Search Results
1. Introduction The precipitating, radiative, and reflectivity properties of warm stratiform clouds strongly depend on the shape of droplet size distributions (DSDs), which can vary substantially at the scales of several tens of meters ( Korolev and Mazin 1993 ; Korolev 1994 , 1995 ). Especially strong changes of DSDs are related to drizzle formation (e.g., Stevens et al. 1998 ; vanZanten et al. 2005 ; Petters et al. 2006 ). The investigations of DSD formation mechanisms, as well as those
1. Introduction The precipitating, radiative, and reflectivity properties of warm stratiform clouds strongly depend on the shape of droplet size distributions (DSDs), which can vary substantially at the scales of several tens of meters ( Korolev and Mazin 1993 ; Korolev 1994 , 1995 ). Especially strong changes of DSDs are related to drizzle formation (e.g., Stevens et al. 1998 ; vanZanten et al. 2005 ; Petters et al. 2006 ). The investigations of DSD formation mechanisms, as well as those
frequently observed embedded in unbroken cloud fields and share similar meteorological conditions of adjacent closed-cellular clouds ( Stevens et al. 2003 ; Wood and Hartmann 2006 ). Such embedded open-cell features, commonly referred to as the pockets of open cells (POCs), are associated with patchy drizzle ( Stevens et al. 2005 ; Rosenfeld et al. 2006 ; Sharon et al. 2006 ; Comstock et al. 2005 , 2007 ; Wood et al. 2011 ). Plentiful aircraft and radar measurements (e.g., Frisch et al. 1995
frequently observed embedded in unbroken cloud fields and share similar meteorological conditions of adjacent closed-cellular clouds ( Stevens et al. 2003 ; Wood and Hartmann 2006 ). Such embedded open-cell features, commonly referred to as the pockets of open cells (POCs), are associated with patchy drizzle ( Stevens et al. 2005 ; Rosenfeld et al. 2006 ; Sharon et al. 2006 ; Comstock et al. 2005 , 2007 ; Wood et al. 2011 ). Plentiful aircraft and radar measurements (e.g., Frisch et al. 1995
any convective clouds where the warm rain process applies through a deep vertical layer. Lognormal fits to forward scattering spectrometer probe (FSSP) spectra observed during the Atlantic stratocumulus transition experiment (ASTEX) yielded reasonable values of effective radius, with greater uncertainty associated with enhanced concentrations of drizzle droplets ( r > 20 μ m) ( Gerber 1996 ). Cerro et al. (1997) found that the gamma distribution was generally able to represent rain drop
any convective clouds where the warm rain process applies through a deep vertical layer. Lognormal fits to forward scattering spectrometer probe (FSSP) spectra observed during the Atlantic stratocumulus transition experiment (ASTEX) yielded reasonable values of effective radius, with greater uncertainty associated with enhanced concentrations of drizzle droplets ( r > 20 μ m) ( Gerber 1996 ). Cerro et al. (1997) found that the gamma distribution was generally able to represent rain drop
strong abilities to simulate various types of boundary layer clouds (see also Cheng and Xu 2006 , 2008 ). The primary objective of this study is to propose a PDF-based microphysical formulation in the Langley Research Center (LaRC) higher-order turbulence closure scheme ( Cheng et al. 2004 ; Cheng and Xu 2006 ) and to test the scheme in simulations of drizzling shallow cumulus and stratocumulus cases. The rest of the paper is organized as follows: Section 2 describes the PDF-based microphysics
strong abilities to simulate various types of boundary layer clouds (see also Cheng and Xu 2006 , 2008 ). The primary objective of this study is to propose a PDF-based microphysical formulation in the Langley Research Center (LaRC) higher-order turbulence closure scheme ( Cheng et al. 2004 ; Cheng and Xu 2006 ) and to test the scheme in simulations of drizzling shallow cumulus and stratocumulus cases. The rest of the paper is organized as follows: Section 2 describes the PDF-based microphysics
1. Introduction The precipitating, radiative, and reflectivity properties of warm stratiform clouds strongly depend on the shape of droplet size distributions (DSDs), which can vary substantially at the scales of several tens of meters ( Korolev and Mazin 1993 ; Korolev 1994 , 1995 ). Especially substantial changes of radiative cloud properties are related to drizzle formation (e.g., Stevens et al. 1998b ; vanZanten et al. 2005 ; Petters et al. 2006 ). The microphysical properties of
1. Introduction The precipitating, radiative, and reflectivity properties of warm stratiform clouds strongly depend on the shape of droplet size distributions (DSDs), which can vary substantially at the scales of several tens of meters ( Korolev and Mazin 1993 ; Korolev 1994 , 1995 ). Especially substantial changes of radiative cloud properties are related to drizzle formation (e.g., Stevens et al. 1998b ; vanZanten et al. 2005 ; Petters et al. 2006 ). The microphysical properties of
