Search NASA⌕ Search

SEARCH · Search NASA

Results for “thin cirrus”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

Detecting Super-Thin Clouds with Polarized Sunlight

We report a novel method for detecting cloud particles in the atmosphere. Solar radiation backscattered from clouds is studied with both satellite data and a radiative transfer model. A distinct feature is found in the angle of linear polarization of solar radiation that is backscattered from clouds. The dominant backscattered electric field from the clear-sky Earth-atmosphere system is nearly parallel to the Earth surface. However, when clouds are present, this electric field can rotate significantly away from the parallel direction. Model results demonstrate that this polarization feature can be used to detect super-thin cirrus clouds having an optical depth of only ~0.06 and super-thin liquid water clouds having an optical depth of only ~0.01. Such clouds are too thin to be sensed using any current passive satellite instruments.

Aerosols and particles↗
NASA NTRS2015

Formation of Cirrus Clouds near the Tropical Tropopause and Their Implications for Stratospheric Humidity, Radiation Budgets, and Climate

Optically-thin cirrus clouds are a nearly ubiquitous feature of the transition layer between the tropical troposphere and stratosphere (known as the Tropical Tropopause Layer). Given their high occurrence frequency, these clouds have significant impacts on the Earth's radiation budget, with a particularly strong influence on the outgoing longwave radiation. Further, ice crystal growth and sedimentation in these clouds dehydrates air in the cold TTL to very low water vapor mixing ratios. Since transport from the troposphere into the stratosphere occurs primarily through the tropical tropopause and the Brewer-Dobson circulation transports air from the TTL throughout the stratosphere, cloud processes in the TTL cold trap essentially regulate the humidity of the entire stratosphere. It has been shown that even small changes in stratospheric humidity can have significant impacts on the Earth's radiation budget and climate, with magnitudes comparable to anthropogenic changes in greenhouse gases. The humidity of air crossing the TTL cold trap depends to first order on tropical tropopause temperatures, but also on deep convection reaching the TTL, large-scale transport (in balance with TTL radiative heating), atmospheric waves, and cloud microphysical processes. Gaps in our understanding of TTL transport and cloud processes motivated the NASA Airborne Tropical TRopopause EXperiment (ATTREX). ATTREX used the long-range (16,000 km), high-altitude (20 km) Global Hawk unmanned aircraft system equipped with twelve instruments measuring clouds, water vapor, meteorological conditions, chemical tracers, chemical radicals, and radiation. I will discuss the physics of TTL cirrus formation and the impact of these clouds on water vapor and radiation budgets, including new results emerging from the ATTREX measurements.

Jensen, Eric↗
NASA NTRS1986

Intercomparison between Nimbus-7 cirrus cloud data and ERB measurements

Nimbus-7 and Earth Radiation Budget (ERB) data were compared with the quantity of high, thin cirrus clouds over a 6 yr period. Three separate data analysis techniques are described which were used to derive cloud cover and total upwelling radiance values from the satellite data. Zonal average cirrus clouds amounts are compared with surface observations and SAGE satellite data, and comparisons are made between the cloud amount estimates made with ERB data and data from other Nimbus-7 instruments. All Nimbus-7 instrumental data indicated cloud amounts and frequency of occurrence patterns which were commensurate with surface observations, except in high latitude zones.

Yeh, H. Y. M.↗
NASA NTRS1990

Cirrus clouds and climate feedback: Is the sky falling and should we go tell the king

It is widely believed that thin cirrus clouds act to enhance the greenhouse effect owing to a particular combination of their optical properties. It is demonstrated how this effect is perhaps based on inadequate resolution of the physics of cirrus clouds and that the more likely impact of cirrus clouds to climate change remains somewhat elusive. These conclusions are developed within the context of a specific feedback mechanism incorporated into a simple mechanistic climate model. A specific scientific question addressed is whether or not the observed relationship between the ice water content and temperature of cirrus provides any significant feedback to the CO2 greenhouse warming. A related question also examined concerns the specific role of cloud microphysics and radiation in this feedback. This raises several pertinent issues about the understanding of cirrus clouds and their likely role in climate change as there presently exists a considerable uncertainty about the microphysics of these clouds (size and shape of ice crystals) and their radiative influences.

