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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Comparison of SBUV and SAGE II ozone profiles: Implications for ozone trends

Solar backscattered ultraviolet (SBUV) ozone profiles have been compared with Stratospheric Aerosol and Gas Experiment (SAGE) II profiles over the period October 1984 through June 1990, when data are available from both instruments. SBUV measurements were selected to closely match the SAGE II latitude/longitude measurement pattern. There are significant differences between the SAGE II sunrise and the sunset zonal mean ozone profiles in the equatorial zone, particularly in the upper stratosphere, that may be connected with extreme SAGE II solar azimuth angles for tropical sunrise measurements. Calculation of the average sunset bias between SBUV and SAGE II ozone profiles shows that allowing for diurnal variation in Umkehr layer 10, SBUV and SAGE II agree to within +/- 5% for the entire stratosphere in the northern midlatitude zone. The worst agreement is seen at southern midlatitudes near the ozone peak (disagreements of +/- 10%), apparently the result of the SBUV ozone profile peaking at a lower altitude than SAGE. The integrated ozone columns (cumulative above 15 km) agree very well, to within +/- 2.3% in all zones for both sunset and sunrise measurements. A comparison of the time dependence of SBUV and SAGE II shows that there was less than +/- 5% relative drift over the 5.5 years for all altitudes except below 25 km, where the SBUV vertical resolution is poor. The best agreement with SAGE is seen in the integrated column ozone (cumulative above 15 km), where SAGE II has a 1% negative trend relative to SBUV over the comparison period. There is a persistent disagreement of the two instruments in Umkehr layers 9 and 10 of +/- 4% over the 5.5-year comparison period. In the equatorial zone this disagreement may be caused in part by a large positive trend (0.8 K per year) in the National Meteorologica Center temperatures used to convert the SAGE II measurement of ozone density versus altitude to a pressure scale for comparison with SBUV. In the middle stratosphere (30-40 km), SBUV shows a 2-4% negative drift relative to SAGE II. If the actual ozone trends are considered, SBUV and SAGE II agree in showing little ozone change (less than 2%) between 1984 and 1990, except in layer 3 where SAGE II measures a large ozone decrease. But over 11 years, SBUV measured a 7% per decade ozone decrease between 40 and 50 km, decreasing in magnitude at lower altitudes, in good agreement with 11-year trends derived from the average of 5 Umkehr stations.

Mcpeters, R. D.↗
NASA NTRS1993

Diffusion of Na and K in the uppermost regolith of Mercury

We examine the conditions under which ions impacting the Hermean surface can act as a regional source of enhanced atmospheric column through ion implantation and subsequent release at the surface. At most latitudes, energetic (a few keV) Na or K ions which impact the nightside surface, are released quickly (well before noon) upon warming of the surface. We show that the relative sunrise/sunset difference produced by ion implantation is ((n)(sub SR) - (n)(sub SS)/(n)(sub Ave) = f, where f is the fraction of the photo-ions recycled, (n)(sub SR) is the average zenith column above the sunrise portion of the illuminated hemisphere, (n)(sub SS) is the average zenith column in the sunset portion, and (n)(sub Ave) is the average column over the sunlit disk. Thus, to produce a large sunrise/sunset difference via ion implantation and subsequent release requires efficient (close to total) recycling. We show that the most extensive set of available data reduced to Na column abundance does not show any sunrise enhancement. We argue that the K data do not permit an unambiguous interpretation in favor of sunrise/sunset differences. We further find that if an efficient surface loss process for the alkali is not operating after sunrise, the initial Na and K distribution will relax into the bulk of the solid. Preserved abundance gradients of Na and K in lunar glasses that the Arrhenius coefficients for impact glasses are likely more modest than those for laboratory glasses derived from rock by nonimpact processes, but the effect of the more modest diffusion rates is only to delay the efficient loss of Na by a few Earth days. We argue that implantation can lead to observable regional increases in the observed Na or K column densities only if it occurs at very high latitudes, where diffusion is slow. It is typically lower energy ions which impact at high latitude and these are both more numerous than the high energy ions and possess smaller average penetration depths; thus there are additional reasons to favor a high-latitude locus for any possible prompt return related increases in zenith column. We find that we cannot rule out sputtering as a source process, as the low-energy ions are efficient sputterers. Finally, we argue that the observed Na/K ratio in the atmopshere may be the expression of their different asymptotic rates of loss from the interiors of the regolith grains. If so, this allows us to fix the importance of sputtering and photon stimulated desorption relative to impact vaporization.

