Dust Ice Research Articles

Evaluating marine dust records as templates for optical dating of Oldest Ice

Abstract. The continuous ice core record extends 800 000 years into the past, covering the period of 100 000-year glacial cycles but not the transition from 40 000-year glacial cycles (the mid-Pleistocene transition, 1.2–0.7 million years ago). A primary goal of the International Partnerships in Ice Core Sciences is therefore to retrieve a 1.5-million-year-old continuous ice core, increasing our understanding of this major change in the climate system and thus of fundamental climate forcings and feedbacks. However, complex glacial processes, limited bedrock data, and young basal ice in previous cores necessitate careful reconnaissance studies before extracting a full core. Ice borehole optical logging reflects the ice dust content and may be used to date ice quickly and inexpensively if a reference record is known. Here we explore the relationship between ice dust records and well-dated marine dust records from sediment cores in the southern Atlantic and Pacific oceans, which lie along paths of dust sources to Antarctica. We evaluate how representative these records are of Antarctic dust both through the existing ice core record and during the older target age range, suggesting that a newly published 1.5-million-year record from Site U1537 near South America is likely the most robust predictor of the Oldest Ice dust signal. We then assess procedures for rapid dating of potential Oldest Ice sites, noting that the ability to detect dating errors is an essential feature. We emphasize that ongoing efforts to identify, recover, date, and interpret an Oldest Ice core should use care to avoid unfounded assumptions about the 40 kyr world based on the 100 kyr world.

Diurnal and seasonal variations of orographic clouds in the Tharsis region with EMM/EXI observations and the Mars Planetary Climate Model

The diurnal and seasonal variations of orographic water ice clouds in the Tharsis region have been investigated with EXI observations for MY 36 and 37. In order to provide context, meteorological fields from the Mars PCM (Mars Planetary Climate Model led by Laboratoire de Météorologie Dynamique Paris, France) have been incorporated. These fields include water ice column, atmospheric temperature, meteorological winds, water vapor, and dust mixing ratio. The diurnal cycle has been studied for sunlit hours (6 am–6 pm) by sampling data into 5 local time bins. Both the EXI observations and the Mars PCM underscore the significant role plays by diurnal thermal tides in controlling the thickness and existence of water ice clouds in the Tharsis region. During Spring and Summer, water ice clouds form in the morning and late-afternoon hours and exhibit greater thickness compared to those that form during the afternoon, primarily due to the influence of thermal tides. During Fall and Winter, water ice clouds are typically observed in the Arsia Mons region, occasionally extending to the Pavonis Mons region. During the Fall and Winter seasons, the clouds that form are mostly thin and have a tendency to develop in the afternoon hours, while the morning hours typically remain cloud-free or exhibit extremely thin clouds. This phenomenon can be attributed to a combination of factors, including the existence of cold temperature zones at higher altitudes formed by the influence of strong trade winds and the impact of diurnal thermal tides. According to the Mars PCM, water ice clouds typically form at altitudes below 25 km during Spring and Summer, whereas during Fall and Winter, cloud formation occurs at altitudes above 25 km.

Quasi-equilibrium chemical evolution in starless cores

ABSTRACT The chemistry of H2O, CO, and other small molecular species in an isolated pre-stellar core, L1544, has been assessed in the context of a comprehensive gas-grain chemical model, coupled to an empirically constrained physical/dynamical model. Our main findings are (i) that the chemical network remains in near equilibrium as the core evolves towards star formation and the molecular abundances change in response to the evolving physical conditions. The gas-phase abundances at any time can be calculated accurately with equilibrium chemistry, and the concept of chemical clocks is meaningless in molecular clouds with similar conditions and dynamical time-scales, and (ii) A comparison of the results of complex and simple chemical networks indicates that the abundances of the dominant oxygen and carbon species, H2O, CO, C, and C+ are reasonably approximated by simple networks. In chemical equilibrium, the time-dependent differential terms vanish, and a simple network reduces to a few algebraic equations. This allows rapid calculation of the abundances most responsible for spectral line radiative cooling in molecular clouds with long dynamical time-scales. The dust ice mantles are highly structured and the ice layers retain a memory of the gas-phase abundances at the time of their deposition. A complex (gas-phase and gas-grain) chemical structure therefore exists, with cosmic-ray induced processes dominating in the inner regions. The inferred H2O abundance profiles for L1544 require that the outer parts of the core and also any medium exterior to the core are essentially transparent to the interstellar radiation field.

