Cloud Ice Water Research Articles

Warm early Mars surface enabled by high-altitude water ice clouds

Despite receiving just 30% of the Earth's present-day insolation, Mars had water lakes and rivers early in the planet's history, due to an unknown warming mechanism. A possible explanation for the >102-y-long lake-forming climates is warming by water ice clouds. However, this suggested cloud greenhouse explanation has proved difficult to replicate and has been argued to require unrealistically optically thick clouds at high altitudes. Here, we use a global climate model (GCM) to show that a cloud greenhouse can warm a Mars-like planet to global average annual-mean temperature ([Formula: see text]) ∼265 K, which is warm enough for low-latitude lakes, and stay warm for centuries or longer, but only if the planet has spatially patchy surface water sources. Warm, stable climates involve surface ice (and low clouds) only at locations much colder than the average surface temperature. At locations horizontally distant from these surface cold traps, clouds are found only at high altitudes, which maximizes warming. Radiatively significant clouds persist because ice particles sublimate as they fall, moistening the subcloud layer so that modest updrafts can sustain relatively large amounts of cloud. The resulting climates are arid (area-averaged surface relative humidity ∼25%). In a warm, arid climate, lakes could be fed by groundwater upwelling, or by melting of ice following a cold-to-warm transition. Our results are consistent with the warm and arid climate favored by interpretation of geologic data, and support the cloud greenhouse hypothesis.

Abnormal Phase Structure of Thermal Tides During Major Dust Storms on Mars: Implications for the Excitation Source of High‐altitude Water Ice Clouds

AbstractInteractions among the thermal tide, airborne dust, and water ice clouds significantly influence the Martian atmosphere. The absence of a stratosphere on Mars allows easier identification of the thermal tides from observational data than that on Earth, making Mars a natural laboratory to study the tidal excitation and propagation processes. However, the global tidal phase structure and its response to the tidal excitation sources on Mars have not been studied from observations. Here, we present a comprehensive analysis of the phase structure of migrating diurnal tide (DW1) using multi‐local‐time observations of the Mars Climate Sounder. The DW1 phase at low‐to‐mid latitudes shows a downward phase progression, which indicates upward tidal energy and momentum propagation throughout the year but with an apparent hemispheric asymmetry. The entire DW1 phase structure rises and falls with the dust height at the southern mid‐latitudes suggesting a modulation of vertical dust extent on the altitude of the excitation source. During major regional dust storms, the DW1 phase propagates anomalously upward from 10 to 1 Pa in the Southern hemisphere. The Hough analysis suggests that the DW1 in the dust layer can only propagate upward to 10 Pa while the downward propagating mode above 10 Pa may be excited from a high‐altitude source. Evidence suggests that the enhanced high‐altitude water ice clouds could be a potential excitation source for these downward propagating tidal modes. These findings demonstrate how thermal tides can locally behave like inertia‐gravity waves and the importance of water ice clouds to Martian atmospheric dynamics.

Aerosols and Tides in the Martian Tropics During Southern Hemisphere Spring Equinox From Mars Climate Sounder Data

AbstractWe analyze Mars Climate Sounder temperature and aerosol data in the tropics, and use Fourier analysis at different local times to study atmospheric tides and their relation to the dust and water ice distributions. Our results reveal that Mars year (MY) 29 has large amplitude non‐migrating thermal tides during southern hemisphere spring equinox that are not observed at the same local time in any other year. The nighttime temperatures are the most perturbed compared to other years, with strong temperature inversions at 35–55 km altitude. The nighttime water ice cloud structure is strongly influenced by the eastward‐propagating diurnal Kelvin waves 1 and 2. Increased nighttime radiative cooling from regions of thicker clouds results in stronger downwelling above the clouds, leading to increased adiabatic warming and a strengthening of the temperature inversions. The temperatures and water ice clouds at 3:45 a.m. in MY29 more closely resemble those at 5:00 a.m. in other years, suggesting there was a shift in the phase of the diurnal tide. This phase shift, and the large amplitude non‐migrating thermal tides, appear to be related to early dust activity. Two early dust storms occurred in MY29 around the time there was upwelling over the tropics, associated with the Hadley circulation. This likely enabled the dust to be transported to higher altitudes where it has a larger radiative influence. The early dust activity in MY29 also increased the strength of the westward‐propagating non‐migrating thermal tides.

