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At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

A Reanalysis for the Seasonal and Longer-Period Cycles and the Trends in Middle Atmosphere Temperature from the HALOE

Previously published analyses for the seasonal and longer-period cycles in middle atmosphere temperature versus pressure (or T(p)) from the Halogen Occultation Experiment (HALOE) are extended to just over 14 years and updated to properly account for the effects of autocorrelation in its time series of zonally-averaged data. The updated seasonal terms and annual averages are provided, and they can be used to generate temperature distributions that are representative of the period 1991-2005. QBO-like terms have also been resolved and are provided, and they exhibit good consistency across the range of latitudes and pressure-altitudes. Further, exploratory analyses of the residuals from each of the 221 time series have yielded significant 11-yr solar cycle (or SC-like) and linear trend terms at a number of latitudes and levels. The amplitudes of the SC-like terms for the upper mesosphere agree reasonably with calculations of the direct solar radiative effects for T(p). Those SC amplitudes increase by about a factor of 2 from the lower to the upper mesosphere and are also larger at the middle than at the low latitudes. The diagnosed cooling trends for the subtropical latitudes are in the range, -0.5 to -1.0 K/decade, which is in good agreement with the findings from models of the radiative effects on pressure surfaces due to known increases in atmospheric CO2. The diagnosed trends are somewhat larger than predicted with models for the upper mesosphere of the northern hemisphere middle latitudes.

Remsberg, Ellis E.↗
NASA NTRS1991

On the seasonal phytoplankton concentration and sea surface temperature cycles of the Gulf of Mexico as determined by satellites

Multiyear series of coastal zone color scanner (CZCS) and AVHRR observations are presently used to derive monthly climatologies of near-surface phytoplankton pigment concentration and SST for the Gulf of Mexico; these, in combination with 1946-1987 SST data and NOAA hydrographic profile data covering 1914-1985, show that the most important single factor controlling seasonal cycle surface-pigment concentration is the depth of the mixed layer. The CZCS images indicate that seasonal variation seaward of the continental shelf is synchronous throughout the Gulf. The combination of ocean color and IR images allows year-round observation of surface circulation spatial structure in the Gulf, as well as of the dispersal pattern of the Mississippi River's plume.

Mueller-Karger, Frank E.↗
NASA NTRS1990

Seasonal variation of the diurnal cycles of earth's radiation budget determined from ERBE

ERBE scanner data from the Earth Radiation Budget Satellite and NOAA-9 satellites obtained from February 1985 through January 1986 are used to investigate the diurnal cycles of both LW radiation and albedo for each month of the year. Seasonal variations of the diurnal cycles are examined for the deserts, vegetated land, and oceans over the globe. Comparisons are made between clear-sky and total-scene conditions. ERBE satellite data showed that many areas of the earth exhibit significant diurnal variations in both LW flux and albedo. The LW diurnal range was found to be greatest for deserts and smallest for oceans, whereas the albedo diurnal amplitude factor is a maximum over the tropical oceans and a minimum over land. Cloud cover and seasonal variations have a major effect on the diurnal cycles. Generally, maximum diurnal ranges were found in the summer hemisphere and minimum values in the winter hemisphere.

Harrison, E. F.↗
NASA NTRS1989

Modelling ionospheric density structures

Large-scale density structures are a common feature in the high-latitude ionsphere. The structures were observed in the dayside cusp, polar cap, and nocturnal auroral region over a range of altitudes, including the E-region, F-region and topside ionosphere. The origins, lifetimes and transport characteristics of large-scale density structures were studied with the aid of a three-dimensional, time-dependent ionospheric model. Blob creation due to particle precipitation, the effect that structured electric fields have on the ionosphere, and the lifetimes and transport characteristics of density structures for different seasonal, solar cycle, and interplanetary magnetic field (IMF) conditions were studied. The main conclusions drawn are: (1) the observed precipitation energy fluxes are sufficient for blob creation if the plasma is exposed to the precipitation for 5 to 10 minutes; (2) structured electric fields produce structured electron densities, ion temperatures, and ion composition; (3) the lifetime of an F-region density structure depends on several factors, including the initial location where it was formed, the magnitude of the perturbation, season, solar cycle and IMF; and (4) depending on the IMF, horizontal plasma convection can cause an initial structure to break up into multiple structures of various sizes, remain as a single distorted structure, or become stretched into elongated segments.