Radiative and Microphysical Impacts of the Saharan Dust on Two Concurrent Tropical Cyclones: Danielle and Earl (2010)

AbstractSaharan dust exerts profound impacts on the genesis and intensification of tropical cyclones (TCs). Such impacts on various stages of the TCs have yet to be explored. In this study, we utilize the Cloud‐Resolving weather research and forecasting model (WRF) to investigate the relative importance of the microphysical and radiative effects of dust on two hurricanes (Earl and Danielle) at different life stages under similar dynamical conditions in 2010. Both TCs were embedded in a dusty environment throughout their lifetime. A new dust ice nucleation scheme was implemented into the aerosol‐aware Texas A&M University two‐moment microphysical scheme in WRF. Moreover, the dust radiative effect was included in the Goddard Shortwave Scheme of WRF. Our sensitivity experiments show that the radiative effect of dust (DRAD) amplified the mid‐level ridge in the Central Atlantic Ocean through temperature perturbation, changing the tracks of Danielle and Earl. Further analyses reveal an early shift of Danielle's maximum intensity for 12 hours but a significantly suppressed Earl in DRAD. In addition, the microphysical effect of dust had little impact on the large‐scale dynamical fields and storm tracks. The inclusion of dust as ice nucleation particles results in more variations in the intensity of Danielle and Earl than in other scenarios. This is owing to the higher maximum diabatic heating rate in the rainband region that perturbs the size of the TC. This study shows the dominant dust radiative effects on both intensity and track of the storm. In addition, there is evidence that dust suppresses the early stage TC but provides favorable conditions for matured TC. Both findings have profound implications for hurricane forecast and address the importance of accounting for detailed cloud microphysics and aerosol‐TC interactions in the operational forecasting models.

Determination of the Branching Ratio of CH3OH + OH Reaction on Water Ice Surface at 10 K

The CH3O and CH2OH radicals can be important precursors of complex organic molecules (COMs) in interstellar dust. The COMs presumably originating from these radicals were abundantly found in various astronomical objects. Because each radical leads to different types of COMs, determining the abundance ratio of CH3O to CH2OH is crucial for a better understanding of the chemical evolution into various COMs. Recent work suggested that the reaction between CH3OH and OH on ice dust plays an important role in forming CH3O and CH2OH radicals. However, quantitative details on the abundance of these radicals have not been presented to date. Herein, we experimentally determined the branching ratio (CH3O/CH2OH) resulting from the CH3OH + OH reaction on the water ice surface at 10 K to be 4.3 ± 0.6. Furthermore, the CH3O product in the reaction would participate in subsequent diffusive reactions even at a temperature as low as 10 K. This fact should provide critical information for COMs formation models in cold molecular clouds.

Radial compositional profile of Saturn's E ring indicates substantial space weathering effects

Abstract Saturn's large and diffuse E ring is populated by microscopic water ice dust particles, which originate from the Enceladus plume. Cassini’s Cosmic Dust Analyser sampled these ice grains, revealing three compositional particle types with different concentrations of salts and organics. Here, we present the analysis of CDA mass spectra from several orbital periods of Cassini, covering the region from interior to Enceladus’ orbit to outside the orbit of Rhea, to map the distribution of the different particle types throughout the radial extent of the E ring. This will provide a better understanding of the potential impact of space weathering effects on to these particles, as the ice grains experience an increasing exposure age during their radially outward migration. In this context, we report the discovery of a new ice particle type (Type 5), which produces spectra indicative of very high salt concentrations, and which we suggest to evolve from less-salty Enceladean ice grains by space weathering. The radial compositional profile, now encompassing four particle types, reveals distinct radial variations in the E ring. At the orbital distance of Enceladus our results are in good agreement with earlier compositional analyses of E ring ice grains in the moon's vicinity. With increasing radial distance to Saturn however, our analysis suggests a growing degree of space weathering and considerable changes to the spatial distribution of the particle types. We also find that the proportion of Type 5 grains – peaking near Rhea's orbit – probably reflects particle charging processes in the E ring.