Water Ice Cloud Variability and Multi-epoch Transmission Spectra of TRAPPIST-1e

Abstract The precise characterization of terrestrial atmospheres with the James Webb Space Telescope (JWST) is one of the utmost goals of exoplanet astronomy in the next decade. With JWST’s impending launch, it is crucial that we are well prepared to understand the subtleties of terrestrial atmospheres—particularly ones that we may have not needed to consider before due to instrumentation limitations. In this work we show that patchy ice cloud variability is present in the upper atmospheres of M-dwarf terrestrial planets, particularly along the limbs. Here we test whether these variable clouds will introduce unexpected biases in the multi-epoch observations necessary to constrain atmospheric abundances. Using 3D ExoCAM general circulation models of TRAPPIST-1e, we simulate five different climates with varying pCO2 to explore the strength of this variability. These models are post-processed using NASA Goddard’s Planetary Spectrum Generator and PandExo to generate simulated observations with JWST’s NIRSpec PRISM mode at 365 different temporal outputs from each climate. Assuming the need for 10 transits of TRAPPIST-1e to detect molecular features at great confidence, we then use CHIMERA to retrieve on several randomly selected weighted averages of our simulated observations to explore the effect of multi-epoch observations with variable cloud cover along the limb on retrieved abundances. We find that the variable spectra do not affect retrieved abundances at detectable levels for our sample of TRAPPIST-1e models.

The behavior of high-CAPE (convective available potential energy) summer convection in large-domain large-eddy simulations with ICON

Abstract. Current state-of-the-art regional numerical weather prediction (NWP) models employ kilometer-scale horizontal grid resolutions, thereby simulating convection within the grey zone. Increasing resolution leads to resolving the 3D motion field and has been shown to improve the representation of clouds and precipitation. Using a hectometer-scale model in forecasting mode on a large domain therefore offers a chance to study processes that require the simulation of the 3D motion field at small horizontal scales, such as deep summertime moist convection, a notorious problem in NWP. We use the ICOsahedral Nonhydrostatic weather and climate model in large-eddy simulation mode (ICON-LEM) to simulate deep moist convection and distinguish between scattered, large-scale dynamically forced, and frontal convection. We use different ground- and satellite-based observational data sets, which supply information on ice water content and path, ice cloud cover, and cloud-top height on a similar scale as the simulations, in order to evaluate and constrain our model simulations. We find that the timing and geometric extent of the convectively generated cloud shield agree well with observations, while the lifetime of the convective anvil was, at least in one case, significantly overestimated. Given the large uncertainties of individual ice water path observations, we use a suite of observations in order to better constrain the simulations. ICON-LEM simulates a cloud ice water path that lies between the different observational data sets, but simulations appear to be biased towards a large frozen water path (all frozen hydrometeors). Modifications of parameters within the microphysical scheme have little effect on the bias in the frozen water path and the longevity of the anvil. In particular, one of our convective days appeared to be very sensitive to the initial and boundary conditions, which had a large impact on the convective triggering but little impact on the high frozen water path and long anvil lifetime bias. Based on this limited set of sensitivity experiments, the evolution of locally forced convection appears to depend more on the uncertainty of the large-scale dynamical state based on data assimilation than of microphysical parameters. Overall, we judge ICON-LEM simulations of deep moist convection to be very close to observations regarding the timing, geometrical structure, and cloud ice water path of the convective anvil, but other frozen hydrometeors, in particular graupel, are likely overestimated. Therefore, ICON-LEM supplies important information for weather forecasting and forms a good basis for parameterization development based on physical processes or machine learning.

Indian dust-rain storm: Possible influences of dust ice nuclei on deep convective clouds.

