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At least 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Direct and semi-direct radiative forcing of biomass-burning aerosols over the southeast Atlantic (SEA) and its sensitivity to absorbing properties: a regional climate modeling study

Simulations are performed for the period 2000-2015 by two different regional climate models, ALADIN and RegCM, to quantify the direct and semi-direct radiative effects of biomass-burning aerosols (BBAs) in the southeast Atlantic (SEA) region. Different simulations have been performed using strongly absorbing BBAs in accordance with recent in situ observations over the SEA. For the July-August-September (JAS) season, the single scattering albedo (SSA) and total aerosol optical depth (AOD) simulated by the ALADIN and RegCM models are consistent with the MACv2 climatology and MERRA-2 and CAMS-RA reanalyses near the biomass-burning emission sources. However, the above-cloud AOD is slightly underestimated compared to satellite (MODIS and POLDER) data during the transport over the SEA. The direct radiative effect exerted at the continental and oceanic surfaces by BBAs is significant in both models and the radiative effects at the top of the atmosphere indicate a remarkable regional contrast over SEA (in all-sky conditions), with a cooling (warming) north (south) of 10°S, which is in agreement with the recent MACv2 climatology. In addition, the two models indicate that BBAs are responsible for an important shortwave radiative heating of ~0.5-1K per day over SEA during JAS with maxima between 2 and 4 km a.m.s.l. (above mean sea level). At these altitudes, BBAs increase air temperature by ~0.2-0.5 K, with the highest values being co-located with low stratocumulus clouds. Vertical changes in air temperature limit the subsidence of air mass over SEA, creating a cyclonic anomaly. The opposite effect is simulated over the continent due to the increase in lower troposphere stability. The BBA semi-direct effect on the lower troposphere circulation is found to be consistent between the two models. Changes in the cloud fraction are moderate in response to the presence of smoke, and the models differ over the Gulf of Guinea. Finally, the results indicate an important sensitivity of the direct and semi-direct effects to the absorbing properties of BBAs. Over the stratocumulus (Sc) region, DRE varies from +0.94 W m -2 (scattering BBAs) to +3.93 W m -2 (most absorbing BBAs).

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1991

Simulation of whistler waves excited in the presence of a cold plasma cloud - Implications for the CRRES mission

A one-dimensional electromagnetic particle simulation model is constructed to study the excitation of whistler waves in the presence of a cold plasma cloud for conditions representative of those after the release of lithium in the inner plasma sheet during the Combined Release and Radiation Effect Satellite mission. The results indicate that a standing-wave pattern with discrete wave frequencies is formed within the cloud. The magnetic wave amplitude inside the cloud, which is limited by quasi-linear diffusion, is of the order of several nanoteslas. Assuming a magnetospheric loss cone of 5 deg, the observed pitch angle diffusion produced by the whistler waves is sufficient to put the electrons on strong diffusion.

Pritchett, P. L.↗
NASA NTRS1990

Measurements of the light-absorbing material inside cloud droplets and its effect on cloud albedo

Most of the measurements of light-absorbing aerosol particles made previously have been in non-cloudy air and therefore provide no insight into aerosol effects on cloud properties. Here, researchers describe an experiment designed to measure light absorption exclusively due to substances inside cloud droplets, compare the results to related light absorption measurements, and evaluate possible effects on the albedo of clouds. The results of this study validate those of Twomey and Cocks and show that the measured levels of light-absorbing material are negligible for the radiative properties of realistic clouds. For the measured clouds, which appear to have been moderately polluted, the amount of elemental carbon (EC) present was insufficient to affect albedo. Much higher contaminant levels or much larger droplets than those measured would be necessary to significantly alter the radiative properties. The effect of the concentrations of EC actually measured on the albedo of snow, however, would be much more pronounced since, in contrast to clouds, snowpacks are usually optically semi-infinite and have large particle sizes.

