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At least 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Updraft dynamics and microphysics: on the added value of the cumulus thermal reference frame in simulations of aerosol–deep convection interactions

One fundamental question about atmospheric moist convection processes that remains debated is whether, or under which conditions, a relevant variability in background aerosol concentrations may have a significant dynamical impact on convective clouds and their associated precipitation. Furthermore, current climate models must parameterize both the microphysical and the cumulus convection processes, but this is usually implemented separately, whereas in nature there is a strong coupling between them. As a first step to improve our understanding of these two problems, we investigate how aerosol concentrations modify key properties of updrafts in eight large-eddy-permitting regional simulations of a case study of scattered convection over Houston, Texas, in which convection is explicitly simulated and microphysical processes are parameterized. Dynamical and liquid-phase microphysical responses are investigated using the following two different reference frames: static cloudy updraft grid cells versus tracked cumulus thermals. In both frameworks, we observe the expected microphysical responses to higher aerosol concentrations, such as higher cloud number concentrations and lower rain number concentrations. In terms of the dynamical responses, both frameworks indicate weak impacts of varying aerosol concentrations relative to the noise between simulations over the observationally derived range of aerosol variability for this case study. On the other hand, results suggest that thermals are more selective than cloudy updraft grid cells in terms of sampling the most active convective air masses. For instance, vertical velocity from thermals is significantly higher at upper levels than when sampled from cloudy updraft grid points, and several microphysical variables have higher average values in the cumulus thermal framework than in the cloudy updraft framework. In addition, the thermal analysis is seen to add rich quantitative information about the rates and covariability of microphysical processes spatially and throughout tracked thermal lifecycles, which can serve as a stronger foundation for improving subgrid-scale parameterizations.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Evaluation of column-averaged methane in models and TCCON with a focus on the stratosphere

The distribution of methane (CH 4 ) in the stratosphere can be a major driver of spatial variability in the dry-air column-averaged CH 4 mixing ratio (XCH 4 ), which is being measured increasingly for the assessment of CH 4 surface emissions. Chemistry-transport models (CTMs) therefore need to simulate the tropospheric and stratospheric fractional columns of XCH 4 accurately for estimating surface emissions from XCH 4 . Simulations from three CTMs are tested against XCH 4 observations from the Total Carbon Column Network (TCCON). We analyze how the model–TCCON agreement in XCH 4 depends on the model representation of stratospheric CH 4 distributions. Model equivalents of TCCON XCH 4 are computed with stratospheric CH 4 fields from both the model simulations and from satellite-based CH 4 distributions from MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) and MIPAS CH 4 fields adjusted to ACE-FTS (Atmospheric Chemistry Experiment Fourier Transform Spectrometer) observations. Using MIPAS-based stratospheric CH 4 fields in place of model simulations improves the model–TCCON XCH 4 agreement for all models. For the Atmospheric Chemistry Transport Model (ACTM) the average XCH 4 bias is significantly reduced from 38.1 to 13.7 ppb, whereas small improvements are found for the models TM5 (Transport Model, version 5; from 8.7 to 4.3 ppb) and LMDz (Laboratoire de Météorologie Dynamique model with zooming capability; from 6.8 to 4.3 ppb). Replacing model simulations with MIPAS stratospheric CH 4 fields adjusted to ACE-FTS reduces the average XCH 4 bias for ACTM (3.3 ppb), but increases the average XCH 4 bias for TM5 (10.8 ppb) and LMDz (20.0 ppb). These findings imply that model errors in simulating stratospheric CH 4 contribute to model biases. Current satellite instruments cannot definitively measure stratospheric CH 4 to sufficient accuracy to eliminate these biases. Applying transport diagnostics to the models indicates that model-to-model differences in the simulation of stratospheric transport, notably the age of stratospheric air, can largely explain the inter-model spread in stratospheric CH 4 and, hence, its contribution to XCH 4 . Furthermore, it would be worthwhile to analyze how individual model components (e.g., physical parameterization, meteorological data sets, model horizontal/vertical resolution) impact the simulation of stratospheric CH 4 and XCH 4 .