Estimating the influence of dust aerosol on clouds, especially deep convective clouds which is closely related to heavy precipitation, still has large uncertainties due to the lack of adequate direct measurements. In this study, a typical dust storm along with thunderstorm (referred to dust-rain storm), occurred in Northwest India on May 2, 2018, was selected to explore the possible effects of dust aerosol on deep convective cloud by combining a series of satellite retrievals and reanalysis data. Results showed that dust aerosol and moisture were carried to Northwest India by southwesterly wind at 700hPa and easterly wind along south foothill of Himalayas at 850hPa, respectively, and then were lifted to upper level of the cloud by robust updraft induced by the deep convection and secondary circulation driven by the upper-level westerly jet. The injection of dust is likely to transfer supercooled water cloud into ice cloud as effective ice nuclei, hence increasing the cloud ice water path and cloud optical depth but decreasing ice particle radius in the cloud. The latent heat released by this phase-change process would enhance the deep convection and further cause heavy rainfall in northern India by drawing moisture from surrounding region. Although we cannot eliminate the effect of large-scale dynamics, this study highlighted the role of dust aerosol in invigorating the deep convective clouds as ice nuclei, providing observation evidence for the investigation of aerosol-cloud-precipitation interaction.

Mars perihelion cloud trails as revealed by MARCI: Mesoscale topographically focused updrafts and gravity wave forcing of high altitude clouds

Daily, global wide angle imaging of Mars clouds in MARCI (MARs Color Imager, (Malin et al., 2008)) ultraviolet and visible bands reveals the spatial/seasonal distributions and physical characteristics of perihelion cloud trails (PCT); a class of high altitude (40–50 km), horizontally extended (200–1000 km, trending W to WSW) water ice clouds formed over specific southern low-to-mid latitude (5S-40S), mesoscale (∼50 km) locations during the Mars perihelion, southern summer season. PCT were first reported in association with rim regions of Valles Marineris (Clancy et al., 2009). The current study employs MARCI 2007–2011 imaging to sample the broader distributions and properties of PCT; and indicates several distinct locations of peak occurrences, including SW Arsia Mons, elevated regions of Syria, Solis, and Thaumasia Planitia, along Valles Marineris margins, and the NE rim of Hellas Basin. PCT are present over Mars solar longitudes (LS) of 210–310°, in late morning to mid afternoon hours (10 am–3 pm), and are among the brightest and most distinctive clouds exhibited during the perihelion portion of the Mars orbit. Their locations (i.e., eastern margin origins) correspond to strong local elevation gradients, and their timing to peak solar heating conditions (perihelion, subsolar latitudes and midday local times). They occur approximately on a daily basis among all locations identified (i.e., not daily at a single location). Based on cloud surface shadow analyses, PCT form at 40–50 km aeroid altitudes, where water vapor is generally at near-saturation conditions in this perihelion period (e.g. Millour et al., 2014). They exhibited notable absences during periods of planet encircling and regional dust storm activity in 2007 and 2009, respectively, presumably due to reduced water saturation conditions above 35–40 km altitudes associated with increased dust heating over the vertically extended atmosphere (e.g. Neary et al., 2019). PCT exhibit smaller particle sizes (Reff=0.2-0.5μm) than typically exhibited in the lower atmosphere, and incorporate significant fractions of available water vapor at these altitudes. PCT ice particles are inferred to form continuously (over ∼4 h) at their PCT eastern origins, associated with localized updrafts, and are entrained in upper level zonal/meridional winds (towards W or WSW with ∼50 m/s speeds at 40–50 km altitudes) to create long, linear cloud trails. PCT cloud formation is apparently forced in the lower atmosphere (≤10–15 km) by strong updrafts associated with distinctive topographic gradients, such as simulated in mesoscale studies (e.g., Tyler and Barnes, 2015) and indicated by the surface-specific PCT locations. These lower scale height updrafts are proposed to generate vertically propagating gravity waves (GW), leading to PCT formation above ∼40 km altitudes where water vapor saturation conditions promote vigorous cloud ice formation. Recent mapping of GW amplitudes at ∼25 km altitudes, from Mars Climate Sounder 15 μm radiance variations (Heavens et al., 2020) in fact demonstrates close correspondences to the detailed spatial distributions of observed PCT, relative to other potential factors such as surface albedo and surface elevation (or related boundary layer depths).