Laboratory experiments on the sublimation of methane through ice dust layers and applications to cometary activity

Context. Comets are small celestial bodies made of ice, dust, and rock that orbit the Sun. Understanding their behavior as they warm up at perihelion unveils many pieces of information about the interior and general morphology of the ices hidden under the dust. Aims. The goal of this research is to study the sublimation of CH4 through amorphous solid water (ASW), with a focus on the structural changes in water and the influence of a layer of indene (as a proxy of the crust) during a period of thermal processing, which we use in a controlled laboratory setting to simulate cometary environments. Methods. Ices at a CH4/H2O abundance ratio of about 0.01 are deposited and layered, or co-deposited, at 30 K and are heated until 200 K (or 140 K) with a ramp of either 1 or 5 K min−1. We use mass spectrometry and infrared spectroscopy to analyze the results. Results. Depending on the heating ramp and type of deposition, the sublimation of methane through ASW varies, being lower in intensity and higher in temperature when the co-deposited structure is considered. When two temperature cycles are applied, the second one sees less intense CH4 desorptions. When indene is placed above the ice mixtures, we find that the thicker its layer, the later the methane desorption. However, this later desorption sees a greater quantity of methane released due to water reorganization and higher desorbed material pressure. Conclusions. The structural changes of water ice drive volatile and hyper-volatile desorption because of the transition from high to low intrinsic density and transformation from amorphous to crystalline. This desorption indicates that such material has been deposited at low temperatures in agreement with previous theories on cometary ices formed in the pre-stellar cloud. During the two temperature cycles of our experiments, most of the released material is seen to be pristine and the processed part, if any, is of a negligible quantity, in agreement with dust-rock cometary studies.

Insights into protective performance of CoCrNi medium entropy alloy coating subjected to supersonic micro-ballistic impact

Medium- and high-entropy alloys (MEAs and HEAs) coatings have attracted increasing attention owing to their exceptional mechanical properties and potential applications in structures protective from supersonic microparticle impact. However, there are no experimental insights into their protective performance. In this study, we fabricated high-quality amorphous CoCrNi MEA coatings with a thickness of 4.5 μm on the rigid and flexible substrates through ion beam-assisted deposition. Based on nanoindentation and laser-induced supersonic microparticle impact experiments, the mechanical properties and protective performance of the CoCrNi MEA coating were characterized and compared with those of the aluminum and copper coating. The results show that the CoCrNi MEA coating exhibits a high hardness of 9.7 GPa and an elastic modulus of 146.8 GPa. Under the supersonic impact, the CoCrNi MEA coating shows high coefficient of restitution, low rebound-to-fracture transition velocity, and small impact-mode ratios. The impact-mode ratios of the CoCrNi MEA coating subjected to microparticles of different materials further indicate that the CoCrNi MEA coating can efficiently withstand the high-velocity impact of most metallic particles except tungsten ones. Our work provides direct experimental insights into the excellent impact resistance of CoCrNi MEA coatings, which holds a great promise for improving the reliability and durability of equipment subjected to high-speed collisions of solid particles entrained within the air such as ice and sand dust.

Outgassing of ice agglomerates

In this work we present the experimental verification of different approaches to calculate the rate of the outgassing of cometary analogues. We investigated both new, and known formulations applicable for the mass flux of water vapor from mixtures of ice agglomerates. For the purpose of the verification we performed experiments using samples composed of different ice agglomerates. We tested both samples made of approximately uniform agglomerates and samples composed of agglomerates of hierarchical structure. The largest agglomerates have diameters about one centimeter. All experiments were performed in vacuum. We have found, that at the temperature above 200 K the pressure of vapor between agglomerates is close to the pressure of the phase equilibrium and exhibits some dependence on the temperature. We propose the appropriate functions. In addition, we present the method of calculating the lifetime of large centimeter sized porous ice–dust particles present in cometary comae.

