High Liquid Water Research Articles

Simulating Mixed‐Phase Open Cellular Clouds Observed During COMBLE: Evaluation of Parameterized Turbulence Closure

AbstractMarine cold‐air outbreaks, or CAOs, are airmass transformations whereby relatively cold boundary layer (BL) air is transported over relatively warm water. To more deeply understand BL and mixed‐phase cloud properties during CAO conditions, the Cold‐Air Outbreaks in the Marine Boundary Layer Experiment (COMBLE) took place from late 2019 into early 2020. During COMBLE, the U.S. Department of Energy's first Atmospheric Radiation Measurement Mobile Facility (AMF1) was deployed to Andenes, Norway, far downstream (∼1,000 km) from the Arctic pack ice. This study examines the two most intense CAOs sampled at the AMF1 site. The observed BL structures are open cellular with high (∼3–5 km) and cold (−30 to −50 C) cloud tops, and they often have pockets of high liquid water paths (LWPs; up to ∼1,000 g ) associated with strong updrafts and enhanced turbulence. We use a high‐resolution mesoscale model to explore how well four turbulence closure methods represent open cellular clouds. After applying a radar simulator to model outputs for direct evaluation, cloud top properties agree well with AMF1 observations (within ∼10%), but radar reflectivity and LWP agreement is more variable. Results suggest that the turbulent Prandtl number may play an important role for the simulated BL and cloud properties. All simulations produce enhanced precipitation rates that are well‐correlated with a cloud transition. Finally, the eddy‐diffusivity/mass‐flux approach produces the deepest cloud layer and therefore the largest and most coherent cellular structures. We recommend the use of a non‐local turbulence closure approach to better capture turbulent processes in intense CAOs.

Quantifying the performances of SU-8 microfluidic devices: high liquid water tightness, long-term stability, and vacuum compatibility

Quantifying the performances of SU-8 microfluidic devices: high liquid water tightness, long-term stability, and vacuum compatibility

Extending the utility of space-borne snow water equivalent observations over vegetated areas with data assimilation

Abstract. Snow is a vital component of the earth system, yet no snow-focused satellite remote sensing platform currently exists. In this study, we investigate how synthetic observations of snow water equivalent (SWE) representative of a synthetic aperture radar remote sensing platform could improve spatiotemporal estimates of snowpack. We use a fraternal twin observing system simulation experiment, specifically investigating how much snow simulated using widely used models and forcing data could be improved by assimilating synthetic observations of SWE. We focus this study across a 24∘×37∘ domain in the western USA and Canada, simulating snow at 250 m resolution and hourly time steps in water year 2019. We perform two data assimilation experiments, including (1) a simulation excluding synthetic observations in forests where canopies obstruct remote sensing retrievals and (2) a simulation inferring snow distribution in forested grid cells using synthetic observations from nearby canopy-free grid cells. Results found that, relative to a nature run, or assumed true simulation of snow evolution, assimilating synthetic SWE observations improved average SWE biases at maximum snowpack timing in shrub, grass, crop, bare-ground, and wetland land cover types from 14 %, to within 1 %. However, forested grid cells contained a disproportionate amount of SWE volume. In forests, SWE mean absolute errors at the time of maximum snow volume were 111 mm and average SWE biases were on the order of 150 %. Here the data assimilation approach that estimated forest SWE using observations from the nearest canopy-free grid cells substantially improved these SWE biases (18 %) and the SWE mean absolute error (27 mm). Simulations employing data assimilation also improved estimates of the temporal evolution of both SWE and runoff, even in spring snowmelt periods when melting snow and high snow liquid water content prevented synthetic SWE retrievals. In fact, in the Upper Colorado River region, melt-season SWE biases were improved from 63 % to within 1 %, and the Nash–Sutcliffe efficiency of runoff improved from −2.59 to 0.22. These results demonstrate the value of data assimilation and a snow-focused globally relevant remote sensing platform for improving the characterization of SWE and associated water availability.

