Liquid Water Content Research Articles

Meteorological impact on gravimeter and seismometer readings

Background. The density of atmospheric air varies with temperature. Therefore, variations in the atmospheric layer temperature leads the emergence of local gravity anomalies. The amplitude of such anomalies can exceed ±0.1 mGal. The results obtained by the Arti Geophysical Observatory(Yekaterinburg, Russia) on the non-tidal variations of gravity confirm the influence of temperature variations on gravimeter readings, which may significantly exceed the calculated data. Aim. To assess the impact of weather changes on seismic and gravity fields.Materials and methods. At the RAS Bishkek Geodynamic Test Area (Bishkek, Kyrgyzstan), RAS Institute of Geophysics (Yekaterinburg, Russia) and Zapolye Observatory (Vladimir, Russia), gravity was measured by CG-5 AUTOGRAV gravimeters. At the Shults Cape (Vladivostok, Russia), Arti (Yekaterinburg, Russia) and BFO (Black Forest, Germany [10]) observatories, gravimetric measurements were conducted by La Coste & Romberg tidal gravimeters. Results. Variations in the atmospheric layer temperature were found to lead to the emergence of local gravity anomalies. The amplitude of such anomalies can exceed ±0.1 mGal. The results obtained by the Arti Geophysical Observatory (Yekaterinburg, Russia) on the non-tidal variations of gravity confirm the influence of temperature on gravimeter readings, which may significantly exceed the calculated data. Conclusion. Meteorological processes, such as liquid-water content and the Earth’s atmospheric temperature, affect the readings of gravimeters and seismometers. The atmospheric air density varies with temperature. Along with temperature, gravimeters and seismometers are affected by pressure, humidity and water content of the atmosphere. This is related to atmospheric deformations under the influence of the Moon and the Sun. Meteor streams and their impact on the Earth’s atmosphere have the greatest influence on the readings of gravimeters and seismometers.

Drivers of Snowfall Accumulation in the Central Idaho Mountains Using Long-Term High-Resolution WRF Simulations

Abstract 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.

A Comparative Investigation of Light Scattering and Digital Holographic Imaging to Measure Liquid Phase Cloud Droplets

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.

Boundary protection based on the anti-icing thermal load surrogated model and the WRF icing meteorological prediction

PurposeThis paper aims to propose a method of the safety boundary protection for unmanned aerial vehicles (UAVs) in the icing conditions.Design/methodology/approachForty icing conditions were sampled in the continuous maximum icing conditions in the Appendix C of the Federal Aviation Regulation Part 25. Icing numerical simulations were carried out for the 40 samples and the anti-icing thermal load distribution in full evaporation mode were obtained. Based on the obtained anti-icing thermal load distribution, the surrogated model of the anti-icing thermal load distribution was established with proper orthogonal decomposition and Kriging interpolation. The weather research and forecasting (WRF) model was used for meteorological simulations to obtain the icing meteorological conditions in the target area. With the obtained icing conditions and surrogated model, the anti-icing thermal load distribution in the target area and the variation with time can be determined. According to the energy supply of the UAVs, the graded safety boundaries can be obtained.FindingsThe surrogated model can predict the effects of five factors, such as temperature, velocity, pressure, median volume diameter (MVD) and liquid water content (LWC), on the anti-icing thermal load quickly and accurately. The simulated results of the WRF mode agree well with the observed results. The method can obtain the graded safety boundaries.Originality/valueThe method has a reference significant for the safety of the UAVs with the limited energy supply in the icing conditions.

