The relevance of different heterogeneous ice formation processes for the precipitation budget

<p>Heterogeneous ice formation in mixed-phase precipitating clouds plays an important role in current weather and climate research. The complex interaction between aerosols, clouds and dynamics taking place within these clouds is still not understood. One major reason for that gap in knowledge is the fact that most of the relevant processes take place inside the complex turbulent environment inside of the cloud, making observations difficult. Also, the unknown impact of ice formation on cloud lifetime and precipitation evolution introduces large uncertainties into numeric weather prediction and climate projections.</p> <p>In the present study, we analyze datasets gathered at four different Cloudnet (Illingworth et al., 2007) sites in order to quantify and disentangle the impact of temperature and vertical air motions on precipitation formation. Basis for the investigation are combined measurements of lidar, cloud radar and ground-based disdrometer/rain sensor measurements processes with the Cloudnet algorithm. Fallstreak tracking methods are applied in order to connect rain events on the ground with their generating level/temperature at cloud top. We have evaluated combined remote sensing data gathered at different Cloudnet sites in order to contrast the relationship between cloud top temperature (CTT) and rain formation processes. The datasets at Leipzig (Germany), Limassol (Cyprus) and Punta Arenas (Chile) were collected with the Leipzig Aerosol and Cloud Remote Observations System (LACROS). The Barbados dataset was acquired with the Barbados Cloud Observatory (BCO) of Max-Planck Institute for Meteorology Hamburg.</p>

Importance of aerosols and shape of the cloud droplet size distribution for convective clouds and precipitation

The predictability of deep moist convection is subject to large uncertainties resulting from inaccurate initial and boundary data, the incomplete description of physical processes, or microphysical uncertainties. In this study, we investigate the response of convective clouds and precipitation over central Europe to varying cloud condensation nuclei (CCN) concentrations and different shape parameters of the cloud droplet size distribution (CDSD), both of which are not well constrained by observations. We systematically evaluate the relative impact of these uncertainties in realistic convection-resolving simulations for multiple cases with different synoptic controls using the new icosahedral nonhydrostatic ICON model. The results show a large systematic increase in total cloud water content with increasing CCN concentrations and narrower CDSDs together with a reduction in the total rain water content. This is related to a suppressed warm-rain formation due to a less efficient collision-coalescence process. It is shown that the evaporation at lower levels is responsible for diminishing these impacts on surface precipitation, which lies between +13 % to −16 % compared to a reference run with continental aerosol assumption. In general, the precipitation response was larger for weakly-forced cases. We also find that the overall timing of convection is not sensitive to the microphysical uncertainties applied, indicating that different rain intensities are responsible for changing precipitation totals at the ground. Furthermore, weaker rain intensities in the developing phase of convective clouds can allow for a higher convective instability at later times, which can lead to a turning point with larger rain intensities later on. The existence of such a turning point and its location in time can have a major impact on precipitation totals. In general, we find that an increase in the shape parameter can produce almost as large a variation in precipitation as a CCN increase from maritime to polluted conditions. Narrowing of the CDSD not only decreases the absolute values of autoconversion and accretion, but also decreases the relative role of the warm-rain formation in general, independent of the prevailing weather regime. We further find that increasing CCN concentrations reduces the effective radius of cloud droplets stronger than larger shape parameters. The cloud optical depth, however, reveals a similar large increase with larger shape parameters as changing the aerosol load from maritime to polluted. By the frequency of updrafts as a function of height, we show a negative aerosol effect on updraft strength, indicating that the larger water load above the freezing level in polluted conditions does not lead to an invigoration of deep convection. These findings demonstrate that both, CCN assumptions and the CDSD shape parameter, are important for quantitative precipitation forecasting and should be carefully chosen if double-moment schemes are used for modeling aerosol-cloud interactions.

