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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Contrails

One of the most visible signs of human influence on the atmosphere is the condensation trail, or contrail, formed behind high altitude aircraft. This anthropogenic cirrus cloud can occur as a single line or in imposing geometrical formations as clusters of criss-crossing or parallel lines, Like natural cirrus clouds, contrails are composed of ice crystals and can produce the same dramatic optical displays, especially around sunrise or sunset. Persistent contrails also play a role in climate because they reflect sunlight and trap infrared radiation just like their naturally formed cousins. Thus, the presence of a contrail cluster in an otherwise clear sky can diminish the amount of solar energy reaching the surface during the daytime and increase the amount of infrared radiation absorbed in the atmosphere at all times of day. These opposing effects can simultaneously cool the surface and warm the air within the troposphere. Currently, the overall impact appears to be a warming effect, but research is continuing to unravel the role of this phenomenon in climate change.

Minnis, Patrick↗
DOE OSTI2021

“Experimental investigation of the governing parameters of atmospheric ice nucleation using field-collected and laboratory generated aerosol particles and its application in cloud resolving models” (Final Report)

The objective of this research project is to improve our understanding of the role of aerosol particles acting as ice-nucleating particles (INPs) which in turn define the mixed-phase and cirrus cloud radiative properties and thus climate. The focus is placed on how the physicochemical particle population properties determine the particles’ ability to initiate ice nucleation. This research project combined micro-spectroscopic particle analysis, experimental ice nucleation studies, and model sensitivity studies to advance our predictive capability of the formation of mixed-phase and cirrus clouds. These project activities have led to new ice nucleation data from laboratory generated and ambient (authentic) aerosol particles furthering process-level understanding, insights in the role of organic aerosol in ice formation, and advancements in the interpretation and parameterization of ice nucleation.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1990

Global distributions of cirrus determined from Sage II occultation measurements between November 1984 and October 1988

This paper describes the morning versus late afternoon differences and the seasonal changes of zonal average cirrus occurrence, and presents an overview of the global distributions of cirrus clouds for both summer and winter months. Results are compared with the corresponding results in the literature to illustrate the complementary nature of these cirrus cloud climatology efforts utilizing various data sets.

Chiou, E. W.↗
NASA NTRS2015

Thermodynamic Derivation of the Activation Energy for Ice Nucleation

Cirrus clouds play a key role in the radiative and hydrological balance of the upper troposphere. Their correct representation in atmospheric models requires an understanding of the microscopic processes leading to ice nucleation. A key parameter in the theoretical description of ice nucleation is the activation energy, which controls the flux of water molecules from the bulk of the liquid to the solid during the early stages of ice formation. In most studies it is estimated by direct association with the bulk properties of water, typically viscosity and self-diffusivity. As the environment in the ice-liquid interface may differ from that of the bulk, this approach may introduce bias in calculated nucleation rates. In this work a theoretical model is proposed to describe the transfer of water molecules across the ice-liquid interface. Within this framework the activation energy naturally emerges from the combination of the energy required to break hydrogen bonds in the liquid, i.e., the bulk diffusion process, and the work dissipated from the molecular rearrangement of water molecules within the ice-liquid interface. The new expression is introduced into a generalized form of classical nucleation theory. Even though no nucleation rate measurements are used to fit any of the parameters of the theory the predicted nucleation rate is in good agreement with experimental results, even at temperature as low as 190 K, where it tends to be underestimated by most models. It is shown that the activation energy has a strong dependency on temperature and a weak dependency on water activity. Such dependencies are masked by thermodynamic effects at temperatures typical of homogeneous freezing of cloud droplets; however, they may affect the formation of ice in haze aerosol particles. The new model provides an independent estimation of the activation energy and the homogeneous ice nucleation rate, and it may help to improve the interpretation of experimental results and the development of parameterizations for cloud formation.