Dynamics of localized extreme heatwaves in the mid‐latitude atmosphere: A conceptual examination

AbstractThis study investigates the adjustment of large‐scale localized buoyancy anomalies in mid‐latitude regions and the nonlinear evolution of associated condensation patterns in both adiabatic and moist‐convective environments. This investigation is carried out utilizing the two‐layer idealized moist‐convective thermal rotating shallow water (mcTRSW) model. Our investigation reveals that the presence of a circular positive potential temperature anomaly in the lower layer initiates an anticyclonic high‐pressure rotation, accompanied by a negative buoyancy anomaly in the upper layer, resulting in an anisotropic northeast–southwest tilted circulation of heat flux. The evolution of eddy heat fluxes, such as poleward heat flux, energy, and meridional elongation of the buoyancy field, heavily depends on the perturbation's strength, size, and vertical structure. The heatwave initiates atmospheric instability, leading to precipitation systems such as rain bands and asymmetric latent heat release due to moist convection in a diabatic environment. This creates a comma cloud pattern in the upper troposphere and a comma‐shaped buoyancy anomaly in the lower layer, accompanied by the emission of inertia gravity waves. The southern and eastern sectors of the buoyancy anomaly show an upward flux, generating a stronger cross‐equatorial flow and inertia‐gravity waves in a southward and eastward direction. Furthermore, the simulations reveal a similar asymmetric pattern of total condensed liquid water content distribution, accompanied by the intensification of moist convection as rain bands. This intensification is more pronounced in barotropic structures than in baroclinic configurations with stagnant upper layers. This study highlights the importance of considering moist convection and its effects on atmospheric and oceanic flows in mid‐latitude regions, as well as the role of buoyancy anomalies in generating heatwaves and precipitation patterns.

High-time-resolution chemical composition and source apportionment of PM2.5 in northern Chinese cities: implications for policy

Abstract. Fine particulate matter (PM2.5) pollution is still one of China's most important environmental issues, especially in northern cities during wintertime. In this study, intensive real-time measurement campaigns were conducted in Xi'an, Shijiazhuang, and Beijing to investigate the chemical characteristics and source contributions of PM2.5 and explore the formation of heavy pollution for policy implications. The chemical compositions of PM2.5 in the three cities were all dominated by organic aerosol (OA) and nitrate (NO3-). Results of source apportionment analyzed by a hybrid environmental receptor model (HERM) showed that the secondary formation source contributed more to PM2.5 compared to other primary sources. Biomass burning was the dominant primary source in the three pilot cities. The contribution of coal combustion to PM2.5 is non-negligible in Xi'an and Shijiazhuang but is no longer an important contributor in the capital city of Beijing due to the execution of a strict coal-banning policy. The potential formation mechanisms of secondary aerosol in the three cities were further explored by establishing the correlations between the secondary formation sources and aerosol liquid water content (ALWC) and Ox (O3+NO2), respectively. The results showed that photochemical oxidation and aqueous-phase reaction were two important pathways of secondary aerosol formation. According to source variations, air pollution events that occurred in campaigns were classified into three types: biomass-combustion-dominated, secondary-formation-source-dominated, and a combination of primary and secondary sources. Additionally, this study compares the changes in chemical composition and source contributions of PM2.5 in past decades. The results suggest that the clean-energy replacements for rural households should be urgently encouraged to reduce the primary source emissions in northern China, and collaborative control on ozone and particulate matter needs to be continuously promoted to weaken the atmosphere oxidation capacity for the sake of reducing secondary aerosol formation.

Investigating the thermal state of permafrost with Bayesian inverse modeling of heat transfer

