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Current weather modification rockets with a single operation mode, limited operating height, and fixed and uncontrollable operating time cannot achieve seeding in different layers, stages, and quantities for different cloud systems. Therefore, a temporally controllable weather modification rocket with spatial seeding capability is developed in this study. This new rocket features an electronic fuse-controlled intelligent ignition system, with eight channels of ignition tube outputs. Additionally, carrier wave communication technology is incorporated to set the seeding time for eight sets of ignition tubes. The temporally controllable rocket is capable of initiating seeding within 2–26 s and can conduct operations for layering, arbitrary altitude, and fractional-dose seeding within the altitude range of 500–5500 m (at a launch angle of 70°), which is calculated based on the flight trajectory of rockets. The minimum time interval of the rocket for seeding can be set to 0.1 s, and all 48 catalyst bullets loaded in a single rocket can be launched within 0.8 s. Thus, the rocket can achieve both concentrated and continuous seeding. Consequently, during weather modification operations, the parameters such as altitude, thickness, and operating temperature of target clouds can be obtained through detection, and they can be used to automatically calculate the suitable seeding time, seeding altitude, and seeding dose by the launch control system based on the flight trajectory of rockets to improve the accuracy and scientificity of cloud catalytic operations. Ground tests show that the reliabilities of the electric ignition tube output, new electronic fuse input and output, and electronic fuse output energy all meet the design specification. The temporally controllable spatial seeding rocket can achieve adjustable and controllable seeding times for catalytic bullets, meeting the safety and reliability requirements of rockets. [ABSTRACT FROM AUTHOR]

Cloud seeding involves boosting precipitation by releasing substances into the air that act as cloud condensation or ice nuclei. These substances encourage the development of clouds and precipitation. It's like giving Mother Nature a gentle push to assist with rainfall in specific areas. The current work aimed to suggest Al2O3 as an alternate compound in cloud seeding rather than silver iodide. In this research, a unique approach is used to identify condensation nuclei, which play a crucial role in cloud formation and droplet growth. Various samples and four sources were included in the current study; refrigerated helfa powder, Himalayan salt, generator powder, and pollen, were analyzed using different physicochemical instruments. The proportions of chemical compounds in the samples show that there is 1.392% of Al2O3 in Refrigerated helfa which is the highest than in the other 3 sources, while the proportions of elements in the samples indicate that refrigerated helfa contains the lowest toxic compound, and although Al2O3 is insoluble in water, it is hygroscopic and can absorb 6.4% of humidity within 24 hours. As for the surface tension, refrigerated helfa shows lower density and surface tension than the other three sources with values of 0.9480 and 47.89 respectively. Al2O3 shows high humid absorptivity and refrigerated helfa can be used as a main source for Al2O3 which has a low effect on biota and is recommended for use in cloud seeding. However further work is recommended to be carried out in using Al2O3 as an alternative compound to silver iodide in cloud seeding. [ABSTRACT FROM AUTHOR]

Membraneless coacervate microdroplets have long been proposed as model protocells as they can grow, divide, and concentrate RNA by natural partitioning. However, the rapid exchange of RNA between these compartments, along with their rapid fusion, both within minutes, means that individual droplets would be unable to maintain their separate genetic identities. Hence, Darwinian evolution would not be possible, and the population would be vulnerable to collapse due to the rapid spread of parasitic RNAs. In this study, we show that distilled water, mimicking rain/freshwater, leads to the formation of electrostatic crosslinks on the interface of coacervate droplets that not only suppress droplet fusion indefinitely but also allow the spatiotemporal compartmentalization of RNA on a timescale of days depending on the length and structure of RNA. We suggest that these nonfusing membraneless droplets could potentially act as protocells with the capacity to evolve compartmentalized ribozymes in prebiotic environments. [ABSTRACT FROM AUTHOR]

In this study, we investigated the feasibility of rain enhancement by cloud seeding over a target area (the Sameura Dam catchment area, Kochi Prefecture) in early summer. The effects of salt micro-powder (MP) and hygroscopic flare (HF) seeding on the initial cloud microphysical structures were investigated using a detailed bin microphysics parcel model with background atmospheric aerosol data collected from ground-based observations conducted on the windward side of the target area and seeding aerosol data collected from the coordinated flights of seeding helicopter and in-situ measurement aircraft. Numerical seeding experiments showed that the size distributions of cloud droplets were broadened, and the onset of raindrop formation was accelerated by MP and HF seeding, although MP seeding showed more notable seeding effects than did HF seeding. MP seeding increased the mean droplet size and decreased the total number concentration of cloud droplets, whereas HF seeding had the opposite effect. Based on the relationship between the increase/decrease ratio of the cloud droplet number concentration and increase/decrease ratio of the surface precipitation by hygroscopic seeding obtained in previous studies, MP seeding had a positive seeding effect, whereas HF seeding had a negative effect. In the numerical seeding experiments, a range of variations in the number concentration and hygroscopicity of background aerosol particles, updraft velocity near the cloud base, the amount of seeding material applied, and the change in the physicochemical properties of the seeding aerosols to improve seeding effects were also considered. However, the outline of the results described above remained unchanged. These results demonstrate the possibility of increasing surface precipitation by MP seeding over the catchment. However, seeding a large amount of MP (NaCl) is necessary to enhance precipitation substantially. Simultaneously, considering the environmental impact is essential, as shown in our study. [ABSTRACT FROM AUTHOR]

The supercooled liquid fraction (SLF) in mixed-phase clouds (MPCs) is an essential variable of cloud microphysical processes and climate sensitivity. However, the SLF is currently calculated in spaceborne remote sensing only as the cloud phase–frequency ratio of adjacent pixels, which results in a loss of the original resolution in observations of cloud liquid or ice content within MPCs. Here, we present a novel method for retrieving the SLF in MPCs based on the differences in radiative properties of supercooled liquid droplets and ice particles at visible (VIS) and shortwave infrared (SWI) channels of the geostationary Himawari-8. Liquid and ice water paths are inferred by assuming that clouds are composed of only liquid or ice, with the real cloud water path (CWP) expressed as a combination of these two water paths (SLF and 1-SLF as coefficients), and the SLF is determined by referring to the CWP from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). The statistically relatively small cloud phase spatial inhomogeneity at a Himawari-8 pixel level indicates an optimal scene for cloud retrieval. The SLF results are comparable to global SLF distributions observed by active instruments, particularly for single-layered cloud systems. While accessing the method's feasibility, SLF averages are estimated between 74 % and 78 % in Southern Ocean (SO) stratocumulus across seasons, contrasting with a range of 29 % to 32 % in northeastern Asia. The former exhibits a minimum SLF around midday in summer and a maximum in winter, while the latter trend differs. This novel algorithm will be valuable for research to track the evolution of MPCs and constrain the related climate impact. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau vortex (TPV), as an α-scale mesoscale weather system, often brings severe weather conditions like torrential rain and severe convective storms. Based on the detections from the Global Precipitation Measurement (GPM) Core Observatory's Dual-frequency Precipitation Radar (DPR) and the FY-4A satellite's Advanced Geostationary Radiation Imager (AGRI), combined with ERA5 reanalysis data, the precipitation characteristics of a TPV moving eastward during 8–13 July 2021 at different developmental stages are explored in this study. It was clear that the near-surface precipitation rate of the TPV during the initial stage at the eastern Tibetan Plateau (TP) was below 1 mm·h−1, implying overall weak precipitation dominated by stratiform clouds. After moving out of the TP, the radar reflectivity factor (Ze), precipitation rate, and normalized intercept parameter (dBNw) significantly increased, while the proportion of convective clouds gradually rose. Following the TPV movement, the distribution range and vertical thickness of Ze, mass-weighted mean diameter (Dm), and dBNw tended to increase. The high-frequency region of Ze appeared at 15–20 dBZ, while Dm and dBNw occurred at around 1 mm and 33 mm−1·m−3, respectively. Near the melting layer, Ze was characterized by a significant increase due to the aggregation and melting of ice crystals. The precipitation rate of convective clouds was generally greater than that of stratiform clouds, whilst both of them increased during the movement of the TPV. Particularly, at 01:00 on 12 July, there was a significant increase in the precipitation rate and Dm of convective clouds, while dBNw noticeably decreased. These findings could provide valuable insights into the three-dimensional structure and microphysical characteristics of the precipitation during the movement of the TPV, contributing to a better understanding of cloud precipitation mechanisms. [ABSTRACT FROM AUTHOR]