Schunk, R. W.↗
DOE OSTI2022

Seasonal Fluctuations in Iron Cycling in Thawing Permafrost Peatlands

In permafrost peatlands, up to 20% of total organic carbon (OC) is bound to reactive iron (Fe) minerals in the active layer overlying intact permafrost, potentially protecting OC from microbial degradation and transformation into greenhouse gases (GHG) such as CO 2 and CH 4 . During the summer, shifts in runoff and soil moisture influence redox conditions and therefore the balance of Fe oxidation and reduction. Whether reactive iron minerals could act as a stable sink for carbon or whether they are continuously dissolved and reprecipitated during redox shifts remains unknown. We deployed bags of synthetic ferrihydrite (FH)-coated sand in the active layer along a permafrost thaw gradient in Stordalen mire (Abisko, Sweden) over the summer (June to September) to capture changes in redox conditions and quantify the formation and dissolution of reactive Fe(III) (oxyhydr)oxides. We found that the bags accumulated Fe(III) under constant oxic conditions in areas overlying intact permafrost over the full summer season. In contrast, in fully thawed areas, conditions were continuously anoxic, and by late summer, 50.4 ± 12.8% of the original Fe(III) (oxyhydr)oxides were lost via dissolution. Periodic redox shifts (from 0 to +300 mV) were observed over the summer season in the partially thawed areas. This resulted in the dissolution and loss of 47.2 ± 20.3% of initial Fe(III) (oxyhydr)oxides when conditions are wetter and more reduced, and new formation of Fe(III) minerals (33.7 ± 8.6% gain in comparison to initial Fe) in the late summer under more dry and oxic conditions, which also led to the sequestration of Fe-bound organic carbon. Our data suggest that there is seasonal turnover of iron minerals in partially thawed permafrost peatlands, but that a fraction of the Fe pool remains stable even under continuously anoxic conditions.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Advancing reliability assessments of photovoltaic modules and materials using combined-accelerated stress testing

Previously undiscovered failure modes in photovoltaic (PV) modules continue to emerge in field installations despite passing protocols for design qualification and quality assurance. Failure to detect these modes prior to widespread use could be attributed to the limitations of present-day standard accelerated stress tests (ASTs), which are primarily designed to identify known degradation or failure modes at the time of development by applying simultaneous or sequential stress factors (usually two at most). Here, we introduce an accelerated testing method known as the combined-accelerated stress test (C-AST), which simultaneously combines multiple stress factors of the natural environment. Simultaneous combination of multiple stress factors allows for improved identification of failure modes with better ability to detect modes not known a priori. A demonstration experiment was conducted that reproduced the field-observed cracking of polyamide- (PA-) and polyvinylidene fluoride (PVDF)–based backsheet films, a failure mode that was not detected by current design qualification and quality assurance testing requirements. In this work, a two-phase testing protocol was implemented. The first cycle (“Tropical”) is a predominantly high-humidity and high-temperature test designed to replicate harsh tropical climates. The second cycle (“Multi-season”) was designed to replicate drier and more temperate conditions found in continental or desert climates. Testing was conducted on 2 × 2-cell crystalline-silicon cell miniature modules constructed with both ultraviolet (UV)–transmitting and UV-blocking encapsulants. Cracking failures were observed within a cumulative 120 days of the Tropical condition for one of the PA-based backsheets and after 84 days of Tropical cycle followed by 42 days of the Multi-season cycle for the PVDF-based backsheet, which are both consistent with failures seen in fielded modules. In addition to backsheet cracking, degradation modes were observed including solder/interconnect fatigue, various light-induced degradation modes, backsheet delamination, discoloration, corrosion, and cell cracking. The ability to simultaneously apply multiple stress factors may allow many of the test sequences within the standardized design qualification procedure to be performed using a single test setup.

