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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Causal Directions Matter: How Environmental Factors Drive Convective Cloud Detrainment Heights

This study investigates how environmental factors influence the level of maximum detrainment (LMD) in deep convective clouds. Through a novel application of the Linear Non‐Gaussian Acyclic Model (LiNGAM), we discover causal structures between environmental variables and LMD, observed at six tropical sites operated by the Atmospheric Radiation Measurement (ARM) user facility. LiNGAM effectively identifies causal directions among variables of interest, revealing robust relationships such as those among the lifting condensation level (LCL), level of free convection (LFC), and convective inhibition (CIN), aligning with prior knowledge. Relative humidity is shown to directly influence LMD; however, this relationship exhibits strong nonlinearity and becomes difficult to detect when the contrast between oceanic and continental environments is excluded from the analysis. This study highlights the importance of establishing causal relationships before performing statistical inference.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Regime dependence of ice cloud heterogeneity – a convective life‐cycle effect?

Cloud condensate varies on scales smaller than those typically resolved by global weather and climate models. In order to accurately predict the radiative and microphysical process rates representative of the entire model grid box, the effect of the subgrid‐scale heterogeneity of cloud must be taken into account. In this study, observed ice water content retrieved from A‐Train satellite observations is used to explore how spatial ice condensate variability, characterized by the fractional standard deviation (FSD, the standard deviation divided by the mean), varies with cloud regime. FSD is generally lower for overcast cloud scenes, but an additional predictor based on convective activity is needed to capture the high FSD associated with more turbulent clouds and reproduce the observed latitudinal and height variations of FSD. Convective clouds that extend only a few kilometres above the freezing level are likely to be smaller at an earlier stage in their life cycle, and actively growing with a higher FSD. In contrast, more mature clouds reaching the tropopause are larger and generally have a lower variability and smaller FSD. To capture this life‐cycle effect, a new parametrization is tested which uses the ratio of a model's convectively detrained condensate to the existing cloud condensate mass as a proxy for the cloud's convective life stage to highlight areas with enhanced condensate variability. The parametrization is scale‐adaptive, situation‐dependent and captures seasonally varying global patterns and the zonal mean vertical structure of observed ice condensate variability well. Ground‐based observations obtained from five Atmospheric Radiation Measurement sites provide independent confirmation that the parametrization satisfactorily captures condensate variability in high‐altitude ice clouds.

Ahlgrimm, Maike↗
NASA NTRS1987

A method for remote sensing the emissivity, fractional cloud cover and cloud top temperature of high-level, thin clouds

A methodology for retrieving the emissivity, cloud cover and cloud top temperature of high-level, thin clouds is developed and described. In the thermal infrared windows, the outgoing radiances from the earth's atmosphere contain information about cloud emissivity and cloud top temperature. This information is clearly demonstrated in the brightness temperature difference curves of two window channels. For the purpose of illustration, two window channels centered at 810 and 930 cm are chosen to construct the brightness temperature difference curves for a range of cloud top temperatures. These curves vary for different cloud top temperatures, and along each of these curves the emissivity changes. The brightness temperature difference method is used in a simulation study to demonstrate the feasibility of retrieving the cloud top temperature and emissivity by the utilization of measurements in two window channels. As expected, a perfect retrieval is found if perfect measurements and ideal atmospheric conditions are assumed. If a random error, which has a normal distribution with a mean of zero and standard deviation of + or - 0.5 C, is imposed to the measurements, a reasonable retrieval is found for emissivity greater than 0.3. The algorithm has been applied to a limited amount of HIRS2 data, which has 3.7, 3.98 and 11 micron channels. The cloud top temperature, emissivity and cloud cover are determined by using these channels.

Wu, Man-Li C.↗
NASA NTRS2006

The Influence of Aerosols on the Shortwave Cloud Radiative Forcing from North Pacific Oceanic Clouds: Results from the Cloud Indirect Forcing Experiment (CIFEX)

Aerosols over the Northeastern Pacific Ocean enhance the cloud drop number concentration and reduce the drop size for marine stratocumulus and cumulus clouds. These microphysical effects result in brighter clouds, as evidenced by a combination of aircraft and satellite observations. In-situ measurements from the Cloud Indirect Forcing Experiment (CIFEX) indicate that the mean cloud drop number concentration in low clouds over the polluted marine boundary layer is greater by 53/cu cm compared to clean clouds, and the mean cloud drop effective radius is smaller by 4 microns. We link these in-situ measurements of cloud modification by aerosols, for the first time, with collocated satellite broadband radiative flux observations from the Clouds and the Earth's Radiant Energy System (CERES) to show that these microphysical effects of aerosols enhance the top-of-atmosphere cooling by -9.9+/-4.3 W/sq m for overcast conditions.

