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NASA NTRS2006

Land Water Storage within the Congo Basin Inferred from GRACE Satellite Gravity Data

GRACE satellite gravity data is used to estimate terrestrial (surface plus ground) water storage within the Congo Basin in Africa for the period of April, 2002 - May, 2006. These estimates exhibit significant seasonal (30 +/- 6 mm of equivalent water thickness) and long-term trends, the latter yielding a total loss of approximately 280 km(exp 3) of water over the 50-month span of data. We also combine GRACE and precipitation data set (CMAP, TRMM) to explore the relative contributions of the source term to the seasonal hydrological balance within the Congo Basin. We find that the seasonal water storage tends to saturate for anomalies greater than 30-44 mm of equivalent water thickness. Furthermore, precipitation contributed roughly three times the peak water storage after anomalously rainy seasons, in early 2003 and 2005, implying an approximately 60-70% loss from runoff and evapotranspiration. Finally, a comparison of residual land water storage (monthly estimates minus best-fitting trends) in the Congo and Amazon Basins shows an anticorrelation, in agreement with the 'see-saw' variability inferred by others from runoff data.

Crowley, John W.↗

NASA NTRS1999

The New 20-Year Global Precipitation Climatology Project (GPCP) Merged Satellite and Rainguage Monthly Analysis

A new 20-year, monthly, globally complete precipitation analysis has been completed as part of the World Climate Research Program's (WCRP/GEWEX) Global Precipitation Climatology Project (GPCP). This Version 2 of the community generated data set is a result of combining the procedures and data sets as described. The global, monthly, 2.5x 2.5 degree latitude-longitude product utilizes precipitation estimates from low-orbit microwave sensors (SSM/1) and geosynchronous IR sensors and raingauge information over land. The low-orbit microwave estimates are used to adjust or correct the geosynchronous IR estimates, thereby maximizing the utility of the more physically-based microwave estimates and the finer time sampling of the geosynchronous observations. Information from raingauges is blended into the analyses over land. In the 1986-present period TOVS-based precipitation estimates are adjusted to GPCP fields and used in polar regions to produce globally-complete results. The extension back to 1979 utilizes the procedures of Xie and Arkin and their OLR Precipitation Index (OPI). The 20-year climatology of the Version 2 GPCP analysis indicates the expected features of a very strong Pacific Ocean ITCZ and SPCZ with maximum 20-year means approaching 10 mm/day. A similar strength maximum over land is evident over Borneo. Weaker maxima in the tropics occur in the Atlantic ITCZ and over South America and Africa. In mid-latitudes of the Northern Hemisphere the Western Pacific and Western Atlantic maxima have values of approximately 7 mm/day, while in the Southern Hemisphere the mid-latitude maxima are located southeast of Africa, in mid-Pacific as an extension of the SPCZ and southeast of South America. In terms of global totals the GPCP analysis shows 2.7 mm/day (3.0 mm/day over ocean; 2.1 mm/day over land), similar to the Jaeger climatology, but not other climatologies. Zonal averages peak at 6 mm/day at 7*N with mid-latitude peaks of about 3 mm/day at 40-45* latitude. Poleward of 45* the GPCP analysis shows larger zonally-averaged values than most previous satellite-based estimates, although the values are similar to tl,ie Jaeger climatology. Over both ocean areas and at high latitudes the analysis requires additional validation and comparison with special, independent data sets from field experiments and from the Tropical Rain Measuring Mission (TRMM) to confirm the absolute magnitude and variations of precipitation seen in the analysis. Interannual and other variations of the global fields will be shown focusing on the recent ('97-'99) ENSO event compared with previous events, including teleconnections at mid and high latitudes. An ENSO Precipitation Index (ESPI) calculated using the new data set will be described and related to the evolution of the ENSO events during the 20-year period.