14 SOLAR ENERGY↗
NASA NTRS1989

A parameterization of eddy transfer coefficients for two-level seasonal statistical dynamical zonally averaged models

This paper examines a parameterization of a quasi-geostrophic eddy transport that takes into account the time variation of eddy transfer coefficients according to Green's (1970) theory. It was found that, in the original eddy transfer relationship of Green, connecting the integral of the northward eddy entropy flux through midlatitudes with the second power of the difference in 500-mb entropy across the region of baroclinic activity, a value of 4 for the exponent is obtained when the temperature gradients at 500 mb are used. When the gradients at 1000 mb are used, an exponent of 1.5 is obtained. The differences in the powers in the eddy transfer relation were explored in a two-level zonally averaged model. It was found that an appropriate choice of power may be of special importance if the model is devised to simulate the seasonal climate cycle or to test astronomical changes inducing different seasonalities.

Neeman, Binyamin U.↗
NASA NTRS2012

Simulating Mars' Dust Cycle with a Mars General Circulation Model: Effects of Water Ice Cloud Formation on Dust Lifting Strength and Seasonality

The dust cycle is critically important for the current climate of Mars. The radiative effects of dust impact the thermal and dynamical state of the atmosphere [1,2,3]. Although dust is present in the Martian atmosphere throughout the year, the level of dustiness varies with season. The atmosphere is generally the dustiest during northern fall and winter and the least dusty during northern spring and summer [4]. Dust particles are lifted into the atmosphere by dust storms that range in size from meters to thousands of kilometers across [5]. Regional storm activity is enhanced before northern winter solstice (Ls~200 degrees - 240 degrees), and after northern solstice (Ls~305 degrees - 340 degrees ), which produces elevated atmospheric dust loadings during these periods [5,6,7]. These pre- and post- solstice increases in dust loading are thought to be associated with transient eddy activity in the northern hemisphere with cross-equatorial transport of dust leading to enhanced dust lifting in the southern hemisphere [6]. Interactive dust cycle studies with Mars General Circulation Models (MGCMs) have included the lifting, transport, and sedimentation of radiatively active dust. Although the predicted global dust loadings from these simulations capture some aspects of the observed dust cycle, there are marked differences between the simulated and observed dust cycles [8,9,10]. Most notably, the maximum dust loading is robustly predicted by models to occur near northern winter solstice and is due to dust lifting associated with down slope flows on the flanks of the Hellas basin. Thus far, models have had difficulty simulating the observed pre- and post- solstice peaks in dust loading.

Kahre, Melinda A.↗
NASA NTRS2019

Seasonal Dependence of SMAP Radiometer-Based Soil Moisture Performance as Observed over Core Validation Sites

The NASA SMAP (Soil Moisture Active Passive) mission provides a global coverage of soil moisture measurements based on its L-band microwave radiometer every 2-3 days at about 40 km resolution. The soil moisture retrieval algorithms model the brightness temperature as a function of soil moisture, surface conditions and vegetation. External data sources inform the algorithms about the surface conditions and vegetation, which enable the retrieval of soil moisture. The inversion process contains uncertainties related to radiometer measurements, forward model assumptions and ancillary data sources. This study focuses on the uncertainties that depend on the seasonal evolution of the surface conditions and vegetation. This study compares the SMAP and core validation site (CVS) soil moisture values over a period of three years to extract the evolution of performance metrics over time. The analysis showed that most CVS that include managed agriculture exhibit significant time-dependent seasonal bias. This bias was linked to seasonal temperature cycle, which is a proxy to several features that can cause seasonally dependent errors in the SMAP product.