Extremely High Concentrations of Ice Particles in East Asian Dust‐Infused Baroclinic Storm (DIBS) Cirrus Shield: Dominant Role of Dust Ice Nucleation Effect

AbstractActing as efficient ice‐nucleating particles, dust particles can affect cirrus cloud properties through heterogeneous nucleation. A dust‐infused baroclinic storm (DIBS) over East Asia in May 2017 was examined using satellite observations and the Weather Research and Forecasting model coupled with chemistry (WRF‐Chem) to study the dust effects on cirrus clouds. Satellite observations showed that the ice number concentration (Nice) was extremely high, exceeding 1–10 cm−3 at the cirrus shield of the DIBS, and the ice effective radius (rei) was about 10–30 μm. An aerosol‐aware heterogeneous ice nucleation parameterization (Ullrich et al., 2017, https://doi.org/10.1175/jas-d-16-0074.1) was implemented into WRF‐Chem to explore the formation mechanism of such a high Nice. The simulated Nice from Ullrich17 was 1–2 orders of magnitude higher than that from the default scheme (Cooper, 1986, https://doi.org/10.1007/978-1-935704-17-1_4), and the rei was 2–3 times smaller. The results from Ullrich17 were more consistent with satellite observations, which can be attributed to the enhanced deposition nucleation from the high dust concentrations. Our results demonstrated that the extremely high Nice could be fully explained by the heterogeneous nucleation of dust particles in DIBS. A conceptual framework is proposed to explain the dust‐cloud interactions in DIBS. This study confirms the significant dust effects on cirrus clouds in DIBS and highlights the importance of using aerosol‐aware ice nucleation parameterizations in modeling cirrus clouds when the dust is present.

Analysis of the retrofitting of a universal vacuum cryogenic spectrophotometer

The paper considers the modernization of the methodology for studying astrophysical ice and cold interstellar dust. An experimental method of physical modeling using a vacuum cryogenic installation is presented. The nodes of the universal vacuum cryogenic spectrophotometer where it is necessary to modernize, retrofit for the subsequent improvement of measuring capabilities in scientific research are considered in detail. The IR spectra of polystyrene were obtained on the IRS-29 and FSM 2203 spectrometers, the results of the obtained characteristic absorption bands were compared with the values of the reference spectrum of polystyrene, and the expanded uncertainty was calculated. To assess the accuracy of the measurement results, we calculated the expanded uncertainty according to the IR spectrometer calibration procedure. The wavenumber scale calibration uncertainty was determined by direct measurements as the difference between the wavenumber value corresponding to the maximum ordinate of the absorption line of a standard polystyrene film sample. In this work, an analysis of the completed retrofitting of a universal vacuum cryogenic spectrophotometer was carried out. N2O spectra were taken, obtained at a temperature of 16 K in the wave number range of IR spectrometers from 370 to 4200 1/cm with the designation of the corresponding absorption bands. The studies carried out in this work are aimed at improving the accuracy of measurements, which guarantees and improves the quality of scientific research.

Study on the Parameters of Ice Clouds Based on 1.5 µm Micropulse Polarization Lidar

Dust aerosols can participate in the heterogeneous nucleation process as effective ice nucleation particles, thus changing the physical properties of clouds. In this paper, we used an eye-safe 1550 nm micropulse polarization single photon lidar combined with meteorological stations, HYSPLIT backward trajectory analysis, ERA5 reanalysis data, CALIPSO, Himawari-8 and Terra-MODIS satellite data to compare the difference in cloud characteristics between dust and clean cirrus cases in Jinan from 26–29 March 2022. The study found that the aerosol affected the cloud effective radius, and the cloud top temperature impacted the properties of depolarization of dust ice clouds. According to the statistical results of the upper and lower quartiles, the depolarization ratio (DPR) range of dust cirrus on 26 March was 0.46–0.49, a similar range to the clean cirrus, while that of dust cirrus on 27 March was 0.54–0.59, which seemed much larger. Different height and temperature conditions lead to differences in the habits of ice crystals in clouds, thus changing the DPR. However, the range of the DPR between clean cirrus and dust cirrus showed no obvious difference, as the former was 0.43–0.53 and the latter was 0.46–0.59. Under the condition of higher aerosol loading, the lidar range-corrected signal (RCS) of cirrus clouds was stronger, and the cloud effective radius was 48 μm, larger than that of clean cirrus (32 μm). This may be the effect of dust on the microphysical properties of clouds. This study discusses the indirect effects of dust aerosols on cirrus clouds and the underlying mechanisms from the perspectives of microphysics and optics, which can provide more references for urban air pollution processes and aerosol-cloud interactions.