Adler, Robert↗

NASA NTRS1999

Miniature EPSPs and sensory encoding in the primary afferents of the vestibular lagena of the toadfish, Opsanus tau

The synaptic activity transmitted from vestibular hair cells of the lagena to primary afferent neurons was recorded in vitro using sharp, intracellular microelectrodes. At rest, the activity was composed of miniature excitatory postsynaptic potentials (mEPSPs) at frequencies from 5 to 20/s and action potentials (APs) at frequencies betwen 0 and 10/s. mEPSPs recorded from a single fiber displayed a large variability. For mEPSPs not triggering APs, amplitudes exhibited an average coefficient of variance (CV) of 0.323 and rise times an average CV of 0.516. APs were only triggered by mEPSPs with larger amplitudes (estimated 4-6 mV) and/or steeper maximum rate of rise (10.9 mV/ms, +/- 3.7 SD, n=4 experiments) compared to (3.50 mV/ms, +/-0.07 SD, n=6 experiments) for nontriggering mEPSPs. The smallest mEPSPs showed a fast rise time (0.99 ms between 10% and 90% of peak amplitude) and limited variability across fibers (CV:0.18) confirming that they were not attenuated signals, but rather represented single-transmitter discharges (TDs). The mEPSP amplitude and rise-time relationship suggests that many mEPSPs represented several, rather than a single pulse of secretion of TDs. According to the estimated overall TD frequency, the coincidence of TDs contributing to the same mEPSP were not statistically independent, indicating a positive interaction between TDs that is reminiscent of the way subminiature signals group to form miniature signals at the neuromuscular junction. Depending on the duration and intensity of efferent stimulation, a complete block of AP initiation occurred either immediately or after a delay of a few seconds. Efferent stimulation did not significantly change AP threshold level, but abruptly decreased mEPSP frequency to a near-complete block that followed the block of APs. Maximum mEPSP rate of rise decreased during, and recovered progressively after, efferent stimulation. After termination of efferent stimulation, mEPSP amplitude did not recover instantly and for a few seconds the amplitude distribution of synaptic events showed fewer large-amplitude events than during the control period. This confirms that mEPSP amplitude and rate of rise properties, which are critical for triggering afferent APs, are modified by efferent activity. The depression of afferent AP firing during efferent stimulation corresponded to a decrease in mEPSP frequency and, to a lesser extent, a decrease in mEPSP amplitude and rate of rise, suggesting, a decrease in the level of interaction among TDs contibuting to a mEPSP.

Non-NASA Center↗

NASA NTRS2000

Leonid Storm Flux Analysis From One Leonid MAC Video AL50R

A detailed meteor flux analysis is presented of a seventeen-minute portion of one videotape, collected on November 18, 1999, during the Leonid Multi-instrument Aircraft Campaign. The data was recorded around the peak of the Leonid meteor storm using an intensified CCD camera pointed towards the low southern horizon. Positions of meteors on the sky were measured. These measured meteor distributions were compared to a Monte Carlo simulation, which is a new approach to parameter estimation for mass ratio and flux. Comparison of simulated flux versus observed flux levels, seen between 1:50:00 and 2:06:41 UT, indicate a magnitude population index of r = 1.8 +/- 0.1 and mass ratio of s = 1.64 +/- 0.06. The average spatial density of the material contributing to the Leonid storm peak is measured at 0.82 +/- 0.19 particles per square kilometer per hour for particles of at least absolute visual magnitude +6.5. Clustering analysis of the arrival times of Leonids impacting the earth's atmosphere over the total observing interval shows no enhancement or clumping down to time scales of the video frame rate. This indicates a uniformly random temporal distribution of particles in the stream encountered during the 1999 epoch. Based on the observed distribution of meteors on the sky and the model distribution, recommendations am made for the optimal pointing directions for video camera meteor counts during future ground and airborne missions.

Gural, Peter S.↗

NASA NTRS2016

Biomass Burning, Land-Cover Change, and the Hydrological Cycle in Northern Sub-Saharan Africa

The Northern Sub-Saharan African (NSSA) region, which accounts for 20%-25%of the global carbon emissions from biomass burning, also suffers from frequent drought episodes and other disruptions to the hydrological cycle whose adverse societal impacts have been widely reported during the last several decades. This paper presents a conceptual framework of the NSSA regional climate system components that may be linked to biomass burning, as well as detailed analyses of a variety of satellite data for 2001-2014 in conjunction with relevant model-assimilated variables. Satellite fire detections in NSSA show that the vast majority (greater than 75%) occurs in the savanna and woody savanna land-cover types. Starting in the 2006-2007 burning season through the end of the analyzed data in 2014, peak burning activity showed a net decrease of 2-7% /yr in different parts of NSSA, especially in the savanna regions. However, fire distribution shows appreciable coincidence with land-cover change. Although there is variable mutual exchange of different land cover types, during 2003-2013, cropland increased at an estimated rate of 0.28% /yr of the total NSSA land area, with most of it (0.18% /yr) coming from savanna.During the last decade, conversion to croplands increased in some areas classified as forests and wetlands, posing a threat to these vital and vulnerable ecosystems. Seasonal peak burning is anti-correlated with annual water-cycle indicators such as precipitation, soil moisture, vegetation greenness, and evapotranspiration, except in humid West Africa (5 deg-10 deg latitude),where this anti-correlation occurs exclusively in the dry season and burning virtually stops when monthly mean precipitation reaches 4 mm/d. These results provide observational evidence of changes in land-cover and hydrological variables that are consistent with feedbacks from biomass burning in NSSA, and encourage more synergistic modeling and observational studies that can elaborate this feedback mechanism.