Cirrus clouds↗
NASA NTRS1976

Wind estimates from cloud motions - Preliminary results from phases I, II and III of an in situ aircraft verification experiment

The accuracy of wind estimates derived from cloud motion is under investigation. Aircraft measurements of the ambient wind field have been compared with simultaneous inertial navigation system descriptions of the extent and motion of 40 tropical cumulus and 5 cirrus clouds. Preliminary results indicate that cloud-motion wind estimates are sufficiently accurate to be used in sensitive divergence, vorticity, and vertical motion calculations. The magnitude of the vector difference between the cirrus cloud velocity and the mean wind of the cloud layer was found to be about 1.6 m/sec. The major source of error is thought to be in determination of the position of the cloud. In the case of cumulus clouds, the magnitude of the vector difference between the aircraft-measured cloud motion and the cloud-base wind is less than 1.3 m/sec.

Hasler, A. F.↗
NASA NTRS1995

Physical and Optical/Radiative Characteristics of Small Particles in Tropical Cirrus

Whether cirrus clouds heat or cool the Earth-atmosphere system depends on the relative importance of the cloud shortwave albedo effect and the cloud thermal greenhouse effect. Both an determined by the distribution of ice condensate with cloud particle size. The microphysics instrument package flown aboard the DC-8 In TOGA/COARE included an ice crystal replicator, a 2D Greyscale Cloud Particle Probe and a Forward Scattering Spectrometer Aerosol Probe. In combination. these instruments permitted particle size measurements between 0.5 micrometers and 2.6 mm diameter. Ice crystal replicas were used to validate signals from the electro-optical instruments. Typical results show a prevalence in tropical cirrus clouds of micron-sized particles, in addition to cloud particles that exceed 100 micrometer radius. The mechanism of their formation is growth of (hygroscopic, possibly ocean-derived) aerosol particles along the Kohler curves. The concentration of small particles is higher and less variable in space and time, and their tropospheric residence time is longer, than those of large cloud particles because of lower sedimentation velocities. Small particles shift effective cloud particle radii to sizes much smaller than the mean diameter of the cloud particles. This causes an increase in shortwave reflectivity and IR emissivity. and a decrease in transmissivity. In the cirrus outflow of tropical cyclone Oliver on 8 February, 1993, the reflectivity increases with altitude (decreasing temperature) stronger than does cloud emissivity, yielding enhanced radiative cooling at higher altitudes.

Pueschel, R. F.↗
NASA NTRS2004

Airborne In Situ and Ground-based Polarimetric Radar Measurements of Tropical Convection in Support of CRYSTAL-FACE

This report describes the work performed by the University of North Dakota (UND) under NASA Grant NAG5-11509, titled Airborne In Situ and Ground-based Polarimetric Radar Measurements of Tropical Convection in Support of CRYSTAL-FACE. This work focused on the collection of data by two key platforms: the UND Citation II research aircraft and the NASA NPOL radar system. The CRYSTAL-FACE (C-F) mission addresses several key issues from the NASA Earth System Enterprise, including the variability of water in the atmosphere, the forcing provided by tropical cirrus and the response of the Earth system to this forcing. In situ measurements and radar observations of tropical convection, cirrus clouds and their environment are core elements of C-F. One of the primary issues that C-F is addressing is the relationship of tropical cirrus anvils to precipitating deep convection. The in situ measurements from C-F are being used to validate remote sensing of Earth-Atmosphere properties, increase our knowledge of upper tropospheric water vapor and its distribution, and increase our knowledge of tropical cirrus cloud morphology and composition. Radar measurements, especially polarimetric diversity observations available fiom the NASA NPOL radar, are providing essential information about the initiation, modulation, and dissipation of convective cores and the generation of associated anvils in tropical convection. Specifically, NPOL radar measurements contain information about convective intensity and its vertical structure for comparison with thermodynamic and kinematic environmental measurements observed from soundings. Because of the polarimetric diversity of MOL, statistics on bulk microphysical properties can be retrieved and compared to the other characteristics of convection and associated cirrus anvils. In summary, the central objectives of this proposal were to deploy the UND Citation research aircraft as an in situ sensing platform for this mission and to provide collaborative analyses of the recorded data and to deploy the NPOL radar to observe the characteristics of cirrus and parent convection.

