Investigation of aerosol indirect effects on monsoon clouds using
ground-based measurements over a high-altitude site in Western Ghats

Kumar, Vivek; Pandithurai, G.; Leena, P.P.; Dani, K. K.; Murugavel, P.; Sonbawne, S. M.; Patil, Rajendra D.; Maheskumar, R. S.

doi:10.5194/acp-16-8423-2016

Cited by 30 publications

(24 citation statements)

References 24 publications

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“…One of the key factors in the cloud microphysics parameterizations is relative dispersion ( ε ), defined as the ratio of standard deviation of droplet radius to mean droplet radius of droplet size distributions. It is well known that ε has significant influences on aerosol indirect effect evaluation, warm‐rain initiation, cloud‐climate feedbacks, through its effects on cloud effective radius, cloud optical depth (Anil Kumar et al, 2016; McComiskey et al, 2009; Peng et al, 2007; Tas et al, 2012; Wang et al, 2011; Wang et al, 2013; Zhao et al, 2006; Zhao et al, 2019), and autoconversion processes (Liu et al, 2004; Liu et al, 2006; Liu et al, 2007; Lu et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Reconciling Contrasting Relationships Between Relative Dispersion and Volume‐Mean Radius of Cloud Droplet Size Distributions

Liu

Yum

et al. 2020

JGR Atmospheres

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Cloud droplet spectral relative dispersion is critical to parameterizations of cloud radiative properties, warm-rain initiation, and aerosol-cloud interactions in models; however, there is no consistent relationship between relative dispersion and volume-mean radius in literature, which hinders improving relative dispersion parameterization and calls for physical explanation. Here we show, by analyzing aircraft observations of cumulus clouds during Routine AAF [Atmospheric Radiation Measurement (ARM) Aerial Facility] Clouds with Low Optical Water Depths (CLOWD) Optical Radiative Observations, that the correlation between relative dispersion and volume-mean radius changes from positive to negative as volume-mean radius increases. With the new observation, we postulate that the sign of the correlation is determined by whether or not condensation (evaporation) occurs simultaneously with significant new activation (deactivation). The hypothesis is validated by simulations of both an adiabatic cloud parcel model and a parcel model accounting for entrainment-mixing. A new quantity, first bin strength, is introduced to quantify this new observation. Theoretical analysis of truncated gamma and modified gamma size distributions further supports the hypothesis and reconciles the contrasting relationships between relative dispersion and volume-mean radius, including the results in polluted fog observations. The results could shed new light on the so-called "twilight zone" between cloudy and cloud-free air, which in turn affects evaluation of aerosol-cloud interactions and retrieval of aerosol optical depth.Plain Language Summary The width of cloud droplet size distribution is critical to aerosol-cloud interactions and warm rain initiation. Relative dispersion represents the relative width of cloud droplet size distribution. Current parameterizations of relative dispersion often relate relative dispersion to volume-mean radius. Based on aircraft observations of cumulus clouds, it is found that relative dispersion is positively correlated with volume-mean radius when volume-mean radius is small, and the correlation becomes negative when volume-mean radius increases. A hypothesis is raised by relating the relationship between the two quantities to microphysical processes (activation, condensation, evaporation, and deactivation) and is substantiated with an adiabatic parcel model, a parcel model considering entrainment-mixing, and theoretical analysis. The results may promote the studies on the zone between cloudy and cloud-free air, which in turn affects evaluation of aerosol-cloud interactions.

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Section: Introductionmentioning

confidence: 99%

Reconciling Contrasting Relationships Between Relative Dispersion and Volume‐Mean Radius of Cloud Droplet Size Distributions

Liu

Yum

et al. 2020

JGR Atmospheres

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“…It is to note that the biological aerosols can act as both ice nuclei and GCCN, and thus, their effect could be very important in cloud and rain processes. The study site, WGs, is rich in vegetation and thus acts as a source for organic and biological aerosols (e.g., pollen, lichen, bacteria, and leaf fragments) (Anil Kumar et al, ). Thus, the presence of GCCN like sea salt along with other organic and biological aerosols are more effective in modifying the intensity and amount of precipitation in clouds with bigger drop size and higher terminal velocity.…”

Section: Resultsmentioning

confidence: 99%

Investigation of Raindrops Fall Velocity During Different Monsoon Seasons Over the Western Ghats, India

