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NASA NTRS1986

Zonal and geographical distributions of cirrus clouds determined from SAGE data

Stratospheric Aerosol and Gas Experiment (SAGE) data obtained from February 1979-November 1981 are analyzed in order to evaluate the spatial extent and frequency occurrence of cirrus clouds. The capabilities of the SAGE measurement system which has a field of view of 100 sq km are discussed. The frequency of occurrence of the cirrus clouds and the frequency penetration of the clouds to fixed altitudes of 5, 7, and 9 km, and to altitudes of 1, 3 and 5 km below the troposphere are examined. It is observed that optically thick cirrus clouds form most frequently in the midlatitudes over the equator, with distinct minima near latitude bands of 20-30 deg north and south; height penetrations to 7 km occur 60 percent of the time in upper latitudes and drop to 30 percent over the tropics. The SAGE data are compared with selective chopper radiometer data and good correlation in shape and seasonal movement is displayed. The seasonal geographical distributions of cirrus clouds in regions of rising moist air associated with low-level convergence zones are described.

Woodbury, G. E.↗

NASA NTRS1991

Bi-directional reflectance of finite and infinite clouds

The transfer of solar irradiance in plane parallel and broken cloud fields is modeled using a Monte Carlo method. The angular distribution pattern of radiances exiting the cloud layer is studied with varying cloud geometries, optical thicknesses, cloudiness and solar zenith angles. A rather large anisotropy of the reflected flux is found, usually increasing with solar zenith angle and with patterns that strongly depend on cloud geometry. The main features are: a local maximum of reflected intensity in the forward direction for all cases; a limb darkening for the plane parallel case; and a limb brightening and a local maximum of reflected intensity in the backward direction for broken clouds. The method is used to study the cloud reflectance sensitivity to various parameters. A more precise description of cloud field internal and external structure is needed in order to obtain accurate bi directional reflectance diagrams.

Breon, Francois-Marie↗

NASA NTRS1992

Reflectance of broken cloud fields - Simulation and parameterization

The transfer of solar irradiance in plane parallel and broken cloud fields is simulated using a Monte Carlo method. The angular distribution pattern of radiances exiting the cloud layer is studied with varying cloud geometries, optical thicknesses, cloudiness, and solar zenith angles. A rather large anisotropy of the reflected flux is found, usually increasing with solar zenith angle and with patterns that strongly depend on cloud geometry. The main features are (1) a local maximum of reflected intensity in the forward direction for all cases, (2) a limb darkening for the plane parallel case, and (3) a limb brightening and a local maximum of reflected intensity in the backward direction for broken clouds. A parameterization for the azimuth-average reflectance function is developed. It reproduces the Monte Carlo simulation with a reasonable accuracy and illustrates that, when azimuthally averaged, the reflectance function is dominated by side viewing and intercloud shadowing effects.

Breon, Francois-Marie↗

NASA NTRS1981

Multichannel scanning radiometer for remote sensing cloud physical parameters

A multichannel scanning radiometer developed for remote observation of cloud physical properties is described. Consisting of six channels in the near infrared and one channel in the thermal infrared, the instrument can observe cloud physical parameters such as optical thickness, thermodynamic phase, cloud top altitude, and cloud top temperature. Measurement accuracy is quantified through flight tests on the NASA CV-990 and the NASA WB-57F, and is found to be limited by the harsh environment of the aircraft at flight altitude. The electronics, data system, and calibration of the instrument are also discussed.

Curran, R. J.↗

NASA NTRS1990

Global, seasonal cloud variations from satellite radiance measurements. II - Cloud properties and radiative effects

Cloud and surface radiative properties and their effects on the earth and surface radiation budgets are obtained based on global daily visible and IR radiance measurements. The magnitude of cloud property variations and their effects on radiation increase strongly with decreasing space/time scales. Cloud properties are systematically different between land and ocean, with ocean having larger cloud cover with somewhat larger optical thicknesses and lower cloud top altitudes. Although cloud variations appear to be the primary cause of regional radiation budget variability at 5-30 daytime scales, the effects of their seasonal variations at larger spatial scales are less important than the changes associated with changes in solar declination and atmospheric/surface temperatures. The largest seasonal variations in radiation occur in the 30-60 deg latitude band in each hemisphere. Although clouds have a net cooling effect on the global, annual mean radiation balance at both the top of the atmosphere and the surface, their net effect on regional, seasonal balances is much more varied.

