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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Geomagnetic Storm Effects in the Low- to Middle-Latitude Upper Thermosphere

In this paper, we use data from the Dynamics Explorer 2 (DE 2) satellite and a theoretical simulation made by using the National Center for Atmospheric Research thermosphere/ionosphere general circulation model (NCAR-TIGCM) to study storm-induced changes in the structure of the upper thermosphere in the low- to middle-latitude (20 deg-40 deg N) region of the winter hemisphere. Our principal results are as follows: (1) The winds associated with the diurnal tide weaken during geomagnetic storms, causing primarily zonally oriented changes in the evening sector, few changes in the middle of the afternoon, a combination of zonal and meridional changes in the late morning region, and mainly meridional changes early in the morning; (2) Decreases in the magnitudes of the horizontal winds associated with the diurnal tide lead to a net downward tendency in the vertical winds blowing through a constant pressure surface; (3) Because of these changes in the vertical wind, there is an increase in compressional heating (or a decrease in cooling through expansion), and thus temperatures in the low- to middle-latitudes of the winter hemisphere increase; (4) Densities of all neutral species increase on a constant height surface, but the pattern of changes in the O/N2 ratio is not well ordered on these surfaces; (5) The pattern of changes in the O/N2 ratio is better ordered on constant pressure surfaces. The increases in this ratio on constant pressure surfaces in the low- to middle-latitude, winter hemisphere are caused by a more downward tendency in the vertical winds that blow through the constant pressure surfaces. Nitrogen-poor air is then advected downward through the pressure surface, increasing the O/N2 ratio; (6) The daytime geographical distribution of the modeled increases in the O/N2 ratio on a constant pressure surface in the low- to middle-latitudes of the winter hemisphere correspond very closely with those of increases in the modeled electron densities at the F2 peak.

Burns, A. G.↗
NASA NTRS1993

In Situ Measurements of CLO at Mid-Latitudes: Is there an Effect from Mt. Pinatubo?

Observations of ClO from 20 to 60 deg N made before and after the eruption of Mt. Pinatubo are compared for changes which may result from increased sulfate aerosol surface area. Using ozone as a vertical coordinate and examining data at similar latitudes and seasons, elevated abundances of ClO are found at low latitudes (20 to 30 deg N), an effect which decreases with increasing latitude. For the flights compared, there appear to be no differences, within the uncertainty of the measurements, at latitudes poleward of 40 deg N. These results are consistent with the idea that the hydrolysis of N2O5 on sulfate aerosols becomes saturated at moderate aerosol loadings.

Avallone, L. M.↗
NASA NTRS1997

Understanding the Latitude Structure of Nitric Oxide in the Mesosphere and Lower Thermosphere

The goal of the proposed work was to understand the latitude structure of nitric oxide in the mesosphere and lower thermosphere. The problem was portrayed by a clear difference between predictions of the nitric oxide distribution from chemical/dynamical models and data from observations made by the Solar Mesosphere Explorer (SMEE) in the early to mid eighties. The data exhibits a flat latitude structure of NO, the models tend to produce at equatorial maximum. The first task was to use the UARS-HALOE data to confirm the SME observations. The purpose of this first phase was to verify the UARS-NO structure is consistent with the SME data. The next task was to determine the cause of the discrepancy between modeled and observed nitric oxide latitude structure. The result from the final phase indicated that the latitude structure in the Photo-Electron (PE) production rate was the most important.

Fuller-Rowell, T.J.↗
NASA NTRS1995

A CME-Driven Solar Wind Disturbance Observed at both Low and High Heliographic Latitudes

A solar wind disturbance produced by a fast coronal mass ejection, CME, that departed from the Sun on February 20, 1994 was observed in the ecliptic plane at 1 AU by IMP 8 and at high heliographic latitudes at 3.53 AU by Ulysses. In the ecliptic the disturbance included a strong forward shock but no reverse shock, while at high latitudes the disturbance was bounded by a relatively weak forward-reverse shock pair. It is clear that the disturbance in the ecliptic plane was driven primarily by the relative speed between the CME and a slower ambient solar wind ahead, whereas at higher latitudes the disturbance was driven by expansion of the CME. The combined IMP 8 and Ulysses observations thus provide a graphic illustration of how a single fast CME can produce very different types of solar wind disturbances at low and high heliographic latitudes. Simple numerical simulations help explain observed differences at the two spacecraft.