The ice phase in clouds is essential for precipitation formation over continents. The underlying processes for ice growth are still poorly understood, leading to large uncertainties in precipitation forecasts and climate simulations. One crucial aspect is the Wegener–Bergeron–Findeisen (WBF) process, which describes the growth of ice crystals at the expense of cloud droplets, leading to a partial or full glaciation of the cloud. In the CLOUDLAB project, we employ glaciogenic cloud seeding to initiate the ice phase in supercooled low-level clouds in Switzerland using uncrewed aerial vehicles with the goal of investigating the WBF process. An extensive setup of ground-based remote-sensing and balloon-borne in situ instrumentation allows us to observe the formation and subsequent growth of ice crystals in great detail. In this study, we compare the seeding signals observed in the field to those simulated using a numerical weather model in large-eddy mode (ICON-LEM). We first demonstrate the capability of the model to accurately simulate and reproduce the seeding experiments across different environmental conditions. Second, we investigate the WBF process in the model by comparing the simulated cloud droplet and ice crystal number concentration changes to in situ measurements. In the field experiments, simultaneous reductions in cloud droplet number concentrations with increased ice crystal number concentrations were observed, with periods showing a full depletion of cloud droplets. The model can reproduce the observed ice crystal number concentrations most of the time; however, it cannot reproduce the observed fast reductions in cloud droplet number concentrations. Our detailed analysis shows that the WBF process appears to be less efficient in the model than in the field. In the model, exaggerated ice crystal number concentrations are required to produce comparable changes in cloud droplet number concentrations, highlighting the inefficiency of the WBF process in the numerical weather model ICON. [ABSTRACT FROM AUTHOR]

[Display omitted] Aerosols greatly influence precipitation characteristics, thereby impacting the regional climate and human life. As an indispensable factor for cloud formation and a critical radiation budget regulator, aerosols can affect precipitation intensity, frequency, geographical distribution, area, and time. However, discrepancies exist among current studies due to aerosol properties, precipitation types, the vertical location of aerosols and meteorological conditions. The development of technology has driven advances in current research, but understanding the aerosol effects on precipitation remain complex and challenging. This paper revolves around the following topics from the two perspectives of Aerosol-Radiation Interaction (ARI) and Aerosol-Cloud Interaction (ACI): (1) the influence of different vertical locations of absorbing/scattering aerosols on the atmospheric thermal structure; (2) the fundamental theories of ARI reducing surface wind speed, redistributing water vapour and energy, and then modulating precipitation intensity; (3) different aerosol types (absorbing versus scattering) and aerosol concentrations causing different precipitation diurnal and weekly variations; (4) microphysical processes (cloud water competition, invigoration effect, and evaporation cooling) and observational evidence of different effects of aerosols on precipitation intensity, including enhancing, inhibiting, and transitional effects from enhancement to suppression; and (5) how meteorology, water vapor and dynamics influencing the effect of ACI and ARI on precipitation. In addition, this review lists the existing issues and future research directions for attaining a more comprehensive understanding of aerosol effects on precipitation. Overall, this review advances our understanding of aerosol effects on precipitation and could guide the improvement of weather and climate models to predict complex aerosol-precipitation interactions more accurately. [ABSTRACT FROM AUTHOR]

Previous modeling studies indicate that even though marine cloud brightening under a susceptibility‐based strategy is effective in reducing the global average surface temperature, it triggers a La Niña‐like sea‐surface temperature response with cooling mostly confined within lower latitudes. Here we explore a different cloud seeding strategy involving seeding of regions with low susceptibility, primarily over the ocean in midlatitudes during the winter. Simulations with the Community Earth System Model, version 2 reveal that because the regional forcing is weaker and more widespread, cooling is more evenly distributed over the globe. This new strategy also does not result in the La Niña‐like state seen in the other strategies. Plain Language Summary: Most previous marine cloud brightening (MCB) simulations have focused on the regions more likely to induce strong cooling. A common response in these simulations across different climate models is a La Niña‐like sea surface temperature pattern which could disrupt the El Niño Southern Oscillation. We explored simulations in which MCB is deployed over the least susceptible regions rather than the most susceptible. This new seeding strategy cools the globe more evenly and no longer triggers a La Niña‐like response. Key Points: We explore the idea of deploying marine cloud brightening (MCB) over broader regions with low susceptibility to cloud seedingThis approach induces fairly uniform cooling over the globe unlike MCB that targets the most susceptible regionsThis new seeding strategy has fewer climatic side effects and does not trigger a La Niña‐like response [ABSTRACT FROM AUTHOR]

Current weather modification rockets with a single operation mode, limited operating height, and fixed and uncontrollable operating time, cannot achieve seeding in different layers, stages and quantities for different cloud systems. Therefore, a temporally controllable weather modification rocket with spatial seeding capability is developed in this study. This new rocket features an electronic fuse-controlled intelligent ignition system, with eight channels of ignition tube outputs. Additionally, carrier wave communication technology is incorporated to set the seeding time for eight sets of ignition tubes. The temporally controllable rocket is capable of initiating seeding within 2 s to 26 s and can conduct operations for layering, arbitrary altitude and fractional-dose seeding within the altitude range of 500–5500 m (at a launch angle of 70°). The minimum time interval of the rocket for seeding can be set to 0.1 s, and all 48 catalyst bullets loaded in a single rocket can be launched within 0.8 s. Thus, the rocket can achieve both concentrated and continuous seeding. Consequently, during weather modification operations, parameters such as altitude, thickness and operating temperature of target clouds can be obtained through detection, and they can be used to automatically calculate the suitable seeding time, seeding altitude and seeding dose in order to improve the accuracy and scientificity of cloud catalytic operations. Ground tests show that the reliabilities of the electric ignition tube output, new electronic fuse input and output, and electronic fuse output energy all meet the design requirements. The temporally controllable spatial-seeding rocket can achieve adjustable and controllable seeding times for catalytic bullets, meeting the safety and reliability requirements of rockets. [ABSTRACT FROM AUTHOR]

