Acidity variations across the cloud drop size spectrum and their influence on rates of atmospheric sulfate production

1994 ◽  
Vol 21 (22) ◽  
pp. 2393-2396 ◽  
Author(s):  
Jeffrey L. Collett ◽  
Aaron Bator ◽  
Xin Rao ◽  
Belay B. Demoz
Keyword(s):  
Drop Size ◽  
Size Spectrum ◽  
Cloud Drop ◽  
Sulfate Production

Theoretical Aspccts of Cloud Drop Distributions

1949 ◽  
Vol 2 (3) ◽  
pp. 376 ◽  
Author(s):  
EB Kraus ◽  
B Smith
Keyword(s):  
Cooling Rate ◽  
Drop Size ◽  
Initial Temperature ◽  
Theoretical Study ◽  
Air Pressure ◽  
Size Spectrum ◽  
Condensation Nuclei ◽  
Cloud Drop ◽  
Rate Of Cooling

A theoretical study indicates that the number and size of the drops formed in a cloud vary with the rate of cooling, the initial temperature, and the air pressure. The faster the cooling rate, the lower the initial temperature, and the lower the altitude, the greater is the number of drops and the smaller their size. The drop size spectrum also depends, to a large extent, on the number of available condensation nuclei. Furthermore, it tends to be widened by sedimentation and turbulence.

scholarly journals Evaluating Light Rain Drop Size Estimates from Multiwavelength Micropulse Lidar Network Profiling

2013 ◽  
Vol 30 (12) ◽  
pp. 2798-2807 ◽  
Author(s):  
Simone Lolli ◽  
Ellsworth J. Welton ◽  
James R. Campbell
Keyword(s):  
Drop Size ◽  
Total Error ◽  
Size Spectrum ◽  
Drop Diameter ◽  
Transmission Losses ◽  
Light Rain ◽  
Color Ratio ◽  
Aerosol Scattering ◽  
Rain Drop ◽  
The Impact

Abstract This paper investigates multiwavelength retrievals of median equivolumetric drop diameter D0 suitable for drizzle and light rain, through collocated 355-/527-nm Micropulse Lidar Network (MPLNET) observations collected during precipitation occurring 9 May 2012 at the Goddard Space Flight Center (GSFC) project site. By applying a previously developed retrieval technique for infrared bands, the method exploits the differential backscatter by liquid water at 355 and 527 nm for water drops larger than ≈50 μm. In the absence of molecular and aerosol scattering and neglecting any transmission losses, the ratio of the backscattering profiles at the two wavelengths (355 and 527 nm), measured from light rain below the cloud melting layer, can be described as a color ratio, which is directly related to D0. The uncertainty associated with this method is related to the unknown shape of the drop size spectrum and to the measurement error. Molecular and aerosol scattering contributions and relative transmission losses due to the various atmospheric constituents should be evaluated to derive D0 from the observed color ratio profiles. This process is responsible for increasing the uncertainty in the retrieval. Multiple scattering, especially for UV lidar, is another source of error, but it exhibits lower overall uncertainty with respect to other identified error sources. It is found that the total error upper limit on D0 approaches 50%. The impact of this retrieval for long-term MPLNET monitoring and its global data archive is discussed.

scholarly journals Estimating drizzle drop size and precipitation rate using two-colour lidar measurements

2010 ◽  
Vol 3 (3) ◽  
pp. 671-681 ◽  
Author(s):  
C. D. Westbrook ◽  
R. J. Hogan ◽  
E. J. O'Connor ◽  
A. J. Illingworth
Keyword(s):  
Water Content ◽  
Liquid Water ◽  
Drop Size ◽  
Liquid Water Content ◽  
Precipitation Rate ◽  
Infrared Light ◽  
Cloud Base ◽  
Size Spectrum ◽  
Drop Diameter ◽  
Lidar Measurements

Abstract. A method to estimate the size and liquid water content of drizzle drops using lidar measurements at two wavelengths is described. The method exploits the differential absorption of infrared light by liquid water at 905 nm and 1.5 μm, which leads to a different backscatter cross section for water drops larger than ≈50 μm. The ratio of backscatter measured from drizzle samples below cloud base at these two wavelengths (the colour ratio) provides a measure of the median volume drop diameter D0. This is a strong effect: for D0=200 μm, a colour ratio of ≈6 dB is predicted. Once D0 is known, the measured backscatter at 905 nm can be used to calculate the liquid water content (LWC) and other moments of the drizzle drop distribution. The method is applied to observations of drizzle falling from stratocumulus and stratus clouds. High resolution (32 s, 36 m) profiles of D0, LWC and precipitation rate R are derived. The main sources of error in the technique are the need to assume a value for the dispersion parameter μ in the drop size spectrum (leading to at most a 35% error in R) and the influence of aerosol returns on the retrieval (≈10% error in R for the cases considered here). Radar reflectivities are also computed from the lidar data, and compared to independent measurements from a colocated cloud radar, offering independent validation of the derived drop size distributions.