Wilcox, Eric M.↗
NASA NTRS2007

Influence of Aerosols on the Shortwave Cloud Radiative Forcing from North Pacific Oceanic Clouds: Results from the Cloud Indirect Forcing Experiment (CIFEX)

Aerosols over the Northeastern Pacific Ocean enhance the cloud drop number concentration and reduce the drop size for marine stratocumulus and cumulus clouds. These microphysical effects result in brighter clouds, as evidenced by a combination of aircraft and satellite observations. In-situ measurements from the Cloud Indirect Forcing Experiment (CIFEX) indicate that the mean cloud drop number concentration in low clouds over the polluted marine boundary layer is greater by 53 cm(sup -3) compared to clean clouds, and the mean cloud drop effective radius is smaller by 4 micrometers. We link these in-situ measurements of cloud modification by aerosols, for the first time, with collocated satellite broadband radiative flux observations from the Clouds and the Earth s Radiant Energy System to show that these microphysical effects of aerosols enhance the top-of-atmosphere cooling by -.9.9 plus or minus 4.3 W m(sup -2) for overcast conditions.

Wilcox, Eric M.↗
DOE OSTI2016

THE TWO MOLECULAR CLOUDS IN RCW 38: EVIDENCE FOR THE FORMATION OF THE YOUNGEST SUPER STAR CLUSTER IN THE MILKY WAY TRIGGERED BY CLOUD–CLOUD COLLISION

We present distributions of two molecular clouds having velocities of 2 and 14 km s{sup −1} toward RCW 38, the youngest super star cluster in the Milky Way, in the {sup 12}CO J = 1–0 and 3–2 and {sup 13}CO J = 1–0 transitions. The two clouds are likely physically associated with the cluster as verified by the high intensity ratio of the J = 3–2 emission to the J = 1–0 emission, the bridging feature connecting the two clouds in velocity, and their morphological correspondence with the infrared dust emission. The velocity difference is too large for the clouds to be gravitationally bound. We frame a hypothesis that the two clouds are colliding with each other by chance to trigger formation of the ∼20 O stars that are localized within ∼0.5 pc of the cluster center in the 2 km s{sup −1} cloud. We suggest that the collision is currently continuing toward part of the 2 km s{sup −1} cloud where the bridging feature is localized. This is the third super star cluster alongside Westerlund 2 and NGC 3603 where cloud–cloud collision has triggered the cluster formation. RCW 38 is the youngest super star cluster in the Milky Way, holding a possible sign of on-going O star formation, and is a promising site where we may be able to witness the moment of O star formation.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1987

The role of orbital dynamics and cloud-cloud collisions in the formation of giant molecular clouds in global spiral structures

The role of orbit crowding and cloud-cloud collisions in the formation of GMCs and their organization in global spiral structure is investigated. Both N-body simulations of the cloud system and a detailed analysis of individual particle orbits are used to develop a conceptual understanding of how individual clouds participate in the collective density response. Detailed comparisons are made between a representative cloud-particle simulation in which the cloud particles collide inelastically with one another and give birth to and subsequently interact with young star associations and stripped down simulations in which the cloud particles are allowed to follow ballistic orbits in the absence of cloud-cloud collisions or any star formation processes. Orbit crowding is then related to the behavior of individual particle trajectories in the galactic potential field. The conceptual picture of how GMCs are formed in the clumpy ISMs of spiral galaxies is formulated, and the results are compared in detail with those published by other authors.