A self-supervised learning based approach to analyze Martian water–ice cloud properties for planetary atmospheric applications

Currently, Martian water–ice cloud properties, such as wind direction and angular wind velocity, are determined through manual analysis of atmospheric movies taken by the Mars Science Laboratory (MSL, Curiosity). These atmospheric movies, known as Zenith Movies (ZM), have a vertical elevational pointing which allows a direct measurement of wind properties from overhead clouds. However, acquiring this observation requires a significant amount of downlinked data volume which impedes on how often it can be taken. To combat this, an algorithm using Computer Vision (CV) and machine learning has been developed to calculate cloud parameters directly.To determine how well the algorithm performs, it has been tested on a previous data set from Campbell et al. (2020) that manually measured the wind direction and angular distance in ZMs. This data set had a variety of movies with different cloud features. When ZMs had strong features, the algorithm matched well with manual results which shows promising results. However, movies that had either lighting changes, multiple cloud decks or camera artifacts caused the algorithm to perform less well. Therefore the algorithm needs improving to more accurately measure these parameters over an assortment of conditions.

Characteristic features of water ice clouds over Olympus and Arsia Mons using MOM and MRO observations

The present study used the observations from Mars Color Camera (MCC) onboard Mars Orbiter Mission, from the two instruments onboard Mars Reconnaissance Orbiter, i.e., Mars Climate Sounder (MCS) and Mars Color Imager (MARCI), for investigating the water ice cloud appearance over two Martian volcanos, Olympus Mons and Arsia Mons. Indeed, these regions offer an opportunity to explore the dynamical effects related to the orographic clouds and give an idea about their interactions with atmospheric transport. Also, the long-term MCS profile observations are much useful to emphasize the sub-seasonal, seasonal, and interannual variability of clouds at different altitudes. The MCC and MARCI images show a cloud patch over Olympus Mons within the aphelion and a thin cloud trails over Arsia Mons within the perihelion of Mars years. Night-time MCS observations suggest an appearance of thick low altitude clouds within 15–32 ​km height during LS ​= ​35–150° and thin high-altitude clouds within 30–50 ​km height during LS ​= ​225–315°. The profile observations over both the volcanic regions show that the atmospheric temperature variations more strongly control the water ice cloud distribution at lower altitudes during northern hemispheric spring and summer. In contrast, the high altitude thin clouds during southern hemispheric spring and summer are found to be more associated with the elevated dustiness and vertical advection of dust-laden mountain induced regional circulation, as suggested by MarsWRF simulated wind. The appearance of the consistent thick followed by thin clouds during aphelion and perihelion season shows a nearly constant cloud water content of ~0.2 and ~0.05 pr μm. The high or low magnitude of cloud water content could be distinguished from the peak water ice extinction within the column, as observed in the inter-annual variations. However, irrespective of low cloud water content during the second half of the year, the presence of high altitude thin clouds leads to an overall cloud vertical depth (≥30 ​km) higher (mostly visible during the night) than the first half of the year. Comparison of the nighttime appearance of thick clouds (centered at ~20 ​km) during the first half and thin clouds (centered at ~40 ​km) during the second half of the year over two volcanos indicates the suitable atmospheric conditions in the case of the Olympus Mons for the former type clouds and over Arsia Mons for the later. Also, the appearance of thick clouds mostly resembles the consistent and stable aphelion cloud cycle. In contrast, the thin high altitude clouds are more variable and influenced by the vertical advection during the perihelion season. Besides, these high altitude clouds drive the more prominent east-west asymmetry in the cloud abundance over the Arsia Mons region during the perihelion period.