Analysis of the Micro-Physical Characteristics of the Sea of Clouds Phenomena in Jiuxian Mountain Based on Multiple Source Observations

The micro-physical characteristics of a typical sea of clouds process in Jiuxian Mountain are investigated by comprehensively analyzing parameters that delineate the micro-physical characteristics of clouds and atmospheric stratification based on data from a cloud radar, wind profiler, meteorological gradient observation in high mountains, and other observations. The results show that water vapor condenses into cloud particles via an entrained and mixing process accompanied by an updraft originating from orographic uplift. During the thickening stage of the sea of clouds, atmospheric motion within the clouds is featured as “downdraft on the top—updraft on the bottom”. The zero vertical velocity area is located closely to the maximum of liquid water content. The thermal inversion layer is formed during the maintenance stage; however, the enhancement of inversion on the cloud top could suppress updraft in areas with a high liquid water content. The values mainly concentrate on the cloud top, and repetitively lifting and falling processes caused by the atmospheric upward and downward motion are in favor of the coalescence growth of cloud particles, which result in the persistence of strong radar echo. At the dissipation stage, warming on the cloud top is greater than that on the cloud bottom due to the short-wave absorption of clouds as the solar radiation enhances. As a result, the inversion layer thickens and elevates, evaporation caused by heating outweighs the condensation caused by cooling, a strong radar echo band descends from the top to the middle part of clouds, a sea of clouds dissipates gradually as cloud particles evaporates, and the particle size and concentration number of cloud particles decrease simultaneously.

The impact of rain‐on‐snow events on the snowmelt process: A field study

AbstractPrevious studies have primarily focused on the hydrological response of snowpack during rain‐on‐snow (ROS) events, with limited attention given to their subsequent stages, despite the significance of these stages. Therefore, this study selected two snow plots with similar initial parameters in the Qilian Mountains at an altitude of 4151 m. One of the snow plots underwent artificial rainfall simulation, and the changes in snow albedo, liquid water content, and snow depth of two snow plots were observed and analysed during the rainfall experiment and for a period of 7 days thereafter. The results indicate that ROS events significantly accelerate the rate of decrease in snow albedo and snow depth, increase the liquid water content within the snowpack, and these effects persist for several days after the rainfall event. Furthermore, the input of liquid water leads to rapid saturation of the snowpack, altering the transport mechanism of water within the snowpack, and transforming a process that would otherwise take a long time to complete into a short time. The decrease in snow albedo enhances the absorption of more energy by the snow, thereby accelerating snowmelt. Compared to natural snowmelt, ROS events cause the snowpack with high liquid water content to rapidly melt over a short period, resulting in a rapid increase in river flow, which may be one of the causes of ROS‐induced flooding. These research findings provide scientific insights for a better understanding of the disaster mechanisms associated with ROS events.

Insights into the relation between vertical cloud structure and dynamics of three polar lows: Observations from COMBLE

AbstractThe vertical structure of three polar lows is described using profiling radar, lidar, and passive remote sensors deployed at a coastal site in northern Norway. The data were collected as part of the Cold‐air Outbreaks in the Marine Boundary Layer Experiment (COMBLE). These data are examined in the context of satellite imagery, operational weather radar reflectivity imagery, and output from the AROME Arctic model. A comparison to satellite images shows that AROME‐Arctic captured the polar lows well. All three polar lows form in marine cold‐air outbreaks and are surrounded by open‐cellular convection typical of such outbreaks. Two of the lows form in a forward shear environment and one under reverse shear. Initially, the three polar lows are comma shaped; two of them transition to be more spiraliform at their mature stage and have mostly cloud‐free warm cores. The warm cores are the result of a warm‐seclusion process. All three lows have stratiform precipitation bands, marked by little cloud liquid water, and rather high surface precipitation rate. The vertical drafts and turbulence in these stratiform clouds are generally weak. All three lows also have convective clouds, which have stronger vertical drafts, stronger turbulence, and pockets of high liquid water content.