Biochar Aerogel Decorated with Thiophene S Manipulated 5-membered Rings Boosts Nitrogen Fixation

Algae, which contains most of the marine biogenic sulfur (S), is the main producer of dimethylsulfide (DMS). The oxidation products of DMS (methanesulfonic acid (MSA) and non-sea salt sulfates (nss-SO42-)) are important contributors to acid rain acidity (~ 40%) and have great influence on global climate change and acid rain formation. The biogenic S of red algae mainly exists in carrageenan molecules, the polysaccharide extract of red algae. In this work, the carrageenan biogenic S was fixed into biochar aerogel (SCA) synchronically by pyrolysis with the assistance of the unique hydrogel property of carrageenan. During this process, 89% of C and 96% of marine biogenic S are preserved in SCA, efficiently preventing the loss of C and S element. More importantly, the thiophene S structure in SCA framework derived from the marine biogenic S could endow the carbon aerogel superior electrocatalysis activity by regulating the charge density of adjacent C atoms. For instance, thiophene S structure can promote the cleavage and protonation of N2 molecules and efficiently lower the energy barrier of the promote the protonation of N2, thus greatly enhance the activity of electrocatalytic NRR. This study provided a promising avenue for the synchronization fixation of marine biogenic S and C to reduce the the formation of acid rain and carbon dioxide emissions. It also developed a green and sustainable way to synthesize high-performance biochar materials for advanced energy conversion.

Warm Cloud Evolution, Precipitation, and Their Weak Linkage in HadGEM3: New Process-Level Diagnostics using A-Train Observations

The latest configuration of the Hadley Centre Global Environmental Model version 3 (HadGEM3) contains significant changes in the formulation of warm rain processes and aerosols. We evaluate the impacts of these changes in the simulation of warm rain formation processes using A-Train observations. We introduce a new model evaluation tool, quartile-based Contoured Frequency by Optical Depth Diagrams (CFODDs), in order to fill in some blind spots that conventional CFODDs have. Results indicate that HadGEM3 has weak linkage between the size of particle radius and warm rain formation processes, and switching to the new warm rain microphysics scheme causes more difference in warm rain formation processes than switching to the new aerosol scheme through reducing overly produced drizzle mode in HadGEM3. Finally, we run an experiment in which we perturb the second aerosol indirect effect (AIE) to study the rainfall-aerosol interaction in HadGEM3. Since the large changes in the cloud droplet number concentration (CDNC) appear in the AIE experiment, a large impact in warm rain diagnostics is expected. However, regions with large fractional changes in CDNC show a muted change in precipitation, arguably because large-scale constraints act to reduce the impact of such a big change in CDNC. The adjustment in cloud liquid water path to the AIE perturbation produces a large negative shortwave forcing in the midlatitudes.

Metastable States of Water Aerosols: Comparison by Experiment

Free energy of water aerosol plasma was calculated using the Debye–Hückel method. It was established that free energies of droplets, ions and simultaneously of all charged particles had local minima (metastable states) at certain concentrations and charges of particles. The calculation results were confirmed by experimental data taken from the literature on a droplet cluster in water vapor and droplet structures in water fog. The possible connection of metastable states with the phenomenon of drop coalescence and rain formation in real clouds, as well as with the generation of stable spatially arranged drop structures, has been indicated.

Acid rain formation through catalytic transformation of sulfur dioxide over clay dusts: remarkable promotion by a vicinal aluminium site

Mechanisms for catalytic SO2 transformation to H2SO4 over clay dusts have been unraveled at a molecular level. All O atoms in ozone (especially molecular oxygen) are effective oxidants due to remarkable promotion of a vicinal Al3+ site.

Impacts of Tropical Cyclones in the Northern Atlantic on Adverse Phenomena Formation in Northeastern Brazil

Tropical cyclone (TC) impacts on adverse phenomena in the tropical region of Northeastern Brazil (NEB) have been analyzed. TC influence on fog and rain formation was not described in the previous papers. The main goal of the chapter is to evaluate the existence of such influence and thus to improve the weather forecasting in this area. TC information from the NHC of the NOAA was used. METAR and SYNOP data were used for the adverse phenomena study. Analysis of the synoptic systems was based on different maps at the pattern levels and on satellite images. These maps were elaborated using reanalysis data from the ECMWF. Thermodynamic analysis was also used. Middle tropospheric cyclonic vortexes (MTCV) in the tropical region of the Southern Atlantic were described recently. Five from 10 MTCVs were associated with tropical cyclones and disturbances in the Northern Atlantic. Circulation patterns between TC and synoptic systems at the NEB are described. These circulations create sinking over the BNE and, as a result, form fog, mist and weak rain in the BNE during TC days. Mechanisms of TC influence on weather formation in the BNE are presented. This information is important for improving weather forecasting methods.