The seeding effect of upper clouds on lower clouds affects the evolution of clouds, especially the seeding from upper ice clouds on lower stratiform clouds or convective clouds, which can stimulate the precipitation of lower clouds and even produce extreme precipitation. When seeders of the seeding cloud enter the feeding cloud, the interaction between cloud particles results in the change in macro- and micro-parameters of the feeding cloud. Based on the observation data of a ground-based Ka-band millimeter-wave cloud radar (MMCR) and microwave radiometer (MWR) in spring and autumn from 2021 to 2022, the seeder–feeder phenomenon among double-layer clouds in Xi'an, China, is studied. The study on 11 cases of seeder–feeder processes shows that the processes can be divided into three types by defining the height difference (HD) between the seeding cloud base and the feeding cloud top and the effective seeding depth (ESD). Through analysis of the reflectivity factor (Z) and the radial velocity (Vr) of cloud particles detected by the MMCR and on the retrieved cloud dynamics parameters (vertical velocity of airflow, Va , and terminal velocity of cloud particles, Vf), it is shown that the reflectivity factor and particle terminal velocity in the cloud are significantly enhanced during the seeder–feeder period for the three types of processes. But the enhancement magnitudes of the three seeder–feeder processes are different. The results also show that the impact of seeding on the feeding cloud is limited. The lower the height and thinner the thickness of the HD, the lower the height and thicker the thickness of the ESD. On the contrary, the higher the height and the thicker the thickness of the HD, the higher the height and the thinner the thickness of the ESD. [ABSTRACT FROM AUTHOR]

The transport and dispersion (T&D) of catalyst particles seeded by weather modification aircraft is crucial for assessing their weather modification effects. This study investigates the capabilities of the Chinese geostationary weather satellite FY-4A for identifying the physical response of cloud seeding with AgI-based catalysts and continuously monitoring its evolution for a weather event that occurred on 15 December 2019 in Henan Province, China. Satellite measurements are also used to verify an operational catalyst T&D algorithm. The results show that FY-4A exhibits a remarkable capability of identifying the cloud-seeding tracks and continuously tracing their evolution for a period of over 3 h. About 60 min after the cloud seeding, the cloud crystallization track became clear in the FY-4A tri-channel composite cloud image and lasted for about 218 min. During this time period, the cloud track moved with the cloud system about 153 km downstream (northeast of the operation area). An operational catalyst T&D model was run to simulate the cloud track, and the outputs were extensively compared with the satellite observations. It was found that the forecast cloud track closely agreed with the satellite observations in terms of the track widths, morphology, and movement. Finally, the FY-4A measurements show that there were significant differences in the microphysical properties across the cloud track. The effective cloud radius inside the cloud track was up to 15 μm larger than that of the surrounding clouds; the cloud optical thickness was about 30 μm smaller; and the cloud-top heights inside the cloud track were up to 1 km lower. These features indicate that the cloud-seeding catalysts led to the development of ice-phase processes within the supercooled cloud, with the formation of large ice particles and some precipitation sedimentation. [ABSTRACT FROM AUTHOR]

Background (BG) aerosol particles (APs) acting as cloud condensation nuclei (CCN) and/or ice nucleating particles (INPs) influence short-range precipitation forecasts and climate change projections by modulating cloud and precipitation microphysical structures and influence the effects of cloud seeding on precipitation enhancement. However, data on the CCN and INP capabilities of BG APs are limited in terms of geographical locations and time. To investigate the characteristics of BG APs, we conducted ground-based measurements of BG AP and CCN in Kochi City, Japan, in June 2010. Comparisons with previously published data on AP and CCN concentrations in East Asia showed that the mean concentrations of APs and CCN at the observation site were considerably affected by air pollution. Our findings also suggest that during the observation period, even air masses from the Pacific Ocean were considerably affected by air pollution in East Asia, including Japan. Moreover, aircraft-measured AP and CCN concentrations in the boundary layer were comparable to those measured concurrently at the surface observation site, although the horizontal positions of the ground- and aircraft-based measurements were not identical; the size distributions of the APs were similar. These results suggest that ground-based measurements represent APs and CCN in the boundary layer, where the air is ingested by clouds. Numerical simulations with a detailed bin microphysics parcel model showed that cloud droplet number concentrations, based on meteorological conditions and aerosol characteristics expected near the observation site environments, would range from 500 droplets cm-3 to 1,500 droplets cm-3. These concentrations were consistent with aircraft measurements. These values are higher than the threshold concentration of ~ 500 droplets cm-3 in clouds suitable for hygroscopic seeding, as suggested by previous studies. Therefore, this area is considered to be suitable for rain enhancement by hygroscopic seeding. [ABSTRACT FROM AUTHOR]

As an essential moisture transport channel over the Tibetan Plateau (TP), accurate simulation of precipitation over the southeastern TP (SETP) is crucial for downstream moisture transport and water resource assessment. To improve SETP's precipitation simulation accuracy, a Turbulent Orographic Form Drag (TOFD) scheme, which represents the TOFD effect of subgrid orography on model grids, is employed. The impact of TOFD on cloud and precipitation during the summer monsoon over the SETP is investigated from dynamical and cloud microphysical perspectives. Through comparison with ground observations and satellite precipitation data, TOFD reduces the simulated precipitation bias. Despite reducing moisture transport, TOFD enhances low-level convergence and high-level divergence by influencing the low-level wind, thereby strengthening updraft and cloud and precipitation processes before the slope of SETP. TOFD also increases total precipitation before the slope by promoting heavy precipitation and reducing weak precipitation. However, TOFD diminishes the updraft and cloud and precipitation processes over the slope of SETP by influencing low-level wind. The reduced moisture transport by TOFD leads to decreased precipitation over the slope. Additionally, TOFD reduces total precipitation over the slope by promoting weak precipitation and reducing heavy precipitation. Furthermore, the impact mechanism of TOFD on precipitation depends on the wind speed, which is weakened during weak precipitation period with reduced wind speed and enhanced during heavy precipitation period with increased wind speed. These findings enhance the understanding of the complex terrain's influence on cloud and precipitation and provide a basis for improving cloud and precipitation simulation over the SETP. [ABSTRACT FROM AUTHOR]

Cloud seeding is considered a practical but unproved method to enhance precipitation or suppress hail, due to insufficient knowledge of ice formation and evolution after seeding clouds with ice nucleating particles. This study investigates the size effects on the immersion freezing of aerosol produced from commercial silver iodide (AgI) containing flares at mixed‐phase cloud temperatures from 243 to 267 K. Flare‐generated aerosol exhibited comparable ice nucleation ability (INA) to pure AgI particles in the size range of 200 and 400 nm. Non‐AgI impurities reduced the INA of flare‐generated particles ≤90 nm, which is lower than pure AgI particles ≤40 nm. The critical mass ice‐active site density of the generated aerosols (critical‐nm) was derived, indicating the minimum mass of AgI particles required for efficient ice nucleation. The new parameterization to predict critical‐nm can serve as a reference to optimize the effectiveness of cloud‐seeding materials for practical use. Plain Language Summary: Ice‐forming aerosol is commonly added to clouds, expecting precipitation enhancement via promotion of ice production. In this work, silver iodide (AgI) containing aerosol was generated from commercial cloud‐seeding products under different wind speed conditions. Its ice‐forming ability was studied at mixed‐phase cloud temperatures. The lower size limit for effective ice‐forming ability of the cloud‐seeding particles (90 nm) is higher than that of pure AgI particles (40 nm). The non‐AgI components produced by cloud‐seeding products are hypothesized to decrease the ice‐forming ability of smaller particles, as the mass fraction of ice‐nucleating AgI decreases. To estimate the minimum mass of AgI in a particle required for efficient ice nucleation under cloud‐seeding relevant conditions, we derived the critical ice‐activated mass fraction of the generated aerosols. These findings provide valuable insights into the optimization of cloud‐seeding practices for enhanced precipitation. Key Points: Silver iodide (AgI) containing cloud‐seeding aerosols exhibit comparable ice‐forming abilities to pure AgI at sizes of 200 and 400 nmNon‐AgI impurities produced from flare burning decrease the ice nucleation ability of particles smaller than 90 nmA new parameterization is presented to estimate the minimum mass of AgI particles required to maximize glaciogenic seeding [ABSTRACT FROM AUTHOR]