Ice Water Content as a Precursor to Tropical Cyclone Rapid Intensification

AbstractThis study examines how the structure and amount of cloud ice water content are related to rates of tropical cyclone (TC) intensification using CloudSat profiling radar measurements and simulations from the Hurricane Weather Research and Forecasting (HWRF) model. Observational studies have demonstrated the signal of TC intensification in the passive satellite measurements of frozen water concentration. However, the vertical and horizontal resolution of passive satellite observations are limited. CloudSat measurements and HWRF simulations provide high‐resolution data sets of ice water content to better understand its relationship with the rate of TC intensification. It is found that rapidly intensifying TCs have larger ice water content compared to TCs with slower intensification rates. Similar results are obtained even after accounting for the effect of initial TC intensity. Such precursors of rapidly intensifying TCs may be used to better understand and improve the prediction of TC intensification.

Martian cloud climatology and life cycle extracted from Mars Express OMEGA spectral images

A Martian water-ice cloud climatology has been extracted from OMEGA data covering 7 Martian years (MY 26–32) on the dayside. We derived two products, the Reversed Ice Cloud Index (ICIR) and the Percentage of Cloudy Pixels (PCP), indicating the mean cloud thickness and nebulosity over a regular grid (1° longitude × 1° latitude × 1° Ls × 1 h Local Time). The ICIR has been shown to be a proxy of the water-ice column derived from the Mars Climate Database.The PCP confirms the existence and location of the main cloud structures mapped with the ICIR, but also gives a more accurate image of the cloud cover. We observed a more dense cloud coverage over Hellas Planitia, the Lunae Planum region and over large volcanoes (Tharsis volcanoes, Olympus and Elysium Montes) in the aphelion belt.For the first time, thanks to the fact that Mars Express is not in Sun-synchronous orbit, we can explore the clouds diurnal cycle at a given season by combining the seven years of observations. However, because of the eccentric orbit, the temporal coverage remains limited. Identified limitations of the dataset are its small size, the difficult distinction between ice clouds and frosts, and the impact of surface albedo on data uncertainty. We could nevertheless study the diurnal cloud life cycle by averaging the data over larger regions: from specific topographic features (covering a few degrees in longitude and latitude) up to large climatic bands (covering all longitudes). We found that in the tropics (25°S – 25°N) around northern summer solstice, the diurnal thermal tide modulates the abundance of clouds, which is reduced around noon (Local Time). At northern midlatitudes (35°N – 55°N), clouds corresponding to the edge of the north polar hood are observed mainly in the morning and around noon during northern winter (Ls = 260° – 30°). Over Chryse Planitia, low lying morning fogs dissipate earlier and earlier in the afternoon during northern winter. Over Argyre, clouds are present over all daytime during two periods, around Ls = 30° and 160°.

Toward Understanding the Simulated Phase Partitioning of Arctic Single‐Layer Mixed‐Phase Clouds in E3SM

AbstractArctic mixed‐phase clouds simulated by the U.S. Department of Energy (DOE) Energy Exascale Earth System Model (E3SM) Atmosphere Model version 1 (EAMv1) are found to be overly dominated by supercooled liquid with little ice production. Sensitivity experiments using the short‐term hindcast approach are performed to isolate the impact of several new parameterizations on the simulated mixed‐phase clouds in EAMv1. These include the Classical Nucleation Theory (CNT) ice nucleation scheme, the Cloud Layer Unified By Binormals (CLUBB) parameterization, and the updated Morrison and Gettelman microphysics scheme (MG2). Results are compared to the DOE's Atmospheric Radiation Measurement (ARM) Mixed‐Phase Arctic Cloud Experiment (M‐PACE) observations. It is found that all of these new parameterizations are responsible for the decrease of cloud ice water content in EAMv1 simulated single‐layer mixed‐phase clouds. A budget analysis of detailed cloud microphysical processes suggests that a lack of initial ice particles from ice nucleation or convective detrainment strongly diminishes the cloud ice water content through the subsequent ice mass growth processes. Reduced heterogeneous ice nucleation by CNT at temperatures warmer than −15°C along with negligible ice processes in CLUBB are primarily responsible for the problem. Because the use of MG2 does not impact initial ice formation, the MG2 cloud microphysics is not the primary reason for the underestimate of cloud ice. However, using MG2 leads to a lower total ice mass due to a higher accretion rate of liquid droplets by rain drops and a lower ice mass growth rate.