Stephens, Graeme L.↗
NASA NTRS1989

Two years of cloud cover statistics using VAS

The CO2 channel radiometric data from VAS are used to chart the frequency of cloud cover, the associated heights, and IR attenuation. Cloud top pressures are calculated from the ratio of VAS CO2 channel radiances in a raditive transfer equation formulation. It is found that VAS CO2 derived cloud top height and emissivity assignments are reliable for most cloud types, including thin cirrus clouds. The observations from 1985 to 1988 show that 20-30 percent of the U.S. was covered with thin semitransparent clouds, 45 percent was covered with thick opaque clouds, and 25-35 had clear sky conditions. The geographical distribution of cloud cover is a latitudinal dependence, mainly over the Pacific Ocean.

Wyle, D. P.↗
NASA NTRS1992

Separation of cirrus cloud from clear surface from AVIRIS data using the 1.38 micron water vapor band

Cirrus clouds play an important role in climate systems because of their large area coverage, persistence, and radiative effects. Thin cirrus clouds are difficult to detect in visible images and infrared images in the 10-12 micron atmospheric window region, particularly over land, because these clouds are partially transparent. Ackerman recently developed a method for detecting cirrus clouds using three narrow channels centered near 8, 11, and 12 microns, respectively, based on the analysis of IR emission spectra measured with a high spectral resolution interferometer. Barton also described a method for estimating cirrus cloud height and amount from measurements with two narrow channel radiometers of the Selective Chopper Radiometer on Nimbus 5. Both channels are located within the strong 2.7 micron water vapor band absorption region. One of the channels includes additional carbon dioxide absorption. A differential absorption technique with sets of empirical coefficients was used in the estimation of cirrus cloud heights and amounts. A technique using narrow channels in the strong 1.38 micron water vapor band absorption region for detecting cirrus clouds from spectral imaging data acquired by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) on 5 Dec. 1991 during the FIRE (The First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment) Phase 2 Field Experiment is described.

Gao, Bo-Cai↗
NASA NTRS1983

Global distributions of cirrus clouds determined from SAGE data

Results are presented from analyses that use SAGE (Stratospheric Aerosol and Gas Experiment) data to determine the spatial extent and frequency of cirrus clouds over much of the earth's surface. The analyses pertain to a period of 15 months extending from February 1979 to April 1980. The results are compared with those from a climatology of ground-based cirrus cloud observations (Hahn et al., 1982). It is found that optically thick cirrus clouds are most often found in the midlatitudes and over the tropics, with distinct minima near the + or - 20 to 30 deg latitude bands. On the other hand, thin cirrus clouds occur much less often than the optically thick cirrus clouds. The comparison of the SAGE cirrus cloud results made zonally with those obtained from ocean-surface-based observations reveals general agreement. Tropospheric observational opportunities for a limb sounding satellite sensor, as evidenced by successful penetrations to 7 km, were found to occur approximately 60 percent of the time in the higher latitudes, falling to a low of 30 percent over the tropics.

Woodbury, G. E.↗
NASA NTRS1990

Cloud and surface textural features in polar regions

The study examines the textural signatures of clouds, ice-covered mountains, solid and broken sea ice and floes, and open water. The textural features are computed from sum and difference histogram and gray-level difference vector statistics defined at various pixel displacement distances derived from Landsat multispectral scanner data. Polar cloudiness, snow-covered mountainous regions, solid sea ice, glaciers, and open water have distinguishable texture features. This suggests that textural measures can be successfully applied to the detection of clouds over snow-covered mountains, an ability of considerable importance for the modeling of snow-melt runoff. However, broken stratocumulus cloud decks and thin cirrus over broken sea ice remain difficult to distinguish texturally. It is concluded that even with high spatial resolution imagery, it may not be possible to distinguish broken stratocumulus and thin clouds from sea ice in the marginal ice zone using the visible channel textural features alone.