Cloud seeding experiments for modifying clouds and precipitation have been underway for nearly a century; yet practically all the attempts to link precipitation enhancement or suppression to the presence of seeding materials within clouds remain elusive. In 2019, the Cloud–Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) investigated residuals of cloud hydrometeors in seeded and non-seeded clouds with an airborne mini aerosol mass spectrometer (mAMS). The mAMS was utilized in conjunction with a counterflow virtual impactor (CVI) inlet with a cutoff diameter size of approximately 7 µ m. The evaporated cloud droplets from the CVI inlet as cloud residuals were evaluated through the mAMS. The chlorine (Cl) associated with hygroscopic materials, i.e. calcium chloride (CaCl 2) and potassium (K), which serve as the oxidizing agents in the flares, is found in relatively higher concentrations in the seeded clouds compared to the non-seeded clouds. In convective clouds, Cl and K as cloud residuals were found even at a vertical distance of 2.25 km from the cloud base. Major findings from the seeding impact are an increase in the number concentration of small (< 20 µ m) droplets and an indication of raindrop formation at 2.25 km above the cloud base. It is demonstrated that the seed particle signature can be traced inside clouds along with the microphysical impacts. [ABSTRACT FROM AUTHOR]

Spread F (SF) in the ionosphere can be observed frequently in mid-latitude regions. It is suggested that atmospheric gravity waves play a significant role for the seeding of mid-latitude SF. Previous research suggested that the source of travelling ionospheric disturbances (TIDs) over China is in the southeastern and northeastern edge of the Qinghai-Tibet Plateau, however, until now there have been no ground-based observations of the ionosphere in this region. Recently, an advanced digital ionosonde was installed at Zhangye station (39.2°N, 100.54°E, Dip Lat 29.6°N) in the northeastern edge of the Qinghai-Tibet Plateau. It is an opportunity to verify the effect of gravity waves on the formation of mid-latitude SF by comparing it with observations in other regions of the Chinese sector. In this study, statistical analysis of SF recorded at Zhangye station during 2017–2022 was carried out. Results show that diurnal, seasonal and solar cycle characteristics of the occurrence rate of SF are similar with previous studies. At Zhangye station, the maximum occurrence rate of SF is during the post-midnight period in summer and winter. The occurrence rate of SF events have a negative relationship with solar activity. There is no obvious relationship between the occurrence rate of SF and geomagnetic activity. Comparing observations of other stations in the mid-latitude region, we found that the occurrence rates of SF (the annual maximum rates are from 33.83% to 53.29%) are much higher at Zhangye station. Further studies show that ionospheric disturbances can be observed frequently at Zhangye station, especially in autumn and winter. Gravity waves/TIDs in the northeast of the Qinghai-Tibet Plateau are suggested to explain the abnormal higher occurrence rate of SF at Zhangye station. [ABSTRACT FROM AUTHOR]

Ritual protocols aimed at rainmaking have been a recurrent sociocultural phenomenon across societies and throughout history. Given the fact that such protocols were likely entirely ineffective, why did they repeatedly emerge and persist, sometimes over millennia, even in populations with writing and recordkeeping? To address this puzzle, many scholars have argued that these protocols were not instrumental at all and that their practitioners were not really endeavoring to employ them to bring about rain. Here, taking advantage of the wealth of historical records available in China, we argue to the contrary: that rainmaking is best viewed as an instrumental, means-end activity and that people have always placed strong emphasis on the outcomes of such activities. To account for the persistence of rainmaking, we then present a set of cultural evolutionary explanations rooted in human psychology that can explain why people's adaptive learning processes did not result in the elimination of ineffective rainmaking methods. We suggest that a commitment to a supernatural worldview provides theoretical support for the plausibility of various rainmaking methods and that people often overestimate the efficacy of rainmaking technologies because of statistical artifacts (some methods appear effective simply by chance) and underreporting of disconfirmatory evidence (failures of rainmaking not reported or transmitted). The inclination to "do something" when a drought hits versus "do nothing" likely also plays a role and persists in the world today. [ABSTRACT FROM AUTHOR]

The complex and diverse cloud vertical distribution (CVD) largely impacts radiative and precipitation properties of clouds. Using 10‐year active satellite observations, we classified CVD over the Tibetan Plateau into 12 categories and found that overlapping clouds have less frequency but stronger radiative effect, heating rate and larger precipitation (partly reflecting the seeding effect) compared with single‐layer non‐strong convective clouds. Under a warming climate due to uniform sea surface temperature increase of 4K (quadrupling CO2 increase), extremely high (>10 km) ice clouds will increase, particularly those below the tropopause will increase slightly (largely), accompanied by clear (weak) increases in stratospheric clouds. Simultaneously, a moderate to rapid decrease will occur in clouds below 10 km. Such CVD changes could further exacerbate tropopause warming. The probability of cloud overlap is also likely to increase in warmer climates, thus possibly further causing non‐convective cloud systems with stronger intra‐atmospheric heating, larger precipitation intensity and proportion. Plain Language Summary: The diverse vertical morphologies of clouds (cloud vertical distribution, CVD) cause great challenges in accurately simulating radiative and precipitation properties, influencing regional radiation budget. As a robust signature of climate change, CVD significantly impacts cloud feedback and will change dramatically with warming. Therefore, knowledge about the CVD and its potential change are essential, especially on the Tibetan Plateau (TP, with high climate sensitivity). Using 10‐year active satellite observations, we classified clouds into 12 classes and found multi‐layer (overlapping) clouds are less frequent but with stronger radiative effect, atmospheric heating and larger precipitation intensity (proportion) than single‐layer clouds excluding convective clouds. Under a warming climate due to uniform sea surface temperature increase of 4K (quadrupling CO2 increase), clouds (especially ice‐cloud) above 10 km will increase, and those below the tropopause increase slightly (largely) accompanied by clear (weak) increases in the stratospheric clouds. Simultaneously, clouds below 10 km will experience a moderate to rapid decrease. Such CVD changes could exacerbate tropopause warming. In addition, the probability of cloud overlap in warmer climates is also likely to increase due to stronger convective available potential energy, possibly resulting in stronger atmospheric heating and larger precipitation intensity and proportion for non‐convective cloud systems. Key Points: Multi‐layer clouds are less frequent on the Tibetan Plateau but with stronger radiation effect and precipitation intensity than single‐layer cloudsIncrease/decrease in clouds above/below tropopause might be tied to a possible convective available potential energy (CAPE)‐induced switch from general to intense convectionThe enhanced CAPE‐induced deep convection may increase the likelihood of cloud overlap, further enhancing intra‐atmospheric heating [ABSTRACT FROM AUTHOR]

Drawing on five years of intermittent ethnographic work at Kariba, I discuss the impoverishment of the Tonga of Mola chiefdom in the context of escalating human–wildlife conflict and frequent drought. I critically examine emerging competing forms of knowledge regarding traditional authority and environmental challenges between the chief and his subjects. I argue that persistent environmental crisis in the region is generating different conflictual forms of knowledge regarding traditional authority. In advancing this argument, I draw extensively upon the broader literature on power, authority and legitimacy. Local people firmly believe that these problems are induced by the current chief's avoidance and reluctance to enact rainmaking ceremonies and to appease ancestors. I document people's opinions about the current chief's 'rebellious' behaviour and how they believe it exacerbates their impoverishment and suffering through drought and attacks by animals. I demonstrate why and how the chief's behaviour contributes to the waning of his authority. The chief offers counter-narratives but, interestingly, both the chief's and the people's narratives relate to their relationship with the spirits and ancestors. By documenting these spiritual and religious narratives of human–wildlife conflicts and droughts, I extend the debates on power, knowledge and authority in southern Africa. [ABSTRACT FROM AUTHOR]