Gosling, J. T.↗
NASA NTRS1996

Radiative Forcing of the Pinatubo Aerosol as a Function of Latitude and Time

We present calculations of the radiative forcing of the Mt. Pinatubo aerosols as a function of latitude and time after the eruption and compare the results with GOES satellite data. The results from the model indicate that the net effect of the aerosol was to cool the earth-atmosphere system with the most significant radiative effect in the tropics (corresponding to the location of the tropical stratospheric reservoir) and at latitudes greater than 60 deg. The high-latitude maximum is a combined effect of the high-latitude peak in optical depth (Trepte et al 1994) and the large solar zenith angles. The comparison of the predicted and measured net flux shows relatively good agreement, with the model consistently under predicting the cooling effect of the aerosol.

Bergstrom, R. W.↗
NASA NTRS2000

Radiative Forcing of the Pinatubo Aerosol as a Function of Latitude and Time

We present calculations of the radiative forcing of the Mt. Pinatubo aerosols as a function of latitude and time after the eruption and compare the results with GOES satellite data. The results from the model indicate that the net effect of the aerosol was to cool the earth-atmosphere system with the most significant radiative effect in the tropics (corresponding to the location of the tropical stratospheric reservoir) and at latitudes greater than 60 degrees. The high-latitude maximum is a combined effect of the high-latitude peak in optical depth (Trepte et al 1994) and the large solar zenith angles. The comparison of the predicted and measured net flux shows relatively good agreement, with the model consistently under predicting the cooling effect of the aerosol.

Bergstrom, Robert W.↗
NASA NTRS2001

Low-Latitude Auroras: The Magnetic Storm of 14-15 May 1921

We review solar geophysical data relating to the great magnetic storm of 14-15 May 1921, with emphasis on observations of the low-latitude visual aurora. From the reports we have gathered for this event the lowest geomagnetic latitude of definite overhead aurora (coronal form) was 40 deg and the lowest geomagnetic latitude from which auroras were observed on the poleward horizon in the northern hemisphere was 30 deg. For comparison, corresponding overhead/low-latitude values of 48 deg/32 deg and 41 deg/20 deg were reported for the great auroras on 28-29 August and 1-2 September 1859, respectively. However for the 1921 event, there is a report of aurora from Apia, Samoa, in the southern hemisphere, within 13 deg of the geomagnetic equator. This report by professional observers appears to be credible, based on the aurora description and timing, but is puzzling because of the discrepancy with the lowest latitude of observation in the northern hemisphere and the great implied aurora height (approximately 2000 km, assuming overhead aurora at Auckland, New Zealand). We discuss various possibilities that might account for this observation.

Silverman, S. M.↗
NASA NTRS2002

High-Latitude Magnetic Reconnection in Sub-Alfvenic Flow as Observed by Interball Tail on 29 May 1996

The Interball/Tail spacecraft crossed the high latitude magnetopause near the cusp region under stable northward IMF conditions on 29 May 1996, with magnetic local time and magnetic latitude approx. 7.3 hours, approx. 65.4 degrees, respectively. The Interball Tail spacecraft observed quasi-steady reconnection and a relatively stable reconnection site at high latitudes. Observed sunward plasma flow and tangential stress balance indicated that reconnection occurred poleward of the magnetic cusp, above the spacecraft location. The spacecraft observed sub-alfvenic flow in the magnetosheath region adjacent to the magnetopause current layer near the reconnection site indicating that the reconnection site may have moved in the sunward direction. These observations suggest that the region of sub-alfvenic flow and stable, quasi-steady reconnection extend to very high latitudes under northward IMF conditions which is not consistent with the gas dynamic model predictions.