Welch, Ronald M.↗
NASA NTRS2006

On Cirrus Cloud Fields Measured by the Atmospheric Infrared Sounder

A viewgraph presentation showing trends in clouds measured by the Atmospheric Infrared Sounder (AIRS) is given. The topics include: 1) Trends in clouds measured by AIRS: Are they reasonable? 2) Single and multilayered cloud trends; 3) Retrievals of thin cirrus D(sub e) and tau: Single-layered cloud only; 4) Relationships between ECF, D(sub e), tau, and T(sub CLD); and 5) MODIS vs. AIRS retrievals.

multilayered cloud trends↗
NASA NTRS1990

The 27-28 October 1986 FIRE IFO cirrus case study - In situ observations of radiation and dynamic properties of a cirrus cloud layer

Observations are presented of cirrus cloud radiative, microphysical, and dynamic properties, their variability, and apparent scale sizes, as observed from NCAR Sabreliner on October 28, 1986. Broadband mass-absorption coefficients were deduced as a function of depth into the cirrus cloud and found to vary with particle dimension. Broadband volume absorption coefficients were deduced. By employing a diffusivity factor of 1.49 this agreement was maximized. Calculated infrared heating rates were typical of thin cirrus layers. The cloud top cooling and cloud base warming were observed to become more accentuated for the denser portions of cloud. The broadband emittances due to the cloud aerosol were found to approach 0.5 to 0.6. The cirrus clouds were observed to exhibit significant horizontal variability and a significant amount of scatter was evident when attempting to relate the broadband infrared and shortwave radiative properties. It is suggested that these radiative properties, which are modulated by the cloud elements, have their scales determined by the eddies detected in the analysis of wind components.

Smith, William L., Jr.↗
NASA NTRS1993

Cirrus cloud detection from airborne imaging spectrometer data using the 1.38 micron water vapor band

Using special images acquired by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) at 20 km altitude, we show that wavelengths close to the center of the strong 1.38 micron water vapor band are useful for detecting thin cirrus clouds. The detection makes use of the fact that cirrus clouds are located above almost all the atmospheric water vapor. Because of the strong water vapor absorption in the lower atmosphere, AVIRIS channels near 1.38 micron receive little scattered solar radiance from the surface of low level clouds. When cirrus clouds are present, however, these channels receive large amounts of scattered solar radiance from the cirrus clouds. Our ability to determine cirrus cloud cover using space-based remote sensing will be improved if channels near the center of the 1.38 micron water vapor band are added to future satellites.

Gao, Bo-Cai↗
NASA NTRS2010

Directly Measured Heating Rates of a Tropical Subvisible Cirrus Cloud

We present the first direct measurements of the infrared and solar heating rates of a tropical subvisible cirrus (SVC) cloud sampled off the east coast of Nicaragua on 25 July 2007 by the NASA ER-2 aircraft during the Tropical Composition, Cloud and Climate Coupling Experiment (TC4). On this day a persistent thin cirrus layer, with mostly clear skies underneath, was detected in real time by the cloud lidar on the ER-2, and the aircraft was directed to profile down through the SVC. Measurements of the net broadband infrared irradiance and spectrally integrated solar irradiance above, below, and through the SVC are used to determine the infrared and solar heating rates of the cloud. The lidar measurements show that the variable SVC layer was located between approximately 13 and 15 km. Its midvisible optical depth varied from 0.01 to 0.10 with a mean of 0.034 +/- 0.033. Its depolarization ratio was approximately 0.4, indicative of ice clouds. From the divergence of the measured net irradiances the infrared heating rate of the SVC was determined to be approximately 2.50 - 3.24 K/d and the solar heating rate was found to be negligible. These values are consistent with previous indirect observations of other SVC and with model-generated heating rates of SVC with similar optical depths. This study illustrates the utility and potential of the profiling sampling strategy employed here. A more fully instrumented high-altitude aircraft that also included in situ cloud and aerosol probes would provide a comprehensive data set for characterizing both the radiative and microphysical properties of these ubiquitous tropical clouds