Abstract. Long-term measurements of permafrost temperatures do not provide a complete picture of the Arctic subsurface thermal regime. Regions with warmer permafrost often show little to no long-term change in ground temperature due to the uptake and release of latent heat during freezing and thawing. Thus, regions where the least warming is observed may also be the most vulnerable to permafrost degradation. Since direct measurements of ice and liquid water contents in the permafrost layer are not widely available, thermal modeling of the subsurface plays a crucial role in understanding how permafrost responds to changes in the local energy balance. In this work, we first analyze trends in observed air and permafrost temperatures at four sites within the continuous permafrost zone, where we find substantial variation in the apparent relationship between long-term changes in permafrost temperatures (0.02–0.16 K yr−1) and air temperature (0.09–0.11 K yr−1). We then apply recently developed Bayesian inversion methods to link observed changes in borehole temperatures to unobserved changes in latent heat and active layer thickness using a transient model of heat conduction with phase change. Our results suggest that the degree to which recent warming trends correlate with permafrost thaw depends strongly on both soil freezing characteristics and historical climatology. At the warmest site, a 9 m borehole near Ny-Ålesund, Svalbard, modeled active layer thickness increases by an average of 13 ± 1 cm K−1 rise in mean annual ground temperature. In stark contrast, modeled rates of thaw at one of the colder sites, a borehole on Samoylov Island in the Lena River delta, appear far less sensitive to temperature change, with a negligible effect of 1 ± 1 cm K−1. Although our study is limited to just four sites, the results urge caution in the interpretation and comparison of warming trends in Arctic boreholes, indicating significant uncertainty in their implications for the current and future thermal state of permafrost.

Thermodynamical framework for effective mitigation of high aerosol loading in the Indo-Gangetic Plain during winter

The Indo-Gangetic Plain (IGP) experiences severe air pollution every winter, with ammonium chloride and ammonium nitrate as the major inorganic fractions of fine aerosols. Many past attempts to tackle air pollution in the IGP were inadequate, as they targeted a subset of the primary pollutants in an environment where the majority of the particulate matter burden is secondary in nature. Here, we provide new mechanistic insight into aerosol mitigation by integrating the ISORROPIA-II thermodynamical model with high-resolution simultaneous measurements of precursor gases and aerosols. A mathematical framework is explored to investigate the complex interaction between hydrochloric acid (HCl), nitrogen oxides (NOx), ammonia (NH3), and aerosol liquid water content (ALWC). Aerosol acidity (pH) and ALWC emerge as governing factors that modulate the gas-to-particle phase partitioning and mass loading of fine aerosols. Six "sensitivity regimes" were defined, where PM1 and PM2.5 fall in the "HCl and HNO3 sensitive regime", emphasizing that HCl and HNO3 reductions would be the most effective pathway for aerosol mitigation in the IGP, which is ammonia-rich during winter. This study provides evidence that precursor abatement for aerosol mitigation should not be based on their descending mass concentrations but instead on their sensitivity to high aerosol loading.

Assessment of submicron aerosol liquid water content and mass-based growth factors in South Asian outflow over the Indian Ocean

Aerosol-bound water, a ubiquitous and abundant component of atmospheric aerosols, has an impact on regional climate, visibility, human health, the hydrological cycle, and atmospheric chemistry. Yet, the intricate relationship between aerosol liquid water (ALWC) and chemical composition and relative humidity (RH) was not well understood. The present study explores ALWC derived from the ISORROPIA II model using real-time, high-resolution data of non-refractory submicron chemical species and meteorological parameters (temperature and RH) collected over the Indian Ocean as part of the ICARB (Integrated Campaign for Aerosols, Gases, and Radiation Budget)-2018 experiment. Results show that ALWC values over the South Eastern Arabian Sea (SEAS) were found to be higher by 4–6 times than those observed over the Equatorial Indian Ocean (EIO) due to a large decrease in aerosol loading from SEAS to EIO. ALWC peaked in the early morning hours (4:00–7:00), with greater values during the nighttime and lower values during the daytime across SEAS, which is comparable with RH variation. While the ratio of organics-to-SO42− mass fraction linearly decreased with increasing mass-based growth factors (MGFs) over EIO, such a scenario was not observed over SEAS. The latitudinal gradient of mass fraction of ALWC had shown a decrease towards EIO, consistent with organic fraction. The extinction coefficient of the dry mass of submicron particles is noticeably increased by 40 % by ALWC over SEAS and EIO. Moreover, ALWC could enhance the aerosol negative forcing by an average of 66 % (64 %) over SEAS (EIO) at the top of the atmosphere during the cruise period. These inferences imply that ALWC is the key factor in assessing the role of aerosols on atmospheric radiative forcing. Overall, the present study highlights the serious need to consider the ALWC in climate forcing simulations, particularly in moist tropical environments where their effect can be significant.