Rossow, William B.↗

NASA NTRS2003

Optical measurements of gravity fields

Optical measurements of a gravitational field with sensitivity close to the sensitivity of atomic devices are possible if one detects properties of light after its interaction with optically thick atomic cloud moving freely in the gravity field. A nondestructive detection of a number of ultracold atoms in a cloud as well as tracking of the ground state population distribution of the atoms is possible by optical means.

whispering gallery modes microwave detection modul↗

NASA NTRS1989

Radiative cooling performance of a converging liquid drop radiator

The liquid drop radiator consists of many directed streams of hot liquid drops that are cooled by passing through space and are then collected for reuse. To facilitate the collection of the cooled liquid, a converging geometry might be useful. As the streams converge toward the collector, the density and optical thickness of the droplet cloud are increased. The increase of optical thickness in the flow direction is shown to reduce the local emittance along the length of the radiator.

Siegel, Robert↗

NASA NTRS1994

Global shortwave energy budget at the earth's surface from ERBE observations

A method is proposed to compute the net solar (shortwave) irradiance at the earth's surface from Earth Radiation Budget Experiment (ERBE) data in the S4 format. The S4 data are monthly averaged broadband planetary albedo collected at selected times during the day. Net surface shortwave irradiance is obtained from the shortwave irradiance incident at the top of the atmosphere (known) by subtracting both the shortwave energy flux reflected by the earth-atmosphere system (measured) and the energy flux absorbed by the atmosphere (modeled). Precalculated atmospheric- and surface-dependent functions that characterize scattering and absorption in the atmosphere are used, which makes the method easily applicable and computationally efficient. Four surface types are distinguished, namely, ocean, vegetation, desert, and snow/ice. Over the tropical Pacific Ocean, the estimates based on ERBE data compare well with those obtained from International Satellite Cloud Climatology Project (ISCCP) B3 data. For the 9 months analyzed the linear correlation coefficient and the standard difference between the two datasets are 0.95 and 14 W/sq m (about 6% of the average shortwave irradiance), respectively, and the bias is 15 W/sq m (higher ERBE values). The bias, a strong function of ISCCP satellite viewing zenith angle, is mostly in the ISCCP-based estimates. Over snow/ice, vegetation, and desert no comparison is made with other satellite-based estimates, but theoretical calculations using the discrete ordinate method suggest that over highly reflective surfaces (snow/ice, desert) the model, which accounts crudely for multiple reflection between the surface and clouds, may substantially overestimate the absorbed solar energy flux at the surface, especially when clouds are optically thick. The monthly surface shortwave irradiance fields produced for 1986 exhibit the main features characteristic of the earth's climate. As found in other studies, our values are generally higher than Esbensen and Kushnir's by as much as 80 W/sq m in the tropical oceans. A cloud parameter, defined as the difference between clear-sky and actual irradiances normalized to top-of-atmosphere clear-sky irradiance, is also examined. This parameter, minimally affected by sun zenith angle, is higher in the midlatitude regions of storm tracks than in the intertropical convergence zone (ITCZ), suggesting that, on average, the higher cloud coverage in midlatitudes is more effective at reducing surface shortwave irradiance than opaque, convective, yet sparser clouds in the ITCZ. Surface albedo estimates are realistic, generally not exceeding 0.06 in the ocean, as high as 0.9 in polar regions, and reaching 0.5 in the Sahara and Arabian deserts.

Breon, Francois-Marie↗

NASA NTRS1985

Far-infrared line intensities of H2O and CO from warm molecular clouds

Takahashi et al. (1983) have studied the role of H2O in the overall energetics of warm molecular clouds with large optical depths. It was found that in molecular clouds associated with nearby or embedded luminosity sources, the dust is likely to be warmer than the molecular gas. Thus, the warm dust represents the primary source of heat for the gas. In some cases, H2O was found to cool the gas. Takahashi et al. (1983) have presented the formalism for treating H2O in an optically thick molecular cloud with embedded sources of luminosity. The total H2O heating and cooling rates were also calculated. In the present investigation, the emergent intensities of far-infrared lines of H2O and excited, rotational CO transitions from relatively warm molecular clouds based on the large-velocity gradient model of the previous study are calculated. It is found that the dominant submillimeter CO transitions are related to emission, while the H2O transitions can be either absorption or emission lines.