Smirnov, V. N.↗
NASA NTRS1992

Relationship of peroxyacetyl nitrate to active and total odd nitrogen at northern high latitudes: influence of reservoir species on NOx and O3

Measurements of peroxyacetyl nitrate (PAN), NO, NO2, HNO3, NOy (total odd nitrogen), and O3 were made in the high-latitude troposphere over North America and Greenland (35 degrees to 82 degrees N) during the Arctic Boundary Layer Expedition (ABLE 3A) (July-August 1988) throughout 0-to 6-km altitudes. These data are analyzed to quantitatively describe the relationships between various odd nitrogen species and assess their significance to global tropospheric chemistry. In the free troposphere, PAN was as much as 25 times more abundant than NOx. PAN to NOx ratio increased with increasing altitude and latitude. PAN was found to be the single most abundant reactive nitrogen species in the free troposphere and constituted a major fraction of NOy, PAN to NOy ratios were about 0.1 in the boundary layer and increased to 0.4 in the free troposphere. A 2-D global photochemical model with C1-C3 hydrocarbon chemistry is used to compare model predictions with measured results. A sizable portion (approximately 50%) of the gaseous reactive nitrogen budget is unaccounted for, and unknown organic nitrates and pernitrates are expected to be present. Model calculations (August 1, 70 degrees N) show that a major fraction of the observed NOx (50 to 70% of median) may find its source in the available PAN reservoir. PAN and the unknown reservoir species may have the potential to control virtually the entire NOx availability of the high latitude troposphere. It is predicted that the summer NOx and O3 mixing ratios in the Arctic/sub-Arctic troposphere would be considerably lower in the absence of the ubiquitous PAN reservoir. Conversely, this PAN reservoir may be responsible for the observed temporal increase in tropospheric O3 at high latitudes.

NASA Center ARC↗
NASA NTRS2003

On the ionospheric impact of recent storm events on satellite-based augmentation systems in middle and low-latitude sectors

The Ionospheric correction algorithms have been characterized extensively for the mid-latitude region of the ionosphere where benign conditions usually exist. The United States Federal Aviation Administration's (FAA) Wide Area Augmentation System (WAAS) for civil aircraft navigation is focused primarily on the Conterminous United States (CONUS). Other Satellite-based Augmentation Systems (SBAS) include the European Geostationary Navigation Overlay Service (EGNOS) and the Japanese Global Navigation Satellite System (MSAS). Researchers are facing a more serious challenge in addressing the ionospheric impact on navigation using SBAS in other parts of the world such as the South American region on India. At equatorial latitudes, geophysical conditions lead to the so-called Appleton-Hartree (equatorial) anomaly phenomenon, which results in significantly larger ionospheric range delays and range delay spatial gradients than is observed in the CONUS or European sectors. In this paper, we use GPS measurements of geomagnetic storm days to perform a quantitative assessment of WAAS-type ionospheric correction algorithms in other parts of the world such as the low-latitude Brazil and mid-latitude Europe. For the study, we access a world-wide network of 400+ dual frequency GPS receivers.

validation↗
NASA NTRS2007

Recent Plasma Observations Related to Magnetic Merging and the Low-Latitude Boundary Layer. Case Study by Polar, March 18, 2006

We have begun an investigation of the nature of the low-latitude boundary layer in the mid-altitude cusp region using data from the Polar spacecraft. Magnetosheath-like plasma is frequently observed deep (in terms of distance from the magnetopause and in invariant latitude) in the magnetosphere. One such case, taken during a long period of northward interplanetary magnetic field (IMP) on March 18, 2006, shows injected magnetosheath ions within the magnetosphere with velocity distributions resulting from two separate merging sites along the same field lines. Cold ionospheric ions were also observed counterstreaming along the field lines, evidence that these field lines were closed. Our results support the idea of double reconnection under northward IMP on the same group of field lines can provide a source for the LLBL. However, the flow direction of the accelerated magnetosheath ions antiparallel to the local magnetic field and given location of the spacecraft suggest that these two injection sites are located northward of the spacecraft position. Observed convection velocities of the magnetic field lines are inconsistent with those expected for double post-cusp reconnection in both hemispheres. These observations favor a scenario in which a group of newly closed field lines was created by a combination of high shear merging at high latitudes in the northern hemisphere and low shear merging at lower latitudes at the dayside magnetopause.