Simulation of the 2018 Global Dust Storm on Mars Using the NASA Ames Mars GCM: A Multitracer Approach

AbstractGlobal dust storms are the most thermodynamically significant dust events on Mars. The most recent of these events occurred in 2018. Although it was monitored by several spacecraft in orbit and on the surface, many questions remain regarding its onset, expansion and decay. Here, we model the 2018 event with the National Aeronautics and Space Administration (NASA) Ames Mars Global Climate Model in order to better understand the evolution of the storm. Our results highlight a mechanism for the expansion of the storm: the initial equatorial regional storm creates a zonal atmospheric temperature gradient causing strong equatorial eastward winds and thus rapid eastward transport of dust and subsequent lifting. The model shows rapid back and forth transfer of dust between western and eastern hemispheres reservoirs, which may also play an important role in the storm's development through teleconnections involving replenishment of surface dust. The model also shows that gigantic dust plumes occur during the storm's mature phase, injecting dust up to 80 km. Our analysis shows that their upward motion in the atmosphere is due to the ascending branches of Hadley cells, whose intensity is reinforced during the storm with increasing dustiness. We show that the global atmospheric warming during the storm cause vapor and water ice clouds to migrate to higher altitudes, in line with recent observations. Finally, we find that the choice of effective radius for the lifted dust particle size distribution impacts the intensity of the Hadley circulation and could explain some of the differences obtained between model results and observations.

Strong Variability of Martian Water Ice Clouds During Dust Storms Revealed From ExoMars Trace Gas Orbiter/NOMAD

AbstractObservations of water ice clouds and aerosols on Mars can provide important insights into the complexity of the water cycle. Recent observations have indicated an important link between dust activity and the water cycle, as intense dust activity can significantly raise the hygropause, and subsequently increase the escape of water after dissociation in the upper atmosphere. Here present observations from Nadir and Occultation for MArs Discovery/Trace Gas Orbiter that investigate the variation of water ice clouds in the perihelion season of Mars year 34 (April 2018–2019), their diurnal and seasonal behavior, and the vertical structure and microphysical properties of water ice and dust. These observations reveal the recurrent presence of a layer of mesospheric water ice clouds subsequent to the 2018 global dust storm. We show that this layer rose from 45 to 80 km in altitude on a time scale of days from heating in the lower atmosphere due to the storm. In addition, we demonstrate that there is a strong dawn‐dusk asymmetry in water ice abundance, related to nighttime nucleation and subsequent daytime sublimation. Water ice particle sizes are retrieved consistently and exhibit sharp vertical gradients (from 0.1 to 4.0 μm), as well as mesospheric differences between the global dust storm (<0.5 μm) and the 2019 regional dust storm (1.0 μm), which suggests differing water ice nucleation efficiencies. These results form the basis to advance our understanding of mesospheric water ice clouds on Mars, and further constrain the interactions between water ice and dust in the middle atmosphere.

Martian Water Ice Clouds During the 2018 Global Dust Storm as Observed by the ACS‐MIR Channel Onboard the Trace Gas Orbiter

AbstractThe Atmospheric Chemistry Suite (ACS) instrument onboard the ExoMars Trace Gas Orbiter (TGO) European Space Agency‐Roscosmos mission began science operations in March 2018. ACS Mid‐InfraRed (MIR) channel notably provides solar occultation observations of the Martian atmosphere in the 2.3‐ to 4.2‐ m spectral range. Here, we use these observations to characterize water ice clouds before and during the MY 34 Global Dust Storm (GDS). We developed a method to detect water ice clouds with mean particle size 2 m and applied it to observations gathered between and . We observe a shift in water ice cloud maximum altitudes from about 60 km before the GDS to above 90 km during the storm. These very high altitude, small‐sized ( m) water ice clouds are more frequent during MY 34 compared to non‐GDS years at the same season. Particle size frequently decreases with altitude, both locally within a given profile and globally in the whole data set. We observe that the maximum altitude at which a given size is observed can increase during the GDS by several tens of kilometers for certain sizes. We notably notice some large water ice particles ( m) at surprisingly high altitudes during the GDS (50–70 km). These results suggest that GDS can significantly impact the formation and properties of high‐altitude water ice clouds as compared to the usual perihelion dust activity.