Poellot, Michael R.↗
DOE OSTI2025

Implementation of Sub‐Grid Scale Temperature Perturbations Induced by Non‐Orographic Gravity Waves in WACCM6

Abstract Atmospheric gravity waves can play a significant role on atmospheric chemistry through temperature fluctuations. A recent modeling study introduced a method to implement subgrid‐scale orographic gravity‐wave‐induced temperature perturbations in the Whole Atmosphere Community Climate Model (WACCM). The model with a wave‐induced temperature parameterization was able to reproduce for example, the influence of mountain wave events on atmospheric chemistry, as highlighted in previous literature. Here we extend the subgrid‐scale wave‐induced temperature parameterization to also include non‐orographic gravity waves arising from frontal activity and convection. We explore the impact of these waves on middle atmosphere chemistry, particularly focusing on reactions that are strongly sensitive to temperature. The non‐orographic gravity waves increase the variability of chemical reaction rates, especially in the lower mesosphere. As an example, we show that this, in turn, leads to increases in the daytime ozone variability. To demonstrate another impact, we briefly investigate the role of non‐orographic gravity waves in cirrus cloud formation in this model. Consistent with findings from the previous study focusing on orographic gravity waves, non‐orographic waves also enhance homogeneous nucleation and increase cirrus clouds. The updated method used enables the global chemistry‐climate model to account for both orographic and non‐orographic gravity‐wave‐induced subgrid‐scale dynamical perturbations in a consistent manner.

Yook, Simchan [Department of Earth Atmospheric and↗
NASA NTRS1993

Normalized vertical ice mass flux profiles from vertically pointing 8-mm-wavelength Doppler radar

During the FIRE 2 (First International Satellite Cloud Climatology Project Regional Experiment) project, NOAA's Wave Propagation Laboratory (WPL) operated its 8-mm wavelength Doppler radar extensively in the vertically pointing mode. This allowed for the calculation of a number of important cirrus cloud parameters, including cloud boundary statistics, cloud particle characteristic sizes and concentrations, and ice mass content (imc). The flux of imc, or, alternatively, ice mass flux (imf), is also an important parameter of a cirrus cloud system. Ice mass flux is important in the vertical redistribution of water substance and thus, in part, determines the cloud evolution. It is important for the development of cloud parameterizations to be able to define the essential physical characteristics of large populations of clouds in the simplest possible way. One method would be to normalize profiles of observed cloud properties, such as those mentioned above, in ways similar to those used in the convective boundary layer. The height then scales from 0.0 at cloud base to 1.0 at cloud top, and the measured cloud parameter scales by its maximum value so that all normalized profiles have 1.0 as their maximum value. The goal is that there will be a 'universal' shape to profiles of the normalized data. This idea was applied to estimates of imf calculated from data obtained by the WPL cloud radar during FIRE II. Other quantities such as median particle diameter, concentration, and ice mass content can also be estimated with this radar, and we expect to also examine normalized profiles of these quantities in time for the 1993 FIRE II meeting.