core validation site↗
DOE OSTI2022

Metal fluxes at the sediment–water interface in a free water surface constructed wetland

Metal biogeochemistry in the sediment, water, and the sediment–water interface (SWI) was studied in a free water surface constructed wetland. Concentrations of labile copper (Cu), zinc (Zn), sulfate, chloride, and dissolved organic carbon (DOC) were measured with the diffusive gradients in thin film (DGT) and peeper. A good agreement between peeper- and DGT-measured metals was observed for Cu (regression r 2 = 0.3, 95% CI of the slopes > 0), but not for Zn (95% CI of the slopes overlapped with 0), which was attributed to the different complexed compounds between Cu and Zn in porewater. The depth profile of labile metals in sediment porewater varied with time and was consistent with the solid-phase metal deposition, showing higher concentrations in the surface layer (3 to –3 cm) than in the bottom layer (–4 to –13 cm). The depth-averaged labile Cu and Zn concentrations measured by DGT were 1.0 and 3.1 µg/L, and labile sulfate, chloride, and DOC concentrations measured by peeper were 1.8, 3.6, and 2.1 mg/L, respectively. A sharp decrease in sulfate occurred in September when sulfate concentrations became the lowest among sampling months. This was caused by the seasonal sulfur cycles in the wetland, where the dominant sulfur reaction is sulfate reduction in warm seasons and sulfide oxidation in cold seasons. Different metal-removal mechanisms were observed in the two wetland cells; sulfur dynamics controlled the removal processes in the cell without frequent disturbance but failed to influence metal removal in the cell with frequent disturbance due to the interruption of anoxic layers. The flux ratios that compare labile element concentrations between the water column and the SWI (R-Cu, R-Zn, R-DOC, R-sulfate, and R-chloride) were generated to determine metal diffusive fluxes at the interface. Labile Zn was mostly transported from the water to the SWI during all seasons (R-Zn < 1 for all months except January). Labile Cu moved from the SWI to the water during the warm months (R-Cu < 1), which was explained by the bioturbation-induced transport of organic matter based on the positive correlations between R-Cu and R-DOC. In general, sediment can serve either as a sink or a source depending on the environmental conditions, metal speciation, and presence of living organisms. Here, metal flux at the SWI is a key component in the biogeochemical cycling of a constructed wetland.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1989

Effect on atmospheric CO2 from seasonal variations in the high latitude ocean

Data from the North Pacific gyre, Bering Sea, and North Atlantic show large seasonal fluctuations in the pCO2 of surface waters. The seasonal variation in these latitudes apparently has a generic pattern: higher surface water pCO2 in winter and lower in summer. Satellite data will eventually help decipher the relative effects of temperature and biological production in the seasonal carbon cycle, but as yet little work has been done on what possible role the seasonality of pCO2 in the high latitudes might have on the average value of atmospheric pCO2. A model is developed that shows the average value for atmospheric pCO2 depends upon the ratio of the rates at which the ocean/atmosphere system moves toward equilibrium values during the summer and winter conditions of the high latitude ocean.

Volk, Tyler↗
NASA NTRS2007

Diurnal Lightning Distributions as Observed by the Optical Transient Detector (OTD) and the Lightning Imaging Sensor (LIS)

Data obtained from the Optical Transient Detector (April 1995 to March 2000) and the Lightning Imaging Sensor (December 1997 to December 2005) satellites (70 and 35 inclination low earth orbits, respectively) are used to statistically determine the number of flashes in the annual and seasonal diurnal cycle as a function of local and universal time. The data are further subdivided by season, land versus ocean, northern versus southern hemisphere, and other spatial (e.g., continents) and temporal (e.g., time of peak diurnal amplitude) categories. The data include corrections for detection efficiency and instrument view time. Continental results display strong diurnal variation, with a lightning peak in the late afternoon and a minimum in late morning. In regions of the world dominated by large mesoscale convective systems the peak in the diurnal curve shifts toward late evening or early morning hours. The maximum diurnal flash rate occurs in June-August, corresponding to the Northern Hemisphere summer, while the minimum occurs in December-February. Summer lightning dominates over winter activity and springtime lightning dominates over autumn activity at most continental locations. This latter behavior occurs especially strongly over the Amazon region in South America in September-November. Oceanic lightning activity in winter and autumn tends to exceed that in summer and spring. Global lightning is well correlated in phase but not in amplitude with the Carnegie curve. The diurnal flash rate varies about 4-35 percent about the mean, while the Carnegie curve varies around 4-15 percent.