Chandler, M.↗
NASA NTRS2007

Inter-annual and Long-term Temperature Variations in the Mesopause Region at High Latitudes Generated by the Stratospheric QBO

The Numerical Spectral Model (NSM) simulates the Quasi-biennial Oscillation (QBO) that dominates the zonal circulation of the lower stratosphere at low latitudes. In the model, the QBO is generated with parameterized small-scale gravity waves (GW), which are partially augmented in 3D with planetary waves owing to baroclinic instability. Due to GW filtering, the QBO extends into the upper mesosphere, evident in UARS zonal wind and TIMED temperature measurements. While the QBO zonal winds are confined to equatorial latitudes, even in simulations with latitude-independent wave source, the associated temperature variations extend to high latitudes. The meridional circulation redistributes some of the QBO energy to focus it partially onto the Polar Regions. The resulting QBO temperature variations away from the equator tend to increase at higher altitudes to produce inter-annual variations that can exceed 5 K in the polar mesopause region -- and our 3D model simulations show that the effect is variable from year to year and can produce large differences between the two hemispheres, presumably due to interactions involving the seasonal variations. Modeling studies with the NSM have shown that long-term variations can also be generated by the QBO interacting with the seasonal cycles through OW node-filtering. A 30-month QBO, optimally synchronized by the 6-month Semi-Annual Oscillation (SAO), thus produces a 5-year or semi-decadal (SD) oscillation -- and observational evidence for that has been provided by a recent analysis of stratospheric NCEP data. In a simulation with the 2D version of the NSM, this SD oscillation extends into the upper mesosphere, and we present results to show that the related temperature variations could contribute significantly to the long-term variations of the polar mesopause region. Quasi-decadal variations could furthermore arise from the modeled solar cycle modulations of the QBO and 12-month annual oscillation. Our numerical results are discussed in the context of the observed low summer temperatures reproduced by the model, to demonstrate that the above interannual and long-term variations could contribute significantly to the climatology of Polar Mesospheric Clouds (PMC) investigated by the Aeronomy of Ice in the Mesosphere (AIM) mission.

Mayr, Hans G.↗
NASA NTRS2008

Irregularities at Sub-Auroral, Middle, and Low Latitudes in the Topside Ionosphere Observed During Geomagnetic Storms with the DEMETER and DMSP Satellites

Detailed observations of the plasma structure and irregularities that characterize the topside ionosphere at sub-auroral, middle, and low-latitudes are presented that were gathered with probes on the DEMETER and DMSP satellites during geomagnetic storms. Data from successive orbits reveal how the density structure and irregularities evolve with changes in the Dst. The observations reveal that precisely during the main phase of severe geomagnetic storms, increased ambient plasma densities and broad regions of irregularities are observed at 700 km, initially at storm commencement near the magnetic equator and then extending to mid- and sub-auroral latitudes within the approximately 8 hour period corresponding to the negative Dst excursions. Furthermore, intense, broadband electric and magnetic field irregularities are often observed at sub-auroral latitudes and are typically associated with the trough region and its poleward plasma density gradient. The observations provide a general framework showing how low, mid, and sub-auroral latitude plasma density structuring and associated irregularities respond to geomagnetic storms.

Pfaff, R.↗
NASA NTRS2012

Redistribution of Lunar Polar Water to Mid-latitudes and its Role in Forming an OH veneer - Revisited

We suggest that energization processes like ion sputtering and impact vaporization can eject/release polar water molecules residing within lunar cold trapped regions with sufficient velocity to allow their redistribution to mid-latitudes. We consider the possibility that these polar-ejected molecules can be an additional (but not dominant) contribution to the water/OH veneer observed as a 3 micron absorption feature at mid-latitudes by Chandrayaan-I, Cassini, and EPOXI. Taking the conservative case that polar water is ejected only from the floor of polar craters with an 0.1 % icy regolith then overall source rates are near 10(exp 18) H20s/s. This outflow amounts to approx 10(exp -7) kg/s of water to be ejected from each pole and is a water source rate that is 10(exp .5 lower than the overall exospheric source rate for all species. Hence, the out-flowing polar water is a perturbation in the overall exosphere composition & dynamics. This polar water 'fountain' model may not fully account for the relatively high concentrations in the mid-latitude water veneer observed in the IR (approx 10-1000 ppm). However, it may account for some part of the veneer. We note that the polar water fountain source rates scale linearly with ice concentration, and larger mass fractions of polar crater water should provide correspondingly larger fractions of water emission out of the poles which then 'spills' on to mid-latitude surfaces.