Killen, R. M.↗
NASA NTRS2008

Cold Start of a Radiator Equipped with Titanium-Water Heat Pipes

Radiator panels utilizing titanium-water heat pipes are being considered for lunar applications. A traditional sandwich structure is envisioned where heat pipes are embedded between two high thermal conductivity face sheets. The heat pipe evaporators are to be thermally connected to the heat source through one or more manifolds containing coolant. Initial radiator operation on the lunar surface would likely follow a cold soak where the water in the heat pipes is purposely frozen. To achieve heat pipe operation, it will be necessary to thaw the heat pipes. One option is to allow the sunlight impinging on the surface at sunrise to achieve this goal. Testing was conducted in a thermal vacuum chamber to simulate the lunar sunrise and additional modeling was conducted to identify steady-state and transient response. It was found that sunlight impinging on the radiator surface at sunrise was insufficient to solely achieve the goal of thawing the water in the heat pipes. However, starting from a frozen condition was accomplished successfully by applying power to the evaporators. Start up in this fashion was demonstrated without evaporator dryout. Concern is raised over thawing thermosyphons, vertical heat pipes operating in a gravity field, with no wick in the condenser section. This paper presents the results of the simulated cold start study and identifies future work to support radiator panels equipped with titanium-water heat pipes.

Jaworske, Donald A.↗
DOE OSTI2023

Diurnal variation of the fair-weather atmospheric electric field in Binchuan, China

With the purpose of understanding the variation of fair-weather atmospheric electric field, the vertical component of atmospheric electric field (recorded as Ez) has been measured in the town Binchuan (25°50'N, 100°34'E, 1438.7 m asl) of Dali city, Yunnan, China from June 14, 2017 to December 1, 2020. Automatic measured visual range is used as a proxy of aerosol concentration. The mean diurnal variation curve of the fair-weather Ez in Binchuan, having two peaks occurred at around 9LT and 20LT, shows little correlation with the well-known Carnegie Curve and other two high-latitude sites' Curves. While strong negative correlation between fair-weather Ez and visual range is found, indicating the variation of fair-weather is dominated by aerosol concentration. The main source of aerosol concentration variation probably sunrise and sunset effect. We support our findings by comparing Ez, visual range with sunrise and sunset times. The peaks (troughs) of Ez (visual range) are proved to have weak correlations with anthropogenic pollution through comparing the Ez, visual range under workdays and holidays.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Loop-by-loop differential equations for dual (elliptic) Feynman integrals

We present a loop-by-loop method for computing the differential equations of Feynman integrals using the recently developed dual form formalism. We give explicit prescriptions for the loop-by-loop fibration of multi-loop dual forms. Then, we test our formalism on a simple, but non-trivial, example: the two-loop three-mass elliptic sunrise family of integrals. We obtain an ε-form differential equation within the correct function space in a sequence of relatively simple algebraic steps. In particular, none of these steps relies on the analysis of q-series. Then, we discuss interesting properties satisfied by our dual basis as well as its simple relation to the known ε-form basis of Feynman integrands. The underlying K3-geometry of the three-loop four-mass sunrise integral is also discussed. Finally, we speculate on how to construct a “good” loop-by-loop basis at three-loop.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Direct Measurement of Small Particle Growth and Aging at the Atmospheric Radiation Measurement Southern Great Plains Observatory Field Campaign Report