scholarly journals Comparison of Observed and Simulated Drop Size Distributions from Large-Eddy Simulations with Bin Microphysics

2019 ◽  
Vol 147 (2) ◽  
pp. 477-493
Author(s):  
Mikael K. Witte ◽  
Patrick Y. Chuang ◽  
Orlando Ayala ◽  
Lian-Ping Wang ◽  
Graham Feingold
Keyword(s):  
Liquid Water ◽  
Drop Size ◽  
Potential Temperature ◽  
Liquid Water Content ◽  
Liquid Water Path ◽  
Cloud Drop ◽  
Large Eddy Simulation Model ◽  
Surface Precipitation ◽  
Large Eddy ◽  
Bin Microphysics

Abstract Two case studies of marine stratocumulus (one nocturnal and drizzling, the other daytime and nonprecipitating) are simulated by the UCLA large-eddy simulation model with bin microphysics for comparison with aircraft in situ observations. A high-bin-resolution variant of the microphysics is implemented for closer comparison with cloud drop size distribution (DSD) observations and a turbulent collision–coalescence kernel to evaluate the role of turbulence on drizzle formation. Simulations agree well with observational constraints, reproducing observed thermodynamic profiles (i.e., liquid water potential temperature and total moisture mixing ratio) as well as liquid water path. Cloud drop number concentration and liquid water content profiles also agree well insofar as the thermodynamic profiles match observations, but there are significant differences in DSD shape among simulations that cause discrepancies in higher-order moments such as sedimentation flux, especially as a function of bin resolution. Counterintuitively, high-bin-resolution simulations produce broader DSDs than standard resolution for both cases. Examination of several metrics of DSD width and percentile drop sizes shows that various discrepancies of model output with respect to the observations can be attributed to specific microphysical processes: condensation spuriously creates DSDs that are too wide as measured by standard deviation, which leads to collisional production of too many large drops. The turbulent kernel has the greatest impact on the low-bin-resolution simulation of the drizzling case, which exhibits greater surface precipitation accumulation and broader DSDs than the control (quiescent kernel) simulations. Turbulence effects on precipitation formation cannot be definitively evaluated using bin microphysics until the artificial condensation broadening issue has been addressed.

Radiative Impacts on the Growth of Drops within Simulated Marine Stratocumulus. Part I: Maximum Solar Heating

2005 ◽  
Vol 62 (7) ◽  
pp. 2323-2338 ◽  
Author(s):  
Christopher M. Hartman ◽  
Jerry Y. Harrington
Keyword(s):  
Drop Size ◽  
Onset Time ◽  
Solar Heating ◽  
Size Spectrum ◽  
Marine Stratocumulus ◽  
Eddy Simulation ◽  
Cloud Properties ◽  
Large Eddy ◽  
Radiative Impacts ◽  
The Mean

Abstract The effects of solar heating and infrared cooling on the vapor depositional growth of cloud drops, and hence the potential for collection enhancement, is investigated. Large eddy simulation (LES) of marine stratocumulus is used to generate 600 parcel trajectories that follow the mean motions of the cloud. Thermodynamic, dynamic, and radiative cloud properties are stored for each trajectory. An offline trajectory ensemble model (TEM) coupled to a bin microphysical model that includes the influences of radiation on drop growth is driven by the 600-parcel dataset. In line with previous results, including infrared cooling causes a reduction in the time for collection onset. This collection enhancement increases with drop concentration. Larger concentrations (400 cm−3) show a reduction in collection onset time of as much as 45 min. Including infrared cooling as well as solar heating in the LES and microphysical bin models has a number of effects on the growth of cloud drops. First, shortwave (SW) heating partially offsets cloud-top longwave (LW) cooling, which naturally reduces the influence of LW cooling on drop growth. Second, SW heating dominates over LW cooling at larger drop radii (≳200 μm), which causes moderately sized drops to evaporate. Third, unlike LW cooling, SW heating occurs throughout the cloud deck, which suppresses drop growth. All three of these effects tend to narrow the drop size spectrum. For intermediate drop concentrations (100–200 cm−3), it is shown that SW heating primarily suppresses collection initiation whereas at larger drop concentrations (≳250 cm−3) LW cooling dominates causing enhancements in collection.