Mechanism for the Efficient Homogeneous Nucleation of Ice in a Weakly Ionized, Ultracold Plasma

It is proposed that the rapid observed homogeneous nucleation of ice dust in a cold, weakly ionized plasma depends on the formation of hydroxide (OH−) by fast electrons impacting water molecules. These OH− ions attract neutral water molecules because of the high dipole moment of the water molecules and so hydrates of the form (OH)−(H2O) n are formed. The hydrates continuously grow in the cold environment to become macroscopic ice grains. These ice grains are negatively charged as a result of electron impact and so continue to attract water molecules. Because hydroxide is a negative ion, unlike positive ions, it does not suffer recombination loss from collision with plasma electrons. Recombination with positive ions is minimal because positive ions are few in number (weak ionization) and slow-moving as result of being in thermal equilibrium with the cold background gas.

Dust coagulation and fragmentation in a collapsing cloud core and their influence on non-ideal magnetohydrodynamic effects

ABSTRACT We determine the time-evolution of the dust particle size distribution during the collapse of a cloud core, accounting for both dust coagulation and dust fragmentation, to investigate the influence of dust growth on non-ideal magnetohydrodynamic (MHD) effects. The density evolution of the collapsing core is given by a one-zone model. We assume two types of dust model: dust composed only of silicate (silicate dust) and dust with a surface covered by H2O ice (H2O ice dust). When only considering collisional coagulation, the non-ideal MHD effects are not effective in the high-density region for both the silicate and H2O ice dust cases. This is because dust coagulation reduces the abundance of small dust particles, resulting in less efficient adsorption of charged particles on the dust surface. For the silicate dust case, when collisional fragmentation is included, the non-ideal MHD effects do apply at a high density of nH > 1012 cm−3 because of the abundant production of small dust particles. On the other hand, for the H2O ice dust case, the production of small dust particles due to fragmentation is not efficient. Therefore, for the H2O ice dust case, non-ideal magnetohydrodynamic effects apply only in the range nH ≳ 1014 cm−3, even when collisional fragmentation is considered. Our results suggest that it is necessary to consider both dust collisional coagulation and fragmentation to activate non-ideal magnetohydrodynamic effects, which should play a significant role in the star and disc formation processes.

Low-speed Impacts into Ice–Dust Granular Mixtures

We present the results of a series of laboratory low-speed impacts (< 4 m s−1) of centimeter-sized spherical projectiles into simulated dry and icy regolith samples. The target material was comprised of JSC-1 (Johnson Space Center) lunar simulant grains in the size range 100–250 μm, mixed with similar-sized water ice grains. Impacts were performed under vacuum, either at room temperature for JSC-1 samples or at cryogenic temperatures (<150 K) for icy mixtures. We measured the ejecta masses from a collection plate and impact crater dimensions from post-impact crater photographs. We find that both the ejecta masses and crater diameters followed trends predicted by established scaling laws, albeit with different fitting parameters, and we were able to fit a strength regime π scaling to our measured crater diameters. The water ice in our target material took two forms: grains mixed with the regolith grains and frost from air condensation coating regolith grains. In both cases, the presence of water ice in the sample led to lower ejected masses and smaller crater sizes. In addition, our measured crater sizes were several orders of magnitude larger than expected for impacts into solid rock or water ice. Using our measured scaling parameters, we applied our findings to a planetary context for the study of secondary craters on icy moons, as well as eroding collisions occurring in Saturn’s rings. We found that the deviation of our measurements from solid targets and from commonly used scaling parameters allowed us to reconcile our measurements with the models in both cases.