Takahashi, T.↗

NASA NTRS2003

Computation of Domain-Averaged Shortwave Irradiance by a One-Dimensional Algorithm Incorporating Correlations between Optical Thickness and Direct Incident Radiation

A one-dimensional radiative transfer algorithm that accounts for correlations between the optical thickness and the incident direct solar radiation is developed to compute the domain-averaged shortwave irradiance profile. It divides the direct irradiance into four components and treats the direct irradiance in two separate, clear and cloudy columns to account for the fact that clouds attenuate the direct irradiance more than clear-sky. The horizontal inhomogeneity of clouds in the cloudy column is treated by the gamma weighted two-stream approximation, which assumes that the optical thickness of clouds follows a gamma distribution. The algorithm inputs the cloud fraction, cumulative cloud fraction as a function of height, and a parameter expressing the shape of the probability density function of the cloud optical thickness distribution in addition to inputs required for a two-stream radiative transfer model. These cloud property inputs can be obtained using ground- and satellite-based instruments. Therefore, the algorithm can treat realistic cloud overlap features and horizontal inhomogeneity of clouds in a framework of one- dimensional radiative transfer. Heating rates computed by the algorithm using cloud fields generated by cloud resolving models agree with those computed with a Monte Carlo model. If optical properties in computational layers that divide a vertically extensive cloud are correlated, the irradiance profile computed by the algorithm further improves.

Kato, S.↗

NASA NTRS1991

Determination of the optical thickness and effective particle radius of clouds from reflected solar radiation measurements. II - Marine stratocumulus observations

A multispectral scanning radiometer has been used to obtain measurements of the reflection function of marine stratocumulus clouds at 0.75 micron and at 1.65 and 2.16 microns. These observations were obtained from the NASA ER-2 aircraft as part of the FIRE, conducted off the coast of southern California during July 1987. Multispectral images of the reflection function were used to derive the optical thickness and the effective particle radius of stratiform cloud layers on four days. In addition to the radiation measurements, in situ microphysical measurements were obtained from an aircraft. In this paper, the remote sensing results are compared with in situ observations, which show a good spatial correlation for both optical thickness and effective radius. These comparisons further show systematic differences between remote sensing and in situ values, with a tendency for remote sensing to overestimate the effective radius by about 2-3 microns, independent of particle radius. The optical thickness, in contrast, is somewhat overestimated for small optical thicknesses and underestimated for large optical thicknesses. An introduction of enhanced gaseous absorption at a wavelength of 2.16 microns successfully explains some of these observed discrepancies.

Nakajima, Teruyuki↗

NASA NTRS2001

Observed and Simulated Radiative and Microphysical Properties of Tropical Convective Storms

Increases in the ice content, albedo and cloud cover of tropical convective storms in a warmer climate produce a large negative contribution to cloud feedback in the GISS GCM. Unfortunately, the physics of convective upward water transport, detrainment, and ice sedimentation, and the relationship of microphysical to radiative properties, are all quite uncertain. We apply a clustering algorithm to TRMM satellite microwave rainfall retrievals to identify contiguous deep precipitating storms throughout the tropics. Each storm is characterized according to its size, albedo, OLR, rain rate, microphysical structure, and presence/absence of lightning. A similar analysis is applied to ISCCP data during the TOGA/COARE experiment to identify optically thick deep cloud systems and relate them to large-scale environmental conditions just before storm onset. We examine the statistics of these storms to understand the relative climatic roles of small and large storms and the factors that regulate convective storm size and albedo. The results are compared to GISS GCM simulated statistics of tropical convective storms to identify areas of agreement and disagreement.

DelGenio, Anthony D.↗

NASA NTRSDate not supplied

Formation of Tropopause Cirrus clouds by Typhoon-induced gravity waves during the Asian Summer Monsoon: A Case Study from the BATAL 2017 Campaign

Cirrus clouds in the Tropical Tropopause Layer (TTL) have a net warming impact on Earth’s climate and they regulate the amount of water vapor entering the lower stratosphere through dehydration process near the cold-point tropopause. During the Boreal summer, Asian Summer Monsoon (ASM) is an important source of cirrus clouds and humidity in the TTL owing to frequent deep convection. However, better representation of convection and TTL cirrus clouds in global climate models is needed for accurate assessment of their response to changing climate. In this study, we investigate the mechanisms involved in the formation of a tropopause cirrus cloud layer observed during the Balloon measurement campaigns of the Asian Tropopause Aerosol Layer (BATAL) over Hyderabad (17.47 °N, 78.58 °E), India on 23 August 2017. A subvisible cirrus cloud layer (optical thickness ~0.025) was detected by a backscatter sonde (COBALD) onboard a balloon near the cold-point tropopause (CPT, temperature~ -86.4 ° C, altitude~17.9 km) which was later confirmed by the CATS lidar on the ISS. Simultaneous measurements from an optical particle counter (Boulder Counter) revealed the presence of ice crystals smaller than 50 microns in this layer. The formation mechanism responsible for this tropopause cirrus is investigated using a technique combining three-dimensional back-trajectories, satellite observations, and ERA5 reanalysis data. Satellite observations revealed that the overshooting convection associated with a category-3 typhoon Hato, which hit Macau and Hong Kong on 23 August 2017 injected ice into the lower stratosphere. This caused a hydration patch that followed the ASM anticyclone subsequently moving towards Hyderabad. The presence of tropopause cirrus cloud layers in the cold temperature anomalies and updrafts along the back-trajectories indicated towards the role of typhoon-induced gravity waves in their formation. This case study highlights the role of typhoons in influencing the formation of tropopause cirrus clouds through stratospheric hydration and gravity waves in the ASM anticyclone.