biomass burning↗

NASA NTRS2023

Revisiting Empirical Solar Energetic Particle Scaling Relations. I. Solar Flares

Aims. The possible influence of solar superflares on the near-Earth space radiation environment are assessed through the investigation of scaling laws between the peak proton flux and fluence of solar energetic particle (SEP) events with the solar flare soft X-ray peak photon flux. Methods. We compiled a catalog of 65 well-connected (W20-90) SEP events during the last three solar cycles covering a period of ∼34 yr (1984–2020) that were associated with flares of class ≥C6.0, and investigated the statistical relations between the recorded peak proton fluxes (I p ) and the fluences (F p ) at a set of integral energies from E > 10, > 30, and > 60 to > 100 MeV versus the associated solar flare peak soft X-ray flux in the 1–8 Å band (F SXR ). Based on the inferred relations, we calculated the integrated energy dependence of the peak proton flux (I p ) and fluence (F p ) of the SEP events, assuming that they follow an inverse power law with respect to energy. Finally, we made use of simple physical assumptions, combining our derived scaling laws, and estimated the upper limits for I p and F p focusing on the flare associated with the strongest ground level enhancement (GLE) directly observed to date (GLE 05 on 23 February 1956), and that inferred for the cosmogenic radionuclide-based SEP event of AD774/775. Results. A scaling law relating I p and F p to the solar soft X-ray peak intensity (F SXR ) as ∝ F 5/6 SXR for a flare with a F SXR = X600 (in the revised scale) is consistent with values of FP inferred for the cosmogenic nuclide event of AD774/775.

Athanasios Papaioannou↗

NASA NTRS1975

Evaluation of the dual differential radiometer for remote sensing of sediment and chlorophyll in turbid waters

The dual differential radiometer (DDR) was tested to determine its capability for measuring suspended sediment and chlorophyll in turbid waters. Measurements were obtained from a boat dock and from a helicopter with combinations of sample and reference filters with peak transmissions at various wavelengths. Water samples were taken concurrently and were analyzed for light scattering, particle count, and total chlorophyll. Least-squares estimates of the linear relationship between DDR output and the water parameters yielded correlation coefficients of less than 0.7. Under the turbid water conditions of the present tests, the DDR did not accurately measure either suspended sediment or chlorophyll. A precise knowledge of the spectral signatures of various pollutants might enable appropriate filters to be selected for tuning the DDR to monitor a particular pollutant.

Witte, W. G.↗

NASA NTRS1976

A comparison of GaAs and Si hybrid solar power systems

An analytical comparison of energy output from various silicon and gallium arsenide hybrid solar power systems, producing electric power and also thermal power for heating or cooling, is made. System performance indices in terms of capital cost, peak power, total power output, and electric power were evaluated. Limiting values for annual energy production from GaAs and Si solar concentrator systems were estimated to be 2 cents and 6.8 cents per kWh for GaAs concentrator systems and between 2.5 cents and 11 cents per kWh for Si concentrator systems.

Heinbockel, J. H.↗

NASA NTRS1977

Estimated probability density functions for the times between flashes in the storms of 12 September 1975, 26 August 1975, and 13 July 1976

A report is given to supplement the progress report of June 17, 1977. In that progress report gamma, lognormal, and Rayleigh probability density functions were fitted to the times between lightning flashes in the storms of 9/12/75, 8/26/75, and 7/13/76 by the maximum likelihood method. The goodness of fit is checked by the Kolmogoroff-Smirnoff test. Plots of the estimated densities along with normalized histograms are included to provide a visual check on the goodness of fit. The lognormal densities are the most peaked and have the highest tails. This results in the best fit to the normalized histogram in most cases. The Rayleigh densities have too broad and rounded peaks to give good fits. In addition, they have the lowest tails. The gamma densities fall inbetween and give the best fit in a few cases.