Self-consistent 3D radiative magnetohydrodynamic simulations of coronal rain formation and evolution

Context. Coronal rain consists of cool and dense plasma condensations formed in coronal loops as a result of thermal instability. Aims. Previous numerical simulations of thermal instability and coronal rain formation have relied on the practice of artificially adding a coronal heating term to the energy equation. To reproduce large-scale characteristics of the corona, the use of more realistic coronal heating prescription is necessary. Methods. We analysed coronal rain formation and evolution in a three-dimensional radiative magnetohydrodynamic simulation spanning from convection zone to corona which is self-consistently heated by magnetic field braiding as a result of convective motions. Results. We investigate the spatial and temporal evolution of energy dissipation along coronal loops which become thermally unstable. Ohmic dissipation in the model leads to the heating events capable of inducing sufficient chromospheric evaporation into the loop to trigger thermal instability and condensation formation. The cooling of the thermally unstable plasma occurs on timescales that are comparable to the duration of the individual impulsive heating events. The impulsive heating has sufficient duration to trigger thermal instability in the loop but does not last long enough to lead to coronal rain limit cycles. We show that condensations can either survive and fall into the chromosphere or be destroyed by strong bursts of Joule heating associated with a magnetic reconnection events. In addition, we find that condensations can also form along open magnetic field lines. Conclusions. We modelled, for the first time, coronal rain formation in a self-consistent 3D radiative magnetohydrodynamic simulation, in which the heating occurs mainly through the braiding and subsequent Ohmic dissipation of the magnetic field. The heating is stratified enough and lasts for long enough along specific field lines to produce the necessary chromospheric evaporation that triggers thermal instability in the corona.

Monitoring rain rate with proximal gamma-ray spectroscopy

<p>We present an exhaustive study of the gamma activity increase measured at ground level for the atmospheric radon daughter <sup>214</sup>Pb. We demonstrate the effectiveness of proximal gamma-ray spectroscopy in continuously gathering reliable measurements of rain-induced <sup>214</sup>Pb gamma signal related to the rain intensity and amount. Since every impulse of rain produces a sudden increase of gamma signal, we study such transient activity to obtain information on precipitations and rain formation.</p><p>A novel spectroscopic instrument specifically tailored for gathering reliable and unbiased estimates of atmospheric and terrestrial gamma emitters has been developed. After seven months of continuous acquisition, we analyze the temporal evolution of the <sup>214</sup>Pb net count rate with an innovative and reproducible mathematical model for extracting information on this radon daughter’s content in the rain water. The effectiveness of the model is proved by an excellent coefficient of determination (r<sup>2</sup> = 0.91) between measured and reconstructed <sup>214</sup>Pb count rates. We observe that the impulsive increase of <sup>214</sup>Pb count rates ΔC is clearly related to the rain rate R by the power law dependence ΔC = A·R<sup>0.50 ± 0.03</sup>, where the parameter A is equipment dependent. This means that the expected increase of atmospheric <sup>214</sup>Pb activity measured at ground level during a rain event is proportional to the square root of the rain rate √R.</p><p>We observe that the <sup>214</sup>Pb abundance (G) of the rain water is inversely related to the rain rate G ∝ 1/R<sup>0.48 ± 0.03</sup> and to the rain median volume diameter λ<sub>m</sub> with G ∝ 1/ λ<sub>m</sub><sup>2.2</sup>.  We proved that, for a fixed rainfall amount, the longer is the rain duration (i.e. the lower is the rainfall intensity and the smaller is the mean raindrop volume), the higher is the <sup>214</sup>Pb content of the rain water.</p><p>Since the developed algorithm is detector independent, it can be used for analysing the data collected by the networks of thousands of gamma sensors distributed around the Earth, typically utilised for monitoring the air radioactivity in case of a nuclear fallout. From this spectroscopic technique we shall learn a lot more about the rain formation and scavenging mechanisms which are responsible for the attachment of <sup>214</sup>Pb to rain droplets in-cloud. Finally, our research provides a comprehensive characterization of the background radiation assessments relevant for radioprotection, earthquake predictions, cosmic rays research and anthropic radiation monitoring.</p>