Characteristics and atmospheric processes of water-soluble ions in PM2.5 and PM10 over an industrial city in the National Capital Region (NCR) of India

This study investigates water-soluble inorganic ions (WSIIs), their potential formation mechanism, particle bound water content and acidity (pH) in ambient aerosols in Ghaziabad, an industrial city located downwind of Delhi, the Indian National Capital. 24-hour integrated PM2.5 and PM10 samples were collected using collocated samplers at two receptor locations every third day throughout the year. The samples were collected on Nylon filter substrates (preceded by a denuder upstream for capturing acidic gases) and Teflon filter substrates for WSII and mass measurements, respectively. Further, on-site meteorological parameters were recorded at both locations. The annual average PM concentrations observed were: PM2.5: 144 ± 81 μgm−3 (Site A), 163 ± 95 μgm−3 (Site B); and PM10: 245 ± 116 μgm−3 (Site A), 279 ± 152 μgm−3 (Site B). On average, SO42−, NO3−, Cl− and NH4+ contributed to ∼90% to PM2.5WSII mass and ∼82% to PM10WSII mass, which in turn made up ∼35% of PM2.5 mass and ∼23% of the PM10 mass across both sites. SO42− concentration was found to be highest followed by NO3−, NH4+ and Cl− for both PM fractions. Mann-Whitney U test revealed that both sites were similar with respect to WSII mass indicating city's airshed average concentration with respect to the major ions. The highest WSII contribution to the total PM was found in winter season (37–40% for PM2.5 and 27–31% for PM10) followed by monsoon (36–38% for PM2.5 and 18–21% for PM10), post-monsoon (28–34% for PM2.5 and 21–23% for PM10) and pre-monsoon (21–27% for PM2.5 and 15% for PM10). High contribution during winter was because of higher emissions of precursor gases in combination with moderate relative humidity (36–59%) and minimal precipitation (average ∼0.2 mm). Sulphur Oxidation Ratio and Nitrogen Oxidation Ratio indicated high photochemical oxidation with a greater extent of SO42− formation compared to NO3−. Although high concentrations of NH3 gas were observed, there was insufficient NH4+ ions for neutralizing counter ions with Ammonium Neutralization Ratio values of 0.76±0.14 for PM2.5 and 0.62±0.14 for PM10. Finally, aerosol liquid water content (ALWC) and acidity were estimated using a thermodynamic equilibrium model, ISORROPIA-II. It was found that PM2.5 pH varied from 2.9 to 6.2 (avg. 4.4±0.8) and the PM2.5 mass doubled at RH ∼90% because of the high particle bound water. Consequently, a reduction in SO2 would result in instantaneous cuts of SO42−, PM2.5, and ALWC.

Liquid water content measurement with SEA multi-element sensor in CARDC icing wind tunnel: Calibration and performance

The measurement of cloud liquid water content (LWC) plays a critical role in the development of icing airworthiness standards for aircraft and the calibration of icing wind tunnels. The SEA multi-element sensor, the modern hot-wire device for LWC measurement, still faces several challenges for performance calibration due to the effects of the baseline drift and droplet retention characteristics. To fully calibrate the performance of the sensor, two wind tunnel tests were conducted in the China Aerodynamics Research and Development Center (CARDC) icing wind tunnel including a dry air calibration test and an icing cloud measurement test. Using the in-situ dry power calibration method developed in this study, the compensation function and the empirical formula of dry air Nusselt number for each sense element are obtained, and present great linear characteristics in the range of the test section velocity VTS from 40 to 110 m/s. However, there is an abnormal peak area of total power for the W1 element at the VTS of 120 and 130 m/s, which may be associated with significant water vapor condensation. The consistency and discrepancy of four LWC calculation methods via the combinations of dry and wet power calculation methods are assessed. Further, the LWC response characteristics of the sense elements are examined and the correlations of the droplet retention efficiency for the W2 and W3 elements are acquired as functions of median volume diameter. Finally, the measurement accuracy of the SEA multi-element sensor is validated compared to the icing blade device. It demonstrates that the uncertainty of the W1 element for the sensor is about ±5% at the low LWC and the W1 element has a better ability in the measurement of the high LWC.