Tretter, S. A.↗

NASA NTRS1983

Increase and seasonal cycles of nitrous oxide in the earth's atmosphere

It is determined that nitrous oxide (N2O) is increasing at about 0.9 ppb/yr in the northern hemisphere and at about 0.7 ppb/yr in the southern hemisphere, based on about 9000 ground-level measurements at Cape Meares, Oregon (45 deg N), and Cape Grim, Tasmania (42 deg S), spanning a three-year period. It is also shown that the N2O concentrations vary with season in the northern hemisphere, where the concentrations are 0.8 ppbv higher during April, May, and June compared to the rest of the year, and in the southern hemisphere where the concentrations are about 0.5 ppbv lower during March, April, and May compared to the rest of the year. An explanation of this increase as a sizeable anthropogenically-controlled land-based source is presented, based on an examination of the existing estimates of natural and anthropogenic sources of N2O. Mass-balance calculations are also presented which suggest that a natural land-based source, peaking in spring, would explain the main features of the observed seasonal cycle. A growth model is employed to extrapolate the observed increase of N2O into the future and the results are compared with exponential extrapolations.

Khalil, M. A. K.↗

NASA NTRS1983

Variation in light intensity with height and time from subsequent lightning return strokes

Photographic measurements of relative light intensity as a function of height and time have been conducted for seven return strokes in two lightning flashes at 7.8 and 8.7 km ranges, using film which possesses an approximately constant spectral response in the 300-670 nm range. The amplitude of the initial light peak is noted to decrease exponentially with height, with a decay constant of 0.6-0.8 km. The logarithm of the peak light intensity near the ground is found to be approximately proportional to the initial peak electric field intensity, implying that the current decrease with height may be much slower than the light decrease. Absolute light intensity is presently estimated through the integration of the photographic signals from individual channel segments, in order to simulate the calibrated, all-sky photoelectric data of Guo and Krider (1982).

Jordan, D. M.↗

NASA NTRS1984

Adaptive optics

An estimation of the costs and potential resolution and sensitivity benefits of adaptive optics systems is presented. The effects of atmospheric disturbances on the peak-to-peak wavefront errors are assessed. Definitions are included of the maximum permissible controlled patch of entrance pupil of the system, the permissible response time, the permissible field radius, and the required magnitude and frequency of a reference star. It is pointed out that adaptive optics system for visible of near-visible wavelengths is likely to be very expensive, whereas operation at 2-3 microns under best seeing conditions is expected to be useful and have reasonable cost.

Woolf, N. J.↗

NASA NTRS1986

Factors influencing elastic stresses in double cantilever beam specimens

An elastic stress analysis was conducted for a double cantilever beam (DCB) specimen using finite-element methods. The purpose of this study was to identify the important parameters that influence stresses ahead of the delamination front. The study focused on an aluminum DCB specimen, typical of adhesively-bonded joints, and on a graphite/epoxy specimen representing a cocured composite. Opening mode sigma sub y stresses ahead of the crack tip were calculated and compared with those for a monolithic reference specimen. Beyond the singularity-dominated region very near the crack tip, the sigma sub y distribution was elevated compared to the monolithic case. Both the adhesive thickness and the adherend transverse (thickness-direction) stiffness were found to influence the elevation of sigma sub y. In contrast, adherend thickness and longitudinal stiffness has very little effect on this stress distribution. Estimates for adhesive yielding beyond the aluminum DCB crack tip showed that both the area and height of the plastic zone increased to a peak value for increasing adhesive thicknesses. Results from this study would provide insight for comparing data from different DCB specimens and for designing new DCB specimens.

Crews, J. H., Jr.↗

NASA NTRS1987

Infrared spectroscopy of IRC + 10420

High resolution 1.6, 3.3 and 4.6 micron spectra were obtained on the F8 supergiant star IRC + 10420 on June 9-11, 1984, using the 4 m Mayall telescope and Fourier Transform Spectrometer at Kitt Peak. IRC + 10420 is distinguished by its hydrogen maser, unusual for stars of this type. The measured column densities of CO led to an estimated isotopic carbon ratio of 7-11, supporting a model of the object as a highly evolved star. The redshift is interpreted as due to scattering by outward-moving circumstellar dust grains. The IR spectrum of IRC + 10420 suggests that the object is a post-asymptotic branch star still surrounded by the thick dust shell it produced while it was much cooler.