Farrell, W. M.↗
NASA NTRS2014

Mid-Latitude Ionospheric Disturbances Due to Geomagnetic Storms at ISS Altitudes

Spacecraft charging of the International Space Station (ISS) is dominated by interaction of the US high voltage solar arrays with the F2-region ionosphere plasma environment. ISS solar array charging is enhanced in a high electron density environment due to the increased thermal electron currents to the edges of the solar cells. High electron temperature environments suppress charging due to formation of barrier potentials on the charged solar cell cover glass that restrict the charging currents to the cell edge [Mandell et al., 2003]. Environments responsible for strong solar array charging are therefore characterized by high electron densities and low electron temperatures. In support of the ISS space environmental effects engineering community, we are working to understand a number of features of solar array charging and to determine how well future charging behavior can be predicted from in-situ plasma density and temperature measurements. One aspect of this work is a need to characterize the magnitude of electron density and temperature variations that occur at ISS orbital altitudes (approximately 400 km) over time scales of days, the latitudes over which significant variations occur, and the time periods over which the disturbances persist once they start. This presentation provides examples of mid-latitude electron density and temperature disturbances at altitudes relevant to ISS using data sets and tools developed for our ISS plasma environment study. "Mid-latitude" is defined as the extra-tropical region between approx. 30 degrees to approx. 60 degrees magnetic latitude sampled by ISS over its 51.6 degree inclination orbit. We focus on geomagnetic storm periods because storms are well known drivers for disturbances in the ionospheric plasma environment.

Minow, Joseph I.↗
NASA NTRS2018

Modeling the Distribution and Type of High-Latitude Natural Wetlands for Methane Studies

High latitude (>50N) natural wetlands emit a substantial amount of methane to the atmosphere, and are located in a region of amplified warming. Northern hemisphere high latitudes are characterized by cold climates, extensive permafrost, poor drainage, short growing seasons, and slow decay rates. Under these conditions, organic carbon accumulates in the soil, sequestering CO2 from the atmosphere. Methanogens produce methane from this carbon reservoir, converting stored carbon into a powerful greenhouse gas. Methane emission from wetland ecosystems depends on vegetation type, climate characteristics (e.g, precipitation amount and seasonality, temperature, snow cover, etc.), and geophysical variables (e.g., permafrost, soil type, and landscape slope). To understand how wetland methane dynamics in this critical region will respond to climate change, we have to first understand how wetlands themselves will change and therefore, what the primary controllers of wetland distribution and type are. Understanding these relationships permits data-anchored, physically-based modeling of wetland distribution and type in other climate scenarios, such as paleoclimates or future climates, a necessary first step toward modeling wetland methane emissions in these scenarios. We investigate techniques and datasets for predicting the distribution and type of high latitude (>50N) natural wetlands from a suite of geophysical and climate predictors. Hierarchical clustering is used to derive an empirical methane-centric wetland model. The model is applied in a multistep process first to predict the distribution of wetlands from relevant geophysical parameters, and then, given the predicted wetland distribution, to classify the wetlands into methane-relevant types using an expanded suite of climate and biogeophysical variables. As the optimum set of predictor variables is not known a priori, the model is applied iteratively, and each simulation is evaluated with respect to observed high-latitude wetlands.