Insights of warm-cloud biases in Community Atmospheric Model 5 and 6 from the single-column modeling framework and Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) observations

Abstract. There has been a growing concern that most climate models predict precipitation that is too frequent, likely due to lack of reliable subgrid variability and vertical variations in microphysical processes in low-level warm clouds. In this study, the warm-cloud physics parameterizations in the singe-column configurations of NCAR Community Atmospheric Model version 6 and 5 (SCAM6 and SCAM5, respectively) are evaluated using ground-based and airborne observations from the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) field campaign near the Azores islands during 2017–2018. The 8-month single-column model (SCM) simulations show that both SCAM6 and SCAM5 can generally reproduce marine boundary layer cloud structure, major macrophysical properties, and their transition. The improvement in warm-cloud properties from the Community Atmospheric Model 5 and 6 (CAM5 to CAM6) physics can be found through comparison with the observations. Meanwhile, both physical schemes underestimate cloud liquid water content, cloud droplet size, and rain liquid water content but overestimate surface rainfall. Modeled cloud condensation nuclei (CCN) concentrations are comparable with aircraft-observed ones in the summer but are overestimated by a factor of 2 in winter, largely due to the biases in the long-range transport of anthropogenic aerosols like sulfate. We also test the newly recalibrated autoconversion and accretion parameterizations that account for vertical variations in droplet size. Compared to the observations, more significant improvement is found in SCAM5 than in SCAM6. This result is likely explained by the introduction of subgrid variations in cloud properties in CAM6 cloud microphysics, which further suppresses the scheme's sensitivity to individual warm-rain microphysical parameters. The predicted cloud susceptibilities to CCN perturbations in CAM6 are within a reasonable range, indicating significant progress since CAM5 which produces an aerosol indirect effect that is too strong. The present study emphasizes the importance of understanding biases in cloud physics parameterizations by combining SCM with in situ observations.

Vortex Structure of Head Bubble in Convective Cloud Starting Plume

Abstract A developing cumulus cloud (Cu) was modeled, and dynamic, thermodynamic, and microphysical properties of an ascending head bubble reproducing the upper part of a developing Cu were investigated. The data for analysis are taken from 10-m-resolution LES of trade wind Cu under BOMEX conditions. The detection of a rising bubble is carried out using wavelet filtering of the velocity fields and microphysical fields, while a low-frequency signal of the filtering is associated with the convective-scale structure of cloud. We substantiate and discuss the representation of the bubble as a vortex ring, and estimate the parameters of this vortex ring. The simplest Hill’s vortex was chosen as a model of a vortex ring inside cloud. Analytical approximations of the radial profiles of the vertical velocity and of conservative quantities (such as total water mixing ratio and liquid water potential temperature inside and outside the bubble) are obtained. The spatial structure of these quantities is investigated using analytical expressions. Analytical models for spatial distributions of liquid water content (LWC) and adiabatic fraction (AF) are also designed and analyzed. The results demonstrate the existence of a cloud core with high values of LWC and AF up to the height of 1800 m. The horizontally averaged value of the adiabatic fraction, calculated analytically using the Hill’s vortex concept, is evaluated as 0.39, which is the typical AF value in the upper parts of such Cu. The vertical profiles of different important quantities characterizing cloud structure are presented. The analysis performed in this study allows us to conclude that a rising vortex ring plays the dominating role in formation of the thermodynamic and microphysical structure of developing Cu. Significance Statement 1) Dynamic and thermodynamic fields of a developing cumulus cloud simulated by high-resolution LES with spectral bin microphysics are separated into convective and turbulent components by means of the wavelet technique. 2) The analysis of convective component of the cloud revealed the existence of a vortex ring at the developing stage of the cloud and evaluate its parameters. 3) The analysis performed in this study allows us to conclude that a rising vortex ring plays the important role in formation of the thermodynamic and microphysical structure of developing Cu. 4) The study provides a novel insight into the cloud–environment interaction. 5) The approximating equations describing the vortex ring can be usefully applied for developing new schemes of convective parameterization.