Orr, Brad W.↗
DOE OSTI2023

Orographic Cirrus and Its Radiative Forcing in NCAR CAM6

Cirrus clouds play an important role in the Earth's radiative energy budget, thereby affecting the climate state and climate change. Orographic gravity wave (OGW)-induced sub-grid scale vertical velocity (i.e., cooling rate) is not resolved by large-scale models and its impact on ice formation in cirrus clouds is not well quantified. In this study, one sub-grid scale OGW scheme (e.g., McFarlane) is used in the Community Atmosphere Model version 6 (CAM6) to generate vertical velocity variance (σw) for cirrus formation. Results from the default model and simulations with the OGW-induced σw are evaluated against the DOE ARM Small Particles in Cirrus (SPARTICUS) campaign observations. The OGW based on the McFarlane scheme increases the sub-grid scale σw over mountains compared to the default model and improves the model agreement with the SPARTICUS observations. Larger σ w due to OGWs can trigger more frequent homogeneous nucleation in orographic cirrus and generates a higher number concentration of ice crystals observed during the SPARTICUS campaign. Moreover, our evaluation of the model simulations against satellite observations indicates that the McFarlane scheme generates high in-cloud ice number concentrations (>200 L -1 ) in the upper troposphere over mountains and high plateaus at mid- and high-latitudes of the winter hemisphere as shown in the observations. More ice crystals with smaller sizes absorb more infrared radiation (+0.523 ± 0.125 W m -2 ). The net radiative cloud forcing change at the top of the atmosphere is +0.330 W m -2 due to the orographic cirrus.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1997

Subsonic Aircraft Contrail and Cloud Effects Special Study (SUCCESS)

During recent years interest in the impact of commercial aircraft on the climate has increased. Aircraft might impact climate in a number of ways. Contrails are clearly a direct radiative forcing mechanism. Exhaust emissions, principally soot and sulfate, might indirectly force the climate by modifying the radiative properties of cirrus clouds. The SUCCESS program was carried out to investigate these issues. It also has several other goals including: better understanding the emissions from aircraft, better understanding the formation of cirrus clouds: better understanding the radiative properties of contrails and clouds and their remote sensing; better understanding the heterogeneous chemistry in the upper atmosphere; and developing new instruments of importance to atmospheric chemistry and cloud physics. SUCCESS took place during April and May of 1997. The NASA DC-8, ER-2, T-39, and 757 aircraft were used as in situ sampling, remote sensing, near field sampling, and emission sources respectively. Most of the operations occurred near the DOE's Atmospheric Radiation Measurement Site in Northern Oklahoma. The DOE operated several other aircraft so that on some days as many as six research aircraft flew together. Numerous new instruments functioned during the mission. This talk will present an overview of SUCCESS from the operational point of view, and provide some of the overall scientific highlights.

Toon, O.B.↗
NASA NTRS1997

Subsonic Aircraft Contrail and Cloud Effects Special Study (SUCCESS)

During recent years interest in the impact of commercial aircraft on the climate has increased. Aircraft might impact climate in a number of ways. Contrails are clearly a direct radiative forcing mechanism. Exhaust emissions, principally soot and sulfate, might indirectly radiative force the climate by modifying the properties of cirrus clouds. The SUCCESS program was carried out to investigate these issues. It also had several other goals including: better understanding the emissions from aircraft, better understanding the formation of cirrus clouds: better understanding the radiative properties of contrail and clouds and their remote sensing; better understanding the heterogeneous chemistry in the upper atmosphere; and developing new instruments of importance to atmospheric chemistry and cloud physics. SUCCESS took place during April and May of 1996. The NASA DC-8, ER-2, T-39, and 757 aircraft were used as in situ sampling, remote sensing, near field sampling, and emission sources respectively. Most of the operations occurred near the DOE's Atmospheric Radiation Measurement Site in Northern Oklahoma. The DOE operated several other aircraft so that on some days as many as six research aircraft operated together. Numerous new instruments operated during the mission. This talk will present an overview of SUCCESS from the operational point of view, and provide some of the overall scientific highlights.

