Impact of hygroscopic seeding on the initiation of precipitation formation: results of a hybrid bin microphysics parcel model

A hybrid bin microphysical scheme is developed in a parcel model framework to study how natural aerosol particles and different types of hygroscopic seeding materials affect the precipitation formation. A novel parameter is introduced to describe the impact of different seeding particles on the evolution of the drop size distribution. The results of more than 100 numerical experiments using the hybrid bin parcel model show that (a) the Ostwald-ripening effect has a substantial contribution to the broadening of the drop size distribution near the cloud base. The efficiency of this effect increases as the updraft velocity decreases. (b) The efficiency of hygroscopic seeding is significant only if the size of the seeding particles is in the coarse particle size range. The presence of the water-soluble background coarse particles reduces the efficiency of the seeding, (c) The efficient broadening of the size distribution due to the seeding depends on the width of the size distribution of water drops in the control cases, but the relation is not as straightforward as in the case of the glaciogenic seeding.

Sensitivity of precipitation formation to secondary ice production in winter orographic mixed-phase clouds

The discrepancy between the observed concentration of ice nucleating particles (INPs) and the ice crystal number concentration (ICNC) remains unresolved and limits our understanding of ice formation and, hence, precipitation amount, location and intensity. Enhanced ice formation through secondary ice production (SIP) could account for this discrepancy. Here, in a region over the eastern Swiss Alps, we perform sensitivity studies of additional simulated SIP processes on precipitation formation and surface precipitation intensity. The SIP processes considered include rime splintering, droplet shattering during freezing and breakup through ice–graupel collisions. We simulated the passage of a cold front at Gotschnagrat, a peak at 2281 m a.s.l. (above sea level), on 7 March 2019 with the Consortium for Small-scale Modeling (COSMO), at a 1 km horizontal grid spacing, as part of the RACLETS (Role of Aerosols and CLouds Enhanced by Topography and Snow) field campaign in the Davos region in Switzerland. The largest simulated difference in the ICNC at the surface originated from the breakup simulations. Indeed, breakup caused a 1 to 3 orders of magnitude increase in the ICNC compared to SIP from rime splintering or without SIP processes in the control simulation. The ICNCs from the collisional breakup simulations at Gotschnagrat were in best agreement with the ICNCs measured on a gondola near the surface. However, these simulations were not able to reproduce the ice crystal habits near the surface. Enhanced ICNCs from collisional breakup reduced localized regions of higher precipitation and, thereby, improved the model performance in terms of surface precipitation over the domain.

Global evidence of aerosol-induced invigoration in marine cumulus clouds

Aerosol–cloud–precipitation interactions can lead to a myriad of responses within shallow cumulus clouds, including an invigoration response, whereby aerosol loading results in a higher rain rate, more turbulence, and deepening of the cloud layer. However few global studies have found direct evidence that invigoration occurs. The few satellite-based studies that report evidence for such effects generally focus on only the deepening response. Here, we show evidence of invigoration beyond a deepening response by investigating the effects of aerosol loading on the latent heating and vertical motion profiles of warm rain. Using latent heating and vertical motion profiles derived from CloudSat radar observations, we show precipitating cumulus clouds in unstable, polluted environments exhibit a marked increase in precipitation formation rates and cloud top entrainment rates. However, invigoration is only discernible when the stability of the boundary layer is explicitly accounted for in the analysis. Without this environmental constraint, the mean polluted and pristine cloud responses are indiscernible from each other due to offsetting cloud responses in stable and unstable environments. Invigoration, or suppression depending on the environment, may induce possible feedbacks in both stable and unstable conditions that could subdue or enhance these effects, respectively. The strength of the invigoration response is found to additionally depend on cloud organization defined here by the size of the warm rain system. These results suggest that warm cloud parameterizations must account for not only the possibility of aerosol-induced cloud invigoration, but also the dependence of this invigorated state on the environment and the organization of the rain system.

Recovery Method for Emergency Situations with Hazardous Substances Emission into the Atmosphere

The objective of this Article is development of a hazardous area extent reducing method in the atmosphere upon emergency situation occurrence with hazardous chemical and radioactive substances emission. To achieve the specified objective it is recommended to use deposition of gaseous, liquid and solid disperse hazardous particles from the atmosphere using artificial precipitation over a zone of emergency. For artificial intensification of precipitation, use of chemical and physical principles of impact on droplets formation processes in the area of clouds is proposed. A pyrotechnic composition was developed for chemical impact, which when combustion generates finely dispersed chemical centers of condensation and modifying components for hazardous chemical substances neutralization. Conducting the ionization of precipitation formation area by a strong impulse electromagnetic irradiation was proposed as a physical impact on the artificial precipitation formation processes. The laboratory study results confirmed the technical feasibility of this method implementation. To reduce the necessary radiator power, application of a multi-position radiators system with radiation focusing to one irradiation zone was proposed. The theoretical and experimental results obtained in the article are the base for development of emergency situation negative consequences reduction practical procedures through artificial precipitation initiation.