Impacts of Drop Clustering and Entrainment‐Mixing on Mixed Phase Shallow Cloud Properties Over the Southern Ocean: Results From SOCRATES

AbstractEntrainment and associated mixing (i.e., entrainment‐mixing) have been shown to impact drop size distributions. However, most past studies have focused on warm clouds and have not considered the impacts on mixed phase clouds (i.e., those containing liquid and ice particles). This study characterizes the impacts of entrainment‐mixing on mixed phase cloud properties over the Southern Ocean using in situ observations. By taking advantage of strong correlations between droplet clustering and entrainment‐mixing, a clustering metric is used as a proxy to assess the degree of mixing. This maximizes the available sample size for a statistical analysis of entrainment‐mixing impacts on mixed phase properties. A positive relationship is found between the magnitude of droplet clustering and large ice concentrations (those with maximum dimensions greater than ∼300 μm), suggesting entrainment‐mixing enhances the Wegener‐Bergeron‐Findeisen (WBF) process. Particle size distributions are averaged over different ranges of liquid (liquid water content (LWC)) to total water content (TWC) ratio. Since the ratio is expected to transition from 1 to 0 during glaciation, differences in the distributions provide insight into the relation of entrainment‐mixing to mixed phase cloud evolution. Mixed phase samples with the greatest large ice concentrations occur at LWC/TWC < 0.4 in low clustering regions. However, these samples are relatively few, whereas high clustering regions have a greater frequency of samples with LWC/TWC < 0.4. This suggests sublimation/vapor sinks associated with entrainment can counteract the enhanced WBF. In high clustering regions, distributions of small droplets are relatively constant and large droplets (>30 μm) are preferentially removed as LWC/TWC transitions from 1 to 0.

What CloudSat cannot see: liquid water content profiles inferred from MODIS and CALIOP observations

Abstract. Single-layer nonprecipitating warm clouds are integral to Earth's climate, and accurate estimates of cloud liquid water content for these clouds are critical for constraining cloud models and understanding climate feedbacks. As the only cloud-sensitive radar currently in space, CloudSat provides very important cloud-profiling capabilities. However, a significant fraction of clouds is missed by CloudSat because they are either too thin or too close to the Earth's surface. We find that the CloudSat Radar-Visible Optical Depth Cloud Water Content Product, 2B-CWC-RVOD, misses about 73 % of nonprecipitating liquid cloudy pixels and about 63 % of total nonprecipitating liquid cloud water content compared to coincident Moderate Resolution Imaging Spectroradiometer (MODIS) observations. Those percentages increase to 84 % and 69 %, respectively, if MODIS “partly cloudy” pixels are included. We develop a method, based on adiabatic parcel theory but modified to account for the fact that observed clouds are often subadiabatic, to estimate profiles of cloud liquid water content based on MODIS observations of cloud-top effective radius and cloud optical depth combined with lidar observations of cloud-top height. We find that, for cloudy pixels that are detected by CloudSat, the resulting subadiabatic profiles of cloud water are similar to what is retrieved from CloudSat. For cloudy pixels that are not detected by CloudSat, the subadiabatic profiles can be used to supplement the CloudSat profiles, recovering much of the missing cloud water and generating realistic-looking merged profiles of cloud water. Adding this missing cloud water to the CWC-RVOD product increases the mean cloud liquid water path by 228 % for single-layer nonprecipitating warm clouds. This method will be included in a subsequent reprocessing of the 2B-CWC-RVOD algorithm.

