Akash Deshmukh

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Papers by Akash Deshmukh

Organization of SIP mechanisms among basic cloud types

Clouds are a fundamental aspect of the Earth’s atmosphere. One of the major challenges in cloud-... more Clouds are a fundamental aspect of the Earth’s atmosphere. One of the major challenges in cloud-resolving models (CRM) is the formation and generation of new cloud ice particles from pre-existed ice and liquid. Based on the basic broad cloud types, it is helpful to distinguish between their fundamental microphysical properties. The four basic cloud types are defined as: (1) warm-based convective and stratiform clouds; and (2) cold-based convective and stratiform clouds. Recent studies of ice initiation in clouds have shown that most ice particles in the mixed-phase region of clouds are from secondary ice production (SIP) mechanisms but have generally concentrated on only one specific cloud system.In this study, Aerosol-Cloud model (AC) is used. AC includes the four mechanisms of secondary ice production as follows: ice-ice collisional breakup, raindrop freezing fragmentation, Hallett-Mossop (HM) process and sublimational breakup. The intent is to generalize the contribution of each...

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Comment on “Review of experimental studies of secondary ice production” by Korolev and Leisner (2020)

Atmospheric Chemistry and Physics

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Dependencies of Four Mechanisms of Secondary Ice Production on Cloud-Top Temperature in a Continental Convective Storm

Journal of the Atmospheric Sciences

Various mechanisms of secondary ice production (SIP) cause multiplication of numbers of ice parti... more Various mechanisms of secondary ice production (SIP) cause multiplication of numbers of ice particle, after the onset of primary ice. A measure of SIP is the ice enhancement ratio (“IE ratio”) defined here as the ratio between number concentrations of total ice (excluding homogeneously nucleated ice) and active ice-nucleating particles (INPs). A convective line observed on 11 May 2011 over the Southern Great Plains in the Mesoscale Continental Convective Cloud Experiment (MC3E) campaign was simulated with the “Aerosol–Cloud” (AC) model. AC is validated against coincident MC3E observations by aircraft, ground-based instruments, and satellite. Four SIP mechanisms are represented in AC: the Hallett–Mossop (HM) process of rime splintering, and fragmentation during ice–ice collisions, raindrop freezing, and sublimation. The vertical profile of the IE ratio, averaged over the entire simulation, is almost uniform (102 to 103) because fragmentation in ice–ice collisions dominates at long ti...

The Microphysics of the Warm-rain and Ice Crystal Processes of Precipitation in Simulated Continental Convective Storms

Precipitation is fundamental to the hydrological cycle. There are two possible mechanisms for its... more Precipitation is fundamental to the hydrological cycle. There are two possible mechanisms for its formation in clouds generally: the "warm-rain process" and the "ice crystal process". This study uses a microphysically advanced aerosol-cloud (AC) model to understand the contributions from the warm (from the warm-rain process) and cold (from the ice crystal process) components of the surface precipitation in a pair of contrasting convective storms that are cold-based (STEPS) and slightly warm-based (MC3E). Tagging-tracer techniques enabled analysis of microphysical pathways leading to the simulated precipitation. The cold components of graupel and rain mass are higher than the corresponding warm components in both simulations of the STEPS and MC3E storms. About ~80% of accumulated surface precipitation is predicted to originate from ice-crystal process in both cases. In sensitivity tests with lowering of cloud base to warmer levels near the ground, the origin of mo...