Twohy, C. H.↗
NASA NTRS2017

Strong Constraints on Aerosol-Cloud Interactions from Volcanic Eruptions

Aerosols have a potentially large effect on climate, particularly through their interactions with clouds, but the magnitude of this effect is highly uncertain. Large volcanic eruptions produce sulfur dioxide, which in turn produces aerosols; these eruptions thus represent a natural experiment through which to quantify aerosol-cloud interactions. Here we show that the massive 2014-2015 fissure eruption in Holuhraun, Iceland, reduced the size of liquid cloud droplets - consistent with expectations - but had no discernible effect on other cloud properties. The reduction in droplet size led to cloud brightening and global-mean radiative forcing of around minus 0.2 watts per square metre for September to October 2014. Changes in cloud amount or cloud liquid water path, however, were undetectable, indicating that these indirect effects, and cloud systems in general, are well buffered against aerosol changes. This result will reduce uncertainties in future climate projections, because we are now able to reject results from climate models with an excessive liquid-water-path response.

atmospheric science↗
NASA NTRS2010

An Assessment of the Surface Longwave Direct Radiative Effect of Airborne Saharan Dust During the NAMMA Field Campaign

In September 2006, NASA Goddard s mobile ground-based laboratories were deployed to Sal Island in Cape Verde (16.73degN, 22.93degW) to support the NASA African Monsoon Multidisciplinary Analysis (NAMMA) field study. The Atmospheric Emitted Radiance Interferometer (AERI), a key instrument for spectrally characterizing the thermal IR, was used to retrieve the dust IR aerosol optical depths (AOTs) in order to examine the diurnal variability of airborne dust with emphasis on three separate dust events. AERI retrievals of dust AOT are compared with those from the coincident/collocated multifilter rotating shadow-band radiometer (MFRSR), micropulse lidar (MPL), and NASA Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) sensors. The retrieved AOTs are then inputted into the Fu-Liou 1D radiative transfer model to evaluate local instantaneous direct longwave radiative effects (DRE(sub LW)) of dust at the surface in cloud-free atmospheres and its sensitivity to dust microphysical parameters. The top-of-atmosphere DRE(sub LW) and longwave heating rate profiles are also evaluated. Instantaneous surface DRE(sub LW) ranges from 2 to 10 W/sq m and exhibits a strong linear dependence with dust AOT yielding a DRE(sub LW) of 16 W/sq m per unit dust AOT. The DRE(sub LW) is estimated to be approx.42% of the diurnally averaged direct shortwave radiative effect at the surface but of opposite sign, partly compensating for the shortwave losses. Certainly nonnegligible, the authors conclude that DRE(sub LW) can significantly impact the atmospheric energetics, representing an important component in the study of regional climate variation.

Hansell, R. A.↗
NASA NTRS1978

Radiation measurements from polar and geosynchronous satellites

The following topics are discussed: (1) cloud effects in climate determination; (2) annual variation in the global heat balance of the earth; (3) the accuracy of precipitation estimates made from passive microwave measurements from satellites; (4) seasonal oceanic precipitation frequencies; (5) determination of mesoscale temperature and moisture fields over land from satellite radiance measurements; and (6) Nimbus 6 scanning microwave spectrometer data evaluation for surface wind and pressure components in tropical storms.

Vonderhaar, T. H.↗
NASA NTRS1983

Diurnal and seasonal variations of clouds from geostationary satellite data

Hourly 8-km visible (0.55-0.75 micron) and infrared (10.5-12.5 microns) data from the eastern Geostationary Operational Environmental Satellite were analyzed with a hybrid bispectral threshold method to yield total, low, middle, and high level cloud fractions and cloud radiative parameters for 250 x 250 sq km regions. These data were analyzed for the area between 45 deg N and 45 deg S, and longitudes 30 deg W and 125 deg W for the autumn of 1978 and the winter of 1979. Preliminary results for winter are presented in the present study. It is shown that diurnal variations of clouds may reveal diurnal variability in regional and large-scale circulation patterns. These diurnal cloud cycles may also have substantial effects on regional and large-scale radiation budgets and, therefore, influence circulation patterns at various spatial scales.