Bucholtz, Anthongy↗
NASA NTRS2006

Properties of CIRRUS Overlapping Clouds as Deduced from the GOES-12 Imagery Data

Understanding the impact of cirrus clouds on modifying both the solar reflected and terrestrial emitted radiations is crucial for climate studies. Unlike most boundary layer stratus and stratocumulus clouds that have a net cooling effect on the climate, high-level thin cirrus clouds can have a warming effect on our climate. Many research efforts have been devoted to retrieving cirrus cloud properties due to their ubiquitous presence. However, using satellite observations to detect and/or retrieve cirrus cloud properties faces two major challenges. First, they are often semitransparent at visible to infrared wavelengths; and secondly, they often occur over a lower cloud system. The overlapping of high-level cirrus and low-level stratus cloud poses a difficulty in determining the individual cloud top altitudes and optical properties, especially when the signals from cirrus clouds are overwhelmed by the signals of stratus clouds. Moreover, the operational satellite retrieval algorithms, which often assume only single layer cloud in the development of cloud retrieval techniques, cannot resolve the cloud overlapping situation properly. The new geostationary satellites, starting with the Twelfth Geostationary Operational Environmental Satellite (GOES-12), are providing a new suite of imager bands that have replaced the conventional 12-micron channel with a 13.3-micron CO2 absorption channel. The replacement of the 13.3-micron channel allows for the application of a CO2-slicing retrieval technique (Chahine et al. 1974; Smith and Platt 1978), which is one of the important passive satellite methods for remote sensing the altitudes of mid to high-level clouds. Using the CO2- slicing technique is more effective in detecting semitransparent cirrus clouds than using the conventional infrared-window method.

Chang, Fu-Lung↗
NASA NTRS2002

Clouds and Water Vapor in the Climate System and Radiative Transfer in Clear Air and Cirrus Clouds in the Tropics

Research supported under this grant was aimed at attacking unanswered scientific questions that lie at the intersection of radiation, dynamics, chemistry, and climate. Considerable emphasis was placed on scientific collaboration and the innovative development of instruments required to address these issues. Specific questions include water vapor distribution in the tropical troposphere, atmospheric radiation, thin cirrus clouds, stratosphere-troposphere exchange, and correlative science with satellite observations.

Anderson, James G.↗
NASA NTRS2005

Impact of Cirrus Crystal Shape on Solar Spectral Irradiance: A Case Study for Subtropical Cirrus

Profiles of in situ measurements of ice crystal size distribution of subtropical cirrus were used to calculate solar spectral irradiances above and below the clouds. Spheres and nonspherical ice crystal habits (columns, hollows, plates, bullets, and aggregates) were assumed in the calculations. The simulation results were compared to irradiance measurements from the NASA Solar Spectral Flux Radiometer. The microphysical and radiation data were collected by three aircraft during CRYSTAL-FACE. Two cirrus cases (optical thickness of about 1 and 7) from two mission dates (26 and 23 July 2002) were investigated in detail. The measured downwelling and upwelling irradiance spectra above the cirrus could mostly be reproduced by the radiation model to within +/- 5-10% for most ice crystal habits. Below the cirrus the simulations disagreed with the measured irradiances due to surface albedo variability along the flight track, and nonoptimal colocation between the microphysical and irradiance measurements. The impact of shape characteristics of the crystals was important for the reflected irradiances above the optically thin cirrus, especially for small solar zenith angles, because in this case single-scattering dominated the solar radiation field. For the cirrus of moderate optical thickness the enhanced multiple scattering tended to diminish particular shape features caused by nonspherical single-scattering. Within the ice absorption bands the shape-related differences in the absorption characteristics of the individual nonspherical ice crystals were amplified if multiple scattering prevailed. Furthermore, it was found that below the cloud the shape sensitivity of the downwelling irradiance spectra is larger compared to the nonsphericity effects on reflected irradiances above the cirrus. Finally, it was shown that the calculated cirrus solar radiative forcing could vary by as much as 26% depending on the ice crystal habit.

Wendisch, Manfred↗
NASA NTRS2010

Evaluation of Satellite-Based Upper Troposphere Cloud Top Height Retrievals in Multilayer Cloud Conditions During TC4