Toon, O. B.↗
NASA NTRS2001

Satellite Remote Sensing of Tropical Precipitation and Ice Clouds for GCM Verification

This project, supported by the NASA New Investigator Program, has primarily been funding a graduate student, Darren McKague. Since August 1999 Darren has been working part time at Raytheon, while continuing his PhD research. Darren is planning to finish his thesis work in May 2001, thus some of the work described here is ongoing. The proposed research was to use GOES visible and infrared imager data and SSM/I microwave data to obtain joint distributions of cirrus cloud ice mass and precipitation for a study region in the Eastern Tropical Pacific. These joint distributions of cirrus cloud and rainfall were to be compared to those from the CSU general circulation model to evaluate the cloud microphysical amd cumulus parameterizations in the GCM. Existing algorithms were to be used for the retrieval of cloud ice water path from GOES (Minnis) and rainfall from SSM/I (Wilheit). A theoretical study using radiative transfer models and realistic variations in cloud and precipitation profiles was to be used to estimate the retrieval errors. Due to the unavailability of the GOES satellite cloud retrieval algorithm from Dr. Minnis (a co-PI), there was a change in the approach and emphasis of the project. The new approach was to develop a completely new type of remote sensing algorithm - one to directly retrieve joint probability density functions (pdf's) of cloud properties from multi-dimensional histograms of satellite radiances. The usual approach is to retrieve individual pixels of variables (i.e. cloud optical depth), and then aggregate the information. Only statistical information is actually needed, however, and so a more direct method is desirable. We developed forward radiative transfer models for the SSM/I and GOES channels, originally for testing the retrieval algorithms. The visible and near infrared ice scattering information is obtained from geometric ray tracing of fractal ice crystals (Andreas Macke), while the mid-infrared and microwave scattering is computed with Mie scattering. The radiative transfer is performed with the Spherical Harmonic Discrete Ordinate Method (developed by the PI), and infrared molecular absorption is included with the correlated k-distribution method. The SHDOM radiances have been validated by comparison to version 2 of DISORT (the community "standard" discrete-ordinates radiative transfer model), however we use SHDOM since it is computationally more efficient.

Evans, K. Franklin↗
NASA NTRS1993

Extinction efficiencies from DDA calculations solved for finite circular cylinders and disks

One of the most commonly noted uncertainties with respect to the modeling of cirrus clouds and their effect upon the planetary radiation balance is the disputed validity of the use of Mie scattering results as an approximation to the scattering results of the hexagonal plates and columns found in cirrus clouds. This approximation has historically been a kind of default, a result of the lack of an appropriate analytical solution of Maxwell's equations to particles other than infinite cylinders and spheroids. Recently, however, the use of such approximate techniques as the Discrete Dipole Approximation has made scattering solutions on such particles a computationally intensive but feasible possibility. In this study, the Discrete Dipole Approximation (DDA) developed by Flatau (1992) is used to find such solutions for homogeneous, circular cylinders and disks. This can serve to not only assess the validity of the current radiative transfer schemes which are available for the study of cirrus but also to extend the current approximation of equivalent spheres to an approximation of second order, homogeneous finite circular cylinders and disks. The results will be presented in the form of a single variable, the extinction efficiency.

Withrow, J. R.↗
NASA NTRS1990

Interpretation of satellite-measured bidirectional reflectance from Cirrus cloudy atmospheres

The interpretation of the observed bidirectional reflectance from cirrus cloudy atmospheres is presented. A theoretical model was developed for the computation of the transfer of solar radiation in an anisotropic medium with particular applications to oriented ice crystals in cirrus clouds. In this model, the adding principle for radiative transfer was used with modifications to account for the anisotropy of scattering particles and the associated scattering phase matrix. The single-scattering properties, including the phase function, single-scattering albedo, and extinction cross sections, were used for randomly and horizontally oriented hexagonal ice crystals in radiative transfer computations. The radiative transfer model developed for the cirrus clouds was modified to account for the scattering contributions from the atmosphere and the surface. In order to test the relevance and significance of the ice crystal model for the interpretation of observed bidirectional reflectance from satellites, visible radiances collected on the half hour by the GOES series were selected. The data are calibrated and corrected with the proper filter functions, then navigated to match selected landmark data. A number of clear and cloudy cases during the cirrus IFO of the Fire experiment were chosen for theoretical analyses. The cloud particle shape and size distributions that were taken during satellite overpasses are used in radiative transfer calculations. The sensitivities of the shape, orientation, and size distribution of ice crystals on the reflected intensities at the top of the atmosphere are investigated. Finally, the relative importance of these cloud microphysical properties in the interpretation of satellite bidirectional reflectance are assessed and presented.