Roberts, William W., Jr.↗
DOE OSTI2023

Vertical Gradient of Size-Resolved Aerosol Compositions over the Arctic Reveals Cloud Processed Aerosol in-Cloud and above Cloud

Arctic aerosols play a significant role in the aerosol-radiation and aerosol-cloud interactions, but ground-based measurements are insufficient to explain the interaction of aerosols and clouds in a vertically stratified Arctic atmosphere. This study shows the vertical variability of aerosol particle composition via tethered balloon system at Oliktok Point, Alaska, in August 2019, at different cloud layers for two case studies (background aerosol condition and polluted condition). Multi-modal micro-spectroscopy analysis of samples during the background case reveals a broadening of chemically specific size distribution above cloud top with a high abundance of sulfate and core-shell morphology, suggesting possible cloud processing of aerosols. The pollution case also indicates a broadening of size distribution at the upper cloud layer with the dominance of carbonaceous aerosol, which suggests the potential of carbonaceous aerosols for Arctic cloud formation. Here this study provides insights into the vertical profile of Arctic aerosols on cloud formation.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

High-resolution photography of clouds from the surface: Retrieval of optical depth of thin clouds down to centimeter scales: High-Resolution Photography of Clouds

This article describes the approach and presents initial results, for a period of several minutes in north central Oklahoma, of an examination of clouds by high resolution digital photography from the surface looking vertically upward. A commercially available camera having 35-mm equivalent focal length up to 1200 mm (nominal resolution as fine as 6 µrad, which corresponds to 9 mm for cloud height 1.5 km) is used to obtain a measure of zenith radiance of a 30 m × 30 m domain as a two-dimensional image consisting of 3456 × 3456 pixels (12 million pixels). Downwelling zenith radiance varies substantially within single images and between successive images obtained at 4-s intervals. Variation in zenith radiance found on scales down to about 10 cm is attributed to variation in cloud optical depth (COD). Attention here is directed primarily to optically thin clouds, COD less than about 2. A radiation transfer model used to relate downwelling zenith radiance to COD and to relate the counts in the camera image to zenith radiance, permits determination of COD on a pixel-by-pixel basis. COD for thin clouds determined in this way exhibits considerable variation, for example, an order of magnitude within 15 m, a factor of 2 within 4 m, and 25% (0.12 to 0.15) over 14 cm. In conclusion, this approach, which examines cloud structure on scales 3 to 5 orders of magnitude finer than satellite products, opens new avenues for examination of cloud structure and evolution.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Investigation of Surface and Marine-Cloud Coupling and its Impact on Cloud Droplet Number Concentrations and Cloud Cover Over the Southern Ocean

The proposed work involves characterizing and quantifying both the thermodynamic and dynamical coupling of marine low clouds (MLC) with the sea surface using Atmospheric Radiation Measurement (ARM) observations during MARCUS field campaign and an LES model. ARM data from multiple sensors will be used (e.g., Doppler cloud radar, ceilometer, and microwave radiometer) to characterize the MLC-surface coupling by virtue of the vertical structure and integrated quantities of boundary-layer clouds, aerosols, as well as atmospheric profiles and surface meteorology. We have used a combination of case studies and statistics-based composite analyses to find any linkages between large-scale dynamics, MLC-surface coupling, and cloud and boundary layer properties, the sequence of which reflects the chain of causality. An LES model with explicit aerosol physics, which includes the cycle of aerosols by being consumed as CCN and be regenerated following cloud droplet evaporation, has been run to determine the sources and sinks of Nd and their dependence on the degree of MLC-surface coupling. We have examined the systematic differences in both Nd and cloud occurrence between the two clusters under different meteorological conditions and further examine their respective roles, as well as causal relationships by means of LES modeling. This study helped improve our understanding of the ACI by differentiating the dynamic role of the coupling and cloud physics denoted by Nd, bridging the linkage in the chain toward understanding mechanisms governing the persistence of MLC over the Southern Ocean, solving the long-lasting problem of the cloud cover underestimation over the SO by GCMs. Ample ARM data and LES model have been employed to achieve the objectives of the study.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Above-cloud concentrations of cloud condensation nuclei help to sustain some Arctic low-level clouds

Abstract. Previous studies have found that low-level Arctic clouds often persist for long periods even in the face of very low surface cloud condensation nuclei (CCN) concentrations. Here, we investigate whether these conditions could occur due to continuous entrainment of aerosol particles from the free troposphere (FT). We use an idealized large eddy simulation (LES) modeling framework, where aerosol concentrations are low in the boundary layer (BL) but increased up to 50× in the free troposphere. We find that the tests with higher tropospheric aerosol concentrations simulated clouds, which persisted for longer and maintained higher liquid water paths (LWPs). This is due to direct entrainment of the tropospheric aerosol into the cloud layer, which results in a precipitation suppression from the increase in cloud droplet number and in stronger cloud-top radiative cooling, which causes stronger circulations maintaining the cloud in the absence of surface forcing. Together, these two responses result in a more well-mixed boundary layer with a top that remains in contact with the tropospheric aerosol reservoir and can maintain entrainment of those aerosol particles. The surface aerosol concentrations, however, remained low in all simulations. The free-tropospheric aerosol concentration necessary to maintain the clouds is consistent with concentrations that are frequently seen in observations.