Summertime cloud phase strongly influences surface melting on the Larsen C ice shelf, Antarctica

AbstractSurface melting on Antarctic Peninsula ice shelves can influence ice shelf mass balance, and consequently sea level rise. We show that summertime cloud phase on the Larsen C ice shelf on the Antarctic Peninsula strongly influences the amount of radiation received at the surface and can determine whether or not melting occurs. While previous work has separately evaluated cloud phase and the surface energy balance (SEB) during summertime over Larsen C, no previous studies have examined this relationship quantitatively. Furthermore, regional climate models frequently produce surface radiation biases related to cloud ice and liquid water content. This study uses a high‐resolution regional configuration of the UK Met Office Unified Model (MetUM) to assess the influence of cloud ice and liquid properties on the SEB, and consequently melting, over the Larsen C ice shelf. Results from a case‐study show that simulations producing a vertical cloud phase structure more comparable to aircraft observations exhibit smaller surface radiative biases. A configuration of the MetUM adapted to improve the simulation of cloud phase reproduces the observed surface melt most closely. During a five‐week simulation of summertime conditions, model melt biases are reduced to <2 W·m−2: a four‐fold improvement on a previous study that used default MetUM settings. This demonstrates the importance of cloud phase in determining summertime melt rates on Larsen C.

Aphelion Cloud Belt phase function investigations with Mars Color Imager (MARCI)

This paper constrains the scattering phase function of water ice clouds (WICs) found within Mars’ Aphelion Cloud Belt (ACB), determined from orbit by processing publicly available raw Mars Color Imager (MARCI) data spanning solar longitudes (LS) 42°–170° during Mars Years (MYs) 28 and 29. MARCI visible wavelength data were calibrated and then pipeline-processed to select the pixels most likely to possess clouds. Mean phase function curves for the MARCI blue filter data were derived, and for all seasons investigated, modeled aggregates, plates, solid and hollow columns, bullet rosettes, and droxtals were all found to be plausible habits. Spheres were found to be the least plausible, but still possible. Additionally, this work probed the opposition surge to examine the slope of the linear relationship between column ice water content and cloud opacity on Mars, and found a significant dependence on particle radius. The half-width-half-maxima (HWHM) of the visible 180° peak of five MARCI images were found to agree better with modeled HWHM for WICs than with modeled HWHM for dust.

A Passive Microwave Retrieval Algorithm with Minimal View-Angle Bias: Application to the TEMPEST-D CubeSat Mission

AbstractThe rapid development of miniaturized satellite instrument technology has created a new opportunity to deploy constellations of passive microwave (PMW) radiometers to permit retrievals of the same Earth scene with very high temporal resolution to monitor cloud evolution and processes. For such a concept to be feasible, it must be shown that it is possible to distinguish actual changes in the atmospheric state from the variability induced by making observations at different Earth incidence angles (EIAs). To this end, we present a flexible and physical optimal estimation-based algorithm designed to retrieve profiles of atmospheric water vapor, cloud liquid water path, and cloud ice water path from cross-track PMW sounders. The algorithm is able to explicitly account for the dependence of forward model errors on EIA and atmospheric regime. When the algorithm is applied to data from the Temporal Experiment for Storms and Tropical Systems Technology Demonstration (TEMPEST-D) CubeSat mission, its retrieved products are generally in agreement with those obtained from the similar but larger Microwave Humidity Sounder instrument. More importantly, when forward model brightness temperature offsets and assumed error covariances are allowed to change with EIA and sea surface temperature, view-angle-related biases are greatly reduced. This finding is confirmed in two ways: through a comparison with reanalysis data and by making use of brief periods in early 2019 during which the TEMPEST-D spacecraft was rotated such that its scan pattern was along track, allowing dozens of separate observations of any given atmospheric feature along the satellite’s ground track.