Romanski, Joy↗
NASA NTRS2022

Leaf-level chlorophyll fluorescence and reflectance spectra of high latitude plants

Little is known about the chlorophyll fluorescence spectra for high latitude plants. A FluoWat leaf clip was used to measure leaf-level reflectance and chlorophyll fluorescence spectra of leaves of common high latitude plants to examine general spectral characteristics of these species. Fluorescence yield (Fyield) was calculated as the ratio of the emitted fluorescence divided by the absorbed radiation for the wavelengths from 400 nm up to the wavelength of the cut-off for the FluoWat low pass filter (either 650 or 700 nm). The Fyield spectra grouped into distinctly different patterns among different plant functional types. Black spruce (Picea mariana) Fyield spectra had little red fluorescence, which was reabsorbed in the shoot, but displayed a distinct far-red peak. Quaking aspen (Populus tremuloides) had both high red and far-red Fyield peaks, as did sweet coltsfoot (Petasites frigidus). Cotton grass (Eriophorum spp.) had both red and far-red Fyield peaks, but these peaks were much lower than for aspen or coltsfoot. Sphagnum moss (Sphagnum spp.) had a distinct Fyield red peak but low far-red fluorescence. Reindeer moss lichen (Cladonia rangiferina) had very low fluorescence levels, although when damp displayed a small red Fyield peak. These high latitude vegetation samples showed wide variations in Fyield spectral shapes. The Fyield values for the individual red or far-red peaks were poorly correlated to chlorophyll content, however the ratio of far-red to red Fyield showed a strong correlation with chlorophyll content. The spectral variability of these plants may provide information for remote sensing of vegetation type but may also confound attempts to measure high latitude vegetation biophysical characteristics and function using solar induced fluorescence (SIF).

K Fred Huemmrich↗
NASA NTRS2021

Impact of Regional Northern Hemisphere Mid-latitude Anthropogenic Sulfur Dioxide Emissions on Local and Remote Tropospheric Oxidants

The unintended consequences of reductions in regional anthropogenic sulfur dioxide (SO2) emissions implemented to protect human health are poorly understood. SO2 decreases began in the 1970s in the US and Europe and are expected to continue into the future, while recent emissions decreases in China are also projected to continue. In addition to the well-documented climate effects (warming) from reducing aerosols, tropospheric oxidation is impacted via aerosol modification of photolysis rates and radical sinks. Impacts on the hydroxyl radical and other trace constituents directly affect climate and air quality metrics such as surface ozone levels. We use the Geophysical Fluid Dynamics Laboratory Atmospheric Model version 3 nudged towards National Centers for Environmental Prediction (NCEP) reanalysis wind velocities to estimate the impact of SO2 emissions from the US, Europe, and China by differencing a control simulation with an otherwise identical simulation in which 2015 anthropogenic SO2 emissions are set to zero over one of the regions. Springtime sulfate aerosol changes occur both locally to the emission region and also throughout the Northern Hemispheric troposphere, including remote oceanic regions and the Arctic. Hydroperoxy (HO2) radicals are directly removed via heterogeneous chemistry on aerosol surfaces, including sulfate, in the model, and we find that sulfate aerosol produced by SO2 emissions from the three individual northern mid-latitude regions strongly reduces both HO2 and hydroxyl (OH) by up to 10 % year-round throughout most of the troposphere north of 30∘ N latitude. Regional SO2 emissions significantly increase nitrogen oxides (NOx) by about 5 %–8 % throughout most of the free troposphere in the Northern Hemisphere by increasing the NOx lifetime as the heterogeneous sink of HO2 on sulfate aerosol declines. Despite the NOx increases, tropospheric ozone decreases at northern mid-latitudes by 1 %–4 % zonally averaged and by up to 5 ppbv in summertime surface air over China, where the decreases in HO2 and OH suppress O3 production. Since 2015 anthropogenic SO2 emissions in China exceed those in the US or Europe, the oxidative response is greatest for the China perturbation simulation. Chemical effects of aerosols on oxidation (reactive uptake) dominate over radiative effects (photolysis rates), the latter of which are only statistically significant locally for the large perturbation over China. We find that the SO2 emissions decrease in China, which has yet to be fully realized, will have the largest impact on oxidants and related species in the Northern Hemisphere free troposphere compared to future decreases in Europe or the US. Our results bolster previous calls for a multipollutant strategy for air pollution mitigation to avoid the unintended consequence of aerosol removal leading to surface ozone increases that offset or mask surface ozone gains achieved by regulation of other pollutants, especially in countries where current usage of high-sulfur emitting fuels may be phased out in the future.

anthropogenic sulfur dioxide emissions↗