Strip-type flexible capacitive humidity sensor based on composite of polyimide and poly(glycidyl methacrylate): Fabrication, humidity sensitive performance and potential for detecting water content in liquids

Flexible humidity sensors show great potentials in the fields of smart apparels, biomedicine, human-machine interaction, etc., and they have attracted much attention in recent years. Herein, strip-type flexible capacitive humidity sensors (SFCHS) were facilely prepared by intertwining copper wires covered with soluble polyimide (PI) and poly(glycidyl methacrylate) (PGMA). The “pine nut” microstructure on copper wire surface and network structure between PGMA and PI strengthened the adhesion between the copper wire electrode and the polymeric sensitive materials, leading to better stability and sensing performance. The SFCHS with a double helix configuration showed good sensitivity (capacitance change of 111.5% between relative humidity (RH) of 11–98%), moderate hysteresis (∼6.6% RH) and fast response (tadsorption/tdesorption: 10.1 s/5.2 s) at room temperature. Furthermore, the self-standing SFCHS revealed stable capacitance under bending and good long-term stability. In addition, the flexible sensor could monitor real-time change of water content in various liquids (transformer oil, hydraulic oil, ethanol and n-dodecane), suggesting potentials for detecting water content in liquids. The work provides references for developing advanced flexible capacitive humidity sensors for measuring moisture in both air and liquids.

An improved heat-water–vapor-salt based salt swelling model for unsaturated sulfate saline soil under cooling

The salt swelling destruction in arid sulfate saline soil areas represents a severe problem in road, railway, and foundation engineering. It is imperative to explore a potential solution to solve the salt swelling for the sulfate saline soil. However, vaporous water has a large effect on the forms of sodium sulfate present in the soil, which has not been taken into account by existing models. This work proposes an improved heat-water-vapour-salt based salt swelling model by considering the vaporous water effect. Experiments on unsaturated saline soils were conducted to validate the accuracy of the model. Besides, the effects of temperature, water content, relative humidity, and solute concentration on salt swelling were reasonably analyzed. The results show that the salt swelling rate increases to 64% when the relative humidity reaches 60–90%; once the relative humidity exceeds 90%, the swelling rate will decline to 0%. Moreover, the salt swelling rate follows an upward convex curve along the relative humidity and decreases with increasing liquid water content. When the liquid water content is above 10%, the salt swelling rate is stable at around 0.3. Overall, the improved model is more accurate in predicting salt swelling than the existing model, which shows exceptional promise in providing useful insight into understanding the mechanism of salt swelling and the prevention of salt swelling in saline soils.

Calorimetric determination of wet snow liquid water content: The effect of test conditions on the calorimeter constant and its impact on the measurement uncertainty

The liquid water content (lwc) of wet snow is a fundamental parameter in determining snow properties like its strength and adhesion force to surfaces. Among the different methods available for the measurement of the lwc, this paper focuses on melting calorimetry: known masses of hot water and snow are mixed into a thermally insulated container, and the lwc is obtained from the difference between the initial hot water temperature and the final mixing temperature; it is a fast and easy to implement method that requires little equipment, making it suitable for both laboratory and field measurements. Tests with “equivalent” wet snow samples whose liquid water content was known in advance were carried out to assess the method, showing that the liquid water content was overestimated by a variable amount that seemed to depend on the test parameters. To account for the heat capacity of the calorimeter, which was found not to be negligible, a constant in terms of equivalent hot water mass (E) was introduced. However, its value also depended on the test conditions. Hence, a correlation between E and the test parameters was found, and the measurements were repeated using a container of a different material, showing a similar behavior. Eventually, a discussion about the effects of choosing different hot water masses and hot water-to-snow mass ratios on measurement accuracy is provided.