Fix, John D.↗

NASA NTRS1988

Factors influencing elastic stresses in double cantilever beam specimens

Crews, J. H., Jr.↗

NASA NTRS1990

The molecular spiral arms of NGC 6946

From CO-12(J=1 to 0) observations at 45 seconds resolution Tacconi and Young (1989) have found evidence for enhancements in both the CO emissivity and the massive star formation efficiency (MSFE) on optical spiral arms of the bright spiral galaxy NGC 6946. In the optically luminous and well-defined spiral arm in the NE quadrant, there are enhancements in both the H2 surface density and MSFE relative to the interarm regions. In contrast, a poorly defined arm in the SW shows no arm-interarm contrast in the MSFE. To further investigate the molecular gas content of these two spiral arms, researchers have made CO-12 J=2 to 1 and 3 to 2 observations with the James Clerk Maxwell Telescope. In the J=2 to 1 line, they made observations of the NE and SW spiral arm and interarm regions in 4 x 9 10 seconds spaced grids (36 points per grid). Because of decreased sensitivity in the J=3 to 2 line, they were limited to mapping the two arm regions in 2 x 3 10 seconds spaced grids (6 points per grid). The centers of each of the grids lie 2.4 minutes to the NE and 2.3 minutes to the SW of the nucleus of NGC 6946. With the CO J=2 to 1 data researchers are able to fully resolve the two observed spiral arms in NGC 6946. In both cases the CO emission is largely confined to the optical spiral arm regions with the peak observed T asterisk sub A being up to 4 times higher on the spiral arms than in the interarm regions. Researchers are currently estimating massive star formation efficiencies on and off the spiral arms through direct comparison of the CO maps with an H alpha image. They are also comparing the CO J=2 to 1 data with an HI map made at similar resolution. Thus, they will be able to determine structure in all components of the IS on scales of less than 20 inches.

Tacconi, L. J.↗

NASA NTRS1993

Extreme Ultraviolet Explorer deep survey observations of a large flare on AU Microscopii

We have made the first extended observation of a stellar flare in the EUV with 100 s time resolution. The flare was detected on AU Mic by the Extreme Ultraviolet Explorer satellite at 12:38 UT on 1992 July 15 during a 4 d observation from 1992 July 14 to 18. This was a large flare detected in the Lexan/boron (65-190 A) band with an observed peak count rate of 7.0 +/- 0.5 counts/s, corresponding to a peak luminosity of 10 exp 30 erg/s in the Lexan/boron bandpass. This is significantly above the measured quiescent level of 0.4 +/- 0.2 counts/s. The flare consisted of a sharp peak lasting about 2 hr, followed by a decaying tail that lasted more than a day. The total EUV energy of the event is estimated to be 3 x 10 exp 34 ergs. A second, smaller flare was also observed and is described. We conclude that the large emission measures on order of 6 x 10 exp 53/cu cm are due to large volumes with characteristic length scales of order the stellar radius. We compare these EUV observations with stellar flare observations in other bandpasses and estimate the likelihood of seeing similar flares in future observations.

Cully, Scott L.↗

NASA NTRS1994

Latitudinal variability of large-scale coronal temperature and its association with the density and the global magnetic field

In this paper we utilize the latitiude distribution of the coronal temperature during the period 1984-1992 that was derived in a paper by Guhathakurta et al, 1993, utilizing ground-based intensity observations of the green (5303 A Fe XIV) and red (6374 A Fe X) coronal forbidden lines from the National Solar Observatory at Sacramento Peak, and establish it association with the global magnetic field and the density distributions in the corona. A determination of plasma temperature, T, was estimated from the intensity ratio Fe X/Fe XIV (where T is inversely proportional to the ratio), since both emission lines come from ionized states of Fe, and the ratio is only weakly dependent on density. We observe that there is a large-scale organization of the inferred coronal temperature distribution that is associated with the large-scale, weak magnetic field structures and bright coronal features; this organization tends to persist through most of the magnetic activity cycle. These high-temperature structures exhibit time-space characteristics which are similar to those of the polar crown filaments. This distribution differs in spatial and temporal characterization from the traditional picture of sunspot and active region evolution over the range of the sunspot cycle, which are manifestations of the small-scale, strong magnetic field regions.

Guhathakurta, M.↗