Bailey, Jeff C.↗
NASA NTRS1993

The Mars water cycle at other epochs - Recent history of the polar caps and layered terrain

A numerical model is presented of the integrated role of seasonal water cycle on the evolution of polar deposits on Mars over the last 10 million years. From the model, it is concluded that the only major difference between the polar caps which affects their long-term behavior is ultimately the difference in their elevations. Because of that difference, there is a preference for CO2 frost to stay longer on the northern polar cap. The average difference in sublimation at the caps results in a net south-to-north transport of water ice over long time scales. Superimposed on any long-term behavior is a transfer of water ice between the caps on the 10 exp 5 - 10 exp 6 yr time scales. The amount of water exchanged is small compared to the total ice content of the polar deposits.

Jakosky, Bruce M.↗
DOE OSTI2021

A Novel Machine Learning Algorithm for Planetary Boundary Layer Height Estimation Using AERI Measurement Data

Accurately determining the height of the planetary boundary layer (PBL) is important since it can affect the climate, weather, and air quality. Ground-based infrared hyperspectral remote sensing is an effective way to obtain this parameter. Compared with radiosonde measurements, its temporal resolution is much higher. In this study, a method to retrieve the PBL height (PBLH) from the ground-based infrared hyperspectral radiance data is proposed based on machine learning. In this method, the channels that are sensitive to temperature and humidity profiles are selected as the feature vectors, and the PBLHs derived from radiosonde are taken as the true values. The support vector machine (SVM) is applied to train and test the data set, and the parameters are optimized in the process. The data set collected at the Atmospheric Radiation Measurement (ARM) program Southern Great Plains (SGP) from 2012 to 2015 is analyzed. The instruments used in this letter include Atmospheric Emitted Radiance Interferometer (AERI), Vaisala CL31 ceilometer, and radiosonde. It shows that the root mean square error (RMSE) between the PBLHs calculated by the proposed method using AERI data and those from radiosonde data can be within 370 m, and the square correlation coefficient (SCC) is greater than 0.7. Compared with the PBLHs derived from the ceilometer, it can be found that the new method is more stable and less affected by clouds.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Microbial community dynamics and cycling of plutonium and iron in a seasonally stratified and radiologically contaminated pond

Plutonium (Pu) cycling and mobility in the environment can be impacted by the iron cycle and microbial community dynamics. We investigated the spatial and temporal changes of the microbiome in an iron (Fe)-rich, plutonium-contaminated, monomictic reservoir (Pond B, Savannah River Site, South Carolina, USA). The microbial community composition varied with depth during seasonal thermal stratification and was strongly correlated with redox. During stratification, Fe(II) oxidizers (e.g., Ferrovum, Rhodoferax, Chlorobium) were most abundant in the hypoxic/anoxic zones, while Fe(III) reducers (e.g., Geothrix, Geobacter) dominated the deep, anoxic zone. Sulfate reducers and methanogens were present in the anoxic layer, likely contributing to iron and plutonium cycling. Multinomial regression of predicted functions/pathways identified metabolisms highly associated with stratification (within the top 5%), including iron reduction, methanogenesis, C1 compound utilization, fermentation, and aromatic compound degradation. Two sediment cores collected at the Inlet and Outlet of the pond were dominated by putative fermenters and organic matter (OM) degraders. Overall, microbiome analyses revealed the potential for three microbial impacts on the plutonium and iron biogeochemical cycles: (1) plutonium bioaccumulation throughout the water column, (2) Pu–Fe-OM-aggregate formation by Fe(II) oxidizers under microaerophilic/aerobic conditions, and (3) Pu–Fe-OM-aggregate or sediment reductive dissolution and organic matter degradation in the deep, anoxic waters.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1988