Investigating the vertical extent and short-wave radiative effects of the ice phase in Arctic summertime low-level clouds

Abstract. Low-level (cloud tops below 2 km) mixed-phase clouds are important in amplifying warming in the Arctic region through positive feedback in cloud fraction, water content and phase. In order to understand the cloud feedbacks in the Arctic region, good knowledge of the vertical distribution of the cloud water content, particle size and phase is required. Here we investigate the vertical extent of the cloud-phase and ice-phase optical properties in six case studies measured in the European Arctic during the ACLOUD campaign. Late spring- and summertime stratiform clouds were sampled in situ over pack ice, marginal sea ice zone and open-ocean surface, with cloud top temperatures varying between −15 and −1.5 ∘C. The results show that, although the liquid phase dominates the upper parts of the clouds, the ice phase was frequently observed in the lower parts down to cloud top temperatures as warm as −3.8 ∘C. In the studied vertical cloud profiles, the maximum of average liquid phase microphysical properties, droplet number concentration, effective radius and liquid water content, varied between 23 and 152 cm−3, 19 and 26 µm, 0.09 and 0.63 g m−3, respectively. The maximum of average ice-phase microphysical properties varied between 0.1 and 57 L−1 for the ice number concentration, 40 and 70 µm for the effective radius, and 0.005 and 0.08 g m−3 for the ice water content. The elevated ice crystal number concentrations and ice water paths observed for clouds, with cloud top temperatures between −3.8 and −8.7 ∘C can be likely attributed to secondary ice production through rime splintering. Low asymmetry parameters between 0.69 and 0.76 were measured for the mixed-phase ice crystals with a mean value of 0.72. The effect of the ice-phase optical properties on the radiative transfer calculations was investigated for the four cloud cases potentially affected by secondary ice production. Generally the choice of ice-phase optical properties only has a minor effect on the cloud transmissivity and albedo, except in a case where the ice phase dominated the upper cloud layer extinction. In this case, cloud albedo at solar wavelengths was increased by 10 % when the ice phase was given its measured optical properties instead of treating it as liquid phase. The presented results highlight the importance of accurate vertical information on cloud phase for radiative transfer and provide a suitable data set for testing microphysical parameterizations in models.

Improvement of research methodology mesostructures of atmospheric fronts on the basis of ground­based microwave radiometry

The paper considers the some results of experimental studies of the mesoscale structure of atmospheric fronts using a ground-based microwave water vapor radiometer. A methodology for studying the mesoscale structure of atmospheric fronts is described, which includes two stages: the stage of syn- optic (frontological) analysis and the stage of mesoscale analysis based on measurements of atmospheric moisture and cloud liquid water content using a microwave water vapor radiometer. The application of the methodology is demonstrated by the example of the analysis of the results of observation of the case of the passage of warm and cold fronts through the Leningrad region on September 9—14, 2020. Based on the analysis of the results of previous studies, the features of changes in the characteristics of moisture content during the passage of atmospheric fronts are generalized. The growth of the atmospheric water vapor and cloud liquid water content is delayed relative to the appearance of harbingers of a warm cloud front of the upper tier. The growth of moisture content characteristics has a wave-like character, which can be explained by the manifestation of the strip mesostructure of the front. Estimates of the characteristic scales of spatial heterogeneities in the structure of atmospheric fronts for the area under consideration differ from similar characteristics obtained by P. Hobbs for the northeastern coast of North America. In the course of mesoscale analysis, the type of atmospheric front crossing the observation point can be clarified. The results obtained determine the prospects for improving the methods of diagnostics and current forecasting of dangerous weather phenomena during the passage of atmospheric fronts using ground-based microwave radiometers