Takano, Y.↗
NASA NTRS1990

The 27-28 October 1986 FIRE IFO cirrus case study - Cloud parameter fields derived from satellite data

A cirrus parameter retrieval methodology and the results of its application over the cirrus Intensive Field Observation (IFO) area using data from the Geostationary Operational Environmental Satellite (GOES) taken during the FIRE cirrus case study days, October 27-28, 1986. An impirical cloud bidirectional reflectance model derived from another IFO analysis was combined with a theoretical ice crystal cloud albedo model to estimate visible cloud optical thickness, which was used to derive the cloud infrared emittance. Cloud altitude was adjusted based on the derived emittance and observed temperatures. The approach developed here produced a very reasonable picture of cirrus cloud fields. It was estimated that the cloud-top and cloud-center heights are derived with a precision of about 0.6 km, except in very broken cloud conditions. Cirrus cloud thicknesses were also estimated and it is found that the derived results are comparable to other case study observations.

Minnis, Patrick↗
NASA NTRS1998

First results from the aerosol lidar and backscatter sonde intercomparison campaign STRAIT'1997 at table mountain facility during February-March 1997

First results of an intercomparison measurement campaign between three aerosol lidar instruments and in-situ backscatter sondes performed at Table Mountain Facility (34.4 deg N, 117.7 deg E, 2280 m asl) in February-March 1997 are presented. During the campaign a total of 414 hours of lidar data were acquired by the Aerosol-Temperature-Lidar (ATL, Goddard Space Flight Center) the Mobile-aerosol-Raman-Lidar (MARL, Alfred Wegener Institute), and the TMF-Aerosol-Lidar (TAL, Jet Propulsion Laboratory), and four backscatter sondes were launched. From the data set altitude profiles of backscatter ratio and volume depolarization of stratospheric background aerosols at altitudes between 15 and 25 km and optically thin high-altitude cirrus clouds at altitudes below 13 km are derived. On the basis of a sulfuric acid aerosol model color ratio profiles obtained from two wavelength lidar data are compared to the corresponding profiles derived from the sonde observations. We find an excellent agreement between the in-situ and ATL lidar data with respect to backscatter and color ratio. Cirrus clouds were present on 16 of 26 nights during the campaign. Lidar observations with 17 minute temporal and 120-300 m spatial resolution indicate high spatial and temporal variability of the cirrus layers. Qualitative agreement is found between concurrent lidar measurements of backscatter ratio and volume depolarization.

Beyerle, G.↗
NASA NTRS1993

Vertical velocity in cirrus case obtained from wind profiler

Cirrus clouds play an important role in the climate and general circulation because they significantly modulate the radiation properties of the atmosphere. However understanding the processes that govern their presence is made difficult by their high altitude, variable thickness, complex microphysical structure, and relatively little knowledge of the vertical motion field. In the FIRE 2 (First International Satellite Cloud Climatology Regional Experiment) experiment, a 404 MHz wind profiler was set up to provide continuous measurements of clear air wind field at Parsons, Kansas. Simultaneously, the NOAA wind profiler network supplied a wider spacial scale observation. On 26 Nov. 1991, the most significant cirrus cloud phenomena during the experiment with a jet streak at 250 Mb occurred. Analyses of the vertical wind velocity are made by utilizing different methods based on wind profiler data, among them the direct measurements from CSU wind profiler and NOAA network wind profilers, VAD (Velocity Azimuth Display) technique and the kinematic method.

Song, Ran↗