Minnis, P.↗
DOE OSTI2020

The Incredible Lightness of Water Vapor

The molar mass of water vapor is much less than that of dry air. This makes a moist parcel lighter than a dry parcel of the same temperature and pressure. This effect is referred to as the vapor buoyancy effect and has often been overlooked in climate studies. We propose that the vapor buoyancy effect increases Earth’s outgoing longwave radiation (OLR) and that this negative radiative effect increases with warming, stabilizing Earth’s climate. We illustrate this mechanism in an idealized tropical atmosphere, where there is no horizontal buoyancy gradient in the free troposphere. Temperature increases toward dry atmosphere columns to compensate the reduced vapor buoyancy, increasing OLR by O(1 W m −2 ) at the reference climate. In warmer climates, the temperature difference between moist and dry columns would increase as a result of increasing atmospheric water vapor, leading to enhanced radiative effect and thereby stabilizing Earth’s climate. We estimate that this feedback strength is about O(0.2 W m −2 K −1 ) in the idealized atmosphere, which compares to cloud feedback and surface albedo feedback in the current climate. We further show evidence from observations and real-gas radiative transfer calculations for a significant radiative effect of vapor buoyancy in the tropical atmosphere.

Yang, Da↗
NASA NTRS1991

Volcanism-Climate Interactions

The range of disciplines in the study of volcanism-climate interactions includes paleoclimate, volcanology, petrology, tectonics, cloud physics and chemistry, and climate and radiation modeling. Questions encountered in understanding the interactions include: the source and evolution of sulfur and sulfur-gaseous species in magmas; their entrainment in volcanic plumes and injection into the stratosphere; their dissipation rates; and their radiative effects. Other issues include modeling and measuring regional and global effects of such large, dense clouds. A broad-range plan of research designed to answer these questions was defined. The plan includes observations of volcanoes, rocks, trees, and ice cores, as well as satellite and aircraft observations of erupting volcanoes and resulting lumes and clouds.

Walter, Louis S.↗
NASA NTRS1995

Surface measurements of solar irradiance: A study of the spatial correlation between simultaneous measurements at separated sites

Pyranometers have been used for many years to measure broadband surface incoming solar irradiance, data that is necessary for surface energy budget, cloud forcing, and satellite validation research. Because such measurements are made at a specific location, it is unclear how representative they may be of a larger area. This study attempts to determine a reasonable spacing between measurement sites for such research by computing the correlation, and standard deviation from perfect correlation, between simultaneous measurements of incoming solar irradiance for a network of surface measurement sites covering a 75 km x 75 km area. Using 1-min data collected from this network of 11 sites during the NASA First ISSCP Radiation Experiment/Surface Radiation Budget (FIRE/SRB) Project temporal averages were calculated. The correlation between any two of these sites was determined by comparing simultaneous measurement averages for the 55 possible combinations of site pairs, along with the distances between them. In an attempt to remove the effect of the diurnal cycle, thus leaving clouds as the primary influence on correlation of the radiation field, model results for a clear day were used to normalize measured irradiances and correlations were again calculated.

Long, Charles N.↗
NASA NTRS2020

Effective radiative forcing and adjustments in CMIP6 models

The effective radiative forcing, which includes the instantaneous forcing plus adjustments from the atmosphere and surface, has emerged as the key metric of evaluating human and natural influence on the climate. We evaluate effective radiative forcing and adjustments in 17 contemporary climate models that are participating in the Coupled Model Intercomparison Project (CMIP6) and have contributed to the Radiative Forcing Model Intercomparison Project (RFMIP). Present-day (2014) global-mean anthropogenic forcing relative to pre-industrial (1850) levels from climate models stands at 2.00 (±0.23) W/sq. m, comprised of 1.81 (±0.09) W/sq. m from CO2, 1.08 (± 0.21) W/sq. m from other well-mixed greenhouse gases, −1.01 (± 0.23) W/sq. m from aerosols and −0.09 (±0.13) W/sq. m from land use change. Quoted uncertainties are 1 standard deviation across model best estimates, and 90 % confidence in the reported forcings, due to internal variability, is typically within 0.1 W/sq. m. The majority of the remaining 0.21 W/sq. m is likely to be from ozone. In most cases, the largest contributors to the spread in effective radiative forcing (ERF) is from the instantaneous radiative forcing (IRF) and from cloud responses, particularly aerosol–cloud interactions to aerosol forcing. As determined in previous studies, cancellation of tropospheric and surface adjustments means that the stratospherically adjusted radiative forcing is approximately equal to ERF for greenhouse gas forcing but not for aerosols, and consequentially, not for the anthropogenic total. The spread of aerosol forcing ranges from −0.63 to −1.37 W/sq. m, exhibiting a less negative mean and narrower range compared to 10 CMIP5 models. The spread in 4×CO2 forcing has also narrowed in CMIP6 compared to 13 CMIP5 models. Aerosol forcing is uncorrelated with climate sensitivity. Therefore, there is no evidence to suggest that the increasing spread in climate sensitivity in CMIP6 models, particularly related to high-sensitivity models, is a consequence of a stronger negative present-day aerosol forcing and little evidence that modelling groups are systematically tuning climate sensitivity or aerosol forcing to recreate observed historical warming.