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Synergy between land use and climate change increases future fire risk in Amazon forests

Tropical forests have been a permanent feature of the Amazon basin for at least 55 million years, yet climate change and land use threaten the forest's future over the next century. Understory forest fires, which are common under the current climate in frontier forests, may accelerate Amazon forest losses from climate-driven dieback and deforestation. Far from land use frontiers, scarce fire ignitions and high moisture levels preclude significant burning, yet projected climate and land use changes may increase fire activity in these remote regions. Here, we used a fire model specifically parameterized for Amazon understory fires to examine the interactions between anthropogenic activities and climate under current and projected conditions. In a scenario of low mitigation efforts with substantial land use expansion and climate change – Representative Concentration Pathway (RCP) 8.5 – projected understory fires increase in frequency and duration, burning 4–28 times more forest in 2080–2100 than during 1990–2010. In contrast, active climate mitigation and land use contraction in RCP4.5 constrain the projected increase in fire activity to 0.9–5.4 times contemporary burned area. Importantly, if climate mitigation is not successful, land use contraction alone is very effective under low to moderate climate change, but does little to reduce fire activity under the most severe climate projections. These results underscore the potential for a fire-driven transformation of Amazon forests if recent regional policies for forest conservation are not paired with global efforts to mitigate climate change.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2013

Campaign datasets for Two-Column Aerosol Project (TCAP)

This campaign was designed to provide a detailed set of observations with which to 1) perform radiative and cloud condensation nuclei (CCN) closure studies, 2) evaluate a new retrieval algorithm for aerosol optical depth (AOD) in the presence of clouds using passive remote sensing 3) extend a previously developed technique to investigate aerosol indirect effects, and 4) evaluate the performance of a detailed regional-scale model and a more parameterized global-scale model in simulating particle activation and AOD associated with the aging of anthropogenic aerosols. To meet these science objectives, the ARM Mobile Facility (AMF) and the Mobile Aerosol Observing System (MAOS) was deployed on Cape Cod, Massachusetts for a 12-month period starting in the summer of 2012 in order to quantify aerosol properties, radiation and cloud characteristics at a location subject to both clear- and cloudy- conditions, and clean- and polluted-conditions. These observations were supplemented by two aircraft intensive observation periods (IOPS), one in the summer and a second in the winter. Each IOP required two aircraft.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1978

On the propagation of cosmic rays in the Galaxy

Cosmic ray propagation in the Galaxy is examined within the framework of the leaky-box model, whereby phenomenological aspects of diffusion and propagation are related to the physical properties of the interstellar medium. The model is parameterized by data on composition, spectra, spectral change as a function of energy, and cosmic ray particle lifetime. It is assumed that electrons and nucleons have a common source within the Galaxy (probably associated with supernova remnants). Lifetime data and leakage length are compared with radio synchrotron and gamma-ray data to establish a place of origin for cosmic rays observed at earth, i.e., at a radius of 0.5-1.0 kpc from earth. It is noted that if the escape length becomes energy independent, all nuclear spectra will flatten, while the electron spectrum remains unchanged.

Ormes, J.↗
NASA NTRS1979

Observing, analyzing, and modeling mesoscale weather phenomena

The objective of the paper is to place current research into mesoscale weather phenomena in proper perspective, and to discuss key problems to be addressed in the coming years. Key observing systems and field programs are examined, along with analysis techniques in context of the dynamic models with which they interact. The discussion covers different classes of dynamic models, including prediction models, simulation models, and parameterization schemes.

Kreitzberg, C. W.↗
NASA NTRS1982

Clouds and wet removal as causes of variability in the trace-gas composition of the marine troposphere

A modeling study of the effects of clouds and wet removal on the chemistry of the remote marine troposphere is described. Using a time-dependent model with parameterized vertical transport to calculate trace-gas concentrations, it is found that large variations in key species (e.g., HNO3, H2CO, and H2O2) result from simulations of sporadic rainfall, changes in cloud cover, and external inputs such as surface NO sources. Depending on the frequency and intensity of an event, the effects of these perturbations may persist for several days, thereby invalidating assumptions of photochemical equilibrium in the interpretation of measurements. Long-term integrations with fixed boundary conditions and regularly occurring cloud and rain episodes demonstrate a strong sensitivity of the mean concentration of longer-lived soluble gases to precipitation frequency but also confirm the validity of using properly chosen parameterizations of wet removal in steady state calculations.

Thompson, A. M.↗
NASA NTRS1984

Detection of the J-10 Manifold of the Pure Rotational Band of Phosphine on Saturn

The detection of the J = 10 manifold of the pure rotational band of PH3 on Saturn is reported. The observations were made from the far-infrared cooled grating spectrometer. The wavelengths and observed brightness temperatures for the full disk plus rings are 89 + or - 3 K at 97.04 micrometer, 77 + or - 3 K at 102.72 micrometer, 77 + or - 3 K at 102.94 micrometer, and 83 + or - 3 K at 105.12 micrometers. The points of 97.04 and 105.12 micrometers establish the continuum level and the two points near 103 micrometers measure the depth of the PH3 manifold. After the flux due to the rings is subtracted, the depth of the feature is 16 + or - 6 K relative to the nearby 102 K continuum. These results are compared to theoretical models which parameterize the PH3 mixing ratio as x = x sub zero (P/P sub zero)(alpha) for P P sub zero and as x = x sub zero for P or = P, where P is the total pressure and alpha = H/h is the ratio of the dynamical scale height (H) and the scale height for decreasing the PH3 mixing ratio (h). The parameters x sub zero, P sub zero, and h were varied, as well as the H/He mixing ratio and the pressure-temperature profile. The data are well fitted using pressure-temperature profiles. The preferred values of h, P sub zero, and x sub zero imply that there is little or no PH3 above the thermal inversion and that the mixing ratio below the inversion is consistent with PH3 being 1 to 4 times overabundant relative to the solar P/H ratio.