Influence of horizontal resolution and complexity of aerosol–cloud interactions on marine stratocumulus and stratocumulus‐to‐cumulus transition in HadGEM3‐GC3.1

AbstractStratocumulus (Sc) clouds and stratocumulus‐to‐cumulus transitions (SCTs) are challenging to represent in global models and they contribute to a large spread in modeled subtropical cloud feedbacks. We evaluate the impact of increasing the horizontal model resolution (∼135, 60 and 25 km, respectively) and increasing the complexity of the aerosol–cloud interaction parameterization (interactive versus non‐interactive at medium resolution) on springtime subtropical marine Sc properties and SCTs in the atmosphere‐only version of HadGEM3‐GC3.1. No significant impact on the spatial location of the SCT could be found between the different model versions. Increasing horizontal resolution led to small but significant increases in liquid water content and a stronger (more negative) shortwave (SW) cloud radiative effect (CRE), in particular over the southern‐hemisphere Sc regions. However, for two out of the four studied regions, the stronger SW CRE also brought the model outside the range of satellite‐derived values of the SW CRE. Applying non‐interactive aerosols instead of interactive aerosols also led to significantly higher liquid water content and a stronger SW CRE over the southern‐hemisphere Sc regions, while over the northern‐hemisphere Sc regions, a competition between a substantial increase in the cloud droplet number concentration and small changes in the liquid water content resulted in a weaker SW CRE or non‐significant changes. In general, using interactive instead of non‐interactive aerosol–cloud interactions brought the model closer to satellite‐retrieved mean values of the SW CRE. Our results suggest that increasing the horizontal resolution or the complexity of the aerosol–cloud parameterization has a small but statistically significant effect on the SW CRE of marine Sc, in particular over regions with high liquid water content. For these regions, the effect of introducing non‐interactive versus interactive aerosol–cloud interactions is about as large as increasing the horizontal resolution from medium to high.

On the importance of multiphase photolysis of organic nitrates on their global atmospheric removal

Abstract. Organic nitrates (RONO2) are secondary compounds, and their fate is related to the transport and removal of NOx in the atmosphere. While previous research studies have focused on the reactivity of these molecules in the gas phase, their reactivity in condensed phases remains poorly explored despite their ubiquitous presence in submicron aerosols. This work investigated for the first time the aqueous-phase photolysis-rate constants and quantum yields of four RONO2 (isopropyl nitrate, isobutyl nitrate, α-nitrooxyacetone, and 1-nitrooxy-2-propanol). Our results showed much lower photolysis-rate constants for these RONO2 in the aqueous phase than in the gas phase. From alkyl nitrates to polyfunctional RONO2, no significant increase of their aqueous-phase photolysis-rate constants was observed, even for RONO2 with conjugated carbonyl groups, in contrast with the corresponding gas-phase photolysis reactions. Using these new results, extrapolated to other alkyl and polyfunctional RONO2, in combination with estimates for the other atmospheric sinks (hydrolysis, gas-phase photolysis, aqueous- and gas-phase ⚫OH oxidation, dry and wet deposition), multiphase atmospheric lifetimes were calculated for 45 atmospherically relevant RONO2 along with the relative importance of each sink. Their lifetimes range from a few minutes to several hours depending on the RONO2 chemical structure and its water solubility. In general, multiphase atmospheric lifetimes are lengthened when RONO2 partition to the aqueous phase, especially for conjugated carbonyl nitrates for which lifetimes can increase by up to 100 %. Furthermore, our results show that aqueous-phase ⚫OH oxidation is a major sink for water-soluble RONO2 (KH>105 M atm−1) ranging from 50 % to 70 % of their total sink at high liquid water content (LWC) (0.35 g m−3). These results highlight the importance of investigating the aqueous-phase RONO2 reactivity to understand how it affects their ability to transport air pollution.