Direct seeding is one of the most feasible techniques in practical, logistical, and economic terms for large‐scale restoration of arid lands. However, several factors are still under study to enhance the outcomes of this restoration alternative, with species selection being a pivotal component. To evaluate differences in the performance of species in direct seeding, we selected five shrubs from the arid region known as "Monte Desert" in Argentina: Atriplex lampa, Hyalis argentea, Larrea divaricata, Neltuma flexuosa var. depressa, and Parkinsonia praecox. Direct seeding was carried out in furrows (4.0 m long, 0.5 m wide, and 0.4 m deep) with seeds previously treated to dormancy alleviation and with a density of 250 seeds/m2. We evaluated results in 12 furrows, where topsoil and hydrogel were deposited. The biological variables considered were seedling emergence, seedlings establishment regarding sowed seeds, and seedling success (survival in relation to emerged seedlings) after almost 3 years. The species with the highest emergence and establishment rates was A. lampa (50.16 and 23.75%, respectively). L. divaricata showed the lowest values for these variables (2.17 and 0.83%, respectively). On the other hand, the survival of N. flexuosa seedlings was >2× that of L. divaricata (65.02 vs. 30.36%). We discuss the notable differences in species performance and the possible role of furrows in the results. [ABSTRACT FROM AUTHOR]

Coating seeds with amendments to increase germination, emergence, and establishment is a promising strategy for dryland restoration. Seed coatings containing fungicides offer a potential solution in regions where fungal pathogens cause seed mortality during the winter stratification period between late fall seeding and spring germination. The effectiveness of the fungicide treatment, however, may be dictated by weather and within‐site microenvironment. We tested how fungicide coating influenced seedling emergence of native grasses within sagebrush stands by planting untreated seeds and seeds coated (encrusted) with and without active fungicide ingredients in furrows that extended from the canopy edge of sagebrush plants (Artemisia tridentata ssp. wyomingensis) into the interspace. This was replicated at four sites across the Intermountain West in two successive years. We planted two native grasses, bottlebrush squirreltail (Elymus elymoides) and bluebunch wheatgrass (Pseudoroegneria spicata). Emergence was extremely low in both years, with a complete seeding failure (i.e. zero emergence) at two sites in the first year and three sites in the second year. At one site where emergence was sufficient for statistical analysis: (1) the coating on the fungicide and blank treatments inhibited emergence under anomalously dry conditions and (2) across seed treatments, proximity to a sagebrush canopy slightly increased seedling emergence. The variable emergence patterns across sites and years (i.e. the highest emergence was for the site–year combination with the lowest precipitation) highlight the sensitivity of seeding outcomes to, and dependence of fungicide seed coatings on, site conditions, and the necessity of repeating experiments across different weather years. [ABSTRACT FROM AUTHOR]

Uncrewed aerial vehicles (UAVs) have become widely used in a range of atmospheric science research applications. Because of their small size, flexible range of motion, adaptability, and low cost, multirotor UAVs are especially well-suited for probing the lower atmosphere. However, their use so far has been limited to conditions outside of clouds, first because of the difficulty of flying beyond visual line of sight and second because of the challenge of flying in icing conditions in supercooled clouds. Here, we present two UAVs for cloud microphysical research: one UAV (the measurement UAV) equipped with a Portable Optical Particle Spectrometer (POPS) and meteorological sensors to probe the aerosol and meteorological properties in the boundary layer and one UAV (the seeding UAV) equipped with seeding flares to produce a plume of particles that can nucleate ice in supercooled clouds. A propeller heating mechanism on both UAVs allows for operating in supercooled clouds with icing conditions. These UAVs are an integral part of the CLOUDLAB project in which glaciogenic cloud seeding of supercooled low stratus clouds is utilized for studying aerosol–cloud interactions and ice crystal formation and growth. In this paper, we first show validations of the POPS on board the measurement UAV, demonstrating that the rotor turbulence has a small effect on measured particle number concentrations. We then exemplify the applicability for profiling the planetary boundary layer, as well as for sampling and characterizing aerosol plumes, in this case, the seeding plume. We also present a new method for filtering out high-concentration data to ensure good data quality of POPS. We explain the different flight patterns that are possible for both UAVs, namely horizontal or vertical leg patterns or hovering, with an extensive and flexible parameter space for designing the flight patterns according to our scientific goals. Finally, we show two examples of seeding experiments: first characterizing an out-of-cloud seeding plume with the measurement UAV flying horizontal transects through the plume and, second, characterizing an in-cloud seeding plume with downstream measurements from a POPS and a holographic imager mounted on a tethered balloon. Particle number concentrations and particle number size distributions of the seeding plume from the experiments reveal that we can successfully produce and measure the seeding plume, both in-cloud (with accompanying elevated ice crystal number concentrations) and out-of-cloud. The methods presented here will be useful for probing the lower atmosphere, for characterizing aerosol plumes, and for deepening our cloud microphysical understanding through cloud seeding experiments, all of which have the potential to benefit the atmospheric science community. [ABSTRACT FROM AUTHOR]

Three cases of microphysical characteristics and kinematic structures in the negative temperature region of summer mesoscale cloud systems over the eastern Tibetan Plateau (TP) were investigated using X-band dual-polarization radar. The time-height series of radar physical variables and mesoscale horizontal divergence δ ¯ derived by quasi-vertical profiles (QVPs) indicated that the dendritic growth layer (DGL, −20°C to −10°C) was ubiquitous, with large-value zones of KDP (specific differential phase), ZDR (differential reflectivity), or both, and corresponded to various dynamic fields (ascent or descent). Ascents in the DGL of cloud systems with vigorous vertical development were coincident with large-value zones of ZDR, signifying ice crystals with a large axis ratio, but with no obvious large values of KDP, which differs from previous findings. It is speculated that ascent in the DGL promoted ice crystals to undergo further growth before sinking. If there was descent in the DGL, a high echo top corresponded to large values of KDP, denoting a large number concentration of ice crystals; but with the echo top descending, small values of KDP formed. This is similar to previous results and reveals that a high echo top is conducive to the generation of ice crystals. When ice particles fall to low levels (−10°C to 0°C), they grow through riming, aggregation, or deposition, and may not be related to the kinematic structure. It is important to note that this study was only based on a limited number of cases and that further research is therefore needed. [ABSTRACT FROM AUTHOR]