Haas, M. R.↗
NASA NTRS1984

Outlook for research on subtropical marine stratiform clouds

A detailed description of the goals and methodology of the First International Satellite Cloud Cover Project Regional Experiment (FIRE) is presented. The purpose of the experiment is to develop physical models and parameterizations of fractional cloud cover over the Pacific Basin. In order to determine fractional cloud cover parameters, satellite observations by radar and lidar instruments will be combined with in situ measurements of the cloud-capped marine boundary layer. A description of a candidate experiment for the program is presented, and some general problems connected with the statistical characterization of satellite imagery are discussed.

Randall, D. A.↗
NASA NTRS1986

The structure of the Uranian atmosphere - Constraints from the geometric albedo spectrum and H2 and CH4 line profiles

Recent high quality spectral observations have allowed the derivation of constraints on the atmospheric structure of Uranus. The present analysis, which is based on the detailed modeling of a broadband geometric albedo spectrum and high resolution observations of the H2 4-0 quadrupole and 6818.9-A CH4 features, yields (1) a family of models which parameterize an upper tropospheric haze layer, (2) a lower, optically infinite cloud at a given pressure level, (3) the cloud-level methane molar fraction, and (4) the mean ortho/para ratio in the visible atmosphere. The single scattering albedo of atmospheric aerosols exhibits a steep darkening between 5890 and 6040 A.

Baines, K. H.↗
NASA NTRS1986

The ortho-para H2 distribution on Uranus: Constraints from the collision-induced 3-0 dipole band and 4-0 S(0) and S(1) quadrupole line profiles

Recent high quality spectral observations have allowed the derivation of constraints on the atmospheric structure of Uranus. The present analysis, which is based on the detailed modeling of a broadband geometric albedo spectrum and high resolution observations of the H2 4-0 quadrupole and 6818.9-A CH4 features, yields (1) a family of models which parameterize an upper tropospheric haze layer, (2) a lower, optically infinite cloud at a given pressure level, (3) the cloud-level methane molar fraction, and (4) the mean ortho/para ratio in the visible atmosphere. The single scattering albedo of atmospheric aerosols exhibits a steep darkening between 5890 and 6040 A.

Baines, K. H.↗
NASA NTRS1988

A two-dimensional model of the quasi biennial oscillation of ozone

The largest amplitudes of the observed Quasi Biennial Oscillation (QBO) in column ozone are found in high latitudes and this must be taken into account in any explanation of the increased depletion of ozone in the southern polar spring during the 1980's. A QBO in zonal wind, temperature and column ozone has been successfully modelled in a two-dimensional dynamical/chemical model by the introduction of a parameterization scheme to model the transfer of momentum to the zonal flow associated with the damping of vertically propagating Kelvin and Rossby-Gravity waves. The largest anomalies in column ozone of approximately 20 DU are present at high latitudes. The equatorial ozone QBO is out of phase with the mid- and high-latitude ozone QBO, in good agreement with observations.

Gray, L. J.↗
NASA NTRS1990

Model simulations of rainout and washout from a warm stratiform cloud

A one-dimensional, time-dependent cloud model with parameterized microphysics is used to investigate the processes which control the rainout and washout of soluble gases from warm, precipitating stratiform clouds. Calculations are presented simulating the distributions of soluble species within and below the cloud layer and in the precipitating raindrops as a function of time and species' solubility. Calculations indicate that for species with low solubility, wet removal processes are relatively slow and thus do not significantly affect the species' gas-phase abundance. As a result, the removal of low-solubility species by rainout and washout is controlled by thermodynamic processes with the concentration of the species in cloud and rainwater largely determined by the species' solubility. For highly soluble species on the other hand, dissolution into cloud droplets and removal in rain is quite rapid and the abundance of highly soluble species within and below the cloud falls rapidly as soon as the precipitation begins.