CFD simulation of a small bubble motion in 3D flow domain: effect of liquid density, viscosity and surface tension

The motion of spherical and slightly deformed bubbles rising rectilinearly in a stagnant liquid was numerically simulated in a fully three-dimensional domain using the CFD solver COMSOL Multiphysics. The interface was tracked by the built-in conservative Level set method on a fixed numerical grid. The purpose of this work was to study the single bubble motion in three industrially used liquids that differ significantly in surface tension, density, and viscosity. The motion of bubbles with diameters up to 1.6 mm was also studied experimentally using a high-speed camera. The data obtained together with the results of theoretical models for bubble motion were used for the validation of the simulation data. Using a 3D domain, very good agreement was obtained in both bubble shape deformations and bubble terminal velocity. The best results were achieved for propanol with low surface tension and low viscosity. In the case of high surface tension and low viscosity liquid (water), both the bubble deformation and the bubble velocity were slightly underestimated. In the case of glycerol (high surface tension and viscosity), the negligible bubble deformation is correctly calculated, but the velocity is again slightly underestimated.Graphical abstract

A Goldilocks Approach to Water Management: Hydrochannel Porous Transport Layers for Unitized Reversible Fuel Cells

AbstractThis work presents a novel porous transport layer (PTL), the hydrochannel PTL, that enables improved water management and record high round trip efficiency in unitized reversible fuel cells (URFCs). URFCs require rapid transport of O2 and H2O to provide high performance in both fuel cell and water electrolyzer operation, but cell design is complicated by conflicting water management requirements: electrolyzers perform best with high liquid water saturation, whereas fuel cells perform best when liquid water saturation is as low as possible while still maintaining effective ionomer hydration. The hydrochannel PTL circumvents this obstacle by providing hydrophilic channels for water transport through an otherwise hydrophobic PTL, enabling optimal performance in both fuel cell and water electrolyzer modes. Neutron radiography measurements of water content in both operating modes confirm that the hydrochannel PTL enables high performance due to its improved water management capabilities.

Vertical Motions Forced by Small-Scale Terrain and Cloud Microphysical Response in Extratropical Precipitation Systems

Abstract Airborne vertically profiling Doppler radar data and output from a ∼1-km-grid-resolution numerical simulation are used to examine how relatively small-scale terrain ridges (∼10–25 km apart and ∼0.5–1.0 km above the surrounding valleys) impact cross-mountain flow, cloud processes, and surface precipitation in deep stratiform precipitation systems. The radar data were collected along fixed flight tracks aligned with the wind, about 100 km long between the Snake River Plain and the Idaho Central Mountains, as part of the 2017 Seeded and Natural Orographic Wintertime clouds: the Idaho Experiment (SNOWIE). Data from repeat flight legs are composited in order to suppress transient features and retain the effect of the underlying terrain. Simulations closely match observed series of terrain-driven deep gravity waves, although the simulated wave amplitude is slightly exaggerated. The deep waves produce pockets of supercooled liquid water in the otherwise ice-dominated clouds (confirmed by flight-level observations and the model) and distort radar-derived hydrometeor trajectories. Snow particles aloft encounter several wave updrafts and downdrafts before reaching the ground. No significant wavelike modulation of radar reflectivity or model ice water content occurs. The model does indicate substantial localized precipitation enhancement (1.8–3.0 times higher than the mean) peaking just downwind of individual ridges, especially those ridges with the most intense wave updrafts, on account of shallow pockets of high liquid water content on the upwind side, leading to the growth of snow and graupel, falling out mostly downwind of the crest. Radar reflectivity values near the surface are complicated by snowmelt, but suggest a more modest enhancement downwind of individual ridges. Significance Statement Mountains in the midlatitude belt and elsewhere receive more precipitation than the surrounding lowlands. The mountain terrain often is complex, and it remains unclear exactly where this precipitation enhancement occurs, because weather radars are challenged by beam blockage and the gauge network is too sparse to capture the precipitation heterogeneity over complex terrain. This study uses airborne profiling radar and high-resolution numerical simulations for four winter storms over a series of ridges in Idaho. One key finding is that while instantaneous airborne radar transects of the cross-mountain flow, vertical drafts, and reflectivity contain much transient small-scale information, time-averaged transects look very much like the model transects. The model indicates substantial surface precipitation enhancement over terrain, peaking over and just downwind of individual ridges. Radar observations suggest less enhancement, but the radar-based assessment is uncertain. The second key conclusion is that, even though orographic gravity waves are felt all the way up into the upper troposphere, the orographic precipitation enhancement is due to processes very close to the terrain.