Recent studies from the Seeded and Natural Orographic Wintertime Clouds: The Idaho Experiment (SNOWIE) demonstrated definitive radar evidence of seeding signatures in winter orographic clouds during three intensive operation periods (IOPs) where the background signal from natural precipitation was weak and a radar signal attributable to seeding could be identified as traceable seeding lines. Except for the three IOPs where seeding was detected, background natural snowfall was present during seeding operations and no clear seeding signatures were detected. This paper provides a quantitative analysis to assess if orographic cloud seeding effects are detectable using radar when background precipitation is present. We show that a 5-dB change in equivalent reflectivity factor Ze is required to stand out against background natural Ze variability. This analysis considers four radar wavelengths, a range of background ice water contents (IWC) from 0.012 to 1.214 g m−3, and additional IWC introduced by seeding ranging from 0.012 to 0.486 g m−3. The upper-limit values of seeded IWC are based on measurements of IWC from the Nevzorov probe employed on the University of Wyoming King Air aircraft during SNOWIE. This analysis implies that seeding effects will be undetectable using radar within background snowfall unless the background IWC is small, and the seeding effects are large. It therefore remains uncertain whether seeding had no effect on cloud microstructure, and therefore produced no signature on radar, or whether seeding did have an effect, but that effect was undetectable against the background reflectivity associated with naturally produced precipitation. Significance Statement: Operational glaciogenic seeding programs targeting wintertime orographic clouds are funded by a range of stakeholders to increase snowpack. Glaciogenic seeding signatures have been observed by radar when natural background snowfall is weak but never when heavy background precipitation was present. This analysis quantitatively shows that seeding effects will be undetectable using radar reflectivity under conditions of background snowfall unless the background snowfall is weak, and the seeding effects are large. It therefore remains uncertain whether seeding had no effect on cloud microstructure, and therefore produced no signature on radar, or whether seeding did have an effect, but that effect was undetectable against the background reflectivity associated with naturally produced precipitation. Alternative assessment methods such as trace element analysis in snow, aircraft measurements, precipitation measurements, and modeling should be used to determine the efficacy of orographic cloud seeding when heavy background precipitation is present. [ABSTRACT FROM AUTHOR]

Precipitation efficiency refers to the amount of water that is lost from the atmosphere through precipitation compared to the available water vapor in the atmosphere. This metric plays a critical role in understanding precipitation patterns. However, calculating precipitation efficiency for extratropical cyclones can be challenging because cyclones are dynamic and move through the atmosphere as they evolve. To overcome this challenge, our study uses ERA5 reanalysis data to estimate precipitation efficiencies for 400 Southern Ocean cyclones, with a frame of reference that moves with the individual cyclones. Our findings indicate that at maximum intensity, average precipitation efficiencies reach a maximum of 60%/6 hr near the warm front where ascent rates are the largest. Typically, within 24–36 hr after cyclogenesis, all of the initial water vapor available within 500 km of a cyclone center is lost due to precipitation. However, a cyclone's precipitating phase is prolonged due to local evaporation and moisture flux convergence (MFC), which replenish the moisture lost via precipitation. Close to the cyclone center, MFC provides additional moisture from the environment into which cyclones are traveling. On average, this extends a cyclone's precipitation phase to over 60 hr after cyclogenesis. Thus, while moisture from the genesis location is quickly removed from the cyclone via precipitation, cyclones are replenished by moisture along their track, which doubles the timescale for a cyclone's precipitating phase. Plain Language Summary: Precipitation efficiency is a measure of how much water in the atmosphere falls as rain compared to how much is available to fall. In this study, we estimate how efficient precipitation is for 400 cyclones in the Southern Ocean. We find that when the cyclones are strongest, about 60% of the available water vapor turns into rain every 6 hr near the warm front of the cyclone where air is rising rapidly. Normally, within a day or two of a cyclone forming, all of the available water vapor in the cyclone gets turned into rain. However, the rain can persist for longer because cyclones pick up more moisture as they move, which gets turned into more rain. This can make the rain from a cyclone last on average for 60 hr, even after the initial moisture is all gone. Key Points: The initial moisture content of extratropical cyclones is removed via precipitation within 30 hr after cyclogenesisLocal evaporation and moisture flux convergence doubles the precipitating phase of extratropical cyclonesThe feeder airstream provides a continuous supply of moisture to cyclones in the developing stage of their evolution [ABSTRACT FROM AUTHOR]

Results of Russian studies on cloud physics, precipitation, and weather modification in 2019–2022 are presented based on a survey prepared for the Russian National Report on Meteorology and Atmospheric Sciences to the 28th General Assembly of the International Union of Geodesy and Geophysics. Results concerning general issues of the observation and modeling of clouds and precipitation, including convective clouds; issues of studying the microphysical and optical characteristics of clouds; and the weather modification are discussed. [ABSTRACT FROM AUTHOR]

Artificial rain, a technology primarily used for drought relief, has recently been used for combating regional air pollution. However, there are limited available measurement data to confirm the effectiveness of this control practice. In this study, we summarize control theories and indirect but relevant observations/findings, including air pollutant reduction after natural rain events and roadside sprinkling. A brief review of artificial rain basics is also provided. Our work shows that artificial rain appears to be a promising management strategy for air pollution control. However, field measurements are needed to further assess the cost-effectiveness of the practice, as well as the other benefits or challenges it may create. [ABSTRACT FROM AUTHOR]

Cycads play a central role in Lobedu cultural mythology, with widespread acknowledgment of their cultural and spiritual values, as well as their instrumental use in rainmaking and coronation ceremonies. They are also widely prized as collectors' items, both nationally and internationally, commanding high prices and placing them in the unenviable position of being among the world's most frequently trafficked plants. South African cycad species, most of which are endangered and all of which are protected, are heavily regulated, with the ownership, trade, and use of cycads requiring a permit. This article explores how regulations are understood by different stakeholders in cycad conservation. Traditional authorities, state institutions, and communities may collaborate in conservation, but also interpret and enact policies divergently. Processes of regulating cycad trade and propagation both reinforce and challenge certain aspects of community identity. [ABSTRACT FROM AUTHOR]

The seeding effect of upper clouds on lower clouds affects the evolution of clouds, especially the seeding from upper ice clouds on lower stratiform clouds or convective clouds, which can stimulate the precipitation of lower clouds and even produce extreme precipitation. Because when seeders of seeding cloud enter the feeding cloud, the interaction between cloud particles results in the change of macro and micro parameters of the feeding cloud. Based on the observation data of the ground-based Ka-band millimeter-wave cloud radar (MMCR) and microwave radiometer (MWR) in spring and autumn from 2020 to 2022, the seeder-feeder phenomenon among double-layer clouds in China Xi'an was studied. The study on 11cases of seeder-feeder processes shows that the processes can be divided into three categories by defining the height difference (HD) between the seeding cloud base and the feeding cloud top, and the effective seeding depth (ESD). Through the analysis on the reflectivity factor and the radial velocity of cloud particles detected by MMCR and on the retrieved cloud dynamics parameters (vertical velocity of airflow and falling velocity of cloud particles), it is shown that the reflectivity factor in the cloud are significantly enhanced during the seeder-feeder period for the three types of processes. But there are different enhancements among the reflectivity factor profiles for the three seeder-feeder processes. The results also showed the limited depth as seeders entering the top of the feeding cloud. The lower and thinner the HD height was, the lower and thicker the ESD height was. On the contrary, the higher the HD height, the higher and thinner the ESD height. [ABSTRACT FROM AUTHOR]