effective radiative forcing↗
DOE OSTI2024

Improving Aerosol Radiative Forcing and Climate in E3SM: Impacts of New Cloud Microphysics and Improved Wet Removal Treatments

Abstract Numerous Earth system models exhibit excessive aerosol effective forcing at the top of the atmosphere (TOA), including the Department of Energy's Energy Exascale Earth System Model (E3SM). Here, in the context of the E3SM version 3 effort, the predicted particle property (P3) stratiform cloud microphysics scheme and an enhanced deep convection parameterization suite (ZM_plus) are implemented into E3SM. The ZM_plus includes a convective cloud microphysics scheme, a multi‐scale coherent structure parameterization for mesoscale convective systems, and a revised cloud base mass flux formulation considering impacts of the large‐scale environment. The P3 scheme improved cloud and radiation particularly over the Northern Hemisphere and the frequency of heavy precipitation over the tropics, and the ZM_plus improved clouds in the tropics. P3 decreases aerosol effective forcing by 0.15 W m −2 , while the ZM_plus increases it by 0.27 W m −2 , resulting from excessive direct (0.31 W m −2 ) and indirect forcing (−1.79 W m −2 ). The excessive aerosol forcings are due to aerosol overestimation associated with insufficient aerosol wet removal. By improving the physical treatments in the aerosol wet removal, we effectively mitigate anthropogenic aerosol overestimation and thus attenuate direct (0.09 W m −2 ) and indirect aerosol forcing (−1.52 W m −2 ). Adjustment to primary organic matter hygroscopicity reduces direct and indirect forcing to more reasonable values: −0.13 W m −2 and −1.31 W m −2 , respectively. On climatology, improved aerosol treatments mitigate overestimation of aerosol optical depth.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1987

Emission line region kinematics in selected Seyfert galaxies

The kinematic state of the emission line regions of active galactic nuclei (AGN) is a fundamental problem which addresses the very nature of these objects. The currently popular model of the energy source of the latter is accretion onto the supermassive black hole which is believed to reside in the nuclear regions of galaxies. If this picture is correct then the emission line gas may be expected to be infalling, and may eventually provide the fuel to power them. It is very difficult to determine the kinematic state of the emission line gas because of the technical problems associated with their small apparent sizes, as seen from the earth. One can only observe the net emission from a large ensemble of clouds, so the emission lines are by necessity composite. Several very long exposures of NGC 1068, one of the very nearest Seyfert galaxies, were obtained. Because of its proximity, it is expected to have the best resolved emission line regions as seen from earth. The La emission line of neutral hydrogen will radiate preferentially in the direction of the central object because of the effects of emission line gas opacity on the transfer of radiation out of the clouds. By obtaining high dispersion observations of Doppler broadening of the line through the small entrance aperture of the IUE one can determine whether this material is in a state of outflow (expected if explosions power the central engine), inflow (expected for accretion onto a massive black hole), or rotation (expected for gas with significant angular momentum near the central regions of a galaxy).

Ferland, G. J.↗
NASA NTRS1980

Observations of the motion and distribution of the ionized gas in the central parsec of the Galaxy. II

Observations of infrared fine-structure line emission from compact clouds of ionized gas within Sgr A West are presented. These clouds have diameters of 0.1-0.5 pc, internal velocity dispersions of 100 km/s (FWHM), and line center velocities up to + or - 260 km/s. Their masses are not accurately determined but are probably between 0.1 and 10 solar masses. They are ionized by radiation like that of stars of effective temperature not greater than 35,000 K. The clouds are shown to have lifetimes of 10,000 yr and so must be generated and dissipated at a rate of a few per 1000 yr. From analysis of the distribution of the velocities of the clouds, a most probable mass distribution is derived which includes a central pointlike mass of several x 10 to the 6th solar masses in addition to several x 10 to the 6th solar masses of stars within 1 pc of the center.