Entrainment rates in the cloud zones of continental shallow cumulus

Entrainment rates from in situ measurements and Large Eddy simulations (LES) of shallow clouds over the Indian peninsula are presented in this study. It is noted that the coherent motions of counter-rotating vortices originate from the updraft zones within clouds, and they subside around shallow clouds. Clouds with stronger updrafts gain depth and have high liquid water content near the cloud top. A three-parameter clustering algorithm (K means) identifies the subregions of the cloud from its core to the surrounding subsiding region. The extreme core region has the highest liquid water content, droplet number concentration, updrafts, and minimum entrainment rates. The varying degree of dilution in the cloud zones is identified here, featuring the dynamics associated with the moist adiabat. Parametric relationships between the entrainment rate and buoyancy in the different cloud zones are illustrated, which could be useful in large-scale models.

Secondary Formation of Submicron and Supermicron Organic and Inorganic Aerosols in a Highly Polluted Urban Area

AbstractDifferent adverse health effects of submicron (PM1) and fine particles (PM2.5) may be attributed to their chemical differences, requiring a better understanding of size‐resolved composition. Herein, extensive online measurements were conducted across seasons in Beijing by two aerosol mass spectrometers, one of which alternately sampled PM1 and PM2.5. Source apportionment of organic aerosol (OA) indicated that traffic‐ and cooking‐related OA together accounted for ∼20%−30% of the OA mass in PM2.5, showing insignificant seasonal variations. Coal‐combustion and biomass‐burning‐related OA had minor contributions. The two secondary OA (SOA) factors together accounted for 59%−73% of the OA mass in PM2.5. The mass distributions of particulate components in PM1 and PM2.5 varied greatly across seasons. Secondary formation played a key role in particle size growth during cold seasons. During severe hazes with high aerosol liquid water content (ALWC), the supermicron mass fraction (MF1−2.5) of secondary components reached ∼40%−50% while those for primary OA remained at ∼20%. Heterogeneous uptake, aqueous processing, and dissolution likely all contributed to the enhanced concentration of secondary components, and the former two were perhaps more important. The increase of MF1−2.5 for secondary components with increasing ALWC in spring was less than that in winter, possibly due to the shorter duration of stagnant conditions limiting secondary formation. Early autumn showed higher MF1−2.5 values than cold seasons with insignificant changes as ALWC varied, plausibly explained by intensive new particle formation hindering persistent particle growth. Our results highlight the importance of heterogeneous uptake and aqueous processing in distributing SOA in supermicron mode in polluted areas.

Lightning Prediction Using Electric Field Measurements Associated with Convective Events at a Tropical Location

Nowcasting of lightning occurrences is essential in tropical locations as lightening causes severe damage to life and property. This study attempts to nowcast lightning events during convective phenomena using an electric field monitor (EFM) at a tropical urban location, Kolkata (22.65°N, 88.45°E). Before the onset of heavy lightning occurrences, definite changes in the atmospheric electric field (EF) are observed, which in turn are associated with high cloud liquid water content (LWC) and low cloud base height (CBH). A model has been proposed to nowcast lightning strikes within about 17.5 km radius of the present location based on the EF standard deviation (EFSD) values. The proposed technique is tested with the lightning data provided by a collocated lightning detector, which yields a prediction efficiency of ~ 0.91 (~ 0.86), a false alarm rate of ~ 0.23 (~ 0.18), and a critical success index of ~ 0.71 (~ 0.72) with an optimal range of other performance parameters during the monsoon (pre-monsoon) periods, thereby generating an alarm 45 min before lightning events.