SIGNIFICANCE STATEMENT: A novel experimental approach to conduct laboratory-type experiments in natural clouds is introduced within the CLOUDLAB project: a unique combination of uncrewed aerial vehicles (UAVs) and state-of-the-art instrumentation is used to perform targeted cloud seeding experiments in persistent supercooled stratus clouds. The results will enhance the process understanding of mixed-phase clouds and improve the ice-phase parameterizations in weather and climate models, ultimately leading to more reliable precipitation forecasts and climate projections. In addition, the gained knowledge will be important to quantify the consequences of artificial weather modification and climate interventions. Ice formation and growth processes play a crucial role in the evolution of cloud systems and the formation of precipitation. However, the initial formation and growth of ice crystals are challenging to study in the real atmosphere resulting in uncertainties in weather forecasts and climate projections. The CLOUDLAB project tackles this problem by using supercooled stratus clouds as a natural laboratory for targeted glaciogenic cloud seeding to advance the understanding of ice processes: Ice nucleating particles are injected from an uncrewed aerial vehicle (UAV) into supercooled stratus clouds to induce ice crystal formation and subsequent growth processes. Microphysical changes induced by seeding are measured 3–15 min downstream of the seeding location using in situ and ground-based remote sensing instrumentation. The novel application of seeding with a multirotor UAV combined with the persistent nature of stratus clouds enables repeated seeding experiments under similar and well-constrained initial conditions. This article describes the scientific goals, experimental design, and first results of CLOUDLAB. First, the seeding plume is characterized by using measurements of a UAV equipped with an optical particle counter. Second, the seeding-induced microphysical changes observed by cloud radars and a tethered balloon system are presented. The seeding signatures were detected by regions of increased radar reflectivity (>−20 dBZ), which were 10–20 dBZ higher than the natural background. Simultaneously, high concentrations of seeding particles and ice crystals (up to 2,000 L−1) were observed. A cloud seeding case was simulated with the numerical weather model ICON to contextualize the findings. [ABSTRACT FROM AUTHOR]

The demand for effective methods to augment precipitation over arid regions of India has been increasing over the past several decades as the changing climate brings warmer average temperatures. In the fourth phase of the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX IV), a scientific investigation was conducted over a rain-shadow region of the Western Ghats mountains in India. The primary objective was to investigate the efficacy of hygroscopic seeding in convective clouds and to develop a cloud seeding protocol. CAIPEEX IV followed the World Meteorological Organization (WMO) recommendations in a peer-reviewed report with physical, statistical, and numerical investigations. The initial results of the campaign in the monsoon period of 2018 and 2019 with two instrumented aircraft, a ground-based dual-polarization C-band radar, a network of rain gauges, radiosondes, and surface aerosol measurements are reported here. The hygroscopic seeding material was detected in cloud droplets and key cloud microphysical processes in the seeding hypothesis were tracked. The formidable challenges of assessing seeding impacts in convective clouds and the results from 150 seed and 122 no-seed samples of randomized experiments are illustrated. Over 5,000 cloud passes from the airborne campaign provided details about the convective cloud properties as the key indicators for a seeding strategy and the evaluation protocol. The experimental results suggest that cloud seeding can be approached scientifically to reduce uncertainty. The results from this study should interest the scientific community and policymakers concerned with climate change's impact on precipitation and how to mitigate rainfall deficiencies. [ABSTRACT FROM AUTHOR]

This study presents the first numerical simulations of seeded clouds over the Snowy Mountains of Australia. WRF-WxMod, a novel glaciogenic cloud-seeding model, was utilized to simulate the cloud response to winter orographic seeding under various meteorological conditions. Three cases during the 2018 seeding periods were selected for model evaluation, coinciding with an intensive ground-based measurement campaign. The campaign data were used for model validation and evaluation. Comparisons between simulations and observations demonstrate that the model realistically represents cloud structures, liquid water path, and precipitation. Sensitivity tests were performed to pinpoint key uncertainties in simulating natural and seeded clouds and precipitation processes. They also shed light on the complex interplay between various physical parameters/processes and their interaction with large-scale meteorology. Our study found that in unseeded scenarios, the warm and cold biases in different initialization datasets can heavily influence the intensity and phase of natural precipitation. Secondary ice production via Hallett–Mossop processes exerts a secondary influence. On the other hand, the seeding impacts are primarily sensitive to aerosol conditions and the natural ice nucleation process. Both factors alter the supercooled liquid water availability and the precipitation phase, consequently impacting the silver iodide (AgI) nucleation rate. Furthermore, model sensitivities were inconsistent across cases, indicating that no single model configuration optimally represents all three cases. This highlights the necessity of employing an ensemble approach for a more comprehensive and accurate assessment of the seeding impact. Significance Statement: Winter orographic cloud seeding has been conducted for decades over the Snowy Mountains of Australia for securing water resources. However, this study is the first to perform cloud-seeding simulation for a robust, event-based seeding impact evaluation. A state-of-the-art cloud-seeding model (WRF-WxMod) was used to simulate the cloud seeding and quantified its impact on the region. The Southern Hemisphere, due to low aerosol emissions and highly pristine cloud conditions, has distinctly different cloud microphysical characteristics than the Northern Hemisphere, where WRF-WxMod has been successfully applied in a few regions over the United States. The results showed that WRF-WxMod could accurately capture the clouds and precipitation in both the natural and seeded conditions. [ABSTRACT FROM AUTHOR]

The North Pacific storm track (NPST) does not peak around midwinter when atmospheric baroclinicity is the strongest, which is known as midwinter suppression. The association of the year-to-year variation in the midwinter suppression of the low-level NPST with the East Asian trough (EAT) and North Pacific atmospheric blocking (PB) is investigated by using NCEP/NCAR reanalysis during 1948–2018. The results show that the year-to-year variation in the midwinter suppression of the NPST is significantly related to those of the EAT and PB. The midwinter suppression is striking when the midwinter EAT or PB strengthens. However, when the midwinter EAT weakens, the midwinter suppression of the NPST becomes inapparent or even disappears. While the seasonal cycle of the eastern NPST exhibits a single peak in January with a nonexistent midwinter suppression during the years with inhibited PB, the western NPST has a prominent midwinter suppression with the maximum amplitude occurring in March. The seasonal march of the Siberian storm track is not in agreement with that of the NPST when the midwinter EAT is weak, which suggests that upstream seeding may not be a dominant mechanism to understand midwinter suppression. The EAT and PB can not only individually but also jointly associate the midwinter suppression of the NPST. In addition, there is a significant in-phase relationship between the EAT and PB intensities. The EAT may affect the PB by modifying the meridional gradient of background potential vorticity. [ABSTRACT FROM AUTHOR]

We investigate whether and how spatial organization affects the pathway to precipitation in large‐domain hectometer simulations of the North Atlantic trades. We decompose the development of surface precipitation (P) in warm shallow trade cumulus into a formation phase, where cloud condensate is converted into rain, and a sedimentation phase, where rain falls toward the ground while some of it evaporates. With strengthened organization, rain forms in weaker updrafts from smaller cloud droplets so that cloud condensate is less efficiently converted into rain. At the same time, organization creates a locally moister environment and modulates the microphysical conversion processes that determine the raindrops' size. This reduces evaporation and more of the formed rain reaches the ground. Organization thus affects how the two phases contribute to P, but only weakly affects the total precipitation efficiency. We conclude that the pathway to precipitation differs with organization and suggest that organization buffers rain development. Plain Language Summary: Clouds in the trade‐wind region organize into a variety of spatial patterns. We investigate how this spatial organization influences rain development in simulations of trade‐wind convection. We divide the formation of surface precipitation into two phases. In the first phase, rain forms from the collision of cloud droplets or the collection of cloud droplets by raindrops. In the second phase, rain falls toward the ground while some of the rain evaporates. Our study shows that as organization strengthens, rain forms less efficiently, but a larger fraction of that rain reaches the ground as evaporation is reduced. Thus, organization in the simulations affects the way surface rain is generated. Our analyses suggest that it does so by modulating the cloud vertical motion in which rain forms, the local moisture environment through which rain falls and the microphysical conversion processes. Key Points: The development of surface precipitation in simulated trade‐wind convection is decomposed into a formation and sedimentation phaseAs organization strengthens, less cloud condensate is converted into rain, but more rain reaches the ground as evaporation is suppressedOrganization affects rain formation by modulating the local moisture environment, cloud vertical motion and microphysical properties [ABSTRACT FROM AUTHOR]