Upper troposphere cloud top heights (CTHs), restricted to cloud top pressures (CTPs) less than 500 hPa, inferred using four satellite retrieval methods applied to Twelfth Geostationary Operational Environmental Satellite (GOES-12) data are evaluated using measurements during the July August 2007 Tropical Composition, Cloud and Climate Coupling Experiment (TC4). The four methods are the single-layer CO2-absorption technique (SCO2AT), a modified CO2-absorption technique (MCO2AT) developed for improving both single-layered and multilayered cloud retrievals, a standard version of the Visible Infrared Solar-infrared Split-window Technique (old VISST), and a new version of VISST (new VISST) recently developed to improve cloud property retrievals. They are evaluated by comparing with ER-2 aircraft-based Cloud Physics Lidar (CPL) data taken during 9 days having extensive upper troposphere cirrus, anvil, and convective clouds. Compared to the 89% coverage by upper tropospheric clouds detected by the CPL, the SCO2AT, MCO2AT, old VISST, and new VISST retrieved CTPs less than 500 hPa in 76, 76, 69, and 74% of the matched pixels, respectively. Most of the differences are due to subvisible and optically thin cirrus clouds occurring near the tropopause that were detected only by the CPL. The mean upper tropospheric CTHs for the 9 days are 14.2 (+/- 2.1) km from the CPL and 10.7 (+/- 2.1), 12.1 (+/- 1.6), 9.7 (+/- 2.9), and 11.4 (+/- 2.8) km from the SCO2AT, MCO2AT, old VISST, and new VISST, respectively. Compared to the CPL, the MCO2AT CTHs had the smallest mean biases for semitransparent high clouds in both single-layered and multilayered situations whereas the new VISST CTHs had the smallest mean biases when upper clouds were opaque and optically thick. The biases for all techniques increased with increasing numbers of cloud layers. The transparency of the upper layer clouds tends to increase with the numbers of cloud layers.

Chang, Fu-Lung↗
NASA NTRS1994

Multilevel cloud retrieval using multispectral HIRS and AVHRR data: Nighttime oceanic analysis

A multispectral, multiresolution (MSMR) method is developed for analyzing scenes of overlapping cloud layers. The MSMR method is applied to data from the NOAA 11 advanced very high resolution radiometer (AVHRR) and the high-resolution infrared radiometer sounder (HIRS-2). The data are from a nighttime oceanic scene in which a semitransparent cirrus veil overlays a large-scale stratus cloud. Low-cloud and clear-sky radiances are determined using a spatial coherence technique. Middle to upper level cloud pressures and radiances are estimated from HIRS-2 15 micrometer CO2 band radiometric data. The MSMR method improves the interpretation of a nighttime, oceanic scene containing thin cirrus over a large-scale stratiform cloud. If, for example, the same scene is analyzed using only the AVHRR 10.8 micrometer channel, the accompanying retrieved cloud heights are found to be between the cirrus and stratus cloud heights and are incorrectly identified as midlevel altostratus clouds. Theoretical radiative transfer model results for both water droplet spheres and randomly oriented hexagonal ice crystals are compared to observed AVHRR brightness temperature differences (BTD) between the 3.7- and 10.8 micrometer channels (BTD(sup 34)) and between the 10.8- and 12- micrometer channels (BTD(sup 45)) to distinguish among the effects of cloud optical depth, particle size, and phase for both single-layer clouds and overlapping two-layer clouds. Theoretical BTD calculations are used to estimate the range of effective particle sizes for eac h cloud layer. The data for the cirrus in the case study region near Bermuda are consistent with theoretical results for relatively small randomly oriented hexagonal ice crystals. The observed BTD(sup 34) and BTD(sup 45) values are lower for the cirrus above a lower-level cloud than for single-level cirrus with no underlying cloud. In certain cases the BTD analysis provides a way to distinguish between clouds composed of supercooled water droplets rather than ice particles. Analysis of nighttime data permits determination of stratus infrared optical depths smaller than 4.

Baum, Bryan A.↗
NASA NTRS2001

Determination of Top-of-Atmosphere Longwave Radiative Fluxes: A Comparison Between Two Approaches Using ScaRaB Data

Two conceptually different approaches (broadband-based ERBE and narrowband-based ISCCP approaches), used to derive the TOA longwave radiative fluxes, are compared using the ScaRaB simultaneous narrowband and broadband measurements. This study directly shows that the ERBE MLE-derived cloud covers implicitly contain some information on the cloud optical properties. A spurious view-zenith-angle dependence of the MLE scene identification scheme is confirmed by this study. Except for very thin cirrus clouds, differences between the ERBE and ISCCP approaches are in general < 10 W/sq m for the TOA LW radiative fluxes. For clear pixels, the model calculated (ISCCP approach) TOA LW radiances are systematically smaller than the observations. Though the bias is found to be correlated on the column precipitable water amount, the exact source of this discrepancy remains undetermined and merits further study. Compared with the radiative transfer model used in this study, the ERBE LW ADMs are too weakly limb-darkened for optically thin clouds, but too strongly limb-darkened for optically thick clouds, indicating that more accurate instantaneous TOA LW flux estimations from the ERBE approach would require additional cloud classes based on cloud height and optical thickness.

Chen, Ting↗