scholarly journals Aerosol–Cloud Interactions in a Mesoscale Model. Part II: Sensitivity to Aqueous-Phase Chemistry

2008 ◽  
Vol 65 (2) ◽  
pp. 309-330 ◽  
Author(s):  
Irena T. Ivanova ◽  
Henry G. Leighton
Keyword(s):  
Aqueous Phase ◽  
Mesoscale Model ◽  
Cloud Condensation Nuclei ◽  
Cloud Microphysics ◽  
Size Spectrum ◽  
Chemical Processing ◽  
Strong Constraint ◽  
Cloud Processing ◽  
Sulfate Production ◽  
The Impact

Abstract The feedbacks between aerosols, cloud microphysics, and cloud chemistry are investigated in a mesoscale model. A simple bulk aqueous-phase sulfur chemistry scheme was fully coupled to the existing aerosol and microphysics schemes. The representation of aerosol and microphysics follows the explicit bulk double-moment approach. A case of summertime stratocumulus cloud system is simulated at high resolution (3-km grid spacing), and the evolution of an observed continental aerosol spectrum that changes during the course of the simulation as a result of cloud processing is examined. The results demonstrate that the bulk approach to the aerosol and droplet spectra correctly represents the feedbacks in the coupled system. The simulations capture the characteristic bimodal aerosol size spectrum resulting from cloud processing, with the first mode consisting of particles that did not participate as cloud condensation nuclei and the second mode, in the region of 0.08–0.12-μm radii, comprising the particles that were affected by processing. New information is revealed about the impact of the two main processing pathways and about the spatial distribution of the processed aerosol. One cycle of physical processing produced a relatively modest impact of 3%–5% on the processed particle mean radius of the order that was comparable to the impact of chemical processing, while continuous physical recycling produced a much larger impact as high as 30%–50%. A strong constraint on the chemical processing was found to be the initial chemistry input and the assumption of bulk chemical composition. Simple tests with a more slowly depleting primary oxidant (H2O2) and including the droplet chemical heterogeneity effect favor stronger sulfate production, by, respectively, the H2O2 and O3 oxidation reaction, and both show a larger impact on the processed particle mean radius of similar magnitude, 10%–20%. Spatially, the impact of processing is found initially in the downdraft regions below cloud and at later times at substantial distances downwind. It is shown that cloud processing can either enhance or suppress the number of activated drops in subsequent cycles.

Dependence of accumulated precipitation on cloud drop size distribution

2010 ◽  
Vol 102 (3-4) ◽  
pp. 471-481 ◽  
Author(s):  
Mladjen Ćurić ◽  
Dejan Janc ◽  
Katarina Veljović
Keyword(s):  
Size Distribution ◽  
Drop Size ◽  
Drop Size Distribution ◽  
Cloud Drop

Characterization of Water Mist Sprays Using a Phase-Doppler-Particle-Analyzer and an Iso-Kinetic Sampling Probe

Volume 4 ◽  
2004 ◽  
Author(s):  
Benjamin Ditch ◽  
Hong-Zeng Yu
Keyword(s):  
Drop Size ◽  
Water Drop ◽  
Water Discharge ◽  
Radial Distance ◽  
Water Mist ◽  
Size Spectrum ◽  
Size Distributions ◽  
Sampling Probe ◽  
Phase Doppler Particle Analyzer ◽  
Drop Size Distributions

A Phase-Doppler-Particle-Analyzer (PDPA) was used to screen candidate water mist nozzles for use in a scaling validation aimed to allow scaled-down testing of water mist systems. A custom-designed iso-kinetic sampling probe (IKSP) was developed to independently measure water mist fluxes at the same locations where PDPA measurements were made. Measurements were taken at two elevations in selected full-cone water mist sprays. The water drop size was found to increase with radial distance from the spray centerline, while the mean drop velocity and drop concentration decrease with radial distance. Gross drop size distributions of water mist sprays were derived from local drop size distributions and water fluxes measured in two spray cross sections. It was found that, for the water mist sprays investigated in this study, both Rosin-Rammler and log-normal distributions are required to correlate the entire drop size spectrum. In general, the agreement between the mist fluxes measured with the PDPA and iso-kinetic sampling was within 7% near the spray centerline. The selected nozzles show appropriate intended scaling in terms of the drop size, nozzle discharge pressure, and water discharge rate.

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