Environmental Sciences & Ecology↗
NASA NTRS1972

Photogrammetry and photo interpretation applied to analyses of cloud cover, cloud type, and cloud motion

A determination was made of the areal extent of terrain obscured by clouds and cloud shadows on a portion of an Apollo 9 photograph at the instant of exposure. This photogrammetrically determined area was then compared to the cloud coverage reported by surface weather observers at approximately the same time and location, as a check on result quality. Stereograms prepared from Apollo 9 vertical photographs, illustrating various percentages of cloud coverage, are presented to help provide a quantitative appreciation of the degradation of terrain photography by clouds and their attendant shadows. A scheme, developed for the U.S. Navy, utilizing pattern recognition techniques for determining cloud motion from sequences of satellite photographs, is summarized. Clouds, turbulence, haze, and solar altitude, four elements of our natural environment which affect aerial photographic missions, are each discussed in terms of their effects on imagery obtained by aerial photography. Data of a type useful to aerial photographic mission planners, expressing photographic ground coverage in terms of flying height above terrain and camera focal length, for a standard aerial photograph format, are provided. Two oblique orbital photographs taken during the Apollo 9 flight are shown, and photo-interpretations, discussing the cloud types imaged and certain visible geographical features, are provided.

Larsen, P. A.↗
NASA NTRS2003

Satellite and Surface Data Synergy for Developing a 3D Cloud Structure and Properties Characterization Over the ARM SGP. Stage 1: Cloud Amounts, Optical Depths, and Cloud Heights Reconciliation

One of the primary Atmospheric Radiation Measurement (ARM) Program objectives is to obtain measurements applicable to the development of models for better understanding of radiative processes in the atmosphere. We address this goal by building a three-dimensional (3D) characterization of the cloud structure and properties over the ARM Southern Great Plains (SGP). We take the approach of juxtaposing the cloud properties as retrieved from independent satellite and ground-based retrievals, and looking at the statistics of the cloud field properties. Once these retrievals are well understood, they will be used to populate the 3D characterization database. As a first step we determine the relationship between surface fractional sky cover and satellite viewing angle dependent cloud fraction (CF). We elaborate on the agreement intercomparing optical depth (OD) datasets from satellite and ground using available retrieval algorithms with relation to the CF, cloud height, multi-layer cloud presence, and solar zenith angle (SZA). For the SGP Central Facility, where output from the active remote sensing cloud layer (ARSCL) valueadded product (VAP) is available, we study the uncertainty of satellite estimated cloud heights and evaluate the impact of this uncertainty for radiative studies.

Genkova, I.↗
NASA NTRS2013

A 19-Month Climatology of Marine Aerosol-Cloud-Radiation Properties Derived From DOE ARM AMF Deployment at the Azores: Part I: Cloud Fraction and Single-Layered MBL Cloud Properties

A 19-month record of total, and single-layered low (0-3 km), middle (3-6 km), and high (> 6 km) cloud fractions (CFs), and the single-layered marine boundary layer (MBL) cloud macrophysical and microphysical properties has been generated from ground-based measurements taken at the ARM Azores site between June 2009 and December 2010. It documents the most comprehensive and longest dataset on marine cloud fraction and MBL cloud properties to date. The annual means of total CF, and single-layered low, middle, and high CFs derived from ARM radar-lidar observations are 0.702, 0.271, 0.01 and 0.106, respectively. More total and single-layered high CFs occurred during winter, while single-layered low CFs were greatest during summer. The diurnal cycles for both total and low CFs are stronger during summer than during winter. The CFs are bimodally distributed in the vertical with a lower peak at approx. 1 km and higher one between 8 and 11 km during all seasons, except summer, when only the low peak occurs. The persistent high pressure and dry conditions produce more single-layered MBL clouds and fewer total clouds during summer, while the low pressure and moist air masses during winter generate more total and multilayered-clouds, and deep frontal clouds associated with midlatitude cyclones.