Spatial and seasonal variation of rainfall contribution by the height spectrum of precipitation systems and associated cloud bulk properties over the South Asia

AbstractThe spatial‐seasonal variation of rainfall contribution by the height spectrum of precipitation systems in terms of maximum echo top height of 20 and 40 dBZ (ETH20 dBZ (max) and ETH40 dBZ (max)) is investigated. The study is carried out during the pre‐monsoon (March–May) and monsoon (June–September) over the continental, coastal and oceanic regions of South‐Asia. For this purpose, 17 years (1998–2014) of TRMM‐PR and 4 years (2007–2010) of CloudSat‐CPR observations are considered. Over the continental (coastal/oceanic) regions, the maximum rainfall contribution is by relatively deeper ETH20 dBZ (max) during the monsoon (pre‐monsoon). During the pre‐monsoon (monsoon), the maximum rainfall contribution by Deep Convective Systems (DCSs) is over the Northern‐Myanmar‐Coast; 55% (Western‐Himalaya‐Indentation; 39%). Over the central Arabian‐Sea and central Bay‐of‐Bengal, rainfall contributions by DCSs are predominantly associated with Tropical Cyclonic Disturbances (TCDs) in the pre‐monsoon season. In terms of ETH40 dBZ (max), the maximum rainfall contribution over the continental region during the pre‐monsoon is by relatively stronger Precipitation Features (PFs) compared to the monsoon. Unlike the other regions, during the pre‐monsoon, over the Western‐Himalaya‐Indentation and Central‐Himalaya‐Foothills, rainfall contribution by Intense Convective Systems (ICSs) is significantly higher compared to DCSs. During the pre‐monsoon (monsoon), the maximum rainfall contribution by ICSs is over the Eastern‐India‐Coast; 35% (Western‐Himalaya‐Indentation; 18%). The rainfall contribution by ICSs during TCDs is insignificant. During both the seasons, the regions of high rainfall contribution by ICSs, DCSs, and shallow PFs are associated with relatively higher (≥400 mg‐m−3), moderate (300–350 mg‐m−3), and low (<150 mg‐m−3) Cloud Ice Water Content (CIWC) in the mixed‐phase region, respectively, suggesting a strong, moderate and weak mixed‐phase processes involved in the respective PFs. TCDs enhance the occurrence of DCSs with moderate CIWC in mixed‐phase region and leading to enhanced rainfall contribution by them over the active cyclone regions.

Inconsistent aerosol indirect effects on water clouds and ice clouds over the Tibetan Plateau

AbstractRecently, satellites have observed that dust events are occurring more frequently over the Tibetan Plateau (TP), which implies a new issue of aerosols influencing cloud properties and presents a new challenge in research on the role of the TP in climate change. In this study, combining satellite observations with Climate Model Intercomparison Project Phase 5 (CMIP5) model simulations, the inconsistent aerosol indirect effects on the properties of water clouds and ice clouds over the TP are compared and quantified. Analyses of satellite observations show that, compared with water clouds, ice clouds are observed more frequently and are more significantly correlated with aerosols over the TP. Correspondingly, the aerosol effect on the radiative forcing of ice clouds is more significant than that on the forcing of water clouds, in which the aerosol indirect effect is dominated by the effect on the shortwave radiative forcing of ice clouds. Both observations and CMIP5 model simulation results show that, due to the variation of aerosols, changes in the ice cloud radiative forcing cover most of the TP, while changes in the water cloud radiative forcing mainly appear over the southern edge of the TP. The CMIP5 simulation results suggest that the aerosol indirect effect on the total radiative forcing of water clouds over the TP is −0.34 (±0.03) W⋅m−2, while that on the forcing of ice clouds is −0.73 (±0.03) W⋅m−2. Overall, both the model simulations and satellite results show that the indirect effect of aerosols on ice clouds is more pronounced than that on water clouds.