997 ) and some continental stratiform liquid water clouds contain a certain amount of
besides CloudSat ( Stephens et al. 2002 ). Although other satellites in the A-train will carry a wealth of different sensors, cloud retrieval algorithms that use only radar reflectivity need to be developed for special uses (e.g., nighttime spaceborne radar retrievals). One important problem for radar-only retrievals in stratiform liquid clouds is caused by drizzle-size drops. Almost all marine ( Fox and Illingworth 1997 ) and some continental stratiform liquid water clouds contain a certain amount of