Two identical Captive Aerosol Growth and Evolution (CAGE) chambers were operated at the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) user facility’s Southern Great Plains (SGP) observatory in the late summer and fall of 2021. The field study was scheduled to begin in spring, 2020, but was delayed because of the pandemic. CAGE chambers are designed to expose particles to an environment that mirrors that of the surroundings with or without a controlled perturbation designed to assess a sensitivity. The analysis here focuses on roughly the last two months of the overall study period during which measurements were almost continuous and when several perturbation experiments were conducted. Though the utility of a dual-chamber system is the ability to measure the influence of a single change on top of ambient conditions, both chambers were initially operated in the same way, with ambient air pulled through the gas exchange channel in both and ammonium sulfate particles injected into both. The similar time-dependent particle growth observed in the chambers for those periods provides confidence in differences observed during the subsequent perturbation experiments. The growth rate of particles in the reference chamber into which only ammonium sulfate particles were injected and for which only ambient air was pulled through were used to describe time-of-day averages. The average growth rate was highest in the evening and in the morning after sunrise and lowest in the late afternoon. The sensitivity of particle growth to secondary aerosol precursor gases was studied by adding them at a controlled rate to the ambient air flow pulled through one of the two chambers. Addition of 5 ppb of α-pinene resulted in an average particle growth rate of 4.4 nm hr -1 , compared with that of just 0.8 nm hr -1 in the reference chamber. The added α-pinene also triggered one new particle formation (NPF) event in the early evening just before sunset and another in the morning just after sunrise. Similarly, addition of 5 ppb of SO 2 to one chamber led to a pair of NPF events and to increased particle growth rate, though unlike the impact of added α-pinene, growth was enhanced only during the daytime when OH concentration is highest. The influence of aerosol liquid water on secondary aerosol formation and particle growth was investigated by injecting ammonium sulfate seed particles into one chamber and potassium sulfate particles into the other. Particles were injected into the two chambers four times over a 1.5-day period. The chamber relative humidity (RH) history during and following each injection was used to determine whether each particle type was crystalline or aqueous. For the case when both particle types remained crystalline throughout the period, they were tracked and for the case when they remained aqueous, the magnitude and time-dependence of the growth of both were almost exactly the same. For the other two cases the ammonium sulfate particles deliquesced upon injection and remained aqueous, while the potassium sulfate particles remained crystalline. For those two cases, the aqueous particles grew substantially faster than did the crystalline particles, providing evidence of the role of aerosol liquid water on secondary aerosol formation and particle growth.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Cloud water adjustments to aerosol perturbations are buffered by solar heating in non-precipitating marine stratocumuli

Abstract. Marine low-level clouds are key to the Earth's energy budget due to their expansive coverage over global oceans and their high reflectance of incoming solar radiation. Their responses to anthropogenic aerosol perturbations remain the largest source of uncertainty in estimating the anthropogenic radiative forcing of climate. A major challenge is the quantification of the cloud water response to aerosol perturbations. In particular, the presence of feedbacks through microphysical, dynamical, and thermodynamical pathways at various spatial and temporal scales could augment or weaken the response. Central to this problem is the temporal evolution in cloud adjustment, governed by entangled feedback mechanisms. We apply an innovative conditional Monte Carlo subsampling approach to a large ensemble of diurnal large-eddy simulation of non-precipitating marine stratocumulus to study the role of solar heating in governing the evolution in the relationship between droplet number and cloud water. We find a persistent negative trend in this relationship at night, confirming that the role of microphysically enhanced cloud-top entrainment. After sunrise, the evolution in this relationship appears buffered and converges to ∼-0.2 in the late afternoon. This buffering effect is attributed to a strong dependence of cloud-layer shortwave absorption on cloud liquid water path. These diurnal cycle characteristics further demonstrate a tight connection between cloud brightening potential and the relationship between cloud water and droplet number at sunrise, which has implications for the impact of the timing of advertent aerosol perturbations.

Zhang, Jianhao (ORCID:0000000169882935)↗
DOE OSTI2024

Diurnal evolution of non-precipitating marine stratocumuli in a large-eddy simulation ensemble