Amit Kumar Pandit↗

NASA NTRS1985

Latitude survey of aerosol optical thickness of the El Chichon eruption cloud in May 1983

The results of measurements of the latitudinal distribution of the El Chichon eruption cloud in May 1983 for the latitude range between 71 deg N and 56 deg S are presented. Aerosol optical thicknesses are calculated from solar spectral extinction measurements made with a sunphotometer on board the NASA Convair 990 aircraft. It is shown that the thicknesses vary in the range between 0.12 and 0.01, that a maximum of about 0.12 is found at middle latitudes, and that distinct minima of 0.01-0.02 are observed at 25-deg latitude in both hemispheres. The median radius of particles is found to be between 0.16 micron and 0.18 micron in the northern hemisphere and between 0.11 micron and 0.15 micron in the southern hemisphere. Rough estimates of aerosol mass indicate that about 1.5 megatonnes of aerosol still persisted in the stratosphere between the equator and 25-deg N one year after the eruption.

Shah, G. M.↗

NASA NTRS1974

Estimates of the Venus atmosphere optical characteristics with application to the problem of photographing its clouds and surface

Optical parameters investigated and solved for included: (1) cloud layer albedo and cloud cover optical thickness; (2) planetary surface self-radiation influence; (3) light flux distribution as function of atmospheric height; (4) upper estimate of the observed contrasts; (5) surface optical parameters; and (6) contrast decrease with altitude.

Biryukov, Y. L.↗

NASA NTRS1981

The albedo of snow for partially cloudy skies

The albedo of snow is defined as the ratio of reflected to incident solar energy, and it is an important parameter in the earth's radiation budget analysis and in the study of snowpack's thermal conditions. An approximate model for calculating the incident spectral flux for partially cloudy skies is presented. The input parameters for the calculation are atmospheric precipitable water, turbidity, ozone content, surface pressure, the optical thickness of clouds, and the grain size of snow crystals. The spectral snow reflectance model considers both specular surface reflection and volumetric multiple scattering. The surface reflection is calculated by using a crystal-shape-dependent bidirectional reflectance distribution function; the volumetric multiple scattering is calculated by using a crystal-size-dependent approximate solution in the radiative transfer equation. The model yields spectral and integrated solar flux and snow reflectance as a function of solar elevation and fractional cloud-cover. The illustrative insolation and albedo values were obtained from spectral reflectance and incident flux for representative parameters of Antarctic coastal regions. A simple relationship between grain size and the overcast albedo was obtained. For a set of grain size and shape, the albedo as a function of solar elevation and fractional cloud cover was tabulated.

Choudhury, B. J.↗

NASA NTRS1982

Visibility of comet nuclei

Photography of the nucleus of comet Halley is the goal of several planned space missions. The nucleus of a comet is surrounded by a cloud of dust particles. If this cloud is optically thick, it will prevent observation of the nuclear surface. Broadband photometry of nine comets has been analyzed to determine the visibility of their nuclei. Only in the case of comet West near perihelion was the dust dense enough to interfere with imaging. Comparison of the visual brightness of the well-observed comets with that of Halley in 1910 leads to the conclusion that the nucleus of Halley can be imaged without significant obscuration by the dust.

Ney, E. P.↗

NASA NTRS1984

Inhomogeneous models of Titan's aerosol distribution

A model of Titan's aerosol is presented which allows the particle size to vary with height. The model assumes a refractive index appropriate to an ethylene polymer and a mass flux independent of height equal to the value derived from laboratory measurements. The free parameters of the model are determined by fitting to the observed geometric albedo at 4000 and 6000 A. A methane spectrum is derived which is in excellent agreement with observations. An aerosol optical depth of about 5 is found in the visible, with the particle radius varying from 0.01 to 8 microns. The presence of an optically thick methane cloud at the temperature minimum is indicated.

Podolak, M.↗