Rainfall enhancement has historically been overlooked as a key component of sustainability and climate change adaptation strategies. In this comment, we argue that rainfall enhancement is emerging as a viable contributor to addressing growing water security concerns in a warming climate. We specifically consider current progress and future directions for rainfall enhancement applications based on the experience of the United Arab Emirates (UAE) with its national decade-long operational cloud seeding program and its grant-based international research and development program. [ABSTRACT FROM AUTHOR]

Flow over orography can be investigated through stationary gravity waves, i.e. those whose speed exactly opposes, and therefore cancels, that of the airstream in which they are embedded. They give rise to persistent zones of ascent and descent, which modulate precipitation patterns and contribute to large accumulations, e.g. through the well-known seeder-feeder mechanism. It is shown here that opposite, stationary waves on the melting-level focus rain, potentially multiplying intensity downwind of hills by a factor of rain fall speed divided by snow fall speed, and that the effect is maximised when the vertical profile near the melting-level is isothermal. A 2D diagnostic model based on linear gravity wave theory is used to investigate the record-breaking rainfall of December 2015 in the Lake District of northwest England. The pattern of vertical velocity is shown to have a good, qualitative fit to that of the Met Office's operational, high-resolution UKV model averaged over 24 hours, suggesting that orographically excited standing waves were the principal cause of the rain. Precipitation trajectories suggest that a persistent, downstream, elevated wave caused by the Isle of Man maintained a spray of seeding ice particles directed towards the Lake District; that these grew whilst suspended in strong upslope flow before being focussed by the undulating melting-level into intense shafts of rain. [ABSTRACT FROM AUTHOR]

loud seeding experiments for modifying cloud and precipitation have been underway for nearly a century; yet practically all the attempts to link precipitation enhancement or suppression to the presence of seeding materials remained inclusive. In 2019, the Cloud-Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) implemented a novel method to detect seeded clouds during its operations in Solapur, India. In this experiment, residuals of cloud hydrometeors in seeded and non-seeded clouds were analyzed with an airborne mini-Aerosol Mass Spectrometer (mAMS). The mAMS instrument was utilized in conjunction with a counterflow virtual impactor (CVI) inlet, which had a cutoff diameter size of approximately 7 µm. Upon traversing the CVI inlet, the cloud droplets underwent a drying process, enabling the subsequent examination of cloud residuals through the mAMS instrument to identify potential seeding signatures. The Chlorine (Cl) associated with hygroscopic materials, i.e., Calcium Chloride (CaCl2) and potassium (K), which serve as the oxidizing agents in the flares, is found in relatively higher concentrations in the seeded clouds compared to the non-seeded clouds. After seeding, small-size cloud droplet concentrations increased in the convective and stratus clouds. In the convective clouds, flare particles propagated to higher cloud depths (≈ 2.25 km, vertical distance from cloud base) and modulate cloud microphysical properties to initiate warm rain. This new technique help to trace activated flare particles in seeded clouds and identify the post-seeding chain of cloud microphysical processes. [ABSTRACT FROM AUTHOR]

To evaluate the hygroscopic cloud seeding in reality, this study develops a hybrid microphysics scheme using a Weather Research and Forecasting (WRF) model, WDM6-NCU (WDM6 modified by National Central University), which involves 43 bins of seeded cloud condensation nuclei (CCN) in the WDM6 bulk method scheme. This scheme can describe the size distribution of seeded CCN and explain the process of the CCN imbedding and cloud and raindrop formation in detail. Furthermore, based on the observational CCN size distribution applied in the modelling, a series of tests on cloud seeding were conducted during the seeding periods of 21–22 October 2020 with stratocumulus clouds. The model simulation results reveal that seeding in in-cloud regions with an appropriate CCN size distribution can yield greater rainfall and that spreading the seeding agents over an area of 40–60 km 2 is the most efficient strategy to create a sufficient precipitation rate. With regard to the microphysical processes, the main process that causes the enhancement of precipitation is the strengthening of the accretion process of raindrops. In addition, hygroscopic particles larger than 0.4 µ m primarily contribute to cloud-seeding effects. The study results could be used as references for model development and warm-cloud-seeding operations. [ABSTRACT FROM AUTHOR]

The western United States region, an economic and agricultural powerhouse, is highly dependent on winter snowpack from the mountain west. Coupled with increasing water and renewable electricity demands, the predictability and viability of snowpack resources in a changing climate are becoming increasingly important. In Idaho, specifically, up to 75% of the state's electricity production comes from hydropower, which is dependent on the timing and volume of spring snowmelt. While we know that 1 April snowpack is declining from SNOTEL observations and is expected to continue to decline as indicated by GCM predictions, our ability to understand the variability of snowfall accumulation and distribution at the regional level is less robust. In this paper, we analyze snowfall events using 0.9-km-resolution WRF simulations to understand the variability of snowfall accumulation and distribution in the mountains of Idaho between 1 October 2016 and 31 April 2017. Various characteristics of snowfall events throughout the season are evaluated, including the spatial coverage, event durations, and snowfall rates, along with the relationship between cloud microphysical variables—particularly liquid and ice water content—on snowfall amounts. Our findings suggest that efficient snowfall conditions—for example, higher levels of elevated supercooled liquid water—can exist throughout the winter season but are more impactful when surface temperatures are near or below freezing. Inefficient snowfall events are common, exceeding 50% of the total snowfall events for the year, with some of those occurring in peak winter. For such events, glaciogenic cloud seeding could make a significant impact on snowpack development and viability in the region. Significance Statement: The purpose and significance of this study is to better understand the variability of snowfall event accumulation and distribution in the Payette Mountains region of Idaho as it relates to the local topography, the drivers of snowfall events, the cloud microphysical properties, and what constitutes an efficient or inefficient snowfall event (i.e., its ability to convert atmospheric liquid water into snowfall). As part of this process, we identify how many snowfall events in a season are inefficient to determine the number of snowfall events in a season that are candidates for enhancement by glaciogenic cloud seeding. [ABSTRACT FROM AUTHOR]

The measurement of cloud microphysical parameters plays an important role in describing characteristics of liquid phase clouds and investigating mutual relationships between clouds and precipitation. In this paper, cloud microphysical parameters at Liupan Mountain Weather Station in Ningxia are measured with a high-resolution coaxial digital holographic imager and a fog monitor 120. There are differences in the measurement results between the two instruments. The number concentration measured by the digital holographic imager is about 1.5 times that of the fog monitor 120. However, their Pearson correlation coefficient is above 0.9. Through analysis, we found that the measurement results of the digital holographic imager and fog monitor 120 are differences in 2–4 µm and 7–50µm. For the droplets with the diameters of 4–7 µm, their measurement results have good consistency. By analyzing the influence of wind field and detection sensitivity on the measurement principle, the reasons which caused the difference are proposed. Advice is given to observe topographic clouds by using the above two instruments. In addition, the differences in liquid water content and visibility are analyzed due to the absence of small and large droplets. The study provides data support for improving the accuracy of instruments in measuring cloud droplets and is useful for research in the field of cloud microphysical processes. [ABSTRACT FROM AUTHOR]