Dong, Xiquan↗
DOE OSTI2021

Mixed-phase clouds and precipitation in Southern Ocean cyclones and cloud systems observed poleward of 64°S by ship-based cloud radar and lidar

Mixed-phase clouds (MPCs), composed of both liquid and ice, are prevalent in Southern Ocean cyclones. A characterisation of these clouds on fine vertical scales is required in order to understand the microphysical processes within these clouds, and for model and satellite evaluations over this region. We investigated three examples of cloud systems collected by ship-mounted remote sensing instruments adjacent to East Antarctica at latitudes between 64°S and 69°S. These cases allow us to examine the properties of mid-level MPCs, with cloud tops between 2 and 6 km. Mid-level MPCs contain multiple layers of supercooled liquid water (SLW) embedded within ice during the passage of cyclones. SLW layers are capped by strong temperature inversions and are observed at temperatures as low as - 31°C. Convective generating cells (GCs) are present inside supercooled liquid-topped mid-level MPCs. The horizontal extent, vertical extent and maximum upward Doppler velocity of these GCs were 0.6 – 3.6 km, 0.7 – 1.0 km and 0.5 – 1.0 m s -1 , respectively, and are consistent with observations from previous lower-latitude studies. Ice precipitation is nearly ubiquitous, except in the thinnest clouds at the trailing end of the observed systems. Seeding of lower SLW layers from above leads to periods with either larger ice particles or greater ice precipitation rates. Additionally, periods of supercooled drizzle lasting up to two hours were observed toward the end of two of the three cyclone systems. This supercooled drizzle turns into predominantly ice precipitation as the result of seeding by ice clouds located above the precipitating SLW layer.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Impacts of Mesoscale Cloud Organization on Aerosol-Induced Cloud Water Adjustment and Cloud Brightness

The role of mesoscale cellular convection (MCC) in regulating aerosol-induced cloud brightness remains unaddressed. Using 7 years of satellite-based observations of cloud water adjustment to aerosol-induced perturbations for closed MCCs across different sizes (8, 16, 32, and 64 km) over the North Atlantic Ocean, we show that MCC cell-size plays a nontrivial role in regulating aerosol-induced cloud brightness via cloud water adjustment. In cells that are primarily non-precipitating, the adjustment in small-scale MCCs can be 10 times more negative than in large-scale MCCs, consistent with stronger evaporation via cloud top entrainment. Consequently, the response of cloud brightness is significantly stronger for large-scale MCCs. We also find notable intra-cell co-variability between cloud liquid water path (LWP) and drop concentration (N d ) within MCCs that varies with cell size. Erroneously considering such co-variability as a LWP response to N d can lead to a significant positive bias, especially for small scale MCCs.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Planning the Next Decade of Coordinated Research to Better Understand and Simulate Marine Low Clouds

Marine low clouds have a large impact on the Earth’s energy and hydrologic cycle. They strongly reflect incoming solar radiation, with little compensating impact on outgoing longwave radiation resulting in a net cooling of the climate. The representation of marine low clouds in climate models is one of the largest uncertainties in the estimation of climate sensitivity (e.g. Bony and Dufresne 2005), and marine low clouds are critical mediators of global aerosol radiative forcing (Zelinka et al. 2014). Despite the importance of these cloud systems to the Earth’s climate, their parameterization continues to be challenging, due to an incomplete understanding of key processes that regulate them and insufficient resolution of these processes in models. To help define research pathways to address outstanding issues related to our understanding of marine low clouds, a workshop was held January 27-29, 2016 at Brookhaven National Laboratory. The overarching goal was to identify current gaps in knowledge or simulation capabilities and promising strategies for addressing them, with a particular emphasis on improving the representation of marine low clouds in climate models and contributions that could be made with U.S. Department of Energy Atmospheric System Research support using Atmospheric Radiation Measurement facility measurements.

Wood, Robert↗
NASA NTRS1999

Cloud-Vegetation Interaction: Use of Normalized Difference Cloud Index for Estimation of Cloud Optical Thickness

A new technique to retrieve cloud optical depth for broken clouds above green vegetation using ground-based zenith radiance measurements is developed. By analogy with the Normalized Difference Vegetation Index NDVI), the Normalized Difference Cloud Index (NDCI) is defined as a ratio between the difference and the sum of two zenith radiances measured for two narrow spectral bands in the visible and near-IR regions. The very different spectral behavior of cloud liquid water drops and green vegetation is the key physics behind the NDCI. It provides extra tools to remove the radiative effects of the 3D cloud structure. Numerical calculations based on fractal clouds and real measurements of NDCI and cloud liquid water path confirm the improvements.

Marshak, A.↗