Das

Simon

Kolte

et al. 2020

Earth and Space Science

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Using the Two‐Dimensional Video Disdrometer measurements, we investigated the fall velocity of raindrops at Mahabaleshwar (17.92°N, 73.6°E, ~1.4 km above mean sea level, AMSL), a tropical site on the Western Ghats of India. The analysis is for different seasons during 2012–2015. To increase the reliability and accuracy of analysis, the raindrops with diameters in the range 0.5–2 mm and horizontal wind speed < 2 m s−1 are considered. The observed raindrop fall velocities have been corrected for the effect of air density. The ratio between the observed velocity and calculated terminal velocity is considered for estimating superterminal (positively skewed; higher than terminal velocity) and subterminal (negatively skewed; lower than terminal velocity) raindrops. The distribution of these skewed raindrops and its relationship with rain rate, drop diameter, and axis ratio for different seasons has been examined. Results indicate the presence of superterminal and subterminal raindrops in definite proportion in all the season with a majority of the drops have a diameter less than 1 mm. It is found that most of the superterminal raindrops occur at rain rates below 5 mm hr−1, while subterminal raindrops are relatively higher above this rain rate. It is observed that the superterminal raindrops are usually small in size and prolate in shape, while the subterminal raindrops are relatively large and oblate in shape. The diurnal variation of these raindrops during different seasons is also studied.

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“…Entrainment in cumulus is primarily lateral with strong dilution of the cloud, which induces LWC to decrease rapidly to approximately 20 % of its adiabatic value (Warner, 1955). Entrainment in stratocumulus is mainly determined by the strength of the gradients in buoyancy and horizon-tal winds (Wang and Albrecht 1994;Gerber et al, 2005;de Roode and Wang 2007;Wood, 2012) and proceeds from the top and mostly affects a thin layer (Gerber et al, 2005), whose dilution effect is much weaker than that in cumulus (Warner, 1955(Warner, , 1969aBlyth et al, 1988;Gerber et al, 2008;Burnet and Brenguier, 2007;Haman et al, 2007). Aircraft observations of marine stratocumulus clouds showed that the vertical profile of LWC is essentially the same as the adiabatic profile; i.e., the cloud is almost adiabatic (Keil and Haywood, 2003).…”

Section: Entrainment In Stratocumulusmentioning

confidence: 99%

Responses to Referee #1’s comments

Jia¹

2019

Preprint

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In situ aircraft measurements obtained during the VAMOS (Variability of the American Monsoons) Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) field campaign are analyzed to study the aerosol-cloud interactions in the stratocumulus clouds over the southeastern Pacific Ocean (SEP), with a focus on three understudied topics (separation of aerosol effects from dynamic effects, dispersion effects, and turbulent entrainmentmixing processes). Our analysis suggests that an increase in aerosol concentration tends to simultaneously increase both cloud droplet number concentration (N d) and relative dispersion (ε), while an increase in vertical velocity (w) often increases N d but decreases ε. After constraining the differences of cloud dynamics, the positive correlation between ε and N d becomes stronger, implying that perturbations of w could weaken the aerosol influence on ε and hence result in an underestimation of dispersion effect. A comparative analysis of the difference of cloud microphysical properties between the entrainment and non-entrainment zones suggests that the entrainment-mixing mechanism is predominantly extremely inhomogeneous in the stratocumulus that capped by a sharp inversion, whereby the variation in liquid water content (25 %) is similar to that of N d (29 %) and the droplet size remains approximately constant. In entrainment zone, drier air entrained from the top induces fewer cloud droplets with respect to total in-cloud particles (0.56 ± 0.22) than the case in the non-entrainment zone (0.73 ± 0.13) by promoting cloud droplet evaporation. This study is helpful in reducing uncertainties in dispersion effects and entrainment mixing for stratocumulus, and the results of this study may benefit cloud parameterizations in global climate models to more accurately assess aerosol indirect effects.

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Investigation of aerosol indirect effects on monsoon clouds using ground-based measurements over a high-altitude site in Western Ghats

Cited by 30 publications

References 24 publications

Reconciling Contrasting Relationships Between Relative Dispersion and Volume‐Mean Radius of Cloud Droplet Size Distributions

Reconciling Contrasting Relationships Between Relative Dispersion and Volume‐Mean Radius of Cloud Droplet Size Distributions

Investigation of Raindrops Fall Velocity During Different Monsoon Seasons Over the Western Ghats, India

Responses to Referee #1’s comments

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