Abstract. We explore the cloud system evolution of non-precipitating marine stratocumuli with a focus on the impacts of the diurnal cycle and free-tropospheric (FT) humidity based on an ensemble of 244 large-eddy simulations generated by perturbing initial thermodynamic profiles and aerosol conditions. Cases are categorized based on their degree of decoupling and the cloud liquid water path (LWPc, based on model columns with cloud optical depths greater than one). A budget analysis method is proposed to analyze the evolution of cloud water in both coupled and decoupled boundary layers. More coupled clouds start with a relatively low LWPc and cloud fraction (fc) but experience the least decrease in LWPc and fc during the daytime. More decoupled clouds undergo greater daytime reduction in LWPc and fc, especially those with higher LWPc at sunrise because they suffer from faster weakening of net radiative cooling. During the nighttime, a positive correlation between FT humidity and the LWPc emerges, consistent with higher FT humidity reducing both radiative cooling and the humidity jump, both of which reduce entrainment and increase LWPc. The LWPc is more likely to decrease during the nighttime for a larger LWPc and greater inversion base height (zi), conditions under which entrainment dominates as turbulence develops. In the morning, the rate of the LWPc reduction depends on the LWPc at sunrise, zi, and the degree of decoupling, with distinct contributions from subsidence and radiation.

Chen, Yao-Sheng (ORCID:0000000208354132)↗
NASA NTRS1973

Broad band solar EUV absorption in the earth's upper atmosphere.

Observation data on solar radiation intensity, based on measurements performed as a function of time for three broad wavelength bands between 280 and 1030 A by a wheel spectrometer on Oso 5 during sunrise and sunset, are compared with predicted intensity variations based on Cira models. The differences between sunrise and sunset data, as well as those between observed and predicted data are discussed.

Allen, K. H.↗
NASA NTRS1974

Evidence for a high altitude distribution of lunar dust

The crew of Apollo 17 saw streamers accompanying spacecraft sunrise. The time variations of the brightness of these streamers indicate that they were produced by light scattering in the lunar vicinity rather than brightness variations of material streamers emanating from the sun. The angular extent of the streamers indicate that the light scattering particulates extended from the lunar surface to above the orbital altitude of the spacecraft. Although observed as typical sunrise phenomena by Apollos 10 and 17, and possibly by 8 and 15 as well, streamers were not observed during the flight of Apollo 16. The scattering particles seem to be present sporadically, most likely lunar dust of tenth micron scale, and not a result of spacecraft contamination.

Mccoy, J. E.↗
NASA NTRS1976

Oso 7 measurements of atomic oxygen and molecular nitrogen densities in the earth's upper atmosphere

Densities of molecular nitrogen and monatomic oxygen are presented as a function of altitude for selected intervals of March-May 1972 Oso 7 satellite data. Results on atmospheric attenuation of solar extreme UV radiation at 200-400 A, at heights from 250 to 500 km, are of particular interest. Satellite sunrise measurements above 330 km are not consistent with the Jacchia (1971) atmospheric model, and may constitute evidence for dynamic phenomena occurring in the heated upper levels. Density and temperature variations are considered mainly responsible for the sunrise anomaly observed. Checks were made for possible errors in the satellite pointing system and other instrumental effects.

Modali, S. B.↗
NASA NTRS1978

Variations in the upper stratosphere's ozone profile

The ozone concentration profile was measured on five balloon flights using an instrument which employs the strong absorption in ultraviolet to measure ozone in situ. Altitudes up to 44 km were obtained. All the flights were made during the daytime except for one that was launched at 3 AM local time to obtain a nighttime profile and to observe sunrise effects. Although the measurements were obtained at different times of day and during different seasons, ozone concentrations in the upper stratosphere varied by only a few percent. Quadratic, least squares fits to the data between 34 km and 40 km for the four daytime flights, yield a mean concentration at 37 km of 1.02 x 10 to the 12th power molecules/cu cm with a 2 percent standard deviation. Measurements made through sunrise show a small increase in ozone at 37 km commencing shortly after the beginning of astronomical twilight. The concentration at 37 km returned to predawn levels about 2 1/2 hours later.

Robbins, D. E.↗
NASA NTRS1980

The influence of NO and ClO variations at twilight on the interpretation of solar occultation measurements

The influence of short lived photochemically produced species on solar occultation measurements of ClO and NO was examined. Time varying altitude profiles of ClO and NO were calculated with a time dependent photochemical model to simulate the distribution of these species during a solar occultation measurement. These distributions were subsequently used to calculate simulated radiances for various tangent paths from which mixing ratios were inferred with a conventional technique that assumes spherical symmetry. These results show that neglecting the variation of ClO in the retrieval process produces less than a 10 percent error between the true and inverted profile for both sunrise and sunset above 18 km. For NO, errors are less than 10 percent for tangent altitudes above about 35 km for sunrise and sunset; at lower altitudes, the error increases, approaching 100 percent at altitudes near 25 km. the results also show that average inhomogeneity factors, which measure the concentration variation along the tangent path and which can be calculated from a photochemical model, can indicate which species require more careful data analysis.