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The influence of multiple groups of biological ice nucleating particles on microphysical properties of mixed-phase clouds observed during MC3E

A new empirical parameterization (EP) for multiple groups of primary biological aerosol particles... more A new empirical parameterization (EP) for multiple groups of primary biological aerosol particles (PBAPs) is implemented in the aerosol-cloud model (AC) to investigate their roles as ice nucleating particles (INPs). The EP describes the heterogeneous ice nucleation by (1) fungal spores, (2) bacteria, (3) pollen, (4) detritus of plants, animals, and viruses, and (5) algae. Each group includes fragments from the originally emitted particles. A high-resolution simulation of a midlatitude mesoscale squall line by AC is validated against airborne and ground observations. Sensitivity tests are carried out by varying the initial vertical profiles of the loadings of individual PBAP groups. The resulting changes in warm and ice cloud microphysical parameters are investigated. The changes in warm microphysical parameters, including liquid water content and cloud droplet number concentration, are minimal (<10 %). Overall, PBAPs have little effect on the ice number concentration (<6 %) in the convective region. In the stratiform region, increasing the initial PBAP loadings by a factor of 1000 resulted in less than 40 % change in ice number concentrations. The total ice concentration is mostly controlled by various mechanisms of secondary ice production (SIP). However, when SIP is intentionally shut down in sensitivity tests, increasing the PBAP loading by a factor of 100 has an effect of less than 3 % on the ice phase. Further sensitivity tests revealed that PBAPs have little effect on surface precipitation and on the shortwave and longwave flux (<4 %) for a 100-fold perturbation in PBAPs.

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New Empirical Formulation for the Sublimational Breakup of Graupel and Dendritic Snow

Journal of the Atmospheric Sciences, 2021

Ice fragments are generated by sublimation of ice particles in subsaturated conditions in natural... more Ice fragments are generated by sublimation of ice particles in subsaturated conditions in natural clouds. Conceivably, such sublimational breakup would be expected to cause ice multiplication in natural clouds. Any fragment that survives will grow to become ice precipitation that may sublimate and fragment further. As a first step toward assessing this overlooked process, a formulation is proposed for the number of ice fragments from sublimation of ice particles for an atmospheric model. This is done by amalgamating laboratory observations from previously published studies. The concept of a “sublimated mass activity spectrum” for the breakup is applied to the dataset. The number of ice fragments is determined by the relative humidity over ice and the initial size of the parent ice particles. The new formulation applies to dendritic crystals and heavily rimed particles only. Finally, a thought experiment is performed for an idealized scenario of subsaturation with in-cloud descent. S...

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Empirical Formulation for number of ice crystal fragments by sublimational breakup

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Role of liquid phase in the development of ice phase in monsoon clouds: Aircraft observations and numerical simulations

Atmospheric Research, 2019

The effect of warm microphysical properties on ice processes is investigated in developing monsoo... more The effect of warm microphysical properties on ice processes is investigated in developing monsoon (MON) and premonsoon (PRE) cumulus clouds growing under different thermodynamic and aerosol conditions. We used airborne observations of cloud microphysical properties during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) and idealized large eddy simulation (LES) with the Weather Research &

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Effects from time dependence of ice nucleus activity for contrasting cloud types

Journal of the Atmospheric Sciences

The role of time-dependent freezing of ice nucleating particles (INPs) is evaluated with the ‘Aer... more The role of time-dependent freezing of ice nucleating particles (INPs) is evaluated with the ‘Aerosol-Cloud’ (AC) model in: 1) deep convection observed over Oklahoma during the Midlatitude Continental Convective Cloud Experiment (MC3E), 2) orographic clouds observed over North California during the Atmospheric Radiation Measurement (ARM) Cloud Aerosol Precipitation Experiment (ACAPEX), and 3) supercooled, stratiform clouds over the UK, observed during the Aerosol Properties, Processes And Influences on the Earth’s climate (APPRAISE) campaign. AC uses the dynamical core of the WRF model and has hybrid bin/bulk microphysics and a 3D mesoscale domain. AC is validated against coincident aircraft, ground-based and satellite observations for all three cases. Filtered concentrations of ice (> 0.1 to 0.2 mm) agree with those observed at all sampled levels. AC forms ice heterogeneously through condensation, contact, deposition, and immersion freezing. AC predicts the INP activity of vario...

Akash Deshmukh

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