) used surface-based observations to investigate the role of cloud dynamics in cloud droplet number concentration and drizzle formation. However, their study was hindered by its limited dataset and its poor temporal resolution. Recently, Chandrakar et al. (2016) found that both the standard deviation of the cloud droplet size distribution and cloud droplet size dispersion (standard deviation normalized by the mean) increase with a decrease of aerosol concentrations. The spectrum broadening observed
) used surface-based observations to investigate the role of cloud dynamics in cloud droplet number concentration and drizzle formation. However, their study was hindered by its limited dataset and its poor temporal resolution. Recently, Chandrakar et al. (2016) found that both the standard deviation of the cloud droplet size distribution and cloud droplet size dispersion (standard deviation normalized by the mean) increase with a decrease of aerosol concentrations. The spectrum broadening observed
) with a high-order monotonic advection scheme ( Wang et al. 2009 ) and a double-moment bulk microphysical scheme ( Feingold et al. 1998 ). The microphysical scheme assumes a lognormal size distribution for CCN, cloud droplets, and rain drops with a prescribed geometric standard deviation of 1.5, 1.2, and 1.2, respectively. The CCN spectrum has a median radius of 0.1 μ m. The cutoff radius between cloud and drizzle drops is 25 μ m. The mean radius of cloud droplets and rain drops is computed based
) with a high-order monotonic advection scheme ( Wang et al. 2009 ) and a double-moment bulk microphysical scheme ( Feingold et al. 1998 ). The microphysical scheme assumes a lognormal size distribution for CCN, cloud droplets, and rain drops with a prescribed geometric standard deviation of 1.5, 1.2, and 1.2, respectively. The CCN spectrum has a median radius of 0.1 μ m. The cutoff radius between cloud and drizzle drops is 25 μ m. The mean radius of cloud droplets and rain drops is computed based
1. Introduction One of the most important goals of the Monterey Area Ship Track (MAST) study was to investigate the microphysical changes in stratus clouds and drizzle within ship tracks. The hypothesis to be tested can be summarized as follows: cloud condensation nuclei (CCN) in the plume of emissions from a ship increase cloud droplet concentrations and decrease cloud droplet radii in a ship track. If drizzle-size drops are present in the ambient cloud, the ship track will have fewer
1. Introduction One of the most important goals of the Monterey Area Ship Track (MAST) study was to investigate the microphysical changes in stratus clouds and drizzle within ship tracks. The hypothesis to be tested can be summarized as follows: cloud condensation nuclei (CCN) in the plume of emissions from a ship increase cloud droplet concentrations and decrease cloud droplet radii in a ship track. If drizzle-size drops are present in the ambient cloud, the ship track will have fewer
). With the onset of drizzle, a solid stratocumulus cloud layer capping a well-mixed boundary layer tends to transform into broken, more cumuliform clouds penetrating the stratocumulus and a boundary layer that is less well mixed on average but is tightly coupled by the cumulus ( Wang and Lenschow 1995 ; Stevens et al. 1998 ). Observations suggest that a characteristic length scale for precipitation in Sc is on the order of 10 km ( Paluch and Lenschow 1991 ) so that precipitation patterns exhibit
). With the onset of drizzle, a solid stratocumulus cloud layer capping a well-mixed boundary layer tends to transform into broken, more cumuliform clouds penetrating the stratocumulus and a boundary layer that is less well mixed on average but is tightly coupled by the cumulus ( Wang and Lenschow 1995 ; Stevens et al. 1998 ). Observations suggest that a characteristic length scale for precipitation in Sc is on the order of 10 km ( Paluch and Lenschow 1991 ) so that precipitation patterns exhibit
1. Introduction Among the pantheon of processes involving stratocumulus, drizzle occupies a peculiar place. Despite observational evidence that it is commonplace, it is conspicuously absent in most of our conceptual and theoretical descriptions of stratocumulus. Already during the late 1970s and early 1980s measurements in stratocumulus ( Brost et al. 1982 ; Nicholls 1984 ; Nicholls and Leighton 1986 ) showed that at times the drizzle flux contributes significantly to the total water budget
1. Introduction Among the pantheon of processes involving stratocumulus, drizzle occupies a peculiar place. Despite observational evidence that it is commonplace, it is conspicuously absent in most of our conceptual and theoretical descriptions of stratocumulus. Already during the late 1970s and early 1980s measurements in stratocumulus ( Brost et al. 1982 ; Nicholls 1984 ; Nicholls and Leighton 1986 ) showed that at times the drizzle flux contributes significantly to the total water budget