Black carbon, organic carbon, and mineral dust in South American tropical glaciers: A review

Tropical glaciers are extremely sensitive to changes of climate variables. Their response to climate change is complex and depends on multiple mechanisms affecting their mass and energy balance, including deposition of light absorbing particles (LAPs) from the atmosphere on snow and ice. Such particles can reduce glaciers surface albedo, thus enhancing the melting process. LAPs include carbonaceous particles (black carbon - BC and organic carbon - OC) and mineral dust aerosol (MDA). Although their relevance in global cryosphere, LAPs observations in the Andes tropical glacier areas are limited and sparse. This review aims at providing a critical evaluation of available data on LAPs in South America tropical glaciers, and highlights research gaps that will help to improve our understanding of natural processes and anthropogenic emissions impacts on the cryosphere of the region. In South American tropical glaciers, LAPs measurements in surface snow are mainly focused in the Cordillera Blanca and limited information are available about their chemical composition (carbonaceous or mineral components), while dust ice core records have been investigated in several sectors of the Andes, including in the Cordillera Blanca, Cordillera Oriental, and Cordillera Real. Remote and field observations in South American tropical glaciers indicate that LAPs might explain a significant fraction of snow albedo variability, however snow albedo reduction from modelling studies varies significantly depending on LAPs concentration and composition. Carbonaceous LAPs sources in South America are dominated by BC emissions from open fires, linked to agricultural and land clearing activities, peaking in the southern hemisphere dry season (August–October). Natural and anthropogenic dust emissions are potentially relevant contributors of LAPs on the Andes glaciers, as well. Satellite and in-situ measurements were deployed to investigate transport episodes of carbonaceous and mineral particles from lower altitudes towards the Andean glaciers. Nevertheless, the small number of atmospheric records of BC, OC, and MDA does not allow a systematic understanding of transport and deposition processes of such species in the region. • LAPs could account for up to 22% of albedo reduction in the Andes. • Knowledge of LAP composition is needed to understand snow albedo change. • LAPs atmospheric and cryosphere data in the Andes are extremely limited. • Relative contribution of natural and anthropogenic dust to snow LAPs is unclear. • Accurate LAP source definition requires understanding of transport and deposition.

Accumulation of windblown sand in impact craters on Mars

Abstract Loose sand, blown away from source regions by winds, is transported across Mars's surface into sand sheets and dunes and accumulates within topographic sinks. In the absence of plate tectonics, impact craters constitute a dominant sink for windblown sediments on Mars today. We analyzed the volume of all mapped eolian sands in martian craters &amp;gt;1 km in diameter to reveal spatiotemporal patterns of sediment accumulation on the planet's surface. We combined our results with global climate simulations, maps of depth to the ice table and dust cover, as well as lithologic and age information of the underlying geologic units, to better understand the controls on intracrater sand accumulation rates. We find that crater age, latitude, and lithology influence the accumulation rate of windblown sand and, notably, that it is enhanced in mechanically weaker substrates, high-latitude craters (suggesting that modern cryogenic processes may enhance sand production), and in Late Noachian and Early Hesperian craters (possibly hinting at increased erosion rates at that time).

Infrared Spectroscopic Survey of the Quiescent Medium of Nearby Clouds. II. Ice Formation and Grain Growth in Perseus and Serpens

The properties of dust change during the transition from diffuse to dense clouds as a result of ice formation and dust coagulation, but much is still unclear about this transformation. We present 2–20 μm spectra of 49 field stars behind the Perseus and Serpens Molecular Clouds and establish relationships between the near-infrared continuum extinction (A K) and the depths of the 9.7 μm silicate (τ 9.7) and 3.0 μm H2O ice (τ 3.0) absorption bands. The τ 9.7/A K ratio varies from large, diffuse interstellar medium-like values (∼0.55), to much lower ratios (∼0.26). Above extinctions of A K ∼ 1.2 (A V ∼ 10; Perseus, Lupus, dense cores) and ∼2.0 (A V ∼ 17; Serpens), the τ 9.7/A K ratio is lowest. The τ 9.7/A K reduction from diffuse to dense clouds is consistent with a moderate degree of grain growth (sizes up to ∼0.5 μm), increasing the near-infrared color excess (and thus A K), but not affecting the ice and silicate band profiles. This grain growth process seems to be related to the ice column densities and dense core formation thresholds, highlighting the importance of density. After correction for Serpens foreground extinction, the H2O ice formation threshold is in the range of A K = 0.31–0.40 (A V = 2.6–3.4) for all clouds, and thus grain growth takes place after the ices are formed. Finally, abundant CH3OH ice (∼21% relative to H2O) is reported for 2MASSJ18285266+0028242 (Serpens), a factor of >4 larger than for the other targets.