Exploring the Environmental Conditions of Snow Particles Using Spaceborne Triple-Frequency Radar Measurements over Ocean

The environmental conditions of snow particles with different particle sizes and bulk effective densities over the ocean are explored using a coincidence dataset of National Aeronautics and Space Administration (NASA) CloudSat Cloud Profiling Radar (CPR) and Global Precipitation Mission (GPM) Dual-frequency Precipitation Radar (DPR). Observed triple-frequency radar signatures for snow particles over the ocean are firstly derived. Based on modeled triple-frequency signatures for various snow particles, DFR Ku/Ka and the ratio of DFR Ku/Ka to DFR Ku/W from observations are selected to indicate the snow particle size and bulk effective density, respectively. The dependences of two indicators on temperature, relative humidity and cloud liquid water content are presented. The snow particle size range becomes wider at warmer temperatures, higher relative humidities or lower cloud liquid water contents. At cold temperatures, low relative humidities or high cloud liquid water contents, large snow particles are prevalent. At high cloud liquid water contents, the riming process mainly contributes to the increase in snow particle bulk effective density. When supersaturation occurs, a large portion of snow particles have large sizes and low bulk effective densities at cold temperatures. This study can improve the understanding of snow microphysics and demonstrate the potential of spaceborne radar measurements in global snowfall retrievals.

Microphysical and Kinematic Characteristics of Anomalous Charge Structure Thunderstorms in Cordoba, Argentina

Some thunderstorms in Cordoba, Argentina, present a charge structure with an enhanced low-level positive charge layer, and practically nonexistent upper-level positive charge. Storms with these characteristics are uncommon in the United States, even when considering regions with a high frequency of anomalous charge structure storms such as Colorado. In this study, we explored the microphysical and kinematic conditions inferred by radar that led to storms with this unique low-level anomalous charge structure in Argentina, and compared them to conditions conducive for anomalous and normal charge structures. As high liquid water contents in the mixed-phase layer lead to positive charging of graupel and anomalous storms through the non-inductive charging mechanism, we explored radar parameters hypothesized to be associated with large cloud supercooled liquid water contents in the mixed-phase layer and anomalous storms, such as mass and volume of hail and high-density graupel, large reflectivity associated with the growth of rimed precipitation to hail size, and parameters that are proxies for strong updrafts such as echo-top and Zdr column heights. We found that anomalous storms had higher values of mass and volume of hail in multiple sub-layers of the mixed-phase zone and higher frequency of high reflectivity values. Low-level anomalous events had higher hail mass in the lower portion of the mixed-phase zone when compared to normal events. Weaker updraft proxies were found for low-level anomalous events due to the shallow nature of these events while there was no distinction between the updraft proxies of normal and anomalous storms.

Optimization of gas diffusion layer thickness for proton exchange membrane fuel cells under steady-state and load-varying conditions

This work proposes a design principle of the optimal thickness for cathode gas diffusion layers (GDLs) of proton exchange membrane fuel cells (PEMFCs) based on a balance of cell performances under both steady-state and load-varying conditions. Using a three-dimensional and two-phase model, the effects of cathode GDL thickness (50, 100, 200, and 400 μm) on steady-state performances and transient response characteristics are studied. The results show that under steady-state conditions, an extremely thin cathode GDL would lead to non-uniform oxygen and liquid water distributions, whereas an especially thick cathode GDL would increase oxygen transport resistance. Thus, there is an optimal cathode GDL thickness, yielding the best steady-state performance. A current overshoot phenomenon, arising from high local oxygen concentrations at cathode catalyst layers (CLs), is observed when the load voltage decreases abruptly. Thinner cathode GDLs would weaken the overshoot and shorten the recovery time of current density. Conversely, low local oxygen concentrations at cathode CLs caused by high liquid water saturation levels lead to a current undershoot phenomenon when the load voltage increases abruptly. Thinner cathode GDLs would strengthen the undershoot but shorten the recovery time of current density. The optimal choice of cathode GDL thickness should weigh up the steady-state and the transient performance. Based on this principle, the optimal cathode GDL thickness is selected as 100 µm.