Xing, Lin↗
NASA NTRS1990

Model simulations of rainout and washout from a warm stratiform cloud

Calculations utilizing a one-dimensional, time-dependent stratiform cloud model with parameterized microphysics to study the washout and rainout of soluble trace gases are presented. It is shown that the in-cloud concentrations of relatively insoluble species remain essentially unaffected by the presence of cloudwater and rainwater, while the concentrations of highly soluble species are rapidly depleted within the cloud. Due to this depletion it is shown that for highly soluble species the below-cloud scavenging via washout can dominate over in-cloud scavenging via rainout; in-cloud, aqueous-phase cloudwater and rainwater concentrations can differ considerably and, near the cloudbase, cloudwater concentrations can exceed rainwater concentrations by factors of two to ten.

Xing, Lin↗
NASA NTRS1993

Scientific investigations planned for the Lidar in-Space Technology Experiment (LITE)

The Lidar In-Space Technology Experiment (LITE) is being developed by NASA/Langley Research Center for a series of flights on the space shuttle beginning in 1994. Employing a three-wavelength Nd:YAG laser and a 1-m-diameter telescope, the system is a test-bed for the development of technology required for future operational spaceborne lidars. The system has been designed to observe clouds, tropospheric and stratospheric aerosols, characteristics of the planetary boundary layer, and stratospheric density and temperature perturbations with much greater resolution than is available from current orbiting sensors. In addition to providing unique datasets on these phenomena, the data obtained will be useful in improving retrieval algorithms currently in use. Observations of clouds and the planetary boundary layer will aid in the development of global climate model (GCM) parameterizations. This article briefly describes the LITE program and discusses the types of scientific investigations planned for the first flight.

Mccormick, M. P.↗
NASA NTRS1993

Seasonal variation of surface and atmospheric cloud radiative forcing over the globe derived from satellite data

Global distributions of surface and atmospheric cloud radiative forcing parameters have been derived using parameterized radiation models with satellite meteorological data from the International Satellite Cloud Climatology Project, and directly measured top-of-atmosphere radiative fluxes from the Earth Radiation Budget Experiment. Specifically, shortwave, longwave, and total cloud forcing at the surface, and column-averaged values of longwave cloud forcing of the atmosphere were derived for the midseasonal months of April, July, and October 1985 and January 1986, covering a complete annual cycle. Seasonal variability is illustrated by comparing the results for July 1985 and January 1986, which represent the seasonal extremes. Surface shortwave cloud forcing is always negative, representing a cooling of the surface, with strongest cooling (-120 to -180 W/sq m) occurring over midlatitude storm tracks of the summer hemisphere. Surface longwave cloud forcing is always positive, representing a warming of the surface, with strongest warming (60 to 75 W/sq m) occurring over storm tracks of the winter hemisphere. Zonal averages show the entire summer hemisphere dominated by shortwave cooling, the middle and high latitudes of the winter hemisphere dominated by longwave warming, and a broad zone of transition in between. The globally averaged total cloud forcing amounts to a cooling throughout the year, ranging from a low of about -12 W/sq m for July 1985 to a high of about -25 W/sq m for January 1986. The longwave cloud forcing of the atmosphere shows a strong warming over deep convective regions in the tropics and a moderate cooling outside the tropics, amounting to a weak cooling (-2 to -5 W/sq m) in the global average. Comparisons of the results with general circulation model simulations show broad qualitative agreement regarding the locations of prominent warming and cooling regions. Quantitative comparisons, on the other hand, show significant differences between the magnitudes of warming and cooling in these regions. Most of the larger differences can be attributed to known deficiences of the general circulation model simulations. Comparisons with satellite-derived results of other investigators show much better agreement.

Gupta, Shashi K.↗
NASA NTRS1995

Raman lidar and sun photometer measurements of aerosols and water vapor during the ARM RCS experiment

The first Atmospheric Radiation Measurement (ARM) Remote Cloud Study (RCS) Intensive Operations Period (IOP) was held during April 1994 at the Southern Great Plains (SGP) Cloud and Radiation Testbed (CART) site near Lamont, Oklahoma. This experiment was conducted to evaluate and calibrate state-of-the-art, ground based remote sensing instruments and to use the data acquired by these instruments to validate retrieval algorithms developed under the ARM program. These activities are part of an overall plan to assess general circulation model (GCM) parameterization research. Since radiation processes are one of the key areas included in this parameterization research, measurements of water vapor and aerosols are required because of the important roles these atmospheric constituents play in radiative transfer. Two instruments were deployed during this IOP to measure water vapor and aerosols and study their relationship. The NASA/Goddard Space Flight Center (GSFC) Scanning Raman Lidar (SRL) acquired water vapor and aerosol profile data during 15 nights of operations. The lidar acquired vertical profiles as well as nearly horizontal profiles directed near an instrumented 60 meter tower. Aerosol optical thickness, phase function, size distribution, and integrated water vapor were derived from measurements with a multiband automatic sun and sky scanning radiometer deployed at this site.

Ferrare, R. A.↗