Assessing the benefits of Imaging Infrared Radiometer observations for the CALIOP version 4 cloud and aerosol discrimination algorithm

Abstract. The features detected in monolayer atmospheric columns sounded by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and classified as cloud or aerosol layers by the CALIOP version 4 (V4) cloud and aerosol discrimination (CAD) algorithm are reassessed using perfectly collocated brightness temperatures measured by the Imaging Infrared Radiometer (IIR) aboard the same satellite. Using the IIR's three wavelength measurements of layers that are confidently classified by the CALIOP CAD algorithm, we calculate two-dimensional (2-D) probability distribution functions (PDFs) of IIR brightness temperature differences (BTDs) for different cloud and aerosol types. We then compare these PDFs with 1-D radiative transfer simulations for ice and water clouds and dust and marine aerosols. Using these IIR 2-D BTD signature PDFs, we develop and deploy a new IIR-based CAD algorithm and compare the classifications obtained to the results reported by the CALIOP-only V4 CAD algorithm. IIR observations are shown to be able to identify clouds with a good accuracy. The IIR cloud identifications agree very well with layers classified as confident clouds by the V4 CAD algorithm (88 %). More importantly, simultaneous use of IIR information reduces the ambiguity in a notable fraction of “not confident” V4 cloud classifications. 28 % and 14 % of the ambiguous V4 cloud classifications are reclassified more appropriately as confident cloud layers through the use of the IIR observations in the tropics and in the midlatitudes, respectively. IIR observations are of relatively little help in deriving high-confidence classifications for most aerosols, as the low altitudes and small optical depths of aerosol layers yield IIR signatures that are similar to those of clear skies. However, misclassifications of aerosol layers, such as dense dust or elevated smoke layers, by the V4 CAD algorithm can be corrected to cloud layer classification by including IIR information. 10 %, 16 %, and 6 % of the ambiguous V4 dust, polluted dust, and tropospheric elevated smoke, respectively, are found to be misclassified cloud layers by the IIR measurements.

A Maritime Cloud-Detection Method Using Visible and Near-Infrared Bands over the Yellow Sea and Bohai Sea

Accurate cloud-masking procedures to distinguish cloud-free pixels from cloudy pixels are essential for optical satellite remote sensing. Many studies on satellite-based cloud-detection have been performed using the spectral characteristics of clouds in terms of reflectance and temperature. This study proposes a cloud-detection method using reflectance in four bands: 0.56 μm, 0.86 μm, 1.38 μm, and 1.61 μm. Methodologically, we present a conversion relationship between the normalized difference water index (NDWI) and the green band in the visible spectrum for thick cloud detection using moderate-resolution imaging spectroradiometer (MODIS) observations. NDWI consists of reflectance at the 0.56 and 0.86 μm bands. For thin cloud detection, the 1.38 and 1.61 μm bands were applied with empirically determined threshold values. Case study analyses for the four seasons from 2000 to 2019 were performed for the sea surface area of the Yellow Sea and Bohai Sea. In the case studies, the comparison of the proposed cloud-detection method with the MODIS cloud mask (CM) and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation data indicated a probability of detection of 0.933, a false-alarm ratio of 0.086, and a Heidke Skill Score of 0.753. Our method demonstrated an additional important benefit in distinguishing clouds from sea ice or yellow dust, compared to the MODIS CM products, which usually misidentify the latter as clouds. Consequently, our cloud-detection method could be applied to a variety of low-orbit and geostationary satellites with 0.56, 0.86, 1.38, and 1.61 μm bands.