Lacy, J. H.↗
NASA NTRS1990

Use of earth-radiation budget measurements for understanding climate change

Setting the baseline for the greenhouse effect, quantification of the water-vapor feedback, validation of longwave radiation models, determination of the trend in the clear sky albedo of the ocean, and determination of the role of clouds in climate are considered. A summary of cloud radiative forcing estimates is presented, and it is noted that the longwave cloud forcing is essentially the greenhouse effect of the clouds, and that the CO2 concentration in the atmosphere has to be increased by a factor of 250 to equal the cloud greenhouse effect. It is pointed out that the short-wave cloud forcing is due to the enhancement of the albedo of the planet by clouds. The decrease in the solar absorption of 48.4 W/sq m by clouds is found to be larger than its greenhouse effect by about 50 pct.

Ramanathan, V.↗
NASA NTRS2022

The Impact of Sampling Strategy on the Cloud Droplet Number Concentration Estimated From Satellite Data

Cloud droplet number concentration (Nd) is of central importance to observation-based estimates of aerosol indirect effects, being used to quantify both the cloud sensitivity to aerosol and the base state of the cloud. However, the derivation of Nd from satellite data depends on a number of assumptions about the cloud and the accuracy of the retrievals of the cloud properties from which it is derived, making it prone to systematic biases. A number of sampling strategies have been proposed to address these biases by selecting the most accurate Nd retrievals in the satellite data. This work compares the impact of these strategies on the accuracy of the satellite retrieved Nd, using a selection of in situ measurements. In stratocumulus regions, the MODIS Nd retrieval is able to achieve a high precision (r2 of 0.5–0.8). This is lower in other cloud regimes but can be increased by appropriate sampling choices. Although the Nd sampling can have significant effects on the Nd climatology, it produces only a 20 % variation in the implied radiative forcing from aerosol–cloud interactions, with the choice of aerosol proxy driving the overall uncertainty. The results are summarised into recommendations for using MODIS Nd products and appropriate sampling.

Edward Gryspeerdt↗
NASA NTRS1983

Local effects of partly-cloudy skies on solar and emitted radiations

Atmospheric aerosol and turbidity measurements were analyzed and the results are presented. The correlation of global insolation with cloud cover fractions for the first complete year's data set was completed. A theoretical model was developed to parameterize the effects of local aerosols upon insolation received at the ground using satellite radiometric data and insolation measurements under clear sky conditions. A February data set, composed of one minute integrated global insolation and direct solar irradiances, cloud cover fractions, meteorological data from nearby weather stations, and GOES East satellite radiometric data was collected to test the model and used to calculate the effects of local aerosols.

Whitney, D. A.↗
NASA NTRS1998

Computation of the Effects of Inhomogeneous Clouds on Retrieval of Remotely Sensed Properties

Current and future earth observation programs depend on satellite measurements of radiance to retrieve the properties of clouds on a global basis. At present, this retrieval is made assuming that the clouds in the instrument field of view are plane parallel and independent of adjacent pixels. While this assumption is known to be false except in very limited cases, its impact can be evaluated, and if possible corrected, based on emerging theoretical techniques. In this study, the Spherical Harmonic Discrete Ordinate Method (SHDOM, Evans, 1996) has been used to assess the sensitivity of the retrieval to a variety of cloud parameters. SHDOM allows the plane parallel assumption to be relaxed and makes 2D and even 3D radiative solutions practical. A previous study (Chambers et al., 1996) assessed the effect of horizontal inhomogeneity in 45 LANDSAT scenes of boundary layer clouds over ocean. The four scenes studied here represent overcast, broken, scattered and strongly thermally forced cloud fields and are used to perform sensitivity studies to a wider variety of parameters. Comparisons are made at three solar zenith angles (theta (sub 0) = 0, 49, and 63 degrees) to avoid ambiguity in the results due to solar zenith angle.

Chambers, Lin H.↗