Impact of hygroscopic seeding on the initiation of precipitation formation: results of a hybrid bin microphysics parcel model

A hybrid bin microphysical scheme is developed in a parcel model framework to study how natural aerosol particles and different types of hygroscopic seeding materials affect the precipitation formation. A novel parameter is introduced to describe the impact of different seeding particles on the evolution of the drop size distribution. The results of more than 100 numerical experiments using the hybrid bin parcel model show that: (a) The Ostwald-ripening effect has a substantial contribution to the broadening of the drop size distribution near the cloud base. The efficiency of this effect increases as the updraft velocity decreases. (b) The efficiency of hygroscopic seeding is significant only if the size of the seeding particles is in the coarse particle size range. The presence of the water-soluble background coarse particles reduces the efficiency of the seeding. (c) The efficient broadening of the size distribution due to the seeding depends on the width of the size distribution of water drops in the control cases, but the relation is not as straightforward as in the case of the glaciogenic seeding.

Global Evidence of Aerosol-induced Invigoration in Marine Cumulus Cloud

Aerosol-cloud-precipitation interactions can lead to a myriad of responses within shallow cumulus clouds including an invigoration response, whereby aerosol loading results in a higher rain rate, more turbulence, and deepening of the cloud layer. However few global studies have found direct evidence that invigoration occurs. The few satellite based studies that report evidence for such effects generally focus on only the deepening response. Here, we show evidence of invigoration beyond a deepening response. Using latent heating and vertical motion profiles derived from CloudSat radar observations, we show precipitating cumulus clouds in unstable, polluted environments exhibit a marked increase in precipitation formation rates and cloud top entrainment rates. However, invigoration is only discernible when the stability of the boundary layer is explicitly accounted for in the analysis. Without this environmental constraint, the mean polluted and pristine cloud responses are indiscernible from each other due to offsetting cloud responses in stable and unstable environments. Invigoration, or suppression depending on the environment, may induce possible feedbacks in both stable and unstable conditions that could subdue or enhance these effects, respectively. The strength of the invigoration response is found to additionally depend on cloud organization defined here by the size of the warm rain system. These results suggest that warm cloud parameterizations must account for not only the possibility of aerosol-induced cloud invigoration, but also the dependence of this invigorated state on the environment and the organization of the rain system.

Using airborne lidar and weather radar measurements to characterize the interplay between aerosol and shallow marine trade wind clouds

<p>The interaction of aerosol, clouds, and water vapor is still a major source of uncertainty in projections of Earth’s future climate. Especially in the trades, the response of shallow marine trade wind convection to external forcings is poorly understood. These low-level clouds have an important cooling effect on surface temperatures, while their amount and height are directly influenced by the radiative cooling by aerosols and water vapor aloft. Furthermore, there is evidence that aerosols can modify the microphysical properties (e.g., by glaciation) and the precipitation formation inside these clouds while water vapor above the trade inversion influences the atmospheric stability in which they form. Due to the small horizontal scale of these clouds, the vertical separation of atmospheric layers, and the temporal evolution of precipitation, the observation of this interplay by geostationary satellites is scarce.</p><p>To alleviate this observational data gap over the tropical North-Atlantic region, airborne lidar and cloud radar measurements were performed in the vicinity of Barbados and complemented with dedicated weather radar measurements during the EUREC4A campaign in February 2020. Aerosol properties and the vertical water vapor profile were characterized with simultaneous high spectral resolution and differential absorption measurements using the WALES lidar onboard the German research aircraft HALO. On the same platform, the vertical cloud extent and the presence of precipitation were sampled with the high-power Ka-band cloud radar HAMP MIRA. To capture the temporal evolution of precipitation patterns, these measurements were complemented with measurements of the C-band polarimetric weather radar POLDIRAD which was installed on the windward side of Barbados. During EUREC4A, measurements flights were conducted in high and low aerosol loads to sample its influence on the marine trade wind convection.</p><p>This presentation will briefly introduce the instrumentation, data processing, and availability and give an overview of gained insights and ongoing studies. By means of case studies, we will give first impressions of the complementary nature of the collocated, highly resolved airborne measurements and the POLDIRAD measurements which provide the horizontal context and temporal evolution of the precipitation formation. By combining the cross-sectional snapshots with the temporal evolution of the precipitation pattern we will provide a detailed insight into the interplay between the aerosol and water vapor layer and the precipitation formation in the shallow marine trade wind convection.</p>