Idealized numerical simulation experiment of ice seeding in convective clouds using a bin microphysics scheme

A 2D axisymmetric bin model is used to conduct idealized numerical experiments of cloud seeding. The simulations are performed for two clouds that differ in their initial wind shear. Results show that, although cloud seeding with an ice concentration of 1000 L−1 in a regime that has relatively high supercooled liquid water can obtain a positive effect, the rainfall enhancement seems more pronounced when the cloud develops in a wind shear environment. In no-shear environment, the change in the microphysical thermodynamic field after seeding shows that, although more graupel is produced via riming and this can increase the surface rainfall intensity, the larger drag force and cooling of melting graupel is unfavorable for the development of cloud. On the contrary, when the cloud develops in a wind shear environment, since the main downdraft is behind the direction of movement of the cloud, its negative effect on precipitation is much weaker.摘要本文采用二维轴对称分档云模式开展了人工催化数值试验, 对两种不同初始风切变的对流云进行了模拟. 结果表明, 尽管在过冷水相对较高的区域播撒 1000 L−1 的冰晶可以增加地面降水, 但当云在风切变环境中发展时, 人工播撒对降雨增强的作用似乎更加明显. 在无切变环境下, 微物理量, 热力场的变化表明播撒后大量的霰所产生的拖曳力和融化冷却有可能切断主上升气流, 从而不利于云的发展. 相反, 当云在风切变环境中发展时, 由于播撒产生的主下沉气流位于云的运动方向之后, 其对降水的负面影响要弱得多.

The Relation of Environmental Conditions With Charge Structure in Central Argentina Thunderstorms

AbstractIn this study we explored the environmental conditions hypothesized to induce a dominant charge structure in thunderstorms in the province of Cordoba, Argentina, during the RELAMPAGO‐CACTI (Remote sensing of Electrification, Lightning, And Mesoscale/microscale Processes with Adaptive Ground Observations‐Clouds, Aerosols, Complex Terrain Interactions) field campaigns. Hypothesized environmental conditions are thought to be related to small warm cloud residence time and warm rain growth suppression, which lead to high cloud liquid water contents in the mixed‐phase zone, contributing to positive charging of graupel and anomalous charge structure storms. Data from radiosondes, a cloud condensation nuclei (CCN) ground‐based instrument and reanalysis were used to characterize the proximity inflow air of storms with anomalous and normal charge structures. Consistent with the initial hypothesis, anomalous storms had small warm cloud depth caused by dry low‐level humidity and low 0°C height. Anomalous storms were associated with lower CCN concentrations than normal storms, an opposite result to the initial expectation. High CAPE is not an important condition for the development of anomalous storms in Argentina, as no clear pattern could be found among the different parameters calculated for updraft proxy that would be consistent with the initial hypothesis.

High atmospheric oxidation capacity drives wintertime nitrate pollution in the eastern Yangtze River Delta of China

Abstract. Nitrate aerosol plays an increasingly important role in wintertime haze pollution in China. Despite intensive research on wintertime nitrate chemistry in recent years, quantitative constraints on the formation mechanisms of nitrate aerosol in the Yangtze River Delta (YRD), one of the most developed and densely populated regions in eastern China, remain inadequate. In this study, we identify the major nitrate formation pathways and their key controlling factors during the winter haze pollution period in the eastern YRD using 2-year (2018–2019) field observations and detailed observation-constrained model simulations. We find that the high atmospheric oxidation capacity, coupled with high aerosol liquid water content (ALWC), made both the heterogeneous hydrolysis of dinitrogen pentoxide (N2O5) and the gas-phase OH oxidation of nitrogen dioxide (NO2) important pathways for wintertime nitrate formation in this region, with contribution percentages of 69 % and 29 % in urban areas and 63 % and 35 % in suburban areas during the haze pollution episodes, respectively. We further find that the gas-to-particle partitioning of nitric acid (HNO3) was very efficient so that the rate-determining step in the overall formation process of nitrate aerosol was the oxidation of NOx to HNO3 through both heterogeneous and gas-phase processes. The atmospheric oxidation capacity (i.e., the availability of O3 and OH radicals) was the key factor controlling the production rate of HNO3 from both processes. During the COVID-19 lockdown (January–February 2020), the enhanced atmospheric oxidation capacity greatly promoted the oxidation of NOx to nitrate and hence weakened the response of nitrate aerosol to the emission reductions in urban areas. Our study sheds light on the detailed formation mechanisms of wintertime nitrate aerosol in the eastern YRD and highlights the demand for the synergetic regulation of atmospheric oxidation capacity and NOx emissions to mitigate wintertime nitrate and haze pollution in eastern China.