Circumpolar hoods and clouds and their relation to the Martian H2O cycle

Water exists in both vapor and solid phases in the Martian atmosphere. The polar hoods are shrouds of condensate clouds which obscure both polar regions at times during their respective fall and winter seasons. The hemispheric asymmetries in the polar hood clouds are reviewed and their significance to the seasonal water cycle is discussed. Comparisons of images acquired using short wavelength filters, which provide maximum cloud contrast, and long wavelength filters, which are sensitive to surface features including the surface cap, provide correlations between cloud formation and large scale planetary dynamics.

James, Philip B.↗
NASA NTRS2004

Spaceborne Microwave Remote Sensing of Seasonal Freeze-Thaw Processes in the Terrestrial High Latitudes: Relationships with Land-Atmosphere CO2 exchange

Landscape transitions between seasonally frozen and thawed conditions occur each year over roughly 50 million square kilometers of Earth's Northern Hemisphere. These relatively abrupt transitions represent the closest analog to a biospheric and hydrologic on/off switch existing in nature, affecting surface meteorological conditions, ecological trace gas dynamics, energy exchange and hydrologic activity profoundly. We utilize time series satellite-borne microwave remote sensing measurements from the Special Sensor Microwave Imager (SSM/I) to examine spatial and temporal variability in seasonal freeze/thaw cycles for the pan-Arctic basin and Alaska. Regional measurements of spring thaw timing are derived using daily brightness temperature measurements from the 19 GHz, horizontally polarized channel, separately for overpasses with 6 AM and 6 PM equatorial crossing times. Spatial and temporal patterns in regional freeze/thaw dynamics show distinct differences between North America and Eurasia, and boreal forest and Arctic tundra biomes. Annual anomalies in the timing of thawing in spring also correspond closely to seasonal atmospheric CO2 concentration anomalies derived from NOAA CMDL arctic and subarctic monitoring stations. Classification differences between AM and PM overpass data average approximately 5 days for the region, though both appear to be effective surrogates for monitoring annual growing seasons at high latitudes.

net primary products↗
DOE OSTI2021

Explaining Globally Inhomogeneous Future Changes in Monsoons Using Simple Moist Energy Diagnostics

Here, this study examines the annual cycle of monsoon precipitation simulated by models from phase 6 of the Coupled Model Intercomparison Project (CMIP6), then uses moist energy diagnostics to explain globally inhomogeneous projected future changes. Rainy season characteristics are quantified using a consistent method across the globe. Model bias is shown to include rainy season onsets tens of days later than observed in some monsoon regions (India, Australia, and North America) and overly large summer precipitation in others (North America, South America, and southern Africa). Projected next-century changes include rainy season lengthening in the two largest Northern Hemisphere monsoon regions (South Asia and central Sahel) and shortening in the two largest Southern Hemisphere regions (South America and southern Africa). Changes in the North American and Australian monsoons are less coherent across models. To understand these changes, relative moist static energy (MSE) is defined as the difference between local and tropical-mean surface air MSE. Future changes in relative MSE in each region correlate well with onset and demise date changes. Furthermore, Southern Hemisphere regions projected to undergo rainy season shortening are spanned by an increasing equator-to-pole MSE gradient, suggesting their rainfall will be increasingly inhibited by fluxes of dry extratropical air; Northern Hemisphere regions with projected lengthening of rainy seasons undergo little change in equator-to-pole MSE gradient. Thus, although model biases raise questions as to the reliability of some projections, these results suggest that globally inhomogeneous future changes in monsoon timing may be understood through simple measures of surface air MSE.

54 ENVIRONMENTAL SCIENCES↗