Boughner, R.↗
NASA NTRS1981

H2O frost point detection on Mars

The Viking Mars landers contain meteorological instrumentation to measure wind, temperature, and pressure but not atmospheric water content. The landings occurred during local summer, and it was observed that the nocturnal temperature decrease at sensor height (1.6 m) did not exhibit a uniform behavior at either site. It was expected that the rate of decrease would gradually slow, leveling off near sunrise. Instead, a leveling occurred several hours earlier. Temperature subsequently began a more rapid decrease which slowed by sunrise. This suggested that the temperature sensors may be detecting the frost point of water vapor. Analysis of alternative hypotheses demonstrates that none of these are viable candidates. The frost point interpretation is consistent with other lander and orbiter observations, with terrestrial experience, and with modeling of Mars' atmospheric behavior. It thus appears that the meteorology experiment can help provide a basis toward understanding the distribution and dynamics of Martian water vapor.

Ryan, J. A.↗
NASA NTRS1982

Spherical harmonic representation of the main geomagnetic field for world charting and investigations of some fundamental problems of physics and geophysics

Progress in the harmonic analysis of MAGSAT data is reported. Single-day data sets were subdivided into information on the sunrise side of the Earth and information on the sunset side of the Earth. Data for the main and external fields each demonstrate a clear and consistent systematic difference between the sets of data which was determined to be, due to ionospheric currents which differ from the sunset to the sunrise terminator. A toroidal field was analyzed for and determined to be an apparent toroidal field resulting from electric currents concentrated in the two terminators. Progressive elimination of auroral zone data demonstrates that the information presented does not arise from complications due to Birkeland currents.

Barraclough, D. R.↗
NASA NTRS1988

Diurnal variation of nitric oxide at 32 km - Measurements and interpretation

Balloon observations of NO and ozone near sunset and sunrise around 32 km were made on September 19 and October 4, 1985 from Aire sur l'Adour, France. The NO concentration built up rapidly after sunrise, remained fairly steady during the day, and decreased slowly near sunset. This variation is interpreted quantitatively in terms of current photochemistry in relation to ozone.

Kondo, Yutaka↗
NASA NTRS1989

SAGE II aerosol data validation - Comparative studies of SAGE II and SAM II data sets

Data from the Stratospheric Aerosol and Gas Experiment (SAGE II) satellite are compared with data from the Stratospheric Aerosol Measurement (SAM II) satellite. Both experiments produce aerosol extinction profiles by measuring the attenuation of solar radiation during each sunrise and sunset observed by the satelltie. The SAGE II obtains profiles at 1.02 microns and three smaller wavelengths, whereas the SAM II measures at only one radiometric channel at 1.0 microns. It is found that the differences between the two sets of data are generally within the error bars associated with each measurement. In addition, the sunrise and sunset data from SAGE II are analyzed.

Yue, G. K.↗
NASA NTRS1990

Diurnal variation of nitric oxide in the upper stratosphere

Two recent measurements of the temporal variation of nitric oxide at constant altitude near 40 km are reported. The observations were made at float altitude with a balloon-borne chemiluminescence detector together with in situ ozone measurements. The first measurement was made at 44 N on September 17, 1987, at an altitude of 40 km from before sunrise until 1000 LT. The second observation was made at the same latitude on June 18, 1988, at 39 km from 0800 to 1230 LT. At an altitude of 40 km, nitric oxide was observed to start increasing very rapidly at sunrise when the solar zenith angle reached about 95 deg. After the rapid initial buildup, the rate of NO increase stabilized for 3 hours at about 1.2 ppbv/hour. Near 1100 LT at 39 km in summer, the NO mixing ratio was observed to become nearly constant. These features of the diurnal variation of NO are in accord with the temporal variation expected from a time-dependent zero-dimensional photochemical model.

Kondo, Y.↗